Modelling and development of a generator for a domestic gas-fired carbon-ammonia adsorption heat pump

Current development of ammonia-carbon gas fired heat pumps at the University of Warwick uses shell and tube adsorption generators with over 1700 water tubes of 1.2 mm outer diameter on a 3 mm pitch filled with vibrated carbon grains and powder. This geometry is not optimised and a dynamic simulation program has been written to determine how far from optimal the design is and also whether an alternative design of finned tubes offer advantages. Three alternative carbon composites that use Expanded Natural Graphite (ENG), silane and lignin binders have been developed and tested to characterise their thermophysical properties so that they can be included in the simulations in order to improve the thermal transfer in the generators. Results presented show that the shell and tube geometry is close to optimal and that the best performing material is the lignin+Fcarbon composite. Other type of geometry, a finned tube design, was modelled as it might offer improvements in performance and help reduce the complexity and cost of the manufacturing technique. Results show that for the same tube radius, the finned tube generator needs 7 times fewer tubes in order to achieve similar performances. Crown Copyright (C) 2017 Published by Elsevier Ltd.