Heat Sink Effect on System Pressure and Mass Flow Rate in a Pumped Refrigerant Loop

Abstract

Pumped refrigerant loops (PRL) which are aimed at eventually cooling electronics often reject heat to a vapor compression cycle. A vapor compression cycle (VCC) uses a proportional, integral, and derivative controller to maintain desired conditions in its evaporator. These controllers apply an algorithm that has an associated time response. The time response and constant adjustment of the expansion valve in the VCC can result in rapid deviations from the set point temperature for the evaporator. When a PRL is coupled to a VCC through an intermediate process fluid, the result in the PRL can be rapid system-wide changes in pressure and mass flow rate depending on equipment specifications. Three options for removing heat from the PRL were evaluated for their effect on PRL system pressure and mass flow rate. Two of the options were variations of the coupling option using an FTS Maxicool RC100 recirculating chiller, while the third eliminated the coupling to the Maxicool’s VCC and used an ice water heat sink in its place. Rejecting heat from a PRL to an ice water heat sink provided more stable system pressures and mass flow rates and less of a propensity for premature dry out than rejecting heat through an intermediate process fluid to the MaxiCool’s VCC. The PRL priming time required when coupled to the ice water heat sink occurred in seconds rather than the minutes required when coupled to the VCC. For certain operating conditions in which thermal storage can be taken advantage of, the ice water heat sink can provide electricity usage cost savings of 10% or more over using a VCC alone. An ice water heat sink for a PRL has potential advantages over being coupled to a VCC, particularly for a laboratory experimental setup and potentially for larger applications.