SYSTEMS AND METHODS FOR IMPROVING THE BOILING HEAT TRANSFER OF A HEAT TRANSFER COIL

Abstract

Systems and methods for improved heating, ventilation, and air conditioning (HVAC) systems are provided with heat exchanger coils with improved boiling heat transfer. An etching solution may be applied to an inner surface of a heat exchanger coil to etch the heat exchanger coil to increase the surface area and the number of nucleate sites. The heat exchanger coil may be connected to a pump and the etching solution may be introduced and pumped through the heat exchanger coil for a set duration and at a set flow rate. A mass flow meter may be connected between the pump and one end of the heat exchanger coil to measure the flow rate of the etching solution. By adjusting the concentration of acid in the etching solution, the flow rate, and the exposure time, the degree to which the inner surface of the heat exchanger coil is eroded may be adjusted.

Description

TECHNICAL FIELD

The present disclosure is generally in the field of heating, ventilation, and air conditioning (HVAC) systems. For example, systems and methods are provided herein for improving boiling heat transfer in HVAC systems.

BACKGROUND

Systems for heating and cooling residential and commercial structures, including heating, ventilation, and air conditioning (HVAC) systems, have been developed and used to moderate temperature in such structures and settings. Many HVAC systems include heat exchangers with heat exchanger coils that receive a fluid such as a refrigerant that may exchange thermal energy with the surrounding environment. A heat pump or air conditioner may include a heat exchanger inside the structure and another heat exchanger outside the structure and the refrigerant and the heat exchangers may cause an interior of the structure to heat or cool as desired.

To increase the amount of thermal energy transferred, a refrigerant may be selected having a large heat transfer coefficient to optimize efficiency of the HVAC system. For example, refrigerants such as R-22 (Freon) and R-410A (Puron) may be used. Such refrigerants may achieve a high heat transfer coefficient during evaporation. The heat exchanger coil is often designed to boil the refrigerant to maximize heat transfer.

The heat exchanger coils may be part of a larger heat exchanger system such as a round tube plate heat exchanger with fins for increasing surface area and thus heat transfer. However, the efficiency of the heat exchanger is often limited by the boiling heat transfer at the heat exchanger coil. For example, nucleate boiling sites along the heat exchanger coil may be suboptimal as the inner diameter of the heat exchanger coil is typically smooth, often due to expansion techniques (e.g., bullet expansion).

Accordingly, there is a need for improved methods and systems for improving the boiling heat transfer of a heat transfer coil of an HCAC system to increase efficiency of an HVAC system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an etching system including a pump, a mass flow meter, a heat exchanger coil, and an etching solution, in accordance with one or more exemplary embodiments of the disclosure.

FIG. 2 is a cross-sectional view of a heat exchanger coil before, during, and after etching, in accordance with one or more exemplary embodiments of the disclosure.

FIG. 3 is a perspective view of an inner surface of a heat exchanger coil after etching, in accordance with one or more exemplary embodiments of the disclosure.

FIG. 4 illustrates cross-sectional views of the heat exchanger coils including nucleate boiling sites before etching and after etching, in accordance with one or more exemplary embodiments of the disclosure.

FIG. 5 is process flow for etching an inner diameter of a heat exchanger coil using an etching system including a pump and a mass flow meter, in accordance with one or more exemplary embodiments of the disclosure.

DETAILED DESCRIPTION

Improved heating, ventilation, and air conditioning (HVAC) systems including heat exchanger coils with increased surface area and nucleate boiling sites for increased heat transfer, and etching systems for making the same have been developed. The improved heat exchanger coils may be treated with or may be exposed to an etching solution (e.g., liquid, compound, agent, etc.) designed to remove and/or erode a portion of an inner surface of the heat exchanger coil leaving behind an uneven and/or grooved inner surface having an increased surface. With the increased surface area and groves and/or uneven surfaces of the inner surface of the heat exchanger coil, additional nucleate boiling sites may be created as compared to the inner surface of the heat exchanger coil.

