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1.
A two–dimensional numerical simulation is performed following a finite volume approach to analyze the forced convection heat transfer for the hydromagnetic flow around a circular cylinder at low Reynolds numbers. The cylinder is placed within a rectangular channel subjected to externally applied magnetic fields and acted upon by the magnetohydrodynamic (MHD) flow of a viscous incompressible and electrically conductive fluid. The magnetic field is applied either along the streamwise or transverse directions. The simulation is carried out for the range of Reynolds number 10 ≤ Re ≤ 80 with Hartmann number 0 ≤ Ha ≤ 10 and for different Prandtl numbers, Pr = 0.02 (liquid metal), 0.71 (air), and 7 (water) for a blockage ratio β = 0.25. The flow is steady for the above range of conditions. Apart from the channel wall, the magnetic field provides additional stability to the flow as a result of which the recirculation region behind the obstacle reduces with increasing magnetic field strength for a particular Reynolds number. The rate of heat transfer is found almost invariant at low Re whereas it increases slightly for higher Re with the applied magnetic field. The heat transfer increases as usual with the Reynolds number for all Hartmann numbers. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21025  相似文献   

2.
Local and average heat transfer by forced convection from a circular cylinder is studied for Reynolds number from 2 × 103 to 9 × 104 and Prandtl number from 0.7 to 176. For subcritical flow, the local heat transfer measurement indicates three regions of flow around the cylinder: laminar boundary layer region, reattachment of shear layer region and periodic vortex flow region. The average heat transfer in each region is calculated and correlated with the Reynolds number and the Prandtl number. The Nusselt number in each region strongly depends on the Reynolds number and the Prandtl number with different power indices. An empirical correlation for predicting the overall heat transfer from the cylinder is developed from the contributions of heat transfer in these three regions.  相似文献   

3.
Local heat transfer by forced convection from a circular cylinder in crossflow is investigated for Reynolds number from 2 × 103 to 9 × 104 and Prandtl number from 7 to 176. The working fluids are water and mixtures of ethylene glycol and water. The cylinder is uniformly heated by passing a direct electric current through a thin surface heater. The influence of Reynolds number and Prandtl number on the distributions of local Nusselt number around a circular cylinder in crossflow is described.  相似文献   

4.
A numerical investigation was conducted to analyze the unsteady flow field and heat transfer characteristics in a horizontal channel with a built-in heated square cylinder. Hydrodynamic behavior and heat transfer results are obtained by the solution of the complete Navier–Stokes and energy equations using a control volume finite element method (CVFEM) adapted to the staggered grid. The Computation was made for two channel blockage ratios (β=1/4 and 1/8), different Reynolds and Richardson numbers ranging from 62 to 200 and from 0 to 0.1 respectively at Pr=0.71. The flow is found to be unstable when the Richardson number crosses the critical value of 0.13. The results are presented to show the effects of the blockage ratio, the Reynolds and the Richardson numbers on the flow pattern and the heat transfer from the square cylinder. Heat transfer correlation are obtained through forced and mixed convection.  相似文献   

5.
In this study, flow-field and heat transfer through a copper–water nanofluid around circular cylinder has been numerically investigated. Governing equations containing continuity, N–S equation and energy equation have been developed in polar coordinate system. The equations have been numerically solved using a finite volume method over a staggered grid system. SIMPLE algorithm has been applied for solving the pressure linked equations. Reynolds and Peclet numbers (based on the cylinder diameter and the velocity of free stream) are within the range of 1 to 40. Furthermore, volume fraction of nanoparticles (φ) varies within the range of 0 to 0.05. Effective thermal conductivity and effective viscosity of nanofluid have been estimated by Hamilton–Crosser and Brinkman models, respectively. The effect of volume fraction of nanoparticles on the fluid flow and heat transfer characteristics are investigated. It is found that the vorticity, pressure coefficient, recirculation length are increased by the addition of nanoparticles into clear fluid. Moreover, the local and mean Nusselt numbers are enhanced due to adding nanoparticles into base fluid.  相似文献   

