Effect of Circumferentially Nonuniform Heating on Laminar Combined Convection in a Horizontal Tube

1978 ◽  
Vol 100 (1) ◽  
pp. 63-70 ◽  
Author(s):  
S. V. Patankar ◽  
S. Ramadhyani ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Forced Convection ◽  
Horizontal Tube ◽  
Nonuniform Heating ◽  
Convection Flow ◽  
Nusselt Numbers ◽  
Wide Range ◽  
Bottom Heating ◽  
Over The Top

An analytical study has been made of how the circumferential distribution of the wall heat flux affects the forced/natural convection flow and heat transfer in a horizontal tube. Two heating conditions were investigated, one in which the tube was uniformly heated over the top half and insulated over the bottom, and the other in which the heated and insulated portions were reversed. The results were obtained numerically for a wide range of the governing buoyancy parameter and for Prandtl numbers of 0.7 and 5. It was found that bottom heating gives rise to a vigorous buoyancy-induced secondary flow, with the result that the average Nusselt numbers are much higher than those for pure forced convection, while the local Nusselt numbers are nearly circumferentially uniform. A less vigorous secondary flow is induced in the case of top heating because of temperature stratification, with average Nusselt numbers that are substantially lower than those for bottom heating and with large circumferential variations of the local Nusselt number. The friction factor is also increased by the secondary flow, but much less than the average heat transfer coefficient. It was also demonstrated that the buoyancy effects are governed solely by a modified Grashof number, without regard for the Reynolds number of the forced convection flow.

Laminar Mixed Convection in a Shrouded Fin Array

1981 ◽  
Vol 103 (3) ◽  
pp. 559-565 ◽  
Author(s):  
S. Acharya ◽  
S. V. Patankar
Keyword(s):  
Secondary Flow ◽  
Forced Convection ◽  
Tip Clearance ◽  
Base Surface ◽  
Nusselt Numbers ◽  
Laminar Mixed Convection ◽  
Friction Factors ◽  
Wide Range ◽  
Laminar Forced Convection ◽  
The Heat Transfer Coefficient

An analytical study is made to investigate the effect of buoyancy on laminar forced convection in a shrouded fin array. Two heating conditions are considered; in one, the fins and the base surface are hotter than the fluid, and in the other, they are colder. The results are obtained numerically for a wide range of the governing buoyancy parameter. It is found that with a hot fin and base, the secondary flow pattern is mostly made up of a single eddy. The influence of buoyancy is significant and leads to Nusselt numbers and friction factors which are much higher than for pure forced convection. With a cold fin and base, the presence of a tip clearance between the fins and the shroud generates a multiple eddy pattern. The resulting stratification is responsible for the existence of high axial velocity and temperature in the clearance region relative to that in the inter-fin space. Compared to the hot fin case, the secondary flow is weaker, and therefore a relatively smaller increase in the friction factor is obtained. The Nusselt number is found to increase only in the absence of tip clearance. The distribution of the heat transfer coefficient along the fin and the base for both heating situations is found to be highly nonuniform.

A Numerical Investigation of Nanofluids Forced Convection Flow in a Horizontal Smooth Tube

2010 ◽  
Author(s):  
Hakan Demir ◽  
Ahmet Selim Dalkılıc¸ ◽  
Nuri Alpay Ku¨rekci ◽  
Bu¨lent Keles¸og˘lu ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Forced Convection ◽  
Smooth Tube ◽  
Convection Flow ◽  
Transfer Coefficients ◽  
Particle Volume ◽  
Constant Wall Temperature ◽  
Nusselt Numbers ◽  
Temperature Dependent Properties

In this study, laminar and turbulent forced convection flows of a nanofluid consisting of water and Al2O3 in a horizontal smooth tube with constant wall temperature are investigated numerically. Studies that are related to the subject in the literature are reviewed. The determination of the nanofluid properties is calculated by means of the correlations of Palm et al. Two-dimensional elliptical governing equations are used to study the hydrodynamics and thermal behaviors of the nanofluid flow. A single-phase model is employed with either constant or temperature dependent properties. The investigation is performed for a constant particle size. The velocity and temperature vectors are presented in the entrance and fully developed region. Effects of nanoparticles concentration and Reynolds number on shear stress and pressure drop are presented. The Nusselt numbers and heat transfer coefficients of nanofluids are obtained for different nanoparticle concentrations. Numerical results show the heat transfer enhancement due to presence of the nanoparticles in the fluid. Heat transfer coefficient increases with increasing the particle volume concentration and also increasing wall shear stress values.

