Evaporatively cooled condenser

Abstract

A plurality of tubes define refrigerant passages extending vertically from a lower end to an upper end for condensing a superheated refrigerant to a subcooled liquid. A bottom header is in fluid communication with the lower end of the tubes, and a top header is in fluid communication with the upper end of the tubes. A plurality of fins extend back and forth between a plurality of apexes joined to the tubes by a connector with a plurality of gaps defined between the fins and the sides of the tubes to allow water to flow through the gaps for greater heat transfer. Methods of fabricating and a method of operating the heat exchanger are also described.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject invention relates to a heat exchanger assembly, a method of fabricating a heat exchanger assembly, and a method of operating a heat exchanger assembly.

2. Description of the Prior Art

Conventional air conditioning systems include an evaporator for transferring heat from ambient air to evaporate a refrigerant, a compressor for compressing the refrigerant into a superheated vapor, and a condenser to condense the refrigerant back to a subcooled liquid so that it can be provided back to the evaporator through an expansion device. Known condenser assemblies include a plurality of tubes spaced apart from one another, each extending between a lower end and an upper end to define a plurality of refrigerant passages for carrying refrigerant flowing between a bottom header and a top header. A plurality of fins extend back and forth between adjacent tubes. Heat from the refrigerant is transferred to the fins and carried away by an airstream flowing through the fins. Attempts have been made to improve the efficiency of this process by using water. Specifically, transferring heat to a source of water allows for increased heat transfer.

One such heat exchanger is disclosed in WO 00/68628 to Phelps et al., which shows a hose connected to a water outlet that drips water over condenser fins. A controller is responsive to a sensed air temperature to shut off the water flow below a certain air temperature. As the temperature increases, the flow rate also increases in stepped amounts. The system is further optimized by visually inspecting the condenser to see if there is excess or insufficient water near the bottom of the unit. However, this system suffers from several disadvantages. First, air temperature is not the only factor affecting the performance of a condenser. Second, the controller only controls the unit in stepped amounts. Finally, the controller must be manually optimized based on a visual inspection, and contains no means for an automatic optimization of the water flow. Finally, the water source does not uniformly wet the condenser surface.

A similar heat exchanger is shown in U.S. Pat. No. 4,672,817 to Croce, which shows a condenser having a perforated copper tube to allow water to saturate a wicking material until it drips vertically down over an array of fins. A common disadvantage of these prior condensers is that the water flows over the fins. While this allows the fins to cool, enabling them to draw more heat away from the refrigerant, it would be advantageous to get the water closer to the tubes. That would allow the water to directly receive heat from the refrigerant.

Another heat exchanger, shown in U.S. Pat. No. 7,062,938 to Lee, shows a combination air cooled and water cooled condenser. The water cooled portion of the condenser consists of a coolant tube and a water tube running beside each other and flowing in opposite directions. In addition, the control system is responsive to condensing load and coolant pressure in addition to ambient temperature. While this arrangement places the water closer to the tubes, it is still separated from the refrigerant tube by its own tube wall. In addition, the two stage system is bulky and includes additional components, such as pumps to drive to water, that are not desired.

SUMMARY OF THE INVENTION AND ADVANTAGES

The subject invention provides such a heat exchanger wherein a plurality of fins extend back and forth between a plurality of apexes and between adjacent tubes, but distinguished by the apexes of the fins being spaced from the adjacent tubes to define a plurality of gaps between the apexes and adjacent tubes.

The invention provides a method of fabricating such a heat exchanger wherein a plurality of fins, extending back and forth between a plurality of apexes, are placed between adjacent tubes with a plurality of gaps defined between the fins and the adjacent tubes.

The invention also provides a method of operating such a heat exchanger including flowing water along the tubes and through a plurality of gaps defined between the fins and the tubes.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a perspective view of a first exemplary embodiment of a heat exchanger of the present invention;

FIG. 2 is a cross sectional view taken along plane 2-2 of FIG. 1 which passes through an apex and spaced tube in accordance with the present invention;

FIG. 3 is a fragmentary view of a second exemplary embodiment of a heat exchanger of the present invention;

FIG. 4 is a cross sectional view taken along a plane similar to plane 2-2 of the second exemplary embodiment which passes through a notched fin and tube in accordance with the present invention;

FIG. 5 is a schematic view of a third exemplary embodiment of a heating and ventilating and air conditioning system according to the present invention;

FIG. 6 is a schematic view of a fourth exemplary embodiment of a heating and ventilating and air conditioning system according to the present invention;

