CN110986639A

CN110986639A - Heat exchanger of thermosiphon

Info

Publication number: CN110986639A
Application number: CN201911367345.XA
Authority: CN
Inventors: 约翰·R·托姆; 张礼政
Original assignee: Novark Technology (Shenzhen) Inc
Current assignee: Novark Technology (Shenzhen) Inc
Priority date: 2019-12-26
Filing date: 2019-12-26
Publication date: 2020-04-10

Abstract

The present invention provides a thermosiphon heat exchanger, comprising: the evaporator, the riser pipe, the condenser and the return pipe; the outlet of the evaporator is connected with the inlet of the riser pipe, the outlet of the riser pipe is connected with the inlet of the condenser, the outlet of the condenser is connected with the top of the return pipe, and the liquid in the return pipe is conveyed downwards to the inlet of the condenser pipe; the riser pipe and the return pipe are rectangular pipes; the evaporator is a micro-channel evaporator, and fins are arranged on a bottom plate of the micro-channel evaporator; the condenser includes at least one flat microchannel tube. The power consumption is reduced; the effective area of the condenser is maximized, the wind resistance is reduced, and the heat dissipation efficiency is improved.

Description

Heat exchanger of thermosiphon

Technical Field

The invention relates to the technical field of thermosiphon, in particular to a thermosiphon heat exchanger.

Background

Existing cooling elements for microprocessor CPUs of data center servers are essentially (i) air cooled units or (ii) air cooled assisted by heat pipe units. Both types of cooling units can only handle low and medium heat flux loads from the CPU and not high heat fluxes. They are limited by the extremely high pressure drop required for operation and the high airflow, both of which cause them to consume significant amounts of fan power, and high fan speeds generate significant amounts of noise. Existing thermosiphon heat exchangers are susceptible to poor thermal hydraulic design of the thermosiphon heat exchanger fluid circuit, which creates large flow resistance, resulting in low flow rates and unnecessary flow instabilities; this means that they cannot withstand high heat fluxes and are prone to premature dry burning, causing overheating and unstable start-up of the electronic device.

Furthermore, the common use of circular pipes for the riser, return and distributor pipes of the prior art thermosiphon heat exchangers results in a large front cross-section, which hinders much of the available surface area for air circulation, which results in a large pressure drop, less heat transfer and a larger condenser area, which limits the lower heat load and requires a larger fan power consumption for the same heat load.

Disclosure of Invention

The invention provides a novel thermosiphon heat exchanger for solving the existing problems.

In order to solve the above problems, the technical solution adopted by the present invention is as follows:

a thermosiphon heat exchanger, comprising: the evaporator, the riser pipe, the condenser and the return pipe; the outlet of the evaporator is connected with the inlet of the riser pipe, the outlet of the riser pipe is connected with the inlet of the condenser, the outlet of the condenser is connected with the top of the return pipe, and the liquid in the return pipe is conveyed downwards to the inlet of the condenser pipe; the riser pipe and the return pipe are rectangular pipes; the evaporator is a micro-channel evaporator, and fins are arranged on a bottom plate of the micro-channel evaporator; the condenser includes at least one flat microchannel tube.

Preferably, two thermosiphon circuits are included: the two thermosiphon loops share one return pipe, and the evaporator is connected with the riser pipe through a microchannel flat pipe; the other end of the riser pipe is connected with the flat microchannel pipe of the condenser; or the two thermosiphon loops share one riser tube, and the evaporator is connected with the return tube through a microchannel flat tube; the other end of the return pipe is connected to the flat microchannel tube of the condenser.

Preferably, the microchannel flat tube comprises at least two channels, and at least one rib is arranged inside the microchannel flat tube.

Preferably, the condensers of the two thermosiphon circuits are the same size or different sizes.

Preferably, the side wall and/or the rear wall of the return pipe, the inner surface or the outer surface of the side wall and/or the rear wall of the return pipe are provided with reinforcing ribs.

Preferably, the base plate and the cover plate of the microchannel evaporator form an inlet slit; the geometry of the inlet slit is formed by the arrangement of micro-ridges on both sides of the bottom plate of the riser pipe or the return pipe.

