Influence of Reynolds Numbers on the Flow and Heat Transfer Around Row of Magnetic Obstacles

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Xidong Zhang ◽  
Guiping Zhu ◽  
Yin Zhang ◽  
Hongyan Wang ◽  
Hulin Huang
Keyword(s):  
Heat Transfer ◽  
Vortex Shedding ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Bluff Bodies ◽  
Vortical Structures ◽  
Magnetic Vortices ◽  
Electrically Conducting ◽  
Flow And Heat Transfer ◽  
Maximum Value

An incompressible electrically conducting viscous fluid flow influenced by a local external magnetic field may develop vortical structures and eventually instabilities similar to those observed in flows around bluff bodies (such as circular cylinder), denominated magnetic obstacle. The present investigation analyzes numerically the three-dimensional flow and heat transfer around row of magnetic obstacles. The vortex structures of magnetic obstacles, heat transfer behaviors in the wake of magnetic obstacles, and flow resistance are analyzed at different Reynolds numbers. It shows that the flow behind magnetic obstacles contains four different regimes: (1) one pair of magnetic vortices, (2) three pairs namely, magnetic, connecting, and attached vortices, (3) smaller vortex shedding from the in-between magnetic obstacles, i.e., quasi-static, and (4) regular vortex shedding from the row of magnetic obstacles. Furthermore, downstream cross-stream mixing induced by the unstable wakes can enhance wall-heat transfer, and the maximum value of percentage heat transfer increment (HI) is equal to about 35%. In this case, the thermal performance factor is more than one.

Influence of Reynolds Numbers on the Flow and Heat Transfer Around Row of Magnetic Obstacles

2016 ◽  
Author(s):  
Xidong Zhang ◽  
Guiping Zhu ◽  
Yin Zhang ◽  
Hongyan Wang ◽  
Hulin Huang
Keyword(s):  
Heat Transfer ◽  
Vortex Shedding ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Bluff Bodies ◽  
Vortical Structures ◽  
Magnetic Vortices ◽  
Electrically Conducting ◽  
Flow And Heat Transfer ◽  
Maximum Value

An incompressible electrically conducting viscous fluid flow influenced by a local external magnetic field may develop vortical structures and eventually instabilities similar to those observed in flows around bluff bodies (such as circular cylinder), denominated magnetic obstacle. The present investigation analyses numerically the three-dimensional flow and heat transfer around row of magnetic obstacles. The vortex structures of magnetic obstacles, heat transfer behaviors in the wake of magnetic obstacles and flow resistance are analyzed at different Reynolds numbers. It shows that the flow behind magnetic obstacles contains four different regimes: (1) one pair of magnetic vortices, (2) three pairs namely, magnetic, connecting, and attached vortices, (3) smaller vortex shedding from the in-between magnetic obstacles, i.e. quasi-static and (4) regular vortex shedding from the row of magnetic obstacles. Furthermore, downstream cross-stream mixing induced by the unstable wakes can enhance wall-heat transfer, and the maximum value of percentage heat transfer increment (HI) is equal to about 35%. In this case, the thermal performance factor is more than one.

Direct Numerical Simulation of Flow and Heat Transfer From a Sphere in a Uniform Cross-Flow

2000 ◽  
Vol 123 (2) ◽  
pp. 347-358 ◽  
Author(s):  
P. Bagchi ◽  
M. Y. Ha ◽  
S. Balachandar
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Vortex Shedding ◽  
Axisymmetric Flow ◽  
Three Dimensional ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Temperature Fields ◽  
Flow And Heat Transfer

Direct numerical solution for flow and heat transfer past a sphere in a uniform flow is obtained using an accurate and efficient Fourier-Chebyshev spectral collocation method for Reynolds numbers up to 500. We investigate the flow and temperature fields over a range of Reynolds numbers, showing steady and axisymmetric flow when the Reynolds number is less than 210, steady and nonaxisymmetric flow without vortex shedding when the Reynolds number is between 210 and 270, and unsteady three-dimensional flow with vortex shedding when the Reynolds number is above 270. Results from three-dimensional simulation are compared with the corresponding axisymmetric simulations for Re>210 in order to see the effect of unsteadiness and three-dimensionality on heat transfer past a sphere. The local Nusselt number distribution obtained from the 3D simulation shows big differences in the wake region compared with axisymmetric one, when there exists strong vortex shedding in the wake. But the differences in surface-average Nusselt number between axisymmetric and three-dimensional simulations are small owing to the smaller surface area associated with the base region. The shedding process is observed to be dominantly one-sided and as a result axisymmetry of the surface heat transfer is broken even after a time-average. The one-sided shedding also results in a time-averaged mean lift force on the sphere.