FIG. 7 is a flow chart demonstrating a method of fabricating a heat exchanger in accordance with the first exemplary embodiment of the present invention; and

FIG. 8 is a flow chart demonstrating a method of operating a heat exchanger in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, a heating and ventilating and air conditioning system 20 is generally shown in FIGS. 5 and 6. Specifically, the system 20 includes an evaporator 22, a compressor 24, a condenser 26, and an expander 28. The condenser 26 is a heat exchanger assembly 26 that receives a superheated gas and condenses it to a subcooled liquid. As shown in FIG. 1, a plurality of tubes 30 is provided having parallel sides spaced apart from one another and extending between front and back closures. The tubes 30 further extend longitudinally from a lower end to an upper end, with a bottom header 32 in fluid communication with the lower ends of the tubes 30 and a top header 34 in fluid communication with the upper ends of the tubes 30. The tubes 30 include a plurality of internal dividers 36 extending longitudinally within the tubes 30 to define a plurality of refrigerant passages in each tube 30. These passages carry a refrigerant flowing between the bottom and top headers 32, 34. In addition, the headers 32, 34 can be sealed to the tubes 30 through a brazing process.

A bottom water tank 38 is in fluid communication with the exterior of the lower ends of the tubes 30 for storing a supply of water. A top water tank 40 in fluid communication with the exterior of the upper ends of the tubes 30 provides additional water. The water tanks 38, 40 can be constructed of plastic and molded in segments so as to be assembled around the tubes 30 after brazing the headers 32, 34. The water tanks 38, 40 can then be bonded to the tubes 30.

A wicking coating 42 lines the parallel sides of the tubes 30 and wicks water from the top and bottom water tanks 40, 38 to the parallel sides of the tubes 30 by capillary action. According to the exemplary embodiments, the wicking coating 42 is formed from sintered metallic particles each having a particle diameter of approximately between 70 to 90 microns. The particles are layered on the tubes 30 to a thickness of approximately between 3 to 5 times the particle diameter, and the coating has a porosity of approximately between 40% to 60%. More specifically, the porosity of the exemplary embodiments is approximately 50%. It is known in the art that the brazing process, as discussed above, may reduce the porosity of the sintered metal coating. This can be compensated for, however, by forming a coating that is more porous than desired so that the final coating will have the desired properties.

A plurality of fins 44 extend back and forth in a zig-zag pattern between a plurality of apexes 46. The fins 44 are located between the exterior parallel sides of adjacent tubes 30 and extend horizontally between the front and back closure. The apexes 46 of the fins 44 are secured to the parallel sides by a connector, and a plurality of gaps are defined between the fins 44 and the parallel sides for fluid communication along the exterior of the parallel sides in the longitudinal direction through the fins 44. The wicking coating 42 extends through the gaps to wick water into the gaps for heat transfer between the tubes 30 and the fins 44. This provides for uniform distribution of the water throughout the tube 30 exterior surface. Heat from the refrigerant flowing through the tubes 30 evaporates the water into vapor. A blower 48, shown in FIGS. 5 and 6, is provided to move air transversely to the tubes 30 to carry the vapor away.

According to a first exemplary embodiment, shown in FIGS. 1 and 2, the apexes 46 of the fins 44 are spaced from the parallel sides of the tubes 30 to define the plurality of gaps. A plurality of bridges 50 extends across a portion of each of the gaps to define the connector. Each bridge 50 may be a tab slotted and bent out of the fin 44 and brazed to the adjacent tube 30, or simply a large weld or a welded piece of compatible metal. The bridges 50 interconnect each of the apexes 46 to the sides of the tubes 30 while maintaining the gaps. These bridges 50 and gaps are more easily seen in the cross section of FIG. 2.

According to a second exemplary embodiment, shown in FIGS. 3 and 4, the fins 44 have triangular-shaped notches 52 cut out from the apexes 46 inward to define the plurality of gaps. The remaining surfaces of the apexes 46 are then in direct contact with the parallel sides of the tubes 30 and are brazed to the sides to form a meld 54 defining the connector. Although other joining methods may be used to form the meld 54, brazing the fins 44 to the tubes 30 can be incorporated with the brazing process for securing the headers 32, 34. Specifically, a braze material is incorporated into the fin 44 stock material, and the interface between the tubes 30 and the headers 32, 34 is wired with a braze material. The assembly 26 is then placed in a braze furnace where the braze material melts and bonds metallurgically to form the meld 54.

