EP0330198B1 - Heat exchanger as an injection evaporator for a refrigeration machine - Google Patents

Heat exchanger as an injection evaporator for a refrigeration machine Download PDF

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Publication number
EP0330198B1
EP0330198B1 EP89103178A EP89103178A EP0330198B1 EP 0330198 B1 EP0330198 B1 EP 0330198B1 EP 89103178 A EP89103178 A EP 89103178A EP 89103178 A EP89103178 A EP 89103178A EP 0330198 B1 EP0330198 B1 EP 0330198B1
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EP
European Patent Office
Prior art keywords
section
evaporator
heat exchanger
refrigerant
exchanger according
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EP89103178A
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German (de)
French (fr)
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EP0330198A2 (en
EP0330198A3 (en
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Ulrich Dipl.- Ing. Klüe
Wilhelm Dipl.- Ing. Hartmann
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Kluee Ulrich Dipl-Ing
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Kluee Ulrich Dipl-Ing
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F3/00—Plate-like or laminated elements; Assemblies of plate-like or laminated elements
    • F28F3/12—Elements constructed in the shape of a hollow panel, e.g. with channels
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B31/00—Compressor arrangements
    • F25B31/002—Lubrication
    • F25B31/004—Lubrication oil recirculating arrangements
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B39/00—Evaporators; Condensers
    • F25B39/02—Evaporators
    • F25B39/022—Evaporators with plate-like or laminated elements
    • F25B39/024—Evaporators with plate-like or laminated elements with elements constructed in the shape of a hollow panel
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
    • F28F13/06—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by affecting the pattern of flow of the heat-exchange media
    • F28F13/08—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by affecting the pattern of flow of the heat-exchange media by varying the cross-section of the flow channels

Definitions

  • evaporators for refrigeration machines which also include heat pumps in the present context
  • the refrigerant is supplied in the liquid phase and discharged with mixed phases, a separator being required for phase separation. Since the pressure loss and the static pressure difference within the evaporator are small, the evaporation temperature, which is determined by the pressure of the refrigerant, is essentially constant over the height of the evaporator. This is favorable for the energy balance and for those applications in which the controllability of the temperature profile in the medium to be cooled is important, for example in the ice-free cooling of water near freezing point with a high heat flux density.
  • the plate heat exchanger for flooded evaporators (DE-A 3147378, US-A 2028213) are characterized by a refrigerant space in which the evaporating refrigerant mixture rises against gravity and which have such a large flow cross section that the mixture spreads across the width of the heat exchanger can distribute sufficiently evenly due to the effects of gravity.
  • the refrigerant is supplied to the evaporator without prior separation as a mixture of the liquid and the gaseous phase and completely evaporated, whereby to reliably avoid liquid hammer in the compressor and to control the injection valve designed as a thermostatic expansion valve a certain amount of overheating has to be accepted.
  • the expenditure on equipment for a refrigeration machine in injection mode is lower, which is why this design is often preferred for smaller systems (for example below 200 KW).
  • the forced flow is intended, on the one hand, to ensure that the compressor lubricating oil, which remains after evaporation of the refrigerant as the only liquid component in the evaporator, is discharged through a sufficient gas velocity.
  • it is intended to ensure that the heat exchanger surfaces are wetted evenly despite the small amount of liquid (only a few% by volume at the evaporator inlet) are.
  • injection evaporators It is known in the case of injection evaporators to provide a plurality of separate sections with different flow cross sections within a plate evaporator; However, these only form a structural unit, but not a functional unit, because they are each separately provided with an injection valve, which requires a high level of control engineering and construction. The basic disadvantage that a high pressure drop and thus a large temperature difference occurs in injection evaporators cannot be avoided by these means.
  • the invention aims to achieve a low pressure drop, comparable to that of a flooded evaporator.
  • the solution according to the invention consists in a method for operating a refrigeration machine, which is characterized in that the refrigerant passes from a first section of the heat exchanger with a second flow cross section and gravity distribution of the rising refrigerant into a second section with a narrower flow cross section in the not yet fully evaporated state, wherein the refrigerant in the second section has a speed sufficient to convey failed oil.
  • the invention is based on the knowledge that, in the case of an injection evaporator, a significantly increased speed of the refrigerant is only required in the area in which the complete evaporation of the liquid phase of the refrigerant takes place, so that there is uniform overheating without entrained residues of the liquid phase and because also it is only here that the concentration of the oil in the liquid refrigerant component becomes so great as a result of refrigerant evaporation that there is a risk of oil failure. Furthermore, the invention is based on the knowledge that even in the injection mode, the liquid portion in the evaporator is still large enough to ensure adequate liquid wetting of the evaporator inner surfaces even at a relatively low medium speed.
  • An evaporator for a household refrigerator is known (US Pat. No. 2,414,952) which, as the refrigerant flow increases, comprises a first section with a number of channels connected in parallel and a second, higher section which is formed by only one channel.
  • the only information about the flow cross-sections is that they should be so large in the second section that liquid refrigerant can flow back to the first section against the gas flow. The gas velocity is therefore not high enough to carry away any oil that falls out. This then accumulates in the evaporator.
  • the size of the first section in relation to the second depends on the type of refrigerant and the type and amount of compressor lubricant to be expected. The more miscible the lubricant is even with small amounts of the liquid refrigerant, the safer it can be that the lubricant is diluted so much by the liquid refrigerant in the end region of the first evaporator section and the viscosity is therefore reduced so much that it is transported with sufficient security.
  • the temperature also plays a role. A calculation has shown that when using the refrigerant Frigen R 22 using oil as a lubricant for a piston compressor, the oil is transported in the evaporator's liquid phase with sufficient certainty as long as the liquid component is not less than about 20 Weight percent of the refrigerant.
  • the first section can be designed in the manner of a flooded evaporator, namely as an essentially uniform space of comparatively large horizontal cross-section, in which the mixture can flow essentially vertically upwards.
  • Constrictions can be limited to the purpose of equalizing the flow movement over the entire cross-section and improving the heat transfer, namely preferably in the form of welded connections between the plates delimiting the flow space, which are alternately offset with respect to the vertical direction and as short welding distances, welding spots or the like can be trained.
  • Each welding point forms an evaporation core.
  • the evaporator can be used in immersed mode, i.e. in the container filled with the liquid to be cooled.
  • a collector forming the upper end of the plate can be thickened horizontally transversely to the plane of the plate in order to give the falling lines of the water flowing down from the outside a stronger horizontal component, which causes the water to spread out as a uniform film.
  • the second evaporator section is designed in the form of horizontal channels which are alternately connected at both ends, it can be provided that the uppermost of these channels is horizontally thicker than the following channels in order to perform this function.
  • an increased threshold is provided on the inlet side at the lower channel boundary.
  • devices can be provided which facilitate the entrainment of the oil to the next upper channel, for example a narrowing of the flow cross section to increase the gas velocity and to intensify the delivery effect.
