GB2317223A

GB2317223A - Controlling the operation of a cooling circuit

Info

Publication number: GB2317223A
Application number: GB9719376A
Authority: GB
Inventors: Reinhard Zeppenfeld
Original assignee: Gwk Gesellschaft Waerme Kaeltetechnik Mbh; GWK Gesellschaft Waerme Kaeltetechnik mbH
Current assignee: Gwk Gesellschaft Waerme Kaeltetechnik Mbh; Technotrans Solutions GmbH
Priority date: 1996-09-13
Filing date: 1997-09-11
Publication date: 1998-03-18
Anticipated expiration: 2017-09-11
Also published as: DE19637248A1; ATA149497A; CH692633A5; NL1006908C1; GB2317223B; AT410975B; DE19637248C2; GB9719376D0

Abstract

In a closed cooling circuit, water is fed from a common gas/water reservoir (6) via a user (5) and pump means (7) to an air/water heat exchanger (1). The gas in the gas/water reservoir (6) is able to pass into a storage means (9) via a compressor (8). When the cooling circuit is switched off, the water present in the heat exchanger is removed from the heat exchanger by a shut-off valve means (10) being opened, thereby allowing the gas to expand and enter the heat exchanger via inflow opening (4). The cooling water from the heat exchanger (1) is then stored in gas/water reservoir (6). When the circuit is switched back on - pump means (7) being operated, gas present in the heat exchanger (1) is forced by the cooling water back into the gas/water reservoir (6) though discharge line (B).

Description

2317223 Method for conducting thermal energy out of a cooling circuit by

means of a user which generates heat The invention relates to a method for conducting thermal energy out of a cooling circuit by means of a user, (or thermal load), which generates heat, the cooling water of the cooling circuit, which is rich in thermal energy, being fed to an air/water heat exchanger and being fed back by the latter to the user which generates heat, the water present in the heat exchanger being removed from the heat 10 exchanger when the cooling circuit is switched of.

In production operations, heat is released due to a large number of processes and has to be conducted away. For instance, for plastics processing plants, cooling circuits are used for cooling and conditioning injection- moulding machines, extruders, thermoforming tools and blowifig - _Machines -or similar components, beat being removed from a polymer melt by means of a cooling liquid to solidify the plastic after processing, and this heat being given off into the atmosphere. A further field of application consists in conditioning light metal diecasting moulds in metal processing.

This excess heat is usually absorbed by circulating cooling water and is conducted away into the atmosphere at a suitable point by a cooling assembly. Cooling circuits of this type are operated in an open manner, which means that the water is enriched' with oxygen via the ambient-air, thus 'resulting in an undesirable forma tion of corrosion in all the components of the system through which the water flows.

For the purpose of avoiding the formation of corrosion, it is possible to conduct away the production heat occUrring via a coupled primary and secondary circuit. However, this method involves some disadvantages since, in the case of such hermetically sealed cooling circuits, a cooling assembly which exchanges heat always has to be connected between the primary and secondary circuits, the excess heat ultimately being transmitted to the atmosphere via the secondary circuit.

2 In order to avoid the cooling water freezing in the secondary circuit in the case of outside temperatures of below OC, involving possible destruction of the system components as a result of ice forming, an antifreeze agent (e.g. glycol) is added to the secondary circuit. if the antifreeze agent is added to the entire cooling circuit, the secondary circuit could be dispensed with. In any event, however, adding an antifreeze agent.has a negative effect-on-the cooling efficacy_of.the surfaces which exchange heat, - since the -intensity,,of the heat transmission is reduced...A cooling circuit of this type is extremely uneconomic to operate as a result of the higher operating costs.

As an alternative to the secondary circuit to is which an antifreeze agent has been added, the use of a compression refrigerating. machine is known. In this case, the heat in - transmitted - in- the.-pr-imary...-circuit via the enthalpy of vaporization of a re-f rigerant circulating in a secondary loop in an evaporator and is f inally con- ducted away into the atmosphere in a condenser. A compression refrigerating machine operates very effectively, but the operation is relatively cost-intensive owing to the high absorption of energy and system costs.

