Natural Convection of Non-Newtonian Fluids About a Horizontal Surface in a Porous Medium

1987 ◽  
Vol 109 (3) ◽  
pp. 119-123 ◽  
Author(s):  
H. T. Chen ◽  
C. K. Chen
Keyword(s):  
Heat Flux ◽  
Porous Medium ◽  
Natural Convection ◽  
Power Law ◽  
Flux Distribution ◽  
Similarity Solutions ◽  
Iteration Scheme ◽  
Heat Flux Distribution ◽  
Runge Kutta Method ◽  
Power Law Index

The problem of natural convection of a non-Newtonian power-law fluid about a horizontal impermeable surface in the porous medium is considered, where the plate is assumed with a nonuniform heat flux distribution. The present study is based on the boundary layer approximation and only suitable for a high Rayleigh number. Similarity solutions are obtained by using the fourth-order Runge-Kutta method and the Nachtsheim-Swigert iteration scheme. The effects of the nonuniform wall heat flux qw(x) and the new power-law index n on the heat transfer characteristics are discussed.

Boundary Optimal Control of Natural Convection by Means of Mode Reduction

2000 ◽  
Vol 124 (1) ◽  
pp. 47-54 ◽  
Author(s):  
H. M. Park ◽  
W. J. Lee
Keyword(s):  
Optimal Control ◽  
Heat Flux ◽  
Natural Convection ◽  
Gradient Method ◽  
Flux Distribution ◽  
Boussinesq Equation ◽  
Heat Flux Distribution ◽  
Projected Gradient Method ◽  
Galerkin Procedure ◽  
Low Dimensional

We consider problems of controlling the intensity of the Rayleigh-Be´nard convection by adjusting the heat flux distribution at the boundary while keeping the heat input the same. The Karhunen-Loe`ve Galerkin procedure is used to reduce the Boussinesq equation to a low dimensional dynamic model, which in turn is employed in a projected gradient method to yield the optimal heat flux distribution. The performance of the Karhunen-Loe`ve Galerkin procedure is assessed in comparison with the traditional technique employing the Boussinesq equation, and is found to be very accurate as well as efficient.

scholarly journals Non-Newtonian effect on heat transfer and entropy generation of natural convection nanofluid flow inside a vertical wavy porous cavity

2021 ◽  
Vol 3 (3) ◽  
Author(s):  
Mahbuba Tasmin ◽  
Preetom Nag ◽  
Zarin T. Hoque ◽  
Md. Mamun Molla
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Entropy Generation ◽  
Power Law ◽  
Volume Fraction ◽  
Local Entropy ◽  
Nanofluid Flow ◽  
Porosity Level ◽  
Power Law Index ◽  
Local Entropy Generation

AbstractA numerical study on heat transfer and entropy generation in natural convection of non-Newtonian nanofluid flow has been explored within a differentially heated two-dimensional wavy porous cavity. In the present study, copper (Cu)–water nanofluid is considered for the investigation where the specific behavior of Cu nanoparticles in water is considered to behave as non-Newtonian based on previously established experimental results. The power-law model and the Brinkman-extended Darcy model has been used to characterize the non-Newtonian porous medium. The governing equations of the flow are solved using the finite volume method with the collocated grid arrangement. Numerical results are presented through streamlines, isotherms, local Nusselt number and entropy generation rate to study the effects of a range of Darcy number (Da), volume fractions (ϕ) of nanofluids, Rayleigh numbers (Ra), and the power-law index (n). Results show that the rate of heat transfer from the wavy wall to the medium becomes enhanced by decreasing the power-law index but increasing the volume fraction of nanoparticles. Increase of porosity level and buoyancy forces of the medium augments flow strength and results in a thinner boundary layer within the cavity. At negligible porosity level of the enclosure, effect of volume fraction of nanoparticles over thermal conductivity of the nanofluids is imperceptible. Interestingly, when the Darcy–Rayleigh number $$Ra^*\gg 10$$ R a ∗ ≫ 10 , the power-law effect becomes more significant than the volume fraction effect in the augmentation of the convective heat transfer process. The local entropy generation is highly dominated by heat transfer irreversibility within the porous enclosure for all conditions of the flow medium. The particular wavy shape of the cavity strongly influences the heat transfer flow pattern and local entropy generation. Interestingly, contour graphs of local entropy generation and local Bejan number show a rotationally symmetric pattern of order two about the center of the wavy cavity.

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.

Studies on heat flux distribution on the membrane walls in a 600 MW supercritical arch-fired boiler

2016 ◽  
Vol 103 ◽  
pp. 264-273 ◽  
Author(s):  
Dalong Zhang ◽  
Chenwei Meng ◽  
Hai Zhang ◽  
Pengyuan Liu ◽  
Zhouhang Li ◽  
...  
Keyword(s):  
Heat Flux ◽  
Flux Distribution ◽  
Heat Flux Distribution
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