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ABSTRACT
In this work, an experimental investigation on heat and fluid flow characteristics of artificially roughened solar air heater duct has been carried out. The roughness and operating parameters covered a range of Reynolds number (Re) from 2000 to 20000, relative roughness pitch (P/e) from 15 to 30, relative rib length (r/g) from 0.4 to 1.0, and relative rib pitch (Pr/P) from 0.2 to 0.8. Other parameters, i.e., relative roughness height (e/D), angle of attack (α), and relative roughness gap are kept constant. Results show that the considerable enhancement in Nusselt number and Thermo-hydraulic performance has been obtained with an increase in friction factor using roughened surface.
Nomenclature
| Ap | = | Area of absorber plate, m2 |
| Ao | = | Throat area orifice plate, m2 |
| Cp | = | Specific heat of air, J/kg-k |
| D | = | Hydraulic diameter of duct, m |
| e | = | Protrusion height, m |
| g | = | Rib gap, m |
| H | = | Duct height, m |
| h | = | Heat transfer coefficient, W/m2-K |
| K | = | Thermal conductivity of air, W/m-K |
| L | = | Length of test section, m |
| ṁ | = | Mass flow rate of air, kg/s |
| P | = | Roughness pitch, m |
| Pr | = | Rib pitch |
| ΔPd | = | Pressure drop across test section, Pa |
| ΔPo | = | Pressure drop across orifice plate, Pa |
| Qu | = | Useful heat gain, W |
| r | = | Rib length, m |
| Tai | = | Air temperature at inlet of test section, K |
| Tao | = | Air temperature at outlet of test section, K |
| Tam | = | Air mean temperature, K |
| Tpm | = | Plate mean temperature, K |
| W | = | Duct width, m |
| V | = | Air velocity, m/s |
Dimensionless parameters/numbers
| d/D | = | Relative print diameter |
| e/D | = | Relative roughness height |
| f | = | Friction factor for roughened duct |
| fs | = | Friction factor for smooth duct |
| g/e | = | Relative rib gap |
| L/e | = | Relative longway length between protrusions |
| Nu | = | Nusselt number for roughened duct |
| Nus | = | Nusselt number for smooth duct |
| P/e | = | Relative roughness pitch |
| Pr/P | = | Relative rib pitch |
| r/g | = | Relative rib length |
| Re | = | Reynolds number |
| Pr | = | Prandtl number |
| S/e | = | Relative shortway length between protrusions |
Greek symbols
| ρ | = | Density of air, kg/m3 |
| ν | = | Kinematics viscosity, m2/s |
| α | = | Angle of attack, ° (degree) |
| βdr | = | Diameter ratio of orifice plate, dimensionless |
Acknowledgments
The first author (Chandra Prakash) thanks to Alternate Hydro Energy Centre and Quality Improvement program (QIP) Centre, IIT Roorkee, India for providing research and experimentation facilities and All India council for Technical Education (AICTE), Government of India for providing financial assistance in the form of research fellowship. The author also thanks to B. T. Kumaon Institute of Technology, Dwarahat, Uttarakhand, India for financially sponsoring him to pursue doctoral study.