The Experiment And Model Of Condensation Heat Transfer On The Surface With Gradient Surface Energy

With the increasing demand of energy consummation, it becomes necessary and urgent to focus our attention on research of energy transportation, decreasing available energy loss and comprehensive utilization. Condensation heat transfer enhancement is one of such technologies. Dropwise condensation is a most efficient heat transfer because of its higher surface heat transfer coefficient. Once it comes to use, the efficiency of energy transport could be greatly improved thus decrease the size of device and temperature differences.The characteristics of the droplet movement on the gradient surface energy supply a method of eliminating the condensation expect for the gravity. Therefore, the gradient surface energy could be capable of eliminating the condensation in time and improve the condensation heat transfer as for horizontal surface or other gravity free state surface.In this paper, the author began from the vapour deposition process, fabricated the surface with gradient surface energy and then visually researched on the performance of the water vapour condensation on the surface with gradient surface energy. A theoretical model was developed for the dropwise condensation heat transfer on the horizontal surface with gradient surface energy firstly. The main works and conclusions would be described as follows:1. By using the chemical vapor deposition (CVD) technology, two tested surface with gradient surface energy was fabricated on a base of silicon wafer with dodecyltri- chlorosilane and octrytrichlorosilane. The thickness of silicon wafer is 0.5mm.2. Using a high-speed video imaging system, the movement of water drop on horizontal surface with gradient surface energy was visualized and measured under ambient condition. The heat transfer experiments were conducted on dropwise condensation of steam on the tested surfaces. During experiments, the condensing surface was placed at various inclination angles of 0o, 30o, 60o, and 90o, respectively. The growth, coalescence, motion, and abscission of condensing droplets were visualized by the high-speed video imaging system. The observed results showed that the condensing droplets larger than about 1 mm in diameter can move at a peak speed of 110 mm/s on horizontal tested condensing surface, but the velocity of droplet on the surface with gradient surface energy in ambient atmosphere only move at a peak speed of 18 mm/s. With an increase of the heat transfer temperature...