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.

We claim: 
     
         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; and   applying 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; and   applying, 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; and   applying, 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; and   a 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; and   a 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.