Thermal analysis of jet impingement on hemispherical protrusion on heated surface Rajesh Maithani a , Anil Kumar a , Geetanjali Raghav a , Mohit Nagpal a , and Bipin Kumar b a Department of Mechanical Engineering, University of Petroleum and Energy Studies, Dehradun, India;; b Department of Mechanical Engineering, DIT University, Dehradun, India ABSTRACT Jet impingement on absorber plate with hemispherical protrusion is taken up for heat and friction characteristics analysis, where the protrusions are provided exactly below the jet holes to provide impingement over the protrusions for generating larger turbulence. The geometric parameters selected for experimental analysis are Relative protrusion diameter to pro- trusion height ratio (d pr =e pr ), Relative streamwise pitch (X =D h ), relative span- wise pitch (Y =D h ). The maximum value of Thermohydraulic performance parameter (η) achieved was 3.01. The Nusselt number (Nu) and friction factor (f ) correlations are developed and second law analysis is carried out for the selected range of geometric and fow parameters. ARTICLE HISTORY Received 20 June 2020 Accepted 6 August 2020 KEYWORDS Jet impingement; solar energy; hemispherical protrusion; thermohydraulic performance Introduction Solar thermal energy fnds application in many domestic and commercial domains [1] and larger energy harvesting can be achieved by addressing the low heat transfer coefcient drawback [2]. Various studies [3] reported that, a direct jet impingement of fuid on the heated surface is an efective technique for enhancing heat transfer coefcient. The review revealed that the impingement of jet [4] augments the heat transfer rate higher than the conventional convection cooling. The impingement of fuid jets is a well-known convective heat transfer method applied in diferent thermal applications [5, 6]. Chance [7], Kercher and Tabakof [8] analyzed the streamwise and spanwise pitchs in a low velocity jet impingement process. The air jets impinging on the heated surface in a two dimensional array was analyzed by Metzger et al. [9], and it was reported that the staggered arrangements does not performs better than the in-line jets. Florscheuetz et al. [10] developed a correlation of Nusselt number (Nu) for a crossfow fuid velocity for jet impingement on heated plate. Brevet et al. [11] studied an array of air jet impinging on a surface, and the air leaving the section from one defned direction. The study recommends the impingement distance and spanwise jet-to-jet spacing to be 3–6 and 4–5, respectively. Impinging air jets studied by Chauhan and Thakur [12] for solar thermal system duct considered various parameters as: diameter of jet, pitches in the streamwise and spanwise direction for Re in the range 3800–16000. A signifcant enhancement in the Nu ratio of 2.67 is achieved. Nadda et al. [13] experimentally analyzed the thermal performance of circular jet impingement on SAH duct for Reynolds number (Re) in the range of 5000 to 19000. Major selected geometric parameters selected are, relative width ratio (W P =W AP ), relative pitch ratio (P P =e P ), relative height ratio (e P =d P ), angle of arc (α a ). The maximum enhancement in the rate of heat transfer and friction losses was found to be 6.29 and 9.25 times, respectively as compared to smooth heated absorber plate. The maximum thermal CONTACT Rajesh Maithani rmaithani@ddn.upes.ac.in Department of Mechanical Engineering, University of Petroleum and Energy Studies, Dehradun, 248007, India. EXPERIMENTAL HEAT TRANSFER https://doi.org/10.1080/08916152.2020.1808117 © 2020 Taylor & Francis