Alternatively, the fins 44 could be formed without the notches 52, such as the fins 44 of FIGS. 1 and 2 and the apexes 46 joined by a meld 54 to the tube 30. The gaps could then be defined by a plurality of indents formed in the tube 30 extending inwardly toward the refrigerant passages and away from the apexes 46 of the fins 44.

A plurality of valves 56, as shown in FIGS. 1, 5 and 6, are each disposed at the upper end of each of the tubes 30 between the top water tank 40 and the fins 44. The valves 56 are movable between an open position and a closed position for controlling the flow of water from the top tank to the wicking coating 42 on the exterior of the tubes 30. An actuator 58 is connected to the valves 56 to selectively move the valves 56 between the open and closed positions, and an actuator controller 60 controls the actuator 58 to determine the appropriate mass flow rate of water {dot over (m)}_w flowing from the top water tank 40. The actuator controller 60 is responsive to a heat transfer rate {dot over (q)} through the condenser 26 and a latent heat of evaporation h_fg of the water. The mass flow rate of water is determined by:

$\begin{array}{cc}{\stackrel{.}{m}}_w=\frac{\stackrel{.}{q}}{h_{\mathrm{fg}}}& \left(1\right)\end{array}$

A heat transfer calculator 62 is also provided for calculating the heat transfer rate {dot over (q)} based on thermodynamic properties of the specific refrigerant as well as the design constraints of the heat exchanger. Specifically, the temperature of the refrigerant entering and exiting the plurality of refrigerant passages, T_ri and T_ro, are determined according to the amount of cooling desired through the evaporator 22. Thus, the amount of heat transfer through the condenser 26 is equivalent to the amount of heat absorbed during the isothermal evaporation in the evaporator 22 plus the heat added by the compressor 24. The thermodynamic properties of the refrigerant are determined according to the states at which the refrigerant exists during the process. As previously discussed, the refrigerant enters the tubes 30 as a superheated vapor, and therefore has a gaseous isobaric specific heat c_pg. The gaseous refrigerant cools across a desuperheating fraction λ_g which is the fraction of the refrigerant passages where the refrigerant cools from a superheated vapor to a saturation temperature T_s. The desuperheating fraction is known from experience to be approximately 0.15. The amount of heat given off in this portion of the condenser 26 is governed by the expression λ_gc_pg(T_ri−T_s). After the refrigerant transitions to a liquid, it has a liquid isobaric specific heat c_pf and cools across a subcooling fraction λ_f, which is the fraction of the refrigerant passages where the refrigerant cools to a subcooled liquid. The subcooling fraction is known from experience to be approximately 0.10 The amount of heat given off in this portion of the condenser 26 is governed by the expression λ_fc_pf(T_s−T_ro). However, additional heat is also given off when transitioning from a gas to a liquid, which is related to the latent heat of evaporation of the refrigerant h_fgr. The expression h_fgr(1−λ_g−λ_f) refers to the amount of heat given off when transitioning the refrigerant to a liquid state. The summation of these three expressions multiplied by the mass flow rate of the refrigerant {dot over (m)}_r flowing through the plurality of refrigerant passages yields the total amount of heat transferred in the condenser 26 per unit time:

{dot over (q)}={dot over (m)}_r[λ_gc_pg(T_ri−T_s)+h_fgr(1−λ_g−λ_f)+λ_fc_pf(T_s−T_ro)]  (2)

According to a third exemplary embodiment, as shown in FIG. 5, the mass flow rate of the refrigerant is determined by measuring the mass flow rate with a flow meter 64. However, use of the flow meter 64 can be expensive. Therefore, according to a fourth exemplary embodiment, shown in FIG. 6, the mass flow rate of the refrigerant is determined by a mass flow calculator 66 based on the volumetric efficiency η_v of the compressor 24, the displacement rate V_d of the compressor 24, the rotational speed N of the compressor 24, the suction pressure P_suc of the compressor 24, the suction temperature T_suc of the compressor 24, and the gas constant R_r of the refrigerant. To accomplish this, a pressure gauge 68 and a temperature sensor 70 are placed within the refrigerant line on the suction side of the compressor 24, as shown in FIG. 4. The mass flow rate of the refrigerant is then determined by the mass flow calculator 66 according to the equation:

$\begin{array}{cc}{\stackrel{.}{m}}_r=\frac{{\eta }_vV_d{\mathrm{NP}}_{\mathrm{suc}}}{R_rT_{\mathrm{suc}}}& \left(3\right)\end{array}$

