Experimental Validation for the dp/dt Assumption of Heat Exchangers in Vapor Compression Refrigeration Cycles

Calculation of time derivatives of refrigerant pressures is important for dynamic simulation of heat exchangers in vapor compression cycles, i.e., typically the condenser and evaporator. This technical brief presents an experimental study on the pressure transient for the condenser and evaporator of a screw chiller with R134a, along with the analysis for the associated time derivatives. The experimental results from eight test cases suggest that the time derivatives of the condenser and evaporator pressures at their inlet are extremely close to those at the respective outlets. This observation can thus justify the key assumption of equal time derivatives of pressures in the dynamic modeling of heat exchangers, which in consequence improves the numerical efficiency and/or convergence, especially for large and complex thermal-fluid systems.