Ammonium Chloride (NH 4 Cl)—Ammonia (NH 3 ): Sorption Characteristics for Heat Pump Applications

George H. Atkinson, Samuel Hinmers, Robert E. Critoph and Michel van der Pal
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George H. Atkinson: Sustainable Thermal Energy Technologies (STET) Research Group, School of Engineering, The University of Warwick, Coventry CV4 7AL, UK
Samuel Hinmers: Sustainable Thermal Energy Technologies (STET) Research Group, School of Engineering, The University of Warwick, Coventry CV4 7AL, UK
Robert E. Critoph: Sustainable Thermal Energy Technologies (STET) Research Group, School of Engineering, The University of Warwick, Coventry CV4 7AL, UK
Michel van der Pal: TNO Energy Transition, Westerduinweg 3, 1755 LE Petten, The Netherlands

Energies, 2021, vol. 14, issue 18, 1-21

Abstract: In a resorption heat pump, the adsorption and desorption reaction of ammonium chloride (NH 4 Cl) with ammonia (NH 3 ) is of interest as a Low Temperature Salt (LTS). Reviewing previously published NH 4 Cl-NH 3 equilibrium lines, ammonium chloride appears to offer useable working temperatures (50–70 °C) in the 10–15 bar pressure range during the adsorption reaction, and provides beneficial working conditions for the desorption reaction, when compared with alternative LTS candidates at atmospheric pressure. The NH 4 Cl-NH 3 adsorption and desorption reactions, using a NH 4 Cl composite salt, have been evaluated under dynamic ‘real-world’ conditions in a Large Temperature Jump (LTJ) experimental testing rig; although there are concerns with mass transfer characteristics, the salt exhibits no hysteresis between the adsorption and desorption reactions, contrary to previous literature. The experimentally obtained equilibrium line values for the reaction enthalpy and entropy are 29,835 J/mol and 207 J/(mol∙K), respectively. Using a semi-empirical model, the NH 4 Cl composite salt has been successfully characterised, enabling the prediction of salt reaction behaviour. The model constants, A and n , identified are 4.5 and 5 for adsorption and 5 and 4 for desorption, with an overall salt active fraction (applicable to both reactions) of 0.98. Overall, the working equilibrium line and the dynamic performance of ammonium chloride has been investigated and the applicability of NH 4 Cl as a LTS for a resorption heat pump determined.

Keywords: adsorption; ammonia; desorption; heat; heat pump; resorption; thermochemical (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
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