Enhancement of heat transfer in a combined solar air heating and water heater system

This paper presents an innovative hybrid system that serves the dual purpose of heating air and water simultaneously. To achieve an enhancement in thermal performance, the rectangular aluminum duct’s inner surface in the air heater and the copper absorber plate in the water heater was roughened using a pressurized shot-blasting technique. Furthermore, the convective heat transfer performance was enhanced using solar glycol (SG) with multi-walled carbon nanotube (MWCNT)-based nanofluids. The performance of this novel combined system for a total collector area of 2 m2 was investigated experimentally. The SG/MWCNT-based nanofluid was prepared by adding a surfactant (i.e., gum arabic) at concentrations of 0.1 and 0.2 vol %. Based on the results of the experimental investigation, it was inferred that the collector efficiency is directly proportional to the volume percentage of the nanomaterials. An average temperature difference of 14.54 °C was achieved in the solar collector, whereas a maximum temperature of 18.32 °C was obtained for 0.2 vol % of MWCNT at a mass flow rate of 0.01 kg/s. Moreover, the maximum thermal efficiency of 51.03% was attained for a 0.2 vol % SG/MWCNT-based nanofluid at a mass flow rate of 0.01 kg/s. •A novel dual-purpose solar collector (DPSC) was developed.•The performance of the shot-blasted absorber surface with nanofluids was examined.•SG/MWCNT-based nanofluid increases system performance significantly.•Increasing nanofluid concentration increases the pumping power and friction factor.•The maximum increase in the rate of useful energy was 669 W for the studied condition.