Preferably, a micro-channel is formed between a base plate and a cover plate of the evaporator, and support ribs are arranged on the base plate and the cover plate; the microchannel has a height to width ratio of at least 5: 1.

Preferably, the condenser and the evaporator are arranged parallel, perpendicular or at an angle to each other.

Preferably the top plates of the riser and return tubes are flat and in line with the tops of the fin areas of the condenser.

Preferably, the system also comprises at least two microchannel evaporators in advection mode, at least two microchannel evaporators in series flow mode, at least four microchannel evaporator arrays in parallel and series combination or at least two microchannel evaporators in split flow mode, which are connected together through microchannel flat tubes.

The invention has the beneficial effects that: the heat siphon tube heat exchanger is provided, the rectangular ascending flow tube and the rectangular return tube are arranged, the bottom plate of the microchannel evaporator is provided with the fins, and the flat microchannel tube is arranged in the condenser, so that the area of the front surface of the heat siphon tube heat exchanger is smaller than that of the traditional round tube, the surface area of airflow is larger, and the condenser only needs lower airflow and lower pressure drop to exchange heat, thereby reducing the power consumption of a fan; the effective area of the condenser is maximized, the wind resistance is reduced, and the heat dissipation efficiency is improved.

Further, the thermosiphon heat exchanger can greatly reduce the flow resistance inside the thermosiphon heat exchanger and greatly increase the flow of the working fluid, thereby greatly increasing the heat load and heat flux that the thermosiphon heat exchanger can remove from the electronic equipment.

Further, an inlet slit having a low flow resistance is used to stabilize the flow of the working fluid at the evaporator inlet to prevent flow instability from occurring.

Drawings

FIG. 1 is a schematic structural diagram of a prior art loop thermosiphon in an embodiment of the present invention.

Fig. 2(a) is a partial structural schematic view of a thermosiphon heat exchanger according to an embodiment of the present invention.

Fig. 2(b) is a schematic structural view of a microchannel flat tube in an embodiment of the present invention.

Fig. 3(a) -3 (i) are schematic structural views of a rectangular riser pipe in an embodiment of the invention.

Fig. 4(a) is a schematic diagram of a dual circuit thermosiphon heat exchanger with two riser tubes and one return tube according to an embodiment of the present invention.

Figure 4(b) is a double circuit thermosiphon heat exchanger with two return lines and one riser line in an embodiment of the invention.

Fig. 4(c) is a schematic structural diagram of a slit opening in an embodiment of the present invention.

Fig. 4(d) is a schematic structural diagram of another slit opening in the embodiment of the present invention.

FIG. 4(e) is a schematic structural diagram of a single-circuit thermosiphon heat exchanger according to an embodiment of the present invention.

Fig. 5 is a schematic structural view of a thermosiphon heat exchanger according to an embodiment of the present invention.

Fig. 6(a) is a partial schematic view of a thermosiphon heat exchanger according to another embodiment of the present invention.

FIG. 6(b) is an enlarged partial schematic view of yet another thermosiphon heat exchanger in an embodiment of the present invention.

Fig. 6(c) is a schematic structural view of another microchannel flat tube in the embodiment of the present invention.

FIG. 7 is a schematic view of one side of a dual circuit thermosiphon heat exchanger in an embodiment of the invention.

Fig. 8(a) -8 (c) are schematic structural views of fins in the embodiment of the present invention.

Fig. 9(a) is a partial structural view of another thermosiphon heat exchanger according to an embodiment of the present invention.

Fig. 9(b) is a schematic structural view of another thermosiphon heat exchanger according to an embodiment of the present invention.

FIG. 10 is a schematic diagram of the structure of a microchannel in an embodiment of the invention.

Fig. 11(a) -11 (b) are schematic structural views of still another thermosiphon heat exchanger according to an embodiment of the present invention.

Fig. 12(a) -12 (f) are schematic views of an electronic component to be cooled and a microchannel evaporator corresponding thereto in an embodiment of the present invention.

