Turbulent Heat Transfer Characteristics of Supercritical Carbon Dioxide for a Vertically Upward Flow in a Pipe Using Computational Fluid Dynamics and Artificial Neural Network

2021 ◽  
Author(s):  
Rajendra Prasad K S ◽  
Krishna V ◽  
Sachin Bharadwaj ◽  
Babu Rao Ponangi
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Turbulence Model ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Ansys Fluent ◽  
Artificial Neural ◽  
Turbulent Models

Abstract Modelling of turbulence heat transfer for supercritical fluids using Computational Fluid Dynamics (CFD) software is always challenging due to the drastic property variations near critical point. Use of Artificial Neural Networks (ANN) along with numerical methods have shown promising results in predicting heat transfer coefficients of heat exchangers. In this study, accuracy of four different turbulent models available in the commercial CFD software - Ansys Fluent is investigated against the available experimental results. The k-e Re Normalization Group (RNG) model with enhanced wall treatment is found to be the best-suited turbulence model. Further, K-e RNG Turbulence Model is used in CFD for parametric analysis to generate the data for ANN studies. A total of 1,34,698 data samples were generated and fed into the ANN program to develop an equation that can predict the heat transfer coefficient. It was found that, for the considered range of values the absolute average relative deviation is 3.49%.

Analysis of Computational Fluid Dynamics Code FLUENT Capabilities for Supercritical Water Heat-Transfer Applications in Vertical Bare Tubes

2016 ◽  
Vol 2 (3) ◽  
Author(s):  
Amjad Farah ◽  
Glenn Harvel ◽  
Igor Pioro
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Supercritical Water ◽  
Wall Temperature ◽  
Transfer Coefficients ◽  
Bulk Fluid ◽  
Additional Information ◽  
Turbulent Models ◽  
Multidimensional Effects

In this paper, the computational fluid dynamics (CFD) code FLUENT was used to predict wall-temperature profiles inside vertical bare tubes with supercritical water (SCW) as the cooling medium, to assess the capabilities of FLUENT for SCW heat-transfer applications. Numerical results are compared to experimental data and current one-dimensional (1D) models represented by existing heat-transfer empirical correlations. Wall-temperature and heat-transfer coefficients were analyzed to select the best model to describe the fluid flow before, at, and after the pseudocritical region. k−ϵ and k−ω turbulent models were evaluated in the process, with variations in the submodel parameters such as viscous heating, thermal effects, and low-Reynolds-number correction. Results of the analysis show a fit of ±10% for wall temperatures using the SST k−ω model within the deteriorated heat-transfer regime and less than ±5% within the normal heat-transfer regime. The accuracy of the model is higher than any empirical correlation tested in the mentioned regimes and provides additional information about the multidimensional effects between the bulk-fluid and wall temperatures.

Periodically Converging-Diverging Tubes and Their Turbulent Heat Transfer, Pressure Drop, Fluid Flow, and Enhancement Characteristics

1984 ◽  
Vol 106 (1) ◽  
pp. 55-63 ◽  
Author(s):  
P. Souza Mendes ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Surface Area ◽  
Equal Mass ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Friction Factors

A comprehensive experimental study was performed to determine entrance region and fully developed heat transfer coefficients, pressure distributions and friction factors, and patterns of fluid flow in periodically converging and diverging tubes. The investigated tubes consisted of a succession of alternately converging and diverging conical sections (i.e., modules) placed end to end. Systematic variations were made in the Reynolds number, the taper angle of the converging and diverging modules, and the module aspect ratio. Flow visualizations were performed using the oil-lampblack technique. A performance analysis comparing periodic tubes and conventional straight tubes was made using the experimentally determined heat transfer coefficients and friction factors as input. For equal mass flow rate and equal transfer surface area, there are large enhancements of the heat transfer coefficient for periodic tubes, with accompanying large pressure drops. For equal pumping power and equal transfer surface area, enhancements in the 30–60 percent range were encountered. These findings indicate that periodic converging-diverging tubes possess favorable enhancement characteristics.