To apply the etching solution to the inner surface of the heat exchanger coil, the heat exchanger coil may be connected to a pump via suitable tubing to form an etching system and the etching solution may be introduced into the system and pumped through the heat exchanger coil for a set duration and at a set flow rate. A mass flow meter may be connected between the pump and one end of the heat exchanger coil to measure the flow rate of the etching solution. By adjusting the concentration of acid in the etching solution, the flow rate, and the exposure time, the degree to which the inner surface of the heat exchanger coil is etched, resulting in an etched surface, may be adjusted.

Referring now to FIG. 1, a schematic of an etching system including a pump, a mass flow meter, a heat exchanger coil, and an etching solution is illustrated, in accordance with one or more exemplary embodiments of the disclosure. Heat exchanger coil 102 may be any heat exchanger coil used with a heating, ventilation, and air conditioning (HVAC) system such as a heat pump, air conditioner, and/or the like. For example, heat exchanger coil may be a heat exchanger coil in a condenser and/or evaporator of a heat pump or air conditioning system.

Heat exchanger coil 102 may be metallic, for example. For example, heat exchanger coil may be made of aluminum or an aluminum alloy. In one example, the heat exchanger coil may be a tubular structure having a circular cross-section with a diameter in a range between 5 mm to 10 mm, such as about 6 mm to 9 mm, about 7 mm to 8 mm, about 7.25 mm to 7.75 mm, etc. In one example, the diameter of heat exchanger coil may be 7 mm. The heat exchanger coil may have a wall thickness of about 0.25 mm to 2 mm, such as about 0.5 mm to 1.75 mm, about 0.75 mm to 1.5 mm, about 1 mm to 1.25 mm, etc.

Heat exchanger coil 102 may initially have a smaller diameter and the inner and/or outer diameters of the heat exchanger coil may be expanded during manufacturing and/or assembly using a suitable expansion techniques such as by using a tube expansion bullet. It is understood that other suitable expansion techniques may be used such as pressure expansion. In one example, the heat exchanger coil may be expanded prior to applying the etching solution.

Heat exchanger coil 102 may be formed into round tube plate heat exchanger 150. Round tube plate heat exchanger 150 may include heat exchanger coil 152 which may form several hair pins about heat exchanger fins 154, through which heat exchanger coil 152 may pierce. Heat exchanger coil 152 may be the same as or similar to heat exchanger coil 102 after the etching solution has been applied. Heat exchanger coil 152 may be formed into round tube plate heat exchanger 150 either before or after the etching solution has been applied to the interior surface of heat exchanger coil 152.

As shown in FIG. 1, heat exchanger coil 102 may be connected at one end to pump 106 via tubing 105, which may be any suitable tubing designed with material resistant to erosion by the etching solution such as plastic. Pump 106 may be any suitable fluid pump, such as a fluid pump with variable speeds to produce variable flow rates of the fluid being pumped. Container 104 may also be connected to tubing 105 and may contain etching solution 104 to be circulated through etching solution system 100. Pump 106 may, for example, be a positive-displacement pump, a centrifugal pump, an axial flow pump, or any other suitable pump.

Etching solution 107 may be any type of acidic solution (e.g., fluid, solution, compound, etc.) for etching the interior surface of heating coil 102. For example, etching solution 107 may be or include hydrochloric acid (HCl) with a molarity of the HCl of the etching solution in a range between 1 to 8 molars, such as about 1.5 to 7 molars, about 3 to 6.5 molars, about 4 to 5 molars, etc. It is understood that the etching solution may be any type of etching solution other than HCl suitable for etching the internal surface of heat exchanger coil 102 (e.g., nitric acid, phosphoric acid, etc.).

Pump 106 optionally may be connected to mass flow meter 150 which may be connected to one end of pump 106 and connected to heat exchanger coil 102 on another end (e.g., via tubing 105), as shown in FIG. 5. Mass flow meter 150 may be any suitable mass flow meter for measuring the flow rate of fluid through tubing 105 and ultimately flowing through heat exchanger coil 102. In the exemplary system shown in FIG. 1, heat exchanger coil 102 may connect to pump 106 at one end, pump 106 may connect to mass flow meter 150 at another end, and mass flow meter 150 may connect to a different end of heat exchanger coil 102.