Wherein, 1-a rectangular riser, 2-a condenser, 3-a rectangular return pipe, 4-a microchannel evaporator, 5-a horizontal microchannel flat pipe riser section, 6-a horizontal microchannel flat pipe return pipe section, 7-an inlet slit of a microchannel in the evaporator, 8-a microchannel flat pipe, 9-a flat microchannel pipe of the condenser, 10-a bottom plate of the riser or the return pipe, 11-a top plate of the riser or the return pipe, 12-a rear wall of the riser, 13-a side wall of the riser, 14-a side wall of the return pipe, 15-an outlet at the bottom of the return pipe, 16-a rear wall of the return pipe, 17-an internal reinforcing rib of the riser or the return pipe, 18-an external reinforcing rib of the riser or the return pipe, 19-an evaporator cover plate, 20-an evaporator base plate, 21-micro ridges, 22-inlet or outlet area of evaporator, 23-micro channels in evaporator base plate, 24-fins on evaporator base plate, 25-cut-off cover of evaporator cover plate, 26-flat fins, 27-fins of louver, 28-strip fins,

29-gap barrier material, 30-top straight line, 31-support rib of evaporator base plate, 32-support rib of evaporator cover plate for fixing evaporator fin, 33-condenser rectangular inlet header, 34-condenser rectangular outlet header, 35-vertical microchannel flat tube riser, 36-vertical microchannel flat tube return pipe, 37-shorter condenser, 38-longer condenser, 39-short horizontal flat tube riser with microchannel, 40-long horizontal flat tube riser with microchannel, 41-evaporator cooling surface, 42-electric element to be cooled, 43-microchannel evaporator in parallel flow mode, 44-series flow microchannel evaporator, 45-4 microchannel evaporator array combined in parallel and series, 46-two microchannel evaporators in split mode, 47-two microchannel evaporators in split mode.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the embodiments of the present invention more clearly apparent, the present invention is further described in detail below with reference to the accompanying drawings and the embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

It will be understood that when an element is referred to as being "secured to" or "disposed on" another element, it can be directly on the other element or be indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or be indirectly connected to the other element. In addition, the connection may be for either a fixing function or a circuit connection function.

It is to be understood that the terms "length," width, "" upper, "" lower, "" front, "" back,

Rear, left, right, vertical, horizontal, top, bottom and inner,

The references to "outside" or the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience in describing embodiments of the present invention and simplifying the description, but do not indicate or imply that the referred devices or elements must have a specific orientation, be constructed and operated in a specific orientation, and thus are not to be construed as limiting the present invention.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the embodiments of the present invention, "a plurality" means two or more unless specifically limited otherwise.

A schematic of a prior art loop thermosiphon heat exchanger is shown in fig. 1. The thermosiphon heat exchanger consists of evaporator, riser pipe, condenser, return pipe, etc. the heated liquid working fluid in the evaporator is partially evaporated into steam to take heat away from electronic equipment, the outlet of the evaporator is connected to the riser pipe, the riser pipe is a microchannel pipe, and the steam flows upwards to the inlet of the condenser. The condenser releases heat from the two-phase flow by condensing the vapor back to the liquid phase, with the outlet of the condenser connected to the top of a return line, which is a pipe that carries the liquid down back to the inlet of the condenser. The flow circulation is counterclockwise in the drawing and the direction of gravity is downward. The two-phase flow of liquid and vapor in the riser tube is of lower density than the flow in the return tube, thus resulting in a pressure imbalance, causing the two-phase working fluid to flow passively upward, and the liquid to flow downward, in addition to the influence of gravity within the heat exchanger, thereby creating a continuous flow circulation within the thermosiphon heat exchanger.