  • the connecting piece discharging the refrigerant gas from the evaporator is expediently connected near the lower limit of the associated channel of the second section, so that the oil does not have to be raised again.
  • the injector supplying the evaporator is expediently a thermostatic control valve which is designed with a connection to an overheated refrigerant gas leading from the evaporator so that the refrigerant supply to the evaporator is regulated as a function of the superheating temperature. This ensures that the thermally undesired overheating area of the evaporator remains as small as possible.
  • the refrigeration machine is set so that the refrigerant essentially has a sufficient liquid portion to prevent lubricant failure when the boundary between the first and the second evaporator section is reached. Non-compliance with this condition is permitted for a short time, namely for such short periods of time that the lubricant cannot accumulate excessively in the first evaporator section and thus endanger the lubrication of the compressor.
  • the goal is achieved in this way, the total pressure loss and the Reduce evaporation temperature change to about a third.
  • the change in the evaporation temperature in a typical application is no longer acceptable at approx. 9 ° C, thanks to the invention it drops to approx. 3 ° C, whereby the greatest drop in temperature is reduced to a small, upper section of the evaporator, in which the water temperature is still comparatively high and the risk of ice formation is therefore low.
  • This makes it possible for the first time to use an injection evaporator to cool water near freezing.
  • the offset weld seam arrangement achieves a better distribution of the water film, an increased heat transfer due to a higher degree of turbulence and thereby a higher wall temperature, which likewise improves the possibilities of cooling closer to the freezing point without ice build-up.
  • the controlled and more uniform temperature curve in the evaporator plate guarantees a more uniform growth of the ice than is possible with injection evaporators of conventional design. Ice blasting from the plates by means of hot gas injection can also be used.
  • the refrigerator consists of evaporator 1, compressor 2, condenser 3 and thermostatic expansion valve 4, the pulse line 5 of which connects to a temperature sensor 6, which is arranged on line 7, which supplies the superheated gas from evaporator 1 to compressor 2.
  • the evaporator 1 is a vertical plate evaporator, through which the refrigerant flows from bottom to top. It consists of a first section 11 and a second section 12. The first section of the refrigerant flows substantially uniformly over its entire width from bottom to top similar to a flooded evaporator, with horizontal welding sections 13 arranged offset to the vertical direction ensuring a uniform flow and good heat transfer . Since the available flow cross-section is large, the pressure loss is low.
  • the flow path is formed by a meandering channel 14, which is composed of a plurality of horizontal channel sections which are alternately connected at the ends and which are formed by horizontal weld seams 15 connecting the sheets forming the plate evaporator.
  • the cross section of the channel 14 is significantly smaller than that of the first evaporator section.
  • the flow cross section in the first section is preferably at least three times, better at least five times and usually at least ten times larger than in the second section, which results in a correspondingly higher gas velocity for the second section.
  • the evaporator is operated so that the refrigerant with a bottom Weight fraction of the liquid phase of, for example, 70% is supplied.
  • the quantity supplied is determined as a function of the temperature of the superheated gas in line 7 by the injection valve. This ensures that the refrigerant always reaches the beginning of the second section 12 with such a large liquid fraction that the transport of the oil into the second section is ensured, where the refrigerant evaporates completely and the gas velocity is so high that the oil is entrained becomes.
  • a threshold 16 can expediently be provided at the beginning of the channel. Instead, it would also be conceivable to arrange the horizontal channels to fall slightly. Furthermore, baffles (not shown) can be provided in the vertical channel connections in order to intensify the gas flow there and to improve the oil transport.
  • the discharge pipe 18 is arranged near the lower boundary of the channel 17 in order to be able to discharge the oil there more easily. Furthermore, the uppermost channel 17 can be bulged more than the ones below it, in order to improve the liquid film formation on the outside of the evaporator when it is sprinkled, as is indicated by dashed lines in FIG. 2.
  • the ascending movement of the refrigerant ensures that the inner surfaces are evenly wetted despite the relatively slow flow without separation phenomena.
  • the predominantly horizontal flow is considered to be advantageous, so that in those areas in which oil must be expected to separate depending on the gas velocity, this can collect in the lower area of the horizontal channels, to a lesser extent by wetting the other inner surfaces deteriorate the heat transfer.
  • a falling connection of the horizontal channels can also be provided, the uppermost channel 17 being connected directly to the first section 11 by a vertical channel 20, as shown in FIG. 3.
  • the two evaporator sections are parts of a uniform, one-piece plate evaporator.
  • the evaporator plate (s) forming the first section being arranged in a group in a different way and at a different location than that forming the second sections. It is important that the evaporator sections form a uniform flow path connected to a single injection valve.
  • FIG. 4 illustrates the temperature profile of the refrigerant and in relation to the temperature profile 19 of the sprinkler water in ° C. over the height H of a plate heat exchanger according to FIG. 1 in solid lines.
  • the refrigerant-side temperature profiles of a flooded evaporator are shown in broken lines and a conventional injection evaporator is shown in dash-dotted lines.
  • the refrigerant and the sprinkling water move in counterflow.
  • the flooded evaporator achieves the most uniform temperature profile, in which, in a typical application example, the low pressure drop causes a temperature difference of only around 0.5 ° C across the height of the evaporator.
  • the conventional desuperheater shows a sharp drop in temperature of, for example, 9 ° C with a risk of icing up in the middle.
  • the temperature profile of the evaporator according to the invention comprises a lower section 11 ', which corresponds to the lower evaporator section 11 and in which the temperature reduction corresponds approximately to that of the flooded evaporator.
  • the second curve section 12 ' follows, which corresponds to that part of the second evaporator section 12 in which the liquid phase is still present and in which the temperature accordingly drops in accordance with the reduction in the evaporation temperature caused by the pressure drop.
  • the flow path length in the narrow flow cross section is much less than in conventional injection evaporators, only a correspondingly lower pressure loss will take place overall.
  • the lowest temperature point is close to the uppermost point of the evaporator, where the temperature of the sprinkling water is relatively high and the risk of icing is therefore low.
  • a curve section 12 ' which corresponds to that part of the second evaporator section 12 in which the overheating of the dry, gaseous refrigerant takes place.
  • the temperature profile of the injection evaporator according to the invention is very similar to that of a flooded evaporator and that it is therefore also suitable for applications in which the temperature profile of the medium to be cooled has to be controlled, for example closely its freezing point, like this is required for the water side with temperature curve 19 in diagram 4 with cooling down to 0.5 ° C.
  • the temperature in the first section remains 11 ′.
  • the dotted temperature curve 12 erargues results, the lowering of the temperature of which in relation to the water curve 19 is somewhat less favorable because the temperature minimum is reached at a lower water temperature; however, this minimum is at a higher temperature than in the case of curve 12 'because the falling arrangement of the second evaporator section enables lower gas velocities and thus less pressure loss.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)
  • Devices That Are Associated With Refrigeration Equipment (AREA)
  • Compression-Type Refrigeration Machines With Reversible Cycles (AREA)

