Theoretical investigations on the cycle performance of a single-pressure diffusion absorption heat transformer with LiBr-H_2O-R134a-TEGDME

摘要

A simulation model using the first thermodynamic law is first proposed to estimate the performance of diffusion absorption heat transformer, which could potentially improve energy utilization efficiency and reduce CO2 emission. Thermodynamic analyses are performed to investigate the cycle performance when H2O is employed as refrigerant, LiBr as absorbent for H2O, R134a as diffusion gas and TEGDME as absorbent for R134a. Analyses aim to optimize system COP under specified temperature of two generators, two absorbers, evaporator and condenser, and compare the influence of the six temperatures on COP. The results under design conditions show that larger generation efficiency of R134a and smaller mass fraction of LiBr in H2O-LiBr solution are beneficial to COP improvement, but they are limited by the operating conditions. There is an optimal ratio of H2O-LiBr solution mass flow rate to R134a mass flow rate for an optimal COP, and the optimal ratio decreases with the increase of LiBr mass fraction in H2O-LiBr solution. The highest COP of 0.1701 is reached with the optimal ratio of 1.743. In addition, under design-off conditions, the temperatures of refrigerant generator and evaporator have the greatest influence on COP while the temperature of diffusion gas generator has the least influence. The diffusion absorption heat transformer will provide a new way to lift temperature of low grade heat without electricity input which can further improve the energy utilization efficiency and reduce the CO2 emission. (C) 2020 Elsevier Ltd. All rights reserved.