Similarity Solution of Unaxisymmetric Heat Transfer in Stagnation-Point Flow on a Cylinder With Simultaneous Axial and Rotational Movements

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
Asghar B. Rahimi ◽  
Reza Saleh
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Stagnation Point ◽  
Wall Temperature ◽  
Similarity Solution ◽  
Free Stream ◽  
Wall Heat Flux ◽  
Cylinder Wall ◽  
Local Coefficient ◽  
Unsteady Viscous Flow

Similarity solution of unaxisymmetric heat transfer of an unsteady viscous flow in the vicinity of an axisymmetric stagnation point of an infinite circular cylinder with simultaneous axial and rotational movement along with transpiration Uo is investigated when the angular velocity, axial velocity, and wall temperature or wall heat flux vary arbitrarily with time. The impinging free stream is steady and with a strain rate of k¯. The results presented are found by numerical integration. The local coefficient of heat transfer (Nusselt number) is found to be independent of time and place, though the cylinder wall temperature or wall heat flux are functions of both time and place.

Numerical Study of the Effects of Different Buoyancy Models on Supercritical Flow and Heat Transfer

2013 ◽  
Author(s):  
X. Y. Xu ◽  
T. Ma ◽  
M. Zeng ◽  
Q. W. Wang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Enhancement ◽  
Wall Temperature ◽  
Mass Flux ◽  
Wall Heat Flux ◽  
Turbulent Heat ◽  
Transfer Enhancement ◽  
Temperature Prediction ◽  
Flow And Heat Transfer

Due to the dramatic changes in physical properties, the flow and heat transfer in supercritical fluid are significantly affected by buoyancy effects, especially when the ratio of inlet mass flux and wall heat flux is relatively small. In this study, the heat transfer of supercritical water in uniformly heated vertical tube is numerically investigated with different buoyancy models which are based on different calculation methods of the turbulent heat flux. The applicabilities of these buoyancy models are analyzed both in heat transfer enhancement and deterioration conditions. The simulation results show that these buoyancy models make few differences and give good wall temperature prediction in heat transfer enhancement condition when the ratio of inlet mass flux and wall heat flux is very small. With the increase of wall heat flux, the accuracy of wall temperature prediction reduces, and the differences between these buoyancy models become larger. No buoyancy model can currently make accurate wall temperature prediction in deterioration condition in this study.

scholarly journals Axisymmetric stagnation-point flow and heat transfer of nanofluid impinging on a cylinder with constant wall heat flux

2019 ◽  
Vol 23 (5 Part B) ◽  
pp. 3153-3164 ◽  
Author(s):  
Hamid Mohammadiun ◽  
Vahid Amerian ◽  
Mohammad Mohammadiun ◽  
Iman Khazaee ◽  
Mohsen Darabi ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Velocity Field ◽  
Stagnation Point ◽  
Base Fluid ◽  
Fluid Velocity ◽  
Wall Heat Flux ◽  
Flow And Heat Transfer ◽  
Constant Wall Heat Flux ◽  
Fluid Velocity Field

The steady-state, viscous flow and heat transfer of nanofluid in the vicinity of an axisymmetric stagnation point of a stationary cylinder with constant wall heat flux is investigated. The impinging free-stream is steady and with a constant strain rate, k ?. Exact solution of the Navier-Stokes equations and energy equation are derived in this problem. A reduction of these equations is obtained by use of appropriate transformations introduced in this research. The general self-similar solution is obtained when the wall heat flux of the cylinder is constant. All the previous solutions are presented for Reynolds number Re = k ?a2/2n f ranging from 0.1 to 1000, selected values of heat flux and selected values of particle fractions where a is cylinder radius and n f is kinematic viscosity of the base fluid. For all Reynolds numbers, as the particle fraction increases, the depth of diffusion of the fluid velocity field in radial direction, the depth of the diffusion of the fluid velocity field in z-direction, shear-stresses and pressure function decreases. However, the depth of diffusion of the thermal boundary-layer increases. It is clear by adding nanoparticles to the base fluid there is a significant enhancement in Nusselt number and heat transfer.