Abstract

A heat exchanger (1) provided as an injection evaporator for a refrigeration machine comprises a first section (11) with a broad flow cross-section, in which the refrigerant mixture can spread, at the bottom in the admission region, under the influence of gravity and subsequently rises in the manner of a flooded evaporator. A second section (12) follows, in which the flow cross-section is so narrow that a gas speed sufficient for oil transport is achieved. The boundary between the two sections lies below the region of complete evaporation of the refrigerant so that the oil reaches the second section mixed with liquid refrigerant. <IMAGE>

Description

Bei Verdampfern für Kältemaschinen, unter denen im vorliegenden Zusammenhang auch Wärmepumpen zu verstehen sind, unterscheidet man zwischen solchen für gefluteten Betrieb und solchen für Einspritzbetrieb. Bei gefluteten Verdampfern (DE-A-3309979) wird das Kältemittel in flüssiger Phase zugeführt und mit gemischten Phasen abgeführt, wobei ein Abscheider zur Phasentrennung erforderlich ist. Da der Druckverlust und der statische Druckunterschied innerhalb des Verdampfers gering sind, ist die Verdampfungstemperatur, die vom Druck des Kältemittels bestimmt ist, über die Höhe des Verdampfers im wesentlichen konstant. Dies ist günstig für die Energiebilanz sowie für solche Anwendungsfälle, in denen es auf die Kontrollierbarkeit des Temperaturverlaufs in dem zu kühlenden Medium ankommt, beispielsweise bei der eisfreien Kühlung von Wasser nahe dem Gefrierpunkt mit hoher Wärmeflußdichte. Nachteilig fällt insbesondere bei kleineren Anlagen der Bau- und Regelungsaufwand für den Abscheider sowie die Notwendigkeit einer besonderen Ölrückführung vom Abscheider zum Kompressor ins Gewicht. Letztere ergibt sich daraus, daß das zur Schmierung des Kompressors erforderliche Öl zum Teil mit dem Kältemittel abgeführt wird, sich im Kondensator im flüssigen Anteil des Kältemittels löst oder damit mischt, damit aus dem Verdampfer in den Abscheider gelangt und sich dort infolge Destillation im flüssigen Anteil anreichert. Die Plattenwärmeaustauscher für geflutete Verdampfer (DE-A 3147378, US-A 2028213) zeichnen sich durch einen Kältemittelraum aus, in welchem das verdampfende Kältemittelgemisch entgegen der Schwerkraft aufsteigt und die einen so großen Strömungsquerschnitt aufweisen, daß sich das Gemisch über die Breite des Wärmeaustauschers im wesentlichen aufgrund von Schwerkraftwirkung hinreichend gleichmäßig verteilen kann.In the case of evaporators for refrigeration machines, which also include heat pumps in the present context, a distinction is made between those for flooded operation and those for injection operation. In the case of flooded evaporators (DE-A-3309979), the refrigerant is supplied in the liquid phase and discharged with mixed phases, a separator being required for phase separation. Since the pressure loss and the static pressure difference within the evaporator are small, the evaporation temperature, which is determined by the pressure of the refrigerant, is essentially constant over the height of the evaporator. This is favorable for the energy balance and for those applications in which the controllability of the temperature profile in the medium to be cooled is important, for example in the ice-free cooling of water near freezing point with a high heat flux density. In the case of smaller systems in particular, the construction and control expenditure for the separator and the need for a special oil return from the separator to the compressor are disadvantageous. The latter results from the fact that the oil required for lubricating the compressor is partly removed with the refrigerant, in the The condenser in the liquid portion of the refrigerant dissolves or mixes with it so that it passes from the evaporator into the separator and accumulates there as a result of distillation in the liquid portion. The plate heat exchanger for flooded evaporators (DE-A 3147378, US-A 2028213) are characterized by a refrigerant space in which the evaporating refrigerant mixture rises against gravity and which have such a large flow cross section that the mixture spreads across the width of the heat exchanger can distribute sufficiently evenly due to the effects of gravity.

Bei Verdampfern mit Einspritzbetrieb (FR-A-2549585) wird das Kältemittel dem Verdampfer ohne vorherige Abscheidung als Gemisch der flüssigen und der gasförmigen Phase zugeführt und vollständig verdampft, wobei zur sicheren Vermeidung von Flüssigkeitsschlägen im Kompressor und für die Regelung des als thermostatisches Expansionsventil ausgeführten Einspritzventils eine gewisse Überhitzung in Kauf genommen werden muß. Der apparative Aufwand für eine Kältemaschine im Einspritzbetrieb ist geringer, weshalb diese Bauweise für kleinere Anlagen (beispielsweise unter 200 KW) oft vorgezogen wird. Jedoch hat sie den Nachteil, daß am Verdampfer infolge Zwangsdurchlaufs ein beträchtlicher Druckabfall und damit kältemittelseitig ein beträchtlicher Temperaturunterschied auftritt, der nicht nur wirtschaftlich unerwünscht ist, sondern auch dem Einsatz bei genauer Temperaturführung des zu kühlenden Mediums, beispielsweise für Wärmepumpen oder Eiswasseranlagen mit nahe dem Gefrierpunkt liegender Wassertemperatur, entgegensteht. Der Zwangsdurchlauf soll zum einen gewährleisten, daß das Kompressorschmieröl, das nach Verdampfung des Kältemittels als einzige flüssige Komponente im Verdampfer verbleibt, durch hinreichende Gasgeschwindigkeit ausgetragen wird. Zum anderen soll er gewährleisten, daß die Wärmeaustauscherflächen trotz des geringen Flüssigkeitsanteils (schon am Verdampfereinlaß nur wenige Vol.-%) gleichmäßig benetzt sind. Bei vergleichsweise geringen Wärmestromdichten, wie sie bei Wärmeaustauschern mit gasförmigem Außenmedium vorliegen, kann man die letztere Bedingung mit mäßigen Geschwindigkeiten und mäßigem Druckabfall erfüllen (FR-A 2549585). Jedoch sind hohe Geschwindigkeiten mit entsprechend hohem Druckverlust erforderlich, wenn hohe Wärmestromdichten erreicht werden sollen, wie dies bei flüssigem Außenmedium (beispielsweise bei Rieselkühlern) möglich ist. Dabei ist es üblich (GB-A 1286446; DE-A 3536325) den Strömungsquerschnitt entsprechend der Zunahme des strömenden Gemischvolumens im Laufe der Wärmeaustauscherstrecke zu vergrößern. Ein gegenteiliger, schon sehr alter Vorschlag für eine Anordnung mit fallender Kältemittelführung (DE-C 161027) steht in Widerspruch zu jahrzehntelanger Praxis und maßgebenden physikalischen Gesichtspunkten.In evaporators with injection operation (FR-A-2549585), the refrigerant is supplied to the evaporator without prior separation as a mixture of the liquid and the gaseous phase and completely evaporated, whereby to reliably avoid liquid hammer in the compressor and to control the injection valve designed as a thermostatic expansion valve a certain amount of overheating has to be accepted. The expenditure on equipment for a refrigeration machine in injection mode is lower, which is why this design is often preferred for smaller systems (for example below 200 KW). However, it has the disadvantage that there is a considerable pressure drop on the evaporator as a result of a forced flow and thus a considerable temperature difference on the refrigerant side, which is not only economically undesirable, but also for use with precise temperature control of the medium to be cooled, for example for heat pumps or ice water systems with near freezing point lying water temperature. The forced flow is intended, on the one hand, to ensure that the compressor lubricating oil, which remains after evaporation of the refrigerant as the only liquid component in the evaporator, is discharged through a sufficient gas velocity. On the other hand, it is intended to ensure that the heat exchanger surfaces are wetted evenly despite the small amount of liquid (only a few% by volume at the evaporator inlet) are. With comparatively low heat flow densities, such as are present in heat exchangers with a gaseous external medium, the latter condition can be met with moderate speeds and a moderate pressure drop (FR-A 2549585). However, high speeds with a correspondingly high pressure loss are required if high heat flow densities are to be achieved, as is possible with a liquid external medium (for example with trickle coolers). It is customary (GB-A 1286446; DE-A 3536325) to increase the flow cross section in accordance with the increase in the flowing mixture volume in the course of the heat exchanger section. A contrary, very old proposal for an arrangement with falling refrigerant flow (DE-C 161027) contradicts decades of practice and relevant physical considerations.

Es ist zwar bei Einspritzverdampfern bekannt, innerhalb eines Plattenverdampfers mehrere, voneinander gesonderte Abschnitte mit unterschiedlichen Strömungsquerschnitten vorzusehen; jedoch bilden diese lediglich eine bauliche, nicht aber eine funktionelle Einheit, weil sie jeweils gesondert mit einem Einspritzventil versehen sind, was einen hohen regelungstechnischen und baulichen Aufwand verlangt. Auch kann der prinzipielle Nachteil, daß in Einspritzverdampfern ein hoher Druckabfall und damit eine große Temperaturdifferenz auftritt, mit diesen Mitteln nicht vermieden werden.It is known in the case of injection evaporators to provide a plurality of separate sections with different flow cross sections within a plate evaporator; However, these only form a structural unit, but not a functional unit, because they are each separately provided with an injection valve, which requires a high level of control engineering and construction. The basic disadvantage that a high pressure drop and thus a large temperature difference occurs in injection evaporators cannot be avoided by these means.

Die Erfindung will bei einem Wärmeaustauscher, der als Einspritzverdampfer für eine Kältemaschine hohe Wärmestromdichte und die Abförderung ausfallenden Öls ermöglicht, einen geringen Druckabfall, vergleichbar demjenigen eines gefluteten Verdampfers, erreichen.In the case of a heat exchanger which, as an injection evaporator for a refrigeration machine, enables a high heat flow density and the removal of oil which has been removed, the invention aims to achieve a low pressure drop, comparable to that of a flooded evaporator.

