CN110382977A - Multi-Cross Section Fluid Path Condenser - Google Patents

Abstract

A refrigerant condenser having sections of straight tubes terminating in segmented headers, each subsequent section having a smaller aggregate cross-sectional area than an initial section which is large enough to substantially reduce vapor velocity and thereby refrigerant Pressure drop; the total cross-sectional area should be specified such that the inlet steam velocity is sufficient to establish an internal film heat transfer coefficient greater than the external heat transfer coefficient, while limiting the internal pressure drop for the intended heat removal.

Description

Multi-Cross Section Fluid Path Condenser

technical field

The invention relates to an air-cooled condenser of a refrigeration system.

Background technique

A typical refrigeration system condenser includes multiple serpentine heat transfer fluid paths (or loops) such that the superheated heat transfer vapor entering each loop (path) will be completely condensed before leaving the heat exchange device. Figure 3 shows an example of a prior art condenser tube bundle. The condenser consists of approximately 50 coils, with an inlet header and an outlet header. Steam enters the upper header (inlet) and is distributed into all 50 tubes, all of the same diameter. The number of tubes is kept constant and the cross-sectional area of each tube is kept constant for the entire fluid flow path. At the bottom of the tube bundle, condensed refrigerant is collected at the outlet header.

Contents of the invention

The overall heat transfer coefficient is dominated by the external heat transfer coefficient and at other times by the internal film heat transfer coefficient. At the inlet (or path) of each circuit, the entire volume exists in the gaseous (or vapor) state. The initial vapor velocity at the inlet of each circuit is significant, resulting in high internal pressure drop per incremental fluid circuit length, which in turn provides a significant internal film heat transfer coefficient. The external heat transfer coefficient controls the heat removal in that part of each circuit. As the heat transfer between the refrigerant and air continues along the length of each circuit, and the heat transfer fluid (still in a vapor state) reaches saturation, the vapor begins to condense. As a result, and continuing along each circuit length, the vapor volume and velocity decrease. The vapor exit velocity from each circuit is nearly zero - the heat transfer fluid leaves the condenser in liquid form. The continuous reduction in vapor velocity along the length of each loop of constant cross-sectional area reduces the internal film heat transfer coefficient. In addition, the internal film heat transfer coefficient prior to approaching the exit region of each loop limits the potential or total heat transfer capacity of the condenser.

The applicant has observed certain deficiencies in the prior art, including that although the volume and velocity of the steam is greatest at the entrance of the first pass, there is almost no steam velocity in the last pass. The significant inlet vapor volume produces a high refrigerant pressure drop in the first pass due to the high vapor velocity. This in turn limits the refrigerant mass flow per tube (or circuit/path). Conversely, the very low vapor velocity in the final pass can adversely affect the internal film heat transfer coefficient, thereby reducing the overall heat transfer capacity of the condenser.

The present invention improves the heat transfer deficiencies of the prior art and the high initial refrigerant pressure drop in the first pass by providing a multi-cross-sectional fluid path (loop) for condensation with segmented headers instead of return bends. Thus, each circuit is provided with a larger cross-sectional area at the inlet of each circuit when the vapor volume is significant. The larger total initial cross-sectional area reduces internal pressure drop and vapor velocity while maintaining a higher internal film heat transfer coefficient than the external one. As the vapor volume decreases along each loop length due to condensation, the total cross-sectional area decreases to maintain a threshold internal film heat transfer coefficient equal to or greater than the external heat transfer coefficient. This reduction in overall cross-sectional area can be achieved by incorporating multiple access circuit options where the initial fluid path has a greater overall cross-sectional area than subsequent accesses. This arrangement reduces the initial heat transfer fluid pressure drop per incremental circuit length and minimizes heat transfer losses in the first pass. Furthermore, the heat transfer deficit of the condenser is significantly improved by increasing the internal film heat transfer coefficient in the subsequent pass compared to the state-of-the-art single cross-sectional area loop devices. In summary, the multi-cross-section condenser of the present invention provides greater heat rejection at lower heat transfer fluid pressure drops. The multi-cross-section fluid path condensers of the present invention can be implemented using larger tubes in the first pass and smaller tubes in subsequent passes, or by using more tubes in the first pass and more tubes in subsequent passes. This is achieved by using fewer tubes, or by a combination of both, i.e. reducing the number of tubes and the cross-sectional area of the tubes in each subsequent pass.

