Effect of Vortices Induced by Corona Discharge on Free-Convection Heat Transfer From a Vertical Plate

1969 ◽  
Vol 91 (3) ◽  
pp. 427-432 ◽  
Author(s):  
M. E. Franke
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Free Convection ◽  
Electric Field ◽  
Corona Discharge ◽  
Heat Transfer Rate ◽  
High Voltage ◽  
Transfer Rate ◽  
Thermal Boundary Layer ◽  
Transfer Rates

Experimental results are presented to show that columnar, counterrotating, vertical vortices can be produced on a heated, vertical, flat plate under free-convection conditions in air using a high-voltage d-c electric field. The vortices result from the corona discharge on 0.002-in.-dia parallel wires of alternate high voltage and ground potential placed vertically on the surface of a phenolic laminate plate. Heat-transfer rates are measured using an energy-balance method, and the thermal boundary layer is made visible using a Mach-Zehnder interferometer. Experimental curves are presented to illustrate the increase in the heat-transfer rate with increase in the electric-field power. Interference photographs and frames from a motion picture show the effects of the vortices on the thermal boundary layer. The convective part of the heat transfer from the 10 × 10 in. plate is more than doubled before the electric-field power becomes as large as 5 percent of the increase in the heat-transfer rate. Local heat-transfer rates are highest at the high-voltage wires and lowest at the grounded wires.

A Numerical Study of Impulsively Started External Convection at Microscale

2014 ◽  
Vol 31 (1) ◽  
pp. 79-90
Author(s):  
K. Ramadan
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Thermal Boundary Layer ◽  
Numerical Study ◽  
Velocity Slip ◽  
Transition Time ◽  
Surface Cooling ◽  
Linear Ordinary Differential Equations

ABSTRACTImpulsively started external convection at microscale level is studied numerically in both planar and axisymmetric geometries. Using similarity transformation, the resulting coupled partial and non-linear ordinary differential equations are simultaneously solved by finite differences together with a well established ordinary differential equation solver, over a range of problem parameters. Rarefaction effects within the slip flow regime on the thermal boundary layer response, heat transfer rate and transition time when system experiences sudden changes in surface temperature are analyzed, and a comparison between sudden surface cooling and heating is presented. The results show that the thermal boundary layer thickness, heat transfer rate and the transition time is considerably influenced by the degree of rarefaction. The transition time tends to be less sensitive with increasing rarefaction. The velocity slip and temperature jump factors are found to have opposite effects on the transition time and the heat transfer rate, with the velocity slip factor having the most profound influence on these parameters.

Heat Transfer Enhancement of Channel Flow via Vortex-Induced Vibration of Flexible Cylinder

2014 ◽  
Author(s):  
Junxiang Shi ◽  
Jingwen Hu ◽  
Steven R. Schafer ◽  
Chung-Lung (C. L. ) Chen
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Convective Heat Transfer ◽  
Heat Transfer Rate ◽  
Channel Flow ◽  
Convective Heat ◽  
Thermal Performance ◽  
Transfer Rate ◽  
Thermal Boundary Layer ◽  
Flexible Cylinder

Thermal diffusion in a developed thermal boundary layer is considered as an obstacle for improving the forced convective heat transfer rate of a channel flow. In this work, a novel, self-agitating method that takes advantage of vortex-induced vibration (VIV) is introduced to disrupt the thermal boundary layer and thereby enhance the thermal performance. A flexible cylinder is placed at the centerline of a rectangular channel. The vortex shedding due to the cylinder gives rise to a periodic vibration of the cylinder. Consequently, the flow-structure-interaction (FSI) strengthens the disruption of the thermal boundary layer by vortex interaction with the walls, and improves the mixing process. This new concept for enhancing the convective heat transfer rate is demonstrated by a three-dimensional modeling study at different Reynolds numbers (84∼168). The fluid dynamics and thermal performance are analyzed in terms of vortex dynamics, temperature fields, local and average Nusselt numbers, and pressure loss. The channel with the self-agitated cylinder is verified to significantly increase the convective heat transfer coefficient. When the Reynolds number is 168, the channel with the VIV improves the average Nu by 234.8% and 51.4% as opposed to the clean channel and the channel with a stationary cylinder, respectively.

Effects of Corona Discharge on Free-Convection Heat Transfer Inside a Vertical Hollow Cylinder

1984 ◽  
Vol 106 (2) ◽  
pp. 346-351 ◽  
Author(s):  
M. E. Franke ◽  
K. E. Hutson
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Corona Discharge ◽  
Heat Transfer Rate ◽  
Hollow Cylinder ◽  
Transfer Rate ◽  
Convection Heat Transfer ◽  
Inside Surface ◽  
Convection Heat ◽  
Free Convection Heat

Vortex rolls induced inside a vertical hollow cylinder are found to increase the free-convection heat transfer rate from the inside surface. The vortex rolls are induced by the corona wind generated between 0.05-mm-dia wire electrodes placed vertically on the inside surface of the vertical hollow cylinder. The increase in heat transfer rate is determined experimentally and is based on the heat input required to maintain the inside surface of the cylinder at constant temperature. The experimental results without corona discharge are compared with an analytical heat balance. A Mach-Zehnder interferometer is used for boundary layer visualization.

