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ISSN Печать: 2151-7975
ISSN Онлайн: 2151-7991
CHARACTERISTICS OF EVAPORATION HEAT TRANSFER ON HEATED SURFACE WITH THIN POWDER POROUS LAYER
Краткое описание
We measured the evaporation heat transfer coefficient from a thin porous layer on a heated horizontal plate at 70-100°C at atmospheric pressure. The porous layer was 0.5-1 mm thick with glass beads that were 0.4 mm in diameter. The gas space conditions were changed for two cases: a small amount of air in the gas space, and no air in the gas space. The experimental results for steady evaporation heat transfer coefficients were 15-500 W/m2K for the small amount of air in the gas space at the temperature of the heated plate of 70-85°C at the thickness of the porous layer of 1 mm. The evaporation heat transfer coefficient was about 1000 W/m2K after water was supplied and about 7000 W/m2K before dry portions appeared when there was no air in the gas space at the temperature of the heated plate of about 100°C. It was very important to create a thin water film in the porous layer to enhance the evaporation heat transfer coefficient. The water liquid film spreading speed in the thin porous layer was measured and compared with calculations from two calculation models.