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

The heat-transformer is a thermal application which can change low-grade heat energy into high-grade heat energy such as industrial waste heat,heat of the earth and solar energy.It is an effective way of utilizing low-grade energy adequately.It only consumes a little electrical energy driving cryogenic fluid pump and solution pump,which can save energy obviously.Moreover,it can use H₂O-LiBr,NH₃-H₂O as the working substance which won't damage the atmospheric ozone layer.So it has some significant value for energy conservation and environmental protection.The solar-driven absorption heat-transformer is a type of absorption heat-transformer driven by solar collector.The optimization of the performance of the solar-driven absorption heat-transformer system consisting of a solar collector and a four-temperature-level absorption heat-transformer is studied,by employing the linear heat-loss model of solar collectors and the optimum relation of four-temperatrue-level irreversible absorption heat-transformer with finite capacity reservoirs.The overall coefficient of performance of the system is adopted to be an objective function.The optimum operating temperature of the solar collector is driven by numerical method. From the result,the effects of the cycle parameters on the optimum operating temperature of the solar collector and the performance of the system are evaluated by detailed numerical examples.The thermoeconomic analysis is very significant for business application.Based on a thermoeconomic objective function,the performance of an absorption heat-transformer cycle with four-temperatrue-level irreversible is analyzed using the linear heat transfer law.The fundamental optimal relation between thermoeconomic objective function with the corresponding coefficient of performance and specific heating load of the cycle are derived using finite-time thermodynamics.Furthermore, the effects of the cycle parameters on the thermoeconomic objective function are studied with detailed numerical examples.Based on the absorption heat-transformer cycle model considering the power consumption of solution pump and the heat quantity of solution heat-exchanger,the fundamental characteristics of absorption heat-transformer effected by heat-transfer irreversibility and internal irreversibility is derived.The performance relation between the heating load and the cycle coefficient with linear heat-transfer law is derived. Moreover,the optimum performance relation between the heating load and the cycle coefficient is derived by numerical method.The effects of the cycle parameters on the cycle characteristic are studied by detailed numerical examples.The results can provide some guidance for the optimal design of practical absorption heat-transformers.