Distribution Of Heat Transfer Parameters Of Large-scale Falling Film Evaporator

Horizontal-tube falling-film evaporator is widely used in the desalination,refrigeration and air-conditioning,chemical engineering,absorption heat pump and waste heat recovery and other fields.It has important practical value of studying the heat transfer process of horizontaltube falling-film evaporator.Aiming at heat transfer process in the horizontal-tube falling-film evaporator of low-temperature multi-effect evaporation desalination system.The lumped parameter method is mostly used for calculation in engineering,that is,a total heat transfer coefficient is used to characterize the heat transfer performance of horizontal-tube falling-film evaporator.It is difficult to acquire well variation of local heat transfer of horizontal-tube falling-film evaporator.The distributed parameter method is used for studying the heat transfer process of horizontal-tube falling-film evaporator.In this paper,a three-dimensional distributed parameter model is established of horizontal-tube falling-film evaporator.The variation of thermal parameters along the tube row direction,the tube array direction and the tube length direction during heat transfer process of horizontaltube falling-film evaporator are considered,and the corresponding calculation program is developed.According to the data from the literature,aiming at application of low-temperature multi-effect evaporation desalination device,applicability evaluation of heat transfer correlations proposed by scholars in literatures is carried out,the difference of calculation results under different spraying density and evaporating temperature on different heat transfer correlations are compared.The calculation of the heat transfer process of horizontal-tube falling-film evaporator is carried out.According to the flow direction of inter-tube secondary vapor,tube bundles in the evaporator can be divided into three areas that are studied separately.The effects of feed seawater temperature,feed seawater spraying density and apparent heat transfer temperature difference on distribution of the tube row direction of seawater salinity,seawater temperature,heat transfer coefficient outside the tube,heat transfer temperature difference,total heat transfer coefficient and heat flux are studied.In this paper,the evaporator is divided into high heat transfer temperature difference region and low heat transfer temperature difference region.With the increase of spraying density and apparent heat transfer temperature difference of feed seawater,the percentage of area in high heat transfer temperature difference increases,and with the increase of feed seawater temperature,the percentage of area in high heat transfer temperature difference decreases.The effects of feed seawater temperature,feed seawater spraying density and apparent heat transfer temperature difference on the effective heat transfer length of heat transfer tube bundles in horizontal-tube falling-film evaporator are studied.The feed seawater temperature has a great influence on the effective heat transfer length of heat transfer tube bundles.Under the same operating parameters,the variation trend of production of secondary vapor in horizontal-tube falling-film evaporator with rotated square pith and regular triangle is compared and analyzed.