In the present work, the single-phase heat transfer of water flowing through the straight and helical minichannel tubes was experimentally studied. The test section was made from the stainless tube with an internal diameter of 1.75mm and 70 cm long. The coil diameters were 34, 48, and 61 mm. The single-phase heat transfer is experimentally determined based on the direct heating operation. The experiments have been carried out by varying the water flow rates and supplying heat fluxes. The Reynolds numbers were performed covering the transition to turbulent flow regimes, while supplying the heat fluxes were approximately 30–70 kW/m2. The experimental results were compared with the existing correlations from the literature. The result illustrates that more enhanced heat transfer increase for tubes with greater curvature ratio.

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