This paper aims at deeper understanding of heat transfer from horizontal-base pin-fin heat sinks with exposed edges in free convection of air. The effects of fin height and fin population density are studied experimentally and numerically. The sinks are made of aluminum, and there is no contact resistance between the base and the fins. All the sinks studied have the same base dimensions and are heated using foil electrical heaters. The fins have a constant square cross section, whereas the fin height and pitch vary. The heat input is set, and temperatures of the base and fins are measured. In the corresponding numerical study, the sinks and their environment are modeled using the FLUENT 6.3 software. The results show that heat-transfer enhancement due to the fins is not monotonic. The differences between sparsely and densely populated sinks are assessed quantitatively and analyzed for various fin heights. Also analyzed is the heat flux distribution at the edges and center of the sink. A relative contribution of outer and inner fin rows in the sink is assessed, together with the effect of fin location in the array on the heat-transfer rate from an individual fin. By decoupling convection from radiation, a dimensional analysis of the results for natural convection is attempted. A correlation presenting the Nusselt number versus the Rayleigh number is suggested, where the “clear” spacing between fins serves as the characteristic length.
The present study explores the process of melting of a phase change material (PCM) in a vertical circular tube. A detailed analysis of the digital experimental pictures, obtained in previous investigations, is performed. In this analysis, the tubes are subdivided by horizontal planes into 1cm high slices. The melt fraction as a function of time is calculated separately for each slice, yielding the local heat transfer rates into the solid. The flow patterns that cause these effects are obtained from the numerical simulation. The simulation provides a detailed heat flux distribution on the inner wall of the tube. The numerical simulations, performed using the Fluent 6 software, model the same commercially available paraffin-type material that was used in the previous experimental investigations.. The simulation results, along with the analysis of the experimental pictures, reveal the effects of convection in the liquid phase, which make heat transfer from the wall to the melting PCM essentially non-radial. Thus, the analysis adopted in the present study provides a comprehensive picture of melting in vertical circular tubes at various locations and instants.
In the present work, horizontal-base pin fin heat sinks exposed to free convection in air are studied. They are made of aluminum, and there is no contact resistance between the base and the fins. The sinks have the same base dimensions whereas the fin height and pitch vary. The fins have a constant square cross-section. The effect of fin height and pitch on the performance of the sink is studied experimentally and numerically. In the experiments, the heat sinks are heated using foil electrical heaters. The heat input is set, and temperatures of the base and fins are measured. In the corresponding numerical study, the sinks and their environment are modeled using the Fluent 6.3 software. The results show that heat transfer enhancement due to the fins is not monotonic. The differences between sparsely and densely populated sinks are analyzed for various fin heights.
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