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1.
An analysis is presented to investigate the flow and heat transfer characteristics of a vertical stretching surface with
suction and blowing, and variable magnetic effects. The magnetic field of variable intensity is applied perpendicular to the
surface. The range of the magnetic parameter M investigated is 0.1 to 1.0. The flow is considered steady, incompressible, and three-dimensional. The governing momentum
and energy equations are solved numerically. Numerical results are presented for velocity distribution, temperature distribution,
surface shear stress, and wall heat transfer rate. Discussion is provided for the effect of the magnetic field strength on
the velocity and temperature fields.
Received on 26 November 1997 相似文献
2.
The paper deals with the experimental investigation of heat transfer from a vertical isothermal plate mounted inside a cabinet
with lateral openings. Ambient air is drawn into the cabinet and cools the plate by natural convection. The experiments were
conducted by varying the distance between the plate and the cabinet walls, the plate-to-ambient temperature difference and
the size, position, shape and number of the vent openings. Local and average heat transfer coefficients along the plate were
measured by the schlieren optical technique. Heat transfer rates from the plate turned out to be significantly influenced
by the geometric and thermal parameters investigated. The results provide a useful tool for thermal design of cooling systems
by air natural ventilation.
Received on 17 January 2000 相似文献
3.
E. R. Meinders G. M. P. van Kempen L. J. van Vliet T. H. van der Meer 《Experiments in fluids》1999,26(1-2):86-96
This paper presents the experimental investigation of the application of an image restoration technique aimed at improving
the accuracy of infrared surface temperature measurements of cubes placed in a vertical channel flow. These cubes, used to
determine distributions of the local heat transfer coefficient, show large spatial temperature gradients. The image restoration
technique, developed to correct the spatial image degradation, is based on the two-dimensional Optical Transfer Function constructed
from line spread functions (LSF). The benefit of the application of the infrared image restoration technique is verified with
temperature measurements acquired from a second independent technique.
Received: 18 July 1997 / Accepted: 23 April 1998 相似文献
4.
Some novel, non-intrusive, high-frequency, localized optical measurements of turbulence in compressible flows are described.
The technique is based upon focusing schlieren optics coupled with high-speed quantitative measurement of light intensity
fluctuations in the schlieren image. Measurements of density gradient fluctuations confined to a thin slice of the flowfield
are thus obtained. The new instrument was used to investigate the structure of a two-dimensional, adiabatic, wind tunnel wall
boundary layer at a Mach number of 3. The measurements were compared to data obtained using hot-wire anemometry and good agreement
was found between the two. Distributions of broadband convection velocity of large-scale structures through the boundary later
were also measured. In marked contrast to earlier results, it is shown here that the convection velocity is essentially identical
to the local mean velocity. Further, results obtained using the VITA conditional sampling technique shed new light on the
turbulent boundary layer structure. Overall, the data presented herein serve to validate the new measurement technique.
Received: 12 February 1997/Accepted: 31 January 1998 相似文献
5.
The rainbow schlieren deflectometry technique was used to measure oxygen concentrations in a laminar, isothermal helium jet
discharged vertically into ambient air. The concentration distributions were inferred from the color schlieren image by taking
into consideration the sampling interval and noise in measurements, especially near the jet center. Excellent quantitative
agreement was reached between measurements from schlieren and a continuous sampling probe. This work demonstrates the capability
of the schlieren technique for providing accurate, spatially-resolved, nonintrusive, full-field of view measurements of species
concentration in an isothermal binary system. Because the basic quantity measured is the refractive index, the present schlieren
technique can be extended for quantitative measurements of other scalar flow properties related to the refractive index.
Received: 21 April 1997 / Accepted: 14 November 1997 相似文献
6.
A novel optical diagnostic technique, dual hologram shearing interferometry, for measuring density gradients of different
phase objects is proposed and demonstrated. The lateral shearing is achieved by using a phase grating. A holographic interferometer
has been developed and designed on the base of a single pass Z type conventional schlieren device. The interferometer’s scheme is insensitive to acoustical disturbances, similarly to the
conventional schlieren layout, and is capable of recording holograms with a continuous wave laser during the wind tunnel run.
