Factors Influencing the Characteristics of Wetting of Parts of a Vapor Chamber
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Journal of Engineering Physics and Thermophysics, Vol. 93, No. 5, September, 2020
FACTORS INFLUENCING THE CHARACTERISTICS OF WETTING OF PARTS OF A VAPOR CHAMBER O. L. Voitik, K. I. Delendik, N. V. Kolyago, and L. Yu. Roshchin
UDC 536.248.2,532.64.08
A study has been made of conditions for the electrochemical deposition of copper on copper plates and of the influence of the microroughness of their surface on the wetting of the plates. This permitted determining the optimum regimes of deposition of coatings on elements of vapor chambers with the aim of creating such elements with controlled wetting properties. Keywords: microroughness, contact wetting angle, hydrophilic and hydrophobic coatings, wetting hysteresis, electrochemical deposition. Introduction. Ensuring necessary thermal regimes of electronics is topical as never before, which is due to the continuous comprehensible miniaturization of electronic components and their functioning in a narrow temperature range (the Kirin 980 Huawei [1] and Apple A12 Bionic [2] processors are fabricated by the 7-nanometer technology, and the processor Exynos 9820 Samsung, by the 8-nanometer technology [3]). The use of compact vapor chambers permits solving the problem of thermal stabilization of electronics elements [4]. A vapor chamber is an evaporating-condensing device serving to remove heat loads from difficult to access thermally stressed elements of devices at low temperature gradients in them and operating on a closed cycle. Capillary limitation of a vapor chamber (on wettability of its wick) is one limit of the chamber′s heat-transport ability [5]. The deeper understanding of the processes of wetting and the ability to control them make it possible to improve the heat-transport ability of vapor chambers. To create an efficient vapor chamber, it is necessary to impart hydrophilicity to the material of the wick and hydrophobicity to the condensation zone of the chamber. It is well known that the degree of wetting of the surface is characterized by the contact angle θ [6–10]. From the propositions of the Dupre and Girifalco–Good theory [7, 9], the maximum possible wetting angle is equal to 120o for a plane surface of the material perfluoro ecosan with the lowest existing surface energy of 6.7 mJ/m2, which points to the impossibility of attaining great values of the contact angle solely due to the use of low-energy surfaces. The same is suggested by the results of investigations of natural objects (lotus leaves, gecko skin, water-skater legs [11]). The hydrophobicity of natural objects is attained due to the surface structural features of the natural objects rather than by the presence of more nonpolar materials as part of them (on the plane wax surface of a lotus leaf, the contact wetting angle is equal to 119o, and the hysteresis, to 71o at a value of the contact wetting angle of the leaf itself of about 150o). The mechanisms used by nature to attain such high water-repellency indices formed the basis for the present work on studying the influence of the microroughne
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