Description of drawings

FIG. 1 is a cutaway perspective view of an evaporative refrigerant condenser;

Figure 2 shows the operating principle of an evaporative refrigerant condenser;

Fig. 3 shows the tube bundle of the evaporative refrigerant condenser of the prior art;

4a is a plan view photograph of a prototype of a tube bundle (also referred to as a "heat exchange bundle" herein) of multiple cross-sectional areas according to an embodiment of the present invention;

Figure 4b is a front view corresponding to the photograph of Figure 4a;

Figure 5a is a perspective view photograph of the prototype shown in Figure 5a;

Figure 5b is a front view corresponding to the photograph of Figure 5a;

Fig. 6a is a plan view photo of Fig. 2a, and arrows indicate refrigerant flow paths;

Figure 6b is a front view corresponding to the photograph of Figure 6a;

Figure 7a is a labeled version of the photograph of Figure 5a;

Figure 7b is a front view corresponding to the photograph of Figure 7a;

Figure 8 is a sketch of an embodiment of the present invention having four condensation sections;

Figure 9 is a perspective view of an embodiment of the invention with three condenser sections such that the inlet header, outlet header and intermediate header are all on the same side of the device.

Detailed ways

The present invention relates in particular to condenser coil bundles for use in refrigerant condensers, especially (although not exclusively) for use in evaporative refrigerant condensers 10 of the type shown in Figures 1 and 2, which are arranged to indirect superheated refrigerant Transfers heat to and from ambient air, operating in wet or dry mode as described below, depending on ambient atmospheric conditions such as temperature, humidity, and pressure.

The device 10 includes a fan 100 for moving air through the device and is located at the top of the housing 15 as shown schematically in FIG. 1 . Under normal ambient atmospheric conditions where freezing of the cooling liquid (usually water) is not considered, air is drawn into the plenum 18 of the unit via the air channel at the bottom of the unit through the open intake damper and enters the evaporative heat transfer section 12, where Heat transfer occurs, including water distribution from water distribution assembly 90 driven by pump 96 . When the ambient temperature and the temperature of the coolant drop to indicate a problem with the frozen coolant, close the coolant distributor assembly.

The prior art refrigerant coil assembly 20 has the general shape of a substantially parallelepiped, held in a frame 21 on six sides and having a main/longitudinal axis 23, wherein each side is rectangular. The coil assembly 20 is made of a plurality of horizontally closely spaced parallel serpentine tubes connected at their ends to form a plurality of circuits through which refrigerant flows. Each individual loop within the coil assembly is a single continuous length of coil tube that is subjected to a bending operation that forms several U-shaped rows of tubes in generally perpendicular and equidistant relationship to each other such that each Each loop has a composite serpentine shape.

The coil assembly 20 has an inlet 22 connected to an intake manifold or manifold 24 which is fluidly connected to the inlet end of the coils of the coil assembly and an outlet 26 connected to the outlet manifold. A tube or header 28, the outlet manifold or header 28, is fluidly connected to the outlet ends of the coils of the coil assembly. The assembled coil assembly 20 can be moved and transported as a unitary structure such that if desired, if its components are made of steel, the entire coil assembly can be dipped in a zinc bath to galvanize it.

Refrigerant gas is discharged from the compressor into the inlet connection of the unit. Heat from the refrigerant is dissipated through the coils into the water, falling heavily over the tubes. At the same time, air is drawn in through the intake louvers at the bottom of the condenser and travels upwards over the coils opposite the water flow. A small portion of the water evaporates, removing heat from the system. Warm, moist air is drawn into the top of the evaporative condenser by a fan and expelled into the atmosphere. The remaining water falls into a sump at the bottom of the condenser, which is recirculated through the water distribution system and back down over the coils.

