scholarly journals Natural Convection Flow along an Isothermal Vertical Flat Plate with Temperature Dependent Viscosity and Heat Generation

2014 ◽  
Vol 2014 ◽  
pp. 1-13 ◽  
Author(s):  
Md. Mamun Molla ◽  
Anita Biswas ◽  
Abdullah Al-Mamun ◽  
Md. Anwar Hossain
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Nusselt Number ◽  
Wall Shear Stress ◽  
Heat Generation ◽  
Average Nusselt Number ◽  
Variation Parameter ◽  
Viscosity Variation ◽  
Wall Shear ◽  
Vertical Flat Plate

The purpose of this study is to investigate the natural convection laminar flow along an isothermal vertical flat plate immersed in a fluid with viscosity which is the exponential function of fluid temperature in presence of internal heat generation. The governing boundary layer equations are transformed into a nondimensional form and the resulting nonlinear system of partial differential equations is reduced to a convenient form which are solved numerically using an efficient marching order implicit finite difference method with double sweep technique. Numerical results are presented in terms of the velocity and temperature distribution of the fluid as well as the heat transfer characteristics, namely, the wall shear stress and the local and average rate of heat transfer in terms of the local skin-friction coefficient, the local and average Nusselt number for a wide range of the viscosity-variation parameter, heat generation parameter, and the Rayleigh number. Increasing viscosity variation parameter and Rayleigh number lead to increasing the local and average Nusselt number and decreasing the wall shear stress. Wall shear stress and the rate of heat transfer decreased due to the increase of heat generation.

Effect of the Broken Rib Locations on the Heat Transfer and Fluid Flow in a Rotating Latticework Duct

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Wei Du ◽  
Lei Luo ◽  
Songtao Wang ◽  
Jian Liu ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Nusselt Number ◽  
Wall Shear Stress ◽  
Flow Structure ◽  
Suction Side ◽  
Spiral Flow ◽  
Numerical Studies ◽  
Rotational Number ◽  
Wall Shear

AbstractA numerical method was used to study the effect of the broken rib locations on the heat transfer and flow structure in the latticework duct with various rotational numbers. The latticework duct had eleven subchannels on both the pressure side and the suction side. The crossing angle for each subchannel was 45 deg. The numerical studies were conducted with five different broken rib locations and six rotational numbers (0–0.5). The Reynolds number was fixed as 44,000. The flow structure, wall shear stress, and Nusselt number distributions were analyzed. It was found that the upward spiral flow and helical flow dominated the flow structure in the latticework duct. In addition, the impingement region (at the beginning of the subchannel) induced by the upward spiral flow was responsible for the high Nusselt number and wall shear stress. After adoption of the broken rib in the latticework duct, the Nusselt number was increased by 6.12% on the pressure endwall surface and increased by 6.02% on the rib surface compared to the traditional latticework duct. As the rotational number was increased, the Nusselt number on the pressure endwall surface was decreased by up to 5.4%. However, the high rotational number enhanced the heat transfer on the suction side. The high rotational number also decreased the friction factor in the latticework duct. Furthermore, the overall thermal performance was increased by 12.12% after adoption of the broken ribs on both the turn region and the impingement region.

Numerical Study of Laminar Flow and Convection Heat Transfer of Nanofluids inside Circular Tube

2014 ◽  
Vol 960-961 ◽  
pp. 299-303
Author(s):  
Ning Bo Zhao ◽  
Shu Ying Li ◽  
Jia Long Yang ◽  
Zhi Tao Wang ◽  
Hui Meng
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Shear Stress ◽  
Nusselt Number ◽  
Laminar Flow ◽  
Wall Shear Stress ◽  
Circular Tube ◽  
Numerical Study ◽  
Nanoparticle Diameter ◽  
Wall Shear

This paper presents a numerical study on laminar flow and convective heat transfer of nanofluids in a circular tube under constant wall heat flux boundary condition. Single phase model is used for simulating the heat transfer and flow behaviors of three different nanofluids. The effects of nanoparticle concentrations, nanoparticle diameter, nanoparticle material and Reynolds number on the Nusselt number and wall shear stress of nanofluids are determined and discussed in details. The comparison of Nusselt number of CuO-EG/water, SiO2-EG/water and Al2O3-EG/water nanofluids are presented. The results show that Nusselt number clearly increases with an increase in the nanoparticle concentration and flow Reynolds number, while the nanoparticle diameter has an opposite effect on the Nusselt number. Compared to SiO2-EG/water and Al2O3-EG/water nanofluids, CuO-EG/water nanofluids give higher Nusselt number with the same nanoparticle concentrations. The results also show that wall shear stress increases with increasing nanoparticle volume concentration.

