FORCED CONVECTION IN ANNULI AND ROD BUNDLES WITH VARIABLE HEAT FLUX DISTRIBUTION

1978 ◽  
Author(s):  
Yuri N. Kuznetsov ◽  
W. I. Kalinin ◽  
M. A. Naumov
Keyword(s):  
Heat Flux ◽  
Forced Convection ◽  
Flux Distribution ◽  
Heat Flux Distribution ◽  
Rod Bundles ◽  
Variable Heat ◽  
Variable Heat Flux

Thermal Spreading Resistance in a Multilayered Orthotropic Circular Disk With Interfacial Resistance and Variable Heat Flux

2015 ◽  
Author(s):  
Y. S. Muzychka
Keyword(s):  
Heat Flux ◽  
Flux Distribution ◽  
Isotropic Layer ◽  
Interfacial Resistance ◽  
Heat Flux Distribution ◽  
Spreading Resistance ◽  
Variable Heat ◽  
Variable Heat Flux ◽  
Special Cases ◽  
Interfacial Contact

Thermal spreading resistance in a multilayered orthotropic disk is considered. Interfacial resistance between each layer is prescribed by means of a contact conductance hc using a Robin type boundary condition. Orthotropic properties are considered by transforming the orthotropic system into an equivalent isotropic system using stretched coordinates. A recursive modeling approach is presented to account for the effects of two or more layers in the structure from the simple case of a single isotropic layer. This approach simplifies the analysis considerably. Finally, variable heat flux distribution is considered for three special cases: uniform, parabolic, and inverse parabolic. Numerous special cases can be derived from the general result including perfect interfacial contact and perfect sink plane conductance. Additional issues are also discussed in detail. The expressions for the total thermal resistance and spreading resistance can be easily implemented in any mathematical software or coded in Fortran, C, or BASIC. Since the method is strictly analytical, thermal analysts can quickly assess changes in layer properties, material sequence, heat flux distribution, and effects of interfacial contact resistance, with little extra effort.

Experimental Estimate of the Continuous One-Dimensional Kernel Function in a Rectangular Duct With Forced Convection

2006 ◽  
Vol 128 (8) ◽  
pp. 811-818 ◽  
Author(s):  
Jinny Rhee ◽  
Robert J. Moffat
Keyword(s):  
Heat Flux ◽  
Forced Convection ◽  
Kernel Function ◽  
Flux Distribution ◽  
Constant Heat Flux ◽  
Kernel Functions ◽  
Rectangular Duct ◽  
Heat Flux Distribution ◽  
Constant Heat ◽  
One Dimensional

Abstract The continuous, one-dimensional kernel function in a rectangular duct subject to forced convection with air was experimentally estimated using liquid crystal thermography techniques. Analytical relationships between the kernel function for internal flow and the temperature distribution resulting from a known heat flux distribution were manipulated to accomplish this objective. The kernel function in the hydrodynamically fully developed region was found to be proportional to the streamwise temperature gradient resulting from a constant heat flux surface. In the hydrodynamic entry region of the rectangular duct, a model for the kernel function was proposed and used in its experimental determination. The kernel functions obtained by the present work were shown to be capable of predicting the highly nonuniform surface temperature rise above the inlet temperature resulting from an arbitrary heat flux distribution to within the experimental uncertainty. This is better than the prediction obtained using the analytically derived kernel function for turbulent flow between parallel plates, and the prediction obtained using the conventional heat transfer coefficient for constant heat flux boundary conditions. The latter prediction fails to capture both the quantitative and qualitative nature of the problem. The results of this work are relevant to applications involving the thermal management of nonuniform temperature surfaces subject to internal convection with air, such as board-level electronics cooling. Reynolds numbers in the turbulent and transition range were examined.

Natural convection on a vertical plate with variable heat flux in supercritical fluids

2013 ◽  
Vol 74 ◽  
pp. 115-127 ◽  
Author(s):  
Ali Reza Teymourtash ◽  
Danyal Rezaei Khonakdar ◽  
Mohammad Reza Raveshi
Keyword(s):  
Heat Flux ◽  
Natural Convection ◽  
Supercritical Fluids ◽  
Vertical Plate ◽  
Variable Heat ◽  
Variable Heat Flux

Analytical and numerical study on cooling flow field designs performance of PEM fuel cell with variable heat flux

2016 ◽  
Vol 30 (16) ◽  
pp. 1650155 ◽  
Author(s):  
Ebrahim Afshari ◽  
Masoud Ziaei-Rad ◽  
Nabi Jahantigh
Keyword(s):  
Heat Flux ◽  
Fuel Cells ◽  
Fuel Cell ◽  
Pressure Drop ◽  
Flow Field ◽  
Pem Fuel Cells ◽  
Coolant Flow ◽  
Temperature Uniformity ◽  
Variable Heat ◽  
Variable Heat Flux

In PEM fuel cells, during electrochemical generation of electricity more than half of the chemical energy of hydrogen is converted to heat. This heat of reactions, if not exhausted properly, would impair the performance and durability of the cell. In general, large scale PEM fuel cells are cooled by liquid water that circulates through coolant flow channels formed in bipolar plates or in dedicated cooling plates. In this paper, a numerical method has been presented to study cooling and temperature distribution of a polymer membrane fuel cell stack. The heat flux on the cooling plate is variable. A three-dimensional model of fluid flow and heat transfer in cooling plates with 15 cm × 15 cm square area is considered and the performances of four different coolant flow field designs, parallel field and serpentine fields are compared in terms of maximum surface temperature, temperature uniformity and pressure drop characteristics. By comparing the results in two cases, the constant and variable heat flux, it is observed that applying constant heat flux instead of variable heat flux which is actually occurring in the fuel cells is not an accurate assumption. The numerical results indicated that the straight flow field model has temperature uniformity index and almost the same temperature difference with the serpentine models, while its pressure drop is less than all of the serpentine models. Another important advantage of this model is the much easier design and building than the spiral models.

Heat Flux Distribution Over a Solar Central Receiver Using an Aiming Strategy Based on a Conventional Closed Control Loop

2017 ◽  
Author(s):  
Jesús García ◽  
Yen Chean Soo Too ◽  
Ricardo Vasquez Padilla ◽  
Rodrigo Barraza Vicencio ◽  
Andrew Beath ◽  
...  
Keyword(s):  
Heat Flux ◽  
Flux Distribution ◽  
Thermal Stresses ◽  
Control Strategies ◽  
Multiple Input Multiple Output ◽  
Control Loop ◽  
Heat Flux Distribution ◽  
Input Multiple Output ◽  
Solar Receiver ◽  
Solar Field

Solar thermal towers are a maturing technology that have the potential to supply a significant part of energy requirements of the future. One of the issues that needs careful attention is the heat flux distribution over the central receiver’s surface. It is imperative to maintain receiver’s thermal stresses below the material limits. Therefore, an adequate aiming strategy for each mirror is crucial. Due to the large number of mirrors present in a solar field, most aiming strategies work using a data base that establishes an aiming point for each mirror depending on the relative position of the sun and heat flux models. This paper proposes a multiple-input multiple-output (MIMO) closed control loop based on a methodology that allows using conventional control strategies such as those based on Proportional Integral Derivative (PID) controllers. Results indicate that even this basic control loop can successfully distribute heat flux on the solar receiver.

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