The Comparative Analgsis And Study On Heat Transfer Characteristics Of Absorption Heat Exchanger

LiBr absorption heat exchanger unit can make high temperature primary water a significant temperature drop in the application of the heat exchange station,so as to improve the efficiency of the heat exchange station.In addition,under the same flow rate of primary water,more heat can be obtained than the plate heat exchanger.Due to the cycle of LiBr absorption heat exchange unit is more complex and has more components,the heat transfer efficiency of unit is very different when the unit increases some equipment,transforms position or the cycle of external water.This paper analyzes and compares the heat transfer performance of primary water cooling system of the evaporator,second water cooling system of the evaporator and external cooling system.This paper analyzes the operation process of three different types of LiBr absorption heat exchangers unit in detail.Based on the law of conservation of energy and the law of conservation of mass,it establishes a unified universal thermodynamic model and a heat transfer model for the common components involved in the three types of units.According to the relationship between energy flow and mass flow among different systems,this paper analyzes and compares thermal states of different key nodes in the three models,and establishes the whole mathematical model of different systems.Through the analysis of the working conditions of the unit,we solve the model,and analyze the influence of the inlet temperature of the primary or secondary and the heat exchanger end difference on the characteristics of the thermal parameters of the different units emphatically.The results show that the temperature drop of the generator in the system 1 is small.Since the system 2 adopts the secondary water to cool the evaporator and then enters,the outlet temperature of the thermocouple is the highest,and the inlet temperature of secondary water is higher than 39 ?,the heat transfer performance of the thermally driven heat exchanger is better;the solution of the system 2 is the best.According to the actual demand,based on the first law of thermodynamics and the second law,two kinds of indexes for evaluating the performance of the absorption heat exchanger are put forward according to the characteristics of the energy flow and exergy flow in the system: the technical characteristics(heat capacity of temperature drive heat exchanger in the total heat capacity,COP),economy(heat capacity of unit area)and the two characteristics of trade-off comprehensive indicators(total area and COP ratio);exergy loss,exergy efficiency,exergy loss ratio and exergy loss coefficient.Based on the first law of thermodynamics,it studies the influence of external water inlet temperature on heat transfer,heat transfer area and flow distribution ratio of single system.It selects heat capacity of temperature drive heat exchanger in the total heat capacity,heat capacity of unit area,total area and COP ratio as evaluating indicator to compare and analyze the three systems.The results show that the secondary water of the system 2 is cooled by the evaporator into the external temperature heat exchanger,the heat capacity of temperature heat exchanger in the total heat capacity accounts for a large proportion.From view of economy,the unit 1 has a large heat transfer per unit area and a minimum of the system 2.From view of technology,the system 3 can be in the smaller COP when it gets the same heat tcapacity.In combination with technology and economy,system 1 has the best performance.In the actual project selection,according to the specific needs and conclusion,we select the appropriate unit.In order to analyze the heat transfer performance of the unit in depth,from the view energy "quality",this paper selects the exergy loss,exergy efficiency,exergy loss ratio as evaluating indicator.Studies have shown that the exergy loss of absorbers,generators and external temperature heat exchanger accountes for the largest proportion.The three components in the three systems were compared laterally.It is found that the external heat exchanger of the system 1 has the largest loss coefficient,and the absorber of the system 2 had the largest loss coefficient and should be optimized.Through the study of the relationship between heat transfer,COP and exergy loss,it is found that the greater the proportion of the loss of the bromine machine in the total exergy loss,the smaller the COP is;the greater the exergy loss of the unit,the smaller the heat transfer.