สำนักราชบัณฑิตยสภา

The Journal of the Royal Institute of Thailand Volume II - 2010 Sira Saisorna, Somchai Wongwises 71 dimensionless parameters. For instance, arbitrary channel classifications based on the hydraulic diameter D h have been proposed. Mehendale et al. (2000) employed the hydraulic diameter as an important parameter for defining heat exchangers and Kandlikar (2002) proposed criteria for small flow channels used in engineering applications. Two-phase flow and heat transfer characteristics in small channels such as micro-channels and mini-channels are likely to be strongly dependent on surface tension effects in addition to viscosity and inertia forces, resulting in significant differences in two-phase flow phenomena between ordinary sized channels and small channels. In the past decade, there has been a relatively small amount of publications available for both mini-channels and micro-channels compared to those for ordinary sized channels. Triplett et al. (1999a, 1999b) studied adiabatic two-phase air-deionized water (DI water) flow characteristics in micro-channels with hydraulic diameter ranging from 1.1 to 1.5 mm. The flow patterns observed were bubbly, slug, churn, slug- annular and annular. The measured void fraction and two-phase pressure drop in the relevant flow regimes were also investigated. The void fraction data were obtained based on the image analysis. Serizawa et al. (2002) investigated the visualization of the two-phase flow pattern in circular micro-channels. The flowing mixture of air and water in channels of 20, 25 and 100 μm in diameter and that of steam and water in a channel of 50 μm in diameter were conducted experimentally. Two-phase flow patterns obtained from both air-water and steam-water flows were quite similar and their detailed structures were described. The study confirmed that the surface wettability had a significant effect on the two-phase flow patterns in very small channels. Chung and Kawaji (2004) performed an experiment in order to distinguish two-phase flow characteristics in micro-channels from those in mini-channels. Four different circular diameters ranging from 50 to 526 μm were employed, to examine a scaling effect on nitrogen-DI water two-phase flow. The results including the flow patterns, void fraction and two-phase pressure drop were analyzed. A flow visualization study to clarify the flow patterns of a vertical upward gas-liquid two-phase flow in rectangular mini-channels with hydraulic diameters ranging from 1.95 to 5.58 mm was carried out by Satitchaicharoen and Wongwises (2004). Air-water, air-20 wt.% glycerol solution, and air-40 wt.% glycerol solution were used as working fluids. In the experiments, they employed various rectangular