As shown in FIG. 1, heat exchanger coil 102 may be in fluid communication with pump 106, pump 106 may be in fluid communication with mass flow meter 150, mass flow meter may be in fluid communication heat exchanger coil 102, tubing 105 may extend between the foregoing components, and etching solution 107 may flow through etching system 100. It is understood that container 104 and/or mass flow meter 150 may be optional.

Pump 106 and/or mass flow meter 150 may be in wired or wireless communication with optional computing device 140, which may be any suitable computing device having memory and a processor. Computing device 140 may cause pump 106 to pump fluid in etching system 100 at certain flow rates and/or for a certain period of time, thereby adjusting the exposure of the etching solution to the inner surface of heat exchanger coil 102. Mass flow meter 150 may further receive flow rate data from mass flow meter 150 which may indicate the flow rate in system 100.

While FIG. 1 illustrates etching system 100 with etching fluid 107, it is understood that any other fluid may be introduced into etching system 100. For example, container 104 may introduce deionized water to flush the heat exchanger coils, acetone, isopropyl alcohol, and/or any other fluids. It is understood that container 104 may be removed from etching system 100 and any such fluids may be otherwise introduced into etching system 100.

While FIG. 1 depicts pump 106 connected to an upper end of heat exchanger coil and mass flow meter 150 connected to a lower end of heat exchanger coil 102, it is understood that mass flow meter may be connected to an upper end of heat exchanger coil 102 and pump 106 may be connected to a lower end of heat exchanger coil 102. It is further understood that heat exchanger coil 102 may be positioned vertically, horizontally, or at an angle.

Referring now to FIG. 2, a cross-sectional view of a heat exchanger coil before, during, and after etching is illustrated, in accordance with one or more exemplary embodiments of the disclosure. Heat exchanger coil 202 may be the same as or similar to heat exchanger coil 102 and may be used with an etching system to apply an etching solution to etch inner surface 204 of heat exchange coil 202 using an etching solution, which may be the same as or similar to etching solution 107 of FIG. 1. As shown in FIG. 2, prior to etching, inner surface 204 of heat exchanger coil 202 may be generally smooth.

Using an etching system similar to etching system 100 of FIG. 1, etching solution 206 may be applied to inner surface 204 at a set flow rate for a set duration. For example, the flow rate may be the same flow rate provided in above with respect to FIG. 1 and the exposure time may be between 1 second to 30 minutes, such as about 5 seconds to 20 minutes, about 5 seconds to 10 minutes, about 10 seconds to 30 seconds etc. In one example, the exposure time for which the etching solution is circulated through the heat exchanger coil may be between 5 seconds and 30 seconds.

After applying etching solution 206 to inner surface 204 of heat exchanger coil 202, etched heat exchanger coil 208 may be formed with inner surface 210 that is an etched version of inner surface 204. As shown in FIG. 2, inner surface 208 may have grooves and uneven surfaces resulting in a surface area of inner surface 208 of heat exchanger 210 that is greater than the surface area of inner surface 204 of heat exchanger coil 202. It is understood that the longer the exposure of the etching solution to inner surface 204 and/or the greater the concentration of acid in the etching solution, the greater the amount of etching and/or erosion of inner surface 204. As shown in FIG. 2, inner surface 208 may have a diameter that is larger than the diameter of inner surface 204.

Referring now to FIG. 3, a perspective view of an inner surface of a heat exchanger coil is illustrated, in accordance with one or more exemplary embodiments of the disclosure. Inner surface 302 may be the same as or similar to inner surface 208 of FIG. 2. Inner surface 302 may include portions that were dissolved or otherwise etched away by the etching solution to form nooks, valleys, channels, divots, pits, and other non-planar surfaces (e.g., pit 304), thereby forming peaks, mounds, protrusions, and the like (e.g., peak 306). The uneven surface of inner surface 302 may have a greater surface area than the generally smooth surface of the inner surface prior to etching.

