Numerical Study of Turbulent Heat Transfer in Annular Pipe with Sudden Contraction

2013 ◽  
Vol 465-466 ◽  
pp. 461-466 ◽  
Author(s):  
Hussein Togun ◽  
Tuqa Abdulrazzaq ◽  
S.N. Kazi ◽  
A. Badarudin ◽  
Mohd Khairol Anuar Ariffin
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbulent Heat Transfer ◽  
Recirculation Region ◽  
Turbulent Heat ◽  
Contraction Ratio ◽  
Sudden Contraction ◽  
Annular Pipe

Turbulent heat transfer to air flow in annular pipe with sudden contraction numerically studied in this paper. The k-ε model with finite volume method used to solve continuity, moment and energy equations. The boundary condition represented by uniform and constant heat flux on inner pipe with range of Reynolds number varied from 7500 to 30,000 and contraction ratio (CR) varied from 1.2 to 2. The numerical result shows increase in local heat transfer coefficient with increase of contraction ratio (CR) and Reynolds number. The maximum of heat transfer coefficient observed at contraction ratio of 2 and Reynolds number of 30,000 in compared with other cases. Also pressure drop coefficient noticed rises with increase contraction ratio due to increase of recirculation flow before and after the step height. In contour of velocity stream line can be seen that increase of recirculation region with increase contraction ratio (CR).

Turbulent Heat Transfer in the Separated, Reattached, and Redevelopment Regions of a Circular Tube

1966 ◽  
Vol 88 (1) ◽  
pp. 131-136 ◽  
Author(s):  
K. M. Krall ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Separation ◽  
Circular Tube ◽  
Turbulent Pipe Flow ◽  
Turbulent Heat Transfer ◽  
Working Fluid ◽  
The Heat Transfer Coefficient

Experiments were performed to determine the effect of flow separation on the heat-transfer characteristics of a turbulent pipe flow. The flow separation was induced by an orifice situated at the inlet of an electrically heated circular tube. The degree of flow separation was varied by employing orifices of various bore diameters. Water was the working fluid. The Reynolds number and the Prandtl number, respectively, ranged from 10,000 to 130,000 and from 3 to 6. The measurements show that the local heat-transfer coefficients in the separated, reattached, and redevelopment regions are several times as large as those for a fully developed flow. For instance, at the point of reattachment, the coefficients were 3 to 9 times greater than the corresponding fully developed values. In general, the increase of the heat-transfer coefficient owing to flow separation is accentuated as the Reynolds number decreases. The point of flow reattachment, which corresponds to a maximum in the distribution of the heat-transfer coefficient, was found to occur from 1.25 to 2.5 pipe dia from the onset of separation.

scholarly journals Experimental Study of Heat Transfer Enhancement through a Tube with Wire-Coil Inserts at Low Turbulent Reynolds Number

2018 ◽  
Vol 3 (3) ◽  
pp. 122-133
Author(s):  
Mohammad Zoynal Abedin ◽  
M. A. Rashid Sarkar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Test Section ◽  
Reynolds Numbers ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Low Reynolds Numbers ◽  
Wire Coil ◽  
Low Reynolds

This paper reports an experimental analysis to investigate the enhancement of turbulent heat transfer flow of air through one smooth tube and four different tubes with wire-coil inserts (Pitches, Pc = 12, 24, 40, and 50 mm with corresponding helix angles, a =100, 200, 350, and 450, respectively) at low Reynolds numbers ranging from 6000 to 22000. The test section of the tube was electrically heated and was cooled by fully developed turbulent air flow. The performance of the tubes was evaluated by considering the condition of maximizing heat transfer rate. From the measured data, the heat transfer characteristics such as heat transfer coefficient, effectiveness and Nusselt number, and the fluid flow behaviours such as friction factor, pressure drops and pumping power along the axial distance of the test section were analyzed at those Reynolds numbers for the tubes. The results indicated that for the tubes with wire-coil inserts at low Reynolds numbers, the turbulent heat transfer coefficient might be as much as two-folds higher, the friction factors could be as much as four-folds higher, and the effectiveness might be as much as 1.25 folds higher than those for the smooth tube with similar flow conditions. A correlation was also developed to predict the turbulent heat transfer coefficients through the tubes at low Reynolds numbers.

Turbulent Heat Transfer in Plane Couette Flow

2005 ◽  
Vol 128 (1) ◽  
pp. 53-62 ◽  
Author(s):  
Phuong M. Le ◽  
Dimitrios V. Papavassiliou
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Prandtl Number ◽  
Transfer Coefficient ◽  
Couette Flow ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Continuous Line ◽  
Plane Couette Flow ◽  
The Heat Transfer Coefficient

Heat transfer in a fully developed plane Couette flow for different Prandtl number fluids was studied using numerical simulations. The flow field was created by two infinite planes moving at the same velocity, but in opposite directions, forming a region of constant total shear stress. Heat markers were released into the flow from the channel wall, and the ground level temperature was calculated for dispersion from continuous line sources of heat. In addition, the temperature profile across the channel was synthesized from the behavior of these continuous line sources. It was found that the heat transfer coefficient for Couette flow is higher than that in channel flow for the same Prandtl numbers. Correlations were also obtained for the heat transfer coefficient for any Prandtl number ranging from 0.1 to 15,000 in fully developed turbulence.

