scholarly journals Thermal-Boundary-Layer Response to Convected Far-Field Fluid Temperature Changes

2008 ◽  
Vol 130 (10) ◽  
Author(s):  
Hongwei Li ◽  
M. Razi Nalim
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Temperature Difference ◽  
Wall Temperature ◽  
Thermal Boundary Layer ◽  
Steady State Solution ◽  
Step Change ◽  
Far Field ◽  
Fluid Temperature ◽  
Constant Wall Temperature

Fluid flows of varying temperature occur in heat exchangers, nuclear reactors, nonsteady-flow devices, and combustion engines, among other applications with heat transfer processes that influence energy conversion efficiency. A general numerical method was developed with the capability to predict the transient laminar thermal-boundary-layer response for similar or nonsimilar flow and thermal behaviors. The method was tested for the step change in the far-field flow temperature of a two-dimensional semi-infinite flat plate with steady hydrodynamic boundary layer and constant wall temperature assumptions. Changes in the magnitude and sign of the fluid-wall temperature difference were considered, including flow with no initial temperature difference and built-up thermal boundary layer. The equations for momentum and energy were solved based on the Keller-box finite-difference method. The accuracy of the method was verified by comparing with related transient solutions, the steady-state solution, and by grid independence tests. The existence of a similarity solution is shown for a step change in the far-field temperature and is verified by the computed general solution. Transient heat transfer correlations are presented, which indicate that both magnitude and direction of heat transfer can be significantly different from predictions by quasisteady models commonly used. The deviation is greater and lasts longer for large Prandtl number fluids.

Thermal Boundary Layer Response to Far-Field Flow Temperature Transitions

2007 ◽  
Author(s):  
Hongwei Li ◽  
M. Razi Nalim
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Temperature Difference ◽  
Wall Temperature ◽  
Thermal Boundary Layer ◽  
Far Field ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Flow Temperature ◽  
Constant Wall Temperature

Gas flows of varying temperature occur in heat exchangers, nuclear reactors, non-steady flow devices, and combustion engines, among other applications with heat transfer processes that influence energy conversion efficiency. A general numerical method is developed for predicting the transient laminar thermal boundary layer response to arbitrarily prescribed changes in the bulk far-field fluid temperature. The method is tested for the step change of the far-field flow temperature of a two-dimensional semi-infinite flat plate with steady hydrodynamic boundary layer and constant wall temperature assumptions. Changes of the fluid-wall temperature difference in magnitude and sign are considered, including flow with no initial temperature difference and built-up thermal boundary layer. The governing differential equations for momentum and energy are solved based on the Keller-Box finite difference method. The accuracy of the solutions is verified through comparing with the steady state solution. Transient heat transfer coefficients are presented, which indicate that both magnitude and direction of heat transfer can be significantly different from quasi-steady models commonly used.

Laminar Heat Transfer for Gas-Liquid Segmented Flows in Circular and Non-Circular Ducts With Constant Wall Temperature

2014 ◽  
Author(s):  
Y. S. Muzychka
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Wall Temperature ◽  
Thermal Boundary Layer ◽  
Additional Parameter ◽  
Residence Times ◽  
Constant Wall Temperature ◽  
Fully Developed Flow ◽  
New Model ◽  
Layer Flow

A new model is developed for gas-liquid segmented flows in ducts and channels. This model is an improvement of an earlier analysis presented and published by the author. In the present work, it is shown that for constant wall temperature, the dimensionless mean wall flux has two characteristic behaviours: thermal boundary layer flow and fully developed flow. These can also be viewed as short and long residence times as the plug train moves through the tube or channel. The boundary layer limit is dominant for short residence times while fully developed flow occurs for longer residence times. An additional parameter, the plug length to duct length ratio, (Ls/L), is shown to have significant impact on the rate of heat transfer. This parameter has the limits 0 < Ls/L < 1. The new model is compared with data from several published studies in which the variables were well controlled. It is also shown that careful experiments must be undertaken to demonstrate the characteristics of this type of flow under constant wall temperature conditions.

