A comparison between two microchannels is studied with carbon dioxide near critical condition — one with an orifice and another without orifice. A heater was placed beneath both microchannels and was located immediately downstream the orifice. Resistive temperature detectors (RTDs) were embedded in both microchannels downstream the orifice for transient temperature measurements. Rapid changes in the thermophysical properties of carbon dioxide near critical point make it a superior coolant for enhancing convective and boiling heat transfer. Large pressure drop that was provided by the sudden contraction in the microchannel resulted in considerable temperature drop of the downstream flow, which can be leveraged to assist the cooling managements in various thermal systems. The results show higher heat transfer coefficients for the microchannel with orifice compared to non-orifice channel, and also, indicate that near critical carbon dioxide is a good candidate for heat removal in components generating high heat fluxes especially electronic components.

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