The Effect of Surface Roughness on the Convection Heat-Transfer Coefficient for Fully Developed Turbulent Flow in Ducts With Uniform Heat Flux

1959 ◽  
Vol 81 (2) ◽  
pp. 168-173 ◽  
Author(s):  
R. T. Lancet
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
Convection Heat Transfer ◽  
Uniform Heat Flux ◽  
Friction Factors ◽  
Fully Developed Turbulent Flow ◽  
The Heat Transfer Coefficient ◽  
Effect Of Surface

Experimental data are presented for the heat-transfer coefficient and friction factor in a smooth and a rough duct with a hydraulic diameter of approximately 0.035 in. The flow was fully developed and turbulent, and the heat addition was uniform over the length of the tube. The rough tube indicated appreciable increases in heat-transfer coefficient and friction factor. The smooth-tube friction factors corresponded to rough-tube values, indicating the difficulty involved in obtaining smooth surfaces for very small ducts.

scholarly journals Cooling of High Heat Flux Flat Surface with Nanofluid Assisted Convective Loop: Experimental Assessment

2017 ◽  
Vol 64 (4) ◽  
pp. 519-531 ◽  
Author(s):  
Amir Arya ◽  
Saeed Shahmiry ◽  
Vahid Nikkhah ◽  
Mohamad Mohsen Sarafraz
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
High Heat ◽  
High Heat Flux ◽  
Overall Heat Transfer Coefficient ◽  
Cooling Loop ◽  
The Heat Transfer Coefficient

Abstract Experimental investigation was conducted on the thermal performance and pressure drop of a convective cooling loop working with ZnO aqueous nanofluids. The loop was used to cool a flat heater connected to an AC autotransformer. Influence of different operating parameters, such as fluid flow rate and mass concentration of nanofluid on surface temperature of heater, pressure drop, friction factor and overall heat transfer coefficient was investigated and briefly discussed. Results of this study showed that, despite a penalty for pressure drop, ZnO/water nanofluid was a promising coolant for cooling the micro-electronic devices and chipsets. It was also found that there is an optimum for concentration of nanofluid so that the heat transfer coefficient is maximum, which was wt. % = 0.3 for ZnO/water used in this research. In addition, presence of nanoparticles enhanced the friction factor and pressure drop as well; however, it is not very significant in comparison with those of registered for the base fluid.

scholarly journals PREDICTING OF STEAM CONDENSATION HEAT TRANSFER COEFFICIENT IN HORIZONTAL FLATTENED TUBE

2020 ◽  
Vol 24 (06) ◽  
pp. 115-126
Author(s):  
Mohammed Ghazi M. Kamil ◽  
◽  
Muna Sabah Kassim ◽  
Louay Abd Alazez Mahdi ◽  
◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Saturation Temperature ◽  
Condensation Heat Transfer ◽  
Uniform Heat Flux ◽  
Steam Condensation ◽  
The Heat Transfer Coefficient ◽  
Condensation Heat Transfer Coefficient

The heat transfer coefficient of steam condensation has a significant role in the performance of air-cooled heat exchangers. The purpose of this work is to predict the local/average local steam condensation heat transfer coefficient inside the horizontal flattened tube under vacuum conditions using numerous correlations that were developed by some researches which have been conducted under specified conditions. The results from these correlations have been compared with experimental data of Davies, therefore more investigate for the values are necessary to improve or/and validate the existing correlations. The effect of such parameters like the uniform heat flux and saturation temperature also have been studied on the local steam condensation heat transfer coefficient as the results show that the heat transfer coefficient decrease as the heat flux increase, while it increases as the steam saturated temperature increase.

Effect of Wall Heat Flux on Entropy Generation in Turbulent Mixed Convection Heat Transfer of a Pipe Flow With Highly Variable Properties

2010 ◽  
Author(s):  
Majid Bazargan ◽  
Mahdi Mohseni
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Entropy Production ◽  
Entropy Generation ◽  
Convection Heat Transfer ◽  
Wall Heat Flux ◽  
Convection Heat ◽  
The Heat Transfer Coefficient

There are many engineering systems with working fluids which have properties varying significantly with temperature. This causes the effect of the wall heat flux on the velocity and temperature fields to become larger with respect to the constant property flows. In this study the effect of the wall heat flux on the entropy generation in the mixed turbulent convection heat transfer of a fluid flow with high property variations has been investigated. The local and total entropy generation is calculated. In addition, the region in which the entropy production is larger has been determined. Furthermore, the contribution of each of the mechanisms of entropy production which is depended on the wall heat flux is determined. It should be noted that the implementation of different heat fluxes at the tube wall affects all mechanisms of entropy generation. The results show that the bulk entropy generation reaches a minimum value when the heat transfer coefficient has a maximum value. The wall heat flux also has an opposite effect on the heat transfer coefficient and entropy generation which is a favorable result.

Effects of Ribs on Internal Blade-Tip Cooling

2011 ◽  
Author(s):  
Tareq Salameh ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
Turbine Blades ◽  
Ccd Camera ◽  
Transfer Coefficients ◽  
Cooling Flow ◽  
Friction Factors ◽  
Blade Tip

This work concerns an experimental study of pressure drop and heat transfer for turbulent flow inside a U-duct with relevance for tip cooling of gas turbine blades. The U-duct models the internal blade cooling flow passages. Both friction factors and convective heat transfer coefficients were measured along the bend (turn) part of the U-duct for three different rib configuration cases, namely (a) single rib at three different rib positions, i.e., inlet, middle and outlet, (b) two ribs with three different configurations, i.e., at the inlet and middle, at the middle and outlet as well as at the inlet and outlet, and (c) three ribs. The rib height-to-hydraulic diameter ratio, e/Dh, was 0.1 and the pitch ratios were 10 and 20. The Reynolds number was varied from 8,000 to 20,000. The test rig has been built in such a way that various experimental setups can be handled as the bend (turn) part of the U-duct can easily be removed and the rib configurations can be changed. The surface temperature was measured by using a high-resolution measurement technique based on narrow band thermochromic liquid crystals (TLC R35C5W) and a CCD camera placed facing the bend (turn) part of the U-duct. The calibration of the TLC is based on the hue-based color decomposition system using an in-house designed calibration box. Both the friction factor and heat transfer coefficient were affected by the position and configuration of the ribs along the bend wall. The highest friction factor was found for two ribs placed at the middle and outlet positions of the bend wall, respectively. The highest heat transfer coefficient was found for two ribs placed at the inlet and middle positions of the bend wall, respectively. The uncertainties in the experiments were estimated to be 3% and 6% for the Nusselt number and friction factor, respectively.

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