scholarly journals The Influence of the Recirculation Region: A Comparison of the Convective Heat Transfer Downstream of a Backward-Facing Step and Behind a Jet in a Cross Flow

1989 ◽  
Author(s):  
V. Scherer ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Cross Flow ◽  
Separated Flows ◽  
Numerical Code ◽  
Recirculation Region ◽  
Backward Facing Step ◽  
Nusselt Numbers ◽  
Wide Range

Convective heat transfer is examined in two typical examples of separated flows, namely: the flow over a backward-facing step and a two-dimensional jet entering a cross flow. Local Nusselt numbers were determined in and behind the recirculation region. The main parameters influencing the heat transfer, the Reynolds number and the momentum flux ratio of the jet and the cross flow, have been varied in a wide range. In addition to heat transfer measurements, the flow field has been documented using a LDA-system and oil film techniques. The static pressure distribution at the wall within the separated flow is also given. The measurements are compared with the results of a numerical code, based on a finite volume method, where the well known k-ε-model is employed. The differences in Nusselt numbers predicted with a one- and a two-layer model are shown to demonstrate the influence of wall functions on heat transfer. The numerical and experimental results are compared with available data, and the differences and similarities in the heat transfer behaviour of separated flows are discussed.

The Influence of the Recirculation Region: A Comparison of the Convective Heat Transfer Downstream of a Backward-Facing Step and Behind a Jet in a Crossflow

1991 ◽  
Vol 113 (1) ◽  
pp. 126-134 ◽  
Author(s):  
V. Scherer ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Flux Ratio ◽  
Separated Flows ◽  
Numerical Code ◽  
Recirculation Region ◽  
Backward Facing Step ◽  
Nusselt Numbers ◽  
Wide Range

Convective heat transfer is examined in two typical examples of separated flows, namely, the flow over a backward-facing step and a two-dimensional jet entering a crossflow. Local Nusselt numbers were determined in and behind the recirculation region. The main parameters influencing the heat transfer, the Reynolds number, and the momentum flux ratio of the jet and the crossflow have been varied over a wide range. In addition to heat transfer measurements, the flow field has been documented using an LDA system and oil film technique. The static pressure distribution at the wall within the separated flow is also given. The measurements are compared with the results of a numerical code, based on a finite volume method, where the well known k-ε model is employed. The differences in Nusselt numbers predicted with one- and two-layer models are shown to demonstrate the influence of wall functions on heat transfer. The numerical and experimental results are compared with available data, and the differences and similarities in the heat transfer behavior of separated flows are discussed.

Experimental Investigation of Dynamically Forced Impingement Cooling

2017 ◽  
Author(s):  
Arne Berthold ◽  
Frank Haucke
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Cross Flow ◽  
Side Wall ◽  
Cooling Efficiency ◽  
Liquid Crystal Thermography ◽  
Nusselt Numbers ◽  
Dynamic Forcing ◽  
The Individual

The influence of dynamic forcing of a 7 by 7 impinging jet array on the cooling efficiency is investigated experimentally. Thereby, this work focused on determining the influence side wall induced cross flow has on the local convective heat transfer on an electrically heated target plate and on enhancing the local convective heat transfer. For the enhancement the main focus is on the influence of the impingement distance, the impingement frequency and the phaseshift between the individual rows of nozzles. Liquid crystal thermography is employed for measuring the local wall temperatures, which are used to calculate the local Nusselt numbers. The cooling efficiency of this dynamic approach is determined by comparing local Nusselt numbers with steady blowing conditions.

Effects of Curvature and Convective Heat Transfer in Curved Square Duct Flows

2006 ◽  
Vol 128 (5) ◽  
pp. 1013-1022 ◽  
Author(s):  
R. N. Mondal ◽  
Y. Kaga ◽  
T. Hyakutake ◽  
S. Yanase
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Outer Wall ◽  
Heated Wall ◽  
Dean Number ◽  
Square Duct ◽  
Nusselt Numbers ◽  
Wide Range ◽  
Steady Solutions

