An Aqueous CaCl2 Solution in the Condenser/Evaporator Instead of Pure Water: Application for the New Adsorptive Cycle “Heat from Cold”

Abstract

This paper addresses the analysis of the applicability of water as a working fluid for the new adsorptive heat transformation (AHT) cycle "Heat from Cold" (HeCol). The cycle proposed for cold countries operates at the ambient temperature below 0 °C. In this work, an aqueous solution of calcium chloride is proposed instead of liquid water to prevent the ice formation in the evaporator and condenser. The proposed water-based cycle is compared with the common methanol-based HeCol one in terms of the specific useful heat generated per cycle. The effect of the CaCl2 solution on the cycle boundary pressures and its useful heat is studied both theoretically and experimentally. This approach can be extended to other adsorptive heat transformation cycles working at an evaporator or condenser temperature below 0 °C.

Adsorptive Systems for Heat Transformation and Heat Storage Applications

“…To prevent ice formation in the evaporator/condenser and expand the temperature range for water application below 0 • C, the authors of [12] suggested adding ethylene glycol to water. In this SI, Girnik et al [13] proposed to use an aqueous salt solution instead of pure water. The solution has a lower freezing point and higher evaporation heat, both being profitable from the thermodynamic point of view.…”

Thermodynamic Analysis of Working Fluids for a New “Heat from Cold” Cycle

“…The comparative analysis was performed in [ 12 ] for the typical HeCol cycle with ( T L / T M / T H = −20/20/40 °C with methanol and a eutectic aqueous solution of CaCl 2 as a liquid in the condenser. The composites (21 wt.%)LiCl/(silica gel) and (33 wt.%)CaCl 2 /(silica gel) were used as sorbents of both water and methanol vapour.…”

“…Thus, the substitution of methanol with water as adsorptive can help to increase the useful heat; however, at the expense of lower heating power as the water vapour pressure is lower than for methanol. More details on applying water as adsorptive in typical HeCol cycles can be found elsewhere [ 12 ].…”

“…It is very promising to use water vapour as adsorptive in the HeCol cycle, but special measures should be made to avoid ice formation in the condenser. Two ways have been proposed and tested in the literature: (i) to mix pure water with ethylene glycol as an anti-freezing agent [33], and (ii) to use an aqueous salt solution instead of pure water [12,34]. One more way to reduce the melting temperature could be confinement of water [35] or an aqueous salt solution [36] into a host matrix with tiny pores.…”