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.

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.

Flow of an Eyring-Powell Fluid with Convective Boundary Conditions

2012 ◽  
Vol 29 (2) ◽  
pp. 217-224 ◽  
Author(s):  
T. Hayat ◽  
Z. Iqbal ◽  
M. Qasim ◽  
A. Alsaedi
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Convective Boundary Condition ◽  
Thermal Boundary Layer Thickness ◽  
Stretching Surface ◽  
Convective Boundary ◽  
Convergence Of Series ◽  
Layer Flow ◽  
Increasing Function

AbstractThe boundary layer flow of an Eyring-Powell fluid over a stretching surface subject to the convective boundary condition is investigated. Nonlinear problem is computed and a comparative study is presented with the existing results in viscous fluid. The constructed differential systems have been solved for homotopic solutions. Convergence of series solutions has been discussed. Special emphasis has been given to the effects of material parameters of fluid (ε), (δ), Biot number (γ) and Prandtl number (Pr) on the velocity and temperature profiles. Tabulated values of Nusselt number and skin friction for different emerging parameters are also illustrated. It is noted that the boundary layer thickness is an increasing function of (ε) and decreasing function of (δ). However the temperature and thermal boundary layer thickness decrease when the values of (ε) and (δ) are increased.

An integral approach to the calculation of skin friction and heat transfer in the laminar flow of a high-Prandtl-number power-law non-Newtonian fluid past a wedge

1991 ◽  
Vol 69 (2) ◽  
pp. 83-89 ◽  
Author(s):  
G. Ramamurty ◽  
K. Narasimha Rao ◽  
K. N. Seetharamu
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Prandtl Number ◽  
Skin Friction ◽  
Layer Thickness ◽  
Power Law ◽  
Boundary Layer Thickness ◽  
Thermal Boundary Layer ◽  
Integral Approach ◽  
High Prandtl Number

An integral approach to the theoretical analysis for the skin friction of a non-Newtonian, power-law-fluid flow over a wedge is presented, when the inertia terms in the boundary-layer equations are small but need consideration. The method adopted for the solution of the equations considers an integrated average value of the inertia terms in the momentum equation. The values of the velocities and the boundary-layer thickness obtained from the hydrodynamic analysis are used for the calculation of the thermal-boundary-layer thickness. A linear velocity profile is assumed for the flow field within the thermal boundary layer as the fluids chosen for the analysis are high-Prandtl-number fluids. The results of the skin friction and the rates of the heat transfer are tabulated for a number of values of the flow behaviour index, n, varying from 0.05 to 5.0. This analysis is applicable to viscous polymer solutions having high Prandtl numbers.

Linear stability and energetics of rotating radial horizontal convection

2016 ◽  
Vol 795 ◽  
pp. 1-35 ◽  
Author(s):  
Gregory J. Sheard ◽  
Wisam K. Hussam ◽  
Tzekih Tsai
Keyword(s):  
Boundary Layer ◽  
Potential Energy ◽  
Boundary Layer Thickness ◽  
Thermal Boundary Layer ◽  
Baroclinic Instability ◽  
Mean Flow ◽  
Thermal Boundary Layer Thickness ◽  
Available Potential Energy ◽  
Horizontal Convection ◽  
The Mean

The effect of rotation on horizontal convection in a cylindrical enclosure is investigated numerically. The thermal forcing is applied radially on the bottom boundary from the coincident axes of rotation and geometric symmetry of the enclosure. First, a spectral element method is used to obtain axisymmetric basic flow solutions to the time-dependent incompressible Navier–Stokes equations coupled via a Boussinesq approximation to a thermal transport equation for temperature. Solutions are obtained primarily at Rayleigh number $\mathit{Ra}=10^{9}$ and rotation parameters up to $Q=60$ (where $Q$ is a non-dimensional ratio between thermal boundary layer thickness and Ekman layer depth) at a fixed Prandtl number $\mathit{Pr}=6.14$ representative of water and enclosure height-to-radius ratio $H/R=0.4$. The axisymmetric solutions are consistently steady state at these parameters, and transition from a regime unaffected by rotation to an intermediate regime occurs at $Q\approx 1$ in which variation in thermal boundary layer thickness and Nusselt number are shown to be governed by a scaling proposed by Stern (1975, Ocean Circulation Physics. Academic). In this regime an increase in $Q$ sees the flow accumulate available potential energy and more strongly satisfy an inviscid change in potential energy criterion for baroclinic instability. At the strongest $Q$ the flow is dominated by rotation, accumulation of available potential energy ceases and horizontal convection is suppressed. A linear stability analysis reveals several instability mode branches, with dominant wavenumbers typically scaling with $Q$. Analysis of contributing terms of an azimuthally averaged perturbation kinetic energy equation applied to instability eigenmodes reveals that energy production by shear in the axisymmetric mean flow is negligible relative to that produced by conversion of available potential energy from the mean flow. An evolution equation for the quantity that facilitates this exchange, the vertical advective buoyancy flux, reveals that a baroclinic instability mechanism dominates over $5\lesssim Q\lesssim 30$, whereas stronger and weaker rotations are destabilised by vertical thermal gradients in the mean flow.

Time-Resolved Thermal Boundary-Layer Structure in a Pulsatile Reversing Channel Flow

2001 ◽  
Vol 123 (4) ◽  
pp. 655-664 ◽  
Author(s):  
Sean P. Kearney ◽  
Anthony M. Jacobi ◽  
Robert P. Lucht
Keyword(s):  
Boundary Layer ◽  
Channel Flow ◽  
Boundary Layer Thickness ◽  
Thermal Boundary Layer ◽  
Layer Structure ◽  
Laminar Regime ◽  
Thermal Boundary Layer Thickness ◽  
Reversed Flow ◽  
Time Resolved ◽  
Primary Impact

In this paper, the results of an experimental study of the time-resolved structure of a thermal boundary layer in a pulsating channel flow are presented. The developing laminar regime is investigated. Two techniques were used for time-resolved temperature measurements: a nonintrusive, pure-rotational CARS method and cold-wire anemometry. Results are presented for differing degrees of flow reversal, and the data show that the primary impact of reversed flow is an increase in the instantaneous thermal boundary-layer thickness and a period of decreased instantaneous Nusselt number. For the developing laminar parameter space spanned by the experiments, time-averaged heat-transfer enhancements as high as a factor of two relative to steady flow are observed for nonreversing and partially reversed pulsating flows. It is concluded that reversal is not necessarily a requirement for enhancement.

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