Numerical Modeling and Physical Simulation of Vortex Heat Transfer Enhancement Mechanisms Over Dimpled Reliefs

2010 ◽  
Author(s):  
Alexander I. Leontiev ◽  
Sergey A. Isaev ◽  
Nikolai V. Kornev ◽  
Yaroslav Chudnovsky ◽  
Egon Hassel
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Physical Simulation ◽  
Stokes Equations ◽  
Numerical Study ◽  
Narrow Channel ◽  
Discrete Models ◽  
Navier Stokes ◽  
Heat Output ◽  
Flow And Heat Transfer

The paper presents a comprehensive analysis of conditions for numerical simulation and physical modeling of convective heat transfer in the vicinity of dimpled surface relief. Contradictory results, unreasonable assumptions, and non-justified conclusions are marked. Based on the analysis of physical experiments the correlation between the predictions and measured data is discussed. Detailed numerical study of turbulent air flow and heat transfer in the narrow channel with three types of dimples (spherical, conic and oval) was carried out. Various mathematical and discrete models, including, those based on solving Reynolds-averaged Navier-Stokes equations (RANS/URANS-SST), and also adaptive scale models (SAS-SST) are compared. The influence of flow parameters (Reynolds number) and geometric sizes (dimple diameter, depth, radius of rounding off of an edge, channel width and height) on local and integral characteristics of flow and heat transfer (total heat output and hydraulic losses) is determined. Special attention is given to reorganizing vortex structures and flow regime (with periodic fluctuations) with increasing relative dimple depth and Reynolds number. For the first time the influence of the scale factor of a constant cross-section channel is detailed. Thermal-hydraulic characteristics of various dimpled reliefs are compared, and the advantage of an oval dimple over a spherical one is shown.

Laminar Heat Transfer in a Channel With Two Right-Angled Bends

1984 ◽  
Vol 106 (3) ◽  
pp. 591-596 ◽  
Author(s):  
R. S. Amano
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Stokes Equations ◽  
Numerical Study ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Flow And Heat Transfer ◽  
Long Channel

A numerical study is reported on the flow and heat transfer in the channel with two right-angled bends. The modified hybrid scheme was employed to solve the steady full Navier-Stokes equations with the energy equation. The computations were performed for different step heights created in a long channel. The local heat transfer rate along the channel wall predicted by employing the present numerical model showed good agreement with the experimental data. The behavior of the flow and the heat transfer were investigated for the range of Reynolds number between 200 and 2000 and for step height ratios H/W = 1, 2, and 3. Finally, the correlation of the average Nusselt number in such channels as a function of Reynolds number is postulated.

Axisymmetric Stagnation—Point Flow and Heat Transfer of a Viscous Fluid on a Rotating Cylinder With Time-Dependent Angular Velocity and Uniform Transpiration

2006 ◽  
Vol 129 (1) ◽  
pp. 106-115 ◽  
Author(s):  
A. B. Rahimi ◽  
R. Saleh
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Angular Velocity ◽  
Stokes Equations ◽  
Time Dependent ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Flow And Heat Transfer ◽  
Self Similar

The unsteady viscous flow and heat transfer in the vicinity of an axisymmetric stagnation point of an infinite rotating circular cylinder with transpiration U0 are investigated when the angular velocity and wall temperature or wall heat flux all vary arbitrarily with time. The free stream is steady and with a strain rate of Γ. An exact solution of the Navier-Stokes equations and energy equation is derived in this problem. A reduction of these equations is obtained by the use of appropriate transformations for the most general case when the transpiration rate is also time-dependent but results are presented only for uniform values of this quantity. The general self-similar solution is obtained when the angular velocity of the cylinder and its wall temperature or its wall heat flux vary as specified time-dependent functions. In particular, the cylinder may rotate with constant speed, with exponentially increasing/decreasing angular velocity, with harmonically varying rotation speed, or with accelerating/decelerating oscillatory angular speed. For self-similar flow, the surface temperature or its surface heat flux must have the same types of behavior as the cylinder motion. For completeness, sample semi-similar solutions of the unsteady Navier-Stokes equations have been obtained numerically using a finite-difference scheme. Some of these solutions are presented for special cases when the time-dependent rotation velocity of the cylinder is, for example, a step-function. All the solutions above are presented for Reynolds numbers, Re=Γa2∕2υ, ranging from 0.1 to 1000 for different values of Prandtl number and for selected values of dimensionless transpiration rate, S=U0∕Γa, where a is cylinder radius and υ is kinematic viscosity of the fluid. Dimensionless shear stresses corresponding to all the cases increase with the increase of Reynolds number and suction rate. The maximum value of the shear stress increases with increasing oscillation frequency and amplitude. An interesting result is obtained in which a cylinder rotating with certain exponential angular velocity function and at particular value of Reynolds number is azimuthally stress-free. Heat transfer is independent of cylinder rotation and its coefficient increases with the increasing suction rate, Reynolds number, and Prandtl number. Interesting means of cooling and heating processes of cylinder surface are obtained using different rates of transpiration.