The present invention constitutes a modification and improvement of the prior art in that instead of a tube bundle comprising a single cross-sectional area through the coil throughout the refrigerant flow path, the indirect heat exchange section has multiple sections, each section having a different cross-sectional area , decreases as the refrigerant travels through the heat exchange section.

4a, 5a, 6a and 7a are photographs of a prototype of a multi-cross-sectional area refrigerant condenser according to an embodiment of the present invention. Figures 4b, 5b, 6b and 7b are front views corresponding to Figures 4a, 5a, 6a and 7a, respectively. The first condensation part 103 includes a plurality of straight pipes 105 having a first total cross-sectional area. Although circular tubes are shown in the prototype, tubes of any shape, size and feature may be used in accordance with the present invention. Virtually any channel capable of allowing refrigerant flow and heat exchange is suitable for use with the present invention in place of the tubes shown in the figures, including microchannel plates and other conduit structures. In order to describe the invention in connection with the prototype shown in Figures 4a, 5a, 6a and 7a, the term "tube" will be used, but it should be understood that "channel" or "duct" can be replaced by "tube" in this description, regardless of the structure How, as long as it can transport the refrigerant and allow heat exchange between the refrigerant inside and the outside air.

As used herein, the term "total cross-sectional area" refers to the sum of cross-sectional areas of individual tubes in the condensation section. The term "total cross-sectional area" as used herein is not calculated to include the area between tubes in the condensation section. The cross-sectional area of each straight pipe 105 in the first condensation part 103 may be the same or different from each other, but the sum of the cross-sectional areas of all the straight pipes 105 in the first condensation part 103 is equal to the first total cross-sectional area. The tubes in the first condensation part 103 are preferably fin-shaped. Each straight tube 105 in the first condenser section 103 terminates at one end in an inlet header or manifold 107 and at a second end in an intermediate header or manifold 109 .

The second condensation part 111 includes a plurality of straight pipes 113 having a second total cross-sectional area. The cross-sectional area of each straight pipe 113 in the second condensing part 111 may be the same or different from each other, but the sum of the cross-sectional areas of all the straight pipes 113 in the second condensing part 111 is equal to the second total cross-sectional area. The second total cross-sectional area is less than the first total cross-sectional area. The cross-sectional area of each straight pipe 113 in the second condensing part may be the same as or different from the cross-sectional area of each straight pipe 105 in the first condensing part, but each straight pipe 113 in the second condensing part The cross-sectional area of is preferably smaller than the cross-sectional area of each straight pipe 105 in the first condensation section. The number of tubes in the second condensation section may be the same as or different from the number of tubes in the first condensation section, but is preferably less. The length of the tubes in the second condensation section is optionally shorter than the length of the tubes in the first condensation section (eg, as shown in Figures 4a and 4b). The tubes in the second condensation part 111 are preferably finned.

The second condensing section receives refrigerant from the first condensing section via an intermediate header or manifold 109 . As shown, for example in Figures 4a and 4b, each straight tube 113 in the second condensing section terminates at one end of an intermediate header or manifold 109 and terminates at an outlet header or manifold (not shown). out) to the second end.

Alternatively, there may be a third condensation part, a fourth condensation part and a fifth condensation part or more condensation parts. Figure 8 is an illustration of an embodiment of the invention having four condensation sections. According to these embodiments, the second intermediate header or manifold 115 directs the refrigerant to the third condensing section 117, and the third condensing section 117, the fourth condensing section 119 and the fifth condensing section or more Each of them is composed of a plurality of straight pipes, and the total cross-sectional area of each of the third condensation part, the fourth condensation part, and the fifth condensation part or more condensation parts is smaller than that of the immediately upstream condensation part of cross-sectional area.

Each of the straight pipes of the third, fourth and fifth condensing sections or more condensing sections is connected at one end to the immediately upstream condensing section through an intermediate header or manifold, and at a second end Connect to another intermediate header or manifold 121 (if followed by a condenser) or to an outlet header or manifold 123.