Heat Transfer in the Laminar Boundary Layer Over an Impulsively Started Flat Plate

1975 ◽  
Vol 97 (3) ◽  
pp. 482-484 ◽  
Author(s):  
C. B. Watkins
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Laminar Flow ◽  
Flat Plate ◽  
Constant Temperature ◽  
Laminar Boundary Layer ◽  
Temperature Difference ◽  
Thermal Boundary Layer ◽  
Numerical Solutions ◽  
Prandtl Numbers

Numerical solutions are described for the unsteady thermal boundary layer in incompressible laminar flow over a semi-infinite flat plate set impulsively into motion, with the simultaneous imposition of a constant temperature difference between the plate and the fluid. Results are presented for several Prandtl numbers.

Protuberances in a Turbulent Thermal Boundary Layer

2011 ◽  
Author(s):  
Steven R. Mart ◽  
Stephen T. McClain
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Flux ◽  
Boundary Layers ◽  
Thermal Boundary Layer ◽  
Leading Edge ◽  
Heated Plate ◽  
Fluid Temperature ◽  
Constant Flux ◽  
Thermal Boundary Layers

Recent efforts to evaluate the effects of isolated protuberances within velocity and thermal boundary layers have been performed using transient heat transfer approaches. While these approaches provide accurate and highly resolved measurements of surface flux, measuring the state of the thermal boundary-layer during transient tests with high spatial resolution presents several challenges. As such, the heat transfer enhancement evaluated during transient tests are presently correlated to a Reynolds number based either on the distance from the leading edge or on the momentum thickness. Heat flux and temperature variations along the surface of a turbine blade may cause significant differences between the shapes and sizes of the velocity and thermal boundary layer profiles. Therefore, correlations are needed which relate the states of both the velocity and thermal boundary layers to protuberance and roughness distribution heat transfer. In this study, a series of three experiments are performed for various freestream velocities to investigate the local temperature details of protuberances interacting with thermal boundary layers. The experimental measurements are performed using isolated protuberances of varying thermal conductivity on a steadily-heated, constant flux flat plate. In the first experiment, detailed surface temperature maps are recorded using infrared thermography. In the second experiment, the unperturbed velocity profile over the plate without heating is measured using hot-wire anemometry. Finally, the thermal boundary layer over the steadily heated plate is measured using a thermocouple probe. Because of the constant flux experimental configuration, the protuberances provide negligible heat flux augmentation. Consequently, the variation in protuberance temperature is investigated using the velocity boundary layer parameters, the thermal boundary layer parameters, and the local fluid temperature at the protuberance apices. A comparison of results using plastic and steel protuberances illuminates the importance of the shape of the thermal and velocity boundary layers in determining the minimum protuberance temperatures.

Heat Transfer in a Laminar Boundary Layer with Constant Fluid Properties and Constant Wall Temperature

1958 ◽  
Vol 62 (565) ◽  
pp. 60-64 ◽  
Author(s):  
A. G. Smith ◽  
D. B. Spalding
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Laminar Flow ◽  
Laminar Boundary Layer ◽  
Wall Temperature ◽  
Two Dimensional ◽  
Constant Wall Temperature ◽  
Simple Method ◽  
Flow Surface ◽  
Fluid Properties

A simple method is given for the calculation of the heat transfer from a laminar flow surface. Computation is by a quadrature. The method is essentially a simplification and extension of the Eckert(1) method, and is applicable both to two–dimensional and to axisymmetric flows.

scholarly journals Transient Thermal Response of Turbulent Compressible Boundary Layers

2008 ◽  
Author(s):  
Hongwei Li ◽  
M. Razi Nalim ◽  
Charles L. Merkle
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Flow ◽  
Thermal Boundary Layer ◽  
Thermal Conditions ◽  
Steady State Solution ◽  
Transient Heat Transfer ◽  
Transfer Coefficients ◽  
Transient Time ◽  
Transient Thermal

A general numerical method is developed with the capability to predict the transient thermal boundary layer response under various flow and thermal conditions. The transient thermal boundary layer variation due to a moving compressible turbulent fluid of varying temperature was numerically studied on a 2-D semi-infinite flat plate. The Reynolds-averaged boundary-layer equations are solved based on the compressible Falkner-Skan transformation. Turbulence is modeled using a two-layer eddy-viscosity model developed by Cebeci and Smith, and the turbulent Prandtl number formulation originally developed by Kays and Crawford. The governing differential equations are discretized with the Keller-box method. The numerical accuracy is validated through grid independence studies and comparison with the steady state solution. In turbulent flow as in laminar, heat transfer coefficient is initially very different from that obtained from quasi-steady analysis. It is found that, both the transient time scale and the magnitude of the transient heat transfer coefficients differ significantly between turbulent and laminar flow. The more complex variation of transient heat transfer rate in turbulent flow is evident, and needs further study.

