scholarly journals Numerical Analysis of Turbulent Heat Transfer in the Case of Minijets Array

Symmetry ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 1785
Author(s):  
Sebastian Gurgul ◽  
Tomasz Kura ◽  
Elzbieta Fornalik-Wajs
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heated Surface ◽  
Cross Flow ◽  
Turbulent Heat Transfer ◽  
Tetragonal Symmetry ◽  
Strength Analysis ◽  
Turbulent Heat ◽  
Phase Array ◽  
Surface Geometry

The presented numerical investigations show an analysis of the turbulent single-phase array of ten minijets impinging a heated surface, which lead to the intensification of heat transfer between the fluid and the surface. Attention was devoted to the comparison between phenomena occurring for the heated flat and concave surface geometry. The selection of the shapes was based on the impinging jets applications. From the numerical point of view, the focus was placed on a comparison of the Reynolds Averaged Navier–Stokes (RANS) turbulence model implementations in ANSYS Fluent software, and their impact on the modeling precision of the thermal and hydrodynamic boundary layers phenomena. The 3D numerical model was based on the continuity, momentum, and energy transport equations, together with three various RANS turbulence models: k-ω SST Kato-Launder, k-ε RNG Kato-Launder, and Intermittency Transition. The water submerged minijets, characterized by three various values of Reynolds number, were considered. Average surface Nusselt number values for all analyzed cases were compared with the experimental correlations and exhibited the same tendency but differed in detail. Numerically obtained average Nusselt number values agreed with the results of two from three correlations in the range of 10–20%. The flat surface was characterized by higher heat transfer than the concave one and an influence of the cross flow, changing the symmetrical distribution of the Nusselt number, was more visible for it. A cross flow impact was found in fuzzy hexagonal or tetragonal symmetry of this distribution. Additionally, the areas of high temperature gradient values were identified in the region of the strongest jets’ interactions, which can be important for mechanical strength analysis.

Splattering and Heat Transfer During Impingement of a Turbulent Liquid Jet

1992 ◽  
Vol 114 (2) ◽  
pp. 362-372 ◽  
Author(s):  
J. H. Lienhard ◽  
X. Liu ◽  
L. A. Gabour
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heated Surface ◽  
Film Surface ◽  
Turbulent Heat Transfer ◽  
Liquid Jet ◽  
Turbulent Heat ◽  
Disturbance Analysis ◽  
Momentum Integral ◽  
Surface Disturbances

Splattering and heat transfer due to impingement of an unsubmerged, fully turbulent liquid jet is investigated experimentally and analytically. Heat transfer measurements were made along a uniformly heated surface onto which a jet impacted, and a Phase Doppler Particle Analyzer was used to measure the size, velocity, and concentration of the droplets splattered after impingement. Splattering is found to occur in proportion to the magnitude of surface disturbances to the incoming jet, and it is observed to occur only within a certain radial range, rather than along the entire film surface. A nondimensional group developed from inviscid capillary disturbance analysis of the circular jet successfully scales the splattering data, yielding predictive results for the onset of splattering and for the mass splattered. A momentum integral analysis incorporating the splattering results is used to formulate a prediction of local Nusselt number. Both the prediction and the experimental data reveal that the Nusselt number is enhanced for radial locations immediately following splattering, but falls below the nonsplattering Nusselt number at larger radii. The turbulent heat transfer enhancement upstream of splattering is also characterized.

Effect of Porous Insert on Heat Transfer in a Backward-Facing Step Flow

2016 ◽  
Author(s):  
Marcelo J. S. de Lemos ◽  
Wagner C. Galuppo
Keyword(s):  
Heat Transfer ◽  
Porous Materials ◽  
Control Volume ◽  
Numerical Technique ◽  
Heated Surface ◽  
Simple Algorithm ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Backward Facing Step ◽  
Porous Insert

We present numerical results for turbulent heat transfer past a backward-facing-step channel with a porous insert. A non-linear eddy viscosity model was applied to handle turbulence. For a constant Darcy number, the thickness of the porous insert was varied in order to analyze its effects on the flow pattern, particularly the damping of the recirculating bubble past the insert. Further, the reduction of the Nusselt number along the bottom heated surface, when using porous materials inside the channel, was investigated. The numerical technique employed for discretizing the governing equations was the control-volume method. The SIMPLE algorithm was used to correct the pressure field and the classical wall function approach was utilized in order to handle flow calculations near the wall. Comparisons of results simulated with different porous materials were presented.

