An experimental study of the characteristics of fluid flow and heat transfer in the multiport microchannel flat tube

This study aims to research on the flow and heat transfer characteristics of a flat aluminum extruded multiport tube using water as working fluid. This kind of tube is composed of numerous parallel of rectangular microchannels and is widely used in industry as heat transfer unit of heat exchanger. Six samples with hydraulic diameter ranging from 0.48 to 0.84 mm, aspect ratio varying from 0.45 to 0.88 and relative roughness ranging from 0.29% to 1.06% are carried on experimental investigation to test friction factor and Nusselt number. The test is performed with Reynolds number varied from 120 to 3750, covering the laminar, critical, and early transition zone. The experimental results show that the laminar-turbulent transition occurs at Recr = 1200-1600 respectively for six samples. For friction factor, entrance effect has a significant impact in turbulent region, while roughness seems to be negligible and no evidence can be found to indicate that aspect ratio has correlation with the early transition. For Nusselt number (convective heat transfer process), both roughness and entrance effect can enhance heat transfer. Roughness is more significantly effective at high Reynolds numbers, while the entrance effect is more effective in the laminar region.