Effect of Apex Angle, Porosity, and Permeability on Flow and Heat Transfer in Triangular Porous Ducts

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
S. Negin Mortazavi ◽  
Fatemeh Hassanipour
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Temperature Distribution ◽  
Apex Angle ◽  
Convection Flow ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Wide Range ◽  
Porosity And Permeability ◽  
Forced Convection Flow

This paper presents an analysis of forced convection flow and heat transfer in triangular ducts containing a porous medium. The porous medium is isotropic and the flow is laminar, fully developed with constant properties. Numerical results for velocity and temperature distribution (in dimensionless format) in the channel are presented for a wide range of porosity, permeability, and apex angles. The effects of apex angle and porous media properties (porosity and permeability) are demonstrated on the velocity and temperature distribution, as well as the friction factor (fRe) and Nusselt numbers in the channel for both Isoflux (NuH) and Isothermal (NuT) boundary conditions. The consistency of our findings has been verified with earlier results in the literature on empty triangular ducts, when the porosity in our models is made to approach one.

Numerical Analysis on Nanofluid Forced Convection in Ducts With Triangular Cross Sections

2011 ◽  
Author(s):  
O. Manca ◽  
S. Nardini ◽  
D. Ricci ◽  
S. Tamburrino
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Forced Convection ◽  
Cross Sections ◽  
Fluid Dynamic ◽  
Pure Water ◽  
Convection Flow ◽  
Uniform Heat Flux ◽  
Surface Shear Stress ◽  
Surface Shear

Heat transfer of fluids is very important to many industrial heating or cooling equipments. Convective heat transfer can be enhanced passively by changing flow geometry, boundary conditions or by enhancing the thermal conductivity of the working fluids. An innovative way of improving the fluid thermal conductivity is to introduce suspended small solid nanoparticles in the base fluids. In this paper a numerical investigation on laminar forced convection flow of a water–Al2O3 nanofluid in a duct having an equilateral triangular cross section is performed. The hydraulic diameter is set equal to 1.0×10−2 m. A constant and uniform heat flux on the external surfaces has been applied and the single-phase model approach has been employed. The analysis has been run in steady state regime for a nanoparticle size equal to 38 nm, considering different volume particle concentrations. The CFD code Fluent has been employed in order to solve the tri-dimensional numerical model. Results are presented in terms of temperature and velocity distributions, surface shear stress and heat transfer convective coefficient, Nusselt number and required pumping power profiles. Comparison with results related to the fluid dynamic and thermal behaviors in pure water are carried out in order to evaluate the enhancement due to the presence of nanoparticles in terms of volumetric concentration.

A Visual Study of Phase Change Heat Transfer in Horizontal Bottom Heating Beads Packed Porous Structures

2008 ◽  
Author(s):  
C. H. Li
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Bubble Dynamics ◽  
Heating Surface ◽  
Bubble Generation ◽  
Wide Range ◽  
Bottom Heating ◽  
Phase Change Heat Transfer ◽  
The Relationship ◽  
Horizontal Bottom

An experimental investigation was conducted to study the influence of the sphere material and size on the bubble generation, growth, and detachment on nucleate pool boiling heat transfer in two different sphere-packed porous media, copper sphere and glass sphere at the same size of 3 mm diameter, respectively. By measuring the heating surface temperatures and visualizing the bubble dynamics over a wide range of heat flux, an effort was made to find the relationship between the normalized bubble dynamics process and the factors of sphere material and size. By comparing the experimental results of two different sphere material porous media, the interfacial heat and mass transport will be analyzed to provide the information how the bubble generation, growth, detachment and the liquid replenished process were influence by the liquid/copper and liquid/glass interfaces in different size porous media.

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