Combined Convective Heat Transfer from Vertical Cylinders in a Horizontal Air-Stream

1978 ◽  
Vol 5 (2) ◽  
pp. 115-117
Author(s):  
P. H. Oosthuizen ◽  
R. Leung
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Convective Heat Transfer ◽  
Heat Transfer Rate ◽  
Convective Heat ◽  
Transfer Rate ◽  
Circular Cylinders ◽  
Transfer Rates ◽  
Air Stream ◽  
Vertical Cylinders

Mean heat transfer rates from a series of circular cylinders mounted vertically in a horizontal air-stream have been measured. Five cylinders were used, having diameters of approximately 19 to 25 mm and heights of approximately 150 to 300 mm. Heat transfer rates from these cylinders were measured at a number of different air velocities ranging from zero to about 1.6 m/s. The results indicate that the heat transfer rate in the combined convection range is higher than it would be under the same conditions with purely free convection or purely forced convection. An attempt has been made to correlate the combined convective heat transfer rates in terms of the heat transfer rates that would exist under the same conditions in these two limiting cases of purely forced and purely free convection.

Electric Field Effects on Natural Convection in Enclosures

1986 ◽  
Vol 108 (4) ◽  
pp. 749-754 ◽  
Author(s):  
D. A. Nelson ◽  
E. J. Shaughnessy
Keyword(s):  
Heat Transfer ◽  
Electric Field ◽  
Convective Heat Transfer ◽  
Heat Transfer Rate ◽  
Convective Heat ◽  
Transfer Rate ◽  
Stokes Equations ◽  
Experimental Studies ◽  
Navier Stokes ◽  
First Order Theory

The enhancement of convective heat transfer by an electric field is but one aspect of the complex thermoelectric phenomena which arise from the interaction of fluid dynamic and electric fields. Our current knowledge of this area is limited to a very few experimental studies. There has been no formal analysis of the basic coupling modes of the Navier–Stokes and Maxwell equations which are developed in the absence of any appreciable magnetic fields. Convective flows in enclosures are particularly sensitive because the limited fluid volumes, recirculation, and generally low velocities allow the relatively weak electric body force to exert a significant influence. In this work, the modes by which the Navier–Stokes equations are coupled to Maxwell’s equations of electrodynamics are reviewed. The conditions governing the most significant coupling modes (Coulombic forces, Joule heating, permittivity gradients) are then derived within the context of a first-order theory of electrohydrodynamics. Situations in which these couplings may have a profound effect on the convective heat transfer rate are postulated. The result is an organized framework for controlling the heat transfer rate in enclosures.

An Analytical Study of Heat Transfer in Finite Tissue With Two Blood Vessels and Uniform Dirichlet Boundary Conditions

2005 ◽  
Vol 127 (2) ◽  
pp. 179-188 ◽  
Author(s):  
Devashish Shrivastava ◽  
Benjamin McKay ◽  
Robert B. Roemer
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Source Term ◽  
Dirichlet Boundary ◽  
Total Heat ◽  
Dirichlet Boundary Conditions ◽  
Total Heat Transfer ◽  
Transfer Rates

Counter-current (vessel–vessel) heat transfer has been postulated as one of the most important heat transfer mechanisms in living systems. Surprisingly, however, the accurate quantification of the vessel–vessel, and vessel–tissue, heat transfer rates has never been performed in the most general and important case of a finite, unheated/heated tissue domain with noninsulated boundary conditions. To quantify these heat transfer rates, an exact analytical expression for the temperature field is derived by solving the 2-D Poisson equation with uniform Dirichlet boundary conditions. The new results obtained using this solution are as follows: first, the vessel–vessel heat transfer rate can be a large fraction of the total heat transfer rate of each vessel, thus quantitatively demonstrating the need to accurately model the vessel–vessel heat transfer for vessels imbedded in tissues. Second, the vessel–vessel heat transfer rate is shown to be independent of the source term; while the heat transfer rates from the vessels to the tissue show a significant dependence on the source term. Third, while many previous studies have assumed that (1) the total heat transfer rate from vessels to tissue is zero, and/or (2) the heat transfer rates from paired vessels (of different sizes and at different temperatures) to tissue are equal to each other the current analysis shows that neither of these conditions is met. The analytical solution approach used to solve this two vessels problem is general and can be extended for the case of “N” arbitrarily located vessels.