As shown in fig. 2(a) -2 (b), the present invention provides a partial schematic view of a thermosiphon heat exchanger, comprising a riser pipe 1, a condenser 2, a return pipe 3, a left side portion of a dual cycle thermosiphon heat exchanger of an evaporator, wherein the split flows to left and right loops of a separator; the device also comprises a section view of the microchannel evaporator 4, a horizontal microchannel flat tube upflow tube section 5 and a microchannel flat tube 8. The reduced frontal area of the horizontal microchannel flat tube riser section 5 compared to the circular tubes of the prior art allows for increased frontal area of the condenser 2 under the same spatial conditions, and the microchannel flat tubes 8 are made as large as possible to reduce flow resistance and thus increase thermosiphon circulation flow. The inner ribs of the microchannels in the horizontal microchannel flat tube upflow section 5 are used to reinforce the microchannel flat tubes 8 to prevent the microchannel flat tubes 8 from being deformed by the working fluid, and if the inner pressure is higher or lower than the external atmospheric pressure, if no ribs are present, the microchannel flat tubes 8 will be deformed.

As shown in fig. 3(a) -3 (i), the structure of the rectangular riser pipe is schematically illustrated. In fig. 3(a) and 3(b) which are top and side views, respectively, of a rectangular riser tube 1, one end of which is connected to one or more flat microchannel tubes 9 of the condenser 2 and the other end of which is connected to a horizontal microchannel flat tube riser section 5. The rectangular riser pipe 1 comprises a base plate 10, a top plate 11, a rear wall 12 and side walls 13. In fig. 3(c) -3 (f) are a top view and a side view, respectively, of a rectangular return tube 3 connected at one end to one or more flat microchannel tubes 9 of a condenser 9 and at the other end to a horizontal flat tube return tube section 6. The rectangular return tube 3 is composed of a bottom plate 10, a top plate 11, a rear wall 16 and side walls 14, and has an opening 15 for fluid to enter and exit at the bottom or lower portion. Fig. 3(c) and 3(e) show a two-circuit thermosiphon heat exchanger, and fig. 3(d) and 3(f) show a single-circuit thermosiphon heat exchanger flow. As shown in fig. 3(g) and 3(h), internal ribs 17 and external ribs 18 may be provided on the inner surface or the outer surface of one or more of the pipe walls, such as the back wall 12 of the riser pipe, the side wall 13 of the riser pipe, the side wall 14 of the return pipe, and the back wall 16 of the return pipe, and the heights of the internal ribs 17 and the external ribs 18 are less than 1 mm to enhance the strength thereof against the internal pressure of the medium-high pressure working fluid or vacuum.

As shown in fig. 4(a) and 4(b), there are two-circuit thermosiphon heat exchangers of two riser pipes and one return pipe, and two-circuit thermosiphon heat exchangers of two return pipes and one riser pipe, respectively. The rectangular shape of the riser 1 and return 3 tubes allows fluid to enter the tube walls through the horizontal microchannel flat tube riser 5 and horizontal microchannel flat tube return 6 tubes without flooding into the interior thereof, without any protrusions in the riser and return tubes that would interfere with the flow of fluid in the riser and return tubes and disturb the smooth flow of fluid into and out of the condenser flat microchannel tubes. The circulation flow of the working fluid in the thermosiphon heat exchanger will increase by 25% or more. The front area of the rectangular riser duct 1 and return duct 3 in the direction of airflow is more than 25% smaller than that of a circular riser duct, and therefore the front width of the condenser 2 is larger in fig. 2 and 4(a) -4 (b), which increases the available heat transfer surface area, reduces the wind speed to reduce the pressure drop of the airflow, thereby reducing the fan power consumption by 25% or more, and makes the apparatus very compact.

In the double circuit thermosiphon heat exchanger with two return pipes and one riser pipe, shown in fig. 4(b), the fluid enters the inlet slit 7 for entry in the microchannel evaporator 4 formed by the evaporator base plate 20 and the evaporator cover plate 19 from the top or side.

As in fig. 4(c) with a single recycle stream from one end of the microchannel evaporator 4 to the other, or with a double recycle stream; wherein the fluid from the return pipes 3 enters the middle of the top cover plate 19 and is split by the riser pipe 1 at both ends, or the fluid from both return pipes 3 enters the microchannel evaporator 4 at both ends and is left at the bottom of the riser pipe 1 from the middle of the top cover plate 19. The inlet flow into the evaporator is stabilized by the inlet slits 7. the inlet slits 7 also allow flow distribution to the plurality of microchannel tubes and prevent vapor from flowing back into the return tube 3.

