Numerical Visualization of Heat Flow and Thermal Mixing in Various Differentially Heated Square Cavities Using Bejan’s Heatlines

2011 ◽  
Author(s):  
Ram Satish Kaluri ◽  
Tanmay Basak
Keyword(s):  
Heat Flow ◽  
Bottom Wall ◽  
Temperature Fields ◽  
Heat Distribution ◽  
Heat Sources ◽  
Large Area ◽  
Thermal Mixing ◽  
Uniform Heat ◽  
High Heat Transfer ◽  
Lower Corner

A comprehensive analysis of heat distribution and thermal mixing in steady laminar natural convective flow in discretely heated square cavities has been carried out via Bejan’s heatlines. Heatlines are analogous to streamlines and heat energy flow may be visualized by heatlines similar to streamlines which display fluid flow. The trajectories of heatlines indicate direction and magnitude of heat flow and zones of high heat transfer. The heatline approach is implemented to study heat flow in the following three different square cavities which are filled with water (Pr = 7): (1) uniformly heated bottom wall (2) distributed heating with heat sources present on central portions of the walls and (3) multiple heat sources on the walls of the cavity. Top wall is maintained adiabatic in all the cases. Galerkin finite element method with penalty parameter has been used to solve non-linear coupled partial differential equations for flow and temperature fields over a range of Rayleigh numbers (Ra = 103–105). The Galerkin method is further employed to solve the Poisson equation for streamfunctions and heatfunctions. Finite discontinuity exists at the junction of hot and cold walls leading to mathematical singularity. Solution of heatfunction for such type of situation demands implementation of non-homogeneous Dirichlet conditions. Heatlines illustrate that in uniformly heated bottom wall case, the heat from the bottom wall is not adequately distributed to the lower portion of side walls which leads to low temperature in those regions (case 1). In order to improve the heat distribution, the uniform heat sources is divided into three parts and are applied along the central regimes of the walls (case 2). It is observed that, heat distribution and thermal mixing in the cavity is significantly enhanced. However, the lower corner portions are still retained cold. In case 3, multiple heat sources are placed along the walls of the cavity along with heat sources at lower corner regions of the cavity. Heatlines indicate that, the temperature at the core is reduced compared to case 2, but uniform heat distribution results in uniformity of temperature across large area of cavity.

Heat Flow Visualization for Natural Convection in Rhombic Enclosures: Bejan’s Heatline Approach

2011 ◽  
Author(s):  
R. Anandalakshmi ◽  
Tanmay Basak
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Flow ◽  
High Heat ◽  
Temperature Fields ◽  
Buoyant Force ◽  
Thermal Mixing ◽  
Nusselt Numbers ◽  
Aspect Ratios ◽  
High Heat Transfer

The phenomena of natural convection within a rhombic enclosure filled with air (Pr = 0.71) for (a) isothermally (case 1) and (b) non-isothermally (case 2) heated bottom walls with various aspect-ratios has been studied numerically. In all the cases, top horizontal wall is maintained adiabatic and side walls are maintained cold. Galerkin finite element method with penalty parameter is used to solve non-linear coupled partial differential equations for flow and temperature fields. Poisson equation of streamfunction and heatfunction is also solved using Galerkin method. Simulations are carried out over a range of Rayleigh numbers and numerical results are presented in terms of streamfunction, heatfunction and temperature contours. Streamlines are useful to visualize the fluid flow whereas heatlines are used to study the heat energy distribution within the rhombic cavity. Heatlines are further used to visualize the trajectories of heat flow and zones of high thermal mixing. At lower Ra, heatlines are smooth circular arcs with low magnitude streamfunctions and heatfunctions and thus the heat transfer is conduction dominant. Asymmetric flow is observed for all the cases due to geometrical asymmetry. As Ra increases, buoyant force starts dominating and the magnitudes of streamfunctions and heatfunctions are found to be greater due to enhanced convection effect. Heatlines are distorted greatly showing complex heat distribution inside the cavity. It is observed that primary heat circulation cell is larger for greater tilt angles and thus thermal mixing is high. Heat transfer rates are also studied via local and average Nusselt numbers as functions of Ra and Pr on bottom, left and right walls. Various quantitative and qualitative features of Nusselt numbers have also been explained based on heatlines.

