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An ultra-thin vapor chamber (UTVC) is an efficient heat transfer component that meets the heat dissipation requirement of miniaturized electronic devices. Heat dissipation is one of the most important issues for UTVCs. With decreasing thickness, the mechanical strength of heat pipes and vapor chambers drops dramatically, and inevitable surface damage occurs during conventional contact thermal testing. Here, we demonstrate a non-contact thermal testing method using laser heating and infrared temperature measurement to evaluate the thermal performance of UTVCs. This non-contact method allows UTVCs to reach a steady-state sooner than traditional contact methods. Use of the characteristic thermal resistance is proposed for more straightforward evaluation of the UTVC thermal performance in non-contact testing setups. This non-contact thermal testing method has proved to be an efficient testing method for UTVCs due to its rapidity, accuracy, and non-destructiveness. [ABSTRACT FROM AUTHOR]

This article is to report results of a joint numerical and experimental investigation of vortex structures of flow past a circular cylinder of diameter D and finite span L in a range of low Reynolds numbers. The aspect ratio (AR) (= L/D) of the cylinder varies from 1.5 to 5, and the Reynolds number Re varies from 10 to 150. Given Re = 80, we study the various cases of AR, and given AR = 5, we study the various cases of Reynolds numbers Re. In a regime of parameters, the flow is found to be steady, separated, and doubly symmetric. Beyond this regime, the present study also covers a range of unsteady flow with vortex shedding in the wake behind the cylinder. This study is focused on the streamline patterns on the two planes of symmetry: the middle cross section plane (MCP) of the circular cylinder as well as on the bisectional cross section plane (BCP) on the circular cylinder. The exclusive phenomenon discovered is the occurrence, in a range of flow conditions, of a point-like or line-like source pattern of streamlines in the wake on the MCP. The center of the singular source is denoted by the center of the source (CS). In the cases of steady flow, there is always a pair of recirculating eddies on the BCP, which forms a saddle point (SP) structure at their far end from the cylinder. At the occurrence of source-like flow patterns, CS coincides with SP, signifying that the source-like points concentrate in a small neighborhood of CS (or SP). The SP is characterized by normalizing the location of the source Ds from the cylinder center. It is given a definition of the strength of the source (SS), determined by normalizing the two-dimensional divergence ∇ 2 · v on the MCP. Moreover, the flow patterns with or without a singular source are classified into four categories on the Re–AR parameter plane. In particular, a criterion on SS is found for the occurrence of a source-like pattern. The formation of the source-like wake flow and variations of the source locations and the source strength with Re and AR are given full physical explanations. The interesting trends of the drag coefficients with AR are explained on the relative importance of the surface friction and the pressure (form) drag. [ABSTRACT FROM AUTHOR]