As shown in fig. 4(d), the geometry of the inlet slot 7 may be such that micro-ridges 21 are provided on both sides of the base plate 10 to prevent brazing or soldering material from flowing into the slot and blocking the narrow slot during the manufacturing process.

As shown in fig. 4(e), with the single-circuit thermosiphon heat exchanger, the lengths of the horizontal microchannel flat tube rising flow pipe section, the horizontal microchannel flat tube return flow pipe section 6 are shortened or lengthened according to the position and size of the electronic equipment to be cooled.

Although the return pipe 3 or the riser pipe 1 is usually centrally located, it can be moved to an off-center position, as shown in fig. 5, depending on the location of the electronic component to be cooled in the electronic package. In this case, the evaporator is shifted to a position corresponding to the electronic equipment to be cooled, and the condenser 37 having a shorter width corresponds to the short horizontal flat tube rising section 39 having the microchannel, and the condenser 38 having a longer width corresponds to the long horizontal flat tube rising section 40 having the microchannel.

As shown in fig. 6(a) -6 (c), the horizontal microchannel flat tube riser section 5, the horizontal microchannel flat tube return section 6 are connected to the outlet and inlet region 22 of the microchannel evaporator 4, and the microchannel flat tubes 8 are provided inside. The microchannel evaporator 4 comprises a microchannel 23, a fin 24 is arranged on the bottom plate of the evaporator, and a stop cover 25 is arranged on the cover plate of the evaporator. Compared with the traditional circular pipe section, the horizontal microchannel flat pipe riser pipe section 5 and the horizontal microchannel flat pipe return pipe section 6 are used for improving the transmission of the working fluid from the outlet of the microchannel evaporator 4 to the inlet at the bottom of the riser pipe 1. By providing cross-sections of the same shape, width and height at the outlet of the plurality of microchannels in the microchannel evaporator 4 and at the inlet of the riser pipe 1, the pressure drop is reduced and the thermosiphon circulation flow is increased. Similarly, the same arrangement may be applied between the outlet of the return pipe shown in fig. 2) and the inlet of the microchannel evaporator 4. This arrangement reduces the flow resistance by at least 20%, increases the thermal efficiency of the flow-circulating thermosiphon heat exchanger, and can dissipate at least 20% of the heat flux.

As shown in fig. 7, which is one side of a dual circuit thermosiphon heat exchanger, the condenser 2, microchannel evaporator 4, riser 1, return 3 and horizontal microchannel flat tube riser 5 are shown. The height, width and depth of the condenser 2 are variable (not shown) and therefore the size thereof can be modified to suit the needs of different electronic products to be cooled. The microchannel evaporator 4 is variable in height, width and length (not shown) to accommodate the size of the electronic component to be cooled. In order to adapt to the size change of the condenser 2 and the microchannel evaporator 4, the size of the horizontal microchannel flat tube upflow section 5 is also variable, and the size of the horizontal microchannel flat tube reflux section 6 is also adaptable.

As shown in fig. 8(a) -8 (c), three different types of fins are used in the condenser 2: plate fins 26 with or without serrations, louvered fins 27 and strip fins 28. One or a combination of any two or all three of these fins may enter the same condenser 2. The fin type is one in which the fins are brazed between the flat microchannel tubes 9 in the condenser. The selection of the most appropriate solution for the fins and their combination in the condenser is made to meet the requirements of volumetric air flow, air pressure drop and fan power consumption.

The width of the flat microchannel tubes 9 and the width of the strip fins 26, louvered fins 27, and flat fins 28 in the condenser can be varied from 25mm to over 100mm to provide additional heat transfer surface area for cooling the condenser 2. The design of the present invention can use many different sizes of condensers, and microchannel evaporators 4 that are compatible with the condenser size, without size limitations. The thermosiphon heat exchanger of the present invention has a very versatile basic shape that can be easily modified to accommodate a wide variety of applications, reducing manufacturing costs.