Numerical heat flow visualization analysis on enhanced thermal processing for various shapes of containers during thermal convection

2019 ◽  
Vol 30 (7) ◽  
pp. 3535-3583 ◽  
Author(s):  
Leo Lukose ◽  
Tanmay Basak
Keyword(s):  
Finite Element ◽  
Heat Flow ◽  
Flow Visualization ◽  
Thermal Processing ◽  
Bottom Wall ◽  
Heat Distribution ◽  
Content Type ◽  
Class 1

Purpose The purpose of this paper is to study thermal (natural) convection in nine different containers involving the same area (area= 1 sq. unit) and identical heat input at the bottom wall (isothermal/sinusoidal heating). Containers are categorized into three classes based on geometric configurations [Class 1 (square, tilted square and parallelogram), Class 2 (trapezoidal type 1, trapezoidal type 2 and triangle) and Class 3 (convex, concave and triangle with curved hypotenuse)]. Design/methodology/approach The governing equations are solved by using the Galerkin finite element method for various processing fluids (Pr = 0.025 and 155) and Rayleigh numbers (103 ≤ Ra ≤ 105) involving nine different containers. Finite element-based heat flow visualization via heatlines has been adopted to study heat distribution at various sections. Average Nusselt number at the bottom wall ( Nub¯) and spatially average temperature (θ^) have also been calculated based on finite element basis functions. Findings Based on enhanced heating criteria (higher Nub¯ and higher θ^), the containers are preferred as follows, Class 1: square and parallelogram, Class 2: trapezoidal type 1 and trapezoidal type 2 and Class 3: convex (higher θ^) and concave (higher Nub¯). Practical implications The comparison of heat flow distributions and isotherms in nine containers gives a clear perspective for choosing appropriate containers at various process parameters (Pr and Ra). The results for current work may be useful to obtain enhancement of the thermal processing rate in various process industries. Originality/value Heatlines provide a complete understanding of heat flow path and heat distribution within nine containers. Various cold zones and thermal mixing zones have been highlighted and these zones are found to be altered with various shapes of containers. The importance of containers with curved walls for enhanced thermal processing rate is clearly established.

Numerical Simulation of the Natural Ventilation in Workshop with Different Air Inlet Openings

2011 ◽  
Vol 250-253 ◽  
pp. 3187-3190 ◽  
Author(s):  
Ya Xin Su ◽  
Xin Wan
Keyword(s):  
Natural Ventilation ◽  
Temperature Fields ◽  
Heat Distribution ◽  
Heat Sources ◽  
Distribution Factor ◽  
Discrete Ordinate ◽  
Air Inlet ◽  
Computational Fluid Dynamics Cfd ◽  
Cfd Method ◽  
Inlet Opening

The authors numerically simulated the natural ventilation in an industrial workshop with heat sources by computational fluid dynamics (CFD) method when the height of air inlet opening was set different values. The flow and temperature fields in the workshop were simulated by realizable k-e turbulent model combined with a Discrete Ordinate (DO) radiation. Results showed the height of air inlet opening strongly influenced the flow and temperature fields in the workshop. When the height of air inlet opening increased, the natural ventilation was improved and more fresh air flowed into the workshop. When the height of air inlet opening increased from 1.7 meters to 3 meters, the temperature in the operation zone of the workshop dropped. When the height of air inlet opening increased from 2.7 meters to 3.7 meters, the temperature in operation zone did not change much, while the temperature in the upper zone of the workshop dropped. The heat distribution factor decreased first with the height of air inlet opening and then increased again. When the height of air inlet opening was 3 meters, the heat distribution factor was minimal.

Numerical analysis of heat flow in oxy-ethylene flame cutting of steel plate

2016 ◽  
Vol 232 (4) ◽  
pp. 742-751 ◽  
Author(s):  
Kang-Yul Bae ◽  
Young-Soo Yang ◽  
Myung-Su Yi ◽  
Chang-Woo Park
Keyword(s):  
Numerical Simulation ◽  
Heat Flow ◽  
Heat Affected Zone ◽  
Steel Plate ◽  
Cutting Parameters ◽  
Cutting Process ◽  
Heat Sources ◽  
Power Functions ◽  
Severe Problem ◽  
Ethylene Flame