A Numerical Study of the Influence of Disc Geometry on the Flow and Heat Transfer in a Rotating Cavity

1990 ◽  
Author(s):  
B. L. Lapworth ◽  
J. W. Chew
Keyword(s):  
Heat Transfer ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Numerical Study ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Model Calculations ◽  
Flow And Heat Transfer ◽  
Rotating Cavity ◽  
Radial Outflow

Numerical solutions of the Reynolds-averaged Navier-Stokes equations have been used to model the influence of cobs and a bolt cover on the flow and heat transfer in a rotating cavity with an imposed radial outflow of air. Axisymmetric turbulent flow is assumed using a mixing length turbulence model. Calculations for the non-plane discs are compared with plane disc calculations and also with the available experimental data. The calculated flow structures show good agreement with the experimentally observed trends. For the cobbed and plane discs, Nusselt numbers are calculated for a combination of flow rates and rotational speeds; these show some discrepancies with the experiments, although the calculations exhibit the more consistent trend. Further calculations indicate that differences in thermal boundary conditions have a greater influence on Nusselt number than differences in disc geometry. The influence of the bolt cover on the heat transfer has also been modelled, although comparative measurements are not available.

A Numerical Study of Unsteady Laminar Flow and Heat Transfer Through an Array of Rotating Rectangular Microchannels

2011 ◽  
Author(s):  
Pratanu Roy ◽  
N. K. Anand ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Laminar Flow ◽  
Fluid Transport ◽  
Stokes Equations ◽  
Numerical Study ◽  
Simple Algorithm ◽  
Centrifugal Microfluidics ◽  
Rectangular Microchannels ◽  
Flow And Heat Transfer

Centrifugal microfluidics plays an important role for enabling many novel applications in life sciences. By controlling the rotating frequency, fluids can be handled and controlled without any actual pumps, actuators or active valves, resulting in cost effective and miniaturized techniques for fluid transport, valving, metering, switching, splitting and separation of fluids. In order to get a vivid picture of the underlying physics of centrifugal microfluidics, we have modeled and simulated fluid flow and heat transfer for water flowing through an array of rotating rectangular microchannels. A finite volume technique based on semi implicit pressure based equation (SIMPLE) algorithm has been developed to solve the Naiver-Stokes equations for unsteady laminar flow. The energy equation has been solved by applying repeated thermal boundary conditions at the wall in cross stream direction. The simulations show significant deviation of velocity and temperature profiles for rotating flow than those of non-rotating case. The results are presented for different flow Reynolds number and rotational Reynolds number.

scholarly journals Experimental and Numerical Study to Enhance of Heat Transfer Coefficient in Air Flow Using Microchannel

2018 ◽  
Vol 26 (7) ◽  
pp. 112-123
Author(s):  
Jalal M. Jalil ◽  
Ghada A. Aziz ◽  
Amjed A. Kadhim
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Stokes Equations ◽  
Numerical Study ◽  
Simple Algorithm ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Flow And Heat Transfer ◽  
The Heat Transfer Coefficient

Experimental and numerical study of fluid flow and heat transfer in microchannel airflow is investigated. The study covers changing the cooling of micro-channel for the velocities and heater powers. The dimensions of the microchannel were, length = 0.1m, width = 0.001m, height = 0.0005 m. The experimental and numerical results were compared with the previous paper for velocities up to 20 m/s and heater powers up to 5 W and the comparison was acceptable. In this paper, the results were extended numerically for velocities up to 60 m/s. The numerical solution used finite volume (SIMPLE algorithm) to solve Navier Stokes equations (continuity, momentum and energy). The results show that the heat transfer coefficient increases up to 220 W/m2 oC for velocity 60 m/s.

