Refrigeration cycle apparatus

Abstract

In a refrigeration cycle apparatus in which carbon dioxide is used as refrigerant and refractory oil is used as lubricating oil in a compressor, it is an object of the present invention to reduce influence of adhesion of lubricating oil to the internal heat exchanger, and to enhance the heat exchanging efficiency of the internal heat exchanger. A refrigeration cycle apparatus in which a compressor 11 , a radiator 12 , an expansion valve 13 and an evaporator 14 are connected to one another through tubes, said refrigeration cycle apparatus comprises an internal heat exchanger 30 for exchanging heat between a high pressure refrigerant which flows out from said radiator 12 and low pressure refrigerant which flows out from said evaporator 14 , wherein carbon dioxide is used as the refrigerant, refractory oil is used as lubricating oil in said compressor 11 , said internal heat exchanger 30 comprises a first heat exchanger tube 31 through which the high pressure refrigerant in a supercritical region flows and a second heat exchanger tube 32 through which the low pressure refrigerant flows, said first heat exchanger tube 31 is disposed in said second heat exchanger tube 32.

1 . A refrigeration cycle apparatus in which a compressor, a radiator, an expansion valve and an evaporator are connected to one another through tubes, said refrigeration cycle apparatus comprises an internal heat exchanger for exchanging heat between a high pressure refrigerant which flows out from said radiator and a low pressure refrigerant which flows out from said evaporator, wherein carbon dioxide is used as the refrigerant, refractory oil is used as lubricating oil in said compressor, said internal heat exchanger comprises a first heat exchanger tube through which the high pressure refrigerant in a supercritical region flows and a second heat exchanger tube through which the low pressure refrigerant flows, and said first heat exchanger tube is disposed in said second heat exchanger tube.  
     
     
         2 . The refrigeration cycle apparatus according to  claim 1 , wherein the number of first heat exchanger tube is two or more.  
     
     
         3 . The refrigeration cycle apparatus according to  claim 1 , wherein a straight tube having a smooth outer surface is used as said first heat exchanger tube, and only said first heat exchanger tube is disposed in said second heat exchanger tube.  
     
     
         4 . The refrigeration cycle apparatus according to  claim 1 , wherein said internal heat exchanger is provided at its opposite ends with connection tubes each having predetermined length, one end side opening of each of said connection tubes is formed smaller than the other end side opening by diameter-increasing machining or diameter-reducing machining, said second heat exchanger tube is connected to said one end side opening, said first heat exchanger tube is connected to said other end side opening, and a tube through which the low pressure refrigerant flows is connected to said other end side opening.  
     
     
         5 . The refrigeration cycle apparatus according to  claim 1 , wherein a flow path cross-sectional area of said low pressure refrigerant formed by said first heat exchanger tube and said second heat exchanger tube is equal to or greater than an inner diameter cross-sectional area of an outlet-side tube of said evaporator.