Flow of a viscous incompressible fluid of temperature dependent viscosity past a permeable wedge with uniform surface heat flux

2000 ◽  
Vol 36 (4) ◽  
pp. 333-341 ◽  
Author(s):  
M. A. Hossain ◽  
M. S. Munir ◽  
M. Z. Hafiz ◽  
H. S. Takhar
Keyword(s):  
Heat Flux ◽  
Incompressible Fluid ◽  
Surface Heat Flux ◽  
Viscous Incompressible Fluid ◽  
Surface Heat ◽  
Temperature Dependent ◽  
Temperature Dependent Viscosity ◽  
Dependent Viscosity

Modified Hazen-Dupuit-Darcy Model for Forced Convection of a Fluid With Temperature-Dependent Viscosity

2000 ◽  
Vol 123 (1) ◽  
pp. 31-38 ◽  
Author(s):  
Arunn Narasimhan ◽  
Jose´ L. Lage
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Surface Heat Flux ◽  
Surface Heat ◽  
Bulk Temperature ◽  
Fluid Viscosity ◽  
Temperature Dependent ◽  
Temperature Dependent Viscosity ◽  
New Model ◽  
Dependent Viscosity

We investigate numerically the global pressure-drop of fluids with temperature dependent viscosity, flowing through a porous medium channel bounded by two parallel isoflux surfaces. By reviewing the development of the Hazen-Dupuit-Darcy (HDD) equation we bring to light the inappropriateness of the model in estimating the global pressure-drop of fluids with temperature dependent viscosity. Albeit this observation, we tested the accuracy of the HDD model in comparison with numerical results by using three alternatives, namely (1) fluid viscosity determined at the average bulk temperature, (2) fluid viscosity determined at the log-mean bulk temperature and (3) fluid viscosity replaced by a channel-length averaged fluid viscosity. The HDD model is inadequate because the temperature dependent fluid viscosity surprisingly affects both, viscous and form, global drag terms. We propose and validate a new global model, which accounts for the effects of temperature dependent viscosity in both drag terms of the original HDD model. Based on our new model, two regimes are discovered as the surface heat flux increases. In the first regime both drag terms are affected, while in the second regime only the form drag term is affected, prior to the model reaching an inviscid limit. Predictive empirical relations correcting the viscous and form drag terms, complementing the new model, are obtained as functions of the surface heat flux.

Entrance and Temperature Dependent Viscosity Effects on Laminar Forced Convection in Straight Ducts With Uniform Wall Heat Flux

2011 ◽  
Vol 133 (10) ◽  
Author(s):  
Stefano Del Giudice ◽  
Stefano Savino ◽  
Carlo Nonino
Keyword(s):  
Heat Flux ◽  
Nusselt Number ◽  
Cross Sections ◽  
Local Nusselt Number ◽  
Temperature Dependent ◽  
Temperature Dependent Viscosity ◽  
Effects Of Temperature ◽  
Dependent Viscosity ◽  
Fanning Friction Factor ◽  
Laminar Forced Convection

Abstract In this paper a parametric investigation is carried out on the effects of temperature dependent viscosity in simultaneously, i.e., hydro-dynamically and thermally, developing laminar flows of liquids in straight ducts of constant cross sections. Uniform heat flux boundary conditions are imposed on the heated walls of the ducts. Different cross-sectional geometries are considered, corresponding to both axisymmetric (circular and concentric annular) and three-dimensional (rectangular and trapezoidal) ducts. Viscosity is assumed to vary with temperature according to an exponential relation, while the other fluid properties are held constant. A finite element procedure is employed for the solution of the parabolized momentum and energy equations. Computed axial distributions of the local Nusselt number and of the apparent Fanning friction factor are presented for different values of the Pearson and Prandtl numbers. Numerical results confirm that, in the laminar forced convection in the entrance region of straight ducts, the effects of temperature dependent viscosity cannot be neglected in a wide range of operative conditions. Correlations are also provided for the local Nusselt number and the apparent Fanning friction factor in simultaneously developing flows in ducts of different cross sections.

Entrance, Viscous Dissipation and Temperature Dependent Viscosity Effects on the Laminar Forced Convection in Straight Microchannels With Uniform Wall Heat Flux

2008 ◽  
Author(s):  
C. Nonino ◽  
S. Savino ◽  
S. Del Giudice
Keyword(s):  
Heat Flux ◽  
Forced Convection ◽  
Viscous Dissipation ◽  
Laminar Flows ◽  
Uniform Heat Flux ◽  
Temperature Dependent ◽  
Temperature Dependent Viscosity ◽  
Wide Range ◽  
Dependent Viscosity ◽  
Laminar Forced Convection

A parametric investigation is carried out on the effects of viscous dissipation and temperature dependent viscosity in simultaneously developing laminar flows of liquids in straight microchannels of constant cross-sections. Reference is made to fluid heating conditions with a uniform heat flux imposed on the walls of the microchannels. Three different cross-sectional geometries are considered, chosen among those usually adopted for microchannels (rectangular, trapezoidal and hexagonal). Viscosity is assumed to vary with temperature according to an exponential relation, while the other fluid properties are held constant. A finite element procedure is employed for the solution of the parabolized momentum and energy equations. Due to the high value of the ratio between the total length and the hydraulic diameter in microchannels, such an approach is very advantageous with respect to the one based on the steady-state solution of the elliptic form of the governing equations in a three-dimensional domain corresponding to the whole duct. Computed axial distributions of the local Nusselt number and of the apparent Fanning friction factor are presented. Numerical results confirm that, in the laminar forced convection in the entrance region of straight microchannels, the effects of viscous dissipation and temperature dependent viscosity cannot be neglected in a wide range of operative conditions.

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