Two phase flow, Flow pattern, Liquid film thickness, laser measurement
Recently, many studies were carried out to investigate the flow and heat transfer characteristics of two-phase flow in microchannels because of its advantage in improving heat exchange efficiency. In these studies, it has been well revealed that liquid film thickness and flow pattern play important roles in determining the heat transfer characteristics. However, these data is still limited to understanding properties of two-phase flow in microchannels because both the effect of tube size, geometry and physical property of working fluids have be taken into account. In this study, visual observation of flow pattern by using a high-speed camera and direct measurement of liquid film thickness by using a laser displacement meter for annular flow inside microchannels with inner diameter of 0.5 mm, 1 mm and 2 mm were conducted. 5 fluids with different surface tension and viscosity (water, ethanol, FC72, 2 different kinds of silicon oil) were selected to investigate the effect of physical properties on the flow pattern and liquid film thickness. Experimental resutls were compared with several existing correlation and numerical simulation results to provide better understanding of two phase flow and heat transfer characteristics at various tube scales and working fluid physical properties.