As shown in fig. 9(a) -9 (b), the top plates of the riser 1 and return 3 tubes are flat and in line 30 with the top of the fin area of the condenser 2, thereby blocking any air bypassing. If necessary, an air barrier material is placed on top of the condenser 2 to establish the duct boundaries. Below the condenser 2, above and below (not shown) the horizontal microchannel flat tube riser section 5, the horizontal microchannel flat tube return section 6, and beside the microchannel evaporator 4, air blocking materials 29 are provided to prevent air from entering.

As shown in fig. 10, in order to make the microchannel evaporator 4 usable for a high-pressure working fluid and prevent its evaporator cover plate 19 and evaporator base plate 20 from being deformed disadvantageously when subjected to a large internal pressure of the working fluid in the fin region, a support rib 31 fixed to the evaporator cover plate 19, a support rib 32 fixed to the evaporator base plate 20 are provided, and the

support ribs

31, 32 are formed by brazing, between the evaporator cover plate 19 and the evaporator base plate 20. The fins 24 on the evaporator bottom plate are used to form the microchannels 23, while the evaporator cover plate 19 is the top of the microchannels. The ratio of height to width of the microchannel is at least 5:1 such that the ratio of heat transfer surface area to heated floor area on the bottom surface of the evaporator substrate 20 is at least 5:1, greatly reduces flow resistance by more than 50% compared to square channels or low aspect ratio channels of the same channel width, and allows the thermosiphon heat exchanger to achieve higher thermosiphon circulation flow rates such that at least 25% of the heat flux is cooled. In one embodiment of the invention, the number and size of the internal fins is variable to suit the application requirements and the choice of different working fluids.

As shown in fig. 11(a), a schematic view when the electronic device to be cooled is perpendicular to the thermosiphon heat exchanger. In this case, the condenser 2 is placed above the microchannel evaporator 4 and is oriented vertically as shown in FIG. 11, with the condenser rectangular inlet header 33 at the top, the condenser rectangular outlet header 34 at the bottom and in a horizontal orientation, the vertical microchannel flat tube riser 35 connecting the outlet of the microchannel evaporator 4 to the rectangular inlet header 33, and the vertical microchannel flat tube return 36 connecting the outlet header 34 to the inlet of the microchannel evaporator 4. The flat microchannel tubes 9 are oriented vertically within the condenser 2. The rectangular outlet header 34 can be above or below the top of the microchannel evaporator 4, depending on the space available.

As shown in fig. 11(b), the condenser 2 is placed horizontally with the condenser rectangular inlet header 33 on one side and the condenser rectangular outlet header 34 on the other side, and both are placed vertically. A vertical microchannel flat tube riser 35 connects the outlet of the microchannel evaporator 4 to the rectangular inlet header 33 and a vertical microchannel flat tube return 36 connects the rectangular outlet header 34 to the inlet of the microchannel evaporator 4. In this case, the flat microchannel tubes 9 are oriented horizontally within the condenser 2.

Alternatively, the condenser 2 is oriented at an angle between vertical and horizontal with the condenser rectangular outlet header 34 below the condenser rectangular inlet header 33. The dual circuit thermosiphon heat exchanger of fig. 4(b) or fig. 4(d) can be used to cool the vertical electronic surface of fig. 11(a) by simply adjusting the positions of the riser 1, the return 3, the vertical microchannel flat tube riser 35, the vertical microchannel flat tube return 36, and the rectangular inlet header 33 and the rectangular outlet header 34 of the condenser.

As shown in fig. 12(a) -12 (f), a case where two or more electronic components 42 are cooled on the evaporator cooling surface 41 side by side, in the front-rear direction and in the vicinity. The electronic components 42 may be of the same size or of different sizes. As shown in fig. 10, the thermosiphon heat exchanger cools these elements through an evaporator cooling surface 41 with microchannels 23, wherein the thermosiphon heat exchanger may be in a single-circuit or dual-circuit configuration as shown in fig. 4(a) -4 (d). In fig. 12, the thermosiphon heat exchanger may also utilize two (or more) microchannel evaporators 43 in parallel flow mode, two (or more) microchannel evaporators 44 in series flow mode, 4 (or more) microchannel evaporator arrays 45 in parallel and series combination, two microchannel evaporators 46 in split flow mode, two microchannel evaporators 47 in split flow mode, connected together by a circular tube or flat microchannel tube 8 for cooling multiple electronic components. Each of these microchannel evaporators is used to cool the electronic components 42 to be cooled. Multiple evaporators can be connected in the thermosyphon flow loop in series flow microchannel evaporator 44 or in parallel flow mode microchannel evaporator 43.