Die erfindungsgemäße Lösung besteht in einem Verfahren zum Betrieb einer Kältemaschine, das sich dadurch auszeichnet, daß das Kältemittel aus einem ersten Abschnitt des Wärmeaustauschers mit zweitem Strömungsquerschnitt und Schwerkraftverteilung des steigend geführten Kältemittels im noch nicht vollständig verdampften Zustand in einen zweiten Abschnitt mit engerem Strömungsquerschnitt übertritt, wobei das Kältemittel im zweiten Abschnitt eine zur Förderung ausgefallenen Öls ausreichende Geschwindigkeit aufweist.The solution according to the invention consists in a method for operating a refrigeration machine, which is characterized in that the refrigerant passes from a first section of the heat exchanger with a second flow cross section and gravity distribution of the rising refrigerant into a second section with a narrower flow cross section in the not yet fully evaporated state, wherein the refrigerant in the second section has a speed sufficient to convey failed oil.

Im ersten Abschnitt des Wärmeaustauschers stellt sich daher ein Betriebsverhalten ähnlich dem eines gefluteten Verdampfers ein. Der Druckabfall in diesem Abschnitt ist daher sehr gering. Dies macht eine genaue Temperaturführung möglich. Bei der Kühlung von Wasser ist daher ein eisfreier Betrieb bis auf beispielsweise 0,5°C möglich. Die Wärmewirtschaftlichkeit wird verbessert. Ein höherer Druck- und Temperaturabfall ergibt sich erst innerhalb des zweiten Verdampferabschnitts.In the first section of the heat exchanger there is therefore an operating behavior similar to that of a flooded evaporator. The pressure drop in this section is therefore very low. This enables precise temperature control. When cooling water, ice-free operation down to, for example, 0.5 ° C is therefore possible. The heat economy is improved. A higher pressure and temperature drop occurs only within the second evaporator section.

Die Erfindung beruht auf der Erkenntnis, daß bei einem Einspritzverdampfer eine wesentlich erhöhte Geschwindigkeit des Kältemittels erst in demjenigen Bereich erforderlich ist, in welchem die vollständige Verdampfung der flüssigen Phase des Kältemittels stattfindet, damit eine gleichmäßige Überhitzung ohne mitgerissene Reste der flüssigen Phase erfolgt und weil auch erst hier die Konzentration des Öls in der flüssigen Kältemittelkomponente infolge von Kältemittelverdampfung so groß wird, daß die Gefahr des Ölausfalls entsteht. Ferner beruht die Erfindung auf der Erkenntnis, daß auch im Einspritzbetrieb anfangs im Verdampfer der Flüssigkeitsanteil noch groß genug ist, um eine hinreichende Flüssigkeitsbenetzung der Verdampferinnenflächen auch bei relativ geringer Mediumsgeschwindigkeit zu gewährleisten. Wenn auch der Flüssigkeitsanteil beim Eintritt in den Verdampfer nur in der Größenordnung von 10 Vol.-% liegt, umfaßt er doch noch rund 80 Gew.-%. Dies reicht aus für eine hinreichende Schwerkraftverteilung des einkommenden Gemisches zumindest im unteren Einführungsbereich des ersten Abschnitts. Eine vollkommen gleichmäßige Dichteverteilung ist nicht erforderlich, weil die Benetzung auch durch die sich anschließende Gasentwicklung und die davon hervorgerufene Turbulenz gefördert wird.The invention is based on the knowledge that, in the case of an injection evaporator, a significantly increased speed of the refrigerant is only required in the area in which the complete evaporation of the liquid phase of the refrigerant takes place, so that there is uniform overheating without entrained residues of the liquid phase and because also it is only here that the concentration of the oil in the liquid refrigerant component becomes so great as a result of refrigerant evaporation that there is a risk of oil failure. Furthermore, the invention is based on the knowledge that even in the injection mode, the liquid portion in the evaporator is still large enough to ensure adequate liquid wetting of the evaporator inner surfaces even at a relatively low medium speed. Even if the proportion of liquid entering the evaporator is only of the order of 10% by volume, it still comprises around 80% by weight. This is sufficient for a sufficient distribution of gravity of the incoming mixture at least in the lower insertion area of the first section. A completely even density distribution is not necessary because the wetting also through the subsequent gas development and the resulting turbulence is promoted.

Zwar ist ein Verdampfer für einen Haushaltskühlschrank bekannt (US-A 2414952), der bei steigender Kältemittelführung einen ersten Abschnitt mit einer Anzahl parallel geschalteter Kanäle sowie einen zweiten, höher liegenden Abschnitt umfaßt, der von lediglich einem Kanal gebildet ist. Die einzige Angabe über die Strömungsquerschnitte besteht darin, daß diese im zweiten Abschnitt so groß sein sollen, daß flüssiges Kältemittel entgegen dem Gasstrom zum ersten Abschnitt zurückfließen kann. Die Gasgeschwindigkeit ist demnach auch nicht groß genug, um ausfallendes Öl mitzureißen. Dieses sammelt sich nachher im Verdampfer an.An evaporator for a household refrigerator is known (US Pat. No. 2,414,952) which, as the refrigerant flow increases, comprises a first section with a number of channels connected in parallel and a second, higher section which is formed by only one channel. The only information about the flow cross-sections is that they should be so large in the second section that liquid refrigerant can flow back to the first section against the gas flow. The gas velocity is therefore not high enough to carry away any oil that falls out. This then accumulates in the evaporator.

Wie groß der erste Abschnitt im Verhältnis zum zweiten gestaltet werden kann, hängt von der Art des Kältemittels sowie von der Art und der zu erwartenden Menge des Kompressorschmiermittels ab. Je besser mischbar das Schmiermittel auch noch mit kleinen Mengen des flüssigen Kältemittels ist, um so sicherer kann man sein, daß das Schmiermittel auch noch im Endbereich des ersten Verdampferabschnitts so stark durch das flüssige Kältemittel verdünnt ist und die Viskosität daher so stark herabgesetzt ist, daß es hinreichend sicher transportiert wird. Auch die Temperatur spielt dabei eine Rolle. Eine Kalkulation hat ergeben, daß bei Verwendung des Kältmittels Frigen R 22 unter Anwendung von Öl als Schmiermittel für einen Kolbenkompressor das Öl so lange noch mit hinreichender Sicherheit in der flüssigen Phase des Kältemittels im Verdampfer transportiert wird, als die flüssige Komponente nicht weniger als etwa 20 Gewichtsprozent des Kältemittels ausmacht. Daraus ergibt sich wiederum, daß bei Ausführung des Verdampfers als vertikaler Plattenverdampfer nicht mehr als das obere Drittel bis Viertel in Gestalt engerer, mäandrierter Strömungskanäle ausgeführt zu werden braucht. Der erste Abschnitt nimmt demnach etwa zwei Drittel bis drei Viertel der Verdampferhöhe ein.The size of the first section in relation to the second depends on the type of refrigerant and the type and amount of compressor lubricant to be expected. The more miscible the lubricant is even with small amounts of the liquid refrigerant, the safer it can be that the lubricant is diluted so much by the liquid refrigerant in the end region of the first evaporator section and the viscosity is therefore reduced so much that it is transported with sufficient security. The temperature also plays a role. A calculation has shown that when using the refrigerant Frigen R 22 using oil as a lubricant for a piston compressor, the oil is transported in the evaporator's liquid phase with sufficient certainty as long as the liquid component is not less than about 20 Weight percent of the refrigerant. This in turn means that when the evaporator is designed as a vertical plate evaporator, no more than the upper third to quarter need to be designed in the form of narrower, meandered flow channels. The first section takes accordingly about two thirds to three quarters of the evaporator height.