6.
Heat transfer from a cylinder in axial turbulent flows   总被引:1,自引:0,他引:1  
Local convective heat transfer coefficients were measured on a two-diameter long cylinder in axial flows of air at conditions unexplored so far, by using thermochromic liquid crystals (TLC) coated on an electrically heated strip-foil consisting bonded to the external surfaces. The Reynolds numbers (Re) based on the cylinder diameter were between 8.9 × 104 and 6.17 × 105, and the flow in front of the cylinder was modified in some cases by the use of a turbulence generating grid, or by circular disc inserts of two sizes placed upstream of the cylinder. These created a major change in the local convective heat transfer coefficient distribution on the cylinder. Increase of the turbulence intensity from Tu < 0.1% to Tu = 6.7% at the same Re increased the average calculated Nusselt number Nu over the cylinder by 25%, and decreased the Nu non-uniformity over the surface. One of the flow modification inserts also reduced significantly the Nu non-uniformity. The position of flow reattachment was measured using tufts. Our heat transfer data agree well with the small amount if data published of others, when extrapolated to their conditions. Correlations between the Nu and Re in the form Nu = CRee were established and presented for the average Nu on the front, middle and rear cylinder surfaces, and the variation of the local exponent e was shown along the cylinder. Introducing a new technique, a TLC-coated heated flat plate mounted in the flow above the cylinder in the meridional plane was demonstrated to help visualize the flow field above the cylinder. A track of maximum convective coefficients on this plate was found similar in position to the stream line dividing the forward and backward flows in a case measured for the separated flow in a past study.  相似文献   

7.
Heat transfer characteristics of a circular cylinder exposed to a slowly oscillating flow with zero-mean velocity were investigated. The flow oscillation amplitude and frequency were changed in the range where the flow remains laminar and fluid particle travels back and forth over much larger distance compared to the cylinder diameter. The time- and space-averaged Nusselt number was measured by transient method, while two-dimensional numerical simulation was conducted to discuss the instantaneous flow and thermal fields around the cylinder. It was found that the time- and space-averaged Nusselt number can be correlated with the oscillating Reynolds number and Richardson number. Unique heat transfer characteristics under oscillating flow condition can be seen at the phases when the cross-sectional mean velocity is small or increasing from small value. During such period, heat transfer can be enhanced due to the local fluid motion induced by the vortices around the cylinder, which once moved away but returned back by the reversed flow. This heat transfer enhancement, however, is countered by the local warming effect of the hot vortices clinging around the cylinder at such phases.  相似文献   

8.
The convective heat transfer coefficient was experimentally investigated in an annulus with an inner rotating cylinder to estimate the thermal fatigue of the inner and outer cylinders on the rotating machine. The following three conclusions were obtained: (1) Within the range of the experimental conditions, the heat transfer coefficient did not depend on the axial flow rate; rather, it showed a larger dependence on the inner cylinder rotating speed. (2) The heat transfer coefficient at the top of the labyrinth was about three times as large as that at the bottom. (3) An empirical correlation equation considering the gap between the inner and outer cylinders is proposed, which predicts the heat transfer coefficient on the rotating machine within ±30 percent. © 1997 Scripta Technica. Inc. Heat Trans Jpn Res. 25 (2): 103–119, 1996  相似文献   

9.
An experimental study has been conducted to determine the heat transfer characteristics around a circular cylinder attached to the separated flow of air shed from a fence. The fence was located vertically to the flow with a height of H = 40 mm. d/H was constant at 0.638, where d is the cylinder diameter of 25.5 mm. X/H were 0.50 and 0.775 and Y/H ranged from 0.525 to 1.50, where X and Y are, respectively, the distances between the axis of the cylinder and the front face of the fence, and the bottom wall of the test section. The Reynolds number based on the cylinder diameter and the velocity of the undisturbed flow ranged from 1.9 × 104 to 6.0 × 104. It was found that the maximum local Nusselt number changes drastically in the vicinity of Y/H = 1.0–1.11 and that the maximum mean Nusselt number occurs in the neighborhood of Y/H = 1.24–1.43 for X/H = 0.50 and 1.3–1.4 for X/H = 0.775. © 1999 Scripta Technica, Heat Trans Asian Res, 28(3): 211–226, 1999  相似文献   

10.
An experimental study of heat transfer on a horizontal rotating cylinder near a flat plate was performed. The cylinder and plate were set in a cross‐flow. Temperature distribution and coefficients of local heat transfer were measured by a Mach–Zehnder interferometer. Flow visualization was made using smoke. Rotating Reynolds numbers (Rer) and cross‐flow Reynolds numbers (Red) were varied from 0 to 2000. The spaces between cylinder and plate were varied from 1 × 10?3 m to 5 × 10?3 m. The rotating direction of cylinder was changed clockwise or counterclockwise. The following results are obtained: When the space between the rotating cylinder and flat plate is the same as the displacement thickness on the plate, the heat transfer on the cylinder near the plate has the best performance. We have procured the empirical equation of heat transfer from a rotating cylinder near the flat plate in the cross‐flow. 8 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/htj.20329  相似文献   

