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.

Numerical Investigation on Heat Transfer of Supercritical Water With a Variable Turbulent Prandtl Number Model

2020 ◽  
Vol 6 (3) ◽  
Author(s):  
Xiangfei Kong ◽  
Dongfeng Sun ◽  
Lingtong Gou ◽  
Siqi Wang ◽  
Nan Yang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Prandtl Number ◽  
Supercritical Fluids ◽  
Supercritical Water ◽  
Viscosity Ratio ◽  
Turbulent Viscosity ◽  
Turbulence Models ◽  
Turbulent Prandtl Number ◽  
Vertical Tubes

Abstract Turbulent Prandtl number (Prt) has a great impact on the performance of turbulence models in predicting heat transfer of supercritical fluids. Unrealistic treatment of Prt may lead to large deviations of the prediction results from experimental data under supercritical conditions. In this study, the effect of Prt on heat transfer of supercritical water was extensively studied by using shear stress transport (SST) k–ω turbulence model, and the results suggested that using the existing Prt models would lead to failures in predicting the heat transfer characteristics of supercritical water under deteriorated heat transfer (dht) conditions. A new variable Prt model was proposed with the Prt varied with pressure, turbulent viscosity ratio, and molecular Prandtl number. The new model was validated by comparing the numerical results with the corresponding experimental data, and it was found that the new variable Prt model exhibited better performance on reproducing the dht of supercritical water in vertical tubes than those of the existing Prt models.

Numerical Comparisons of Heat Transfer From a Single Jet Emanating From a Slot Nozzle Impinging on an Isothermal Plate

2019 ◽  
Author(s):  
Cristian Tibabisco ◽  
Salvador Vargas-Díaz ◽  
Samir A. Salamah
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Stagnation Point ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Thermal Design ◽  
Navier Stokes ◽  
Reynolds Average Navier Stokes ◽  
Single Jet ◽  
Reynolds Average

Abstract Impingement jets are used in different cooling applications where it is required to remove large amounts of heat. Heat transfer in the stagnation point for a single jet impinging on an isothermal plate is investigated with four turbulence models. Two models are RANS (Reynolds Average Navier-Stokes): Transition SST and Transition κ–κl–ω. The other two models are URANS (Unsteady Reynolds Average Navier-Stokes): SAS and DES-SST. This paper explores the best turbulence model for thermal design and cooling purposes. Results are validated with experimental data reported by Gardon & Akfirat. These four turbulence models are available in the commercial CFD software package ANSYS FLUENT 18.1. Special attention is paid to the heat transfer in the impingement region through evaluation of Nusselt number in the stagnation point. Different dimensionless nozzle-to-plate distances are considered in this work (z/b = 14 to z/b = 40), and two different Reynolds numbers are used Re = 11,000 y Re = 22,000. Three turbulence models are within reasonable accuracy (10%) of the experimental data, but some turbulence models have problems with convergence and grid independence, especially the URANS models. Based on these results, the best turbulence model for applications in heating and cooling systems where impingement heat transfer is critical is the Transition κ–κl–ω.

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 II. Results From Numerical Simulation with Differential Turbulent Viscosity Models

2020 ◽  
Author(s):  
Georgii Glebovich Yankov ◽  
Vladimir Kurganov ◽  
Yury Zeigarnik ◽  
Irina Maslakova
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Turbulent Viscosity ◽  
Turbulence Models ◽  
Model Verification ◽  
Wall Functions ◽  
Flow And Heat Transfer ◽  
Numerical Studies ◽  
Viscosity Models ◽  
Mesh Independence

