The paper presents the results of an experimental study of the exothermal and endothermal effects occurring on the dissolution of potassium nitrate KNO³, ammonium nitrate NH⁴NO³, potassium hydroxide KOH and sodium hydroxide NaOH, in distilled water with natural mixing and forced stirring. It is shown that for natural mixing, NH⁴NO³ and KOH are the most appropriate working substances for cooling and heat generation respectively, while for forced stirring, NH⁴NO³ and NaOH display better performance. The optimal concentrations of the liquid solutions for achieving extreme temperatures and maximal enthalpy changes are also defined. In addition, the regression function and regression coefficients describing correlations between the total enthalpy change of the calorimetric system and the solution concentration are found, for the most suitable liquid solutions. The experimental results obtained can be used to develop generating reactors for exothermal heating and endothermal cooling for a thermochemical seasonal storage system able to store solar heat or heat from combined heat and power (CHP) units of biogas plants in summer, for heating purposes in winter, while generating cooling to support air conditioning systems in summer.

This work evaluates the performance of three configurations (V1, V2, and V3) of novel membraneless continuous-flow ultrasonic-assisted plasma-driven solution electrolysis (PDSE) reactors (CombiSonoPlasma^®) operated at near-ambient temperature and pressure, for the single-pass treatment of model hypersaline produced water (HPW) originating from the oil extraction industry, with simultaneous hydrogen co-production. The performance of the reactors was assessed based on (i) the formation of gaseous oil decomposition products (CO, CO₂, and CH₄) as indicators of crude oil destruction and (ii) hydrogen generation as a valuable energy co-product. The results demonstrate that coupling ultrasonication with PDSE provides a bidirectional synergistic effect: ultrasonication reduces the PDSE electric power demand, while PDSE operation simultaneously decreases the power consumption of the ultrasonic generator. Among the investigated configurations, along with improved oil decomposition, Reactor V2 delivered the most pronounced energy benefits, achieving reductions in electrical power consumption of 33.5% for PDSE and 44.5% for the ultrasonic generator. These findings highlight the potential of continuous-flow ultrasound-assisted PDSE as an energy-efficient process intensification strategy for oilfield HPW treatment combined with hydrogen co-generation.