Fig. 9 shows another embodiment of the present invention, wherein the inlet header, outlet header and intermediate header are arranged on the same side of the equipment, and each condensing section contains two sets of straight pipe sections, which are composed of U-shaped bends The header is attached at the end opposite the header end. Thus, the inlet header 201 receives superheated refrigerant vapor and distributes it to the first set of straight tubes 203 in the first condensing section 205 . The first group of straight pipes 203 is connected at the other end to the second group of straight pipes 207 in the first condensation section by a U-shaped elbow 209 . The first group of tubes and the second group of tubes in the first condensation section have the same number of tubes, and the tubes have the same diameter. The U-bend 209 has approximately the same cross-sectional size/diameter as the first and second sets of tubes in the first condensation section. The sides of the second set of tubes in the first condensation section are connected to the first intermediate header 211 at the end opposite to the U-bend end. Then, the first intermediate header delivers the refrigerant to the second condensing part 213, and the second condensing part 213 has a first set of tubes 215 of the second condenser and a second set of tubes 217 of the second condenser, and the second set of tubes 217 of the second condenser The second set of tubes 217 of the condenser are connected to the other end of the intermediate header through another set of U-shaped elbows 219 . The first group of tubes and the second group of tubes in the second condensation section have the same cross-sectional size and are equal in number. The U-bends 219 connecting the first and second sets of tubes in the second condensation section also have approximately the same cross-sectional dimensions as the first and second sets of tubes they connect. The second set of tubes 217 of the second condenser section ends at a second intermediate header 221 . The second intermediate header 221 receives refrigerant from the second set of tubes 217 of the second condensing part and guides it to the third condensing part 223 . The first set of pipes 225 of the third condensing section is connected to the second intermediate header at the first end, and is connected to another set of U-shaped elbows (not shown) at the other end, and the set of U-shaped elbows is connected in turn. To the first end of the second set of pipes 227 of the third condensing section. The third condenser section second set of tubes 227 is connected to an outlet header 229 at the header end. The tubes of each condensing section are tapered, while (according to the embodiment shown in Figure 9) the number of tubes per condensing section is equal. However, as in the above embodiment, the size of the tubes can be kept the same, and the number of tubes can be reduced so that the total cross-sectional area of each condensation section is smaller than that of the first section, and preferably smaller than that of each upstream section.

By increasing the number of circuits (tubes) in the first condensing section and increasing the cross-sectional area of each tube in the first condensing section, the present invention can reduce the inlet steam velocity by more than 50%, thereby reducing the refrigerant pressure drop to less than 25% of the original value. In addition, the inlet steam velocity of each loop is sufficient to establish an internal film heat transfer coefficient greater than the external heat transfer coefficient, while limiting the internal pressure drop for the desired heat removal. The subsequent reduction of the total cross-sectional area will take place after the first path or even in the heat transfer fluid path, depending on the operating conditions. The number of tubes in the second condensing section can be adjusted to additionally reduce the vapor velocity, which in turn reduces the refrigerant pressure drop. The second group also shows in this figure that the total cross-sectional area is smaller than that of the first group, thus maintaining the steam velocity before entering the final decrease in cross-sectional area. The third condensing section may have a further reduced cross-sectional area to re-establish vapor velocity before exiting the condenser. Most preferably, each condensation section comprises a path of smaller or the same cross-sectional area as compared to the initial loop. In doing so, the fluid (steam) velocity is re-established such that the associated internal film heat transfer coefficient is greater than the coefficient combining the initial total cross-sectional area with the initial loop volume. The (average) heat transfer fluid (steam) velocity into the final pass can be maintained as required, preferably using multi-cross-section interfaces throughout the condenser by segmented headers (see eg Figures 4a, 4b and 9). There are many permutations of path cross-sectional area combined with the number of paths per segment that can be used with the present invention to optimize performance. Iterative calculations can be performed based on operating conditions, refrigerant and heat rejection requirements. Still other advantages of the present invention include reduced refrigerant inventory due to reduced refrigerant pressure drop and increased condenser efficiency.