Non-axisymmetric Homann stagnation point flow and heat transfer past a stretching/shrinking sheet using hybrid nanofluid

2020 ◽  
Vol 30 (10) ◽  
pp. 4583-4606 ◽  
Author(s):  
Najiyah Safwa Khashi’ie ◽  
Norihan Md Arifin ◽  
Ioan Pop ◽  
Roslinda Nazar ◽  
Ezad Hafidz Hafidzuddin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Strain Rate ◽  
Stagnation Point ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Hybrid Nanofluid ◽  
Ambient Fluid ◽  
Content Type ◽  
Flow And Heat Transfer

Purpose This paper aims to scrutinize the analysis of non-axisymmetric Homann stagnation point flow and heat transfer of hybrid Cu-Al2O3/water nanofluid over a stretching/shrinking flat plate. Design/methodology/approach The similarity transformation which fulfils the continuity equation is opted to transform the coupled momentum and energy equations into the nonlinear ordinary differential equations. Numerical solutions which are elucidated in the tables and graphs are obtained using the bvp4c solver. Findings Non-unique solutions (first and second) are feasible for both stretching and shrinking cases within the specific values of the parameters. First solution is the physical/real solution based on the execution of stability analysis. An upsurge of the ratio of the ambient fluid strain rate to the plate strain rate can delay the boundary layer separation, whereas a boost of the ratio of the ambient fluid shear rate to the plate strain rate only accelerates the separation of boundary layer. The heat transfer rate of hybrid nanofluid is greater for the stretching case than the shrinking case. However, for the shrinking case, the heat transfer rate intensifies with the increment of the copper (Cu) nanoparticles volume fraction, whereas a contrary result is found for the stretching case. Originality/value The present numerical results are original and new. It can contribute to other researchers on electing the relevant parameters to optimize the heat transfer process in the modern industry, and the right parameters to generate non-unique solution so that no misjudgment on flow and heat transfer features.

The impacts of non-uniform magnetic field on free convection heat transfer of a magnetizable micropolar nanofluid

2019 ◽  
Vol 29 (10) ◽  
pp. 3685-3706
Author(s):  
Zafar Namazian ◽  
S.A.M. Mehryan
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Volume Fraction ◽  
Convection Heat Transfer ◽  
Content Type ◽  
Viscosity Parameter ◽  
Micropolar Nanofluid ◽  
Free Convection Heat

Purpose The purpose of this study is to numerically study the heat transfer of free convection of a magnetizable micropolar nanofluid inside a semicircular enclosure. Design/methodology/approach The flow domain is under simultaneous influences of two non-uniform magnetic fields generated by current carrying wires. The directions of the currents are the same. Although the geometry is symmetric, it is physically asymmetric. The impacts of key parameters, including Rayleigh number Ra = 103-106, Hartman number Ha = 0-50, vortex viscosity parameter Δ = 0-4, nanoparticles volume fraction φ = 0-0.04 and magnetic number Mnf = 0-1000, on the macro- and micro-scales flows, temperature and heat transfer rate are studied. Finding The outcomes show that dispersing of the nanoparticles in the host fluid increases the strength of macro- and micro-scale flows. When Mnf = 0, the increment of the vortex viscosity parameter increases the strength of the particles micro-rotations, while this characteristic is decreased by growing Δ for Mnf ≠ 0. The increment of Δ and Ha decreases the rate of heat transfer. The increment of Ha decreases the enhancement percentage of heat transfer rate because of dispersing nanoparticles, known as En parameter. In addition, the value of Δ has no effect on En. Moreover, the average Nusselt number Nuavg and En remain constant by increasing the magnetic number Mnf for different volume fraction values. Originality/value The authors believe that all of the results, both numerical and asymptotic, are original and have not been published elsewhere yet.

Numerical Simulation of Heat Sink Performance With Interrupted and Staggered Fins

2009 ◽  
Author(s):  
Suabsakul Gururatana ◽  
Xianchang Li
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Heat Transfer Rate ◽  
Heat Sink ◽  
Pressure Loss ◽  
Transfer Rate ◽  
Flow Direction ◽  
Heat Sinks ◽  
High Heat Transfer

Extended surfaces (fins) have been used to enhance heat transfer in many applications. In electronics cooling, fin-based heat sinks are commonly designed so that coolants (gas or liquid) are forced to pass through the narrow straight channel. To improve the overall heat sink performance, this study investigated numerically the details of heat sinks with interrupted and staggered fins cooled by forced convection. Long and narrow flow passages or channels are widely seen in heat sinks. Based on the fundamental theory of heat transfer, however, a new boundary layer can be created periodically with interrupted fins, and the entrance region can produce a very high heat transfer coefficient. The staggered fins can take advantage of the lower temperature flow from the upstream. The tradeoff is the higher pressure loss. A major challenge for heat sink design is to reduce the pressure loss while keeping the heat transfer rate high. The effect of fin shapes on the heat sink performance was also examined. Two different shapes under study are rectangular and elliptic with various gaps between the interrupted fins in the flow direction. In addition, studies were also conducted on the parametric effects of Reynolds number and gap length. It is observed that heat transfer increases with the Reynolds number due to the feature of developing boundary layer. If the same pressure drop is considered, the heat transfer rate of elliptic fins is higher than that of rectangular fins.

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