Search

As a contribution to the development of the thermal management of the cooling of electronics, a measurement technique of the convective heat transfer coefficient on the electronic wiring boards is presented here. The technique consists of measuring, by the infrared thermography, the temporal evolution of the thermal field on the electronic board during its normal functioning and after supplying of additive luminous energy. The technique was tested on the mainboard of a personal commercialised computer. Whereas, it may be used in characterization of the heat transfer on the electronic cards that are included in desktops and laptops computers, telecommunications servers, automotive and aerospace engines. The convective heat transfer coefficient was evaluated between the main microprocessor and the air-flow in the direction parallel to the printed board. The evaluation method consists of analysing the transient temperature of the microprocessor after a sudden energy pulse with a fixed duration given by two lamps. For the validation of the method, two cooling configurations were tested and evaluated. The first one considers the air-flow in the lengthwise of the main wiring board, and the second one concerns the case where the flow is along the widthways. In each configuration, the heat transfer coefficient was evaluated for three flow velocities. [ABSTRACT FROM AUTHOR]

Unsteady free convection in the vicinity of vertical wall-mounted insulated short cylinders is considered under isoflux thermal conditions used for wall heating. Especially, this study is aimed at analyzing how free convection heat transfer at the wall cart be locally modified by the presence of a short protrusion. For this purpose, the idea is to correlate local heat transfer at a given abscissa on the wall with the flow patterns at the junction for a large range of angular cylinder positions α around this abscissa. In contrast to a circular shape, it is shown that the presence of a cylinder with sharp edges embedded in a free-convection boundary layer induces heat transfer enhancement at a given abscissa for α < 50 °. It is argued that flow visualization can be a powerful technique in the understanding of the complex local heat transfer process, especially by identifying both the position of the wake separation and the rotational flow features. [ABSTRACT FROM AUTHOR]

This paper aims to renew interest on mixed thermal convection research and to emphasize three issues that arise from the present analysis: (i) a clear definition of the reference temperature in the Boussinesq approximation; (ii) a practical delimitation of the three convective modes, which are the forced convection (FC), mixed convection (MC) and natural (or free) convection (NC); (iii) and, finally, a uniform description of the set FC/MC/NC in the similarity framework. The planar case, for which analytical solutions are available, allows a detailed illustration of the answers here advanced to the above issues.