Der erste Abschnitt kann in der Art eines gefluteten Verdampfers ausgebildet sein, nämlich als im wesentlichen einheitlicher Raum vergleichsweise großen Horizontalquerschnitts, in welchem das Gemisch im wesentlichen senkrecht aufwärts strömen kann. Verengungen können sich auf den Zweck der Vergleichmäßigung der Strömungsbewegung über den gesamten Querschnitt und der Verbesserung des Wärmeübergangs beschränken, nämlich vorzugsweise in der Form von Schweißverbindungen zwischen den den Strömungsraum begrenzenden Platten, die gegenüber der Vertikalrichtung wechselnd versetzt sind und als kurze Schweißstrecken, Schweißpunkte oder dgl. ausgebildet sein können. Jede Schweißstelle bildet einen Verdampfungskern.The first section can be designed in the manner of a flooded evaporator, namely as an essentially uniform space of comparatively large horizontal cross-section, in which the mixture can flow essentially vertically upwards. Constrictions can be limited to the purpose of equalizing the flow movement over the entire cross-section and improving the heat transfer, namely preferably in the form of welded connections between the plates delimiting the flow space, which are alternately offset with respect to the vertical direction and as short welding distances, welding spots or the like can be trained. Each welding point forms an evaporation core.

Der Verdampfer kann in getauchter Betriebsweise, d.h. in dem mit der zu kühlenden Flüssigkeit gefüllten Behälter angewendet werden. Jedoch zeigen sich seine Vorteile besonders dann, wenn er als Berieselungsverdampfer ausgeführt ist. Dabei kann, wie an sich bekannt, ein den oberen Abschluß der Platte bildender Sammler horizontal quer zur Plattenebene verdickt ausgeführt sein, um den Fallinien des außen herabströmenden Wassers eine stärkere Horizontalkomponente zu verleihen, wodurch das Wasser veranlaßt wird, sich als gleichmäßiger Film auszubreiten. Wenn im Zusammenhang der Erfindung der zweite Verdampferabschnitt in Form von horizontalen, wechselnd an beiden Enden miteinander in Verbindung stehenden Kanälen ausgeführt ist, kann vorgesehen sein, daß der oberste dieser Kanäle horizontal stärker als die folgenden Kanäle verdickt ist, um diese Funktion zu übernehmen.The evaporator can be used in immersed mode, i.e. in the container filled with the liquid to be cooled. However, its advantages are particularly evident when it is designed as a sprinkler evaporator. In this case, as is known per se, a collector forming the upper end of the plate can be thickened horizontally transversely to the plane of the plate in order to give the falling lines of the water flowing down from the outside a stronger horizontal component, which causes the water to spread out as a uniform film. If, in the context of the invention, the second evaporator section is designed in the form of horizontal channels which are alternately connected at both ends, it can be provided that the uppermost of these channels is horizontally thicker than the following channels in order to perform this function.

Besonderes Augenmerk gilt der Überhitzung des Kältemittelgases und der Förderung des Öls in diesen Kanälen, wenn das Kältemittel gänzlich oder überwiegend verdampft ist. Damit das Öl, das sich vornehmlich im unteren Bereich der Horizontalkanäle sammelt, nicht entgegen der Gasströmung zurückfließen kann, wird gemäß der Erfindung jeweils einlaufseitig eine erhöhte Schwelle an der unteren Kanalbegrenzung vorgesehen. An dem in Strömungsrichtung hinteren Ende jedes Horizontalkanals können Einrichtungen vorgesehen sein, die die Mitnahme des Öls zu dem nächstoberen Kanal erleichtern, beispielsweise eine Verengung des Strömungsquerschnitts zur Erhöhung der Gasgeschwindigkeit und zur Intensivierung der Förderwirkung. Der das Kältemittelgas vom Verdampfer abführende Stutzen wird zweckmäßigerweise nahe der unteren Begrenzung des zugehörigen Kanals des zweiten Abschnitts angeschlossen, damit das Öl nicht abermals angehoben zu werden braucht.Particular attention is paid to the overheating of the refrigerant gas and the extraction of the oil in these channels when the refrigerant has completely or predominantly evaporated. In order to the oil, which mainly collects in the lower area of the horizontal channels, cannot flow back against the gas flow, according to the invention an increased threshold is provided on the inlet side at the lower channel boundary. At the rear end of each horizontal channel in the direction of flow, devices can be provided which facilitate the entrainment of the oil to the next upper channel, for example a narrowing of the flow cross section to increase the gas velocity and to intensify the delivery effect. The connecting piece discharging the refrigerant gas from the evaporator is expediently connected near the lower limit of the associated channel of the second section, so that the oil does not have to be raised again.

Das den Verdampfer versorgende Einspritzventil ist zweckmäßigerweise ein thermostatisches Regelventil, das mit Anschluß an eine überhitztes Kältemittelgas vom Verdampfer abführende Leitung ausgeführt ist, damit die Kältemittelzufuhr zum Verdampfer abhängig von der Überhitzungstemperatur geregelt wird. Dadurch wird Gewähr dafür gegeben, daß der wärmewirtschaftlich unerwünschte Überhitzungsbereich des Verdampfers so klein wie möglich bleibt.The injector supplying the evaporator is expediently a thermostatic control valve which is designed with a connection to an overheated refrigerant gas leading from the evaporator so that the refrigerant supply to the evaporator is regulated as a function of the superheating temperature. This ensures that the thermally undesired overheating area of the evaporator remains as small as possible.

Die Kältemaschine wird so eingestellt, daß das Kältemittel beim Erreichen der Grenze zwischen dem ersten und dem zweiten Verdampferabschnitt im wesentlichen ständig einen zur Verhinderung von Schmiermittelausfall ausreichenden flüssigen Anteil aufweist. Die Nichteinhaltung dieser Bedingung ist kurzzeitig gestattet, nämlich für so kurze Zeitabschnitte, daß sich das Schmiermittel währenddessen nicht unzulässig stark im ersten Verdampferabschnitt ansammeln und damit die Schmierung des Kompressors gefährden kann.The refrigeration machine is set so that the refrigerant essentially has a sufficient liquid portion to prevent lubricant failure when the boundary between the first and the second evaporator section is reached. Non-compliance with this condition is permitted for a short time, namely for such short periods of time that the lubricant cannot accumulate excessively in the first evaporator section and thus endanger the lubrication of the compressor.

Erreicht wird auf diese Weise das Ziel, bei einem Einspritzverdampfer den Gesamtdruckverlust sowie die Veränderung der Verdampfungstemperatur auf etwa ein Drittel zu reduzieren. Während beispielsweise bei einer herkömmlichen Einspritzverdampferplatte für einen Rieselkühler mit einer Wärmestromdichte von 3 KW/m² die Veränderung der Verdampfungstemperatur in einem typischen Anwendungsfall mit ca. 9°C nicht mehr akzeptabel ist, sinkt sie dank der Erfindung dabei auf ca. 3°C, wobei die stärkste Temperaturabsenkung auf einen kleinen, oberen Abschnitt des Verdampfers reduziert ist, in welchem die Wassertemperatur noch vergleichweise hoch und daher die Eisbildungsgefahr gering ist. Dadurch wird erstmals die Möglichkeit geschaffen, einen Einspritzverdampfer zur Kühlung von Wasser nahe dem Gefrierpunkt zu verwenden. In dem unteren, ersten Verdampferabschnitt wird dabei durch die versetzte Schweißnahtanordnung eine bessere Verteilung des Wasserfilms, ein erhöhter Wärmeübergang durch höheren Turbulenzgrad und dadurch eine höhere Wandtemperatur erreicht, was gleichfalls die Möglichkeiten verbessert, ohne Eisansatz näher an den Gefrierpunkt heranzukühlen.The goal is achieved in this way, the total pressure loss and the Reduce evaporation temperature change to about a third. For example, while in a conventional injection evaporator plate for a trickle cooler with a heat flow density of 3 KW / m², the change in the evaporation temperature in a typical application is no longer acceptable at approx. 9 ° C, thanks to the invention it drops to approx. 3 ° C, whereby the greatest drop in temperature is reduced to a small, upper section of the evaporator, in which the water temperature is still comparatively high and the risk of ice formation is therefore low. This makes it possible for the first time to use an injection evaporator to cool water near freezing. In the lower, first evaporator section, the offset weld seam arrangement achieves a better distribution of the water film, an increased heat transfer due to a higher degree of turbulence and thereby a higher wall temperature, which likewise improves the possibilities of cooling closer to the freezing point without ice build-up.

