scholarly journals Heat Transfer in Air Flow Past a Bottom Channel Wall-Attached Diamond-Shaped Baffle – Using a CFD Technique

2019 ◽  
Vol 63 (2) ◽  
pp. 100-112 ◽  
Author(s):  
Younes Menni ◽  
Ali J. Chamkha ◽  
Chafika Zidani ◽  
Boumédiène Benyoucef
Keyword(s):  
Heat Transfer ◽  
Skin Friction ◽  
Dynamic Pressure ◽  
Turbulent Viscosity ◽  
Pressure Coefficient ◽  
Operating Conditions ◽  
Computational Domain ◽  
Thermal Transfer ◽  
Transfer Characteristics ◽  
Convective Thermal

A computational analysis has been conducted to investigate turbulent flow and convective thermal transfer characteristics in a two-dimensional horizontal rectangular section channel with a hot lower wall-mounted diamond-shaped baffle. The calculations are based on the finite volume method, by means of Commercial Computational Fluid Dynamics software FLUENT, standard k-epsilon turbulence model with QUICK numerical scheme, and the SIMPLE discretization algorithm has been applied. The fluid flow and heat transfer characteristics, i.e., dynamic pressure coefficient, stream function, mean, axial, and transverse velocities, turbulent viscosity, temperature field, skin friction coefficients, local and average Nusselt numbers, and thermal enhancement factor are presented for flow Reynolds numbers based on the aeraulic diameter of the computational domain ranging from 12,000 to 32,000 at constant surface temperature condition along the upper and lower walls. Effect of the diamond configuration of the insulated baffle is studied numerically and the data obtained from this same baffle model are also compared with that of the simple flat rectangular baffle under similar operating conditions. Over the range under investigation, the improvements are found to be around 3.962 and 29.820 times higher than the smooth air channel with no baffle for heat thermal transfer and skin friction factor, respectively. The maximum TEF is around 1.292 at the highest Reynolds number value, Re = 32,000.

scholarly journals The effects of the axis ratio on the flow and heat transfer characteristics around a drop-shaped tube

2021 ◽  
Vol 2057 (1) ◽  
pp. 012001
Author(s):  
R Deeb ◽  
D V Sidenkov
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Coefficient ◽  
Maximum Velocity ◽  
Computational Domain ◽  
Heat Transfer Characteristics ◽  
Axis Ratio ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Shaped Tube

Abstract Flow and heat transfer characteristics around single drop-shaped tubes with different axis ratio (L/D) in cross-flow are studied numerically for values of Reynolds number in the range 1.3×103 to 20×103. The results are obtained using the commercial software ANSYS Fluent for a two-dimensional (2D) computational domain. The axis ratio of the studied tubes is varied from 1 to 4, when L/D =1, the tube is circular. The simulation results agree well with the available literature. The distribution of local coefficients of pressure and friction over half of the tube’s surface is plotted and analysed. It found that the drop-shaped tubes delay the separation of the boundary layer from the tube wall. The results confirm that the minimum value of pressure coefficient decreases as L/D decreases, and the maximum value of the friction coefficient gradually increases with the growth of L/D. The result of the numerical simulation indicates the superior overall performance of drop-shaped tube with L/D=4 over the rest of the tubes. Correlations of the average Nusselt number and the friction factor in terms of Reynolds number, calculated by the maximum velocity in the minimum free cross-section, and axis ratios for the studied cases are proposed.

Numerical Investigation of Heat Transfer Characteristics of Different Nanoparticles Using Modified Eulerian-Eulerian Model

2020 ◽  
Author(s):  
Muzafar Hussain ◽  
Shahbaz Tahir
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Exchangers ◽  
Single Phase ◽  
Reynolds Numbers ◽  
Operating Conditions ◽  
Phase Model ◽  
Heat Transfer Characteristics ◽  
Eulerian Model ◽  
Transfer Characteristics

Abstract Nanofluids are widely adopted nowadays to enhance the heat transfer characteristics in the solar applications because of their excellent thermophysical properties. In this paper, a modified Eulerian-Eulerian model recently developed based on experiments was validated numerically to account for the deviations from the experimental data. The modified Eulerian-Eulerian model is compared with the single-phase model, Eulerian-Eulerian models for TiO2-water at different operating conditions and deviation from the experimental data for each of the model was documented. However, the modified Eulerian-Eulerian model gave much closer results when compared to the experimental data. For the further extension of work, the modified Eulerian-Eulerian model was applied to different nanofluids in order to investigate their heat transfer characteristics. Three different nanoparticles were investigated namely Cu, MgO, and Ag and their heat transfer characteristics is calculated based on the modified Eulerian-Eulerian model as well as the single-phase model for the comparison. For lower values of Reynolds numbers, the average heat transfer coefficient was almost identical for both models with small percentage of error but for higher Reynolds numbers, the deviation got larger. Therefore, single-phase model is not appropriate for higher Reynolds numbers and modified Eulerian-Eulerian model should be used to accurately predict the heat transfer characteristics of the nanofluids at higher Reynolds numbers. From the analysis it is found that the Ag-water nanofluid have the highest heat transfer characteristics among others and can be employed in the solar heat exchangers to enhance the heat transfer characteristics and to further improve the efficiency.

