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ABSTRACT
Solar Air Heaters (SAHs) are widely used to harness solar energy for various heating applications. Recent research aims to improve the ability to capture maximum irradiation, addressing the weather-dependent and intermittent nature of solar energy availability. The incorporation of Phase Change Materials (PCMs) in SAHs can improve the capacity to absorb the irradiation due to their high latent storage capacity. However, conventional PCMs often exhibit low thermal conductivity. Various enhancement techniques can improve the thermal conductivity of pure PCMs and enhance the system’s performance. This review article explores single-pass and double-pass SAHs with Integrated Collector PCM Storage (IC-PCMS) systems and various techniques to enhance the thermal conductivity of PCMs. The findings are based on the detailed analysis of systems and provide quantitative results showing the performance improvements of PCM-integrated SAHs. The inclusion of PCM not only maximizes irradiation capture but also extends the duration of hot air availability during periods of uneven irradiation. Further, carbon-based nanocomposites and metal foams have shown the most significant improvements in the thermal conductivity of PCMs and thus enhance the system’s performance. Future research should focus on optimization and economic analysis to commercialize these systems for various thermal applications.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Nomenclature
| SAH | = | Solar Air Heater |
| IEA | = | International energy agency |
| SPSAH | = | Single-pass solar air heater |
| DPSAH | = | Double-pass solar air heater |
| LHS | = | Latent heat storage |
| SHS | = | Sensible heat storage |
| TCS | = | Thermochemical storage |
| TES | = | Thermal energy storage |
| LHSU | = | Latent heat storage unit |
| IC-PCMS | = | Integrated collector PCM-based storage system |
| NIC-PCMS | = | Non-Integrated collector PCM-based storage systems |
| PCM | = | Phase change material |
| CPCM | = | Composite phase change material |
| = | Volume of PCP | |
| = | Heat transfer area of PCM | |
| PW | = | Paraffin wax |
| PV | = | Photovoltaic |
| HTF | = | Heat Transfer Flow |
| CFD | = | Computational fluid dynamics |
| GCP | = | Granular carbon powder |
| = | Useful heat gain by air | |
| = | Total Solar Irradiation (W/m2) | |
| = | Area of absorber plate(m2) | |
| = | Heat removal factor | |
| = | Heat storage by PCM | |
| = | Total thermal energy (MJ) | |
| = | Charging thermal energy (MJ) | |
| = | Discharging thermal energy (MJ) | |
| = | Mass flow rate of air (Kg/s) | |
| = | Mass flow rate of PCM (Kg/s) | |
| = | Mass of PCM (kg) | |
| = | Inlet temperature of air (K) | |
| = | Outlet temperature of air (K) | |
| = | Ambient temperature (K) | |
| = | Melting temperature of PCM (K) | |
| = | Lower melting temperature (K) | |
| = | Higher melting temperature (K) | |
| = | Final temperature of PCM (K) | |
| = | Reference temperature (K) | |
| = | Molten fraction | |
| = | Specific enthalpy (kJ/kg) | |
| L | = | Latent heat/mass (J/kg) |
| = | Latent heat of nano composite PCM (J/kg) | |
| = | Mushy zone constant | |
| = | Specific heat of air (kJ/kgK) | |
| = | Specific heat of PCM (kJ/kgK) | |
| = | Specific heat of solid PCM (kJ/kgK) | |
| = | Specific heat of liquid PCM (kJ/kgK) | |
| = | Specific heat of nanoparticles (kJ/kgK) | |
| = | Specific heat of nano composite PCM (kJ/kgK) | |
| = | Thermal conductivity of nanocomposite PCM (W/mK) | |
| = | Thermal conductivity of PCM (W/mK) | |
| = | Thermal conductivity of nanoparticles (W/mK) | |
| = | Velocity vector | |
| = | Source term correspond to mushy zone | |
| Subscript | = | |
| a | = | ambient |
| i | = | Inlet |
| o | = | Outlet |
| u | = | useful |
| t | = | Total |
| s | = | solid |
| l | = | liquid |
| n | = | nanoparticle |
| th | = | Thermal |
| ref | = | reference |
| Greek Symbols | = | |
| = | Absorptivity | |
| = | Transmittance | |
| = | Concentration by Wt% | |
| λ | = | Liquid fraction of PCM |
| = | Coefficient of thermal expansion | |
| = | Thermal efficiency | |
| = | Total efficiency | |
| = | Storage efficiency | |
| = | Discharging efficiency | |
| = | Density of PCM (Kg/m3) | |
| = | Density of nanoparticles (Kg/m3) | |
| = | Density of nanocomposite PCM (Kg/m3) | |
| = | Dynamic viscosity of PCM (Kg/ms) | |
| = | Dynamic viscosity of nanocomposite PCM (Kg/ms) |
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