Assessment methods for selecting organic absorbents of HFC refrigerant in absorption system

Absorption refrigeration is one of the refrigeration methods which can make use of low quality heat sources. Some HFC refrigerants have been put forward in the absorption refrigeration systems for their good properties. R161 and R134a are both potential refrigerants. However, which absorbent is more suitable for them in the common absorbents, and how to evaluate the HFC working fluid pairs have not been clearly presented. On the basis of these, we need to obtain an assessment method for selecting organic absorbents of HFC refrigerant. In this work, R161 and R134a were selected as the refrigerants. DMEDEG/DMAC/NMP/DMF were selected as the absorbents of R161, and DMEDEG/MEGDME/DMETrEG/DMF were selected as the absorbents of R134a. Firstly, a single-grade absorption refrigeration cycle simulation was adopted, and the coefficient of performance (COP), the circulation ratio (f) and the power consumption of solution pump (Wp) of the systems with the investigated working pairs were evaluated. Secondly, three assessment criteria including bubble point pressure (p), excess Gibbs free energy (GE) and deflation ratio (dR) were estimated with NRTL model. By comparing the relationships between the criteria and system performance, it could be found that: 1) Bubble point pressure (p) influenced the pressure differential in system but had little relationship with system performance; 2) The GE influenced the system performance remarkably, and the working pair whose extreme value of excess Gibbs free energy (GEmax) within an appropriate range had the best thermal performance, and for R161 and R134a working pairs the range was -400 J/mol ~ -300 J/mol; 3) The bigger dR meant the better cycle performance, and when dR > 6%, the preferable performance could be achieved. Overall, the combined assessment method can preliminarily evaluate the performance of the organic absorbents of HFC refrigerant and help us to select suitable absorbent for the specified refrigerant in absorption system.