scholarly journals A study of turbulent heat transfer in convergent-divergent shaped microchannel with ribs and cavities using CFD

2020 ◽  
Vol 14 (1) ◽  
pp. 6344-6361
Author(s):  
Pankaj Srivastava ◽  
Anupam Dewan
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Thermal Resistance ◽  
Average Nusselt Number ◽  
Three Dimensional ◽  
Fluid Mixing ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Rectangular Microchannel ◽  
Better Than

This paper presents the effects of microchannel shape with ribs and cavities on turbulent heat transfer. Three-dimensional conjugate heat transfer using the SST k-ω turbulence model has been investigated for four different microchannels, namely, rectangular, rectangular with ribs and cavities, convergent-divergent (CD) and convergent-divergent with Ribs and Cavities (CD-RC). The flow field, pressure and temperature distributions and friction factor are analyzed, and thermal resistance and average Nusselt number are compared. The thermal performance of the CD-RC microchannel is found to be better than that of other microchannels considered in terms of an average Nusselt number increased from 16% to 40%. Heat transfer increases due to a strong fluid mixing and periodic interruption of boundary-layer. It is observed that with an increase in Reynolds number (Re), the thermal resitance drops rapidly. The thermal resistance of the CD-RC microchannel is decreased by 30% than that of the rectangular microchannel for Re ranging from 2500 to 7000. However, such design of microchannel loses its heat transfer effectiveness due to a high pumping power at high values of Re.

Turbulent Heat Transfer Over a Free Rotating Disk: Analytical and Numerical Predictions Using Solutions of Direct and Inverse Problems

2001 ◽  
Author(s):  
I. V. Shevchuk
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Wall Temperature ◽  
Direct Problem ◽  
Rotating Disk ◽  
Analytical Form ◽  
Turbulent Heat Transfer ◽  
Radial Coordinate ◽  
Turbulent Heat ◽  
Numerical Predictions

Abstract All known analytical solutions of the integral equation of the turbulent thermal boundary layer for a rotating disk have been obtained for the case of direct problem. This means finding the Nusselt number at a given distribution of the wall temperature. This distribution is described by power law and is monotone (derivative of wall temperature with respect to the radial coordinate does not change its sign). Outlined in this paper is an analytical form of non-monotone distribution of the wall temperature, which provided a new analytical solution for the turbulent Nusselt number including earlier known equations as a specific particular case. The solution is based on the integral method, which proved to be more precise than known Dorfman’s approach. Chosen for validation of the proposed method were turbulent heat transfer experiments of Northrop and Owen (1988). Predictions presented include analytical studies using inverse and direct problem solutions as well as numerical simulations using polynomial approximations of the experimental wall temperature distributions.

Two-Phase Heat Transfer in a Wall-Driven Cubical Heat Sink

2016 ◽  
Author(s):  
Majid Molki
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Sink ◽  
Volume Fraction ◽  
Turbulent Heat Transfer ◽  
Liquid Volume ◽  
Turbulent Heat ◽  
Fluid Temperature ◽  
Complex Flow ◽  
Liquid Volume Fraction

Turbulent heat transfer for flow of water-air mixture driven by moving walls in a cubical heat sink is investigated. One wall is maintained at an elevated temperature, while the vertical walls are at a low temperature. The cubical enclosure functions as a heat sink using water-air mixture with no phase change. Different arrangements for wall motion are considered, which include 1 to 4 moving walls. As the number of moving walls increases, the flow and heat transfer become more complex. In general, the flow reveals complex and multi-scale structures with an unsteady and evolving nature. The larger structure of the flow is resolved using Large Eddy Simulation, while the sub-grid scales are captured by the dynamic k-equation eddy-viscosity model. The focus of this work is on thermal field and heat transfer as affected by the complex flow field generated by multiple moving walls. The results indicate that the Nusselt number for the heat sink varies from 5202.8 to 7356.1, depending on the number of moving walls. Contours of fluid temperature, liquid volume fraction, local and average values of Nusselt number are among the results presented in this paper.

