Applicability, progress and prospect of water−based and ionic liquid−based working pairs in absorption refrigeration system

The traditional working pairs in absorption refrigeration system are ammonia−water and aqueous lithium bromide solutions. In recent years, several new water−based and ionic liquid−based working pairs are proposed. This paper discusses the applicability, research progress and future prospects of these new types of working pairs. For water−based working pairs, the optimization methods of absorbents are as follows: 1) Adding alcohol can improve the absorption capacity and reduce the surface tension; 2) Adding lithium salts can reduce the corrosiveness of the solution and improve its thermal stability; 3) Adding other highly hygroscopic substances can improve the hygroscopicity and reduce costs; 4) Adding nanoparticles to improve the heat and mass transfer. For the ionic liquid−based working pairs, the selection and optimization methods of absorbents are predicted as follows: 1) Selecting cations and anions with appropriate alkyl chain lengths, the longer the alkyl chain, the higher the viscosity; 2) Adding salts to reduce viscosity; 3) Adding surfactants to improve absorption capacity. Meanwhile, the refrigerants with great potential are as follows: 1) RE170 exhibits excellent overall performance; 2) New hydrofluoroolefins (HFOs) have great trade−off advantage in environmentally friendly and ‘drop−in’ substitution; 3) R744 is environmentally friendly and highly safe. For system optimization, there are three attracting methods: 1) Developing membrane−type absorbers; 2) Using double−effect or multi−effect systems; 3) Using compression−assisted refrigeration systems. In the future, by following the optimization methods and using AI technology, which enables the absorption refrigeration system to develop in a more low−carbon way.