Numerical Simulation of Flow and Heat Transfer in Rotating Cooling Passage With Turning Vane in Hub Region

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Hung-Chieh Chu ◽  
Hamn-Ching Chen ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Three Dimensional ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Complex Flow ◽  
Flow And Heat Transfer ◽  
Cooling Passage ◽  
Turn Region

Numerical simulation of three-dimensional turbulent flow and heat transfer was performed in a multipass rectangular (AR = 2:1) rotating cooling channel with and without turning vane in the hub region under various flow conditions, with two different Reynolds numbers of 10,000 and 25,000, two different channel orientations of 45-deg and 90-deg, and the rotation number varies from 0 to 0.2. This study shows that the addition of the turning vane in the hub turn region does not cause much impact to the flow before the hub. However, it significantly alters the flow reattachment and vortex distribution in the hub turn region and after the hub turn portion. The local heat transfer is deeply influenced by this complex flow field and this turning vane effect lasts from the hub turn region to the portion after it.

Effect of Local Magnetic Fields on Electrically Conducting Fluid Flow and Heat Transfer

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Xidong Zhang ◽  
Hulin Huang
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Reynolds Number ◽  
Vortex Shedding ◽  
Conducting Fluid ◽  
Local Magnetic Field ◽  
Electrically Conducting ◽  
Flow And Heat Transfer ◽  
Electrically Conducting Fluid ◽  
The Impact

The prediction of electrically conducting fluid past a localized zone of applied magnetic field is the key for many practical applications. In this paper, the characteristics of flow and heat transfer (HI) for a liquid metal in a rectangular duct under a local magnetic field are investigated numerically using a three-dimensional model and the impact of some parameters, such as constrainment factor, κ, interaction parameter, N, and Reynolds number, Re, is also discussed. It is found that, in the range of Reynolds number 100 ≤ Re ≤ 900, the flow structures can be classified into the following four typical categories: no vortices, one pair of magnetic vortices, three pairs of vortices and vortex shedding. The simulation results indicate that the local heterogeneous magnetic field can enhance the wall-heat transfer and the maximum value of the overall increment of HI is about 13.6%. Moreover, the pressure drop penalty (ΔPpenalty) does not increasingly depend on the N for constant κ and Re. Thus, the high overall increment of HI can be obtained when the vortex shedding occurs.

Computation of Flow and Heat Transfer of a Blade Internal Cooling Passage With Truncated V-Shaped Ribs on Opposite Walls

2012 ◽  
Author(s):  
Shian Li ◽  
Gongnan Xie ◽  
Weihong Zhang ◽  
Bengt Sundén
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Inlet Temperature ◽  
Internal Cooling ◽  
Turbine Engine ◽  
Flow And Heat Transfer ◽  
Cooling Passage ◽  
Internal Cooling Passage

The inlet temperature of gas turbine engine is continuously increased to achieve higher thermal efficiency and power output. To prevent from the temperature exceeding the melting point of the blade material, ribs are commonly used in the mid-section of internal blade to augment the heat transfer from blade wall to the coolant. In this study, turbulent flow and heat transfer of a rectangular cooling passage with continuous or truncated 45-deg V-shaped ribs on opposite walls have been investigated numerically. The inlet Reynolds numbers are ranging from 12,000 to 60,000 and the low-Re k-ε model is selected for the turbulent computations. The complex three-dimensional fluid flow in the internal coolant passages and the corresponding heat transfer over the side-walls and rib-walls are presented and the thermal performances of the ribbed passages are compared as well. It is shown that the passage with truncated V-shaped ribs on opposite walls is very effective in improving the heat transfer performance with a low pressure loss, and thus could be suggested to be applied to gas turbine blade internal cooling.