A Numerical Study of the Influence of Disk Geometry on the Flow and Heat Transfer in a Rotating Cavity

1992 ◽  
Vol 114 (1) ◽  
pp. 256-263 ◽  
Author(s):  
B. L. Lapworth ◽  
J. W. Chew
Keyword(s):  
Heat Transfer ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Numerical Study ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Model Calculations ◽  
Flow And Heat Transfer ◽  
Rotating Cavity ◽  
Radial Outflow

Numerical solutions of the Reynolds-averaged Navier–Stokes equations have been used to model the influence of cobs and a bolt cover on the flow and heat transfer in a rotating cavity with an imposed radial outflow of air. Axisymmetric turbulent flow is assumed using a mixing length turbulence model. Calculations for the non-plane disks are compared with plane disk calculations and also with the available experimental data. The calculated flow structures show good agreement with the experimentally observed trends. For the cobbed and plane disks, Nusselt numbers are calculated for a combination of flow rates and rotational speeds; these show some discrepancies with the experiments, although the calculations exhibit the more consistent trend. Further calculations indicate that differences in thermal boundary conditions have a greater influence on Nusselt number than differences in disk geometry. The influence of the bolt cover on the heat transfer has also been modeled, although comparative measurements are not available.

Effect of wall-mounted V-baffle position in a turbulent flow through a channel

2019 ◽  
Vol 29 (10) ◽  
pp. 3908-3937 ◽  
Author(s):  
Younes Menni ◽  
Ahmed Azzi ◽  
Ali J. Chamkha ◽  
Souad Harmand
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Stokes Equations ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Simple Algorithm ◽  
Two Dimensions ◽  
Large Reynolds Number ◽  
Constant Property ◽  
Content Type

Purpose The purpose of this paper is to carry out a numerical study on the dynamic and thermal behavior of a fluid with a constant property and flowing turbulently through a two-dimensional horizontal rectangular channel. The upper surface was put in a constant temperature condition, while the lower one was thermally insulated. Two transverse, solid-type obstacles, having different shapes, i.e. flat rectangular and V-shaped, were inserted into the channel and fixed to the top and bottom walls of the channel, in a periodically staggered manner to force vortices to improve the mixing, and consequently the heat transfer. The flat rectangular obstacle was put in the first position and was placed on the hot top wall of the channel. However, the second V-shaped obstacle was placed on the insulated bottom wall, at an attack angle of 45°; its position was varied to find the optimum configuration for optimal heat transfer. Design/methodology/approach The fluid is considered Newtonian, incompressible with constant properties. The Reynolds averaged Navier–Stokes equations, along with the standard k-epsilon turbulence model and the energy equation, are used to control the channel flow model. The finite volume method is used to integrate all the equations in two-dimensions; the commercial CFD software FLUENT along with the SIMPLE-algorithm is used for pressure-velocity coupling. Various values of the Reynolds number and obstacle spacing were selected to perform the numerical runs, using air as the working medium. Findings The channel containing the flat fin and the 45° V-shaped baffle with a large Reynolds number gave higher heat transfer and friction loss than the one with a smaller Reynolds number. Also, short separation distances between obstacles provided higher values of the ratios Nu/Nu0 and f/f0 and a larger thermal enhancement factor (TEF) than do larger distances. Originality/value This is an original work, as it uses a novel method for the improvement of heat transfer in completely new flow geometry.

Axisymmetric Stagnation-Point Flow and Heat Transfer of a Viscous Fluid on a Moving Cylinder With Time-Dependent Axial Velocity and Uniform Transpiration

2004 ◽  
Vol 126 (6) ◽  
pp. 997-1005 ◽  
Author(s):  
R. Saleh ◽  
A. B. Rahimi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Axial Velocity ◽  
Time Dependent ◽  
Navier Stokes ◽  
Flow And Heat Transfer ◽  
Moving Cylinder ◽  
Self Similar ◽  
Suction Rate ◽  
Axial Speed