A blower controller 72 is provided to control mass flow rate of air {dot over (m)}_a from the blower 48 in response to the mass flow rate of water {dot over (m)}_w, incoming absolute humidity ω_i of the air entering the fins 44 and the outgoing absolute humidity ω_o of the air exiting the fins 44 according to the equation:

$\begin{array}{cc}{\stackrel{.}{m}}_a=\frac{{\stackrel{.}{m}}_w}{{\omega }_o-{\omega }_i}& \left(4\right)\end{array}$

According to the third exemplary embodiment, the controllers 60, 72 and the heat transfer calculator 62 are separate processors in electrical communication with one another. For example, the heat transfer calculator 62 is a separate hardware component in electrical communication with the actuator controller 60. The controllers 60, 72 are separate hardware components in electrical communications with each other and with the respective parts that they control. The controllers 60, 72 are in electrical communication with a master controller that is also in communication with other components of the system 20.

According to the fourth exemplary embodiment, the controllers 60, 72 and calculators 62, 66 are subcomponents of a master controller. This embodiment includes the various controllers 60, 72 and calculators 62, 66 being integrated into a housing and controlled by a single processor. It should further be noted that the controllers 60, 72 and calculators 62, 66 could alternatively be software subcomponents (i.e. a plurality of algorithms) stored in the memory of the master controller.

A method of fabricating a heat exchanger is also provided. The method includes spacing a plurality of tubes 30 apart from one another. A plurality of refrigerant passages are defined within each tube 30 extending from a lower end to an upper end. A bottom header 32 is secured to the lower ends, and a top header 34 is secured to the upper ends of the tubes 30. Both headers 32, 34 are in fluid communication with the refrigerant passages. The securing could be accomplished by any suitable method, as alluded to above, such as welding or brazing. A plurality of fins 44 extending back and forth between a plurality of apexes 46 are placed between adjacent tubes 30.

According to the first exemplary embodiment, shown in FIG. 7, the apexes 46 are then spaced from the tubes 30 to define a plurality of gaps between the apexes 46 and the adjacent tubes 30. A bridge 50 is formed to connect each of the apexes 46 across a portion of the gaps. This interconnects each apex 46 to the adjacent tube 30 while maintaining the gaps. As alluded to above, the bridges 50 could be formed by any suitable method, such as welding or brazing.

According to the second exemplary embodiment, the fins 44 are formed from stock material by feeding the material through a progressive die to cut a plurality of notches 52 extending inwardly from the apexes 46 of the fins 44. The apexes 46 could then be brazed to the tubes 30 while brazing the headers 32, 34.

Alternatively, if the fins 44 are formed without the notches 52, the gaps can be defined by a plurality of indents formed in the tubes 30 extending inwardly toward the refrigerant passages and away from the apexes 46 of the fins 44. These indents could be formed by forming dimples on the tube 30 exterior during the extrusion process, or they could be formed by stamping the tubes 30 after the extrusion process.

A wicking coating 42 is formed along the exterior of the tubes 30 and extends through the gaps. This provides for uniform distribution of water throughout the tube 30 exterior surface. The tubes 30 of the exemplary embodiments are made by extrusion, and the wicking coating 42 can then be applied to the exterior surface of the tubes 30, for example, by flame spraying or chemical etching. The wicking coating 42 of the exemplary embodiments is formed as a sintered metal coating along the tubes 30 having a porosity approximately between 40% to 60%. According to the exemplary embodiments, the porosity is approximately 50%. The wicking coating 42 is formed from a plurality of particles each having a diameter of approximately 70 to 90 microns and layered to a thickness of approximately between 3 to 5 times the diameter of the particles. As noted earlier, the brazing process can reduce the porosity of the coating, so the coating could be formed with a higher porosity prior to brazing to compensate for the loss.

A bottom water tank 38 is secured adjacent the lower ends of the tubes 30 and a top water tank 40 is secured adjacent the upper ends of the tubes 30, both in fluid communication with the wicking coating 42 on the exterior of the tubes 30. As alluded to above, the water tanks 38, 40 can be secured to the assembly 26 after the brazing process. A valve 56 is secured to the top water tank 40 between the top water tank 40 and the fins 44, and an actuator 58 is secured to the valves 56 to selectively move the valves 56 between the open and closed positions.