The features of the technique make it tolerant to both the temporal coherence of the laser light source and to the relatively
low, schlieren quality optical windows of the wind tunnel’s test section. The obtained reconstructed lateral shearing interferograms
with a large region of overlap have high contrast and may have an arbitrary orientation and/or spacing of the background interference
fringes.
It is believed that the proposed approach will become a useful tool for visualization and accurate mapping of the density
gradients of gas dynamic flow fields, in wind and shock tunnels, where acoustic noise problems may dramatically affect reference
beam holographic schemes.
Received: 9 January 1997 / Accepted: 12 April 1997 相似文献
7.
The effect of buoyancy forces on laminar convection with viscous dissipation in a vertical channel 总被引:1,自引:0,他引:1
The interaction of the viscous dissipation effect with the presence of buoyancy forces is investigated for laminar-flow heat
transfer in a parallel-plate vertical channel. One of the channel walls is considered as isothermal with a prescribed temperature,
while the other wall is considered as insulated. The velocity field is assumed to be parallel. The velocity field, the temperature
field and the Nusselt number are obtained by a perturbation series method which employs the ratio between the Grashof number
and the Reynolds number as the perturbation parameter. The radius of convergence of the perturbation series is estimated.
Received on 10 December 1997 相似文献
8.
A numerical solution for the transient natural convection flow over a vertical cylinder under the combined buoyancy effect
of heat and mass transfer is presented. The velocity, temperature and concentration profiles, local and average skin-friction,
Nusselt number and Sherwood number are shown graphically. It is observed that time taken to reach steady state increases with
Schmidt number and decreases as combined buoyancy ratio parameter N increases. Stability and convergence of the finite difference scheme are established.
Received on 8 July 1997 相似文献
9.
Application of PIV in a Mach 7 double-ramp flow 总被引:2,自引:0,他引:2
The flow over a two-dimensional double compression ramp configuration is investigated by means of schlieren visualization, quantitative infrared thermography and particle image velocimetry (PIV) in a short-duration facility producing a free-stream flow at Mach 7. The study focuses upon the accuracy assessment of PIV in the hypersonic flow regime including flow facility effects such as repeatability of test conditions. The solid tracer particles are characterized by means of electron microscopy as well as by measuring the dynamic response across a planar oblique shock wave with PIV. The experiments display a strong variation in the light scattering intensity of the seeded flow over the flow field, due to the large flow compressibility. The mean velocity spatial distribution allows to clearly identify the shock pattern and the main features of the flow downstream of the shocks. However, the spatial resolution is insufficient to determine the wall flow properties. Furthermore the velocity data obtained with the PIV technique allow the determination of the spatial distribution of the Mach number under the hypothesis of adiabatic flow. The double ramp configuration with a variable second compression angle exhibits shock–shock interactions of Edney type VI or V for the lowest and highest ramp angle, respectively. A single heat transfer peak is detected with infrared thermography on the second ramp in case of a type VI interaction while for the type V shock interaction a double heat transfer peak is found. Shock wave angles measured with PIV are in good agreement with theory and the overall flow topology is consistent with schlieren visualization. Also in this respect the results are in agreement with compressible flow theory. 相似文献
10.