Abstract The review of numerical studies on the turbulent flow and heat transfer of supercritical pressure (SCP) coolants in heated vertical round tubes, which were conducted using different differential turbulent viscosity models, is presented. It is shown that most often the turbulent viscosity models only qualitatively predict the deteriorated heat transfer effects, which appear due do buoyancy forces and thermal acceleration effects at strongly variable physical properties of a coolant. At the same time, the regimes of normal heat transfer are successfully reproduced by "standard" k- and RNG models with wall functions, as well as by two-layer models. The conclusion is made that none of the presently known turbulent viscosity models can be confidently recommended for predicting any flow regimes and heat transfer of SCP coolants. Strongly variable properties of SCP coolant stipulate more strict demands for validating mesh independence of the obtained results and for an accuracy of approximation of the tabulated values of the coolant properties. It was ascertained that using more and more numerous calculation codes and the results from their application requires certain caution and circumspection. In some works, the parameters of the regimes used for turbulent viscosity model verification and those of the experiments attracted for such verification did not correspond each other. It is pointed out that the crying discrepancy in the predictions of different authors conducted using the same CFD codes and turbulence models and possible reasons for such a discrepancy are not analyzed.

Numerical Simulation of Turbine Blade Boundary Layer and Heat Transfer and Assessment of Turbulence Models

1997 ◽  
Vol 119 (4) ◽  
pp. 794-801 ◽  
Author(s):  
J. Luo ◽  
B. Lakshminarayana
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Bypass Transition ◽  
Boundary Layer Development ◽  
Low Reynolds ◽  
Layer Development

The boundary layer development and convective heat transfer on transonic turbine nozzle vanes are investigated using a compressible Navier–Stokes code with three low-Reynolds-number k–ε models. The mean-flow and turbulence transport equations are integrated by a four-stage Runge–Kutta scheme. Numerical predictions are compared with the experimental data acquired at Allison Engine Company. An assessment of the performance of various turbulence models is carried out. The two modes of transition, bypass transition and separation-induced transition, are studied comparatively. Effects of blade surface pressure gradients, free-stream turbulence level, and Reynolds number on the blade boundary layer development, particularly transition onset, are examined. Predictions from a parabolic boundary layer code are included for comparison with those from the elliptic Navier–Stokes code. The present study indicates that the turbine external heat transfer, under real engine conditions, can be predicted well by the Navier–Stokes procedure with the low-Reynolds-number k–ε models employed.

Modified methodology of computation of admissible continuous currents of plain conductors of overhead transmission lines and catenaries

2021 ◽  
Vol 2 (2) ◽  
pp. 36-43
Author(s):  
Evgeniy P. FIGURNOV ◽  
◽  
Yury I. ZHARKOV ◽  
Valeriy I. KHARCHEVNIKOV ◽  
◽  
...  
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Transmission Lines ◽  
Power Transmission ◽  
Convection Heat Transfer ◽  
Heating And Cooling ◽  
Continuous Current ◽  
The Subject ◽  
The Common ◽  
Overhead Power Transmission Line

Methodology provided summarizes published, original and foreign theoretic and experimental data on the subject of heating and cooling of standard and shaped conductors of overhead power transmission line and uses those of them which are most affected to fundamental heat-transfer laws. Computation surface area of standard and shaped wire formulas are given. The common formula of convection heat transfer coefficient is provided, based on wind speed and direction, concerning antiicing mode. Parameters of this formula do not coincide with those existing, as they are based on experimental data on standard and shaped conductors but not on round tubes. Formula of computation of heat transfer power under the influence of solar radiation is given. Summarized formula of admissible continuous current computation is given, all the components have detailed description in the article.

Direct Numerical Simulations of a Transonic Tip Flow With Free-Stream Disturbances

2013 ◽  
Author(s):  
Andrew P. S. Wheeler ◽  
Richard D. Sandberg
Keyword(s):  
Heat Transfer ◽  
High Performance ◽  
Free Stream ◽  
Separation Bubble ◽  
Cross Flow ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Computational Domain ◽  
Free Stream Turbulence ◽  
Gap Height

