scholarly journals Studi Numerik 2-D Perpindahan Panas Aliran Crossflow Pada Silinder Sirkular Tunggal Dan Tandem Dengan Modifikasi Turbulent Viscosity

2017 ◽  
pp. 82
Author(s):  
Arif Kurniawan
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Shear Layer ◽  
Numerical Study ◽  
Turbulent Viscosity ◽  
Turbulence Models ◽  
Flow Regimes ◽  
Heat Transfer Process ◽  
Navier Stokes ◽  
Tube Banks

The  crossflow in cylinder marked by the phenomenon of stagnation point, shear layer separation and wake formation. Characteristics of flow regimes can be unsteady laminar flow (the formation of vortex shedding regime), transitional (regime with the transition to turbulent flow pattern in the wake area) and sub-critical (regime formation of the turbulent on shear layer). The value of the Reynolds number is very influential on the flow regimes characteristics of the flow, while the heat transfer process is heavily influenced by the value of Prandtl number. The amount of heat transfer is indicated by the parameter of  Nusselt number. This study uses a numerical study by modifying the quantity of turbulent, ie the turbulent viscosity by interpreting UDF (user defined function). The results of numerical studies in the form of Nusselt number will be compared with the value of Nusselt number of experimental results and to create a basis consept for studying the mechanism of the flow phenomenon and  heat transfer in the heat exchanger tube banks. The method used is a steady and unsteady 2-DRANS (Reynolds-averaged Navier Stokes) numerical simulations with 3 modeling, namely the standard k-є, standard k-ω and SST k-ω turbulence models. 

Heat Transfer and Hydraulic Resistance in Turbulent Flow in Vertical Round Tubes At Supercritical Pressures. Part 1. Results From Numerical Simulations Using Algebraic Turbulent Viscosity Models

2020 ◽  
Author(s):  
Georgii Glebovich Yankov ◽  
Vladimir Kurganov ◽  
Yury Zeigarnik ◽  
Irina Maslakova
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Turbulent Flow ◽  
Hydraulic Resistance ◽  
Turbulent Viscosity ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Heating And Cooling ◽  
Prediction Techniques ◽  
Vertical Tubes

Abstract The review of numerical studies on supercritical pressure (SCP) coolants heat transfer and hydraulic resistance in turbulent flow in vertical round tubes based on Reynolds-averaged Navier-Stokes (RANS) equations and different models for turbulent viscosity is presented. The paper is the first part of the general analysis, the works based on using algebraic turbulence models of different complexity are considered in it. The main attention is paid to Petukhov-Medvetskaya and Popov et al. models. They were developed especially for simulating heat transfer in tubes of the coolants with significantly variable properties (droplet liquids, gases, SCP fluids) under heating and cooling conditions. These predictions were verified on the entire reliable experimental data base. It is shown that in the case of turbulent flow in vertical round tubes these models make it possible predicting heat transfer and hydraulic resistance characteristics of SCP flows that agree well with the existed reliable experimental data on normal and certain modes of deteriorated heat transfer, if significant influence of buoyancy and radical flow restructuring are absent. For the more complicated cases than a flow in round vertical tubes, as well as for the case of rather strong buoyancy effect, more sophisticated prediction techniques must be applied. The state-of-the-art of these methods and the problems of their application are considered in the Part II of the analysis.

Natural Convective Flow and Heat Transfer in a Collector Storage with an Immersed Heat Exchanger: Numerical Study

2005 ◽  
Vol 127 (3) ◽  
pp. 324-332 ◽  
Author(s):  
Yan Su ◽  
Jane H. Davidson
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Numerical Study ◽  
Storage System ◽  
Fluid Motion ◽  
Heat Transfer Process ◽  
Strong Mixing ◽  
Scale Analysis ◽  
Three Dimensional Model

