开式吸收式热泵系统的研究及应用进展

State-of-the-art Open Absorption Heat Pump Systems and Their Applications

闭式蒸气吸收式热泵系统以热能和少量泵功驱动代替蒸气压缩热泵系统的压缩机驱动,分别实现工质的流动和内能的增加,节省了高品位电能的压缩功。开式吸收式系统相比于闭式吸收式热泵(制冷)系统,以蒸气压差和温度差同时驱动的直接接触式传热传质代替闭式系统温差驱动的间接传热,实现系统与外界环境的热质交换。针对开式吸收式系统的研究目前主要为不同应用相关研究,在闭式吸收系统的基础上精简结构,优化性能。本文主要从工质对、构型、部件三个方面总结目前开式吸收式系统的研究进展。因开式吸收式系统常与环境发生物质交换,对其工质对的研究需要在蒸气压低、不易结晶等传统吸收式工质对需要的物性基础上,更强调腐蚀性低、环境友好等特性。广义的开式吸收式系统有D型、AD型、ADC型、EAD型、EADC型5种基本构型,本文总结了5种基本构型在直接蒸发冷却制冷、气体除湿加湿处理、热湿气体潜热回收、制冷制热、蒸馏提纯等不同应用领域的研究。与闭式吸收式系统相比,强化环境与系统的传热传质是开式吸收式系统的研究重点。对于直接接触式传热传质部件,填料塔仍然是绝热开式吸收器/发生器的主要形式,基于膜的非直接接触式吸收/发生换热器作为直接接触式换热器的替代部件,其传热传质系数相对于直接接触式换热器仍有待提高。

The driven heat and circulating pump in a closed absorption system replaces the compressor in a vapor compression heat pump system and circulates the working fluid while increasing its internal energy,thus saving the compression work from consuming high-grade electric power.Unlike in the closed absorption heat pump(refrigeration)system,in the open absorption system,the indirect heat transfer driven by the temperature difference is replaced with the mass transfer driven by the vapor pressure difference and the heat transfer driven by the temperature difference simultaneously.Heat and mass transfer with the environment can occur in different components(evaporator E,absorber A,generator D,and condenser C)in open absorption systems.For applications in different fields,the structure is simplified based on a closed absorption system,and the performance is optimized.This paper summarizes state-of-the-art open absorption systems in terms of three aspects:working fluid pairs,configurations,and components.Research on the working fluid pairs of open absorption systems has mainly focused on aqueous working fluid pairs with water as the refrigerant.Common salt solutions LiBr-H_(2)O and LiCl-H_(2)O have high performance,but they are corrosive and easy to crystallize.CaCl_(2)-H_(2)O is less corrosive but unsuitable for high-temperature applications.The performance of HCOOK-H_(2)O is between those of LiBr/LiCl-H_(2)O and CaCl_(2)-H_(2)O,resulting in low corrosion to the system.Further experimental studies are required for ionic liquids as potential alternative working fluids.A typical open absorption system has five basic configurations:D,AD,ADC,EAD,and EADC types.The D-type configuration can be used for direct evaporative cooling,refrigeration,and recovery of latent heat from moisture in air.When the evaporation temperature is low in the EAD-type,the evaporator can be used for cooling.In the EAD type,the absorption heat transfer absorber can be used for heating and the generator can be used for humidification.These can also be used for seawater desalination and purification.The ADC-type configuration can be used to recover latent heat from moisture and distillation.The EADC-type open absorption system is similar to the traditional closed absorption system and can be used for refrigeration,heat pumps,and distillation purification.Enhancing the heat and mass transfer between the environment and the system is the focus of the research on open absorption systems.For direct-contact heat and mass transfer components,packed towers are still the main form of adiabatic absorbers/generators.The use of indirect-contact absorption/generation heat exchangers based on membranes is required to fundamentally solve the carryover problem.However,the heat and mass transfer coefficients of the membrane absorption/generation heat exchanger still need to be improved compared with those of direct-contact heat exchangers.