Using Direct Simulation Monte Carlo With Improved Boundary Conditions for Heat and Mass Transfer in Microchannels

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
J. Yang ◽  
J. J. Ye ◽  
J. Y. Zheng ◽  
I. Wong ◽  
C. K. Lam ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Flux ◽  
Aspect Ratio ◽  
Heat And Mass Transfer ◽  
Wall Temperature ◽  
Gas Flow ◽  
Wall Heat Flux ◽  
Entrance Region ◽  
Mass Flowrate

Micro-electromechanical systems and nano-electromechanical systems have attracted a great deal of attention in recent years. The flow and heat transfer behaviors of micromachines for separation applications are usually different from that of macro counterparts. In this paper, heat and mass transfer characteristics of rarefied nitrogen gas flows in microchannels are investigated using direct simulation Monte Carlo with improved pressure boundary conditions. The influence of aspect ratio and wall temperature on mass flowrate and wall heat flux in microchannels are studied parametrically. In order to examine the aspect ratio effect on heat and mass transfer behaviors, the wall temperature is set constant at 350 K and the aspect ratio of the microchannel varies from 5 to 20. The results show that as the aspect ratio increases, the velocity of the flow decreases, so does the mass flowrate. In a small aspect ratio channel, the heat transfer occurs throughout the microchannel; as the aspect ratio of the microchannel increases, the region of thermal equilibrium extends. To investigate the effects of wall temperature (Tw) on the mass flowrate and wall heat flux in a microchannel, the temperature of the incoming gas flow (Tin) is set constant at 300 K and the wall temperature varies from 200 K to 800 K while the aspect ratio is remained unchanged. Results show that majority of the wall heat flux stays within the channel entrance region and drops to nearly zero at the halfway in the channel. When Tw<Tin, under the restriction of pressure-driven condition and continuity of pressure, the molecular number density of the flow decreases along the flow direction after a short increase at the entrance region. When Tw>Tin, the molecular number density of the flow drops rapidly near the inlet and the temperature of the gas flow increases along the channel. As Tw increases, the flow becomes more rarefied, the mass flowrate decreases, and the resistance at the entrance region increases. Furthermore, when Tw>Tin, a sudden jump of heat transfer flux and temperature are observed at the exit region of the channel.

scholarly journals Oblique Stagnation Point Flow of Nanofluids over Stretching/Shrinking Sheet with Cattaneo–Christov Heat Flux Model: Existence of Dual Solution

Symmetry ◽  
2019 ◽  
Vol 11 (9) ◽  
pp. 1070 ◽  
Author(s):  
Xiangling Li ◽  
Arif Ullah Khan ◽  
Muhammad Riaz Khan ◽  
Sohail Nadeem ◽  
Sami Ullah Khan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Stagnation Point ◽  
Free Stream ◽  
Skin Friction Coefficient ◽  
Stagnation Point Flow ◽  
Shrinking Sheet ◽  
Branch Solution ◽  
Flux Model ◽  
Heat Flux Model

In the present work we consider a numerical solution for laminar, incompressible, and steady oblique stagnation point flow of Cu − water nanofluid over a stretching/shrinking sheet with mass suction S . We make use of the Cattaneo–Christov heat flux model to develop the equation of energy and investigate the qualities of surface heat transfer. The governing flow and energy equations are modified into the ordinary differential equations by similarity method for reasonable change. The subsequent ordinary differential equations are illuminated numerically through the function bvp4c in MATLAB. The impact of different flow parameters for example thermal relaxation parameter, suction parameter, stretching/shrinking parameter, free stream parameter, and nanoparticles volume fraction on the skin friction coefficient, local Nusselt number, and streamlines are contemplated and exposed through graphs. It turns out that the lower branch solution for the skin friction coefficient becomes singular in shrinking area, although the upper branch solution is smooth in both stretching and shrinking domain. For oblique stagnation-point flow the streamlines pattern are not symmetric, and reversed phenomenon are detected close to the shrinking surface. Also, we observed that the free stream parameter changes the direction of the oncoming flow and controls the obliqueness of the flow. The existing work mostly includes heat and mass transfer as a mechanism for improving the heat transfer rate, which is the main objective of the authors.

