Influence of geometrical shapes and modes of cooling for the convective heat transfer – experimental study

Saif Rahman Khan, Farhan Azim, Atif Shahriar, Md. Sabit Shahriar Haque, Abid Hasan Rafi, Dewan Hasan Ahmed

Abstract The effective heat transfer from the heated objects of different geometrical configurations poses a critical challenge for numerous industrial applications. Indeed, the heat transfer characteristics for the hollow-shaped geometries and concurrent heating and forced cooling along with usual free and forced convection heat transfer are common in many industrial and electrical and electronic devices. This investigation examines the impact of geometric shapes and cooling techniques on enhancing heat transfer. The experiments were conducted on four different geometrical shapes, i.e., Solid Circular Cylinder (SCC), Hollow Circular Cylinder (HCC), Hollow Square Cylinder (HSC) and, Hollow Hexagonal Cylinder (HHC), having same material and nominally similar outer surface area with some variation arising from fabrication. The models were experimented under three distinct scenarios: natural, forced, and concurrent heating and forced cooling (the cartridge heater and blower were operated simultaneously from the start of the test) conditions. The heat transfer coefficient was determined using the Churchill and Chu equation for natural convection and the Churchill and Bernstein equation for the forced convection, and concurrent conditions for a wide range of parametric variations. The results revealed that the heat transfer coefficient is significantly higher in the concurrent case than in forced convection as well as free convection and found that boundary layer thickness plays a significant role. The hollow-shaped geometries performed better, and the HSC and HCC showed comparable results in terms of heat transfer coefficients and rates, exceeding those of the HHC. The heat transfer coefficient increases by about 6.7–11.5% in concurrent heating and forced cooling scenarios as compared to forced convection when both cases are compared against a velocity of 7.2 m/s. Whereas at the same velocity, the concurrent case demonstrates the smallest convective heat transfer rate on the exterior surface, a decrease of 81.6 to 89.7% compared to the forced convection cases.