M. A. Ezzat A. A. El-Bary A. S. Hatem 《Journal of Applied Mechanics and Technical Physics》2014,55(4):660-671
A technique of the state space approach and the inversion of the Laplace transform method are applied to dimensionless equations of an unsteady one-dimensional boundary-layer flow due to heat and mass transfer through a porous medium saturated with a viscoelastic fluid bounded by an infinite vertical plate in the presence of a uniform magnetic field is described. Complete analytical solutions for the temperature, concentration, velocity, and induced magnetic and electric fields are presented. The inversion of the Laplace transforms is carried out by using a numerical approach. The proposed method is used to solve two problems: boundary-layer flow in a viscoelastic fluid near a vertical wall subjected to the initial conditions of a stepwise temperature and concentration and viscoelastic fluid flow between two vertical walls. The solutions are found to be dependent on the governing parameters including the Prandtl number, the Schmidt number, the Grashof number, reaction rate coefficient, viscoelastic parameter, and permeability of the porous medium. Effects of these major parameters on the transport behavior are investigated methodically, and typical results are illustrated to reveal the tendency of the solutions. Representative results are presented for the velocity, temperature, concentration, and induced magnetic and electric field distributions, as well as the local skin-friction coefficient and the local Nusselt and Sherwood numbers. 相似文献
11.
12.
combined laser-doppler and cold wire anemometry technique for determining turbulent heat flux is described. The system can
be used in flows of arbitrarily high turbulent intensity and large temperature variations. Its potential is demonstrated via
measurements in a simulated stable atmospheric boundary layer, for which the Monin-Obukhov length scale was about 70% of the
boundary layer depth. Mean and turbulence properties were obtained throughout the boundary layer and the results are shown
to be both internally consistent and similar to corresponding field data. Measurements in the highly turbulent, separated
flow behind a bluff body mounted in the stable boundary layer are also presented.
Received: 9 May 1997 / Accepted: 2 September 1997 相似文献
13.
G. Palani A. R. Ragavan E. Thandapani 《Journal of Applied Mechanics and Technical Physics》2013,54(6):960-970
An analysis is presented to investigate the influence of viscous dissipation on a free convection flow over a vertical cone with a variable surface heat flux under the action of a transverse magnetic field. The heat transfer characteristics of the free convection flow are investigated numerically. Numerical solutions for transformed governing equations with a variable surface heat flux are obtained. Velocity, temperature, local shear stress, and heat transfer coefficients are calculated for various values of the problem parameters and presented in the graphical form. The effects of the magnetic parameter, the dissipation number, the power-law index, the angle between the cone generatrix and the vertical line, and the Prandtl number on the flow are discussed. For validation of the present numerical results, they are compared with available experimental data and are found to agree well. 相似文献
14.
We consider unsteady laminar natural convection flow of water subject to density inversion in a rectangular cavity formed by isothermal vertical walls with internal heat generation. The top and bottom horizontal walls are considered to be adiabatic, whereas the temperature of the left vertical wall is assumed to be greater than that of the right vertical wall. The equations are non-dimensionalized and are solved numerically by an upwind finite difference method together with a successive over-relaxation (SOR) technique. The effects of both heat generation and variations in the aspect ratio on the streamlines, isotherms and the rate of heat transfer from the walls of the enclosure are presented. Investigations are performed for water taking Prandtl number to be Pr=11.58 and the Rayleigh number to be Ra=105. 相似文献
15.
K. A. Yih 《Heat and Mass Transfer》1998,34(1):55-61
A boundary layer analysis is used to investigate the heat and mass transfer characteristics of mixed convection about a vertical
flat plate embedded in a saturated porous medium under the coupled effects of thermal and mass diffusion. The plate is maintained
at prescribed surface temperature/concentration (PST/PSC) or prescribed heat/mass flux (PHF/PMF). The nonsimilar governing
equations are obtained by using a suitable transformation and solved by Keller box method. Numerical results for the local
heat transfer rate and the local mass transfer rate are presented for various parameters. The local heat and mass transfer
rates increase with increasing n and m and buoyancy parameter ξ. When buoyancy parameter ξ is very small (large) the value of local Nusselt and the local Sherwood
number correspond with the pure forced (free) convection, respectively. Increasing buoyancy ratio N (or N
*) increases the local heat and mass transfer rates. It is apparent that Lewis number has a pronounced effect on the local
mass transfer rate than it does on the local heat transfer rate. Furthermore, increasing Lewis number decreases (increases)
the local heat (mass) transfer rate.
Received on 8 December 1997 相似文献
16.
