Experimental investigation of heat transfer and friction factor in laminar, transition and turbulence region for water flow in mini-micro channels

In this study, heat transfer and friction factor were experimentally investigated for laminar, transitional, and turbulent flow regimes in circular mini-micro channels carrying pure water flow. Unlike many studies in the literature, a systematic experimental study was conducted under a constant surface temperature condition, encompassing multiple hydraulic diameters (381, 500, 750, and 1000 μm) and a wide range of Reynolds numbers (from 228 to 3120, with different flow rate 0–50 mL/min). The experimental setup consisted of a piston pump with precise flow and pressure control, a pressure regulator, heating–cooling baths, and high-accuracy temperature and pressure sensors. Thermo-hydraulic performance, including heat transfer, friction factor, pumping power, and entropy generation, were determined by simultaneously measuring the inlet and outlet temperatures and the pressure drop in the mini-micro channel. The obtained results were found to be in good agreement with the experimental data studied in the literature with similar hydraulic diameters. Based on the results at a flow rate of 50 mL/min, the maximum heat transfer was 45.96 W at a hydraulic diameter of 750 μm, while the minimum heat transfer at the same flow rate was 37.20 W at a hydraulic diameter of 381 μm. In terms of pressure drop, the highest was 16.358 bar at a flow rate of 50 mL/min and a hydraulic diameter of 381 μm, while the lowest was 0.089 bar at a flow rate of 50 mL/min and a hydraulic diameter of 1000 μm. These findings reveal the balance between heat transfer performance and pumping power requirements in mini-micro channel systems, offering comprehensive and original contributions to the literature on operational performance and efficiency optimization.