Local Heat Transfer in a Rotating Two-Pass Triangular Duct With Smooth Walls

1994 ◽  
Author(s):  
Sandip Dutta ◽  
Je-Chin Han ◽  
Yuming Zhang ◽  
C. Pang Lee
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Cross Section ◽  
Rotation Number ◽  
Secondary Flows ◽  
Rate Of Change ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

Earlier heat transfer studies with orthogonal rotation were conducted mostly on ducts of square cross-section. This paper reports a different cross-section, a triangular duct. Unlike a square cross-section, the triangular shape provides more restriction to the formation of the secondary flows. Moreover, the studied orientation of the right triangular duct avoids formation of symmetric vortex structures in the cross flow plane. This paper presents turbulent heat transfer characteristics of a two-pass smooth walled triangular duct. One pass is for radial outward flow and the other for radial inward flow. With rotation the radial outward and inward flow directions show different surface heat transfer characteristics. Like a square duct, differences between the trailing and the leading Nusselt number ratios for the triangular duct increase with rotation number. However, the rate of change of Nusselt number ratios with rotation number varies for the two duct geometries. Standard k-ε model predictions for a radial outward flow situation show that the Nusselt number ratio variations with Reynolds number are not drastic for the same rotation number.

Heat Transfer in Thermal Barrier Coated Rods With Circumferential and Radial Temperature Gradients

1985 ◽  
Vol 107 (1) ◽  
pp. 135-141 ◽  
Author(s):  
B. T. F. Chung ◽  
M. M. Kermani ◽  
M. J. Braun ◽  
J. Padovan ◽  
R. C. Hendricks
Keyword(s):  
Heat Transfer ◽  
Angular Position ◽  
Cross Flow ◽  
Thermal Response ◽  
Axial Direction ◽  
Ambient Air ◽  
Ceramic Coatings ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Radial Temperature

To study the heat transfer in ceramic coatings applied to the heated side of internally cooled hot section components of the gas turbine engine, a mathematical model is developed for the thermal response of plasma-sprayed ZrO2-Y2 O3 ceramic materials with a Ni-Cr-AL-Y bond coat on a Rene 41 rod substrate subject to thermal cycling. This multilayered cylinder with temperature dependent thermal properties is heated in a cross-flow by a high veloctiy flame and then cooled by ambient air. Due to high temperature and high velocity of the flame, both gas radiation and forced convection are taken into consideration. Furthermore, the local turbulent heat transfer coefficient is employed which varies with angular position as well as the surface temperature. The transient two-dimensional (heat transfer along axial direction is neglected) temperature distribution of the composite cylinder is determined numerically.

scholarly journals Steady interaction of a turbulent plane jet with a rectangular heated cavity

2016 ◽  
Vol 20 (5) ◽  
pp. 1485-1498
Author(s):  
Farida Iachachene ◽  
Amina Mataoui ◽  
Yacine Halouane
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Flow Structure ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heated Wall ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Potential Core

Turbulent heat transfer between a confined jet flowing in a hot rectangular cavity is studied numerically by finite volume method using the k-w SST one point closure turbulence model. The location of the jet inside the cavity is chosen so that the flow is in the non-oscillation regime. The flow structure is described for different jet-to-bottom-wall distances. A parametrical study was conducted to identify the influence of the jet exit location and the Reynolds number on the heat transfer coefficient. The parameters of this study are: the jet exit Reynolds number (Re, 1560< Re <33333), the temperature difference between the cavity heated wall and the jet exit (DT=60?C) and the jet location inside the cavity (Lf, 2? Lf? 10 and Lh 2.5<Lh?10). The Nusselt number increased and attained its maximum value at the stagnation points and then decreased. The flow structure is found in good agreement with the available experimental data. The maximum local heat transfer between the cavity walls and the flow occurs at the potential core end. The ratio between the stagnation point Nusselt numbers of the cavity bottom (NuB0) to the maximum Nusselt number on the lateral cavity wall (NuLmax) decreased with the Reynolds number for all considered impinging distances. For a given lateral confinement, the stagnation Nusselt number of the asymmetrical interaction Lh?10 is almost equal to that of the symmetrical interaction Lh=10.

On the Simulation of Turbulent Heat Transfer for Low-Pr Fluid Cross-Flow in Tube Banks

2021 ◽  
Author(s):  
Alessandro Tassone ◽  
Jasper Meeusen ◽  
Andrea Serafini ◽  
Gianfranco Caruso
Keyword(s):  
Heat Transfer ◽  
Cross Flow ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Tube Banks
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