A three-dimensional model and dimensionless scale analysis of the transient fluid dynamics and heat transfer in an inclined adiabatic water-filled enclosure with an immersed cylindrical cold sink is presented. The geometry represents an integral collector storage system with an immersed heat exchanger. The modeled enclosure has an aspect ratio of 6:1 and is inclined at 30deg to the horizontal. The heat exchanger is represented by a constant surface temperature horizontal cylinder positioned near the top of the enclosure. A scale analysis of the transient heat transfer process identifies four temporal periods: conduction, quasi-steady, fluctuating, and decay. It also provides general formulations for the transient Nusselt number, and volume-averaged water temperature in the enclosure. Insight to the transient fluid and thermal processes is provided by presentation of instantaneous flow streamlines and isotherm contours during each transient period. The flow field consists of two distinct zones. The zone above the cold sink is nearly stagnant. The larger zone below the sink is one of strong mixing and recirculation initiated by the cold plume formed in the boundary layer of the cylindrical sink. Correlations for the transient Nusselt number and the dimensionless volume-averaged tank temperature predicted from the model compare favorably to prior measured data. Fluid motion in the enclosure enhances heat transfer compared to that of a cylinder in an unbounded fluid.

Empirical Heat Transfer Correlations during Frost Deposition on a Triangular Tube Banks Arrangement

2016 ◽  
Vol 366 ◽  
pp. 88-96
Author(s):  
Raquel da Cunha Ribeiro da Silva ◽  
Carlos Salinas Sedano ◽  
Kamal A.R. Ismail ◽  
Paúl Adrian Delgado Maldonado
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Numerical Study ◽  
Experimental Measurements ◽  
Empirical Correlations ◽  
Frost Formation ◽  
Cylindrical System ◽  
Experimental Correlation ◽  
Tube Banks ◽  
Dimensionless Correlations

An experimental study was reported earlier on the development of frost formation by humid flow passing over the cylinder. In this study, dimensionless correlations used in previous experimental data, and reported empirical correlations of the Nusselt number, were used. This paper reports results of an experimental and numerical investigation where the emphasis was placed on obtaining empirical correlation for the Nusselt number. In this work some experimental results of the frost thickness around every cylinder in a triangular arrangement are presented, an estimated experimental correlation to find Nusselt number. This correlation is based on the experimental measurements in a wind tunnel situated in the Laboratory of Thermal storage and Fluids in the Mechanical Engineering Faculty at Unicamp. A numerical study is performed to study the frost formation in the cylindrical system.

Numerical Study on Heat Transfer Enhancement and Friction Factor of LS-2 Parabolic Solar Collector

2013 ◽  
Vol 6 (1) ◽  
Author(s):  
Omid Karimi Sadaghiyani ◽  
Seyed Mehdi Pesteei ◽  
Iraj Mirzaee
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Solar Collector ◽  
Numerical Study ◽  
Simulation Method ◽  
Finite Volume Methods ◽  
Statistical Technique ◽  
Heat Transfer Process ◽  
Outlet Temperature

In this work, the distribution of solar heat flux around receiver was calculated by Mont-Carlo statistical technique that has been written using matlab. The numerical investigations of convective heat transfer process, friction factor, and efficiency of LS-2 parabolic collector have been performed. Based on finite volume methods, the influence of Rayleigh number (Ra), diameter of plugs, and thermal conductivity of the tube were studied on Nusselt number, outlet temperature, and the efficiency of collector. Because of using several central plugs with different diameters, the amounts of flow velocity have been changed, as the mass flow rate of each case study was considered constant. The diameters of plug were as: 10, 15, and 25 mm, respectively. The diameter of LS-2 collector plug was 50.8 mm (r* = 0.765). So, in order to validate the numerical simulation method, the outlet temperature of LS-2 collector (Dp = 50.8 mm) was compared with Dudley et al. (Dudley, V., Kolb, G., Sloan, M., and Kearney, D., 1994, “SEGS LS2 Solar Collector—Test Results,” Report of Sandia National Laboratories, Report No. SANDIA94-1884) experimental results. Finally, the results show that, for r*<0.6 m, the natural convection conquers to forced convection and for r*>0.6 m the mixed convection is the dominant mechanism of heat transfer. Also, with the increase of plug diameter, friction factor decreases and the minimum amount of Nusselt number is occurred at r*=0.6 m.

scholarly journals Natural convection in tilted square cavities with triangular shaped top cold wall

