Investigations On The Thermodynamic Optimization For The Four-Temperature-Level Absorption Heat Pump

Lithium-bromide absorption heat pump can recover and utilize waste heat with lower temperature.Using environment-friendly substance as the refrigerant and consuming electric energy a little,AHP is more available in using low-grade energy and protecting environment then other method of heating.This paper focuses on the studies of finite-size optimal performance of single effect Lithium-bromide absorption heat pump cycle,the conclusion obtained here can serve as a theoretical guide for the optimal design and operation of practical heat pump.Solution heat exchanger and solution pump are two important devices of absorption heat pump.Chapter 2 builds up the models of four-temperature-level AHP cycle considering solution pump,solution heat exchanger and they two simultaneously, derives the general relation between heating load and coefficient of performance (COP),and gives the numerical calculation method for optimizing distribution of the total heat transfer surface area and the total heat inventory,and analyses the effects of internal irreversibility,the power of solution pump,the heat recycling through the solution heat exchanger,heat reservoir inlet fluid temperature and heat reservoir capacity on the optimal performance using numerical examples.It is found that the heating load versus COP characteristic of the irreversible cycle model is monotonous, and the power of solution pump and the heat recycling through the solution heat exchanger have no influence on the curve form,but they have influence on the heating load and COP.The engineering data is adopted to conform the validity of the thermodynamic models and the numerical calculation method. Based on the cycle model of irreversible four-temperature-level AHP with infinite and finite capacity reservoirs,the heating load of the total cost per unit time is taken as the thermoeconomic objective function in Chapter 3.The fundamental optimal relation between the non-dimensional thermoeconomic objective function and the COP is derived with infinite heat capacity reservoirs,and the maximum non-dimensional thermoeconomic objective function and the corresponding performance parameters are calculated.When the total heat inventory is fixed,the heat inventory optimizing distributions and the optimum working substance temperature are derived.The general relation between heating load and COP is derived with finite capacity reservoirs,and gives the numerical calculation method for optimizing distribution of the total heat transfer surface area and the total heat inventory,and analyses the effects of cycle parameter on the thermoeconomic optimal performance using numerical examples.The model and the derived performance relation are testified by comparing the prediction results of the model with engineering results for real AHP.Taking the overall coefficient of performance as objective function,the optimization performance of the solar-driven absorption heat pump system consisting of a solar collector and a four-temperature-level absorption heat pump is studied,by employing the linear heat-loss model and the radiation model of solar collectors and the optimum relation of irreversible four-temperature-level absorption heat pump with finite and infinite capacity reservoirs.The fundamental optimal relation between the overall COP and the temperature of the collector is calculated with infinite heat capacity reservoirs,and the maximum overall COP and the corresponding performance parameters are calculated.The general relation between the overall COP and the outlet temperature of the collector is derived with finite capacity reservoirs, the effects of the cycle parameters on the performance of the system are evaluated by detailed numerical examples.