Claims (24)

1. A heat exchange bundle for a refrigerant condenser comprising: a first condensing section comprising a first set of straight refrigerant passages having a first total cross-sectional area; a second condensing section comprising a second set of straight refrigerant passages having a second total cross-sectional area; inlet header; first intermediate header; said first set of straight refrigerant passages are each connected at a first end to said inlet header and at a second end to said first intermediate header; The second set of straight refrigerant passages are each connected at a first end to the first intermediate header; The second total cross-sectional area is less than the first total cross-sectional area. 2. The heat exchange bundle for a refrigerant condenser according to claim 1, further comprising: outlet header; The second set of straight refrigerant passages are each connected to the outlet header at a second end. 3. The heat exchange bundle for a refrigerant condenser according to claim 1, further comprising: a third condensing section comprising a third set of straight refrigerant passages having a third total cross-sectional area; second intermediate header; The second set of straight refrigerant passages are each connected at a second end to the second intermediate header; The third set of straight refrigerant passages are each connected at a first end to the second intermediate header; The third total cross-sectional area is smaller than the second total cross-sectional area. 4. The heat exchange bundle for a refrigerant condenser according to claim 3, further comprising: outlet header; The third set of straight refrigerant passages are each connected to the outlet header at a second end. 5. The heat exchange bundle for a refrigerant condenser according to claim 3, further comprising: The fourth condensing part includes a fourth set of straight refrigerant passages with a fourth total cross-sectional area; third intermediate header; The third set of straight refrigerant passages are each connected at a second end to the third intermediate header; The fourth set of straight refrigerant passages are each connected to the third intermediate header at a first end; The fourth total cross-sectional area is smaller than the second total cross-sectional area. 6. The heat exchange bundle for a refrigerant condenser according to claim 5, further comprising: outlet header; The fourth set of straight refrigerant passages are each connected to the outlet header at a second end. 7. The heat exchange bundle for a refrigerant condenser according to any one of claims 1 to 6, wherein the first condensation part and the second condensation part have the same number of refrigerant passages, and A cross-sectional area of each refrigerant channel in the second condensing part is smaller than a cross-sectional area of each refrigerant channel in the first condensing part. 8. The heat exchange bundle for a refrigerant condenser according to any one of claims 1 to 6, wherein a cross-sectional area of each refrigerant channel in the second condenser part is smaller than that of the first condenser The cross-sectional area of each refrigerant channel in the first condensing part and the number of refrigerant channels in the second condensing part are the same. 9. The heat exchange bundle for a refrigerant condenser according to any one of claims 1 to 6, wherein a cross-sectional area of each refrigerant channel in the second condensing part is smaller than that of the first The cross-sectional area of each refrigerant channel in the condensing part, and the second condensing part has fewer refrigerant channels than the first condensing part. 10. An evaporative refrigerant condenser comprising: a housing defining an indirect heat exchange portion positioned above the plenum; a fan located at the top of the housing and configured to draw ambient air from the plenum through the opening in the bottom of the housing and the coil portion through the fan and out of the top of the housing; a water distribution assembly located in the housing and above the coil portion for selectively distributing water over the coil portion; a water collecting part, located at the bottom of the housing, for collecting the water distributed by the water distribution assembly; a water pump for delivering water from the water collection to the water distribution assembly; A heat exchange assembly located in the indirect heat exchange section, the heat exchange assembly comprising the heat exchange bundle according to any one of claims 1-9. 11. A method of increasing heat exchange efficiency of an evaporative refrigerant condenser having a shell defining an indirect heat exchange portion above a plenum; a fan at the top of the housing configured to draw ambient air from the plenum through the opening in the bottom of the housing and the coil portion through the fan and out of the top of the housing; a water distribution assembly located in the housing and above the coil portion for selectively distributing water over the coil portion; a water collecting part, located at the bottom of the housing, for collecting the water distributed by the water distribution assembly; a water pump for delivering water from the water collection to the water distribution assembly; The first coil assembly is located in the indirect heat exchange part, and the coil assembly includes a plurality of individual serpentine heat exchange tubes that are gathered close to each other; Each serpentine heat exchange tube is connected at a first end to an inlet header and at a second end to an outlet header; The method comprises replacing the first coil assembly with a heat exchange bundle according to any one of claims 1-9. 