The Effect Of ? Rings On Direct Contact Evaporative Heat Transfer Performance

Due to no metal heat transfer surface, direct contact heat transfer holds the advantages of little heat transfer resistance, high heat transfer coefficient, simple structure, little corrosion that traditional heat transfer doesn't hold. However, heat transfer performance in bubble column is relatively limited, bringing out backmixing and droplets wake that hinder heat transfer. Thus, the purpose of the paper is to focus on the effect of ? rings on direct contact heat transfer performance in bubble column with n-pentane and tap-water. Meanwhile, the influences of different parameters like pentane flow rate, temperature difference and distributor aperture on axial temperature distribution, evaporative height and volumetric heat transfer coefficient were studied. Based on experiment, the direct contact heat transfer theoretical derivation in bubble column was also carried out and validated with experimental data. The results obtained are as follows:(1) After ? rings packed in bubble column, axial temperature drops more largely and quickly and evaporative height decreases more than that without packing. Besides, volumetric heat transfer coefficient with packing is double that without packing when pentane flow rate of 23.868L/h, distributor aperture of 2.5mm. On one hand, the average diameter of pentane droplets are limited due to the blockage and cutting,then the heat transfer areas increase. On the other hand, packing prevents the axial and radial movement of liquid which brings down backmixing to some extent. Thus, the heat transfer performance with packing is proved better than that without packing.(2) In bubble column with packing, the axial temperature drops more largely with less distributor aperture and larger water inlet temperature and varies little with pentane flow rate increases. Evaporative height increases with an increase of pentane flow rate and distributor aperture and a decrease of temperature difference. And when temperature difference is above 8?, evaporative height changes little. Volumetric heat transfer coefficient increases with an increase of pentane flow rate and a decrease of distributor aperture. Volumetric heat transfer coefficient has exponent relation with temperature difference. Under the condition of temperature difference below 3?, the volumetric heat transfer coefficient increases sharply as temperature difference decreases. And when temperature is above 8?, volumetric heat transfer coefficient changes little.(3) The droplets heat transfer is linked with single droplet heat transfer in bubble column without packing. and average volumetric heat transfer coefficient of evaporation process is obtained. Then the average heat transfer coefficient with packing is derived from that without packing. The errors are all below 20% after compared with experiment data.