Estimation of the Transient Surface Temperature, Heat Flux and Effective Heat Transfer Coefficient of a Slab in an Industrial Reheating Furnace by using an Inverse Method

2007 ◽  
Vol 78 (1) ◽  
pp. 63-70 ◽  
Author(s):  
Patrik Wikström ◽  
Wlodzimierz Blasiak ◽  
Fredrik Berntsson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Surface Temperature ◽  
Transfer Coefficient ◽  
Inverse Method ◽  
Reheating Furnace ◽  
Effective Heat ◽  
Temperature Heat ◽  
Effective Heat Transfer Coefficient

Characterization and Modeling of the Heat Transfer Performance of Nanostructured Cu Micropost Wicks

2011 ◽  
Vol 133 (10) ◽  
Author(s):  
Youngsuk Nam ◽  
Stephen Sharratt ◽  
Gilhwan Cha ◽  
Y. Sungtaek Ju
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Management ◽  
Critical Heat Flux ◽  
Heat Transfer Performance ◽  
Transfer Performance ◽  
Effective Heat ◽  
Effective Heat Transfer Coefficient

Micro heat pipes incorporating advanced wicks are promising for the thermal management of power electronics. We report the heat transfer performance of superhydrophilic Cu micropost wicks fabricated on thin silicon substrates using electrochemical deposition and controlled chemical oxidation. For a fixed post diameter, the interpost spacing and hence solid fraction is found to be a main design factor affecting the effective heat transfer coefficient and critical heat flux. The effective heat transfer coefficient >10 W/cm2 K and the critical heat flux >500 W/cm2 over 2 mm × 2 mm heating areas are demonstrated. Copper oxide nanostructures formed on the micropost surfaces significantly enhance the critical heat flux without compromising the effective heat transfer coefficient. An approximate numerical model is developed to help interpret the experimental data. A surface energy minimization algorithm is used to predict the static equilibrium shape of a liquid meniscus, which is then imported into a finite element model to predict the effective heat transfer coefficient. The advanced wick structures and experimental and modeling approaches developed in this work will help develop thin and lightweight thermal management solutions for high-power-density semiconductor devices.

Heat Transfer Performance of Superhydrophilic Nanostructured Cu Micropost Wicks for Micro Heat Pipes

2010 ◽  
Author(s):  
Youngsuk Nam ◽  
Stephen Sharratt ◽  
Y. Sungtaek Ju
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Management ◽  
Critical Heat Flux ◽  
Heat Pipes ◽  
Effective Heat ◽  
Effective Heat Transfer Coefficient ◽  
Micro Heat Pipes

Micro-heat pipes incorporating advanced wicks are promising for the thermal management of power electronics. We report the heat transfer performance of superhydrophilic Cu micropost wicks fabricated on thin silicon substrates using electrochemical deposition and controlled chemical oxidation. For a fixed post diameter, the inter-post spacing and hence solid fraction is found to be a main design factor affecting the effective heat transfer coefficient and critical heat flux. The effective heat transfer coefficient as high as 20 W/cm2 K and the critical heat flux >500 W/cm2 over 2 mm × 2 mm heating areas are demonstrated. Copper oxide nanostructures formed on the micropost surfaces significantly enhance the critical heat flux without compromising the effective heat transfer coefficient. The advanced wick structures and experimental approaches developed in this work will help develop thin and lightweight thermal management solutions for high-power density semiconductor devices.

scholarly journals Experimental Determination of the Heat Transfer Coefficient of Real Cooled Geometry Using Linear Regression Method

Energies ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 180
Author(s):  
Asif Ali ◽  
Lorenzo Cocchi ◽  
Alessio Picchi ◽  
Bruno Facchini
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Linear Regression ◽  
Surface Temperature ◽  
Transfer Coefficient ◽  
External Surface ◽  
Internal Surface ◽  
Regression Method ◽  
Thermal Transient

The scope of this work was to develop a technique based on the regression method and apply it on a real cooled geometry for measuring its internal heat transfer distribution. The proposed methodology is based upon an already available literature approach. For implementation of the methodology, the geometry is initially heated to a known steady temperature, followed by thermal transient, induced by injection of ambient air to its internal cooling system. During the thermal transient, external surface temperature of the geometry is recorded with the help of infrared camera. Then, a numerical procedure based upon a series of transient finite element analyses of the geometry is applied by using the obtained experimental data. The total test duration is divided into time steps, during which the heat flux on the internal surface is iteratively updated to target the measured external surface temperature. The final procured heat flux and internal surface temperature data of each time step is used to find the convective heat transfer coefficient via linear regression. This methodology is successfully implemented on three geometries: a circular duct, a blade with U-bend internal channel, and a cooled high pressure vane of real engine, with the help of a test rig developed at the University of Florence, Italy. The results are compared with the ones retrieved with similar approach available in the open literature, and the pros and cons of both methodologies are discussed in detail for each geometry.

