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Experimental Study on Heat Transfer Enhancement in Solar Air Heater By Using Semi-Circular Conical Roughness Geometry

Neeraj Prakash Kulkarni, Pratik S. Dange

Abstract


Its purpose is to promote turbulence and enhance convective heat transfer adjacent to the wall, by breaking laminar sub layer, thus greatly enhancing the cooling effect. Applications include fuel rods of gas cooled nuclear reactors, internal surfaces of pipes & plates used in heat exchangers, electronic equipment’s, shipping machineries (in big marine boiler), combustion chamber liners, missiles, reentry vehicles, and solar air heaters etc. Artificial surface roughness was provided with semi-circular conical type with and without a hole. The turbulators were prepared in such a way that the edges of geometry should cut the viscous laminar sub layer. To obtain maximum turbulent effect, the geometry with fixed size hole of 8 mm was used. The effect of turbulators was studied for a wide range of Reynolds number, Re: 3500 to 12000. The relative roughness height e/Dh = 0.2182 (Hydraulic diameter, Dh = 36.67 mm & turbulator height, e = 8 mm) was kept as constant throughout the investigation. The experimental investigation has been done by varying longitudinal pitch and transverse pitch only at a fixed but optimized longitudinal pitch (80 mm). For longitudinal pitch variation, relative pitch roughness was varied from P/e =7.5 to 12.5 (P = 60 to 100 mm and e = 8 mm) for both with and without a hole geometry to optimize Turbulator-roughness longitudinal pitch. Similarly in second stage of transverse pitch variation, relative pitch roughness was varied as P/e = 2.5, 3.125 and 3.75 (P = 20, 25, 30 mm and e = 8 mm) for both with and without hole geometry to optimize Turbulator-roughness transverse pitch. The roughened duct enhances the heat transfer coefficient and friction factor 1.65 and 2.25 on an average for geometry without hole, and 1.82 and 2.17 on an average for geometry with hole, respectively. Whereas In case of transverse pitch variation, a heat transfer enhancement and friction facto 1.75 and 2.18 on an average for geometry without hole, and 1.92 and 2.15 on an average for geometry with hole, respectively.

Keywords


Roughness, Solar Air heater, Heat transfer enhancement, PEF, Semi Circular Conical shape, Turbulence flow.

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