Heat Transfer Enhancement in Rectangular Channels Using a Corona Jet Caused by Longitudinal Flat Electrodes

2011 ◽  
Author(s):  
Reza Baghaei Lakeh ◽  
Majid Molki
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Electric Field ◽  
Convective Heat Transfer ◽  
Cross Section ◽  
Convective Heat ◽  
Body Force ◽  
Rectangular Channels ◽  
Induced Flow ◽  
Gas Molecules

Heat transfer in rectangular channels can be significantly enhanced by formation of secondary flows. Secondary flow fields appear within the channels and influence the boundary layer growth and improve the convective heat transfer. When a high potential is applied to two electrodes, the consequent high electric field in the gap between the electrodes may exceed the partial break-down limit of the gas molecules. The neutral gas molecules are ionized close to the emitting electrode and accelerate in the direction of the electric field. The accelerating ions impose an electric body-force to the gas and induce a bulk flow. Depending on the location and geometry of the electrodes, the electrically-induced flow field might have different specifications. If the electrodes are laid on the opposite walls of channel and extended in the longitudinal direction, the electric body-force would cause a secondary flow on the cross section of the channel. The electrically-induced flow field disturbs the boundary layer and enhances the convective heat transfer coefficient. However, the enhancement level is more remarkable in natural convection. In this study, the influence of a corona jet on heat transfer in rectangular channels with flat and longitudinal electrodes will be studied. The emitting and collecting electrodes are metallic strips attached to opposite walls of the channel and are extended along the axis of the channel. The electric field governing equations are solved numerically using finite-volume method and the third-order QUICK scheme is utilized for discretization of the charge fluxes. The distribution of electric field and charge density on the cross section of the channel is obtained to find the electric body-force at each point. In the presence of electric and buoyancy forces, the momentum and energy equations are solved to determine the level of enhancement of convective heat transfer using corona discharge.

Heat Transfer Enhancement of Laminar Internal Flows Using Electrically-Induced Swirling Effect

2012 ◽  
Author(s):  
Reza Baghaei Lakeh ◽  
Majid Molki
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Flow Field ◽  
Electric Field ◽  
Convective Heat Transfer ◽  
Cross Section ◽  
Convective Heat ◽  
Parallel Plates ◽  
Internal Flows ◽  
The Cross

A computational and experimental approach is conducted to enhance the convective heat transfer in fully developed laminar flow in parallel-plates configuration. Laminar internal flows are associated with unchanging Nusselt number along the channel due to the fully developed condition of the boundary layer. Inducing a swirling effect along the flow can disturb the flow field and enhance the convective heat transfer from the plates to the flow. The interaction between an electrically-induced secondary flow and the pressure-driven main flow complicates the flow field and causes a swirling effect. In this study, the electric field governing equations are solved numerically using finite volume method. In order to obtain a proper boundary condition for the charge density, an experimental setup was utilized to measure the time-averaged corona current. The distribution of electric field and charge density on the cross section of the channel is obtained and adopted to find the electric body-force at each point. The flow field computations are performed with FLUENT CFD code on a three-dimensional model using second-order upwind scheme. The secondary flow field is imposed on the cross section of the channel by corona discharge. An array of emitting and receiving flat electrodes are embedded in the parallel plates to induce a corona jet on the cross section of the channel. The axial component of velocity along with an array of corona jets gives birth to a swirling flow which can significantly enhance the convection coefficient and Nusselt number in the fully developed regime. This investigation indicated that the convective heat transfer can be enhanced up to 173% with an applied potential of 24 kV.

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.

Mechanical Augmentation of Convective Heat Transfer in Air

1975 ◽  
Vol 97 (4) ◽  
pp. 516-520 ◽  
Author(s):  
J. K. Hagge ◽  
G. H. Junkhan
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Convective Heat Transfer ◽  
Boundary Layers ◽  
Convective Heat ◽  
Convection Heat Transfer ◽  
Renewal Theory ◽  
Surface Renewal ◽  
Mechanical Removal ◽  
Blade Element

An experimental investigation was conducted into augmentation of forced convection heat transfer in air by mechanical removal of the boundary layer. A rotating blade element passing in close proximity to a flat plate convective surface was found to increase the rate of convective heat transfer by up to eleven times in certain situations. The blade element effectively scrapes away the boundary layer, thus reducing the resistance to heat flow. Parameters investigated include scraping frequency, scraper clearance, and type of boundary layer. Increased coefficients were found for higher scraping frequencies. Significant augmentation was obtained with clearance as large as 0.15 in. (0.0038 m) between the moving blade element and the convective surface. The technique appears most useful for laminar and transitional boundary layers, although some improvement was obtained for the turbulent boundary layers investigated. The simple surface renewal theory developed for scraped surface augmentation in liquids was found to approximately predict the coefficients obtained. A new relation is proposed which gives a better prediction and includes the effect of scraper clearance.

Sign in / Sign up

Export Citation Format

Share Document