scholarly journals Simulation of Thermal Transfer Through the Polyamide Intake Manifold

2019 ◽  
Vol 56 (1) ◽  
pp. 190-193
Author(s):  
Corneliu Birtok-Baneasa ◽  
Adina Budiul-Berghian ◽  
Virginia Ana Socalici ◽  
Robert Bucevschi
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Boundary Layer ◽  
Numerical Model ◽  
Air Temperature ◽  
Wall Temperature ◽  
Thermal Boundary Layer ◽  
Intake Manifold ◽  
Thermal Transfer ◽  
Steady Heat

The aim of the present study is to model the steady heat transfer of the engine polyamide intake manifold. Under the condition of a steady flow, the intake manifold wall temperature and the intake air temperature were measured to examine the effect of the thermal boundary layer on the heat transfer. Experimental data is used to generate the numerical model of airflow simulation through the intake manifold.

Protuberances in a Turbulent Thermal Boundary Layer

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Steven R. Mart ◽  
Stephen T. McClain
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Flux ◽  
Boundary Layers ◽  
Thermal Boundary Layer ◽  
Leading Edge ◽  
Heated Plate ◽  
Fluid Temperature ◽  
Constant Flux ◽  
Thermal Boundary Layers

Recent efforts to evaluate the effects of isolated protuberances within velocity and thermal boundary layers have been performed using transient heat transfer approaches. While these approaches provide accurate and highly resolved measurements of surface flux, measuring the state of the thermal boundary layer during transient tests with high spatial resolution presents several challenges. As such, the heat transfer enhancement evaluated during transient tests is presently correlated to a Reynolds number based either on the distance from the leading edge or on the momentum thickness. Heat flux and temperature variations along the surface of a turbine blade may cause significant differences between the shapes and sizes of the velocity and thermal boundary layer profiles. Therefore, correlations are needed which relate the states of both the velocity and thermal boundary layers to protuberance and roughness distribution heat transfer. In this study, a series of three experiments are performed for various freestream velocities to investigate the local temperature details of protuberances interacting with thermal boundary layers. The experimental measurements are performed using isolated protuberances of varying thermal conductivity on a steadily heated, constant flux flat plate. In the first experiment, detailed surface temperature maps are recorded using infrared thermography. In the second experiment, the unperturbed velocity profile over the plate without heating is measured using hot-wire anemometry. Finally, the thermal boundary layer over the steadily heated plate is measured using a thermocouple probe. Because of the constant flux experimental configuration, the protuberances provide negligible heat flux augmentation. Consequently, the variation in protuberance temperature is investigated using the velocity boundary layer parameters, the thermal boundary layer parameters, and the local fluid temperature at the protuberance apices. A comparison of results using plastic and steel protuberances illuminates the importance of the shape of the thermal and velocity boundary layers in determining the minimum protuberance temperatures.

Unsteady Stagnation Point Heat Transfer

1965 ◽  
Vol 87 (2) ◽  
pp. 221-230 ◽  
Author(s):  
B. T. Chao ◽  
D. R. Jeng
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Thermal Boundary Layer ◽  
Essential Feature ◽  
Step Change ◽  
Stream Velocity ◽  
Two Dimensional ◽  
Time Solution

An analysis is presented for the unsteady laminar, forced-convection heat transfer at a two-dimensional and axisymmetrical front stagnation due to an arbitrarily prescribed wall temperature or heat flux variation. The flow is incompressible and steady. The procedure begins with a consideration of the thermal boundary-layer response caused by either a step change in surface temperature or heat flux. Two appropriate asymptotic solutions, valid for small and large times, respectively, are found and satisfactorily joined for Prandtl numbers ranging from 0.01 to 100. The key to the small time solution is the transformation of the energy equation in the Laplace transform plane to an ordinary differential equation with a large parameter. An essential feature of the large time solution is the use of Meksyn’s transformation variable and the method of steepest descent in the evaluation of integrals. It is found that, for both two-dimensional and axisymmetrical stagnation, the time required for the thermal boundary layer to attain steady condition, for either a step change in surface temperature or heat flux, varies inversely with the free stream velocity and directly with 1/4 power of the Prandtl number of the fluid.

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