Al-Qadisiyah Journal for Engineering Sciences

Abstract The mixed convection investigation of various design parameters utilizing finned pipes in the cylindrical enclosure has been investigated computationally. Various geometries of fins are used (circular and longitudinal). The effect of fins number (12-16), aspect ratio (1.83-2.7), radius ratio (2-3) and fins geometry have been introduced within the present study. The observations show that when Richardson number=0.5 and 5.5, the heat transfer decreases by 12.22% and 7.777%.,. Values of the Nusselt number rise as the number of fins increases. While, when the Rayleigh number is high, no noticeable variations in the numbers of fins (12 and 14). The purpose of using fins is to increase the surface area of heat transmission. The highest heat transfer improvement is shown to be 4.2%, when log (Rayleigh)=7.342 and 16 fins are utilized. The radius ratio does not affect Nusselt number throughout the whole Richardson and Rayleigh in both hot and cold locales. The turbulence sub-layer does not affect the free stream behaviour for different Richardson number. In the case of high Richardson number, the geometry does not influence the Nu. Longitudinal fins do not have dead zones, unlike circular fins, which have channelling generated by geometrical arrangement. To reach thermal equilibrium in a cold environment, the Nu in rectangular fins was reduced by 18% as compared to circular fins with a low Richardson number. Flow development would increase the impact of channelling. The heat transfer improvement decreases as the number of fins increases, as illustrated in temperature and velocity profiles for various values.

Abstract This research studies the heat transfer in porous medium experimentally. Experimental investigation is carried out of free convection heat transfer for three dimensional in a box. The box filled with saturated porous medium, manufactured from glass with dimensions (30 × 30 × 30) cm. The porous media of plastic balls is used with homogeneous in diameter (11.7 mm). The lower wall of the box is heated by an electrical heater, while the other walls are thermally isolated. The effect of a porous medium on free convection heat transfer is studied for five values of heat fluxes (348, 576, 839, 1147, and 1384W/m2).Rayleigh number is ranging between () and for average Nusselt number between (). The results showed that the temperature inside the space increases as Rayleigh number increases. Also, the average Nusselt number increases with increase of Rayleigh number for the first three values of heat flux, but it decreases after heat flux because of domination of the conduction heat transfer on convection heat transfer. Also an empirical correlations were obtained in this study.