Effect of Turbulent Intensity and Axial Gap on Turbine Heat Transfer Using Steady and Harmonic Models

2013 ◽  
Author(s):  
Sridhar Murari ◽  
Sunnam Sathish ◽  
Ramakumar Bommisetty ◽  
Jong S. Liu
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Flow Field ◽  
Turbulence Intensity ◽  
Pressure Coefficient ◽  
Heat Transfer Characteristics ◽  
Complex Flow ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Heat Loads

The knowledge of heat loads on the turbine is of great interest to turbine designers. Turbulence intensity and stator-rotor axial gap plays a key role in affecting the heat loads. Flow field and associated heat transfer characteristics in turbines are complex and unsteady. Computational fluid dynamics (CFD) has emerged as a powerful tool for analyzing these complex flow systems. Honeywell has been exploring the use of CFD tools for analysis of flow and heat transfer characteristics of various gas turbine components. The current study has two objectives. The first objective aims at development of CFD methodology by validation. The commercially available CFD code Fine/Turbo is used to validate the predicted results against the benchmark experimental data. Predicted results of pressure coefficient and Stanton number distributions are compared with available experimental data of Dring et al. [1]. The second objective is to investigate the influence of turbulence (0.5% and 10% Tu) and axial gaps (15% and 65% of axial chord) on flow and heat transfer characteristics. Simulations are carried out using both steady state and harmonic models. Turbulence intensity has shown a strong influence on turbine blade heat transfer near the stagnation region, transition and when the turbulent boundary layer is presented. Results show that a mixing plane is not able to capture the flow unsteady features for a small axial gap. Relatively close agreement is obtained with the harmonic model in these situations. Contours of pressure and temperature on the blade surface are presented to understand the behavior of the flow field across the interface.

Heat Transfer Characteristics of a Radial Jet Reattachment Flame

1997 ◽  
Vol 119 (2) ◽  
pp. 258-264 ◽  
Author(s):  
J. W. Mohr ◽  
J. Seyed-Yagoobi ◽  
R. H. Page
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Combustion Process ◽  
Local Heat ◽  
Operating Conditions ◽  
Recirculation Region ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Impingement Surface

A Radial Jet Reattachment Combustion (RJRC) nozzle forces primary combustion air to exit radially from the combustion nozzle and to mix with gaseous fuel in a highly turbulent recirculation region generated between the combustion nozzle and impingement surface. High convective heat transfer properties and improved fuel/ air mixing characterize this external mixing combustor for use in impingement flame heating processes. To understand the heat transfer characteristics of this new innovative practical RJRC nozzle, statistical design and analysis of experiments was utilized. A regression model was developed which allowed for determination of the total heat transfer to the impingement surface as well as the NOx emission index over a wide variety of operating conditions. In addition, spatially resolved flame temperatures and impingement surface temperature and heat flux profiles enabled determination of the extent of the combustion process with regards to the impingement surface. Specifically, the relative sizes of the reaction envelope, high temperature reaction zone, and low temperature recirculation zone were all determined. At the impingement surface in the reattachment zone very high local heat flux values were measured. This study provides the first detailed local heat transfer characteristics for the RJRC nozzle.

Steady and Unsteady Modeling for Heat Transfer Predictions of High Pressure Turbine Blade Internal Cooling

2012 ◽  
Author(s):  
Rémy Fransen ◽  
Nicolas Gourdain ◽  
Laurent Y. M. Gicquel
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Cooling System ◽  
Transfer Problem ◽  
Operating Conditions ◽  
Navier Stokes ◽  
Wall Region ◽  
Internal Cooling ◽  
Computational Domain ◽  
Complex Flow

This work focuses on numerical simulations of flows in blade internal cooling system. Large Eddy Simulation (LES) and Reynolds-Averaged Navier Stokes (RANS) approaches are compared in a typical blade cooling related problem. The case is a straight rib-roughened channel with high blockage ratio, computed and compared for both a periodic and full spatial domains. The configuration was measured at the Von Karman Institute (VKI) using Particle Image Velocimetry (PIV) in near gas turbine operating conditions. Results show that RANS models used fail to predict the full evolution of the flow within the channels where massive separation and large scale unsteady features are evidenced. In contrast LES succeeds in reproducing these complex flow motions and both mean and fluctuating components are clearly improved in the channels and in the near wall region. Periodic computations are gauged against the spatial computational domain and results on the heat transfer problem are addressed.

