Heat transfer characteristics of water flow in microtubes

This study provides an experimental investigation on forced convective heat transfer performance of water flowing through six microtubes with inner diameters ranging from 123 to 962 μm. A non-contacted liquid crystal thermography (LCT) temperature measurement method that proposed by Lin and Yang [T.-Y. Lin, C.-Y. Yang, An experimental investigation on forced convection heat transfer performance in microtubes by the method of liquid crystal thermography, International Journal of Heat and Mass Transfer (2007), doi:10.1016/j.ijheatmasstransfer.2007.03.038] was used in this study to measure the surface temperature of microtubes. The test results show that the conventional heat transfer correlations for laminar and turbulent flow can be well applied for predicting the fully developed heat transfer performance in microtubes. The transition occurs at Reynolds number from 2300 to 3000. This is also the same range as that for conventional tubes. There is no significant size effect for water flow in tubes within this diameter range. The laminar thermal entrance length for microtubes is longer than that estimated by the conventional correlation. The developing Nusselt numbers for 962 μm tube agree well with those predicted by the Shah and Bhatti [R.K. Shah, M.S. Bhatti, Laminar convective heat transfer in ducts, in: S. Kakac, R.K. Shah, W. Aung, (Eds.), Handbook of Single-Phase Convective Heat Transfer, Willy, New York, 1987] correlations. However, as the tube size decreases, the discrepancy between the test results and the predicting value increases.