1970 ◽  
Vol 39 (1) ◽  
pp. 30-39 ◽  
Author(s):  
Tamanna Sultana ◽  
Sumon Saha ◽  
Goutam Saha ◽  
Md Quamrul Islam
Keyword(s):  
Heat Transfer ◽  
Finite Element ◽  
Nusselt Number ◽  
Natural Convection ◽  
Numerical Study ◽  
Constant Heat Flux ◽  
Heat Transfer Process ◽  
Bottom Wall ◽  
Grashof Number ◽  
Inclination Angles

A numerical study of natural convection in a tilted square cavity with heated horizontal base and cold upper wall is presented. The present study is based in such a configuration where the top triangular wall of two different shapes is maintained at a constant low temperature. A constant heat flux source whose length is 20% of the total length of the cavity is discretely embedded at the left corner of the bottom wall. The remaining part of the bottom wall and the two sidewalls are considered to be adiabatic. The study includes computations for inclination angles of the cavity from 0° to 45°, where the Grashof number, Gr varies from 103 to 106. The Penalty finite element method has been used to see the effects of inclination angles and Grashof number on heat transfer process in the cavity. Results are presented in the form of streamline and isotherm plots as well as the variation of the average Nusselt number. Observation shows the significant effect of different triangular top surface on the heat transfer characteristics at the higher Grashof number and inclination angle. Keywords: Natural convection, Penalty finite element, Nusselt number, Isoflux heating. doi:10.3329/jme.v39i1.1831 Journal of Mechanical Engineering, vol. ME39, No. 1, June 2008 30-39  

Natural Convective Flow and Heat Transfer in a Collector Storage With an Immersed Heat Exchanger: Numerical Study

Solar Energy ◽  
2005 ◽  
Author(s):  
Yan Su ◽  
Jane H. Davidson
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Numerical Study ◽  
Storage System ◽  
Three Dimensional ◽  
Heat Transfer Process ◽  
Strong Mixing ◽  
Scale Analysis ◽  
Three Dimensional Model

A three-dimensional model and dimensionless scale analysis of the transient fluid dynamics and heat transfer in an inclined adiabatic water-filled enclosure with an immersed cylindrical cold sink is presented. The geometry represents an integral collector storage system with an immersed heat exchanger. The modeled enclosure has an aspect ratio of 6:1 and is inclined at 30 degrees to the horizontal. The heat exchanger is represented by a constant surface temperature horizontal cylinder positioned near the top of the enclosure. A scale analysis of the transient heat transfer process identifies four temporal periods: conduction, quasi-steady, fluctuating and decay. It also provides general formulations for the transient Nusselt number, and volume averaged water temperature in the enclosure. Insight to the transient fluid and thermal processes is provided by presentation of instantaneous flow streamlines and isotherm contours during each transient period. The flow field consists of two distinct zones. The zone above the cold sink is nearly stagnant. The larger zone below the sink is one of strong mixing and recirculation initiated by the cold plume formed in the boundary layer of the cylindrical sink. Correlations predicted with the model for the transient Nusselt number and the dimensionless volume averaged tank temperature expressed in terms of the initial Rayleigh number compare favorably to prior measured data.

scholarly journals A Numerical Analysis on Flow and Heat Transfer in the Entrance Region of an Axially Rotating Pipe

1995 ◽  
Vol 2 (2) ◽  
pp. 123-129 ◽  
Author(s):  
Shuichi Torii ◽  
Wen-Jei Yang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Numerical Study ◽  
Turbulence Models ◽  
Axial Rotation ◽  
Entrance Region ◽  
Heat Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Radial Profiles ◽  
Thermal Development

A numerical study is performed to investigate turbulent flow and heat transfer characteristics in the entrance region of a pipe rotating around its axis. Various different k-ε turbulence models are employed whose function consists of the Richardson number in the e model to take swirling into account. The axial rotation of the pipe suppresses thermal development and causes a substantial decrease in the Nusselt number along the flow. It is disclosed from the study that an increase in the rotation rate induces a reduction in the velocity gradient, turbulent kinetic energy and Reynolds stress in the vicinity of the wall and a substantial deformation of these radial profiles in the downstream direction. It results in both a suppression of the thermal development and an attenuation in the Nusselt number along the flow.