Inner surface 302 may include nooks, valleys, channels, divots, and/or pits that may have a width in a range between 5 μm to 200 μm, such as about 50 μm to 150 μm, about 100 μm to 120 μm, etc. Inner surface 302 may have a width in a length in a range between 10 μm to 500 μm, such as about 50 μm to 350 μm, about 100 μm to 200 μm, etc. Inner surface 302 may have a depth measured from the initial inner surface prior to etching in a range between 1 μm to 100 μm, such as about 5 μm to 75 μm, about 10 μm to 50 μm, about 20 μm to 40 μm, etc.

Referring now to FIG. 4, cross-sectional views of the heat exchanger coils including nucleate boiling sites before etching and after etching are illustrated, in accordance with one or more exemplary embodiments of the disclosure. Heat exchange coil 402 may be the same as or similar to heat exchange coil 202 of FIG. 2 and heat exchange coil 404 may be the same as or similar to heat exchange coil 210 of FIG. 2.

As shown in FIG. 4, heat exchange coil 402 may not have been etched yet and may include inner surface 402, shown in zoomed in view 405, which may have a relatively smooth surface. As shown in zoomed in view 405, inner surface 406 with a generally smooth surface may only have one nucleate boiling site. For example, the number of nucleate boiling sites may be reduced due to surface tension with the smooth inner surface.

As shown in FIG. 4, heat exchange coil 404 may have been etched resulting in an inner surface 404 that is etched. For example, inner surface 404 may be the same as or similar to inner surface 208 of FIG. 2, which may have multiple nooks, pits, divots, valleys, channels, peaks, mounds, protrusions and the like. As shown in zoomed in view 415, inner surface 404 may include more nucleate boiling sites than inner surface 406. For example, inner surface 404 may include nucleate boiling site 412 releasing vapor 418, nucleate boiling site 414 releasing vapor 420, and nucleate boiling site 416 releasing vapor 422.

As the etched inner surface of the heat exchanger coil increases the surface area as well as the number of nucleate boiling sites the boiling heat transfer for the heat exchanger coil is improved without a significant pressure drop or decrease in pressure. With the improved boiling heat transfer an HVAC system incorporating etches heat exchanger coils may experience improved heat transfer efficiency which may result in improved energy efficiency of the HVAC system. For example, the heat exchanger coil with additional nucleate boiling sites due to etching may result in a heat transfer efficiency increase (e.g., an increase in HVAC system efficiency) of the heat exchanger coil of ten percent or least ten percent compared to the heat exchanger coil with the amount of nucleate boiling sites prior to etching. In one example, a forty percent or more increase in efficiency may result for refrigerant convective boiling heat transfer.

Referring now to FIG. 5, a process flow for etching an inner diameter of a heat exchanger coil using an etching system including a pump and a mass flow meter is illustrated, in accordance with one or more exemplary embodiments of the disclosure. Some of the blocks of process flow 500 may be optional and may be performed in a different order.

At block 502, a heat exchanger coil may be provided having an inner surface and a certain amount of nucleate boiling sites. The heat exchanger coil may be the same as or similar to heat exchanger coil 102 of FIG. 1. The heat exchanger coil may be a heat exchanger coil that may be part of a round tube plate heat exchanger or may be any other suitable heat exchanger coil suitable for HVAC systems.

At block 504, heat exchanger coil may be expanded to expand an inner diameter and optionally an outer diameter of the heat exchanger coil. For example, a tube expansion bullet may be used. It is understood that other suitable expansion techniques may be used such as pressure expansion and/or that such expansion may occur at later time (e.g., after etching the inner surface of the heat exchanger coil.

At block 506, the heat exchanger coil may be connected to the etching system which may include a pump and a mass flow meter. For example, the etching system may be the same as or similar to etching system 100 of FIG. 1. At optional block 508, the inner surface of the heat exchanger coil may be prepared for etching by applying first acetone to the inner surface of the heat exchanger coil (e.g., using the etching system), then applying isopropyl alcohol (IPA) (using the etching system), and finally deionized water (e.g., using the etching system). At optional block 510, deionized water may again be applied to the heat exchanger or may be applied for a first time. Alternatively, block 510 may be performed before block 508.

