A critical review on the various techniques for the thermal performance improvement of solar air heaters

ABSTRACTSolar air heating system plays an important role in industries. However, in the solar air heating system efficiency considered as important parameters of the solar thermal systems, in particular, the solar air heaters (SAHs) system efficiency is quite low because of the inherent properties of air. The inherent properties include the formation of viscous sublayer, poor heat carrying capacity, etc. The active and passive approaches have been conceded to lessen this problem. The most promising approach is passive because of hassle-free operations. The best passive approaches have been placing ribs, baffles, fins, winglets, etc., on the heat-absorbing surface of SAHs to break the viscous sublayer and promote turbulence. In the present study, various ribs and baffles profiles have been summarized so that they can be used for future research. Along with that, this paper mainly focuses on the need for solar air heating for industrial applications. The performance of SAHs in terms of thermo-hydraulic performance (THP) and thermal and effective efficiencies has been studied and compared for ribs and baffles. Use of fins on the absorber plate and different surface geometries of the absorber plate enhanced the rate of heat transfer during the sunshine hours and use of phase change material for the supply of heat energy during off-sunshine hours. As a result, maximum thermal efficiency of SAHs having ribs, baffles and fins has been found to be 81.9% but the effective efficiency is 28.3% because of large friction factor. Solar air heaters mainly gain popularity in the wide range of industrial applications.KEYWORDS: Bafflesribscorrelationsthermal and effective efficiencythermohydraulic performance Nomenclatures Ap=Area of absorber plate (m2)Cp=Specific heat of air at bulk mean temperature. J/kg KDh=Hydraulic diameter (m)e=Rib/baffle height (m)fs=Friction factor of smooth surfacefr=Friction factor of roughened surfaceH=Duct height (m)h=Heat transfer coefficient (W/m2KI=Heat insolation (W/m2)k=Thermal conductivity of air (W/mK)m=Mass flow rate of air (Kg/s)L=Duct length (m)Nus=Nusselt number of smooth surfaceNur=Nusselt number of roughened surfaceP=Pitch of roughness (m)Pr=Prandtl numberHrrp=Relative rib pitchHrbp=Relative baffle pitch(△p)=Pressure drop (Pascal)Re=Reynolds numberTa=Ambient temperature (k)Tp=Plate temperature (k)Ti=Inlet air temperature (k)To=Outlet air temperature (k)Tsa=Temperature of fluid inside duct (k)Tsun=Sun Temperature (k)W=Duct width (m)Greek Symbols=ρ=Density (kg/m3)μ=Dynamic Viscosity (N.s/m2)α=Angle of attack (0)εp=Emissivity of absorber plateεg=Emissivity of glass sheetτaab=Product of transmittance–absorptanceDisclosure statementNo potential conflict of interest was reported by the author(s).Additional informationNotes on contributorsS. A. KedarS. A. Kedar is an Assistant Professor at Mechanical Engineering from MKSSS’s Cummins College of Engineering for Women, Karvenagar Pune. He completed a Master’s degree in Energy Studies from S. P. Pune University, Pune. He had completed Ph.D (Mechanical Engineering) from Koneru Lakshmaiah Education Foundation, deemed to be University, India. His areas of interest are Solar thermal energy, Renewable Energy, Thermal Engineering. He had total 14 years teaching and 1 year industrial experience.Ganesh Vijay MoreGanesh Vijay More is currently working in PVG's College of Engineering and Technology & G. K. Pate (Wani) Institute of Management, Pune, India- 411009 in the department of Mechanical enginnering as an assistant professor. He has Ph.D. in Mechanical Engineering from Koneru Lakshmaiah Education Foundation, Deemed to be University, Vaddeswaram, India and masters from Vidya Pratishthan's Kamalnayan Bajaj Institute of Engineering and Technology, Baramati, India. He has 6 years of experience in research and academics.D. S. WatvisaveD. S. Watvisave is currently working in Cummins College of Engineeroing for Women, Pune in the department of Mechanical enginnering as an associate professor. He has PhD in thermal and fluids from IIT Bobmay and masters from COEP Tech University, Pune. He has 28 years of experience in industry, research and academics.H. M. ShindeH. M. Shinde received his degree in mechanical engineering from COEP, Tech University, Pune in 2005. This was followed by a master’s degree in mechanical engineering (automotive engineering) in 2013. Followed by a Ph.D. in mechanical engineering in 2022 from Savitribai Phule Pune University. He is currently employed as an assistant professor at the Mechanical Engineering Department of MKSSS’s Cummins College of Engineering for Women, S.P. Pune University, Pune. His research interests revolve around automotive technology and energy.