Simultaneous Heat Transfer and Pressure Drop Measurements for a Horizontal Micro-Tube

Heat transfer and pressure drop measurements for horizontal macro-tubes under uniform wall heat flux boundary condition have been conducted by various researchers in recent years. From their studies, it was shown that good agreements were observed in the laminar and turbulent regions. However, for the transition region, the heat transfer and pressure drop characteristics depended on various factors, such as inlet configuration, buoyancy effect, and surface roughness. In a recent study by Tam et al. (2010), they measured the heat transfer and pressure drop simultaneously for a horizontal macro-tube with and without internally micro-fins and concluded that under the heating condition, the transition Reynolds number range for heat transfer and pressure drop were completely different. The transition Reynolds number range was documented in their research in great detail. However, for horizontal micro-tubes, there is no information in the literature on the simultaneous behavior of the heat transfer and pressure drop, especially in the transition region. In order to fill in this gap, an experimental setup was built to measure the heat transfer and pressure drop simultaneously for a horizontal micro-tube under uniform wall heat flux boundary condition. Water was used as the test fluid and the test section was a stainless steel micro-tube with 1000μm diameter. For heat transfer, the results indicated that the micro-tube had an earlier start and end of transition compared to the macro-tube and, in the turbulent region, an increase in heat transfer due to the surface roughness was observed. For friction factor under isothermal condition, the micro-tube had a narrower transition range due to the roughness compared to the macro-tube. For friction factor under heating condition, the laminar data and the start of transition were different from the isothermal case, and the effect of heating was not seen on the end of transition.