Emerging sorption pairs for heat pump applications: an overview

Abstract

The research efforts to find an alternative system for the cooling/heating application have been intensified worldwide since the imposition of international restrictions on production and use of refrigerants accountable for ODP and GWP. Nowadays, the demand for the cooling/heating system is increased also due to safeguarding the adverse environmental effect which results in additional consumption of electrical energy and ecological problem. The use of adsorption system is considering as a promising alternative for the last few decades. The low heat and mass transfer coefficient of the adsorbent material is the main bottleneck of the adsorption cooling/heating system and resulting in large size and low performance. To make the system commercially competitive with the conventional system, high-performance refrigerant/adsorbent pairs are required. In this review, the favorable achievement in adsorbent development in terms of porous properties and their interaction with natural refrigerants is focused. Current application of different working pairs and their future prospect with special reference to their utilization are studied. Future research direction of adsorption working pairs is also analyzed. Keywords Adsorbent · Coefficient of performance · Heat pump · Synthesis Nomenclature A 0 ~ A 3 Adjustable parameter (−) B 0 ~ B 3 Adjustable parameter (−) b 0 Equilibrium constant (kPa −1 or MPa −1) c p,Ad Specific heat capacity of adsorbent (J g −1 K −1) c p,ref Specific heat capacity of refrigerant (J g −1 K −1) E Adsorption characteristic energy (kJ mol −1) t Heterogeneity constant in Tóth equation (-) h f Fluid enthalpy (kJ kg −1) h fg Latent heat of vaporization (kJ kg −1) k Freundlich constant (-) n Exponent of D-A equation (-) P Pressure (kPa or MPa) P c Pressure at critical point (kPa or MPa) P s Saturation pressure (kPa or MPa) Q Heat energy (J) Q st Isosteric heat of adsorption (kJ kg −1) q Volumetric adsorption uptake (cm 3 g −1) q 0 Maximum volumetric adsorption capacity (cm 3 g −1) R Gas constant (J mol −1 K −1) T Temperature (°C or K) T C Temperature at critical point (°C or K) TPh Preheating temperature (°C) V m Molar volume (cm 3 g −1) v m Pore volume of the adsorbent (cm 3 g −1) V t Specific volume of liquid carbon dioxide (cm 3 g −1) W Equilibrium uptake (kg kg −1) W 0 Maximum equilibrium uptake (kg kg −1) z Constant for pseudo saturated vapor pressure (−) Greek symbols Thermal diffusivity (m 2 s −1) * Thermal expansion of the adsorbed gas (K −1) Density (kg m −3) ΔW Effective uptake (-)