The advent of modern electronic technology lead to miniaturization and high power density of electronic devices, then the existing electronic cooling techniques cannot be used, directly affecting the performance, cost, and reliability of electronic devices. Thus, the thermal management of electronic packaging has become a key technique in many products. Passive heat transfer devices can be a good alternative to the stabilization of electronic devices temperature. In this research, an experimental evaluation of the thermal performance of four different passive devices was accomplished. The considered devices were a rod, a thermosyphon, a heat pipe with a metal screen as the capillary structure, and a heat pipe with microgrooves. The heat pipe is a highly efficient device that carries large amounts of power with a small temperature difference. The heat pipe consists of the involucre, the working fluid, and the capillary structure. The thermosyphon is a kind of heat pipe assisted by gravity. In other words, it has no wick structure to return the working fluid. The devices were made of copper with a total length of 200 mm and an outer diameter of 9.45 mm. The thermosyphon and the heat pipes used deionized water as working fluid with a filling ratio of 60% of the evaporator volume. The devices were tested in vertical and horizontal positions under thermal loads between 5 W and 45 W. All the devices have operated satisfactorily when tested in accordance with the behavior of the thermal resistance. The heat pipes were the best among the tested devices and the best position was vertical.
Original scientific paper https://doi.org/10.2298/TSCI180227206BThis work presents the use of electrical discharge machining (EDM) technology for manufacturing of three different types of axial microgrooves in heat pipes. This specific process, called wire electrical discharge machining (wire-EDM), allows the fabrication of microgrooves on the inner wall of a heat pipe with accuracy. Different from other capillary structures, such as composite wick and screen mesh, the material is removed from the pipe's container in order to conceive the capillary structure, which contributes with the mass reduction of the passive two-phase heat transfer device. The heat pipes were manufactured from a straight copper pipe with the external diameter of 9.45 mm, the inner diameter of 6.20 mm, and a total length of 200 mm. Three types of axial microgrooves were manufactured for constant width (35 μm) and varying the depth (from 30-48 μm), and thickness (from 35-70 μm). The number of microgrooves was also varied from 21-32 microgrooves. Water was used as the working fluid and the loading filling ratio was 60% of the evaporator volume. The condenser was cooled by air forced convection, the adiabatic section was insulated and the evaporator was heated by an electrical resistor and it was insulated from the environment with aeronautic thermal insulation. The thermal performance of the heat pipes are analyzed based on experimental results, so the heat pipes were tested at the horizontal and different inclinations under different low heat loads (from 5-50 W or a heat flux from 0.21-2.10 W/cm 2 ). The experimental results showed that the axial microgrooves manufactured by the wire-EDM process worked satisfactorily in all analyzed cases and microgrooves of Type 1 showed a better thermal performance when compared with the others.
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