Analysis Of Turbulent Heat Transfer Research Articles

Mechanism Analysis of Turbulent Heat Transfer in Porous Coking of Hydrocarbon Fuels under Supercritical Pressure

Mechanism Analysis of Turbulent Heat Transfer in Porous Coking of Hydrocarbon Fuels under Supercritical Pressure

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

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.

Turbulent heat transfer analysis in supercritical hydrogen fuel flow considering thermal stratification

Due to the single-side heating on the rectangular channel, the coolant faces a serious thermal stratification problem, and thus the heat transfer performance is reduced. To effectively improve flow and heat transfer characteristics, and weaken nonuniform distribution problem, a new cooling structure with combining fin and spherical convexity is built in this paper. The study results indicate that the new structure effectively reduced the maximum heat wall temperature, and weakened the fluid nonuniform distribution problem. Comparing with smooth channel and spherical convexity structure, the maximum temperature is decreased by 18.4% and 10.3%, and temperature nonuniform index is decreased by 25.1% and 20.8%. In addition, as the higher fluid temperature means the higher specific heat capacity, the new structure made full use of the heat sink of hydrogen, making the more heat can be quickly taken away from the heat wall. The thermal stratification phenomenon can be obviously weakened.

CFD analysis of turbulent heat transfer and thermal striping phenomena in T-junctions with liquid sodium

This paper describes the methodology adopted to perform a CFD analysis with the aim to study thermal striping in T-junctions with liquid sodium; in particular, a portion of the Phenix reactor’s secondary circuit has been taken into account, by implementing a detailed 3D model of both fluid and solid domain; RANS and LES turbulence models are used and their results are compared, then frequency analysis of temperature fluctuations has been performed. One of the main results of this analysis is that LES turbulence models are not yet completely reliable in evaluating.

Analysis of Turbulent Heat Transfer in Rectangular Flow Channels inside the First Wall of Blanket Modules

To precisely calculate the temperature field of the first wall (FW) in blanket modules, the important thermo-hydraulic parameter, turbulent heat transfer coefficient (HTC), is needed firstly. In this paper, the HTC of turbulent flow in a fully developed rectangular channel in which only one side wall was uniformly heated to model the high heat flux from plasma discharge in a fusion reactor was detailedly studied using the computational fluid dynamics (CFD) method. The effects of three turbulent models (standard k − ɛ, SST, and SSG) and the aspect ratios on HTC were primarily analyzed. The accuracy of the empirical correlations for HTCs which are used commonly in fusion engineering applications was also investigated. The results show that the predict HTCs using the CFD method agree well with those of the experiments. The averaged HTCs in the whole heated wall calculated by all three kinds of turbulent models have very small differences. But the SSG turbulent model can reasonably predict the secondary flow motion and has superior performance to the two others for modeling the details of the turbulent flow and heat transfer. The averaged HTCs slightly decrease with the increase of aspect ratios at the same Reynolds number. The averaged HTCs calculated with empirical correlations have little differences with those calculated with the CFD method and so the empirical correlations should be carefully used, especially the Dittus–Boelter correlation. These results are helpful to the precise simulation of the designed FW with rectangular flow channels.

Turbulent Heat Transfer Analysis of a Three-Dimensional Array of Perforated Fins Due to Changes in Perforation Sizes

Turbulent heat transfer characteristics of three-dimensional and rectangular perforated fins, including perforation like channels along the length of the fins, are investigated. Both dimensions and numbers of perforations are changed at the highest porosity in the study of Shaeri and Yaghoubi [7] to determine the effects of perforation sizes on the heat transfer characteristics of the perforated fins. Results show that at a specific porosity, a fin with a higher number of perforations enhances the heat transfer rate more efficiently. Also, total drag is not only remarkably lower in perforated fins compared with a solid fin, but also becomes smaller by decreasing the number of perforations.

Numerical Analysis of Turbulent Heat Transfer and Flow through Mixing Split Vane in a Sub-channel of AP1000 Nuclear Reactor

This paper evaluates three-dimensional turbulent flow and convective heat transfer through mixing split vane in a single-phase and steady-state sub-channel of AP1000 nuclear reactor core by using general computational fluid dynamics code, Fluent6.3.26.Realizable K-ɛ model is used as a turbulent closure model, and the sub-channel is analyzed by numerical simulation. The results show that the mixing split vanes, which affect strongly the heat transfer in the sub-channel, are lateral flow, swirl and turbulent intensity between the sub-channels, and give reasonable agreements with experimental equations and AP1000 thermal hydraulic design.

