Charge Tolerant Microchannel Heat Exchanger

Abstract

A microchannel heat exchanger has an upper portion connected in fluid communication with an undivided header, and a lower portion connected in fluid communication with the undivided header at a location that is vertically lower on the undivided header than the upper portion. Under normal steady state operating conditions, the heat exchanger may condense a first amount of liquid phase refrigerant, wherein the first volume of liquid phase refrigerant substantially fills the lower portion, and wherein substantially none of the refrigerant is condensed into liquid phase refrigerant in the lower portion, and under abnormal steady state operating conditions, the heat exchanger may condense a second amount of liquid phase refrigerant in the upper portion, wherein an additional amount of the second amount of liquid phase refrigerant in excess of the first amount of liquid phase refrigerant is accommodated in the undivided header as opposed to further filling the lower portion.

What is claimed is: 
     
         1 . A microchannel heat exchanger, comprising:
 a first portion connected in fluid communication with an undivided header; and   a second portion connected in fluid communication with the undivided header at a location that is vertically lower on the undivided header than the first portion;   wherein ratio of the first portion to the second portion is greater than 2:1.   
     
     
         2 . The microchannel heat exchanger of  claim 1 ,
 wherein the first portion comprises a first set of microchannel tubes and the second portion comprises a second set of microchannel tubes; and   wherein the ratio of the first set of microchannel tubes to the second set of microchannel tubes is greater than 2:1.   
     
     
         3 . The microchannel heat exchanger of  claim 1 ,
 wherein the first portion comprises a first volume of microchannels and the second portion comprises a second volume of microchannels; and   wherein the ratio of the first volume of microchannels to the second volume of microchannels is greater than 2:1.   
     
     
         4 . The microchannel heat exchanger of  claim 1 ,
 wherein the first portion comprises a first frontal area and the second portion comprises a second frontal area; and   wherein the ratio of the first frontal area to the second frontal area is greater than 2:1.   
     
     
         5 . The microchannel heat exchanger of  claim 1 ,
 wherein the ratio of the first portion to the second portion is at least one of 2.5:1 to 15:1, 3:1 to 15:1, 4:1 to 14:1, 5:1 to 13:1, 7:1 to 12:1, 8:1 to 12:1, 9:1 to 11:1, and 9.5:1 to 10.5:1.   
     
     
         6 . The microchannel heat exchanger of  claim 1 ,
 wherein the ratio of the first portion to the second portion is about 10:1.   
     
     
         7 . The microchannel heat exchanger of  claim 6 ,
 wherein the first portion comprises a first set of microchannel tubes and the second portion comprises a second set of microchannel tubes; and   wherein each of the microchannel tubes of the first set and each of the microchannel tubes of the second set comprise a substantially similar number of microchannels.   
     
     
         8 . The microchannel heat exchanger of  claim 7 ,
 wherein each of the microchannel tubes of the first set and each of the microchannel tubes of the second set comprise substantially similar lengths.   
     
     
         9 . The microchannel heat exchanger of  claim 8 ,
 wherein each of the microchannel tubes of the first set and each of the microchannel tubes of the second set comprise substantially similar microchannel volumes.   
     
     
         10 . A method of operating a microchannel heat exchanger, comprising:
 providing a microchannel heat exchanger in an HVAC system, the microchannel heat exchanger comprising an upper portion connected in fluid communication with an undivided header, and a lower portion connected in fluid communication with the undivided header at a location that is vertically lower on the undivided header than the upper portion, wherein the ratio of the upper portion to the lower portion is greater than 2:1;   introducing a refrigerant into the upper portion;   under normal steady state operating conditions, condensing a first amount of liquid phase refrigerant in the upper portion, wherein the first volume of liquid phase refrigerant substantially fills the lower portion, and wherein substantially none of the refrigerant is condensed into liquid phase refrigerant in the lower portion; and   under abnormal steady state operating conditions, condensing a second amount of liquid phase refrigerant in the upper portion, wherein an additional amount of the second amount of liquid phase refrigerant in excess of the first amount of liquid phase refrigerant is accommodated in the undivided header as opposed to further filling the lower portion.   
     
     
         11 . The method of  claim 10 ,
 wherein the first portion comprises a first set of microchannel tubes and the second portion comprises a second set of microchannel tubes; and   wherein the ratio of the first set of microchannel tubes to the second set of microchannel tubes is greater than 2:1.   
     
     
         12 . The method of  claim 10 ,
 wherein the first portion comprises a first volume of microchannels and the second portion comprises a second volume of microchannels; and   wherein the ratio of the first volume of microchannels to the second volume of microchannels is greater than 2:1.   
     
     
         13 . The method of  claim 10 ,
 wherein the first portion comprises a first frontal area and the second portion comprises a second frontal area; and   wherein the ratio of the first frontal area to the second frontal area is greater than 2:1.   
     
     
         14 . The method of  claim 10 ,
 wherein the ratio of the first portion to the second portion is at least one of 2.5:1 to 15:1, 3:1 to 15:1, 4:1 to 14:1, 5:1 to 13:1, 7:1 to 12:1, 8:1 to 12:1, 9:1 to 11:1, and 9.5:1 to 10.5:1.   
     
     
         15 . The method of  claim 10 ,
 wherein the ratio of the first portion to the second portion is about 10:1.   
     
     
         16 . The method of  claim 15 ,
 wherein the first portion comprises a first set of microchannel tubes and the second portion comprises a second set of microchannel tubes; and   wherein each of the microchannel tubes of the first set and each of the microchannel tubes of the second set comprise a substantially similar number of microchannels.   
     
     
         17 . The method of  claim 16 ,
 wherein each of the microchannel tubes of the first set and each of the microchannel tubes of the second set comprise substantially similar lengths.   
     
     
         18 . The method of  claim 17 ,
 wherein each of the microchannel tubes of the first set and each of the microchannel tubes of the second set comprise substantially similar microchannel volumes.   
     
     
         19 . The method of  claim 18 ,
 wherein abnormal operating conditions comprise at least one of (1) the HVAC system is overcharged with too much refrigerant and is operating under normal ambient temperature conditions, (2) the HVAC system is properly charged but is operating under very high ambient temperature conditions, and (3) the HVAC system is both overcharged and is operating under very high ambient temperature conditions.