For the purpose of avoiding the cost-intensive secondary circuit, suitable air/water heat exchangers are known (DE 42 39 455 C2 and UM 296 06 912.4), which, when the system is switched off, can automatically run empty by means of appropriate aeration. However, these crosscurrent heat exchangers can only be operated in open circuits, which means that the cooling water is enriched with oxygen as a result of the contact with the ambient air and causes corrosion in all the system components involved. In this case, the emptying of the heat exchangers takes place by utilizing the e arth's gravitation, that is to say by a free gradient. For this purpose, the heat exchangers have heat-exchanger pipes which are inclined relative to the horizontal plane with correspondingly low-lying inflow and outflow devices. As a result of the free gradient, heat exchangers of this 3 type require long emptying times and can therefore easily freeze and be destroyed when outside temperatures are below freezing point. The water flowing back is always collected in open containers, which means that (undesir- able) contact of the aerated heat-exchanger surfaces with air oxygen is unavoidable.

As an alternative to utilizing the free gradient, a method of emptying the heat exchanger by means of compressed air is known, in this case, too, the heat- exchanger connection pipes being separated_ from the cooling circuit before emptying begins.

Starting from this prior art, the invention is based on the alm of providing a method of operating a hermetically sealed, frost-protected cooling circuit with is direct heat exchange by means of a transverse-flow heat exchanger, which can only be operated with water and dispenses with.the operation of a refrigerant circuit.

For the solution, it is proposed that the circuit is hermetically sealed, and that, for removal of the cooling water from the heat exchanger when the cooling circuit has been shut down, a controllable gas cushion is integrated in the circuit, by means of which gas cushion the cooling water is pressed out of the heat exchanger and which, when the cooling circuit is started up, is pressed completely out of the heat exchanger by the cooling water located in the circuit.

The essential advantage of the method according to the invention consists in that the cooling system is designed to be frost-protected despite using pure water, and in that the formation of corrosion is avoided in all components of the system owing to the integration of the emptying device in the hermetically sealed circuit which is not in direct contact with the ambient air.

Provision is preferably made for the gas cushion to be formed from an inert gas, thus avoiding any reaction with the cooling water and no solution of the gas in the cooling water taking place. For cost reasons, provision is preferably made for nitrogen to be used.

Furthermore, provision is preferably made for the displacement of the cooling wat er to be carried out by expansion of the gas stored under pressure in a suitable container.

Provision is preferably made for the gas and 5 cooling water to be stored in a common reservoir.

Additionally, provision is preferably made for the container to be able to be f illed with compressed gas independently of the cooling operation.

Furthermore, provision is preferably made for gas to be removed completely from the heat exchanger during the cooling operation by means of suitable auction venting, thus guaranteeing the greatest possible cooling effect.

Provision is preferably made for the venting to is be controlled and regulated fully automatically, so that cooling circuits of this type can also be operated in unmanned shifts or with a.. reduced workforce. --.

Furthermore, provision is preferably made, depending on the operating state, for flow through the feedline and discharge line of the heat exchanger to take place alternatively in one direction or-the other...As -a result, the outlay for piping on the air/water heat exchanger is reduced to a minimum.

Finally, preference is given to the gas circuit being integrated in the cooling circuit to, the extent that, in addition to the connections for,--the coolingwater inflow and outflow,. the heat exchanger has. a further connection, preferably centrally in relation-to the length of the cooling pipe of the heat.. exchanger, for the gas inlet, so that the cooling water.is displaced-by means of the gas, when the cooling circuit has been shut down, in opposite and parallel flow through the feedline and discharge line or alternatively only in parallel flow through the discharge line, but in any case into the reservoir, whereasi af terstart-up, the -gas is conveyed into the reservoir via the cooling-water feedline, that is to say via the same branch.

A device which is preferred for carrying out the method is envisaged in the.fact: that the. cooling circuit comprises at least one user, an air/water heat exchanger, a common reservoir for the cooling water and the gaseous medium, a conveying means, preferably an operating pump, for circulating the cooling water, which components are connected via a line which forms.the cooling circuit, the gas circuit, comprising a means for compressing the gas, preferably a pump, a means for storing the compressed gas, and a controllable shut-off means, preferably a valve, being connected to the cooling circuit on the input side at the reservoir and on the output side at the heat exchanger, preferably centrally in relation to the length of the cooling pipe of the heat exchanger, so that gas can be removed from the reservoir, and the cooling water can be displaced into the common reservoir.

is Finally, provision is preferably made for there to be a connecting line between the heat-exchanger feedline and discharge line, which connecting line is interrupted during cooling operation by a shut-off means, preferably a valve, and, when the cooling operation is switched off, blocks the inflow and diverts the displaced flow of cooling water in the heat-exchanger feedline via a connection into the heat- exchanger discharge line.

