Fluid circuit and refrigeration cycle apparatus using the same

Abstract

Disclosed herein is a fluid circuit in which a compressible fluid and an incompressible fluid flow in a mixed state including an upstream side space and a downstream side space in which internal pressures repeatedly alternate between high pressure and low pressure, and a pump unit having an inlet connected to the upstream side space and an outlet connected to the downstream side space. The pump unit has two check valves arranged in series in a direction in which fluid movement is allowed from the upstream side space to the downstream side space, and a middle part, having a predetermined capacity, formed between the check valves.

1 . A fluid circuit in which a compressible fluid and an incompressible fluid flow in a mixed state, the fluid circuit comprising:
 an upstream side space and a downstream side space in which internal pressures repeatedly alternate between high pressure and low pressure; and   a pump unit having an inlet connected to the upstream side space and an outlet connected to the downstream side space, the pump unit including two check valves arranged in series in a direction in which fluid movement is allowed from the upstream side space to the downstream side space, and a middle part, having a predetermined capacity, formed between the check valves.   
     
     
         2 . The fluid circuit according to  claim 1 , wherein the middle part has a capacity (Vs) set to be within a range as represented by the following inequality. 
       
         
           
             
               { 
               
                 
                   
                     
                       
                         
                           V 
                           s 
                         
                         ≥ 
                         
                           
                             ( 
                             
                               
                                 N 
                                 a 
                               
                               × 
                               
                                 T 
                                 c 
                               
                             
                             ) 
                           
                           / 
                           
                             ( 
                             
                               1 
                               - 
                               
                                 
                                   ρ 
                                   l 
                                 
                                 / 
                                 
                                   ρ 
                                   h 
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                         
                           V 
                           s 
                         
                         ≤ 
                         
                           
                             ( 
                             
                               
                                 ∫ 
                                 0 
                                 
                                   T 
                                   l 
                                 
                               
                                
                               
                                 
                                   C 
                                   l 
                                 
                                 × 
                                 
                                   p 
                                 
                                  
                                 
                                     
                                 
                                  
                                 
                                    
                                   p 
                                 
                               
                             
                             ) 
                           
                           / 
                           
                             ( 
                             
                               1 
                               - 
                               
                                 
                                   ρ 
                                   l 
                                 
                                 / 
                                 
                                   ρ 
                                   h 
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
                   
               
             
           
         
         where, ρh is a density of the compressible fluid at high pressure, ρl is a density of the compressible fluid at low pressure, Tc is a cycle in which change between high pressure and low pressure occurs, Na is a volume flow rate of the incompressible fluid, p is pressure loss, Cl is an integer, Tl is time until pressure of the pump unit equals to pressure of the upstream side space. 
       
     
     
         3 . The fluid circuit according to  claim 1 , wherein the middle part of the pump unit is provided at a bottom thereof with a fluid outlet hole. 
     
     
         4 . A refrigeration cycle apparatus, comprising:
 a plurality of compressors; and   a uniform lubricant distribution mechanism to perform uniform lubricant distribution between the respective compressors, the uniform lubricant distribution mechanism having at least one fluid circuit including an upstream side space and a downstream side space in which internal pressures repeatedly alternate between high pressure and low pressure, and a pump unit having an inlet connected to the upstream side space and an outlet connected to the downstream side space, the pump unit including two check valves arranged in series in a direction in which fluid movement is allowed from the upstream side space to the downstream side space, and a middle part, having a predetermined capacity, formed between the check valves.   
     
     
         5 . The refrigeration cycle apparatus according to  claim 4 , wherein
 the uniform lubricant distribution mechanism has a uniform lubricant distribution pipe to interconnect lubricant storage parts of the respective compressors to store a lubricant, the at least one fluid circuit being formed at the uniform lubricant distribution pipe, and   at least one of the compressors comprises a variable capacity type compressor in which internal pressures of the upstream side space and the downstream side space are changed between high pressure and low pressure based on a change in a discharge capacity of the compressor.   
     
     
         6 . The refrigeration cycle apparatus according to  claim 4 , wherein
 the compressors are variable capacity low-pressure shell type compressors,   the uniform lubricant distribution mechanism has a uniform lubricant distribution pipe connected between each of the lubricant storage parts of the compressors and each of suction pipes connected to the compressors to suction a lubricant, and   the at least one fluid circuit is mounted on the uniform lubricant distribution pipe.   
     
     
         7 . The refrigeration cycle apparatus according to  claim 6 , wherein an upstream side of the fluid circuit is connected to a lubricant outlet port of the compressor, and a downstream side of the fluid circuit is connected to the suction pipe extending to the compressor. 
     
     
         8 . The refrigeration cycle apparatus according to  claim 4 , wherein
 the compressors are variable capacity high-pressure shell type compressors,   the uniform lubricant distribution mechanism has a uniform lubricant distribution pipe connected between each of the lubricant storage parts of the compressors and each of discharge pipes connected to the compressors to discharge a lubricant, and   the at least one fluid circuit is mounted on the uniform lubricant distribution pipe.   
     
     
         9 . The refrigeration cycle apparatus according to  claim 8 , wherein an upstream side of the fluid circuit is connected to a lubricant output port of the compressor, and a downstream side of the fluid circuit is connected to the discharge pipe extending from the compressor. 
     
     
         10 . The refrigeration cycle apparatus according to  claim 4 , wherein
 at least one of the plurality of compressors is an inverter type compressor, and   the uniform lubricant distribution mechanism has a discharge pipe connected to the inverter type compressor to discharge a lubricant, a suction pipe to suction the lubricant, a bypass pipe connected between the discharge pipe and the suction pipe, and a valve mounted on the bypass pipe to allow refrigerant gas from the discharge pipe to be bypassed to the suction pipe to perform a pseudo-unload operation.   
     
     
         11 . The refrigeration cycle apparatus according to  claim 4 , further comprising discharge pipes to discharge a lubricant from the plurality of compressors, a lubricant separator connected to the discharge pipes to separate a lubricant from a refrigerant discharged from the plurality of compressors, and a lubricant return pipe mounted between the lubricant separator and a suction pipe to suction lubricant of one of the compressors to return the lubricant to the one of the compressors. 
     
     
         12 . The refrigeration cycle apparatus according to  claim 4 , wherein
 each of the plurality of compressors includes a lubricant storage part,   the uniform lubricant distribution mechanism has a plurality of uniform lubricant distribution pipes connecting each of the lubricant storage parts of the compressors to each other such that the compressors form a circular ring, and   fluid circuits are mounted between respective compressors to convey surplus lubricant between the compressors.