Multiphase Flows in Passive Waste-heat-driven Absorption Heat Pumps

Alexander Rattner, Georgia Institute of Technology

Over 90 percent of U.S. electricity is generated by converting high-grade chemical and thermal energy to work at typically 30 to 40 percent thermal efficiency. Thus, even at low coefficients of performance, a large fraction of national, and potentially worldwide, cooling and heating needs could be satisfied by thermally driven refrigeration and heat pump systems powered by such abundant waste- and low-grade-heat. Such applications, combined with the environmental benefits of the employed low ODP and GWP working fluids, have led to renewed interest in absorption thermal systems. The diffusion absorption refrigeration (DAR) cycle is an attractive technology for such applications, especially in remote locations, since it can be driven solely by thermal energy without any mechanical input from a pump or compressor. However, design of DAR systems has historically been a challenging and iterative process since the internal flows must be fully passively driven and incorporate complex flow phenomena. In this effort, open-source multiphase VOF CFD software (OpenFOAMĀ®) is being extended to enable detailed investigation of such flows. A key objective is to model the "bubble pump" component, which requires development and implementation of algorithms for coupled heat and mass transfer, fast, consistent liquid-vapor equilibrium properties, realistic liquid-vapor-solid boundary conditions, phase change, and absorption phenomena. By conducting and analyzing large parametric studies of these flows on HPC resources, practical engineering tools and guidelines will be developed to streamline the DAR design process. Ultimately this effort will enable wide-scale implementation of fully thermally driven heat pump technology to improve national energy efficiency and help stem continued demand for additional energy resources.

Abstract Author(s): Alexander RattnerSrinivas Garimella