A method of operating a heat exchanger is also provided as shown in FIG. 8. The heat exchanger is of the type including a plurality of tubes 30 extending axially to define a plurality of refrigerant passages. A plurality of fins 44 extend between adjacent tubes 30 and back and forth between a plurality of apexes 46. A plurality of gaps are defined between the fins 44 and adjacent tubes 30 for fluid communication axially along the exterior surface of the tubes 30. The method includes flowing a refrigerant through the plurality of refrigerant passages and extracting heat from the refrigerant. The heat is transferred to a source of water, which causes the water to evaporate. The method is characterized by flowing the water along the tubes 30 and through the plurality of gaps for uniform distribution. According to the exemplary embodiment, the water is wicked through the gaps with a wicking coating 42. Evaporation of the water draws sufficient heat from the refrigerant to compensate for the lack of conductivity between the tubes 30 and the fins 44.

The exemplary embodiment further provides for regulating the flow of water according to equation 1. In addition, the heat transfer rate q is determined according to equation 2. The refrigerant mass flow rate {dot over (m)}_r may be obtained from a mass flow meter 64, or determined according to equation 3.

In addition, air is conveyed through the plurality of fins 44 to carry the evaporated water away from the tubes 30. The necessary mass flow rate {dot over (m)}_a of the air is determined according to equation 4. However, if the condenser 26 is operated without water, such as during a water shortage, the mass flow rate of air {dot over (m)}_a can still be determined based on the heat transfer rate {dot over (q)}, the specific heat of the air entering the fins 44 c_pa, the condenser 26 effectiveness ε, the inlet temperature of the refrigerant T_ri and the dry bulb temperature of the incoming air T_i according to the equation:

$\begin{array}{cc}{\stackrel{.}{m}}_a=\frac{\stackrel{.}{q}}{c_{\mathrm{pa}}\varepsilon \left(T_{\mathrm{ri}}-T_i\right)}& \left(5\right)\end{array}$

To convey the air, a power input H_fan is provided to a blower 48 based on the proportionality constant g_c (a universal constant equal to 32.174 lb_m ft/lb_fs²), the fan efficiency η_fan, the hydraulic diameter of the airflow passage of the blower 48 d, dynamic viscosity of the air μ_a, and the density of the air ρ_a according to the equation:

$\begin{array}{cc}{H}_{\mathrm{fan}}=\frac{0.2414}{g_c}\left(\frac{1}{{\eta }_{\mathrm{fan}}}\right)\left(\frac{1}{d^{19/4}}\right)\left(\frac{{\mu }_a^{1/4}}{{\rho }_a}\right){\stackrel{.}{m}}_a& \left(6\right)\end{array}$

While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A heat exchanger assembly for a heating and ventilating and air conditioning system also including an evaporator and a compressor, said assembly comprising;

a plurality of tubes having an exterior surface and extending axially between a lower end and an upper end and spaced apart from one another to define a plurality of refrigerant passages,

a bottom header in fluid communication with said lower ends of said tubes,

a top header in fluid communication with said upper ends of said tubes,

a plurality of fins extending back and forth between a plurality of apexes,

a connector for joining said apexes of said fins to adjacent tubes, and

said fins and adjacent tubes defining at least one gap therebetween for fluid communication axially along said exterior surface of said tubes.

2. An assembly as set forth in claim 1 including a plurality of said gaps between said fins and said adjacent tubes.

3. An assembly as set forth in claim 2 wherein said connector comprises a meld between said apexes of said fins and said adjacent tubes.

4. An assembly as set forth in claim 3 wherein said connector comprises a brazed joint.

5. An assembly as set forth in claim 3 wherein said fins include a plurality of notches extending inwardly from each of said apexes of said fins to define said plurality of gaps.

6. An assembly as set forth in claim 2 wherein said apexes are spaced from said adjacent tubes and said connector comprises a plurality of bridges extending from said apexes to interconnect each apex to said adjacent tubes to define said gaps between said apexes and said bridges and said adjacent tubes.

7. An assembly as set forth in claim 2 including a wicking coating lining said exterior surface of said tubes and extending through said gaps to wick a source of water through said gaps.

8. An assembly as set forth in claim 7 wherein said wicking coating comprises a sintered metal coating having a porosity approximately between 40% and 60%.

9. An assembly as set forth in claim 8 wherein said porosity is approximately 50%.

10. An assembly as set forth in claim 7 wherein said wicking coating includes a plurality of sintered metal particles.

11. An assembly as set forth in claim 10 wherein said wicking coating has a thickness of approximately between 3 to 5 times a diameter of said particles.

12. An assembly as set forth in claim 10 wherein said sintered metal particles have a diameter of approximately between 70 microns and 90 microns.

13. An assembly as set forth in claim 7 including a bottom water tank to provide the source of water to said wicking material.

