| A flow boiling test rig with flow visualization assisted by high speed video camera system was designed and built. Experiments with Isopentane flowing through structured-porous fins were conducted. The fin test articles were made by diffusion-bonding multi-layer staggered-stacked plain-weaved copper wire mesh screens. Seven test articles, sized by 3.7mmx9.8mmx48mm, with mesh number ranging from 50 to 200, and two thin test articles, sized by 2.0mmx9.8mmx48mm, 1.0mmx9.8mmx48mm respectively, with mesh number 200, were made and tested. Experiments were conducted at pressures of 2bar, 3bar and 5bar with channel Reynolds number ranging from 1000 to 10000 for each test article. Pressure drop across the porous fins was measured under cold running state. The influences of pressure, flow rate and mesh number (pore size) on overall boiling performance are investigated. The results show that: (1) Increased system pressure does not display an observable effect on the boiling performance at the tested pressure range. (2) Increase of flow rate generally improves boiling performance. The influence is pronounced only when the heat loading is big enough for the specific boiling surfaces. (3) Influence of mesh number (pore sizes) is complicated. Generally speaking, high meshnumber test article tends to perform better at low heat loading, while rough mesh test articles generally perform better at high heat loading. (4) An Ergun-type correlation for predicting friction factor was developed based on pressure drop data obtained in this study. The correlation can predict the friction factor for test articles (including the thinner ones) made in this study, with 99% of the experimental data fall into +/-14% of the predicted values. (5) A model is developed for assessing entropy generation rate for a flow boiling system. A 90% entropy generation decrease was achieved with the M200 (New) test article comparing to an unenhanced plain surface. |
