Convection at the Entrance of Micropipes With Sudden Wall Temperature Change

2002 ◽  
Author(s):  
Gokturk Tunc ◽  
Yildiz Bayazitoglu
Keyword(s):  
Wall Temperature ◽  
Integral Transform ◽  
Velocity Slip ◽  
Viscous Heating ◽  
Developing Flow ◽  
Heating Effects ◽  
Temperature Boundary ◽  
The Laplace Transform ◽  
Circular Microchannel ◽  
Temperature Boundary Condition

Transient heat convection in a circular microchannel for hydrodynamically fully developed and thermally developing flow conditions is analytically solved by the integral transform and the Laplace transform techniques. A prescribed wall temperature boundary condition is assumed. The effects of velocity slip, temperature jump, and viscous heating are investigated. The results confirm that the viscous heating effects increase the Nusselt number for the specified conditions.

A Numerical Study on Taylor Flow Heat Transfer in Square Microchannels Under Constant Wall Temperature Boundary Condition

2012 ◽  
Author(s):  
V. Talimi ◽  
Y. S. Muzychka ◽  
S. Kocabiyik
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Transfer Process ◽  
Wall Temperature ◽  
Heat Transfer Process ◽  
Constant Wall Temperature ◽  
Temperature Boundary ◽  
Slug Flows ◽  
Temperature Boundary Condition

Heat transfer in Taylor flows or slug flows has been examined exclusively by researchers. Noncircular microchannels have not been widely considered in the literature. There is a large gap in research since noncircular microchannels are common structures in microcooling processes. Square and rectangular microchannels are the most important examples. In the present study the heat transfer process in slug flows in square microchannels has been investigated numerically under constant wall temperature boundary condition. The local heat flux for the moving slugs has been converted to total microchannel heat flux using the integration methods suggested recently by the authors. This leads to microchannel wall average heat flux which is the parameter of interest in heat sink problems. Finally, effects of liquid film around bubbles on heat transfer process have been discussed.

Prediction of Sand Deposition in a Two-Pass Internal Cooling Duct

2015 ◽  
Author(s):  
Sukhjinder Singh ◽  
Danesh Tafti
Keyword(s):  
Wall Temperature ◽  
Particle Deposition ◽  
Effect Of Temperature ◽  
Sand Transport ◽  
Internal Cooling ◽  
Transfer Constant ◽  
Constant Wall Temperature ◽  
Temperature Boundary ◽  
Temperature Impact ◽  
Temperature Boundary Condition

Sand transport and deposition is investigated in a two pass internal cooling ribbed geometry at near engine conditions. LES calculations are performed for bulk Reynolds number of 25,000 to calculate flow field and heat transfer. Constant wall temperature boundary condition is used to investigate the effect of temperature on particle deposition. Three different wall temperatures of 950 °C, 1000 °C and 1050 °C are considered. Particle sizes in range 0.5–25 microns are considered. A new deposition model which accounts for particle composition, temperature, impact velocity and angle and material properties of particle and surface is developed and applied. Calculated impingement and deposition patterns are discussed for different exposed surfaces in the two pass geometry. The highest particle impingement and deposition is observed in the bend region and first quarter of the second pass. Significant deposition is observed in the two pass geometry for all three wall temperatures considered. Particle impingement and hence deposition is dominated by larger particles except in the downstream half of the bend region. In total, approximately 38%, 59% and 67% of the injected particles deposit in the two passes, for the three wall temperatures of 950 °C, 1000 °C and 1050 °C, respectively. While particle impingement is highest for wall temperature of 950 °C, higher deposition is observed for 1000 °C and 1050 °C cases. Deposition increases significantly with wall temperature. For 1000 °C, roughly 12% of the impacting particles deposit. For 1050 °C, approximately 23% of the particles deposit on impact. For all the three cases, the second pass experiences higher deposition compared to the first pass due to higher turbulence and direct impingement.

Numerical Investigation of the Thermally Developing Flow in a Curved Elliptic Duct With Internal Fins

2006 ◽  
Vol 129 (6) ◽  
pp. 759-762 ◽  
Author(s):  
P. K. Papadopoulos ◽  
P. M. Hatzikonstantinou
Keyword(s):  
Aspect Ratio ◽  
Low Friction ◽  
Cross Sectional ◽  
Transfer Rates ◽  
Nusselt Numbers ◽  
Developing Flow ◽  
Temperature Boundary ◽  
Prandtl Numbers ◽  
Internal Fins ◽  
Temperature Boundary Condition

The hydrodynamically fully developed and thermally developing flow inside a curved elliptic duct with internal longitudinal fins is studied numerically. The duct is subjected to the uniform temperature boundary condition on its wall and fins. The local and mean Nusselt numbers are examined for various values of the Dean and Prandtl numbers, the cross-sectional aspect ratio, and the fin height. The characteristics of the optimum duct, which achieves enhanced heat transfer rates combined with low friction losses, are determined in terms of the aspect ratio and the fin height.

Shear work, viscous dissipation and axial conduction effects on microchannel heat transfer with a constant wall temperature

2015 ◽  
Vol 230 (14) ◽  
pp. 2496-2507 ◽  
Author(s):  
K Ramadan ◽  
Iskander Tlili
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Wall Temperature ◽  
Slip Flow ◽  
Brinkman Number ◽  
Constant Wall Temperature ◽  
Fully Developed Flow ◽  
Boundary Shear ◽  
Temperature Boundary ◽  
Temperature Boundary Condition

Convective heat transfer in a microchannel rarefied gas flow with a constant wall temperature boundary condition is investigated numerically. The boundary shear work, viscous dissipation and axial conduction are all included in the study. An analytical solution is also derived for the fully developed flow condition including the boundary shear work. The proper thermal boundary condition considering the sliding friction at the wall is implemented. A comparative study is performed to quantify the effect of the shear work on heat transfer in the entrance – and the fully developed – regions of the microchannel for both gas cooling and heating. The results demonstrate that the effect of shear work on heat transfer is significant and it increases with increasing both the Knudsen number and Brinkman number. Neglecting the shear work in a microchannel slip flow leads to over- or under estimation of the Nusselt number considerably. For a fully developed flow in a microchannel with constant wall temperature boundary condition, the contribution of the shear work to heat transfer can be around 55% in the vicinity of the upper limit of the slip flow regime, regardless of how small the non-zero Brinkman number can be. Including the shear work is therefore crucial in the analysis of microchannel heat transfer and should not be neglected.

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