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ABSTRACT
The heat transfer coefficient of solar air heaters (SAHs) is limited due to the active viscous laminar sub-layer on the absorber’s surface. Artificial roughness is introduced to destroy the viscous sub-layer formed underside of the absorber surface of the SAH duct. An experimental investigation was performed upon a novel roughness geometry multi v-pattern convex protrusion planted on an absorber to analyze Nu and f augmentation of rough ducts compared to smooth ones. The investigation was conducted for Re range 2500 -18,500, relative protrusion width (Wd/Wv) 1, 2, 3, 4, and 5, relative protrusion height (e/Dh) = 0.03, relative protrusion pitch (p/e) = 10, relative print diameter (e/d) = 0.5, α = 60º, and W/H = 12. The investigation is conducted with the objective to achieve the optimum roughness geometrical parameter amongst investigated values. Results for thermal and thermohydraulic performance parameters have also been worked out and reported. The key findings in the present work were compared with single and multi v roughness in rib shapes. The findings were conclusive and worth evaluating. The maximum Nusselt number and friction is obtained corresponding to Wd/Wv = 4 and 5, respectively. The maximum thermal efficiency is 66% obtained at Wd/Wv = 4, p/e = 10, and e/Dh = 0.03. The maximum THPP is observed to be 3.29 at Re = 13000.
Nomenclature
| Parameters | = | Symbol |
| Length of SAH duct (mm) | = | L |
| Width of the SAH duct(mm) | = | W |
| Height of the SAH duct (mm) | = | H |
| Area of cross-section (mm2) | = | A |
| Collector Area (m2) | = | Ac |
| Throat area of orifice meter | = | Ao |
| Hydraulic diameter of SAH duct | = | Dh |
| Protrusion height | = | e |
| Relative protrusion height | = | e/Dh |
| Protrusion pitch | = | p |
| Relative protrusion pitch | = | p/e |
| Roughness to protrusion diameter ratio | = | e/d |
| Ratio of Duct width to single v-protrusion | = | Wd/Wv |
| Reynolds number | = | Re |
| Nusselt number for roughened duct | = | Nur |
| Nusselt number for smooth duct | = | Nus |
| Friction factor for roughened duct | = | fs |
| Friction factor for smooth duct | = | fr |
| Mass flow rate | = | ṁ |
| Heat transfer coefficient | = | h |
| Useful heat gain | = | Qu |
| Pressure drop across orifice meter | = | ∆Po |
| Pressure drop across test section | = | ∆Pd |
| Density of air | = | ρ |
| Specific heat of air | = | Cp |
| Orifice diameter (D2)/pipe inner diameter (D1) | = | β |
| Fluid temperature at the inlet of test duct | = | Tfi |
| Fluid temperature at the exit of test duct | = | Tfo |
| Mean plate temperature | = | Tpm |
| Mean fluid temperature | = | Tfm |
| Solar radiation intensity (W/m2) | = | I |
| Solar air heater | = | SAH |
Disclosure statement
No potential conflict of interest was reported by the author.
Additional information
Notes on contributors
Vikash Kumar
Dr. Vikash Kumar is currently working as an Assistant Professor in the Department of Mechanical Engineering, MANIT Bhopal, India. He has completed his research on the topic “Thermal Performance Investigation of Three Sides Concave Dimple Shape Roughened Solar Air Heater” from National Institute of Technology, Jamshedpur. He received his Doctor of Philosophy from the Department of Mechanical Engineering at the National Institute of Technology, Jamshedpur. He did his Masters from IIT (ISM) Dhanbad in the area of Fuel and Combustion from the Department of Fuel Engineering. He completed his UG from Meenakshi Academy of Higher Education and Research (MAHER) in the Department of Mechanical Engineering. His area of interest includes: Mechanical/Thermal Engineering, Renewable Energy, Solar Energy, Heat Transfer, Thermodynamics, Optimization Techniques, Artificial Neural Network, Computational Methods, Flow in Multi Channels, Nanoparticles, etc. He has guided over 10 UG projects, 07 M. Tech. and currently 04 students are doing PhD under his guidance. He is having over 09 years’ experience in teaching, administration and research.