Analysis of turbulent heat transfer and fluid flow in channels with various ribbed internal surfaces

This paper presents results of a numerical investigation of heat transfer and flow pattern characteristics of a channel with repeated ribs on one broad wall. Numerical computations are performed for seven ribs placed on the bottom wall of a channel for Reynolds numbers ranging from 10,000 to 30,000. The newly modified ribs (the ones with convex pointing upstream/downstream rib, wedge pointing upstream/downstream rib, concave pointing upstream/downstream rib and also concave-concave rib as well as convex-concave rib), are proposed for simulation with prospect to reduce flow separation and extend reattachment area compared to the unmodified square rib. The numerical results are reported in forms of flow structure, temperature field, turbulent kinetic energy, Nusselt number, friction factor and thermal enhancement factor. The results indicate the rib with concave-concave surfaces efficiently suppresses flow separation bubble in the corner of the rib and induces large recirculation zone over those of the others, hence giving the highest Nusselt number and friction factor. On the other hand, the one with convex-concave surface provides the lowest friction factor with moderate Nusselt number. Due to the prominent effect of its low friction factor, the rib with convex-concave surface offers the highest thermal enhancement factor of 1.19.

2105 屈曲管路内の乱流熱伝達数値解析(G06-2 熱工学(2) 伝熱(2),21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

2105 屈曲管路内の乱流熱伝達数値解析(G06-2 熱工学(2) 伝熱(2),21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

Numerical Simulation of Turbulent Flow and Heat Transfer in a Cooling Channel of IFMIF High Flux Test Module

In the high flux test module of the International Fusion Materials Irradiation Facility, temperature control of irradiated specimens are done by gas cooling and electric heating. The width of cooling channels is supposed to be 1 mm in the module vessel which is a rectangular duct with wall thickness of 1 mm. Since there is large pressure difference up to several atmospheric pressure between the inside and outside the vessel, it is considered that the vessel wall and the cooling channels easily deforms. In order to estimate cooling performances for the coolant flowing in the deformed channel, we conduct a finite element analysis of turbulent heat transfer in a mildly curved channel using large-eddy simulation. It is found\\from the simulation that heat transfer on the concave wall drastically changes according to local change in flow aspect such as separation while that on the opposite flat wall is affected only by average flow velocity and is not largely changed by the channel deformation.

Shape optimization of three-dimensional channel roughened by angled ribs with RANS analysis of turbulent heat transfer

A numerical procedure for optimizing the shape of three-dimensional channel with angled ribs extruded on both walls is presented to enhance turbulent heat transfer. The response surface based optimization is used as an optimization technique with Reynolds-averaged Navier–Stokes analysis of fluid flow and heat transfer. Shear stress transport (SST) turbulence model is used as a turbulence closure. Computational results for heat transfer rate show good agreements with experimental data. Four dimensionless variables such as, rib pitch-to-rib height ratio, rib height-to-channel height ratio, streamwise rib distance on opposite wall to rib height ratio, and the attack angle of the rib are chosen as design variables. The objective function is defined as a linear combination of heat transfer and friction loss related terms with a weighting factor. D-optimal method is used to determine the training points as a mean of design of experiment. Sensitivity of the objective function to each design variable has been evaluated. And, optimal values of the design variables have been obtained in a range of the weighting factor.

Turbulent heat transfer in a confined jet

Using the triaxial thermoanemometer probe with a temperature sensor provided an experimental analysis of turbulent heat transfer in the recirculation zone of a confined jet. The measured raw data were analysed to obtain time-averaged characteristic of turbulence. The results allowed an evaluation of the turbulent heat flux components, which took their maximal values in the mixing region of primary and secondary streams. For better understanding of the heat transfer processes, a budget of turbulent heat flux was analysed, based on the derived equations presented in the cylindrical coordinate system. Applying derived equations and the measured turbulence characteristic, the values of particular components of heat flux budget were estimated and discussed. The heat and fluid flow data can be offered as a database for non-isothermal turbulent flow modelling.

Numerical Analysis of Turbulent Heat Transfer in a Square Duct with Different Rib Shapes

Numerical analysis has been performed for three-dimensional developed turbulent flow in a square duct with rib-roughened walls. Special attention pays for the prediction of turbulent heat transfer with roughened wall. Roughened wall is composed of small ribs which are located periodically on bottom wall of square duct. In order to clarify the influence of rib cross sectional shape on flow and temperature fields, three kinds of ribs, that are square, triangular and elliptical cross section, is examined from the point of heat transfer. In numerical calculation, algebraic Reynolds stress model is selected for flow field in order to predict anisotropic turbulent flow precisely and zero equation model assuming constant Prandtl number is applied for temperature field to make clear whether such simple model is able to evaluate Nusselt number correctly. Periodic boundary condition has been used for this flow to save computational time. Calculated results of temperature field are compared with the experimental data in order to examine the validity of the presented numerical method. As a result of this calculation, it has been found out that the present method could predict temperature contour lines and Nusselt number qualitatively although agreement is certainly not perfect in all detail. Adding to this, turbulent structure is affected by rib cross section shape, although rib height is small compared with side length of square. Especially, elliptical cross section promotes the production of vertical fluctuating velocity and shear stress which leads to generate the secondary flow of the second kind more actively than the other rib shapes. At the same time, calculated results suggest that heat transfer is enhanced by the elliptical cross section.