The system is operated to the effect that cooling water is conveyed from a reservoir by a conveying means, in particular an operating pump, through the user network to a cross-flow heat exchanger, flows through the latter whilst giving off excess heat and subsequently returns to the reservoir again. The reservoir is dimensioned to the effect that, in addition to a specific amount of water, it additionally stores a volume of gas above the water level. This volume of gas, which also serves as a buffer in the case of different heights of the water level, is sucked off via a separate line by a compression means, preferably a pump, is compressed, and is stored in a storage means, preferably a pressure vessel. The emptying operation of the cooling circuit is initiated via an actuator, preferably a control valve, which releases the connection between the storage means and one or more heat-exchanger pipes. As a result of the expansion of the gas which is rich in pressurized energy, the cooling water is completely displaced in the heat exchanger via the cooling-water feedline and discharge line. When the cooling operation is started up again, the gas is fed, by starting up the conveying means and filling the heatexchanger pipes, from the inflow via the outflow line back to the reservoir again, so that a new filling operation of the store can be initiated.

The heat exchanger is designed as a cross-flow heat exchanger, comprising a pipe, but usuall - y a plurality of pipes, through which cooling water flows and which are guided in a meandering manner, are positioned horizontally or obliquely and are additionally fitted with lamellae to enlarge the heat-exchanger surface. An is air flow flows around the pipes and lamellae, which air f low is by f ans and by means of which the transmitted heat flow is conducted away into the atmos phere. With the aid of an air volume f low control, the quantity of heat to be exchanged can be set within narrow tolerances._ An exemplary embodiment of the invention is illustrated in the drawing and is described in greater detail below.

Figure 1 shows a diagrammatic illustration of the method with all the components relevant to the function.

According to Figure 1, the device comprises a closed cooling circuit and an integrated pipe section to provide the gas for displacing the cooling water out of the airlwater heat exchanger (1). In the cooling circuit, cooling water from a gas/water reservoir (6) is circulated with the aid of a conveying means (7) connected downstream of at least one user (5) and is fed via the feedline (A) via a connection device (2) into the cooling line of the air/water heat exchanger (1). Air flows transversely, in relation to the cooling line, around the air/water heat exchanger (1) (not illustrated in detail here), the air volume flow (F) being maintained by means of suitable ventilation.

The cooling water flows through the air/water 7 heat exchanger (1) and passes via the connection device to the cooling- water outlet (1) into the cooling-water discharge line (B) back into the gas/water reservoir (6). in addition to the cooling water, the gas is also stored in the gas/water reservoir (6), which gas is conveyed into a storage means (9) via a gas removal (D), connected separately to the gas/water reservoir (6), a means for compressing the gas (8). In the case of an emptying operation'. a shut-off means (10) is opened, as a result of which the gas from the storage means (9) expands, passes via a connection means for the gas inflow (4) into the air/water heat exchanger (1) and displaces the cooling water located in the air/water heat exchanger (1). The connection means to the gas inlet (4) should be is arranged preferably centrally, in relation to the length of the cooling pipe of the air/water heat exchanger (1). The displacement of the cooling water takes place in a parallel flow through the cooling-water discharge line (B) and in counter-flow through the cooling-water feed- line (A), flow through the conveying means (7) being counter to the conveying direction, or only in a parallel flow through the cooling-water discharge line (B).

Additionally, a connecting line (E) may be provided between the coolingwater feedline (A) and cooling-water discharge line (B), via which connecting line the cooling water can be diverted, by switching a switchover means (11), from the cooling-water f eedline (A) into the cooling-water discharge line (B) when the cooling water is emptied from the heat exchanger.

The cooling water which is displaced from the air/water heat exchanger (1) as a result of the expansion of the gas is stored in the gas/water reservoir (6), the filling level rising in the gas/water reservoir (6) in accordance with the volume of cooling water displaced.