Turbulent Heat Transfer Downstream of a Contraction-Related, Forward-Facing Step in a Duct

1987 ◽  
Vol 109 (3) ◽  
pp. 621-626 ◽  
Author(s):  
A. Garcia ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Sherwood Number ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Axial Distribution ◽  
Contraction Ratio ◽  
Abrupt Contraction ◽  
Forward Facing Step ◽  
The Heat Transfer Coefficient

Experiments were performed to investigate the axial distribution of the heat transfer coefficient downstream of an abrupt contraction in a flat rectangular duct. The contraction was created by the presence of a forward-facing step in one of the walls of the duct. The flow arriving at the step was hydrodynamically developed and isothermal. In the contracted duct, the duct wall that constituted the continuation of the step was maintained at a uniform temperature different from that of the entering flow, while the other walls were adiabatic. During the course of the experiments, the Reynolds number of the flow in the contracted duct ranged from 4000 to 24,000, while the ratio of the post-contraction to the precontraction duct heights took on values of 1 (no contraction), 0.8, 0.6, and 0.4. In the presence of the contraction, the axial distribution of the Sherwood number increased at first, attained a maximum, and then decreased monotonically to a fully developed value. In contrast, the no-contraction Sherwood number decreased monotonically and subsequently became fully developed. At a given Reynolds number, the peak Sherwood number for the contraction case was virtually independent of the contraction ratio and exceeded the largest measured Sherwood number for the no-contraction case by about a factor of two.

Turbulent Heat Transfer Measurements on a Wall With Concave and Cylindrical Dimples in a Square Channel

2002 ◽  
Author(s):  
S. W. Moon ◽  
S. C. Lau
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Internal Cooling ◽  
Experimental Conditions ◽  
Square Channel ◽  
Fully Developed Turbulent Flow

Dimpled surfaces may be considered for heat transfer enhancement in internal cooling of gas turbine airfoils. In this study, convective heat transfer and pressure drop for turbulent airflow in a square channel with a dimpled wall were examined. Experiments were conducted to determine the average heat transfer coefficient on the dimpled wall and the overall pressure drop across the channel, for nine concave and cylindrical dimples with various diameters and depths, and for Reynolds numbers (based on the channel hydraulic diameter) between 10,000 and 65,000. For the concave and cylindrical dimple configurations studied, the dimples were found to enhance the heat transfer coefficient by 70% (1.7 times) to over three times the value for fully developed turbulent flow through a smooth tube, with increase of the overall pressure drop of over four times. For both the concave and cylindrical dimples, heat transfer was enhanced more when the dimples covered a larger portion of the surface of the wall. The cylindrical dimples caused higher overall heat transfer coefficient (based on the projected area) and lower pressure drop than the concave dimples with the same diameters and depths. Thus, cylindrical dimple configuration may be a better alternative than concave dimples in enhancing heat transfer, for the experimental conditions and dimple configurations investigated. Further experiments are recommended to determine if cylindrical dimples of other dimensions also give higher thermal performances than concave dimples of the same dimensions, subjected to other flow and thermal boundary conditions, such as irregular channels with or without rotation.

scholarly journals Effect of flow separation of TiO2 nanofluid on heat transfer in the annular space of two concentric cylinders

2020 ◽  
Vol 24 (2 Part A) ◽  
pp. 1007-1018 ◽  
Author(s):  
Tuqa Abdulrazzaq ◽  
Hussein Togun ◽  
Safaei Reza ◽  
Salim Kazi ◽  
Mohd Ariffin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Separation Flow ◽  
Annular Space ◽  
Flux Boundary Condition ◽  
Number Range ◽  
Concentric Cylinders ◽  
Contraction Ratio

In the wake of energy crises, the researchers are encouraged to explore new ways of enhancement in the thermal performance of heat exchanging equipment. In the current research, the SST k-? model and finite volume method were employed to augment heat transfer into the separation flow of TiO2 nanofluid in the annular space of two concentric cylinders. In the present investigation TiO2 nanoparticles of volume fractions, 0.5%-2% at Reynolds number range of 10000-40000, and contraction ratios from 1 to 2 were considered at constant heat flux boundary condition. Simulation results reveal that the highest enhancement in the heat transfer coefficient is corresponding to the annular pipe with a contraction ratio of 2 due to the generated re-circulation flow zone that begins after the separation point on the wall. Further, the surface heat transfer coefficient enhances with the increase of nanoparticles volume fraction and Reynolds number. The velocity distribution profile before and after the steps reveals that increasing the height of the step and Reynolds number, re-circulation regions also increases. Numerical results indicate that the highest pressure drop occurs at the Re = 40000 and contraction ratio of 2.