The present invention proposes a new and more compact thermosiphon heat exchanger which significantly reduces the flow resistance of the internal fluid flow circuit of the thermosiphon heat exchanger and increases the effective heat exchange fin area of the air flow into the front of the condenser, thus greatly increasing the removable heat load and heat flux given a limited height between the condenser and the evaporator (typically less than 90 mm). In particular, the frontal rectangular riser and return ducts have only about half the frontal area of a conventional circular riser, which results in a larger surface area for airflow (20-40% increase), and a larger condenser surface area that can exchange heat with lower airflow and lower pressure drop, thereby significantly reducing fan power consumption (20-90% reduction). The distribution pipe from the evaporator outlet to the bottom of the riser pipe also changes from round (with a larger front surface area) to flat tubes with internal microchannels (with higher mechanical strength) and a larger front area. In addition, the novel thermosiphon heat exchanger can be changed from a single circulation flow circuit to two circulation circuits running in parallel with a common central return pipe, or to have a common central riser pipe and two return pipes connected in parallel; the use of two parallel flow circuits greatly reduces the flow resistance inside the thermosiphon heat exchanger and greatly increases the flow of the working fluid, thereby greatly increasing the heat load and heat flux that the thermosiphon heat exchanger can remove from the electronic equipment. In addition, a narrow slit with low flow resistance is used to stabilize the flow of the working fluid at the evaporator inlet to prevent flow instability from occurring.

The thermosiphon heat exchanger proposed by the present invention handles higher heat fluxes by improving performance and reduces the energy consumption of cooling its condenser. First, rectangular riser and return ducts have been developed, reducing the frontal area thereof with respect to the circular former ducts of the prior art, thus increasing the frontal area of the condenser for the cooling air flow; secondly, a microchannel flat tube with internal ribs is provided for connecting the evaporator to the riser tube and the return tube; third, a new type of evaporator is proposed in which the entrance slit of the microchannel is located at the entrance of each microchannel in the microchannel evaporator to stabilize the flow rate and prevent vapor bubbles from flowing back; fourth, a dual circuit thermosiphon heat exchanger is proposed, in which two thermosiphon circuits are connected together to form a fluid system by sharing a return pipe or an up-flow pipe. All of these have two common goals:

(i) increasing the flow in the thermosiphon heat exchanger to increase the level of heat flux that the evaporator can dissipate;

(ii) the cooling capacity of the condenser is increased so that cooling can be accomplished with a lower fluid volume, thereby reducing the power consumption of the fan.

