scholarly journals THERMAL BOUNDARY LAYER EQUIVALENT TO CONVECTIVE HEAT TRANSFER IN THE CORNER OF WALL ON OVERALL HEAT TRANSMISSION ANALYSIS

1988 ◽  
Vol 393 (0) ◽  
pp. 10-16
Author(s):  
HARUHISA YAMAGUCHI ◽  
YOSHIKAZU NAKANE
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Thermal Boundary Layer ◽  
Heat Transmission

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.

Numerical Modeling for the Energy Conversion and Thermal Transmission Accompanying the Process of Oily Cuttings Agitation

2016 ◽  
Author(s):  
Zhipeng Sun ◽  
Hongwu Zhu ◽  
Jian Hua
Keyword(s):  
Heat Transfer ◽  
Energy Conversion ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Solid Phase ◽  
Conductive Heat ◽  
Heat Transmission ◽  
Gas Reservoirs ◽  
Coupling Approach ◽  
Solid Motion

As a kind of unconventional gas reservoirs, shale gas reservoirs are full of potential to develop and have attracted global attention. Accompanying the exploiting of shale gas, a large amount of drilling cuttings contaminated by the oil-based drilling fluid are generated inevitably. How to deal with the drilling cuttings in a environmental-friendly way is tough especially for offshore oilfield. So it is important to investigate this aspect deeply and develop methods to clean the contaminated drilling cuttings. As is known to all, the thermal desorption technology has outstanding performance in oily cuttings cleaning. This paper bases on a kind of mechanical-thermal cuttings cleaning apparatus where the contaminated drilling cuttings are heated up by friction heat produced by the friction between the cuttings and the agitating vanes. And the harmful substance is separated from the cuttings in the agitated and high temperature flow field. This thesis investigates the fundamental of the energy conversion in the frictional process, infer formulas analyzing the thermo-physical phenomena and quantitatively model the energy conversion and thermal transmission accompanying the friction. Firstly, the principle of heat transfer and the law of conservation of energy are employed to investigate the natural law of the energy conversion in the frictional process. Based on the investigation, taking the liquid bridge between the oily cuttings and the agitating vane into account, this paper deduces the physical equations and the frictional energy model to calculate the total frictional heat, heat density and temperature distribution. Following up the frictional model, in the Eulerian-Lagrangian coupling framework, this paper develops a parallel numerical platform of computational fluid dynamics combined with discrete element method (CFD-DEM). In the coupling approach, the gas motion is solved at the computational grid level while the solid motion is resolved at the particle-scale level. Furthermore, the coupling approach is extended with the frictional energy model. The numerical platform can calculate the dense gas-solid motion in the fluidizing apparatus, the convective heat transfer between gas and solid phase, and the conductive heat transfer between particles. Based on the platform, the mechanical-thermal energy conversion and the convective heat transfer between gas and oily cuttings, and the conductive heat transfer between cuttings and the agitating vanes are investigated. Meanwhile an experiment is conducted. By comparing the numerical results with the experiment data, the paper can come to the conclusion that how to dispose the nonlinear parameters such as the friction contact area, the friction coefficient and the normal pressure is the key to accurately model the energy conversion and the heat transmission. What’s more, it can be understood that the convective heat transfer between gas and solid phase play an important role in the heat transmission.

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.

Transient Method for Convective Heat Transfer Measurement With Lateral Conduction—Part II: Application to an Isolated Spherical Roughness Element

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
J. Bons ◽  
Daniel Fletcher ◽  
Brad Borchert
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Convective Heat Transfer ◽  
Finite Volume ◽  
Convective Heat ◽  
Roughness Element ◽  
Measurement Techniques ◽  
Stanton Number ◽  
3D Analysis ◽  
Transient Conduction

The effect of lateral conduction on convective heat transfer measurements using a transient infrared technique over an isolated spherical roughness element (bump) is evaluated. Comparisons are made between a full 3D finite-volume analysis and a simpler 1D transient conduction model. The surface temperature history was measured with a high resolution infrared camera during an impulsively started hot-gas flow at a flow Reynolds number of 860,000. The boundary layer was turbulent with the bump heights equivalent to 0.75, 1.5, and 3 times the boundary layer momentum thickness. When considering transient conduction effects only in the bump wake, the 1D approximate method underestimates the actual Stanton number estimated with the 3D model. This discrepancy is only 10% for a 75% change in St number occurring over a surface distance of 10 mm (the half-width of the wake). When the actual bump topology is accounted for in estimating the Stanton number on the bump itself with the 3D analysis technique, the increased surface area of the finite-volume cells on the protruding bump actually decreases the predicted value of St locally. The net result is that the two effects can cancel each other, and in some cases the 1D approximate technique can provide a reasonably accurate estimate of the surface heat transfer without the added complexity of the 3D finite-volume method. For the case of the largest bump tested, with maximum surface angularity exceeding 60 deg, the correction for 3D topology yields a 1D St estimate that is within 20–30% of the 3D estimate over much of the bump surface. These observed effects are valid for transient measurement techniques while the opposite is true for steady-state measurement techniques.

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