Micro cryogenic coolers (MCCs) are useful to a number of small electronic devices which require low cooling power. The cooling power of MCCs operating with mixed refrigerants in a Joule-Thompson (J-T) cycle can be calculated based on enthalpy calculations for the mixture. This letter demonstrates a method to measure the isothermal enthalpy change in a mixture undergoing J-T expansion in an MCC for different refrigerant flow regimes. This shows that the enthalpy change for a mixture undergoing steady flow is an order of magnitude below that calculated; whereas the enthalpy change for the mixture undergoing pulsating flow agrees with the calculations below a certain temperature, and is over-predicted above that temperature. In the case of steady flow, the low enthalpy change is due to liquid holdup in the annular flow regime, and for pulsating flow, the discrepancy is due to periods of liquid slug flow interrupted by periods of annular flow.
Pub Type: Journals
microcryocooler, mixed refrigerants