Flow and Thermal Fields in a Pendant Droplet Moving on Lyophobic Surface

2010 ◽  
Author(s):  
Basant Singh Sikarwar ◽  
K. Muralidhar ◽  
Sameer Khandekar
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Reynolds Number ◽  
Shear Stress ◽  
Heat Transfer Coefficient ◽  
Wall Shear Stress ◽  
Transfer Coefficient ◽  
Maximum Shear Stress ◽  
Computational Domain ◽  
Wall Shear

Clusters of liquid drops growing and moving on physically or chemically textured lyophobic surfaces are encountered in drop-wise mode of vapor condensation. As opposed to film-wise condensation, drops permit a large heat transfer coefficient and are hence attractive. However, the temporal sustainability of drop formation on a surface is a challenging task, primarily because the sliding drops eventually leach away the lyophobicity promoter layer. Assuming that there is no chemical reaction between the promoter and the condensing liquid, the wall shear stress (viscous resistance) is the prime parameter for controlling physical leaching. The dynamic shape of individual droplets, as they form and roll/slide on such surfaces, determines the effective shear interaction at the wall. Given a shear stress distribution of an individual droplet, the net effect of droplet ensemble can be determined using the time averaged population density during condensation. In this paper, we solve the Navier-Stokes and the energy equation in three-dimensions on an unstructured tetrahedral grid representing the computational domain corresponding to an isolated pendant droplet sliding on a lyophobic substrate. We correlate the droplet Reynolds number (Re = 10–500, based on droplet hydraulic diameter), contact angle and shape of droplet with wall shear stress and heat transfer coefficient. The simulations presented here are for Prandtl Number (Pr) = 5.8. We see that, both Poiseuille number (Po) and Nusselt number (Nu), increase with increasing the droplet Reynolds number. The maximum shear stress as well as heat transfer occurs at the droplet corners. For a given droplet volume, increasing contact angle decreases the transport coefficients.

Study on the Characteristics of Flow and Heat Transfer of Polymeric-Fluid-Based Cu Nanofluids

2017 ◽  
Author(s):  
Weihua Cai ◽  
Yongyao Li ◽  
Yue Wang ◽  
Xin Zheng ◽  
Mengsheng Zhu
Keyword(s):  
Heat Transfer ◽  
Aqueous Solution ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Drag Reduction ◽  
Volume Fraction ◽  
Solution Flow ◽  
Flow And Heat Transfer ◽  
Wall Shear ◽  
Polymer Aqueous Solution

In this paper, we propose a new fluid: drag-reducing-fluid-based nanofluids (DRFBN), i.e., nanoparticles are added into polymer aqueous solution. In order to investigate the flow and heat transfer characteristics of this new fluid, the Reynolds stress turbulence model and equivalent viscosity model are used in the simulations. Wall shear stress and Nusselt number (Nu) are chosen to represent the effects of drag reduction and heat enhancement respectively. The numerical studies mainly focus on the effects of different parameters on wall shear stress and Nu. The results show that comparison with water flow, DRFBN flow still has remarkable drag-reducing effect; comparison with polymer aqueous solution flow, DRFBN flow has some improvement on heat transfer. Therefore, DRFBN has duel effects: drag reduction and heat transfer enhancement. Besides, it is found that the parameters of nanoparticle volume fraction, Reynolds number and drag-reducing parameter have remarkable effects on wall shear stress and Nu of DRFBN flow.

Entropy hemodynamics particle-fluid suspension model through eccentric catheterization for time-variant stenotic arterial wall: Catheter injection

2019 ◽  
Vol 16 (11) ◽  
pp. 1950164 ◽  
Author(s):  
Kh. S. Mekheimer ◽  
A. Z. Zaher ◽  
A. I. Abdellateef
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Temperature Distribution ◽  
Wall Shear Stress ◽  
Outer Cylinder ◽  
Flow Characteristics ◽  
Two Phase ◽  
Eccentric Cylinder ◽  
Wall Shear ◽  
Suspension Model

