Investigations on a bubble-pump-aided diffusion absorption heat transformer using deep eutectic solvent for harvesting and upgrading thermal energy

Abstract

Absorption heat transformer shows promising potential in thermal energy harvesting and upgrading, while the corrosion and crystallization risks of existing working substance restrict its promotion. A bubble-pump-aided diffusion absorption heat transformer using deep eutectic solvent is proposed in this study. The influence of operating parameters of bubble pump is analyzed, indicating that motive head should be as large as possible while diffusion gas flow rate has the optimum. Because of worse pumping ability, deep eutectic solvent has narrower normal operating range compared with LiBr, but the optimal energy performance shows little difference. Ethaline exhibits the best performance among deep eutectic solvents. With heat source of 90 ℃, COP and ηEX of 0.401 and 48.9% can be reached to output thermal energy of 120 ℃, leading to a CO2 emission reduction of 20.1 Mt per year. Parametric analysis demonstrates that single-stage diffusion absorption heat transformer using ethaline can realize temperature lift up to 50 ℃, which delivers comparative performance against existing AHT systems, except for operating range. Approaches are discussed to enlarge its operating range and further improve its performance as well. The results in this paper contribute to: 1) providing a promising absorption heat transformer configuration for large-scale and long-term use; 2) quantitatively demonstrating the prospect of deep eutectic solvent; 3) enlightening insights in the recovery of industrial waste heat, the upgrading of thermal energy and the reduction of CO2 emission.