Analysis of chemical heat pumps (CHPS): Basic concepts and numerical model description

Thermochemical phenomena occurring during the reaction between a gas and solid porous media (thermochemical materials) have been modelled. The practical application envisaged is the use of these thermochemical materials in chemical heat pumps (CHP) to produce both heat and cold. In the synthesis part of the cycle, a gas (e.g. ammonia) at a moderate pressure reacts uniformly with the salt (e.g. MnCl(2) . 2NH(3)) component of a thermochemical material. Subsequently the ammoniated salt (MnCl(2) . 6NH(3)) is decomposed to release the gas at an elevated pressure. A detailed numerical model is presented for the decomposition phase of the CHP reaction cycle. The numerical simulation of a CHP reactor during a synthesis-decomposition reaction cycle has several specific requirements. The phase change problem involving discontinuities in the thermal properties of the two different salts at their reaction interface needs special care for numerical solution. In this paper, the source-based method which is a fixed grid enthalpy approach, was used. The solution of the partial differential equation was obtained, using a control volume approach around each spacial node. This thermal study examined configurations that had different reactor diameters, and other parameters that influenced heat transfer. Typical results included conversions, power generated as a function of reactor diameter and time-on-stream, required heat exchange area, and heat losses. (C) 1997 Published by Elsevier Science Ltd.