Computer-aided molecular design of diffusion–absorption refrigeration modules for low-temperature solar collectors

Abstract

Diffusion absorption refrigeration (DAR) is an attractive thermally-driven cooling technology that can be powered using renewable heat, e.g. , from solar-thermal collectors. This technology can address refrigeration security challenges, rising electricity costs, as well as energy, resource-use and emissions concerns. Commercial DAR modules typically use NH 3 —H 2 O as the working fluid pair, which requires temperatures above 150 °C to be supplied to initiate cooling. Due to their lower saturation temperatures, organic working fluids can be attractive substitutes in enabling DAR modules to be used in conjunction with low-cost, non- or low-concentrating solar-thermal collectors (50 °C to 150 °C). In this paper, an integrated computer-aided molecular and DAR (CAMD-DAR) system design framework is proposed that uses a group-contribution equation-of-state based on the statistical associating fluid theory (SAFT-γ Mie) for working-fluid design and property prediction simultaneously with the DAR module design. Following a detailed presentation of this CAMD-DAR system framework, the framework is employed to identify optimal organic working fluids and DAR-system designs simultaneously for a specified solar-cooling application. The results suggest that non-polar organic refrigerants with polar absorbents are to be selected if maximum cooling rates are required from an otherwise conventional DAR module design. In particular, a mixture of 2-butene (2-C 4 H 8 ) and ethanol (C 2 H 5 OH) pressurised by He is identified as the optimum working fluid for a wide range of cooling and ambient temperatures. The use of this fluid can produce maximum cooling rates up to 146 W from 440 W of heat supplied to the generator at 82 °C, corresponding to a specific purchase cost ( S P C ) of £ 7.46 per W of cooling, and a coefficient of performance (COP) of 0.33 at a cooling temperature of 4 °C and an ambient of 20 °C. Overall, the proposed CAMD-DAR framework is capable of suggesting alternative organic working fluid mixtures that compete with the standard NH 3 — H 2 O pair, thanks to the lower generator temperatures ( < 150 °C) required by these fluids to activate the DAR modules, which is especially advantageous in solar-cooling applications, when non- or low-concentrating collectors are to be used.

Topics & Concepts