Analysis Of Heat Transfer Performance And Experimental Study Of Thin Film Evaporator

The thin-film evaporator (TFE) is a new-type highly efficient evaporating equipment. Itutilizes the rotational blade to disperse the fluid as uniform thin film so as to concentrate thematerial. Up to now, the foundational data for design of TFE are still limited due to thecomplication of boiling heat transfer and forming film by agitating blade. How to get thedistribution of the velocity field, temperature field and concentration field which are formedin the process of evaporation is a valuable research subject.On the basis of the 0.4m2 steel TFE test equipment which was developed by TheChemical Equipment Design Institute of Nanjing University of Technology, the heat transferperformance of different liquid of TFE was investigated by numerical simulation andexperimental study. The main work and conclusions are as follows:1) The heat transfer performance of TFE was numerically analysised by using CFDsoftware CFX4.4. The effect of operating parameters on the evaporation length and film heattransfer coefficient was obtained by changing the feed rate, inlet temperature and rotor speed.It was found that on different operating conditions, there is one common optimum feed ratewhich has a maxim film heat transfer coefficient. The effect of fluid flow field on heattransfer process was explained quantitatively by analyzing the relation between thecross-section velocity in fillet and film heat transfer coefficient, which lay the foundation forfarther research of fluid flow and heat transfer mechanism. Also, the correlation of heattransfer coefficient of water was obtained.2) Also using CFX4.4, the heat transfer performance of different viscosity and differentdensity materials in TFE was numerically analyzed by changing the feed rate and rotor speed.The relations between film heat transfer coefficient and viscosity, density were obtained. Acalculating film thickness method was put forward for high viscosity liquid.3) A newly developed 0.4m2 TFE system was tested. The variation curves of overallheat transfer coefficient K and evaporation intensity of TFE for water were obtained bychanging the operating parameters such as feed rate, inlet temperature, rotor speed, oiltemperature and vacuum. It was also found that there is an optimum feed rate which is similarto the numerical calculation value. - i -4) A comparison between the experimental results and the numerical calculation resultsreveals that the same variation trend has been obtained for both of them.5) Experiments with CMC as feed liquid were made by changing the feed rate andconcentration. It was should that TFE is very suitable for the evaporation of non-Newton typefluid. Under the experiment condition, the heat transfer coefficient and evaporator intensity ofhigh viscosity fluid were both larger than those of water.Based on the above calculation analysis and experimental research of TFE with different fluid, afoundation for farther research in heat transfer and mass transfer mechanism of TFE was laid.