This paper studies mixed convection, double dispersion and chemical reaction effects on heat and mass transfer in a non-Darcy non-Newtonian fluid over a vertical surface in a porous medium under the constant temperature and concentration. The governing boundary layer equations, namely, momentum, energy and concentration, are converted to ordinary differential equations by introducing similarity variables and then are solved numerically by means of fourth-order Runge-Kutta method coupled with double-shooting technique. The velocity, temperature concentration, heat and mass transfer profiles are presented graphically for various values of the parameters, and the influence of viscosity index n, thermal and solute dispersion, chemical reaction parameter χ are observed. 相似文献
17.
I. Dincer 《Heat and Mass Transfer》1998,34(2-3):101-105
In this paper, an analysis of transient heat transfer during heat sterilization and cooling processes of a cylindrical canned
product is presented. In the analysis, most practical case including the boundary condition of third kind (i.e., convection
boundary condition, leading to 0.1 ≤ Bi ≤ 100) was employed. A simple analytical model for determining effective heat transfer
coefficients for such products is developed. For the heat sterilization process, heating coefficient is incorporated into
heat transfer coefficient model. An experimental study was performed to measure the thermal center temperatures of the short-cylindrical
canned products (i.e., Tuna fish) during heat sterilization at the retort medium temperatures of 115∘C and 121∘C, and during cooling process at 16∘C. The effective heat transfer coefficient model used the experimental temperature data. Using these effective heat transfer
coefficients the center temperature distributions were calculated and compared with the experimental temperature distributions.
Agreement was found considerably high. The results of the present study indicate that the heat-transfer analysis technique
and heat-transfer coefficient model are reliable, and can provide accurate results for such problems.
Received on 12 November 1997 相似文献
18.
Saeed Dinarvand 《国际流体数值方法杂志》2011,67(12):2141-2156
This paper deals with the study of the laminar free‐convection boundary‐layer flow about a heated and rotating down‐pointing vertical cone in the presence of a transverse magnetic field. Two cases of heat transfer analysis are discussed. These are: (i) the rotating cone with prescribed surface temperature and (ii) the rotating cone with prescribed surface heat flux. By means of similarity transformation, the governing partial differential equations are reduced into highly non‐linear ordinary differential equations. The resulting non‐linear system has been solved analytically using a very efficient technique, namely homotopy analysis method. Expressions for velocity and temperature fields are developed in a series form. The influence of various pertinent parameters is also seen on the velocity and temperature fields. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
19.
Armando Piña-Ortiz Jesús F. Hinojosa-Palafox Jesús B. Pérez-Valenzuela 《Heat and Mass Transfer》2013,49(7):933-945
In this work the numerical and experimental results of heat transfer in a vertical tall closed cavity are presented. The cavity has an aspect ratio of 20, one of the vertical walls receive a constant and uniform heat flux, while the opposite wall is kept at a constant temperature. The remaining walls are assumed adiabatic. The cavity is full of air. The computational fluid dynamics software Fluent 6.3 was used for the simulation and an experimental prototype was built to obtain the heat transfer coefficients. The air temperature and the fluid velocity values are higher when emissivity (ε) is 0.03 (almost pure natural convection). The experimental total heat transfer coefficient increases between 119.9 and 159.9 % when the emissivity of the walls changes from 0.03 to 0.95. 相似文献
20.
P. R. Hakenesch 《Experiments in fluids》1999,26(3):257-265
In order to overcome the shortcomings of conventional temperature instrumentation to compute heat transfer rates, a novel
technique for heat transfer measurement is presented. Stemming from infrared thermography, the potential for further development
of the ‘Thin Layer Thermography’ is demonstrated. This new measurement technique is based on the wavelength dependent transmissivity
of thin layers. It captures temperature distributions on the wall surface and simultaneously in a prescribed and well defined
depth of the wall of a given object of interest. This enables the calculation of a temperature gradient normal to the surface
and therefore the determination of the wall heat flux.
Received: 8 April 1998/Accepted: 12 August 1998 相似文献