Bei Eisspeicherbetrieb (sowohl im Berieselungsverfahren als auch unter Wasser) wird durch den kontrollierten und gleichmäßigeren Temperaturverlauf in der Verdampferplatte ein gleichmäßigeres Anwachsen des Eises garantiert, als es bei Einspritzverdampfern herkömmlicher Bauweise möglich ist. Es kann auch die Eisabsprengung von den Platten mittels Heißgaseinspeisung angewendet werden.In ice storage mode (both in the sprinkling process and under water), the controlled and more uniform temperature curve in the evaporator plate guarantees a more uniform growth of the ice than is possible with injection evaporators of conventional design. Ice blasting from the plates by means of hot gas injection can also be used.

Weitere Einzelheiten der Erfindung werden im folgenden anhand der Zeichnung dargestellt. Darin zeigt:

Fig. 1
eine erste Ausführungsform des Verdampfers im Querschnitt mit einer schematischen Darstellung der Kältemaschine,
Fig. 2
Einzelheiten des Verdampferaufbaus im zweiten Abschnitt,
Fig. 3
eine zweite Verdampferausführung und
Fig. 4
den Temperaturverlauf über die Höhe des Verdampfers im Vergleich mit anderen Verdampferbauarten.

Further details of the invention are shown below with reference to the drawing. It shows:
Fig. 1
a first embodiment of the evaporator in cross section with a schematic representation of the refrigerator,
Fig. 2
Details of the evaporator structure in the second section,
Fig. 3
a second evaporator version and
Fig. 4
the temperature curve over the height of the evaporator in comparison with other evaporator types.

Gemäß Fig. 1 besteht die Kältemaschine aus Verdampfer 1, Kompressor 2, Kondensator 3 und thermostatischem Expansionsventil 4, dessen Impulsleitung 5 an einen Temperaturfühler 6 anschließt, der an der Leitung 7 angeordnet ist, die das überhitzte Gas vom Verdampfer 1 dem Kompressor 2 zuführt.1, the refrigerator consists of evaporator 1, compressor 2, condenser 3 and thermostatic expansion valve 4, the pulse line 5 of which connects to a temperature sensor 6, which is arranged on line 7, which supplies the superheated gas from evaporator 1 to compressor 2.

Der Verdampfer 1 ist ein vertikaler Plattenverdampfer, der von dem Kältemittel von unten nach oben durchströmt ist. Er besteht aus einem ersten Abschnitt 11 und einem zweiten Abschnitt 12. Den ersten Abschnitt durchströmt das Kältemittel über seine ganze Breite im wesentlichen gleichmäßig von unten nach oben ähnlich einem gefluteten Verdampfer, wobei versetzt zur Vertikalrichtung angeordnete Horizontalschweißstrecken 13 für eine gleichmäßige Durchströmung und guten Wärmeübergang sorgen. Da der zur Verfügung stehende Strömungsquerschnitt groß ist, ist der Druckverlust gering.The evaporator 1 is a vertical plate evaporator, through which the refrigerant flows from bottom to top. It consists of a first section 11 and a second section 12. The first section of the refrigerant flows substantially uniformly over its entire width from bottom to top similar to a flooded evaporator, with horizontal welding sections 13 arranged offset to the vertical direction ensuring a uniform flow and good heat transfer . Since the available flow cross-section is large, the pressure loss is low.

Im zweiten Abschnitt 12 wird der Strömungsweg von einem Mäanderkanal 14 gebildet, der sich aus mehreren horizontalen, an den Enden wechselnd miteinander verbundenen Kanalstrecken zusammensetzt, die durch horizontale, die dem Plattenverdampfer bildenden Bleche verbindende Schweißnähte 15 gebildet sind. Der Querschnitt des Kanals 14 ist wesentlich geringer als der des ersten Verdampferabschnitts. Vorzugsweise ist nämlich der Strömungsquerschnitt im ersten Abschnitt mindestens dreimal, besser mindestens fünfmal und meist mindestens zehnmal größer als im zweiten Abschnitt, woraus sich für den zweiten Abschnitt eine entsprechend größere Gasgeschwindigkeit ergibt. Der Verdampfer wird so betrieben, daß das Kältemittel ihm unten mit einem Gewichtsanteil der flüssigen Phase von bspw. 70% zugeführt ist. Die zugeführte Menge wird abhängig von der Temperatur des überhitzten Gases in der Leitung 7 von dem Einspritzventil bestimmt. Dadurch wird sichergestellt, daß das Kältemittel den Beginn des zweiten Abschnitts 12 stets mit einem so großen flüssigen Anteil erreicht, daß der Transport des Öls in den zweiten Abschnitt gewährleistet ist, wo das Kältemittel vollständig verdampft und die Gasgeschwindigkeit so hoch ist, daß das Öl mitgerissen wird.In the second section 12, the flow path is formed by a meandering channel 14, which is composed of a plurality of horizontal channel sections which are alternately connected at the ends and which are formed by horizontal weld seams 15 connecting the sheets forming the plate evaporator. The cross section of the channel 14 is significantly smaller than that of the first evaporator section. The flow cross section in the first section is preferably at least three times, better at least five times and usually at least ten times larger than in the second section, which results in a correspondingly higher gas velocity for the second section. The evaporator is operated so that the refrigerant with a bottom Weight fraction of the liquid phase of, for example, 70% is supplied. The quantity supplied is determined as a function of the temperature of the superheated gas in line 7 by the injection valve. This ensures that the refrigerant always reaches the beginning of the second section 12 with such a large liquid fraction that the transport of the oil into the second section is ensured, where the refrigerant evaporates completely and the gas velocity is so high that the oil is entrained becomes.

Damit das sich im unteren Bereich der den Kanal 14 bildenden Horizontalstrecken sammelnde Öl nicht zurückfließen kann, kann zweckmäßigerweise jeweils am Kanalanfang eine Schwelle 16 vorgesehen sein. Statt dessen wäre es auch denkbar, die Horizontalkanäle leicht fallend anzuordnen. Ferner können nicht dargestellte Schikanen bei den vertikalen Kanalverbindungen vorgesehen sein, um dort die Gasströmung zu intensivieren und den Öltransport zu verbessern. An den obersten Kanal 17 ist der Abführungsstutzen 18 nahe der unteren Begrenzung des Kanals 17 angeordnet, um das Öl dort leichter abführen zu können. Ferner kann der oberste Kanal 17 stärker gebaucht sein als die darunter befindlichen, um die Flüssigkeitsfilmbildung auf der Außenseite des Verdampfers bei Berieselung zu verbessern, wie dies in Fig. 2 gestrichelt angedeutet ist.So that the oil collecting in the lower region of the horizontal sections forming the channel 14 cannot flow back, a threshold 16 can expediently be provided at the beginning of the channel. Instead, it would also be conceivable to arrange the horizontal channels to fall slightly. Furthermore, baffles (not shown) can be provided in the vertical channel connections in order to intensify the gas flow there and to improve the oil transport. On the uppermost channel 17, the discharge pipe 18 is arranged near the lower boundary of the channel 17 in order to be able to discharge the oil there more easily. Furthermore, the uppermost channel 17 can be bulged more than the ones below it, in order to improve the liquid film formation on the outside of the evaporator when it is sprinkled, as is indicated by dashed lines in FIG. 2.