Computational Fluid Dynamics Modeling of Mixed Convection Flows in Building Enclosures

2013 ◽  
Author(s):  
Alexander Kayne ◽  
Ramesh Agarwal
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Experimental Data ◽  
Computational Fluid Dynamics ◽  
Mixed Convection ◽  
Turbulence Model ◽  
Numerical Algorithm ◽  
Navier Stokes ◽  
Cfd Simulations ◽  
Flow And Heat Transfer

In recent years Computational Fluid Dynamics (CFD) simulations are increasingly used to model the air circulation and temperature environment inside the rooms of residential and office buildings to gain insight into the relative energy consumptions of various HVAC systems for cooling/heating for climate control and thermal comfort. This requires accurate simulation of turbulent flow and heat transfer for various types of ventilation systems using the Reynolds-Averaged Navier-Stokes (RANS) equations of fluid dynamics. Large Eddy Simulation (LES) or Direct Numerical Simulation (DNS) of Navier-Stokes equations is computationally intensive and expensive for simulations of this kind. As a result, vast majority of CFD simulations employ RANS equations in conjunction with a turbulence model. In order to assess the modeling requirements (mesh, numerical algorithm, turbulence model etc.) for accurate simulations, it is critical to validate the calculations against the experimental data. For this purpose, we use three well known benchmark validation cases, one for natural convection in 2D closed vertical cavity, second for forced convection in a 2D rectangular cavity and the third for mixed convection in a 2D square cavity. The simulations are performed on a number of meshes of different density using a number of turbulence models. It is found that k-epsilon two-equation turbulence model with a second-order algorithm on a reasonable mesh gives the best results. This information is then used to determine the modeling requirements (mesh, numerical algorithm, turbulence model etc.) for flows in 3D enclosures with different ventilation systems. In particular two cases are considered for which the experimental data is available. These cases are (1) air flow and heat transfer in a naturally ventilated room and (2) airflow and temperature distribution in an atrium. Good agreement with the experimental data and computations of other investigators is obtained.

Investigation of MHD RANS Modeling Base on DNS Database Under the Advanced Blanket Design Conditions Utilized Molten Salt

2014 ◽  
Author(s):  
Naoki Osawa ◽  
Yoshinobu Yamamoto ◽  
Tomoaki Kunugi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbulence Model ◽  
Turbulent Channel Flow ◽  
Turbulent Heat Transfer ◽  
Navier Stokes ◽  
Turbulent Heat ◽  
Mhd Turbulence ◽  
Rans Modeling ◽  
Heat Transfer Degradation

In this study, validations of Reynolds Averaged Navier-Stokes Simulation (RANS) based on Kenjeres & Hanjalic MHD turbulence model (Int. J. Heat & Fluid Flow, 21, 2000) coupled with the low-Reynolds number k-epsilon model have been conducted with the usage of Direct Numerical Simulation (DNS) database. DNS database of turbulent channel flow imposed wall-normal magnetic field on, are established in condition of bulk Reynolds number 40000, Hartmann number 24, and Prandtl number 5. As the results, the Nagano & Shimada model (Trans. JSME series B. 59, 1993) coupled with Kenjeres & Hanjalic MHD turbulence model has the better availability compared with Myong & Kasagi model (Int. Fluid Eng, 109, 1990) in estimation of the heat transfer degradation in MHD turbulent heat transfer.