Catheterization has an imperative rule in heat transfer investigations, which are frequently applied to analyze and deal with the heart transfer studies. Here, the entering of a catheter adjusts the flow of the blood and it affects the hemodynamic status in the artery region. In practical clinical cases, catheters cannot be precisely concentric with the artery. The impartial of this work is to investigate the behavior of a blood streaming characteristics, in the case of injecting the catheter eccentrically all the way through a stenotic overlapping artery. In this paper, we consider the heat transfer within the presence of blood corpuscle which has been characterized by a macroscopic two-phase model (i.e. a suspension of erythrocytes in plasma). The model here considers the blood fluid as a liquid fluid with adjourned particles in the gap bounded by the eccentric cylinder. The inside cylinder is identically rigid demonstrating the movable thin catheter and kept at constant temperature, where the outer cylinder is a taper cylinder demonstrating the artery that has overlapping stenosis and it is cooled and maintained at zero temperature. The coupled differential equations for both fluid (plasma) and particle (erythrocyte) phases have been solved. The expressions for the flow characteristics, namely, the flow rate, the impedance (resistance to flow), the wall shear stress and the temperature distribution, have been derived. The model is very useful in medicine, where the hemodynamic speed is higher for eccentric case than that of concentric one. Also, the temperature distribution and the entropy generation in the state of eccentric position are higher than in the case of the concentric position. A significant increase in the magnitude of the impedance and the wall shear stress occurs for an increase in the hematocrit, C for diseased blood.

Mixed convective heat transfer and heat generation simulation in lid-driven enclosure filled with porous medium

2021 ◽  
pp. 2150106
Author(s):  
Basma Souayeh ◽  
Najib Hdhiri
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Generation ◽  
Average Nusselt Number ◽  
Internal Heat ◽  
Internal Heat Generation ◽  
Bottom Wall ◽  
Maximum Temperature ◽  
Grashof Number ◽  
Number Formula

Researchers in heat transfer field always attempt to find new solutions to optimize the performance of energy devices through heat transfer enhancement. Among various methods which are implemented to reinforce the thermal performance of energy systems, one is utilizing porous media in heat exchangers. In this study, characteristics of laminar mixed convection in a porous two-sided lid-driven square cavity induced by an internal heat generation at the bottom wall have been carried out by using a numerical methodology based on the finite volume method and the full multigrid acceleration. The two-sided and top walls of the enclosure are assumed to have cold temperature while the remaining walls of the bottom wall are insulated. The working fluid is air so that the Prandtl number equates 0.71. The behavior of different physical parameters is shown graphically so that computations have been conducted over a wide range of pertinent parameters; (10[Formula: see text] Ri [Formula: see text]), Darcy number ([Formula: see text] Da [Formula: see text]), internal Rayleigh number ([Formula: see text] Ra[Formula: see text]), the porosity ([Formula: see text]) and the Grashof number (10[Formula: see text] Gr [Formula: see text]). Results revealed that heat transfer mechanism and the flow characteristics inside the enclosure are strongly dependent on the Grashof number. For instance, the best heat transfer rates at the considered values of internal Rayleigh numbers are obtained for a high Grashof number. Furthermore, an increase of internal heat generation (RaI) leads to a higher flow and temperature intensities for Grashof numbers ranging from [Formula: see text] to [Formula: see text] and a specific Richardson number value. Besides, an increase in porosity values ([Formula: see text]) leads to an obvious decrease in the average Nusselt number. Maximum temperature [Formula: see text] is optimal for high ([Formula: see text]) value. A correlation expression for the average Nusselt number relative to the internal heat source was established in function of two control parameters such as Darcy and Richardson numbers.

Buoyancy Driven Flow, Heat Transfer and Entropy Generation Characteristics for Different Heater Geometries Placed in Cryogenic Liquid: A CFD Study

2021 ◽  
pp. 1-20
Author(s):  
Someshwar Ade ◽  
Sushil Rathore
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Entropy Generation ◽  
Heat Generation ◽  
Average Nusselt Number ◽  
Cryogenic Liquid ◽  
Heat Generation Rate ◽  
Heat Transfer Characteristics ◽  
Flow And Heat Transfer

Abstract The present work reports 3D computational study of buoyancy driven flow and heat transfer characteristics for a localized heater (analogous to superconductor) submerged in cryogenic liquid nitrogen in an enclosure. Seven different heater geometries are considered and the effect of heater geometry on flow and heat transfer characteristics are illustrated. The heater is generating heat at a constant rate (W/m3). Continuity, momentum and energy equations are solved using finite volume method. Liquid flow and heat transfer features are demonstrated with the help of velocity vector and temperature contours. Rayleigh number, average Nusselt number, maximum vertical velocity of fluid flow, average velocity of fluid flow are the parameters which are considered for comparing seven different geometries of heater. Additionally, an analysis of the entropy generation owing to transfer of heat and friction due to fluid flow are reported. Furthermore, the dependency of average Nusselt number, maximum velocity of fluid, entropy generation owing to transfer of heat and fluid friction as a function of heat generation rate is illustrated graphically. The results of this study indicate that heater geometry can considerably affect the transfer of heat, fluid flow features and entropy generation under same heat generation rate in the heater. Highest average Nusselt number on heater surface is obtained when heater geometry is circular; whereas lowest value of total entropy generation in the domain is obtained when heater geometry is equilateral triangle.

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