In this paper we use direct numerical simulation to investigate the unsteady flow over a model turbine blade-tip at engine scale Reynolds and Mach numbers. The DNS is performed with a new in-house multi-block structured compressible Navier-Stokes solver purposely developed for exploiting high-performance computing systems. The particular case of a transonic tip flow is studied since previous work has suggested compressibility has an important influence on the turbulent nature of the separation bubble at the inlet to the gap and subsequent flow reattachment. The effects of free-stream turbulence, cross-flow and pressure-side boundary-layer on the tip flow aerodynamics and heat transfer are investigated. For ‘clean’ in-flow cases we find that even at engine scale Reynolds numbers the tip flow is intermittent in nature (neither laminar nor fully turbulent). The breakdown to turbulence occurs through the development of spanwise modes with wavelengths around 25% of the gap height. Cross-flows of 25% of the streamwise gap exit velocity are found to increase the stability of the tip flow, and to significantly reduce the turbulence production in the separation bubble. This is predicted through in-house linear stability analysis, and confirmed by the DNS. For the case when the inlet flow has free-stream turbulence, viscous dissipation and the rapid acceleration of the flow at the inlet to the tip-gap causes significant distortion of the vorticity field and reductions of turbulence intensity as the flow enters the tip gap. This means that only very high turbulence levels at the inlet to the computational domain significantly affect the tip heat transfer. The DNS results are compared with RANS predictions using the Spalart-Allmaras and k–ω SST turbulence models. The RANS and DNS predictions give similar qualitative features for the tip flow, but the size and shape of the inlet separation bubble and shock positions differ noticeably. The RANS predictions are particularly insensitive to free-stream turbulence.

A Study of Flow of Plastics Through Pipes

1946 ◽  
Vol 13 (2) ◽  
pp. A101-A105
Author(s):  
R. C. Binder ◽  
J. E. Busher
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Friction Coefficient ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Dynamic Viscosity ◽  
Apparent Viscosity ◽  
Turbulent Viscosity ◽  
Yield Value

Abstract The pipe friction coefficient for true fluids is usually expressed as a function of Reynolds number. This method of organizing data has been extended to tests on the flow of different suspensions which behaved as ideal plastics in the laminar-flow range and as true fluids in the turbulent-flow range. In the laminar-flow range, Reynolds number below about 2100, the denominator in Reynolds number is taken as the apparent viscosity. The apparent viscosity can be determined from the yield value and the coefficient of rigidity. In the turbulent-flow range, the denominator in Reynolds number is an equivalent or turbulent viscosity equal to the dynamic viscosity of a true fluid having the same friction coefficient, velocity, diameter, and density as that of the plastic. The various experimental data on plastics correlate well with this extension of the method for true fluids.

Modifying a meshless method to solving κ−ε turbulent natural convection heat transfer

2019 ◽  
Vol 31 (01) ◽  
pp. 2050014
Author(s):  
Nasrin Sheikhi ◽  
Mohammad Najafi ◽  
Vali Enjilela
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Numerical Methods ◽  
Turbulent Flow ◽  
Turbulent Viscosity ◽  
Convection Heat Transfer ◽  
New Technique ◽  
Test Cases ◽  
Convection Heat ◽  
Transfer Problems

The conventional meshless local Petrov–Galerkin method is modified to enable the method to solve turbulent convection heat transfer problems. The modifications include developing a new computer code which empowers the method to adopt nonlinear equations. A source term expressed in terms of turbulent viscosity gradients is appended to the code to optimize the accuracy for turbulent flow domains. The standard [Formula: see text] transport equations, one of the most applicable two equation turbulent viscosity models, is incorporated, appropriately, into the developed code to bring about both versibility and stability for turbulent natural heat transfer applications. The amenability of the new developed technique is tested by applying the modified method to two conventional turbulent fluid flow test cases. Upon the obtained acceptable results, the modified technique is, next, applied to two conventional natural heat transfer test cases for their turbulent domain. Based on comparing the results of the new technique with those of the available experimental or conventional numerical methods, the proposed method shows good adaptability and accuracy for both the fluid flow and convection heat transfer applications in turbulent domains. The new technique, now, furthers the applicability of the mesh-free local Petrov-Galerkin (MLPG) method to turbulent flow and heat transfer problems and provides much closer results to those of the available experimental or conventional numerical methods.

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