The quantity of gas in the device is dimensioned to the effect that there is still a sufficient quantity of gas in the gas/water reservoir (6) on completion of the emptying operation and closure of the shut-off means (10), so that the storage means (9) can be filled once more.

For the purpose of venting the device, the conveying means (7) is set in motion and any connecting line (E) present is separated from the coolingwater feedline (A) with the aid of the switchover means (11) so that the gas present in the air/water heat exchanger (1) is conveyed by the cooling water via the cooling-water discharge line (B) back into the gas/water reservoir (6). By means of suction venting (not illustrated in detail here), it is guaranteed that the air/water heat exchanger (1) is always free from gas and is completely filled with cooling water.

The invention is not restricted to"the exemplary embodiment, but can be varied in many ways within the is scope of the disclosure.

9

Claims

CLAIMS:

1. Method for conducting thermal energy out of a cooling circuit by means of a user which generates heat, the cooling water of the cooling circuit, which is rich in thermal energy, being fed to an air/water heat exchanger and being fed back by the latter to the user which generates heat, the water present in the heat exchanger being removed from the heat exchanger when the cooling circuit is switched off, wherein the circuit is hermetically sealed, and for removal of the cooling water from the heat exchanger when the cooling circuit has been shut down, a controllable gas cushion is integrated in the circuit, by means of which gas cushion the cooling water is pressed out of the heat exchanger and which, when the cooling circuit is started up, is pressed completed out of the heat exchanger by the cooling water located in the circuit.

2. Method according to claim 1, wherein the gas cushion is formed from an inert gas, preferably nitrogen.

3. Method according to either of claims 1 and 2, wherein the displacement of the cooling water takes place by expansion of a gaseous medium which is stored under pressure in a container.

4. Method according any one of claims 1 to 3, where gas and cooling water are stored in a common reservoir.

5. Method according to claim 3, wherein the container can be filled with compressed gas independently of the cooling operation.

6. Method according to any one of claims 1 to 5, wherein the gas is removed completely from the heat exchanger during the cooling operation by means of suitable suction venting.

7. method according to any one of claims 1 to 6, wherein the aeration and venting of the heat exchanger is controlled and regulated fully automatically.

8. Method according to any one of claims 1 to 7, wherein, depending on the operating state, flow through the feedline and discharge line of the heat exchanger takes place alternatively in one direction or the other.

9. Method according to any one of Claims 1 to 8, wherein the gas circuit is integrated in the cooling circuit to the extent that, in addition to the connections for the cooling-water inflow and outflow, the heat exchanger has a further connection, preferably centrally in relation to the length of the cooling pipe of the heat exchanger, for the gas infeed, so that the cooling water is displaced by means of the gas, when the cooling circuit has been shut down, in opposite and parallel flow through the feedline and discharge line or alternatively only in parallel flow through the discharge line, but in any case into the reservoir, whereas, after start-up, the gas is conveyed into the reservoir via the coolingwater feedline, that is to say via the same branch.

10. Device for carrying out the method according to any one of claims 1 to 9, wherein the cooling circuit comprises at least one user, an air/water heat exchanger, a common reservoir for the cooling water and the gaseous medium, a conveying means, preferably an operating pump, for circulating the cooling water, which components are connected via lines which form the cooling circuit, the gas circuit, comprising a means for compressing the gas, preferably a pump, a means for storing the compressed gas, and a controllable shut-off means, preferably a valve, being connected to the cooling circuit on the input side at the reservoir and on the output side at the heat exchanger, preferably centrally in relation to the length of the cooling pipe of the heat exchanger, so that gas can be removed from the reservoir, and the cooling water can be displaced into the common reservoir.

11. Device for carrying out the method according to claim 10, wherein there is a connecting line between the heatexchanger feedline and discharge line, which connecting line is interrupted during a cooling operation by a shutoff means, preferably a valve, and, when the cooling operation is switched off, blocks the inflow and diverts the displaced flow of cooling water in the heat-exchanger feedline via the connection into the heat-exchanger discharge line.

12. Method for conducting thermal energy out of a cooling circuit substantially as hereinbefore described with reference to Figure 1.

13. Device for carrying out the method of claim 12.