Momentum and Thermal Boundary-layer Thickness in a Stagnation Flow Chemical Vapor Deposition Reactor

1997 ◽  
Vol 12 (4) ◽  
pp. 1112-1121 ◽  
Author(s):  
David S. Dandy ◽  
Jungheum Yun
Keyword(s):  
Boundary Layer ◽  
Chemical Vapor Deposition ◽  
Layer Thickness ◽  
Vapor Deposition ◽  
Boundary Layer Thickness ◽  
Thermal Boundary Layer ◽  
Numerical Solutions ◽  
Chemical Vapor ◽  
Square Root ◽  
Thermal Boundary Layer Thickness

Explicit expressions have been derived for momentum and thermal boundary-layer thickness of the laminar, uniform stagnation flows characteristic of highly convective chemical vapor deposition pedestal reactors. Expressions for the velocity and temperature profiles within the boundary layers have also been obtained. The results indicate that, to leading order, the momentum boundary-layer thickness is inversely proportional to the square root of the Reynolds number, while the thermal boundary-layer thickness is inversely proportional to the square root of the Peclet number. Values computed using the approximate expressions are compared directly with numerical solutions of the equations of motion and thermal energy equation, for a specific set of conditions typical of diamond chemical vapor deposition. Because values of the Lewis number do not vary significantly from unity for many different chemical vapor deposition systems, the expression derived here for thermal boundary-layer thickness may be used directly as an approximate concentration boundary-layer thickness.

A CFD Evaluation of Multiple RANS Turbulence Models for Prediction of Boundary Layer Flows on a Turbine Vane

2013 ◽  
Author(s):  
Thomas E. Dyson ◽  
David G. Bogard ◽  
Sean D. Bradshaw
Keyword(s):  
Boundary Layer ◽  
Prandtl Number ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Thermal Boundary Layer ◽  
Turbulence Models ◽  
Experimental Measurements ◽  
Thermal Boundary Layer Thickness ◽  
Mean Velocity ◽  
High Turbulence

There is a growing trend toward the use of conjugate CFD for use in prediction of turbine cooling performance. While many studies have evaluated the performance of RANS simulations relative to experimental measurements of the momentum boundary layer, no studies have evaluated their performance in prediction of the accompanying thermal boundary layer. This is largely due to the fact that, until recently, no appropriate experimental data existed to validate these models. This study compares several popular RANS models — including the realizable k-ε and k-ω SST models — with a four equation k-ω model (“Transition SST”) and experimental measurements at selected positions on the pressure and suction sides of a model C3X vane. Comparisons were made using mean velocity and temperature in the boundary layer without film cooling under conditions of high and low mainstream turbulence. The best performing model was evaluated using modification of the turbulent Prandtl number to attempt to better match the data for the high turbulence case. Overall, the models did not perform well for the low turbulence case; they greatly over-predicted the thermal boundary layer thickness. For the high turbulence case, their performance was better. The Transition SST model performed the best with an average thermal boundary layer thickness within 15% of the experimentally measured values. Prandtl number variation proved to be an inadequate means of improving the thermal boundary layer predictions.

scholarly journals KARAKTERISASI TEBAL LAPISAN BATAS FLUIDA NANO ZrO2 DI PERMUKAAN PEMANAS PADA PROSES KONVEKSI ALAMIAH

2015 ◽  
Vol 17 (3) ◽  
pp. 167
Author(s):  
V. Indriati Sri Wardhani ◽  
Henky P. Rahardjo
Keyword(s):  
Boundary Layer ◽  
Natural Convection ◽  
Heat Source ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Thermal Boundary Layer ◽  
Cooling System ◽  
Thermal Boundary Layer Thickness ◽  
Cooling Fluid ◽  
Nano Fluid

ABSTRAK KARAKTERISASI Tebal Lapisan Batas Fluida Nano ZrO2 di permukaan pemanas pada Proses Konveksi Alamiah. Pendinginan sistem sangat dipengaruhi oleh proses perpindahan panas konveksi dari sumber panas ke fluida pendingin. Biasanya sebagai fluida pendingin digunakan fluida konvensional seperti air. Pendinginan suatu sistem dengan air tersebut dapat ditingkatkan dengan menggunakan fluida lain seperti fluida nano, yaitu fluida yang dibuat dari campuran air ditambah partikel dengan ukuran nano. Peneliti Batan Bandung telah membuat fluida nano ZrO2 dari bahan local. Telah dibuat pula peralatan eksperimen untuk mempelajari sifat-sifat termohidrolik fluida nano tersebut. Hal ini dilakukan untuk mendapatkan fluida nano yang tepat jika digunakan sebagai fluida pendingin sistem. Dalam penelitian ini dilakukan eksperimen untuk mempelajari sifat-sifat termohidrolik fluida nano ZrO2 yang terbuat dari campuran air dengan partikel nano ZrO2 yang berukuran 10-7-10-９nm dengan konsentrasi 1 gr/lt yang digunakan sebagai pendingin pada proses pendinginan konveksi alamiah. Proses tersebut sangat bergantung pada perubahan temperatur dari sumber panas ke fluida pendingin. Dalam pendinginan konveksi alamiah perubahan temperatur itu akan terjadi di dalam tebal lapisan batas termalnya. Oleh karena itu perlu diteliti tebal lapisan batas termal dari fluida nano ZrO2 yang selanjutnya juga dapat untuk menentukan kecepatan aliran lokalnya. Eksperimen dilakukan melalui proses perpindahan panas konveksi alamiah dengan memasukkan beberapa variasi daya pemanas, kemudian dilakukan pengukuran temperatur di beberapa titik secara horizontal untuk melihat distribusi temperaturnya. Hasil pengukuran distribusi temperatur tersebut dapat digunakan untuk menentukan tebal lapisan batas dan kecepatan alirannya. Diperoleh bahwa tebal lapisan batas termal dan kecepatan konveksi alamiah fluida nano ZrO2 tidak jauh berbeda dari fluida konvensional air. Kata kunci: Lapisan batas, fluida nano ZrO2, konveksi alamiah.  ABSTRACT CHARACTERIZATION of boundary layer thickness OF nano FLUID ZrO2 on natural convection process. Cooling system is highly influenced by the process of convection heat transfer from the heat source to the cooling fluid. The cooling fluid usually used conventional fluid such as water. Cooling system performance can be improved by using fluids other than water such as nano fluid that is made from a mixture of water and nano-sized particles. Researchers at Batan Bandung have made nano fluid ZrO2 from local materials, as well as experimental equipment for studying the thermohidraulic characteristics of nano fluid as the cooling fluid. In this study, thermohidraulic characteristics of nano fluid ZrO2 are observed through experimentation.  Nano fluid ZrO2 is made from a mixture of water with ZrO2 nano-sized particles of 10-7-10-9 nm whose concentration is 1 g/ltr. This nano fluid is used as coolant in the cooling process of natural convection. The natural convection process depends on the temperature difference between heat source and the cooling fluid, which occur in the thermal boundary layer. Therefore it is necessary to study the thermal boundary layer thickness of nano fluid ZrO2, which is also able to determine the local velocity. Experimentations are done with several variation of the heater power and then the temperature are measured at several horizontal points to see the distribution of the temperatures. The temperature distribution measurement results can be used to determine the boundary layer thickness and flow rate. It is obtained that thermal boundary layer thickness and velocity of nano fluid ZrO2 is not much different from the conventional fluid water. Keywords: Boundary layer, nanofluid ZrO2, natural convection.

