Study On Performances Of LiBr/H₂O Double Absorption Heat Transformer System With Solution/Coolant Regeneration

There are large amount of waste heat in industrial production.Absorption heat pump technology is used as an effective waste heat recovery technology in many different industrial productions.Absorption heat pumps can reclaim or uppergrade the industrial waste heat,solar,geothermal energy and some other renewable energy with broad prospects,because they can not only save energy but also reduce the damage to the environment.Double absorption heat transformers have better application with simpler structure than that of two-stage absorption heat transformers,and have greater temperature lift than that of single-stage ones.Researching and modifing the double absorption heat transformer cycle,and providing optimal operation parameters of double absorption heat transformer system are of great significance to improve the performance of the system.The traditional double absorption heat transformer cycle,double absorption heat transformer without regeneration and with solution heat regeneration cycle were analyzed and compared in this paper.Based on the cycle of double absorption heat transformer with solution heat regeneration,a modified cycle of double absorption heat transformer with both solution and coolant heat regeneration was proposed by adding a heat exchanger at the inlet of coolant and outlet of dilute solution of the absorber-evaporator.This heat exchanger makes coolant entering the absorber-evaporator preheated,and the obtained energy is eventually transported into the absorber.This enhancement can make it more reasonable for the energy utilization and improve the performance of the cycle system.Mathematical models for double absorption heat transformers without regeneration,with solution heat regeneration and with both solution and coolant heat regeneration for absorber-evaporator were established and simulated.Both the variation trends of coefficient of performance(COP)and exergy efficiency of the three cycles versus the temperatures of absorption-evaporation,condensation,generation and absorption were sensibly calculated and annalized respectively.The results show that the new cycle of double absorption heat transformer with solution and coolant heat regeneration has a wider operating range of absorption-evaporation temperature and higher COP and exergy efficiency in the whole discussed scope.In the range of discussed absorption temperature,when the temperatures of condensation,generation and absorption-evaporation are 25?,70? and 80?to 115?respectively,the COP and exergy efficiency of the new cycle increases by 2.5%to 3.5%than the one with solution heat regeneration only.When the temperatures of generation,absorption-evaporation and condensation are 70?,100?and 25?to 40? respectively,the COP and exergy efficiency of the new cycle increases by 2.6%to 3%than the one with solution heat regeneration only.When the temperatures of generation and absorption are 70?,75?,80? and 120? to 170? respectively,the COP and exergy efficiency of the new cycle increases by 3%than the one with solution heat regeneration only in the range of discussed temperature of condensation and absorption-evaporation.The variation trends of exergy loss efficiency,flow rate ratio and concentration difference of the double absorption heat transformer with both solution and coolant heat regeneration versus the temperature of absorption-evaporation were also analyzed.The optimum absorption-evaporation temperature and its corresponding maximal value of COP and exergy efficiency at corresponding condensation temperature were calculated by setting the temperatures of both absorption and generation according to the principle of orthogonal,which helps to reveal the mechanism of promoting the performance of the system and to provide the optimal operation parameters for the new cycle system.