11.
This article discusses the results obtained through a two‐dimensional numerical simulation following a finite volume approach on the forced convection heat transfer for the hydromagnetic flow around a square cylinder at low Reynolds and Hartmann numbers. The magnetohydrodynamic (MHD) flow of a viscous incompressible and electrically conducting fluid is assumed to take place in a rectangular channel subjected to externally imposed magnetic fields and the cylinder is fixed within the channel. The magnetic fields may be applied either along the streamwise or transverse directions. Simulations are performed for the range of kinetic Reynolds number 10 ≤ Re ≤ 60 with Hartmann number 0 ≤ Ha ≤ 15 and for different thermal Prandtl numbers, Pr = 0.02 (liquid metal), 0.71 (air), and 7 (water) for a blockage ratio β = 0.25. A steady flow can be expected for the above range of conditions. Besides the channel wall, the magnetic field imparts additional stability to the flow as a consequence of which the recirculation region behind the obstacle reduces with increasing magnetic field strength for a particular Re. The critical Hartmann numbers for the complete suppression of flow separation in the case of a transversely applied magnetic field are computed. The rate of heat transfer is found almost invariant at low Re whereas it increases moderately for higher Re with the applied magnetic field. The heat transfer increases in general with the Reynolds number for all Hartmann numbers. Finally, the influence of obstacle shape on the thermohydrodynamic quantities is noted. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(5): 459–475, 2014; Published online 3 October 2013 in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21091  相似文献   

12.
The melting of a vertical ice cylinder into a homogeneous calcium chloride aqueous solution inside a rotating cylindrical cavity with several rotating speeds is considered experimentally. The melting mass and temperature are measured on four initial conditions of the solution and four rotating speeds of the cavity. The temperature of the liquid layer becomes uniform by the mixing effect resulting from cavity rotation and it enhances the melting rate of the ice cylinder. As the cavity‐rotating speed increases, the melting rate increases. The dimensionless melting mass is related to the Fourier number and the rotating Reynolds number in each initial condition, therefore an experimental equation that is able to quantitatively calculate the dimensionless melting mass is presented. It is seen that the melting Nusselt numbers increase again in the middle of the melting process. The ice cylinder continues to melt in spite of the small temperature difference between the ice cylinder and the solution. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(6): 359–373, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20211  相似文献   

13.
A Fredholm-type boundary integral expression for evaluation of the forced convection heat transfer from an object with arbitrary surface temperature distributions is proposed. The Fredholm kernel function for a heated circular cylinder was calculated by numerical simulation of the forced convection fields, and then generalized heat transfer coefficients for arbitrary surface temperature distributions were defined. By use of the generalized heat transfer coefficients, it is shown that the difference in local heat transfer characteristics between the case of an isothermal cylinder and that of a uniform heat flux one can be interpreted only as the difference of the surface temperature distributions. Moreover, the mechanism of the effect of the surface temperature distribution on the characteristics of forced convection heat transfer from a cylinder is clarified in detail through the generalized heat transfer coefficients. © 1999 Scripta Technica, Heat Trans Asian Res, 28(6): 484–499, 1999  相似文献   

14.
Experimental investigations have been carried out for combined convective flows of air induced around uniformly heated, horizontal cylinders. Three cases of aiding, opposing, and cross flows were examined. The experiments covered the ranges of the Reynolds and modified Rayleigh numbers of Red=50 to 900 and Rad*=5×104 to 3×106. The flow fields around the cylinders were visualized with smoke. The results showed that separation points gradually shift from those of the forced convection to the top edge of the cylinder with increasing wall heat fluxes. The local heat transfer coefficients of the cylinders were also measured. Although the local coefficients show complex variations with the forced flow velocities and the wall heat fluxes, the overall coefficients become higher than those estimated from pure forced and natural convections throughout the cases of aiding, opposing, and cross flows. Moreover, it was confirmed that the overall Nusselt numbers as well as the separation points can be predicted with the non‐dimensional parameter (Grd*/NudRed2). © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(8): 474–488, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20180  相似文献   