The invention provides a thermosiphon heat exchanger for electronic product cooling, which consists of a microchannel evaporator, the microchannel evaporator is connected to one or more rectangular riser pipes, the riser pipes are connected to one or more condensers, and the condensers are connected to one or more rectangular return pipes and are also connected to the inlets of the microchannel evaporator. The rectangular cross-sectional shape of the riser and return conduits replaces the conventional circular shape and has a small internal volume, thereby reducing the mass of working fluid required to operate the thermosiphon cooling system by 25% or more; the rectangular shape also allows for a reduction in the frontal area of the condenser by 25% or more relative to circular riser and return ducts, which allows for a much larger width of the condenser to increase air flow, increase the surface area(s) of the condenser or reduce the flow resistance of the air through the condenser, thereby reducing the air consumption power of the fan. The vertical riser pipe (or return pipe) may further include an inlet (or outlet) microchannel flat pipe between the outlet (or inlet) of the evaporator, the microchannel flat pipe having a shape that a front region is narrow compared to a circular pipe, which may increase a front area of the condenser, but is wider in an air flow direction, so as not to increase a flow resistance of the internal working fluid, and the horizontal microchannel flat pipe may have one or more channels inside, and may also be provided with a plurality of internal reinforcing ribs to bear an internal pressure of the working fluid. The microchannel flat tubes constituting the condenser are welded to the rectangular riser and return pipes, and do not protrude inside the riser and return pipes as in the conventional condenser due to the provision of the limit steps, which makes the flow resistance inside the riser and return pipes small. Thus, the flow rate of the working fluid of the thermosiphon heat exchanger is increased by more than 25%. Very low flow and low pressure drop resistances are present in the evaporator, condenser, riser and return conduits and at the connections between these components to achieve thermosiphon flow, thereby increasing the thermosiphon flow rate by 25% or more. The increase in thermosiphon flow rate reduces the outlet vapor fraction leaving the evaporator, thereby avoiding reaching a dry-out condition. In addition, the higher thermosiphon circulation flow increases the heat load and heat flux removed between the condenser and evaporator at a given height for gravity driven flow by more than 25%. In addition, the single circulation flow loop in the thermosiphon heat exchanger can be modified so that both circulation loops operate in parallel with a common return line or a common riser.

The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several equivalent substitutions or obvious modifications can be made without departing from the spirit of the invention, and all the properties or uses are considered to be within the scope of the invention.

Claims

1. A thermosiphon heat exchanger, comprising: the evaporator, the riser pipe, the condenser and the return pipe;

the outlet of the evaporator is connected with the inlet of the riser pipe, the outlet of the riser pipe is connected with the inlet of the condenser, the outlet of the condenser is connected with the top of the return pipe, and the liquid in the return pipe is conveyed downwards to the inlet of the condenser pipe;

the riser pipe and the return pipe are rectangular pipes; the evaporator is a micro-channel evaporator, and fins are arranged on a bottom plate of the micro-channel evaporator; the condenser includes at least one flat microchannel tube.

2. A thermosiphon heat exchanger according to claim 1, comprising two thermosiphon loops: the two thermosiphon loops share one return pipe, and the evaporator is connected with the riser pipe through a microchannel flat pipe; the other end of the riser pipe is connected with the flat microchannel pipe of the condenser;

or the two thermosiphon loops share one riser tube, and the evaporator is connected with the return tube through a microchannel flat tube; the other end of the return pipe is connected to the flat microchannel tube of the condenser.

3. A thermosiphon heat exchanger according to claim 2, wherein the microchannel flat tube comprises at least two channels and wherein the microchannel flat tube has at least one rib disposed therein.

4. A thermosiphon heat exchanger according to claim 2, wherein the condensers of the two thermosiphon circuits are the same or different size.

5. A thermosiphon heat exchanger according to any one of claims 1 to 4, characterised in that the side and/or rear wall of the return tube, the inner or outer surface of the side and/or rear wall of the return tube is provided with ribs.

6. A thermosiphon heat exchanger according to any of claims 1 to 4, wherein the base plate and the cover plate of the microchannel evaporator define an inlet slit; the geometry of the inlet slit is formed by the arrangement of micro-ridges on both sides of the bottom plate of the riser pipe or the return pipe.

7. A thermosiphon heat exchanger according to any of claims 1 to 4, wherein microchannels are formed between the base plate and the cover plate of the evaporator, and wherein support ribs are provided on the base plate and the cover plate; the microchannel has a height to width ratio of at least 5: 1.

8. A thermosiphon heat exchanger according to any of claims 1 to 4, wherein the condenser and the evaporator are arranged parallel, perpendicular or at an angle to each other.

9. A thermosiphon heat exchanger according to any one of claims 1 to 4, characterised in that the top plates of the up-flow and return lines are flat and in line with the tops of the fin areas of the condenser.

10. A thermosiphon heat exchanger according to any one of claims 1 to 4, further comprising at least two advection mode microchannel evaporators, at least two series flow microchannel evaporators, at least four parallel and series combination microchannel evaporator arrays, or at least two split mode microchannel evaporators connected together by microchannel flat tubes.