scholarly journals Numerical results for influence the flow of MHD nanofluids on heat and mass transfer past a stretched surface

2021 ◽  
Vol 10 (1) ◽  
pp. 28-38
Author(s):  
Nader Y. Abd Elazem
Keyword(s):  
Boundary Layer ◽  
Temperature Field ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Thermal Boundary Layer ◽  
Lewis Number ◽  
Numerical Results ◽  
Eckert Number ◽  
Concentration Profiles ◽  
Thermal Boundary Layer Thickness

Abstract Due to its significant applications in physics, chemistry, and engineering, some interest has been given in recent years to research the boundary layer flow of magnetohydrodynamic nanofluids. The numerical results were analyzed for temperature profile, concentration profile, reduced number of Nusselt and reduced number of Sherwood. It has also been shown that the magnetic field, the Eckert number, and the thermophoresis parameter boost the temperature field and raise the thermal boundary layer thickness while the Prandtl number reduces the temperature field at high values and lowers the thermal boundary layer thickness. However, if Lewis number is higher than the unit and the Eckert number increases, the concentration profiles decrease as well. Ultimately, the concentration profiles are reduced for the variance of the Brownian motion parameter and the Eckert number, where the thickness of the boundary layer for the mass friction feature is reduced.

scholarly journals Electromagnetic Wave Shielding Effectiveness Based on Carbon Microcoil-Polyurethane Composites

2014 ◽  
Vol 2014 ◽  
pp. 1-6 ◽  
Author(s):  
Gi-Hwan Kang ◽  
Sung-Hoon Kim
Keyword(s):  
Electromagnetic Wave ◽  
Chemical Vapor Deposition ◽  
Layer Thickness ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Shielding Effectiveness ◽  
Frequency Range ◽  
Thermal Chemical Vapor Deposition ◽  
Shielding Properties ◽  
Polyurethane Composites

Carbon microcoils (CMCs) were deposited onto Al2O3substrates using C2H2/H2as source gases and SF6as an incorporated additive gas in a thermal chemical vapor deposition system. CMC-polyurethane (PU) composites were obtained by dispersing the CMCs in the PU with a dimethylformamide additive. The electromagnetic wave shielding properties of the CMC-PU composites were examined in the frequency range of 0.25–1.5 GHz. The shielding effectiveness (SE) of the CMCs-PU systematically increases with increasing the content of CMCs and/or the layer thickness. Based on these results, the main SE mechanism for this work was suggested and discussed.

Mass Transfer around a Sphere Buried in a Packed Bed

2014 ◽  
Vol 353 ◽  
pp. 306-310
Author(s):  
João M.P.Q. Delgado ◽  
M. Vázquez da Silva
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Numerical Solutions ◽  
Concentration Field ◽  
Particle Diameter ◽  
Packed Bed ◽  
Concentration Boundary Layer ◽  
Concentration Boundary ◽  
Mass Transfers

The transport phenomenon of mass transfers between a moving fluid and a reacting sphere buried in a packed bed, with “uniform velocity”, was analysed numerically, for solute transport by both advection and diffusion to obtain the concentration field and, from it, the dimensionless concentration boundary layer thickness, , for , and . The bed of inert particles is taken to have uniform voidage. For this purpose, numerical solutions of the partial differential equations describing mass concentration of the solute were undertaken to obtain the concentration boundary layer thickness as a function of the relevant parameters. Finally, mathematical expressions that relate the dependence with the Peclet number and inert particle diameter are proposed to describe the approximate size of the concentration boundary layer thickness.

Boundary Layer Profiles in Plasma Chemical Vapor Deposition

Science ◽  
1993 ◽  
Vol 259 (5102) ◽  
pp. 1726-1729 ◽  
Author(s):  
D. S. Green ◽  
T. G. Owano ◽  
S. Williams ◽  
D. G. Goodwin ◽  
R. N. Zare ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Plasma Chemical ◽  
Plasma Chemical Vapor Deposition
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