Optimal fluids for adsorptive cooling and heating

Abstract

The search for optimal fluid/adsorbent working pairs in adsorption heat transformers is featured by trial and error method. In the last decades this approach has produced relevant progresses especially resulted in new advanced adsorption materials. On the refrigerant fluid side water, ammonia, methanol and ethanol still seem to be the only viable options. This work aims to explain the reason of that and the requirement that a refrigerant fluid must fulfil in order to be considered as promising for adsorptive cooling and heating. A thermodynamic framework is developed that merges the corresponding states principle with the characteristic curve of adsorption. Finally the framework is applied to assess the theoretical coefficient of performance of 258 fluids on 16 adsorption materials belonging to activated carbons, silica gels and zeolites, by avoiding in this way blind search strategy of the optimal working pair. Furthermore, the approach is used also to identify more generally the refrigerant thermodynamic properties for maximum performance. Fluid critical temperature is often the chief property enabling higher performance, although not always all the adsorption materials share the same sensitivity to the same thermodynamic properties.

Insights into the water adsorption mechanism in the chemically stable zirconium-based MOF DUT-67 – a prospective material for adsorption-driven heat transformations

“…[4][5][6][7] Various working uids are considered ranging from ammonia, hydrocarbons, uorinated hydrocarbons, alcohols to water. 8,9 Their coefficient of performance is strongly dependent on their critical temperature and density. The desired material should feature high adsorption capacity with adsorption steps at desired relative pressure, which is hard to achieve with established classical porous materials.…”

Ammonia/Ethanol Mixture for Adsorption Refrigeration

“…As extensively reported in the literature, the most significant physical properties in the choice of a refrigerant are the latent heat of vaporization (λ vap ) and the saturation pressure (P sat ). Table 1 reports the relevant physical properties of the most common fluids used for refrigeration at 283 K. In a recent study by Santori and Di Santis [9], performances of the thermodynamic cycle were also related to the fluid critical temperature (T cr ), critical pressure (P cr ), critical density (ρ cr ), acentric factor (ω), and molar heat capacity of ideal gas at critical point (c p 0 ,cr ). This approach confirmed the advantage of using traditional fluids for adsorption refrigeration and showed that other fluids, such as isopropanol, have promising properties, anticipating values of coefficient of performance (COP) not far from ethanol and methanol (Table 1).…”

Supported ionic liquid water sorbent for high throughput desalination and drying

“…In all cases sorption indicates the presence of a bond between the sorbent and the sorbate which in many applications is water. This is the case of sorption drying and desalination but also of many closed systems such as cooling, heating and heat storage where water can enable performance which rule out other fluids [16]. Many water sorbents have been proposed over the last decades.…”