Abstract
This work has focussed on the development of an accurate method for testing and modelling the reaction kinetics involved in ammonia-salt adsorption reactions, something not achieved consistently to date. A Large Temperature Jump (LTJ) test cell has been developed for testing ammonia-salt reactions in real machine conditions. A Large Temperature Jump (LTJ) test cell has been developed for testing ammonia-salt reactions in real machine conditions. This was used to validate a new approach to modelling the behaviour and simulate the performance of chemisorption machines. A derivation of the heat transfer and thermodynamic equations are presented, and a finite difference model described which has been validated for the adsorption and desorption reactions of ammonia into halide salts within a porous matrix. The model is implemented in a MATLAB® program. Large Temperature Jump (LTJ) tests have been conducted on manganese chloride and barium chloride to validate the model and to identify the physical parameters which characterise the dynamic performance of the sorbent. The manganese chloride and barium chloride were impregnated in expanded natural graphite (ENG) (SGL SIGRATHERM®) board. The ENG board gave rise to practicable samples (31.5 mm OD ø over ½” tube) undergoing a desorption reaction in under 250 seconds with the fluid temperature 15°C above the equilibrium temperature, an order of magnitude faster than observed elsewhere. A new test method has been developed enabling an accurate single heat of reaction to be identified due to reduced hysteresis, which is reported for barium and manganese chloride. The model has been validated using experimental data from LTJ tests of two geometric configurations in radial heat transfer: discs heated/cooled from the outside radius (‘tube-side’) and annuli heated from the inner radius (‘shell-side’). The empirical data obtained is a milestone towards designed and optimised salt generators.
Highlights
The chemisorption of ammonia into halide salts has been studied over many years: it was first observed by Faraday who recognised its potential for generating a heating or cooling effect (Faraday, 1823); more recently it garnered attention in the ‘80s and ‘90s, primarily by Spinner (Spinner, 1988), and many others (Goetz et al, 1993; Lebrun and Spinner, 1990b; Mazet and Spinner, 1994)
The experimental results show the reaction rate is limited by the rate of heat transfer, characterised by a linear pressure change during the adsorption and desorption reactions
The wall heat transfer resistance modelled by an ammonia gas-filled gap has the greatest effect on rate, illustrating how it is limited by rate of heat transfer
Summary
The chemisorption of ammonia into halide salts has been studied over many years: it was first observed by Faraday who recognised its potential for generating a heating or cooling effect (Faraday, 1823); more recently it garnered attention in the ‘80s and ‘90s, primarily by Spinner (Spinner, 1988), and many others (Goetz et al, 1993; Lebrun and Spinner, 1990b; Mazet and Spinner, 1994). Cycles using chemisorption can be applied to refrigeration, heat pumping, and thermal transformation and may either use a single salt in a reactor together with a system for evaporating and condensing the refrigerant, or a resorption cycle in which the refrigerant is adsorbed or desorbed between two salts. The work reported here, which is mainly concerned with two-salt resorption cycles for heat pumping and thermal transformation applications, aims to prove that with careful salt-pairing selection (for the High Temperature Salt (HTS) and Low Temperature Salt (LTS)), coupled with an inherent understanding of the hysteresis phenomena and the final-use application, the dynamic performance of halide-salts can be predicted and utilised effectively for prototype systems One of the main conclusions related to the material-salt combination is that the “hysteresis of sorbent salts [...] can significantly affect the performance or even viability of the chemisorption system.” The work reported here, which is mainly concerned with two-salt resorption cycles for heat pumping and thermal transformation applications, aims to prove that with careful salt-pairing selection (for the High Temperature Salt (HTS) and Low Temperature Salt (LTS)), coupled with an inherent understanding of the hysteresis phenomena and the final-use application, the dynamic performance of halide-salts can be predicted and utilised effectively for prototype systems
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
