Flame Structure and Diamond Growth Mechanism of Acetylene Torch

Abstract

Heat dissipation is one of the most important issues for the reliability of electronic equipment. Boiling can be a very efficient heat transfer mechanism when used to face with the electronic technology needs of efficient and compact heat sinks. Recently, cellular structured materials both stochastic and periodic, particularly open cell metal foams, have been proposed as possible enhanced surfaces to lower the junction temperatures at high heat fluxes. Up today, most of the research on metal foams only regards single phase flow, whereas the two phase flow is still almost unexplored. This paper presents an experimental study on the heat transfer of R134a during flow boiling inside a 5 PPI (Pores Per linear Inch) copper foam, which is 5 mm high, 10 mm wide and 200 mm long, and it is brazed on a 10 mm thick copper plate. The experimental measurements were carried out by imposing three different heat fluxes (50, 75, and 100 kW m -2 ) and by varying the refrigerant mass velocity between 50 and 200 kg m -2 s -1 and the vapour quality from 0.2 to 0.90, at constant saturation temperature (30°C). The effects of the refrigerant mass flow rate, heat flux and vapour quality on the heat transfer coefficient, dry out phenomenon, and pressure drop are studied.

Diamond growth by chemical vapour deposition

“…The substrate temperature is adjusted by varying the substrate surface position relative to the water cooled copper mount and its temperature is measured by a two-colour pyrometer which is insensitive to the flame's emission. Hydrogen addition to the oxygen-acetylene flame was found to reduce the amount of amorphous carbon in the diamond films [50]. Normally the oxygen acetylene torch is used with an excess of oxygen.…”

Spatial distributions of atomic hydrogen and C2 in an oxyacetylene flame in relation to diamond growth

“…8,11 Once adsorbed, atomic hydrogen may also stabilize the diamond surface structure. [12][13][14] The role of atomic hydrogen in diamond CVD has been studied from a theoretical point of view by several authors, including Frenklach et al, [15][16][17] Matsui et al, 18,19 Janssen et al, 12 Harris, 20,21 and Goodwin. [22][23][24] Okkerse et al have recently presented a compact gas phase and surface reaction mechanism that can be used in multidimensional simulations of diamond growth in oxyacetylene flames.…”

Growth on the reconstructed diamond (100) surface

“…One proposed chemical kinetics mechanism [21, which takes CH 3 as the growth species, successfully predicts [20][21][22], experimental growth rates for both RF [211 and DC [23] plasma torches, for flames at low and atmospheric pressure [15,24,25], and for filament systems as a function of pressure and composition [16,17], without the use of adjustable parameters. Its predictions are compared to experiment in Figure 1.…”