Heat Transfer to Laminar Flow in Tapered Passages

1965 ◽  
Vol 32 (3) ◽  
pp. 684-689 ◽  
Author(s):  
E. M. Sparrow ◽  
J. B. Starr
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Wall Temperature ◽  
Parallel Plate ◽  
Laminar Flows ◽  
Wall Heat Flux ◽  
Heat Transfer Analysis ◽  
Plate Channel

Consideration is given to the fully developed heat-transfer characteristics of laminar flows in converging and diverging plane-walled passages. The analysis is carried out for the two fundamental thermal boundary conditions of prescribed wall heat flux and prescribed wall temperature. As a prelude to the heat-transfer analysis, a new solution for the velocity distribution is derived on the basis of a linearized momentum equation. The Nusselt number for flow in tapered passages is found to depend on the Reynolds number; this is in contrast to the situation for passages of longitudinally unchanging cross section wherein the Nusselt number is independent of the Reynolds number. In general, the Nusselt number for flow in a plane-walled diverging passage falls below that for the parallel-plate channel, while the Nusselt number for a converging flow is usually higher than that for a parallel-plate channel. Moreover, the fully developed Nusselt numbers for prescribed wall heat flux exceed those for prescribed wall temperature.

Analysis of Transient Laminar Forced Convection of Nanofluids in Circular Channels

2012 ◽  
Author(s):  
İsmail Ozan Sert ◽  
Nilay Sezer-Uzol ◽  
Sadik Kakac
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Steady State ◽  
Numerical Analysis ◽  
Forced Convection ◽  
Wall Temperature ◽  
Particle Diameter ◽  
Wall Heat Flux ◽  
Transient And Steady State

In this study, forced convection heat transfer characteristics of nanofluids are investigated by numerical analysis of incompressible transient laminar flow in a circular duct under step change in wall temperature and wall heat flux. The thermal responses of the system are obtained by solving energy equation under both transient and steady-state conditions for hydrodynamically fully developed flow. In the analyses, temperature dependent thermo-physical properties are also considered. In the numerical analysis, Al2O3/water nanofluid is assumed as a homogenous single-phase fluid. For the effective thermal conductivity of nanofluids, Hamilton-Crosser model is used together with a model for Brownian motion in the analysis which takes the effects of temperature and the particle diameter into account. Temperature distributions across the tube for a step jump of wall temperature and also wall heat flux are obtained for various times during the transient calculations at a given location for a constant value of Peclet number and a particle diameter. Variations of thermal conductivity in turn, heat transfer enhancement is obtained at various times as a function of nanoparticle volume fractions, at a given nanoparticle diameter and Peclet number. The results are given under transient and steady-state conditions; steady-state conditions are obtained at larger times and enhancements are found by comparison to the base fluid heat transfer coefficient under the same conditions.

An Experimental Study of Natural Convection in Vertical, Open-Ended, Concentric, and Eccentric Annular Channels

2011 ◽  
Vol 133 (12) ◽  
Author(s):  
G. H. Choueiri ◽  
S. Tavoularis
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Natural Convection ◽  
Heat Transfer Rate ◽  
Wall Temperature ◽  
Transfer Rate ◽  
Wall Heat Flux ◽  
Annular Channels ◽  
Cylindrical Annulus

The effects of eccentricity on the natural convection heat transfer from a vertical open-ended cylindrical annulus with diameter ratio of 1.63 and aspect ratio of 18:1 have been investigated experimentally. Within the range of present conditions, and with the possible exclusion of the highest eccentricities, it was found that the flow was thermally fully developed in a considerable section of the apparatus, as indicated by the linear variation of wall temperature with height. This made it possible to estimate the mass flow rate from the wall temperature gradient in the mid-section of the annulus, and use it to calculate the bulk Reynolds number, which was found to be weakly sensitive to eccentricity for a constant wall heat flux and to increase with increased wall heat flux. With the exception of the very low eccentricity range in which it was insensitive to eccentricity, the overall heat transfer rate diminished monotonically with increasing eccentricity. Plots of the local azimuthal variation of the Nusselt number showed that, at low eccentricities, the heat transfer rate increased near the wider gap but decreased near the narrower gap. The average Nusselt number was found to decrease measurably with increasing eccentricity and to increase slightly with increasing heat flux within the examined range. In contrast, the Grashof number was found to be much more sensitive to changes in heat flux and only had a weak dependence on eccentricity.

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