Thermal performance assessment of endothermic salts for next-generation cooling systems

Growing global cooling demand and the limitations of conventional electricity-driven cooling systems highlight the need for sustainable, low-energy alternatives. Endothermic salts offer an attractive thermochemical pathway for cooling due to their high heat of dissolution, reusability, and compatibility with low-grade heat regeneration. This study experimentally evaluates the potential of urea ((NH₂)₂CO), potassium nitrate (KNO₃), and ammonium chloride (NH₄Cl) for use in endothermic cooling applications. Experiments were conducted to determine optimal salt-water ratios (x), quantify cooling performances over 100 regeneration cycles, evaluate pH levels during regeneration cycles, analyze the effect of mixing, assess deionized (DI) water, tap water, and seawater as solvents, measure salt recovery ratios, determine moisture-induced degradation of salt cooling potentials, and finally estimate regeneration energy requirements. The acquired results show that urea achieves maximum cooling at x = 0.7, whereas KNO₃ and NH₄Cl peak at x = 0.3 due to solubility limits. Higher solvent temperatures enhance cooling for all salts, especially KNO₃. All salts demonstrate excellent thermochemical durability across 100 cycles with no measurable loss in cooling capacity. pH values of the solutions remain nearly stable for urea and NH₄Cl, while KNO₃ shows a mild shift without chemical degradation. Mixing substantially improves dissolution-driven cooling, most significantly for diffusion-limited salts (such as KNO₃ and NH₄Cl). DI and tap water maintain stable performance, whereas seawater causes progressive deterioration due to high ionic strength. Residual moisture reduces cooling capacity, most prominently for urea. All salts exhibit high recovery ratios (>0.98). Overall, this work provides actionable performance insights that directly support the practical implementation of endothermic salt-based cooling technologies.