scholarly journals Internal Passage Heat Transfer Prediction Using Multiblock Grids and a k-ω Turbulence Model

1996 ◽  
Author(s):  
David L. Rigby ◽  
A. A. Ameri ◽  
E. Steinthorsson
Keyword(s):  
Heat Transfer ◽  
Turbulence Model ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Three Dimensional Flow ◽  
Flow And Heat Transfer ◽  
Aspect Ratios ◽  
Single Block ◽  
Multiblock Grid ◽  
Good Agreement

Numerical simulations of the three-dimensional flow and heat transfer in a rectangular duct with a 180° bend were performed. Results are presented for Reynolds numbers of 17,000 and 37,000 and for aspect ratios of 0.5 and 1.0. A k-ω turbulence model with no reference to distance to a wall is used. Direct comparison between single block and multiblock grid calculations are made. Heat transfer and velocity distributions are compared to available literature with good agreement. The multi-block grid system is seen to produce more accurate results compared to a single-block grid with the same number of cells.

scholarly journals Thermal-hydraulic performance of TiO2-water nanofluids in an offset strip fin heat exchanger

2021 ◽  
pp. 63-63
Author(s):  
Emre Elibol ◽  
Oguz Turgut
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Single Phase ◽  
Volume Concentration ◽  
Three Dimensional ◽  
Evaluation Criteria ◽  
Reynolds Numbers ◽  
Tio2 Nanoparticle ◽  
Flow And Heat Transfer ◽  
Offset Strip Fin

The flow and heat transfer characteristics of the TiO2-water nanofluid assuming as a single-phase in the rectangular offset strip fin structure for different Reynolds number (500-1000) and TiO2 nanoparticle volume concentration values (0%-4%) were investigated numerically under three-dimensional, steady state and laminar flow conditions. Simulations were also performed for 1% and 4% nanoparticle volume concentrations of Al2O3-water nanofluid, and the results were compared with those of TiO2-water nanofluid. Results show that when the TiO2-water nanofluid is used, the heat transfer rate, heat transfer coefficient and Nusselt number increase with increasing both Reynolds number and nanoparticle volume concentration, and parallel to these, both pressure loss and pumping power increase. Considering the values of the performance evaluation criteria (PEC) number, it is clear that the use of TiO2-water nanofluid in offset strip fin structure at all Reynolds numbers examined between 1%-4% volume concentration values is quite advantageous. It is observed that TiO2-water nanofluid is much superior to Al2O3-water considering the PEC number. When the Reynolds number is 1000 and the volume concentration value of the TiO2 nanoparticle is 4%, the PEC number value is found to be 1.19, that is, there is a 19% increase compared to water. It is considered that the results of this study can be used as important data on the design of automobile radiators, air-conditioning and defense.

scholarly journals Computations of Flow and Heat Transfer in a Channel With Rows of Hemispherical Cavities

1999 ◽  
Author(s):  
Y.-L. Lin ◽  
T. I-P. Shih ◽  
M. K. Chyu
Keyword(s):  
Heat Transfer ◽  
Computational Study ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Wall Functions ◽  
Time Stepping ◽  
Flow And Heat Transfer ◽  
A Cell ◽  
Volume Method

Computations were performed to investigate the three-dimensional flow and heat transfer in a high aspect ratio channel in which one or two wall are lined with four rows of hemispherical cavities arranged in a staggered fashion with two Reynolds numbers (23,000 and 46,000). The focus is on understanding the flow induced by cavities and how that flow affects surface heat transfer. Computed results were compared with available experimental data. This computational study is based on the ensemble-averaged conservation equations of mass, momentum (compressible Navier-Stokes), and energy closed by the low Reynolds number shear-stress transport k-ω turbulence model (wall functions were not used). Solutions were generated by a cell-centered finite-volume method that uses third-order accurate flux-difference splitting of Roe with limiters, multigrid acceleration of a diagonalized ADI scheme with local time stepping, and patched/overlapped structured grids.

Sign in / Sign up

Export Citation Format

Share Document