Direct numerical simulation of turbulent heat transfer across a sheared wind-driven gas–liquid interface

2016 ◽  
Vol 804 ◽  
pp. 646-687 ◽  
Author(s):  
Ryoichi Kurose ◽  
Naohisa Takagaki ◽  
Atsushi Kimura ◽  
Satoru Komori
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Mass Transfer ◽  
Heat Flux ◽  
Streamwise Velocity ◽  
Liquid Interface ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Turbulent Eddies

Turbulent heat transfer across a sheared wind-driven gas–liquid interface is investigated by means of a direct numerical simulation of gas–liquid two-phase turbulent flows under non-breaking wave conditions. The wind-driven wavy gas–liquid interface is captured using the arbitrary Lagrangian–Eulerian method with boundary-fitted coordinates on moving grids, and the temperature fields on both the gas and liquid sides, and the humidity field on the gas side are solved. The results show that although the distributions of the total, latent, sensible and radiative heat fluxes at the gas–liquid interface exhibit streak features such that low-heat-flux regions correspond to both low-streamwise-velocity regions on the gas side and high-streamwise-velocity regions on the liquid side, the similarity between the heat-flux streak and velocity streak on the gas side is more significant than that on the liquid side. This means that, under the condition of a fully developed wind-driven turbulent field on both the gas and liquid sides, the heat transfer across the sheared wind-driven gas–liquid interface is strongly affected by the turbulent eddies on the gas side, rather than by the turbulent eddies and Langmuir circulations on the liquid side. This trend is quite different from that of the mass transfer (i.e. $\text{CO}_{2}$ gas). This is because the resistance to heat transfer is normally lower than the resistance to mass transfer on the liquid side, and therefore the heat transfer is controlled by the turbulent eddies on the gas side. It is also verified that the predicted total heat, latent heat, sensible heat and enthalpy transfer coefficients agree well with previously measured values in both laboratory and field experiments. To estimate the heat transfer coefficients on both the gas and liquid sides, the surface divergence could be a useful parameter, even when Langmuir circulations exist.

Analysis of Enhanced Heat Transfer on a Turbine Blade Tip-Wall With and Without Guide Ribs

2010 ◽  
Author(s):  
Gongnan Xie ◽  
Bengt Sunde´n ◽  
Weihong Zhang ◽  
Esa Utriainen ◽  
Lieke Wang
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Turbine Blade ◽  
Turbulent Heat Transfer ◽  
Channel Height ◽  
Turbulent Heat ◽  
Wall Heat Transfer ◽  
Transfer Coefficients ◽  
Numerical Predictions ◽  
Blade Tip

Cooling methods are needed for gas turbine blade tips that are exposed to high temperature gas. A common way to cool the blade and its tip is to design serpentine passages with 180-deg turn under the blade tip-cap inside the turbine blade. Improved internal convective cooling is therefore required to increase the blade tip lifetime. This paper presents numerical predictions of turbulent heat transfer through two-pass channels with and without guide ribs (guide vanes) placed in the turn regions using RANS turbulence modeling. The effects of adding guide ribs on the tip-wall heat transfer enhancement and the channel pressure drop have been analyzed. The inlet Reynolds numbers are ranging from 100,000 to 600,000, and the rib cross-section blockage ratio (rib height to channel height, 2e/H) is 0.182. The detailed fluid flow and heat transfer over the tip-wall are presented. The overall performances of three two-pass channels are evaluated and compared. It is found that the tip heat transfer coefficients of the channels with guide ribs are 20%∼50% higher than that of a channel without guide ribs. The presence of guide ribs could lead to an increased (about 15%) or decreased (up to about 12%) pressure drop, depending upon the geometry and placement of guide ribs. It is suggested that the usage of guide ribs is a suitable way to improve the flow structure and augment the blade tip heat transfer, but is not the most effective way to augment tip-wall heat transfer compared to the augmentation by surface modifications imposed on the tip directly.

scholarly journals Heat dissipation from a stationary brake disc, Part 2: CFD modelling and experimental validations

2017 ◽  
Vol 232 (10) ◽  
pp. 1898-1924 ◽  
Author(s):  
Marko Tirovic ◽  
Kevin Stevens
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Heat Dissipation ◽  
Axial Flow ◽  
Flow Visualisation ◽  
Brake Disc ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Static Conditions