To manufacture a steel structure, in the first step, raw steel plate needs to be cut into proper sizes. Oxy-fuel flame is widely used in the cutting process due to its flexibility with respect to accessibility, plate thickness, cost, and material handling. However, the deformation caused by the cutting process frequently becomes a severe problem for the next process in the production of steel product. To decrease the deformation, the thermo-elasto-plastic behavior of the steel plate in the cutting process should be analyzed in advance. In this study, heat sources in oxy-ethylene flame cutting of steel plate were modeled first, and the heat flow in the steel plate was then analyzed by the models of the heat sources using a numerical simulation based on the finite element method. To verify the analysis by the numerical simulation including the models, a series of experiments were performed, and the temperature histories at several points on the steel plate during the cutting process were measured. Moreover, the predicted sizes of the heat-affected zone by the numerical simulations according to the variation in the cutting parameters were compared to the experimental results. The power functions of the relationship between the sizes of the heat-affected zone and cutting parameters were obtained by the recursion analysis using the correlation between the results and parameters. The results of the numerical simulation showed good agreement with those of the experiments, indicating that the proposed models of the heat sources and thermal analysis were feasible to analyze the heat flow in the steel plate during the cutting process.

Direct numerical simulation of a turbulent jet impinging on a heated wall

2015 ◽  
Vol 764 ◽  
pp. 362-394 ◽  
Author(s):  
T. Dairay ◽  
V. Fortuné ◽  
E. Lamballais ◽  
L.-E. Brizzi
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Nusselt Number ◽  
Direct Numerical Simulation ◽  
Temperature Fields ◽  
Heated Wall ◽  
Small Scale ◽  
Turbulent Regime ◽  
High Heat Transfer ◽  
Radial Evolution

AbstractDirect numerical simulation (DNS) of an impinging jet flow with a nozzle-to-plate distance of two jet diameters and a Reynolds number of 10 000 is carried out at high spatial resolution using high-order numerical methods. The flow configuration is designed to enable the development of a fully turbulent regime with the appearance of a well-marked secondary maximum in the radial distribution of the mean heat transfer. The velocity and temperature statistics are validated with documented experiments. The DNS database is then analysed focusing on the role of unsteady processes to explain the spatial distribution of the heat transfer coefficient at the wall. A phenomenological scenario is proposed on the basis of instantaneous flow visualisations in order to explain the non-monotonic radial evolution of the Nusselt number in the stagnation region. This scenario is then assessed by analysing the wall temperature and the wall shear stress distributions and also through the use of conditional averaging of velocity and temperature fields. On one hand, the heat transfer is primarily driven by the large-scale toroidal primary and secondary vortices emitted periodically. On the other hand, these vortices are subjected to azimuthal distortions associated with the production of radially elongated structures at small scale. These distortions are responsible for the appearance of very high heat transfer zones organised as cold fluid spots on the heated wall. These cold spots are shaped by the radial structures through a filament propagation of the heat transfer. The analysis of probability density functions shows that these strong events are highly intermittent in time and space while contributing essentially to the secondary peak observed in the radial evolution of the Nusselt number.

Development of Convective Heat Transfer Near Suddenly Heated, Vertically Aligned Horizontal Wires

1987 ◽  
Vol 109 (4) ◽  
pp. 912-918 ◽  
Author(s):  
J. R. Parsons ◽  
M. L. Arey
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Fluid Layer ◽  
Convective Motion ◽  
Transient Behavior ◽  
Temperature Fields ◽  
Heat Sources ◽  
Transfer Coefficients ◽  
Vertically Aligned ◽  
The Wire

Experiments have been performed which describe the transient development of natural convective flow from both a single and two vertically aligned horizontal cylindrical heat sources. The temperature of the wire heat sources was monitored with a resistance bridge arrangement while the development of the flow field was observed optically with a Mach–Zehnder interferometer. Results for the single wire show that after an initial regime where the wire temperature follows pure conductive response to a motionless fluid, two types of fluid motion will begin. The first is characterized as a local buoyancy, wherein the heated fluid adjacent to the wire begins to rise. The second is the onset of global convective motion, this being governed by the thermal stability of the fluid layer immediately above the cylinder. The interaction of these two motions is dependent on the heating rate and relative heat capacities of the cylinder and fluid, and governs whether the temperature response will exceed the steady value during the transient (overshoot). The two heat source experiments show that the merging of the two developing temperature fields is hydrodynamically stabilizing and thermally insulating. For small spacing-to-diameter ratios, the development of convective motion is delayed and the heat transfer coefficients degraded by the proximity of another heat source. For larger spacings, the transient behavior approaches that of a single isolated cylinder.

Sign in / Sign up

Export Citation Format

Share Document