Flow and Thermal Fields in a Pendant Droplet Moving on Lyophobic Surface

2010 ◽  
Author(s):  
Basant Singh Sikarwar ◽  
K. Muralidhar ◽  
Sameer Khandekar
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Reynolds Number ◽  
Shear Stress ◽  
Heat Transfer Coefficient ◽  
Wall Shear Stress ◽  
Transfer Coefficient ◽  
Maximum Shear Stress ◽  
Computational Domain ◽  
Wall Shear

Clusters of liquid drops growing and moving on physically or chemically textured lyophobic surfaces are encountered in drop-wise mode of vapor condensation. As opposed to film-wise condensation, drops permit a large heat transfer coefficient and are hence attractive. However, the temporal sustainability of drop formation on a surface is a challenging task, primarily because the sliding drops eventually leach away the lyophobicity promoter layer. Assuming that there is no chemical reaction between the promoter and the condensing liquid, the wall shear stress (viscous resistance) is the prime parameter for controlling physical leaching. The dynamic shape of individual droplets, as they form and roll/slide on such surfaces, determines the effective shear interaction at the wall. Given a shear stress distribution of an individual droplet, the net effect of droplet ensemble can be determined using the time averaged population density during condensation. In this paper, we solve the Navier-Stokes and the energy equation in three-dimensions on an unstructured tetrahedral grid representing the computational domain corresponding to an isolated pendant droplet sliding on a lyophobic substrate. We correlate the droplet Reynolds number (Re = 10–500, based on droplet hydraulic diameter), contact angle and shape of droplet with wall shear stress and heat transfer coefficient. The simulations presented here are for Prandtl Number (Pr) = 5.8. We see that, both Poiseuille number (Po) and Nusselt number (Nu), increase with increasing the droplet Reynolds number. The maximum shear stress as well as heat transfer occurs at the droplet corners. For a given droplet volume, increasing contact angle decreases the transport coefficients.

scholarly journals Toward improved heat dissipation of the turbulent regime over backward-facing step for the AL2O3-water nanofluids: An experimental approach

2019 ◽  
Vol 23 (3 Part B) ◽  
pp. 1779-1789 ◽  
Author(s):  
Syed Ahmed ◽  
Salim Kazi ◽  
Ghulamullah Khan ◽  
Mohd Zubir ◽  
Mahidzal Dahari ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbulent Regime ◽  
Al2o3 Nanoparticles ◽  
Backward Facing Step ◽  
Constant Weight ◽  
Weight Concentration

Experimental study of nanofluid flow and heat transfer to fully developed turbulent forced convection flow in a uniformly heated tubular horizontal backward-facing step has reported in the present study. To study the forced convective heat transfer coefficient in the turbulent regime, an experimental study is performed at a different weight concentration of Al2O3 nanoparticles. The experiment had conducted for water and Al2O3 -water nanofluid for the concentration range of 0 to 0.1 wt.% and Reynolds number of 4000 to 16000. The average heat transfer coefficient ratio increases significantly as Reynolds number increasing, increased from 9.6% at Reynolds number of 4000 to 26.3% at Reynolds number of 16000 at the constant weight concentration of 0.1%. The Al2O3 water nanofluid exhibited excellent thermal performance in the tube with a backwardfacing step in comparison to distilled water. However, the pressure losses increased with the increase of the Reynolds number and/or the weight concentrations, but the enhancement rates were insignificant.

scholarly journals 3D Numerical simulation of turbulent heat transfer and Fe3O4/nanofluid annular flow in sudden enlargement

2021 ◽  
Vol 321 ◽  
pp. 04014
Author(s):  
Hussein Togun
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Transport ◽  
Annular Flow ◽  
Volume Concentration ◽  
Convection Heat Transfer ◽  
Turbulent Heat Transfer ◽  
Recirculation Region ◽  
Convection Heat

In this paper, 3D Simulation of turbulent Fe3O4/Nanofluid annular flow and heat transfer in sudden expansion are presented. k-ε turbulence standard model and FVM are applied with Reynolds number different from 20000 to 50000, enlargement ratio (ER) varied 1.25, 1.67, and 2, , and volume concentration of Fe3O4/Nanofluid ranging from 0 to 2% at constant heat flux of 4000 W/m2. The main significant effect on surface Nusselt number found by increases in volume concentration of Fe3O4/Nanofluid for all cases because of nanoparticles heat transport in normal fluid as produced increases in convection heat transfer. Also the results showed that suddenly increment in Nusselt number happened after the abrupt enlargement and reach to maximum value then reduction to the exit passage flow due to recirculation flow as created. Moreover the size of recirculation region enlarged with the rise in enlargement ratio and Reynolds number. Increase of volume Fe3O4/nanofluid enhances the Nusselt number due to nanoparticles heat transport in base fluid which raises the convection heat transfer. Increase of Reynolds number was observed with increased Nusselt number and maximum thermal performance was found with enlargement ratio of (ER=2) and 2% of volume concentration of Fe3O4/nanofluid. Further increases in Reynolds number and enlargement ratio found lead to reductions in static pressure.

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