Following from the analytical modelling presented in Part 1, this paper details a comprehensive computational fluid dynamics modelling of the three-dimensional flow field around, and heat dissipation from, a stationary brake disc. Four commonly used turbulence models were compared and the shear stress turbulence model was found to be most suitable for these studies. Inferior cooling of the anti-coning disc type is well known but the core cause in static conditions was only now established. The air flow exiting the lower vane channels at the inner rotor diameter changes direction and flows axially over the hat region. This axial flow acts as a blocker to the higher vane inlets, drastically reducing convective cooling from the upper half of the disc. The complexity of disc stationary cooling is further caused by the change of flow patterns during disc cooling. The above axial flow effects slowly vanish as the disc temperatures reduce. Consequently, convective heat transfer coefficients are affected by both, the change in the flow pattern and decrease in air velocities due to reduced air buoyancy as the disc cools down. As in Part 1, the special thermal rig was used to validate the computational fluid dynamics results quantitatively and qualitatively. The former used numerous thermocouples positioned strategically around the brake disc, with the latter introducing the concept of laser generated light plane combined with a smoke generator to enable flow visualisation. Predicted average heat transfer coefficients using computational fluid dynamics correlate well with the experimental values, and even two-dimensional analytical values (as presented in Part 1) reasonably closely follow the trends. The results present an important step in establishing cooling characteristics related to the electric parking brake application in commercial vehicles, with future publications detailing heat transfer from the entire brake assembly.

Numerical and Experimental Study of Turbulent Heat Transfer and Fluid Flow in Longitudinal Fin Arrays

1986 ◽  
Vol 108 (1) ◽  
pp. 16-23 ◽  
Author(s):  
D. S. Kadle ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Base Plate ◽  
Local Heat ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Numerical Work ◽  
Model Average ◽  
Air Stream

Heat transfer from an array of parallel longitudinal fins to a turbulent air stream passing through the interfin spaces has been investigated both analytically/numerically and experimentally. The fins were integrally attached to a heated base plate, while the fin tips were shrouded to avoid leakage. In the analytical/numerical work, a conjugate problem was solved which encompassed turbulent flow and heat transfer in the air stream and heat conduction in the fins and in the base plate. The turbulence model and computational scheme were verified by comparison with experiment. It was found that the local heat transfer coefficients varied along the fins and along the surface of the base plate, with the lowest values in the corners formed by the fin/base plate intersections and the fin/shroud intersections. The numerically determined fin efficiencies did not differ appreciably from those calculated from the conventional pure-conduction fin model. Average Nusselt numbers, evaluated from the experimental data in conjunction with the numerically determined fin efficiencies (for derating the fin surface area), agreed well with those for fully developed heat transfer in a uniformly heated circular tube.

Heat Transfer and Flow Characteristics of an Oblique Turbulent Impinging Jet Within Confined Walls

1995 ◽  
Vol 117 (2) ◽  
pp. 316-322 ◽  
Author(s):  
K. Ichimiya
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Flow Characteristics ◽  
Local Heat Transfer ◽  
Flow Region ◽  
Turbulent Heat Transfer ◽  
Working Fluid ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Impingement Surface

Experiments were conducted to determine the turbulent heat transfer and flow characteristics of an oblique impinging circular jet within closely confined walls using air as a working fluid. The local temperature distribution on the impingement surface was obtained in detail by a thermocamera using a liquid crystal sheet. A correction to the heat flux was evaluated by using the detailed temperature distribution and solving numerically the three-dimensional equation of heat conduction in the heated section. Two-dimensional profiles of the local Nusselt numbers and temperatures changed with jet angle and Reynolds number. These showed a peak shift toward the minor flow region and a plateau of the local heat transfer coefficients in the major flow region. The local velocity and turbulent intensity in the gap between the confined insulated wall and impingement surface were also obtained in detail by a thermal anemometer.

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