The Research Of Heat Transfer Effect Of Horizontal Tube Falling Film Evaporator In Mechanical Vapor Recompression

Horizontal tube falling film evaporation has the advantages of high heat transfer efficiency,small heat transfer temperature difference and can make use of low temperature heat source,it has been used widely in seawater desalination,refrigeration,the petroleum chemical industry,food processing and other industries.Mechanical vapor recompression evaporating system combined the horizontal tube falling film evaporation process and steam compression technology is currently more advanced evaporation and concentration technology.The system has simple and compact structure,operate without external heat source,easy adjustment and convenient operation etc.,it has a great application prospect,but the research about mechanical vapor recompression evaporation system is not comprehensive in the domestic.Horizontal tube falling film evaporator is one of the core equipment in mechanical vapor recompression evaporation system,its performance has important influence on the operation of the system.So the heat transfer performance of the horizontal tube falling film evaporator has important significance on mechanical vapor recompression evaporating system application.The task establishes the heat transfer mathematical model of horizontal tube falling film evaporator,through simulating the heat transfer process of falling film evaporation,the influence of spray density,heat transfer temperature difference and evaporation temperature on the heat transfer coefficient of horizontal tube falling film evaporator in this system have been studied,and heat transfer characteristics of horizontal tube falling film evaporator have been investigated.The study build mechanical vapor recompression evaporation system and experimental study the effects of various factors on evaporation performance in the system and the influence rule,to provide the basic experimental data for the design and performance analysis of the system.Evaporation experiments use a 25.4mm diameter,650mm long smooth stainless steel tube bundle;using the vacuum pump control the vacuum degree in evaporator.Experimental results show:When the evaporation temperature is 80 ?,the heat transfer temperature difference between inside and outside of heat transfer tube is 7 ?,the material spray density increasing in 0.0976-0.164 kg/?m·s?will improve heat transfer coefficient of heat transfer tube in horizontal tube falling film evaporator,heat transfer coefficient increases from 1412 W/?m²·K?to 2067 W/?m²·K?;When the heat transfer temperature difference is 7 ?,the spray density is 0.135 kg/?m-s?,the evaporating temperature increasing in 73-85 ? will improve the heat transfer coefficient of heat transfer tube in horizontal tube falling film evaporator,heat transfer coefficient increases from 1673 W/?m²·K?to 1838 W/?m²·K?;When the evaporation temperature is 80 ?,the spray density is 0.135 kg/?m·s?,the heat transfer temperature difference between inside and outside of heat transfer tube increasing in 3-10 ? will reduce the total heat transfer coefficient of heat transfer tube,heat transfer coefficient reduces from 2243 W/?m²·K?to 1440 W/?m²·K?.Through the evaporation concentration experiments of Na₂SO₄ solution compared with pure water evaporation experiment shows that the heat transfer coefficient of heat transfer tube in Na₂SO₄ solution evaporation is smaller than in pure water evaporation,it's caused by Na₂SO₄ solution viscosity larger than the pure water,therefore,it's need to consider physical property change of material liquid when falling film evaporator in the wastewater treatment of evaporation on the surface of the heat tube heat transfer performance influence.