14. An assembly as set forth in claim 7 including a top water tank in fluid communication with said exterior surface of said upper ends of said tubes to provide the source of water to said wicking coating.

15. An assembly as set forth in claim 14 including a plurality of valves each disposed at said upper end of each tube between said top water tank and said fins and movable between an open position and a closed position for controlling the flow of water from said top tank.

16. An assembly as set forth in claim 15 including an actuator connected to said valves to selectively move said valves between said open and closed positions.

17. An assembly as set forth in claim 16 including an actuator controller for controlling said actuator in response to a heat transfer rate {dot over (q)} and a latent heat of evaporation hfg of the water to determine the mass flow rate of water {dot over (m)}w flowing from the top water tank according to the equation m. w = q. h fg.

18. An assembly as set forth in claim 17 including a heat transfer calculator for advising said actuator controller of the heat transfer rate {dot over (q)} according to the equation {dot over (q)}={dot over (m)}r[λgcpg(Tri−Ts)+hfgr(1−λg−λf)+λfcpf(Ts−Tro)] wherein,

{dot over (m)}r is the mass flow rate of the refrigerant flowing through the plurality of refrigerant passages,

Tri is the temperature of the refrigerant entering the plurality of refrigerant passages,

Tro is the temperature of the refrigerant exiting the plurality of refrigerant passages,

λg is the fraction of the refrigerant passages where the heat extracted from the refrigerant cools the refrigerant from a superheated vapor,

cpg is the specific heat of the refrigerant in a gaseous state,

hfgr is the latent heat of evaporation of the refrigerant flowing through the plurality of refrigerant passages,

λf is the fraction of the refrigerant passages where the heat extracted from the refrigerant cools the refrigerant to a subcooled liquid,

cpf is the specific heat of the refrigerant in a liquid state, and

Ts is the surface temperature of the tube.

19. An assembly as set forth in claim 18 including a flow meter in communication with said heat transfer calculator for sensing the mass flow rate of refrigerant {dot over (m)}r through the refrigerant passages.

20. An assembly as set forth in claim 18 including a mass flow calculator for advising said heat transfer calculator of the mass flow rate of refrigerant {dot over (m)}r through the refrigerant passages according to the equation m. r = η v  V d  NP suc R r  T suc wherein;

ηv is a volumetric efficiency of said compressor,

Vd is a displacement rate of said compressor,

N is a rotational speed of said compressor,

Psuc is a suction pressure of said compressor,

Tsuc is a suction temperature of said compressor, and

Rr is a gas constant of the refrigerant.

21. An assembly as set forth in claim 20 including a pressure gauge for measuring the suction pressure of said compressor.

22. An assembly as set forth in claim 20 including a temperature sensor for sensing the suction temperature of said compressor.

23. An assembly as set forth in claim 16 including a blower for moving air transversely to said tubes.

24. An assembly as set forth in claim 23 including a blower controller for controlling said blower in response to a mass flow rate of water {dot over (m)}w according to the equation m. a = m. w ω o - ω i wherein {dot over (m)}w is the mass flow rate of water flowing from the top water tank and ωi is an incoming absolute humidity of the air entering the fins and ωo is an outgoing absolute humidity of the air exiting the fins.

25. A heat exchanger assembly for a heating and ventilating and air conditioning system also including an evaporator and a compressor, said assembly comprising; m. w = q. h fg, m. a = m. w ω o - ω i

a plurality of tubes each having parallel sides spaced apart from one another and extending between a front closure and a back closure and longitudinally from a lower end to an upper end,

a bottom header in fluid communication with said lower ends of said tubes,

a top header in fluid communication with said upper ends of said tubes,

said tubes including a plurality of internal dividers extending longitudinally to define a plurality of refrigerant passages in each tube for carrying refrigerant flowing between said bottom and top headers,

a bottom water tank in fluid communication with said lower ends of said tubes for storing a supply of water to provide to said parallel sides of said tubes,

a top water tank in fluid communication said upper ends of said tubes for supplementing the supply of water provided to said parallel sides of said tubes,

a blower for moving air transversely to said tubes,

a plurality of fins extending back and forth between a plurality of apexes and extending between said front closure and said back closure,

a connector for joining said apexes of said fins to adjacent parallel sides,

a sintered metal coating of approximately 50% porosity and a particle diameter of approximately between 70 microns to 90 microns and a thickness of approximately between 3 to 5 times said particle diameter to define a wicking coating on said parallel sides of said tubes for wicking water from said top and bottom water tanks to said parallel sides of said tubes by capillary action,