At block 512, an etching solution may be prepared and/or provided. The etching solution may be the same as or similar to etching solution 107 of FIG. 1 and/or may be any other suitable etching solution for etching an interior surface of the heat exchanger coil. In one example, a solution of hydrochloric acid (HCl) may be prepared by mixing HCl acid and deionized water. At block 514, the etching solution may be applied to the heat exchanger coil at a set flow rate (e.g., flow rate of 0.02 to 0.3 gallons per minute, flow rate of 0.2 to 0.3 gallons per minute etc.) for a set period of time (e.g., 5 seconds to 10 minutes, 5 seconds to 10 seconds, etc.).

At optional block 516, deionized water may be applied to the inner surface of the heat exchanger coil (e.g., using the etching system). At optional block 518, the inner surface of the heat exchanger coil may be prepared for etching by applying first acetone to the inner surface of the heat exchanger coil (e.g., using the etching system), then applying isopropyl alcohol (IPA) (using the etching system), and finally deionized water (e.g., using the etching system).

At optional block 520, an inspection may be performed on the interior surface of the heat exchanger coil to confirm that sufficient and/or proper etching occurred. In one example, a microscope or similar imaging system may be used. At block 522 the heat exchanger coil may be formed into the round tube plate heat exchanger. It is understood that this step may be performed before etching and/or before expansion of the heat exchanger coil.

Although embodiments have been described in language specific to structural features and/or methodological acts, it is to be understood that the disclosure is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as illustrative forms of implementing the embodiments. Conditional language, such as, among others, “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments could include, while other embodiments do not include, certain features, elements, and/or steps. Thus, such conditional language is not generally intended to imply that features, elements, and/or steps are in any way required for one or more embodiments.

The foregoing description of illustrative embodiments has been presented for purposes of illustration and of description. It is not intended to be exhaustive or limiting with respect to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosed embodiments. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims

1. A method for improving boiling heat transfer in a heat exchanger coil of a heating, ventilation, and air conditioning (HVAC) system, the method comprising: providing the heat exchanger coil, the heat exchanger coil having an outer diameter and an inner diameter and configured to contain and exchange thermal energy with a refrigerant fluid, the inner diameter having a first surface area and a first amount of nucleate boiling sites;providing an etching solution; andapplying the etching solution to the inner diameter of the heat exchanger coil,wherein, after applying the etching solution, the inner diameter of the heat exchanger coil has a second surface area larger than the first surface area and a second amount of nucleate boiling sites larger than the first amount of nucleate boiling sites.

2. The method of claim 1, further comprising connecting the heat exchanger coil to a pump and a flow meter, the pump adapted to circulate the etching solution through the heat exchanger coil at the flow rate, and the flow meter adapted to measure the flow rate, wherein the etching solution is applied to the inner diameter of the heat exchanger coil by pumping the etching solution into the heat exchanger coil using the pump.

3. The method of claim 1, wherein the etching solution comprises hydrochloric acid (HCl) and a molarity of the HCl of the etching solution is 1.5 to 6 molars, and wherein the etching solution is applied for a set period of time of 5 seconds to 10 minutes at a flow rate of 0.02 to 0.3 gallons per minute.

4. The method of claim 1, further comprising expanding, before applying the etching solution to the inner diameter of the heat exchanger coil, the inner diameter and the outer diameter of the heat exchanger coil.

5. The method of claim 1, further comprising, before applying the etching solution to the inner diameter of the heat exchanger coil: applying a first fluid comprising acetone to the inner diameter of the heat exchanger coil; andapplying, after applying the first fluid, a second fluid comprising Isopropyl Alcohol (ISA) to the inner diameter of the heat exchanger coil.

6. The method of claim 5, further comprising applying, after applying the second fluid, deionized water to the inner diameter of the heat exchanger coil.