Experimental and Numerical Investigation of Heat Transfer Characteristics of Liquid Flow With Micro-Encapsulated Phase Change Material

2008 ◽  
Author(s):  
Rami Sabbah ◽  
Jamal Yagoobi ◽  
Said Al Hallaj
Keyword(s):  
Heat Transfer ◽  
Numerical Model ◽  
Pressure Drop ◽  
Phase Change ◽  
Phase Change Material ◽  
Operating Conditions ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Encapsulated Phase Change Material ◽  
Change Material

This experimental and numerical study investigates Micro-Encapsulated Phase Change Material (MEPCM) heat transfer characteristics and corresponding pressure drop. To conduct this study, an experimental setup consisting of a steel tube with an inner diameter of 4.3mm, outer diameter of 6.5mm and a length of 1,016mm is selected. A MEPCM mass concentration of 20% slurry with particle diameter ranging between 5–15μm is included in this study. Tube wall temperature profile, fluid inlet, outlet temperatures, the pressure drop across the tube are measured and corresponding Nusselt number are determined for various operating conditions. The experimental results are used to validate the numerical model predictions. The numerical model results show good agreement with the experimental data under various operating conditions. The controlling parameters are identified and their effects on the heat transfer characteristics of micro-channels with MEPCM slurries are evaluated.

Air Side Heat Transfer Characteristics of Wavy-Finned-Tube in a Forced Draft Direct Air-Cooled Steam Condenser

2012 ◽  
Vol 516-517 ◽  
pp. 3-8
Author(s):  
Zhao Ying Zhang ◽  
Jian Guo Yang ◽  
Hai Zhen Zhang
Keyword(s):  
Heat Transfer ◽  
Environmental Temperature ◽  
Finned Tube ◽  
Operating Conditions ◽  
Heat Transfer Characteristics ◽  
Power Generating Unit ◽  
Transfer Characteristics ◽  
Actual Operating ◽  
Forced Draft ◽  
Face Velocity

An experimental study was performed on wavy-finned-tube used in forced draft direct air-cooled steam condenser (DACSC) under actual working conditions of the power generating unit. Tests were carried out to study the air side heat transfer characteristics of wavy-finned-tube in actual operating conditions of DACSC, such as: air temperature, air face velocity, environmental temperature, exhaust pressure of steam turbine and temperature of exhaust steam. The air-side heat transfer characteristics of wavy-finned-tube heat exchangers were tested and analyzed by varying air face velocity .One empirical correlations for predicting the h-factor was developed.

Thermal Stability and Heat Transfer Characteristics of Methane and Natural Gas Fuels

1994 ◽  
Author(s):  
Douglas Chin ◽  
James C. Hermanson ◽  
Louis J. Spadaccini
Keyword(s):  
Heat Transfer ◽  
Thermal Stability ◽  
Natural Gas ◽  
High Purity ◽  
Operating Conditions ◽  
Stainless Steel Tube ◽  
Heat Transfer Characteristics ◽  
Hydrocarbon Mixtures ◽  
Transfer Characteristics ◽  
Gas Fuel

The thermal decomposition and heat transfer characteristics of gaseous, high-purity methane, several methane-hydrocarbon mixtures and a typical natural gas fuel were evaluated using an electrically heated, stainless-steel tube test apparatus. Of several candidate heat transfer correlations, the Dittus-Boelter heat transfer correlation provided the best fit of the methane heat transfer data over the range of Reynolds numbers 10,000 to 215,000. The thermal stability (i.e. deposit formation) characteristics of the methane-hydrocarbon mixtures and the natural gas fuel were established and compared with the deposition characteristics of high-purity methane. Testing was conducted at wall temperatures up to 900 K (fuel temperatures to 835 K) for durations of up to 60 hours. Measurements of deposit mass indicated that there was essentially no deposit buildup for wall temperatures below 650 K. Deposit began to form at wall temperatures between 650 K and 775 K. Above 775 K, there was a rapid monotonic increase in deposition. The data suggest that the use of high-purity methane instead of natural gas at temperatures above 775 K could reduce the deposit thickness under similar operating conditions by as much as a factor of three, or permit operation at higher temperatures.

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