Study on a wire-type Joule Thomson microcooler with a concentric heat exchanger

This study examines the performance of a wire-type Joule Thomson microcooler utilizing a flexible concentric counterflow heat exchanger. Three gases: C2H4, CO2 and N2 were used separately for trials conducted at inlet pressures ranging from 0.5 MPa to 5 MPa with C2H4 having the best performance. During unloaded tests at an inlet pressure of 2.0 MPa, C2H4 obtained a minimum temperature of 225 K while CO2 obtained a minimum temperature of 232 K. Using CO2 the microcooler was able to maintain a temperature of 273 K at 100 mW heat input and 2 MPa inlet pressure. An inlet pressure of 3 MPa allowed a 550 mW heat input at 273 K. Theoretical performance calculations were conducted and compared to experimental results revealing considerable reduction of microcooler performance due to the presence of heat in-leak. Results have displayed that the JT coefficient of the coolant gas is a more dominant factor than heat transfer properties in determining the performance of the coolant. Due to the microscale of the device, relevant scaling effects were evaluated, particularly entrance effects, surface roughness and axial conduction.