scholarly journals RANS and LES Investigations of Vertical Flows in the Fuel Passages of Gas-Cooled Nuclear Reactors

2008 ◽  
Author(s):  
Amir Keshmiri ◽  
Mark A. Cotton ◽  
Yacine Addad ◽  
Stefano Rolfo ◽  
Flavien Billard
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Forced Convection ◽  
Turbulent Flows ◽  
Nuclear Reactors ◽  
Broad Class ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Turbulence Structure ◽  
Eddy Simulation

Coolant flows in the cores of current gas-cooled nuclear reactors consist of ascending vertical flows in a large number of parallel passages. Under post-trip conditions such heated turbulent flows may be significantly modified from the forced convection condition by the action of buoyancy, and the thermal-hydraulic regime is no longer one of pure forced convection. These modifications are primarily associated with changes to the turbulence structure, and indeed flow laminarization may occur. In the laminarization situation heat transfer rates may be as low as 40% of those in the corresponding forced convection case. The heat transfer performance of such ‘mixed’ convection flows is investigated here using a range of refined Reynolds-Averaged-Navier-Stokes (RANS) turbulence models. While all belong to the broad class of Eddy Viscosity Models (EVMs), the various RANS closures have different physical parameterizations and might therefore be expected to show different responses to externally-imposed conditions. Comparison is made against experimental and Direct Numerical Simulation (DNS) data. In addition, Large Eddy Simulation (LES) results have been generated as part of the study. Three different CFD codes have been employed in the work: ‘CONVERT’, ‘STAR-CD’, and ‘Code_Saturne’, which are respectively in-house, commercial, and industrial packages. It is found that the early EVM scheme of Launder and Sharma [1] is in the closest agreement with consistently-normalized DNS results for the ratio of mixed-to-forced convection Nusselt number (Nu/Nu0). However, in relation to DNS and experimental data for forced convection Nusselt number, other models perform better than the Launder-Sharma scheme. The present investigation has revealed discrepancies between direct-simulation, experimental, and the current LES studies.

CFD modeling and validation of heat transfer inside an autoclave based on a mesh independency study

2021 ◽  
pp. 002199832097904
Author(s):  
Junhong Zhu ◽  
Tim Frerich ◽  
Axel S Herrmann
Keyword(s):  
Heat Transfer ◽  
Cfd Simulation ◽  
Stokes Equations ◽  
Numerical Study ◽  
Fluid Velocity ◽  
Turbulence Models ◽  
Cfd Modeling ◽  
Navier Stokes ◽  
Cost Calculation ◽  
Numerical Effort

Autoclave processing is the main technology used in the manufacturing of structural aerospace composite parts. To optimize the autoclave process, the thermal behavior of the part and mold can be investigated through simulations. Computational fluid dynamics (CFD) provide a significant contribution to studies on heat transfer and airflow patterns, which are key points in an optimization applied to achieve a homogeneous temperature distribution inside composite parts. The solution is produced by solving the 3 D unsteady Navier–Stokes equations. This paper describes a systematic numerical study using the CFD approach to significantly improve the modeling efficiency of the heat transfer coefficient (HTC) inside an autoclave and maintain a high level of accuracy. Considering the modeling cost, calculation time, and accuracy of the results, a reasonable hybrid mesh is used based on a mesh independency study. The level of grid independence is examined using the general Richardson extrapolation method. In addition, a more robust autoclave model is presented, which is unaffected by the inlet turbulence. Further, the inlet fluid velocity and turbulence models have been identified as sensitive influencing factors. In this study, the Spalart–Allmaras turbulence model shows the best performance compared with the standard [Formula: see text] and [Formula: see text] SST models. Finally, the results are validated with the experimental data. The mean error of the simulated temperatures in the calorimeter for the front, middle and rear positions are [Formula: see text]C, [Formula: see text]C, and [Formula: see text]C, indicating a good agreement with the experiments. This paper provides guidelines on the use of a CFD simulation to predict the heat transfer during the autoclave curing process with high accuracy and reduced numerical effort.

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