A Microfabricated Flow Controller for Refrigerant Expansion

A flow controller for refrigerant expansion is reported. Devices are fabricated using a micromolding technique that is developed for thick nickel electrodeposition. The device consists of a short-tube restrictor with an integrated normally open valve, which, when actuated, presents a controllable blockage into the flow passage to obstruct the flow. Fabricated devices are evaluated with compressed air, with up to 22% reduction in mass flow rate at maximum actuation of the restrictor. The devices are also evaluated in an R134a vapor compression system of 1.5-2 kW, with the ability to control mass flow that is found to be greatly influenced by the vapor compression cycle´s operational parameters. After the inlet pressure, the level of subcooling proved to be the most important parameter. For a cycle operating between 29 deg C and 4 deg C , saturation temperatures in the condenser and evaporator, respectively, actuation of the device reduced the refrigerant mass flow rate by 3.5% with 0.6 ^oC subcooling and up to 10.8 % with 5 deg C subcooling.