15.
Magnetohydrodynamic (MHD) free‐surface flow and heat transfer of liquid metal around a cylinder under different Reynolds numbers were simulated numerically. The effects of the application of a magnetic field on wake and vortex shedding were analyzed. The characteristics of flow fields and temperature as well as Lorentz forces under two different Reynolds numbers were presented. The results showed that magnetic field could not only change substantially the flow pattern, but also suppress turbulent viscosity and surface renewal, which degraded heat transfer. Under the same Hartmann numbers, compared with the MHD‐flow and heat transfer of lower Reynolds numbers, the turbulence intensity and interaction between free surface and wake were still stronger for higher Reynolds numbers; consequently, the heat transfer was still high. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(1): 11–19, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20189  相似文献   

16.
The two-dimensional vortex structure behind a highly heated cylinder has been studied experimentally. The air velocity was set at 1.0 m/s. The surface temperature of the heated cylinder was varied up to 600 °C. Particle image velocimetry (PIV) was used to measure the two-dimensional instantaneous and average velocities. Just downstream of the heated cylinder, the vortex was intensified by increasing the wall temperature of the heated cylinder. The vortex frequency decreased when the wall temperature increased. This indicates that the local kinematic viscosity plays a key role in the vortex structure. As a result, the vortex frequency of the heated cylinder can be expressed as a function of the Strouhal and Reynolds numbers, when the local kinematic viscosity is reasonably estimated by taking into account the effect of the wall heating. © 1999 Scripta Technica, Heat Trans Asian Res, 28(8): 706-718, 1999  相似文献   

17.
18.
Mixed convection heat transfer in a lid-driven cavity along with a heated circular hollow cylinder positioned at the center of the cavity has been analyzed numerically. The present study simulates a realistic system such as air-cooled electronic equipment with a heat component or an oven with heater. A Galerkin weighted residual finite element method with a Newton–Raphson iterative algorithm is adopted to solve the governing equations. The computation is carried out for wide ranges of the Richardson numbers, cylinder diameter and solid fluid thermal conductivity ratio. Results are presented in the form of streamlines, isothermal lines, average Nusselt number at the heated surface and fluid temperature in the cavity for the mentioned parameters. It is found that the flow field and temperature distribution strongly depend on the cylinder diameter and also the solid–fluid thermal conductivity ratio at the three convective regimes.  相似文献   

19.
The flow field around a circular cylinder elastically suspended with a cantilever‐type plate spring in the jet impingement region was visualized to investigate the mechanism of the impingement heat transfer. The impingement distance H was kept constant at 3 or 5 times as large as the jet slot width, h = 15 mm.The Reynolds number was fixed at 10,000, or 5000 in the case of flow visualization. The self‐induced periodic swing motion of the cylinder across the jet axis was caused by the interaction between the jet and the elastically suspended cylinder. It was found that this swing motion has direct effects on the flow and heat transfer characteristics of the stagnation region. The ensemble‐averaged values of the flow velocity and its fluctuations depended on the cylinder diameter and the impingement distance. The local Nusselt number in the case of H/h = 3 with the oscillating cylinder of the smallest diameter D = 4 mm was increased to 1.15 times as large as that without the cylinder. The interesting patterns of the intermittency function defined with a certain threshold level of turbulence intensity were obtained under the above experimental conditions. © 2001 Scripta Technica, Heat Trans Asian Res, 30(4): 313–330, 2001  相似文献   

20.
This paper presents a numerical analysis of the flow and heat transfer characteristics of forced convection in a micropolar fluid flowing along a vertical slender hollow circular cylinder with wall conduction and buoyancy effects. The non-linear formulation governing equations and their associated boundary conditions are solved using the cubic spline collocation method and the finite difference scheme with a local non-similar transformation. This study investigates the effects of the conjugate heat transfer parameter, the Richardson number, the micropolar parameter, and the Prandtl number on the flow and the thermal fields. The effect of wall conduction on the thermal and the flow fields are found to be more pronounced in a system with a greater buoyancy effect or Prandtl number but is less sensitive with a greater micropolar material parameter. Compared to the case of pure forced convection, buoyancy effect is found to result in a lower interfacial temperature but higher the local heat transfer rate and the skin friction factor. Finally, compared to Newtonian fluid, an increase in the interfacial temperature, a reduction in the skin friction factor, and a reduction in the local heat transfer rate are identified in the current micropolar fluid case.  相似文献   

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