Design and manufacture of a proof-of-concept resorption heat pump using ammonia-salt chemisorption reactions

• Published in: Cleaner Energy Systems 2023-12, Vol.6, p.100082, Article 100082
• Main Authors: Atkinson, G.H., Metcalf, S.J., Critoph, R.E., Shire, G.S.F., van der Pal, M.
• Format: Article
• Language: English
• Subjects: Ammonia; composite matrix; experimental; halide salts; heat pump; resorption, thermochemical
• ISSN: 2772-7831; 2772-7831
• DOI: 10.1016/j.cles.2023.100082

•Hysteresis effects are identified in sodium bromide-ammonia sorption reactions•A mass-based finite difference model correctly predicts salt-ammonia reactions•The design and manufacture of a novel proof-of-concept sorption system is presented Using the Large Temperature Jump (LTJ) experimental technique, alongside a review of the literature, sodium bromide (NaBr) and manganese chloride (MnCl2) have been identified as a suitable working pair with ammonia refrigerant for a proof-of-concept resorption heat pump system. LTJ tests using a tube-side and shell-side unit cell reactor (sorption heat exchanger), show that the experimentally obtained equilibrium lines for adsorption and desorption of sodium bromide are: ΔHADS = 30102.5 J/mol; ΔSADS = 207.7 J/(mol∙K); ΔHDES = 30216.4 J/mol; and ΔSDES = 206.8 J/(mol∙K). Using a semi-empirical model, the NaBr composite salt (salt impregnated in expanded natural graphite (ENG)) has been characterised for use as a low temperature salt in a resorption heat pump, with manganese chloride as the high-temperature salt. The model constants, A and n, for adsorption are 1 and 3, and for desorption are 5 and 4 respectively for NaBr. Manganese chloride data has been previously reported (Hinmers et al., 2022). With an appreciation of the reaction dynamics and behaviour of the NaBr and MnCl2 composite salts, a proof-of-concept resorption system has been designed and manufactured. The reactor design, alongside the overall experimental rig design (including data acquisition system) is reported. Initial filling and flushing tests show the success of the data acquisition and control system, and thus the overall suitability of the proof of-concept system for investigations into the coupled nature of ammonia salt reactions for a resorption heat pump application. [Display omitted]