Local Measurement of Forced Convection Heat Transfer in a Micro Glass Tube

The pressure drop and the convective heat transfer characteristics of ethanol and water in a 600 μm diameter tube with and without phase change has been studied experimentally. The test section consists of a glass tube coated with a transparent ITO (indium tin oxide) heater film. For single phase flow it was found that the measured Nusselt numbers and friction factors are in good agreement with the theoretical values expected from Poiseuille flow. Subsequently, the boiling heat transfer of ethanol was studied. It was found that boiling with bubble growth in both upstream and downstream directions leaving behind a thin evaporating liquid film on the tube wall is the dominant phase change process. Local Nusselt numbers are calculated for the two phase flow at different heat fluxes and Reynolds numbers. Compared to single phase flow the heat transfer is enhanced by a factor of 3 to 8.