12. A method of increasing the heat exchange efficiency of an evaporative refrigerant condenser, comprising: reducing the total cross-sectional area of the second condensing section compared to the first condensing section sufficient to establish a larger than the external The internal film heat transfer coefficient for Heat Transfer Coefficient. 13. The method of claim 12, comprising reducing the total cross-sectional area of the continuous condensation section sufficiently to maintain the inner film heat transfer coefficient greater than the outer heat transfer coefficient. 14. The heat exchange bundle according to any one of claims 1 to 9, wherein the straight refrigerant channels are selected from oval tubes, round tubes, oval tubes and microchannel plates. 15. A heat exchange bundle for a refrigerant condenser comprising: The first condensing part includes a first set of straight refrigerant passages and a second set of straight refrigerant passages, which have a first total cross-sectional area and are connected at one end by a set of first condensing part U-shaped elbows; The second condensing part includes a third group of straight refrigerant passages and a fourth group of straight refrigerant passages, which have a second total cross-sectional area and are connected at one end by a set of U-shaped elbows of the second condensing part group; inlet header; first intermediate header; The first set of straight refrigerant passages and the second set of straight refrigerant passages are each connected to the inlet header at a first end and to the first intermediate header at a second end; The third set of straight refrigerant passages and the fourth set of straight refrigerant passages are each connected to the first intermediate header at a first end and to an outlet header at a second end; The second total cross-sectional area is less than the first total cross-sectional area. 16. A heat exchange bundle for a refrigerant condenser comprising: a first condensing section comprising a first set of straight refrigerant passages having a first total cross-sectional area; a second condensing section comprising a second set of straight refrigerant passages having a second total cross-sectional area; inlet header; first intermediate header; said first set of straight refrigerant passages are each connected at a first end to said inlet header and at a second end to said first intermediate header; The second set of straight refrigerant passages are each connected at a first end to the first intermediate header; The second total cross-sectional area is less than the first total cross-sectional area. 17. The heat exchange bundle for a refrigerant condenser according to claim 16, further comprising: outlet header; The second set of straight refrigerant passages are each connected to the outlet header at a second end. 18. The heat exchange bundle for a refrigerant condenser according to claim 16, further comprising: a third condensing section comprising a third set of straight refrigerant passages having a third total cross-sectional area; second intermediate header; The second set of straight refrigerant passages are each connected at a second end to the second intermediate header; The third set of straight refrigerant passages are each connected at a first end to the second intermediate header; The third total cross-sectional area is smaller than the second total cross-sectional area. 19. The heat exchange bundle for a refrigerant condenser according to claim 18, further comprising: outlet header; The third set of straight refrigerant passages are each connected to the outlet header at a second end. 20. The heat exchange bundle for a refrigerant condenser according to claim 18, further comprising: The fourth condensing part includes a fourth set of straight refrigerant passages with a fourth total cross-sectional area; third intermediate header; The third set of straight refrigerant passages are each connected at a second end to the third intermediate header; The fourth set of straight refrigerant passages are each connected to the third intermediate header at a first end; The fourth total cross-sectional area is smaller than the third total cross-sectional area. 21. The heat exchange bundle for a refrigerant condenser according to claim 20, further comprising: outlet header; The fourth set of straight refrigerant passages are each connected to the outlet header at a second end. 22. The heat exchange bundle for a refrigerant condenser according to any one of claims 16 to 21, wherein the first condensation part and the second condensation part have the same number of refrigerant passages, and A cross-sectional area of each refrigerant channel in the second condensing part is smaller than a cross-sectional area of each refrigerant channel in the first condensing part. 23. The heat exchange bundle for a refrigerant condenser according to any one of claims 16 to 21, wherein the cross-sectional area of each refrigerant channel in the second condensing part is smaller than that of the first condensing part The cross-sectional area of each refrigerant channel in the first condensing part and the number of refrigerant channels in the second condensing part are the same. 24. The heat exchange bundle for a refrigerant condenser according to any one of claims 16 to 21, wherein the cross-sectional area of each refrigerant channel in the second condensing part is smaller than that of the first The cross-sectional area of each refrigerant channel in the condensing part, and the second condensing part has fewer refrigerant channels than the first condensing part.