said fins and adjacent tubes defining a plurality of gaps therebetween for fluid communication longitudinally along said parallel sides,

said wicking coating extending through said gaps for wicking water from said top and bottom water tanks and along said parallel sides of said tubes,

a plurality of valves each disposed at said upper ends of each tube between said top water tank and said fins and movable between an open position and a closed position for controlling the flow of water from said top water tank,

an actuator connected to said valves to selectively move said valves between said open and closed positions,

an actuator controller for controlling said actuator in response to a heat transfer rate {dot over (q)} and a latent heat of evaporation hfg of the water to determine the mass flow rate of water {dot over (m)}w flowing from said top water tank according to the equation

a heat transfer calculator for advising said actuator controller of the heat transfer rate {dot over (q)} according to the equation {dot over (q)}={dot over (m)}r[λgcpg(Tri−Ts)+hfgr(1−λg−λf)+λfcpf(Ts−Tro)] wherein, {dot over (m)}r is the mass flow rate of the refrigerant flowing through the plurality of refrigerant passages, Tri is the temperature of the refrigerant entering the plurality of refrigerant passages, Tro is the temperature of the refrigerant exiting the plurality of refrigerant passages, λg is the fraction of the refrigerant passages where the heat extracted from the refrigerant cools the refrigerant from a superheated vapor, cpg is the specific heat of the refrigerant in a gaseous state, hfgr is the latent heat of evaporation of the refrigerant flowing through the plurality of refrigerant passages, λf is the fraction of the refrigerant passages where the heat extracted from the refrigerant cools the refrigerant to a subcooled liquid, cpf is the specific heat of the refrigerant in a liquid state, Ts is the surface temperature of the tube, and

a blower controller for controlling said blower in response to the mass flow rate of water {dot over (m)}w according to the equation

 wherein ωi is an incoming absolute humidity of the air entering the fins and ωo is an outgoing absolute humidity of the air exiting the fins.

26. An assembly as set forth in claim 25 wherein said connector comprises a meld between said apexes of said fins and said adjacent tubes.

27. An assembly as set forth in claim 26 wherein said connector comprises a brazed joint.

28. An assembly as set forth in claim 26 wherein said fins include a plurality of notches extending inwardly from each of said apexes of said fins to define said plurality of gaps.

29. An assembly as set forth in claim 25 wherein said apexes are spaced from said adjacent tubes and said connector comprises a plurality of bridges extending from said apexes to interconnect each apex to said adjacent tubes to define said gaps between said apexes and said bridges and said adjacent tubes.

30. An assembly as set forth in claim 25 including a flow meter in communication with said heat transfer calculator for sensing the mass flow rate of refrigerant {dot over (m)}r through the refrigerant passages.

31. An assembly as set forth in claim 25 including a mass flow calculator for advising said heat transfer calculator of the mass flow rate of refrigerant {dot over (m)}r through the refrigerant passages according to the equation m. r = η v  V d  NP suc R r  T suc wherein;

ηv is a volumetric efficiency of the compressor,

Vd is a displacement rate of said compressor,

N is a rotational speed of said compressor,

Psuc is a suction pressure of said compressor,

Tsuc is a suction temperature of said compressor, and

Rr is a gas constant of the refrigerant.

32. An assembly as set forth in claim 31 including a pressure gauge for measuring the suction pressure of said compressor.

33. An assembly as set forth in claim 31 including a temperature sensor for sensing the suction temperature of said compressor.

34. A method of fabricating a heat exchanger comprising;

spacing a plurality of tubes apart from one another to define a plurality of refrigerant passages each having an exterior surface and extending axially from a lower end to an upper end,

securing a bottom header to the lower ends of the tubes in fluid communication with the refrigerant passages,

securing a top header to the upper ends of the tubes in fluid communication with the refrigerant passages,

placing a plurality of fins extending back and forth between a plurality of apexes between adjacent tubes,

securing the fins to the adjacent tubes, and

forming a plurality of gaps between the fins and the adjacent tubes for fluid communication axially along the exterior surface of the tubes.

35. A method as set forth in claim 34 further including forming a bridge to connect each of the apexes across a portion of the gaps to maintain the gaps and to interconnect each apex to the adjacent tube.

36. A method as set forth in claim 34 further including forming a wicking coating along an exterior surface of the tubes.

37. A method as set forth in claim 36 further including extending the wicking coating through the gaps between the apexes and the adjacent tube.

38. A method as set forth in claim 36 wherein the forming is further defined as forming a sintered metal coating along the tubes having a porosity approximately between 40% to 60%.

