Purpose The purpose of this paper is to carry out an in-depth analysis of heat dissipation performance by natural convection phenomenon inside light-emitting diode (LED) lamps containing hot pin-fins because of its significant industrial applications. Design/methodology/approach The problem is assimilated to heat transfer inside air-filled rectangular cavity with various governing parameters appraised in ranges interesting engineering application and scientific research. The lattice Boltzmann method is used to predict the dynamic and thermal behaviors. Effects of monitoring parameters such as Rayleigh number Ra (103-106), fin length (0-0.25) and its position, pin-fins number (1-8), the tilting-angle (0-180°) and cavity aspect ratio Ar (0.25-4) are carried out. Findings The rising behaviors of the dynamic and thermal structures and heat transfer rate (Nu), the heatlines distribution and the irreversibility rate are appraised. It was found that the flow is constantly two contra-rotating symmetric cells. The heat transfer is almost doubled by increasing Ra. A lack of cooling performance was identified between Ar = 0.5 and 0.75. The inclination 45° is the most appropriate cooling case. At constant Ra, the maximum stream-function and the global entropy generation remain almost unchanged by increasing the pin number from 1 to 8 and the entropy generation is of thermal origin for low Ra, so that the fluid friction irreversibility becomes dominant for Ra larger than 105. Research limitations/implications Improvements may include three-dimensional complex geometries, accounting for thermal radiation, high unit power and turbulence modelling. Such factors effects will be conducted in the future. Practical implications The cooling performance/heat dissipation in LED lamps is a key manufacturing factors, which determines the lifetime of the electronic components. The best design and installation give the opportunity to increase further the product shelf-life. Originality/value Both cooling performance, irreversibility rate and enclosure configuration (aspect ratio and inclination) are taken into account. This cooling scheme will give a superior operating mode of the hot components in an era where energy harvesting, storage and consumption is met with considerable attention in the worldwide.
The basic objective of this study was to better knowledge the fine flow structure of thermal plume created by a heated disk, evolving in an unlimited and in a semi-enclosed environment. The flow visualization and the study of the temperature fluctuations spectrum show clearly a considerable change of the turbulent structure of the internal flow in comparison with the free plume. This difference is especially caused by the thermosiphon effect. Indeed, this study shows that the thermosiphon affects the flow structure plume and causes the appearance of a supplementary zone, just at the system entrance, that is added to the two classic zones concerning the free plume, mentioned in the previous works. This zone is characterised by two symmetrical rotating rolls created in the vicinity to the hot source. The energy spectrum study permits to obtain certain spectral power laws, which characterize the energy transfer between the structures that are present in the flow. In fact, three qualitatively different regions were identified: first, a production region, secondly, a region with behavior as per n-3 associated with a buoyancy region and; finally, a dissipation region associated with an n-7 law. The n-1 Tchen low is observed for the free plume in the large frequency region. The existence of the n-1 region is related to an important turbulent production. These spectral regions characterize the energy transfers mechanisms among the length scales of flow investigated here
The aim of this paper is to analyze the laminar free convective flow generated by two identical hot blocks in two-dimensional enclosure cooled by the sides in order to optimize the heat transfer. The top wall and the flat surfaces on bottom wall are adiabatic except for the active sources located symmetrically. Each source of a rectangular form is heated at a uniform temperature while the Prandtl number is fixed at 0.71. Thermal Lattice Boltzmann model of D2Q4-D2Q9 is applied to solve the thermal flow problem. Numerical simulations have been conducted to reveal the effects of various parameters; Rayleigh number 10 3 ≤ Ra ≤ 10 6 , spacing between blocks 0.1 ≤ D ≤ 0.6, block height 0.05 ≤ H ≤ 0.4 and aspect ratio of the enclosure 1 ≤ A ≤ 4 on fluid flow and heat transfer. The computational results by Lattice Boltzmann method have been found to be in good agreement with previous works. The results are presented in the form of isotherms and streamlines plots as well as the variation of the average Nusselt number along horizontal and vertical hot walls. It is found that increasing Rayleigh number and distance between active blocks enhance the heat transfer. The simulations show that the block height and aspect ratio are the most important parameters affecting dynamic and thermal fields and consequently the heat transfer efficiency in the enclosure.
This investigation analyses the turbulent structure of a thermal plume created by a heated disk, evolving between vertical plates. The objective of the study was to understand the development mechanisms of this buoyancy driven flow. The analysis of the average and the fluctuating fields of the temperature as well as the flow visualisation show the existence of three different zones. The first zone of the plume air feeding was characterized by the thermal profiles in three extrema structures. These extrema disappear in the second zone where the profiles present on maximum. In the last zone, the profiles are flattened and self-similar. Thus, the turbulence was fully developed. A flow visualisation show that the vertical channel around the hot disk affects the flow structure plume and causes the appearance of a new zone at the system entrance. This supplementary zone characterizes by the development of the two rotating rolls in the vicinity of the hot source. The skewness and flatness factors of the temperature fluctuations show that the latter have a nearly Gaussian distribution in the most turbulent regions of the flow (in the region where the turbulence was fully developed), but that deviates gradually from the Gaussian distribution in the other region
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