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Developing flow of Newtonian fluids over superhydrophobic transverse grooves in circular tube
Kok Hwa Yu,Han Wei Lee,Yew Heng Teoh,Mohd Azmi Ismail 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.1
In this paper, the effects of dimensionless gas area fraction ( δ ) and normalized groove-rib periodic spacing ( Λ ) on developing flow for Newtonian fluid past circular tube having alternating superhydrophobic transverse grooves were numerically investigated. Fluid flow at Re ranging from 0.001 to 10 over various superhydrophobic microstructures scales ( 0.05 < Λ < 1, 0 < δ < 1 ) were studied. Numerical results show that the presence of superhydrophobic transverse grooves would consistently yield a longer hydrodynamic entrance length ( ) h L as compared to that of smooth surface. This is principally owing to the flow redistribution with higher flow rate that is permitted in the vicinity of the superhydrophobic wall. However, the scale of the superhydrophobic transverse grooves yield non-monotonic trend on hydrodynamic entrance length, with reduced delaying effect at higher Λ . Despite the h L alteration, h L arising from the presence of superhydrophobic transverse grooves in tube of diameter D , at low Re (i.e., Re < 1 ), is still bounded within tube length of D .
Siew Aun Tan,Kok Hwa Yu,Mohd Zulkifly Abdullah 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.6
This study employs a three-dimensional numerical model to simulate a vertical furnace for wafer annealing process. For a conventional furnace design, it is revealed that the top 5 pieces of the stacked wafers are exposed to lower temperatures, approximately 3-5 % lower than the operating heater temperature. Temperature distribution and the heat losses from the furnace, especially on the heat dissipated through the top header and the process door of the furnace chamber, are examined. To reduce the heat losses, furnace design improvements comprised of a thicker top header and a better thermal insulated process door are recommended. With such implementations, up to 28 % and 22 % reduction of heat dissipation through the top header and the process door, respectively, could be attained. In addition, the design of the boat cover is found to influence the temperature uniformity across the stacked wafers. To attain better temperature uniformity at the top region of stacked wafers, a furnace with a full boat cover is thus recommended.