scholarly journals Numerical analysis of choked converging nozzle flows with surface roughness and heat flux conditions

Sadhana ◽  
2006 ◽  
Vol 31 (1) ◽  
pp. 31-46 ◽  
Author(s):  
A. Alper Ozalp
Keyword(s):  
Heat Flux ◽  
Surface Roughness ◽  
Numerical Analysis ◽  
Nozzle Flows

Numerical analysis of two dimensional pin fins with non-constant base heat flux

2005 ◽  
Vol 46 (6) ◽  
pp. 881-892 ◽  
Author(s):  
Yu-Ching Yang ◽  
Haw-Long Lee ◽  
Eing-Jer Wei ◽  
Jenn-Fa Lee ◽  
Tser-Son Wu
Keyword(s):  
Heat Flux ◽  
Numerical Analysis ◽  
Two Dimensional ◽  
Pin Fins

Heat flux enhancement by regular surface roughness in turbulent thermal convection

2014 ◽  
Vol 763 ◽  
pp. 109-135 ◽  
Author(s):  
Sebastian Wagner ◽  
Olga Shishkina
Keyword(s):  
Heat Flux ◽  
Surface Roughness ◽  
Thermal Convection ◽  
Large Scale ◽  
Secondary Flows ◽  
Scaling Exponent ◽  
Wall Roughness ◽  
Regular Surface ◽  
Large Scale Circulation ◽  
Flux Enhancement

AbstractDirect numerical simulations (DNS) of turbulent thermal convection in a box-shaped domain with regular surface roughness at the heated bottom and cooled top surfaces are conducted for Prandtl number $\mathit{Pr}=0.786$ and Rayleigh numbers $\mathit{Ra}$ between $10^{6}$ and $10^{8}$. The surface roughness is introduced by four parallelepiped equidistantly distributed obstacles attached to the bottom plate, and four obstacles located symmetrically at the top plate. By varying $\mathit{Ra}$ and the height and width of the obstacles, we investigate the influence of the regular wall roughness on the turbulent heat transport, measured by the Nusselt number $\mathit{Nu}$. For fixed $\mathit{Ra}$, the change in the value of $\mathit{Nu}$ is determined not only by the covering area of the surface, i.e. the obstacle height, but also by the distance between the obstacles. The heat flux enhancement is found to be largest for wide cavities between the obstacles which can be ‘washed out’ by the flow. This is also manifested in an empirical relation, which is based on the DNS data. We further discuss theoretical limiting cases for very wide and very narrow obstacles and combine them into a simple model for the heat flux enhancement due to the wall roughness, without introducing any free parameters. This model predicts well the general trends and the order of magnitude of the heat flux enhancement obtained in the DNS. In the $\mathit{Nu}$ versus $\mathit{Ra}$ scaling, the obstacles work in two ways: for smaller $\mathit{Ra}$ an increase of the scaling exponent compared to the smooth case is found, which is connected to the heat flux entering the cavities from below. For larger $\mathit{Ra}$ the scaling exponent saturates to the one for smooth plates, which can be understood as a full washing-out of the cavities. The latter is also investigated by considering the strength of the mean secondary flow in the cavities and its relation to the wind (i.e. the large-scale circulation), that develops in the core part of the domain. Generally, an increase in the roughness height leads to stronger flows both in the cavities and in the bulk region, while an increase in the width of the obstacles strengthens only the large-scale circulation of the fluid and weakens the secondary flows. An increase of the Rayleigh number always leads to stronger flows, both in the cavities and in the bulk.

Numerical analysis of the radiation losses due to surface roughness in integrated optics devices

1996 ◽  
Vol 8 (9) ◽  
pp. 1202-1204 ◽  
Author(s):  
G.H. Jin ◽  
J. Harari ◽  
L. Joannes ◽  
J.P. Vilcot ◽  
D. Decoster
Keyword(s):  
Surface Roughness ◽  
Numerical Analysis ◽  
Integrated Optics ◽  
Integrated Optics Devices ◽  
Radiation Losses

scholarly journals The effect of different aspect ratio and bottom heat flux towards contaminant removal using numerical analysis

2013 ◽  
Vol 50 ◽  
pp. 012015
Author(s):  
M N A Saadun ◽  
C S Nor Azwadi ◽  
Z A A Malek ◽  
M Z A Manaf ◽  
M S Zakaria ◽  
...  
Keyword(s):  
Heat Flux ◽  
Numerical Analysis ◽  
Aspect Ratio ◽  
Contaminant Removal ◽  
Bottom Heat

scholarly journals A Numerical Analysis on Nanofluid Mixed Convection in Triangular Cross-Sectioned Ducts Heated by a Uniform Heat Flux

2015 ◽  
Vol 7 (1) ◽  
pp. 292973 ◽  
Author(s):  
Oronzio Manca ◽  
Sergio Nardini ◽  
Daniele Ricci ◽  
Salvatore Tamburrino
Keyword(s):  
Heat Flux ◽  
Numerical Analysis ◽  
Mixed Convection ◽  
Uniform Heat Flux ◽  
Uniform Heat

An Experimental Study of Boiling Heat Transfer During Quenching of Nanofluids With Carbon Nanotubes of Various Sizes

2016 ◽  
Author(s):  
Jia-Qi Li ◽  
Li-Wu Fan ◽  
Liang Zhang ◽  
Zi-Tao Yu
Keyword(s):  
Carbon Nanotubes ◽  
Heat Flux ◽  
Surface Roughness ◽  
Initial Temperature ◽  
Nucleation Site ◽  
Transient Temperature ◽  
Porous Layers ◽  
Site Density ◽  
Nucleation Site Density ◽  
Walled Cnts

Quenching experiments were performed with hot stainless steel spheres in a pool of water-based nanofluids in the presence of carbon nanotubes (CNTs) of various sizes. In order to explore the size effect, a test matrix was developed by choosing multi-walled CNTs with lengths from 1 μm to 5 μm and outer diameters from 30 nm to 60 nm. The concentration was fixed at 0.5% by mass for all types of CNTs. The initial temperature was 400 °C and the transient temperature variations at the center of the sphere were recorded as quenching curves. By establishing a lumped capacitance model, the transient surface heat flux variations were obtained as boiling curves. The original and boiled surfaces were both subjected to a series of characterizations to determine the changes in morphology, roughness, and wettability to identify the effects of CNT size on the surface properties of the formed deposition layers as well as to elucidate the mechanisms for regulation of the boiling and quenching behaviors. The results suggested that the critical heat flux (CHF) and the Leidenfrost point (LFP) are enhanced to various degrees due to the discrepancy in the size of the CNTs in nanofluids. It was shown that the CNTs deposited on the surfaces create various morphologies depending on their size. The CNTs with a length of 5 μm and a diameter of 60 nm exhibited the most significant effect on the boiling behaviors. In comparison to CNTs with a shorter length of 1 μm, the 5 μm long CNTs were much easier to form porous layers. The results of the contact angle and roughness tests showed that the porous layers tend to affect the surface roughness instead of surface wettability. The increases of the nucleation site density and surface roughness due to the presence of porous layers were identified as the primary cause for the modified boiling behaviors during quenching.

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