The unsteady viscous flow and heat transfer in the vicinity of an axisymmetric stagnation point of an infinite moving cylinder with time-dependent axial velocity and with uniform normal transpiration Uo are investigated. The impinging free stream is steady and with a constant strain rate k¯. An exact solution of the Navier–Stokes equations and energy equation is derived in this problem. A reduction of these equations is obtained by use of appropriate transformations for the most general case when the transpiration rate is also time-dependent but results are presented only for uniform values of this quantity. The general self-similar solution is obtained when the axial velocity of the cylinder and its wall temperature or its wall heat flux vary as specified time-dependent functions. In particular, the cylinder may move with constant speed, with exponentially increasing–decreasing axial velocity, with harmonically varying axial speed, or with accelerating–decelerating oscillatory axial speed. For self-similar flow, the surface temperature or its surface heat flux must have the same types of behavior as the cylinder motion. For completeness, sample semisimilar solutions of the unsteady Navier–Stokes and energy equations have been obtained numerically using a finite-difference scheme. Some of these solutions are presented for special cases when the time-dependent axial velocity of the cylinder is a step-function, and a ramp function. All the solutions above are presented for Reynolds numbers, Re=ka¯2/2υ, ranging from 0.1 to 100 for different values of dimensionless transpiration rate, S=Uo/ka¯, where a is cylinder radius and υ is kinematic viscosity of the fluid. Absolute value of the shear-stresses corresponding to all the cases increase with the increase of Reynolds number and suction rate. The maximum value of the shear- stress increases with increasing oscillation frequency and amplitude. An interesting result is obtained in which a cylinder moving with certain exponential axial velocity function at any particular value of Reynolds number and suction rate is axially stress-free. The heat transfer coefficient increases with the increasing suction rate, Reynolds number, Prandtl number, oscillation frequency and amplitude. Interesting means of cooling and heating processes of cylinder surface are obtained using different rates of transpiration. It is shown that a cylinder with certain type of exponential wall temperature exposed to a temperature difference has no heat transfer.

The Numerical Prediction of Viscous Flow and Heat Transfer in Tube Banks

1978 ◽  
Vol 100 (4) ◽  
pp. 565-571 ◽  
Author(s):  
B. E. Launder ◽  
T. H. Massey
Keyword(s):  
Heat Transfer ◽  
Viscous Flow ◽  
Stokes Equations ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Substantial Contribution ◽  
Navier Stokes Equations ◽  
Flow And Heat Transfer ◽  
Flow Domain ◽  
Tube Banks

A scheme for handling the numerical analysis of viscous flow and heat transfer in tube banks is presented. It involves the use of a cylindrical network of nodes in the vicinity of the tubes with a Cartesian mesh covering the remainder of the flow domain. The approach has been incorporated into the numerical solving algorithm for the Navier Stokes equations of Gasman, et al. [8]. A number of demonstration calculations is presented including a numerical simulation of the staggered square bank for which Bergelin and co-workers [4, 9] have reported experimental results for pressure drop and heat transfer rate. Agreement between predicted and measured characteristics is satisfactory when account is taken of end and entry effects that are present in the experiments but necessarily omitted from the calculations. Indeed the close agreement of the laminar predictions with measurements extends to Reynolds numbers in excess of 1000, a level at which it has hitherto been supposed that turbulent motion in the fluid made a substantial contribution to friction and heat transfer.

A Numerical Study of the Flow and Heat Transfer in the Pin Fin-Dimple Channels With Various Dimple Depths

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
Yu Rao ◽  
Yamin Xu ◽  
Chaoyi Wan
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Convective Heat Transfer ◽  
Heat Transfer Performance ◽  
Numerical Study ◽  
Transfer Performance ◽  
Number Range ◽  
Flow Friction ◽  
Pin Fin ◽  
Flow And Heat Transfer

A numerical study was conducted to investigate the effects of dimple depth on the flow and heat transfer characteristics in a pin fin-dimple channel, where dimples are located spanwisely between the pin fins. The study aimed at promoting the understanding of the underlying convective heat transfer mechanisms in the pin fin-dimple channels and improving the cooling design for the gas turbine components. The flow structure, friction factor, and heat transfer performance of the pin fin-dimple channels with various dimple depths have been obtained and compared with each other for the Reynolds number range of 8200–80,800. The study showed that, compared to the pin fin channel, the pin fin-dimple channels have further improved convective heat transfer performance, and the pin fin-dimple channel with deeper dimples shows relatively higher Nusselt number values. The study still showed a dimple depth-dependent flow friction performance for the pin fin-dimple channels compared to the pin fin channel, and the pin fin-dimple channel with shallower dimples shows relatively lower friction factors over the studied Reynolds number range. Furthermore, the computations showed the detailed characteristics in the distribution of the velocity and turbulence level in the flow, which revealed the underlying mechanisms for the heat transfer enhancement and flow friction reduction phenomenon in the pin fin-dimple channels.

Sign in / Sign up

Export Citation Format

Share Document