Analysis of Laminar Heat Transfer on Super-Hydrophobic Surface With Slip Velocity

2009 ◽  
Author(s):  
Wei Sun ◽  
Yuhong Zhou ◽  
Xinxin Fan ◽  
Tianqing Liu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Thermal Resistance ◽  
Transfer Coefficient ◽  
Slip Velocity ◽  
Structural Parameters ◽  
Hydrophobic Surface ◽  
Trapped Air ◽  
Effective Heat ◽  
Effective Heat Transfer Coefficient

It is still in suspense for the effects of slip velocity and structural parameters on the heat transfer on a super-hydrophobic surface. It is thus necessary to study it in both theory and experiments. In this paper, the convective heat transfer with constant heat flux condition inside a circular microchannel was investigated. The velocity and temperature profiles when slip velocity exists were derived firstly, and then the heat transfer coefficient and Nusselt number were obtained. Furthermore, an effective conduction model for the super-hydrophobic surface with different structural parameters was proposed and the thermal resistance of the surface with trapped air was calculated. Finally, the effective heat transfer coefficient of super-hydrophobic surface was found with the integration of heat transfer coefficient and surface thermal resistance. The calculation results show that 1) the slip of fluid on a super-hydrophobic surface makes the temperature profile inside the channel more uniform, and the heat transfer coefficient or Nusselt number increased, 1.8 times higher maximally under constant heat flux condition; 2) the thermal resistance of super-hydrophobic surface increases with trapped air volume; 3) the effective heat transfer coefficient on super-hydrophobic surface declines seriously with trapped air volume, especially with the trapped air area; 4) there exists a critical thickness for the trapped air on a super-hydrophobic surface with given surface structural parameters, under which the effective heat transfer coefficient is not less than that on normal surfaces without slip. Therefore, it is necessary to consider the structural parameters of super-hydrophobic surfaces, such as rib height and distance between ribs, so that the heat transfer on the super-hydrophobic surface will not be impacted by the trapped air.

Numerical and Parametric Investigation of the Effect of Heat Spreading On Boiling of a Dielectric Liquid for Immersion Cooling of Electronics

2021 ◽  
Author(s):  
Wei Tong ◽  
Alireza Ganjali ◽  
Omidreza Ghaffari ◽  
Chady Alsayed ◽  
Luc Frechette ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Surface Temperature ◽  
Transfer Coefficient ◽  
Critical Heat Flux ◽  
Heat Removal ◽  
Nucleate Boiling ◽  
Input Power ◽  
Immersion Cooling

Abstract In a two-phase immersion cooling system, boiling on the spreader surface has been experimentally found to be non-uniform, and it is highly related to the surface temperature and the heat transfer coefficient. An experimentally obtained temperature-dependent boiling heat transfer coefficient has been applied to a numerical model to investigate the spreader's cooling performance. It is found that the surface temperature distribution becomes less uniform with higher input power. But it is more uniform when the thickness is increased. By defining the characteristic temperatures that represent different boiling regimes on the surface, the fraction of the surface area that has reached the critical heat flux has been numerically calculated, showing that increasing the thickness from 1 mm to 6 mm decreases the critical heat flux reached area by 23% at saturation liquid temperatures. Therefore, on the thicker spreader, more of the surface is utilized for nucleate boiling while localized hot regions that lead to surface dry-out are avoided. At a base temperature of 90 oC, the optimal thickness is found to be 4 mm, beyond which no significant improvement in heat removal can be obtained. Lower coolant temperatures can further increase the heat removal; it is reduced from an 18% improvement in the input power for the 1 mm case to only 3% in the 6 mm case for a coolant temperature drop of 24 oC. Therefore, a trade-off exists between the cost of maintaining the low liquid temperature and the increased heat removal capacity.

On Selection of Reference Temperature of Heat Transfer Coefficient for Complicated Flows

2007 ◽  
Author(s):  
X. C. Li ◽  
J. Zhou ◽  
K. Aung
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Surface Temperature ◽  
Transfer Coefficient ◽  
Wall Temperature ◽  
Convective Heat Transfer Coefficient ◽  
Internal Heat ◽  
Reference Temperature ◽  
The Heat Transfer Coefficient

One of the most fundamental concepts in heat transfer is the convective heat transfer coefficient, which is closely related with the flow Reynolds number, flow geometry and the thermal conditions on the heat transfer surface. To define the heat transfer coefficient, a reference temperature is needed besides the surface temperature and heat flux. The reference temperature can be chosen differently, such as the fluid bulk mean temperature (for internal flows) and the temperature at the far field (for external flows). For complicated flows, the adiabatic wall temperature, defined as the wall temperature when the surface heat flux is zero, is commonly adopted as the reference temperature. Other options can also be applied to complicated flows. This paper analyzed some of the potential selections of the reference temperature for different flow settings, including film cooling, jet impingement with cross flows and a mixing flow in a straight duct with or without internal heat source. Both laminar and turbulent flows are considered with different boundary conditions. Dramatic changes of heat transfer coefficient are observed with different reference temperatures. In some special conditions the heat transfer coefficient becomes negative, which means the heat flux has a different direction with the driving temperature difference defined. An innovative method is proposed to calculate the heat transfer coefficient of complicated flows with constant surface temperature.

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