https://orcid.org/0000-0002-6857-6925
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ABSTRACT
This article presents the heat transfer augmentation in a solar air heater (SAH) using arc-shaped ribs with multiple gaps. Multiple gaps in arc-shaped ribs are used to enhance the heat transfer by interrupting the growth of the boundary layer. Thermal performance analysis of a SAH has been carried out experimentally for the roughness parameters: number of gaps (Ng) ranging from 2 to 5 and flow parameters; Reynolds number (Re) ranging from 3000 to 18000 at a constant heat flux of 1000 W/m2. The data obtained from the experimental investigation are validated and compared with the smooth duct under similar conditions. For roughened SAH duct, the heat transfer and pressure drop are found to be 274% and 169% higher than that for smooth SAH duct at Ng = 3. Thermo-hydraulic performance is determined for considered parameters and maximum value is observed to be 2.75.
Disclosure statement
There is no conflict of interest by the authors.
Nomenclature
| D | = | Duct hydraulic diameter, mm |
| e | = | Rib height, mm |
| h | = | Heat transfer coefficient, W/m2-K |
| H | = | Duct depth, mm |
| ∆P | = | Pressure drop in the duct, Pa |
| q | = | Heat flux, W/m2 |
| Tpm | = | Mean temperature of absorber plate, K |
| Tfm | = | Mean temperature of fluid, K |
| W | = | Duct width, mm |
Dimensionless parameter
| e/D | = | Relative roughness height |
| f | = | Friction factor |
| g/e | = | Relative gap width |
| Nu | = | Nusselt number |
| P/e | = | Relative roughness pitch |
| Re | = | Reynolds number |
| W/H | = | Duct aspect ratio |
Greek symbols
| α | = | Arc angle, ° |
| ρ | = | Density of air, kg/m3 |
Abbreviations
| SAH | = | Solar air heater |
| THP | = | Thermo-hydraulic performance |
Subscripts
| r | = | Roughened |
| s | = | Smooth |