7. The method of claim 1, further comprising, after applying the etching solution to the inner diameter of the heat exchanger: applying a first fluid comprising acetone to the inner diameter of the heat exchanger coil; andapplying, after applying the first fluid, a second fluid comprising Isopropyl Alcohol (ISA) to the inner diameter of the heat exchanger coil.

8. The method of claim 7, further comprising applying, after applying the second fluid, deionized water to the inner diameter of the heat exchanger coil.

9. The method of claim 1, wherein the etching solution is applied to the inner diameter of the heat exchanger coil at a flow rate between 0.2 and 0.3 gallons per minute and the etching solution has a HCl molarity of 5 to 6 molars.

10. The method of claim 9, wherein the etching solution is applied to the inner diameter of the heat exchanger for a set period of time of 5 seconds to 30 seconds.

11. The method of claim 1, wherein the heat exchanger coil is made of aluminum or aluminum alloy.

12. The method of claim 1, further comprising forming a round tube plate heat exchanger using the heat exchanger coil.

13. A system for improving the heat transfer of a heat exchanger coil of a heating, ventilation, and air conditioning (HVAC) system, the heat exchanger coil comprising an outer diameter and an inner diameter configured to contain a refrigerant fluid and to exchange thermal energy with the refrigerant fluid, the inner diameter having a first surface area and a first amount of nucleate boiling sites, the system comprising: an etching solution; anda pump in fluid communication with the heat exchanger coil and configured to pump the etching solution through the heat exchanger coil,wherein pumping the etching solution through the heat exchanger coil using the pump results in the inner diameter of the heat exchanger having a second surface area larger than the first surface area and a second amount of nucleate boiling sites larger than the first amount of nucleate boiling sites.

14. The system of claim 13, wherein the etching solution is applied to the inner diameter of the heat exchanger coil at a flow rate between 0.2 and 0.3 gallons per minute and the etching solution has a HCl molarity of 5 to 6 molars.

15. The system of claim 13, further comprising a flow meter in fluid communication with the pump and the heat exchanger coil and configured to determine the flow rate of the etching solution.

16. The system of claim 13, wherein the inner diameter and the outer diameter of the heat exchanger coil is expanded before the etching solution is pumped through the heat exchanger coil, and wherein the second amount of nucleate boiling sites corresponds to a heat transfer efficiency increase of the heat exchanger coil of at least ten percent compared to the heat exchanger coil with the first amount of nucleate boiling sites.

17. The system of claim 13, wherein the pump is further configured to, before pumping the etching solution through the heat exchanger coil, pump a first fluid comprising acetone through the heat exchanger coil, pump a second fluid comprising Isopropyl Alcohol (ISA) through the heat exchanger coil after pumping the first fluid, and pump deionized water through the heat exchanger coil after pumping the second fluid.

18. The system of claim 13, wherein the pump is further configured to, after pumping the etching solution through the heat exchanger coil, pump a first fluid comprising acetone through the heat exchanger coil, pump a second fluid comprising Isopropyl Alcohol (ISA) through the heat exchanger coil after pumping the first fluid, and pump deionized water through the heat exchanger coil after pumping the second fluid.

19. The system of claim 13, wherein the etching solution is hydrochloric acid (HCl) having a molarity of HCl of 5 to 6 molars, wherein the pump is configured to pump the etching solution through the heat exchanger coil at a flow rate between of 0.2 to 0.3 gallons per minute, and the set period of time is 5 seconds to 30 seconds.

20. A heat exchanger coil of a heating, ventilation, and air conditioning (HVAC) system, the heat exchanger coil comprising: a first end configured to couple to a primary end of the HVAC system, the HVAC system comprising a compressor, an expansion valve, tubing, and a second heat exchanger;a second end configured to couple to a secondary end of the HVAC system; anda tubular body extending between the first end and the second end and having an inner surface and an outer surface, the tubular body configured to contain and exchange thermal energy with a refrigerant fluid,wherein the interior surface of the tubular body comprises an etched surface having a plurality of peaks and a plurality of valleys.