39. A method as set forth in claim 38 wherein the forming is further defined as forming the sintered metal coating having a porosity of approximately 50%.

40. A method as set forth in claim 36 wherein the forming is further defined as forming the wicking coating from a plurality of particles each having a diameter and layering the coating to a thickness of approximately between 3 to 5 times the diameter of the particles.

41. A method as set forth in claim 36 wherein the forming is further defined as forming a plurality of particles each having a diameter approximately between 70 microns to 90 microns.

42. A method as set forth in claim 36 further including securing a bottom water tank adjacent the lower ends of the tubes in fluid communication with the wicking coating.

43. A method as set forth in claim 36 further including securing a top water tank adjacent the upper ends of the tubes in fluid communication with the wicking coating.

44. A method as set forth in claim 43 further including securing a valve movable between an open position and a closed position at the upper ends of each of the tubes between the top water tank and the fins.

45. A method as set forth in claim 44 further including securing an actuator to the valves to selectively move the valves between the open and closed positions.

46. A method of operating a heat exchanger of the type including a plurality of tubes extending axially to define a plurality of refrigerant passages and a plurality of fins extending between adjacent tubes and extending back and forth between a plurality of apexes and a plurality of gaps defined between the fins and adjacent tubes for fluid communication axially along an exterior surface of the tubes, the method comprising;

flowing a refrigerant through the plurality of refrigerant passages,

extracting heat from the refrigerant,

transferring the extracted heat to a source of water to evaporate the water, and

flowing the source of water along an exterior surface of the tubes and through the plurality of gaps.

47. A method as set forth in claim 46 wherein the flowing is further defined as wicking water through the gaps.

48. A method as set forth in claim 47 further defined as regulating the flow of the source of water to a wicking coating.

49. A method as set forth in claim 48 wherein the regulating is according to the equation m. w = q. h fg wherein {dot over (q)} is the rate at which heat is extracted from the refrigerant and hfg is the latent heat of evaporation of the water.

50. A method as set forth in claim 49 further defined as determining the heat transfer rate {dot over (q)} according to the equation {dot over (q)}={dot over (m)}r[λgcpg(Tri−Ts)+hfgr(1−λg−λf)+λfcpf(Ts−Tro)] wherein;

{dot over (m)}r is the mass flow rate of the refrigerant flowing through the plurality of refrigerant passages,

Tri is the temperature of the refrigerant entering the plurality of refrigerant passages,

Tro is the temperature of the refrigerant exiting the plurality of refrigerant passages,

λg is the fraction of the refrigerant passages where the heat extracted from the refrigerant cools the refrigerant from a superheated vapor,

cpg is the specific heat of the refrigerant in a gaseous state,

hfgr is the latent heat of evaporation of the refrigerant flowing through the plurality of refrigerant passages,

λf is the fraction of the refrigerant passages where the heat extracted from the refrigerant cools the refrigerant to a subcooled liquid,

cpf is the specific heat of the refrigerant in a liquid state, and

Ts is the surface temperature of the tube.

51. A method as set forth in claim 50 further defined as obtaining the refrigerant mass flow rate {dot over (m)}r from a mass flow meter.

52. A method as set forth in claim 50 further defined as determining the mass flow rate {dot over (m)}r of the refrigerant according to the equation m. r = η v  V d  NP suc R r  T suc wherein;

ηv is a volumetric efficiency of the compressor,

Vd is a displacement rate of the compressor,

N is a rotational speed of the compressor,

Psuc is a suction pressure of the compressor,

Tsuc is a suction temperature of the compressor, and

Rr is a refrigerant gas constant of the refrigerant.

53. A method as set forth in claim 49 further defined as conveying air through the plurality of fins to carry the evaporated water away from the tubes.

54. A method as set forth in claim 53 further defined as determining a mass flow rate {dot over (m)}a of the air according to the equation m. a = m. w ω o - ω i wherein ωi is an incoming absolute humidity of the air entering the fins and ωo is an outgoing absolute humidity of the air exiting the fins.

55. A method as set forth in claim 54 further defined as providing a power input Hfan to a blower according to the equation H fan = 0.2414 g c  ( 1 η fan )  ( 1 d 19 / 4 )  ( μ a 1 / 4 ρ a )  m. a wherein;

gc is the universal proportionality constant,

ηfan is a blower efficiency,

d is a hydraulic diameter of an airflow passage of the blower,

μa is a dynamic viscosity of the air, and

ρa is a density of the air.