Heat Transfer and Pressure Drop in Single-Phase Flows in Tapered Microchannels

This paper presents a comparison of heat transfer and pressure drop during single-phase flows inside diverging, converging, and uniform microgaps using distilled water as the working fluid. The microgaps were created with a plain 10 mm x 10 mm heated copper surface and a polysulfone cover that was either uniform or tapered with an angle of 3.4 deg, and average gap heights of 400 and 800 mu m. Experiments were conducted with single-phase water flow with an inlet temperature of 30 degrees C for flow rates varying from 57 to 498 mL/min and heat flux from 27 to 153 W/cm(2) depending on the flowrate and microgap configuration. The uniform configuration resulted in the lowest pressure drop due to the less constricted flow. A slight decrease of pressure drop with heat flux was observed due to temperature dependent properties. The best heat transfer performance was obtained with the converging configuration, which was especially significant at low flow rates and shorter average gap. This behavior could be explained by an increase in the heat transfer coefficient due to flow acceleration in the converging gaps, which compensates for the decrease in temperature difference between the fluid and the surface along the flow length. Overall, the converging microgaps have better performance than uniform or diverging ones for single-phase flows, and this effect is more pronounced at lower flow rates, where the fluid experiences higher temperature changes.