Study Of Heat And Mass Transfer Performance In Fixed-Valve Tray Column Applied In Evaporation Water Tower

In this thesis, the performances of the evaporating water tower using fixed-trays column were discussed. The heat and mass transfer performance and capturing efficiency of solid phase were researched in the column. The results of paper had theoretical guidance to design evaporating water tower.Based on steam and water direct contact condensation process in hot water tower, transfer units correlation were established on condition of vapor-liquid countercurrent contact conditions. The relationships between heat transfer efficiency and measurement parameters were found to predict the direct contact condensation process in downcommerless trays. Furthermore, the tray geometry parameters of hole area, hole diameter, valve height and hole center distance were investigated in the process. The experimental results indicated that heat transfer Efficiency (HTE) would be increased by reducing the hole area, valve height and hole diameter. By changing the temperature difference between vapor and liquid, it had found that the temperature difference had a dual effect on the heat transfer process.Fly ash was taken into the column by non-condensable gas (NCG) to study the effects of NCG and particles on the process. It was found that small droplets would be broken into smaller ones after adding a small amount of particles. It prompted to increase the vapor-liquid contact area and be in favor of heat and mass transfer. However, with further increase of NCG, sensible heat was taken away and heat transfer performance would be deteriorated. With the increase of gas-ash mixtures, heat transfer first decreased and then increased.By means of Malvern particle size analyzer and scanning electron microscopy, solid particles characteristics were observed and particle capturing efficiency in the vapor phase was studied. It showed that fly ash was generally spherical in the vapor phase but irregular in the liquid. The particles capturing efficiencies would be decreased with liquid flow rate increased. However, it would be increase with NCG rate increased. The particle capturing efficiency first increased and then decreased when increased steam flow rate.