TY - JOUR N2 - Flow mechanism under roughened solar air heater is quite complex. This paper is an effort towards determining the governing equations for heat transfer and friction factor for inclined spherical balls roughened ducts. With the availability of these equations, it is easier to predict the thermal and thermohydraulic performance of such roughened solar air heaters. The governing equations are derived based on the experimental data generated under actual outdoor condition at the test rig designed and fabricated at the terrace of the Mechanical Engineering Department, the National Institute of Technology Jamshedpur in India, in terms of roughness and flow parameters. Maximum augmentation in Nusselt number and friction factor for varying relative roughness pitch, relative roughness height, spherical ball height to diameter ratio, and angle of attack was respectively found to be of the order of 2.1 to 3.54 times, 1.87 to 3.21 times, 2.89 to 3.27 times and 1.74 to 3.56 times for Nusselt number and 0.84 to 1.79 times, 1.46 to 1.91 times, 1.67 to 2.34 times and 1.21 to 2.67 times for friction factor in comparison to non-roughened duct. The optimum roughness parameters under present investigation have been found. L1 - http://www.czasopisma.pan.pl/Content/116180/PDF/01_paper.pdf L2 - http://www.czasopisma.pan.pl/Content/116180 PY - 2020 IS - No 2 EP - 34 DO - 10.24425/ather.2020.132958 KW - renewable energy KW - spherical ball KW - Relative roughness pitch KW - Relative rough-ness height KW - Nusselt number KW - Friction factor KW - Angle of attack A1 - Murmu, Ramesh A1 - Kumar, Parmanand A1 - Singh, Hari N. PB - The Committee of Thermodynamics and Combustion of the Polish Academy of Sciences and The Institute of Fluid-Flow Machinery Polish Academy of Sciences VL - vol. 41 DA - 2020.06.25 T1 - Heat transfer and friction factor correlation for inclined spherical ball roughened solar air heater SP - 3 UR - http://www.czasopisma.pan.pl/dlibra/publication/edition/116180 T2 - Archives of Thermodynamics ER -