Im ersten Verdampferabschnitt sorgt die aufsteigende Bewegung des Kältemittels dafür, daß ohne Separationserscheinungen trotz relativ langsamer Durchströmung eine gleichmäßige Benetzung der inneren Oberflächen gewährleistet ist. Für den zweiten Verdampferabschnitt gilt hingegen die überwiegend horizontale Durchströmung als vorteilhaft, damit in denjenigen Bereichen, in denen je nach Gasgeschwindigkeit mit Separation von Öl gerechnet werden muß, dieses sich im unteren Bereich der Horizontalkanäle sammeln kann, um in geringerem Maße durch Benetzung der übrigen Innenoberflächen den Wärmeübergang zu verschlechtern. Anders als in Fig. 1 kann im zweiten Abschnitt zur Verbesserung der Ölförderung (insbesondere für die Flüssigkeitsabkühlung) auch eine fallende Verbindung der Horizontalkanäle vorgesehen sein, wobei entsprechend der schematischen Darstellung in Fig. 3 der oberste Kanal 17 durch einen Vertikalkanal 20 unmittelbar mit dem ersten Abschnitt 11 verbunden ist. Dies ergibt die Möglichkeit, die Strömungsgeschwindigkeit im zweiten Abschnitt 12 geringer zu halten, als es sonst mit Rücksicht auf die Ölförderung möglich wäre, so daß auch der Druckverlust und damit die Temperaturabsenkung gering bleiben. Dies kompensiert für manche Anwendungsfälle den Nachteil, daß die tiefste Temperatur nicht am höchsten Punkt des Verdampfers auftritt.In the first evaporator section, the ascending movement of the refrigerant ensures that the inner surfaces are evenly wetted despite the relatively slow flow without separation phenomena. For the second evaporator section, on the other hand, the predominantly horizontal flow is considered to be advantageous, so that in those areas in which oil must be expected to separate depending on the gas velocity, this can collect in the lower area of the horizontal channels, to a lesser extent by wetting the other inner surfaces deteriorate the heat transfer. Unlike in Fig. 1 In the second section to improve oil production (in particular for liquid cooling), a falling connection of the horizontal channels can also be provided, the uppermost channel 17 being connected directly to the first section 11 by a vertical channel 20, as shown in FIG. 3. This gives the possibility of keeping the flow velocity in the second section 12 lower than would otherwise be possible with regard to the oil production, so that the pressure loss and thus the temperature drop also remain low. For some applications, this compensates for the disadvantage that the lowest temperature does not occur at the highest point of the evaporator.

Zwar ist es zweckmäßig, wenn die beiden Verdampferabschnitte Teile eines einheitlichen, einstückigen Plattenverdampfers sind. Jedoch soll eine mehrstückige Ausbildung nicht ausgeschlossen bleiben, wobei die den ersten Abschnitt bildende(n) Verdampferplatte(n) bei Gruppenanordnung in anderer Weise und an anderer Stelle angeordnet sein können als die die zweiten Abschnitte bildenden. Wichtig ist, daß die Verdampferabschnitte einen an ein einziges Einspritzventil angeschlossenen, einheitlichen Strömungsweg bilden.It is expedient if the two evaporator sections are parts of a uniform, one-piece plate evaporator. However, a multi-part design should not be ruled out, the evaporator plate (s) forming the first section being arranged in a group in a different way and at a different location than that forming the second sections. It is important that the evaporator sections form a uniform flow path connected to a single injection valve.

Es ist nicht erforderlich, daß die beiden Abschnitte durch eine plötzliche Querschnittsänderung voneinander abgrenzbar sind. Vielmehr ist auch ein allmählicher Übergang denkbar.It is not necessary that the two sections can be distinguished from one another by a sudden change in cross-section. Rather, a gradual transition is also conceivable.

Das Diagramm Fig. 4 veranschaulicht den Temperaturverlauf des Kältemittels und gegenüber dem Temperaturverlauf 19 des Berieselungswassers in °C über die Höhe H eines Plattenwärmeaustauschers gemäß Fig. 1 in durchgezogenen Linien. Dem sind die kältemittelseitigen Temperaturverläufe eines gefluteten Verdampfers gestrichelt und eines herkömmlichen Einspritzverdampfers strichpunktiert gegenübergestellt. Das Kältemittel und das berieselnde Wasser bewegen sich im Gegenstrom.The diagram in FIG. 4 illustrates the temperature profile of the refrigerant and in relation to the temperature profile 19 of the sprinkler water in ° C. over the height H of a plate heat exchanger according to FIG. 1 in solid lines. The refrigerant-side temperature profiles of a flooded evaporator are shown in broken lines and a conventional injection evaporator is shown in dash-dotted lines. The refrigerant and the sprinkling water move in counterflow.

Den gleichmäßigsten Temperaturverlauf erreicht der geflutete Verdampfer, bei dem in einem typischen Anwendungsbeispiel der geringe Druckabfall einen lediglich in der Größenordnung von 0,5°C liegenden Temperaturunterschied über die Höhe des Verdampfers verursacht. Hingegen erkennt man beim herkömmlichen Einspritzkühler einen starken Temperaturabfall von bspw. 9°C mit Vereisungsgefahr in mittlerer Höhe.The flooded evaporator achieves the most uniform temperature profile, in which, in a typical application example, the low pressure drop causes a temperature difference of only around 0.5 ° C across the height of the evaporator. On the other hand, the conventional desuperheater shows a sharp drop in temperature of, for example, 9 ° C with a risk of icing up in the middle.

Der Temperaturverlauf des erfindungsgemäßen Verdampfers umfaßt einen unteren Abschnitt 11′, der dem unteren Verdampferabschnitt 11 entspricht und in welchem die Temperaturverminderung etwa der des gefluteten Verdampfers entspricht. Nach oben schließt sich der zweite Kurvenabschnitt 12′ an, der demjenigen Teil des zweiten Verdampferabschnitts 12 entspricht, in welchem noch flüssige Phase gegenwärtig ist und in welchem demzufolge die Temperatur entsprechend der durch Druckabfall verursachten Verringerung der Verdampfungstemperatur absinkt. Da die Fließweglänge im engen Strömungsquerschnitt aber viel geringer ist als bei herkömmlichen Einspritzverdampfern wird insgesamt nur ein entsprechend geringerer Druckverlust stattfinden. Außerdem liegt der Punkt niedrigster Temperatur nahe dem obersten Punkt des Verdampfers, wo die Temperatur des Berieselungswassers verhältnismäßig hoch und daher die Vereisungsgefahr gering ist. Es schließt sich ein Kurvenabschnitt 12˝ an, der demjenigen Teil des zweiten Verdampferabschnitts 12 entspricht, in welchem die Überhitzung des trockenen, gasförmigen Kältemittels stattfindet.The temperature profile of the evaporator according to the invention comprises a lower section 11 ', which corresponds to the lower evaporator section 11 and in which the temperature reduction corresponds approximately to that of the flooded evaporator. At the top, the second curve section 12 'follows, which corresponds to that part of the second evaporator section 12 in which the liquid phase is still present and in which the temperature accordingly drops in accordance with the reduction in the evaporation temperature caused by the pressure drop. However, since the flow path length in the narrow flow cross section is much less than in conventional injection evaporators, only a correspondingly lower pressure loss will take place overall. In addition, the lowest temperature point is close to the uppermost point of the evaporator, where the temperature of the sprinkling water is relatively high and the risk of icing is therefore low. This is followed by a curve section 12 'which corresponds to that part of the second evaporator section 12 in which the overheating of the dry, gaseous refrigerant takes place.