Three-Dimensional Analysis of Turbulent Heat Transfer and Flow through Mixing Vane in A Subchannel of Nuclear Reactor

The present work evaluates the effects of mixing vane shape on the flow structure and heat transfer downstream of mixing vane in a subchannel of fuel assembly, by obtaining velocity and pressure fields, turbulent intensity, flow-mixing factors, heat transfer coefficient, and friction factor using three-dimensional RANS analysis. Four different shapes of mixing vane designed by the authors, are tested to evaluate the performances in enhancing the heat transfer, in comparison with commercialized split vane. Standard k-ε model are used as a turbulence closure model, and, periodic and symmetry conditions are set as boundary conditions. The flow blockage ratio is kept constant, but the twist angle of mixing vane is changed. The results with three turbulence models are compared with experimental data.

Three-Dimensional Analysis of Turbulent Heat Transfer and Flow through Mixing Vane in A Subchannel of Nuclear Reactor

Three-Dimensional Analysis of Turbulent Heat Transfer and Flow through Mixing Vane in A Subchannel of Nuclear Reactor

A scale analysis of turbulent heat transfer driven by buoyancy in a porous layer with homogeneous heat sources

A heat transfer analysis is conducted for the turbulent natural convection in a porous layer with homogeneous heat sources. It is assumed that the top and the bottom of the layer is cooled at a constant temperature and insulated, respectively. Darcy's law is used to explain characteristics of fluid motion. Through a scale analysis on the turbulent heat and momentum transfer, a scale relation for Nusselt number is derived as a function of Rayleigh number. With the aid of available experimental and analytical results, Nusselt number correlations are proposed. The critical Rayleigh number for the onset of convection is also mentioned.

A123 DNS による回転曲りチャネル内の熱流動および回転曲りパラメーターの検討

A123 DNS による回転曲りチャネル内の熱流動および回転曲りパラメーターの検討

Analysis of turbulent heat transfer from sinusoidal profile finned dissipators

In the present work the effectiveness of thermal dissipators cooled by a fluid in turbulent flow is studied by varying the fins spacing and shape. The profile of the fin is described by a sinusoidal function depending on two parameters that define its amplitude and number of oscillations. The velocity distribution in the fluid, and the temperature distribution in the dissipator and in the fluid are determined with the help of a finite element method. The model allows to study the variations of the heat transfer coefficient due to the fluid dynamic conditions imposed by the fin profile. Lastly, a combination of geometrical parameters is proposed, which yields the best dissipator performance under particular conditions.

Numerical Analysis of Turbulent Heat Transfer in a Square Duct with One Rough Wall by Algebraic Turbulent Heat Flux Models.

A numerical analysis has been performed for fully developed turbulent flow and heat transfer in a rectangular duct with smooth and rough walls by using algebraic Reynolds stress and turbulent heat flux models. The wall functions and the universal law of the wall, which are used as the boundary conditions of turbulent energy and dissipation, apply in the present analysis instead of taking shape of roughness element into account. Therefore, the roughness enters through the log law relating the velocity at the first grid point away from the wall with the friction velocity. In this numerical analysis, two kinds of turbulent heat flux models, i. e. Lumley-Launder model and Jones-Musonge model, are examined to compare the contour distributions of turbulent heat fluxes in three dimensions which have been measured in detail. In numerical analysis, convection and diffusion terms for the transport equation of turbulent heat flux are modelled as an algebraic turbulent heat flux model. From the comparison calculated results with the experimental data, it is found that two models can predict the mean temparature distributions which are distorted near the smooth wall located opposite to rough wall side. On top of that, Lumley-Launder model is able to better realize mean temperature near smooth and rough walls than Jones-Musonge model. As for comparison of the turbulent heat flux, calculated results suggest that two models predict characteristic features while two models have tendency to overestimate the experimental values.

Preliminary Numerical Analysis of Turbulent Heat Transfer in Helium-Cooling Porous Channels for Fusion Reactors

An analytical study of the turbulent heat transfer in the helium-cooling porous channels for fusion reactors was performed using a direct-simulation numerical approach with no empirical correlations such as the Darcy's law and effective thermal conduction in the porous media. A numerical analysis code for the helium-cooling porous channels was developed and preliminary numerical analyses were carried out. A new porous calculation model was proposed. The porous media was simulated as cubic solids and the direct-contact thermal conduction in the channel was simulated using solid bars. From the numerical analysis results, it was identiñed that the present porous model is useful to predict the turbulent heat transfer characteristics in the helium-cooling porous channel.