Performance evaluation of an aqueous sodium hydroxide based thermochemical storage system: Energy, exergy and entransy analysis and a novel entransy based optimisation approach for storage systems

• Membrane based microchannel design evaluation for NaOH-H 2 O pair. • Critical performance factor identification through thermodynamic analysis. • Design optimisation through an alternative approach for mass transfer entransy. • Novel entransy based approach to balance storage density and discharge power. • Over 60 % of maximum storage density and discharge power with optimised parameters. To contribute towards the adoption of energy storage technologies for peak demand tackling and environmental concerns, the present study explores an aqueous sodium hydroxide solution (NaOH) based thermochemical storage design. Membrane-based microchannel heat exchanger design, which is relatively underexplored for storage systems is considered for absorption performance evaluation. The performance is analysed for various geometric and operational parameters through energy, exergy and entransy evaluations. While the energy and exergy analyses help to assess the impact of various design and operational parameters, a novel entransy based approach is proposed to assist towards the optimal selection of the heat exchanger length and solution flow rate. The cumulative heat and mass transfer entransy dissipations are evaluated as the external entransy while the solution storage potential is evaluated as the internal entransy. Such an entransy characterisation along with a new parameter called entransy capacitance, aid to address the limitation of the existing entransy and exergy based approaches in balancing the storage density and discharge power components of thermochemical storage systems. With the proposed approach, optimized storage density values exceeding 60 % of their respective theoretical maximum values are observed. For an optimised solution flow rate of 70 g/min and a typical space heating temperature operating condition, the NaOH-H 2 O pair has shown potential with the discharge power and storage density values exceeding 1.1 kW and 1450 MJ/m 3 respectively. With the proposed entransy approach expected to advance research on thermal storage system optimization, the findings of this study aim to facilitate the development of compact and cost-effective storage systems.