Zusammenfassend läßt sich sagen, daß in dem kritischen, unteren Verdampferbereich der Temperaturverlauf des erfindungsgemäßen Einspritzverdampfers demjenigen eines gefluteten Verdampfers sehr ähnlich ist und daß er sich daher auch für solche Einsatzfälle eignet, in denen der Temperaturverlauf des zu kühlenden Mediums genau zu kontrollieren ist, beispielsweise nahe dessen Gefrierpunkt, wie dies für die Wasserseite mit Temperaturverlauf 19 in Diagramm 4 bei Kühlung bis auf 0,5°C vorausgesetzt ist.In summary, it can be said that in the critical, lower evaporator area, the temperature profile of the injection evaporator according to the invention is very similar to that of a flooded evaporator and that it is therefore also suitable for applications in which the temperature profile of the medium to be cooled has to be controlled, for example closely its freezing point, like this is required for the water side with temperature curve 19 in diagram 4 with cooling down to 0.5 ° C.

Wählt man statt der Verdampferanordnung gemäß Fig. 1 diejenige gemäß Fig. 3, so bleibt es im ersten Abschnitt bei dem Temperaturverlauf 11′. Für den zweiten Abschnitt ergibt sich der gepunktet dargestellte Temperaturverlauf 12‴, dessen Temperaturabsenkung im Verhältnis zur Wasserkurve 19 zwar einen etwas ungünstigeren Verlauf hat, weil das Temperaturminimum beiniedrigerer Wassertemperatur erreicht wird; jedoch liegt dieses Minimum bei höherer Temperatur als im Falle der Kurve 12′, weil die fallende Anordnung des zweiten Verdampferabschnitts geringere Gasgeschwindigkeiten und damit geringeren Druckverlust ermöglicht.If, instead of the evaporator arrangement according to FIG. 1, one chooses that according to FIG. 3, the temperature in the first section remains 11 ′. For the second section, the dotted temperature curve 12 ergibt results, the lowering of the temperature of which in relation to the water curve 19 is somewhat less favorable because the temperature minimum is reached at a lower water temperature; however, this minimum is at a higher temperature than in the case of curve 12 'because the falling arrangement of the second evaporator section enables lower gas velocities and thus less pressure loss.

Claims (12)

1. A method of operating a refrigerator having a heat exchanger as an injection evaporator, in which the refrigerant from a first section of the heat exchanger of broad flow cross-section and gravity distribution of the upwardly conveyed refrigerant passes in the not yet completely evaporated state into a second section of narrower flow cross-section, wherein it has a sufficiently fluid component to prevent precipitation of lubricant, and in that in the second section, in which it is completely evaporated, the refrigerant has sufficient velocity to convey precipitated oil.
2. A heat exchanger for carrying out the method according to Claim 1, having a first section (11) of broad flow cross-section and gravity distribution of the upwardly conveyed refrigerant, and having a second section (12) of narrower flow cross-section, wherein the heat exchanger is in the form of a vertical plate evaporator.
3. A heat exchanger according to Claim 2, characterised in that the first section (11) is in the form of a flooded evaporator.
4. A heat exchanger according to Claim 2 or 3, characterised in that the first section (11) is formed with a substantially vertical flow direction.
5. A heat exchanger according to Claim 4, characterised in that the interior of the first section is divided by welded joints offset with respect to the vertical direction.
6. A heat exchanger according to any one of Claims 2 to 5, characterised in that the first section (11) occupies approximately half to three quarters of the evaporator height.
7. A heat exchanger according to any one of Claims 2 to 6, characterised in that horizontal passages (14) provided in the second portion (12) have a raised barrier (16) at their lower boundary (15) on the inlet side.
8. A heat exchanger according to any one of Claims 2 to 7, characterised in that the horizontal passages (14) forming the second portion (12) are connected to one another in ascending sequence.
9. A heat exchanger according to any one of Claims 2 to 7, characterised in that the horizontal passages forming the second evaporator portion are connected to one another in descending sequence.
10. A heat exchanger according to any one of Claims 2 to 9, characterised in that the evaporator takes the form of a trickle evaporator.
11. A heat exchanger according to any one of Claims 2 to 10, characterised in that outlet connectors (18) are connected near to the lower boundary (15) of one passage of the second section.
12. A heat exchanger according to any one of Claims 2 to 11, characterised in that it is connected to an injection valve (4) which is a thermostatic control valve with a connection (5) to a duct (7) for removing overheated refrigerant gas from the evaporator (1).
EP89103178A 1988-02-23 1989-02-23 Heat exchanger as an injection evaporator for a refrigeration machine Expired - Lifetime EP0330198B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT89103178T ATE71709T1 (en) 1988-02-23 1989-02-23 HEAT EXCHANGER AS INJECTION EVAPORATOR FOR A REFRIGERATION MACHINE.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE8802339U DE8802339U1 (en) 1988-02-23 1988-02-23 Heat exchanger with low pressure loss
DE8802339U 1988-02-23

Publications (3)

Publication Number Publication Date
EP0330198A2 EP0330198A2 (en) 1989-08-30
EP0330198A3 EP0330198A3 (en) 1990-09-19
EP0330198B1 true EP0330198B1 (en) 1992-01-15

Family

ID=6820997

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EP89103178A Expired - Lifetime EP0330198B1 (en) 1988-02-23 1989-02-23 Heat exchanger as an injection evaporator for a refrigeration machine

Country Status (5)

Country Link
EP (1) EP0330198B1 (en)
AT (1) ATE71709T1 (en)
CH (1) CH676036A5 (en)
DE (2) DE8802339U1 (en)
ES (1) ES2029732T3 (en)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6557371B1 (en) * 2001-02-08 2003-05-06 York International Corporation Apparatus and method for discharging fluid
ES2884624T3 (en) * 2019-02-04 2021-12-10 Carrier Corp Heat exchanger
EP4324666A1 (en) * 2021-04-13 2024-02-21 Zhejiang Sanhua Automotive Components Co., Ltd. Fluid management apparatus

Family Cites Families (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE161027C (en) *
US1622376A (en) * 1925-09-08 1927-03-29 Chicago Pneumatic Tool Co Apparatus for refrigerating systems
DE570166C (en) * 1932-04-26 1933-02-11 Linde Eismasch Ag Method of equalizing the liquid level in multi-element evaporators of refrigeration machines
US2028213A (en) * 1933-04-21 1936-01-21 Arthur R Hemphill Heat exchanger or cooler
DE690583C (en) * 1936-08-28 1940-04-30 Pfaudler Co Tube evaporator for refrigeration machines
US2414952A (en) * 1944-09-08 1947-01-28 Houdaille Hershey Corp Evaporator unit
GB1286446A (en) * 1970-01-30 1972-08-23 Johannes Burmester & Co Plate heat exchanger
NL7905978A (en) * 1979-08-03 1981-02-05 Brink Luchtverwarming Bv Gas fired heat exchanger - has element sides alternately indented and fan connected to smoke box outlet
DE3147378C2 (en) * 1981-11-30 1985-05-23 Johs. Burmester & Co GmbH, 2054 Geesthacht Falling film evaporator plate for a refrigeration system
DE3309979A1 (en) * 1983-03-19 1984-09-20 Hans 2000 Hamburg Sladky Evaporator
FR2549585A1 (en) * 1983-07-21 1985-01-25 Axergie Sa Evaporator for an installation with a closed thermodynamic loop for the flow of a working fluid, and installation incorporating this evaporator
JPS60200089A (en) * 1984-03-23 1985-10-09 Hitachi Ltd Direct expansion type regenerative heat exchanger
US4712612A (en) * 1984-10-12 1987-12-15 Showa Aluminum Kabushiki Kaisha Horizontal stack type evaporator

Also Published As

Publication number Publication date
CH676036A5 (en) 1990-11-30
ATE71709T1 (en) 1992-02-15
DE58900709D1 (en) 1992-02-27
DE8802339U1 (en) 1988-04-14
ES2029732T3 (en) 1992-09-01
EP0330198A2 (en) 1989-08-30
EP0330198A3 (en) 1990-09-19

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