Non-isothermal flows with convective heat transfer through a curved duct of square cross section are numerically studied by using a spectral method, and covering a wide range of curvature, δ, 0<δ≤0.5 and the Dean number, Dn, 0≤Dn≤6000. A temperature difference is applied across the vertical sidewalls for the Grashof number Gr=100, where the outer wall is heated and the inner one cooled. Steady solutions are obtained by the Newton-Raphson iteration method and their linear stability is investigated. It is found that the stability characteristics drastically change due to an increase of curvature from δ = 0.23 to 0.24. When there is no stable steady solution, time evolution calculations as well as their spectral analyses show that the steady flow turns into chaos through periodic or multi-periodic flows if Dn is increased no matter what δ is. The transition to a periodic or chaotic state is retarded with an increase of δ. Nusselt numbers are calculated as an index of horizontal heat transfer and it is found that the convection due to the secondary flow, enhanced by the centrifugal force, increases heat transfer significantly from the heated wall to the fluid. If the flow becomes periodic and then chaotic, as Dn increases, the rate of heat transfer increases remarkably.

scholarly journals Heat Transfer Coefficients in Concentric Annuli

2002 ◽  
Vol 124 (6) ◽  
pp. 1200-1203 ◽  
Author(s):  
Jaco Dirker ◽  
Josua P. Meyer
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Heat Transfer Correlation ◽  
Transfer Coefficients ◽  
Number Range ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Wide Range ◽  
Wilson Plot

The geometric shape of a passage’s cross-section has an effect on its convective heat transfer capabilities. For concentric annuli, the diameter ratio of the annular space plays an important role. The purpose of this investigation was to find a correlation that will accurately predict heat transfer coefficients at the inner wall of smooth concentric annuli for turbulent flow of water. Experiments were conducted with a wide range of annular diameter ratios and the Wilson plot method was used to develop a convective heat transfer correlation. The deduced correlation predicted Nusselt numbers accurately within 3 percent of measured values for annular diameter ratios between 1.7 and 3.2 and a Reynolds number range, based on the hydraulic diameter, of 4 000 to 30,000.

Simulation of electrically conductive liquid convection in a spherical layer when heat is applied to the inner sphere

2019 ◽  
Author(s):  
С.В. Соловьев
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Magnetic Induction ◽  
Spherical Layer ◽  
Gravity Vector ◽  
Joule Dissipation ◽  
Conductive Liquid ◽  
Nusselt Numbers

Представлены результаты численного моделирования конвективного теплообмена электропроводящей жидкости между концентрическими сферами при подводе тепла к внутренней сфере. Исследовано влияние числа Грасгофа и джоулевой диссипации на структуру течения жидкости, поля температуры, магнитной индукции и распределение локальных чисел Нуссельта. Получено уравнение подобия теплообмена, когда ускорение свободного падения направлено к центру сферического слоя. The Boussinesq approximation is used for modelling a large class of problems of convective heat transfer in spherical concentric layers in which the gravity vector is directed vertically downwards. But for problems of geophysics and astrophysics there is a fundamental difference, the gravity vector is directed along the radius to the center of the spherical layer. Therefore, the study of convective heat transfer in spherical layers, when the vector of gravitational acceleration is directed along the radius to the center of the spherical layer, is of independent interest. In this paper, the influence of the Grashof number, the Joule dissipation heat on the fluid flow structure, temperature field, magnetic induction, and the distribution of Nusselt numbers when heat is applied from below are studied. To solve the problem, the finite element method is used. In a dimensionless formulation, the problem is solved taking into account both the heat of the Joule dissipation, magnetic, inertial, viscous and lifting forces in a spherical coordinate system and the symmetry in longitude. The stationary fields of temperature, stream functions, vortex strength, radial and meridional components of magnetic induction and the distribution of local Nusselt numbers of electro conductive liquid in a concentric spherical layer for different Grashof numbers with and without accounting for the heat of Joule dissipation are obtained when heat is applied to the inner sphere. Two critical values of the Grashof number are numerically determined. The equation of heat exchange similarity is obtained, when the acceleration of gravity is directed to the center of the spherical layer. The mathematical model and the presented results may be useful for the study of convective heat exchange of electrically conducting fluid in space technologies and in the geophysical and astrophysical problems.

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