Spreading Resistance in Flux Tubes With Variable Heat Flux and Nonuniform Convection

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.

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

The Journal of Supercritical Fluids ◽

10.1016/j.supflu.2012.12.010 ◽

2013 ◽

Vol 74 ◽

pp. 115-127 ◽

Cited By ~ 17

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

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

Modern Physics Letters B ◽

10.1142/s0217984916501554 ◽

2016 ◽

Vol 30 (16) ◽

pp. 1650155 ◽

Cited By ~ 9

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.

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