Analysis of Thermal Creep Effects on Fluid Flow and Heat Transfer in a Microchannel Gas Heating

2021 ◽  
Vol 13 (6) ◽  
Author(s):  
K. M. Ramadan ◽  
Mohammed Kamil ◽  
I. Tlili ◽  
O. Qisieh
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Heat Exchange ◽  
Channel Wall ◽  
Stokes Equations ◽  
Thermal Creep ◽  
Flow And Heat Transfer ◽  
Creep Effect ◽  
Gas Heating

Abstract Thermal creep effects on fluid flow and heat transfer in a microchannel gas flow at low velocities are studied numerically. The continuity and Navier–Stokes equations in vorticity–stream function form, coupled with the energy equation, are solved, considering the thermal creep effect due to the longitudinal temperature gradient along the channel wall in addition to the combined effects of viscous dissipation, pressure work, axial conduction, shear work, and nonequilibrium conditions at the gas–wall interface. The governing equations are also solved without thermal creep, and comparisons between the two solutions are presented to evaluate the thermal creep effect on the flow field in the slip flow regime at relatively low Reynolds numbers. The results presented show that the thermal creep effect on both velocity and temperature fields become more significant as the Reynolds number decreases. Thermal creep effect on the velocity field also extends a longer distance downstream the channel as the Reynolds number decreases, hence increasing the hydrodynamics entrance length. Thermal creep can cause high positive velocity gradients at the upper channel wall for gas heating and hence reverse the flow rotation in the fluid layers adjacent to the wall. Thermal creep also results in a higher gas temperature in the developing region and higher heat exchange between the fluid and the channel wall in the entrance region. Thermal creep effect on heat exchange between the gas and the channel wall becomes more significant as the Knudsen number decreases.

Thermofluid Characteristics on Natural and Mixed Convection Heat Transfer From a Vertical Rotating Hollow Cylinder Immersed in Air: A Numerical Exercise

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Basanta Kumar Rana ◽  
Bhajneet Singh ◽  
Jnana Ranjan Senapati
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Mixed Convection ◽  
Hollow Cylinder ◽  
Vertical Cylinder ◽  
Cylinder Wall ◽  
Flow And Heat Transfer

Abstract Numerical investigations are performed on natural and mixed convection around stationary and rotating vertical heated hollow cylinder with negligible wall thickness suspended in the air. The fluid flow and heat transfer characterization around the hollow cylinder are obtained by varying the following parameters, namely, Rayleigh number (Ra), Reynolds number (ReD), and cylindrical aspect ratio (L/D). The heat transfer quantities are estimated by varying the Rayleigh number (Ra) from 104 to 108 and aspect ratio (L/D) ranging from 1 to 20. Steady mixed convection with active rotation of hollow vertical cylinder is further studied by varying the Reynolds number (ReD) from 0 to 2100. The velocity vectors and temperature contours are shown in order to understand the fluid flow and heat transfer around the vertical hollow cylinder for both rotating and nonrotating cases. The surface average Nusselt number trends are presented for various instances of Ra, ReD, and L/D and found out that the higher rate of heat loss from the cylinder wall occurs at high Ra, low L/D (short cylinder) and high ReD.

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.

Temporally- and Spatially-Periodic Laminar Flow and Heat Transfer in Staggered-Plate Arrays

2007 ◽  
Author(s):  
Alexandre Lamoureux ◽  
B. Rabi Baliga
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Numerical Solutions ◽  
Initial Conditions ◽  
Plate Thickness ◽  
Geometrical Parameters ◽  
Reduced Pressure ◽  
Flow And Heat Transfer ◽  
Spatially Periodic

A computational investigation of temporally- and spatially-periodic laminar two-dimensional fluid flow and heat transfer in staggered-plate arrays is presented in this paper. The objective and the novel aspect of this study is the investigation of the influence (on the numerical solutions) of including single and multiple representative geometric modules in the calculation domain, with spatially-periodic boundary conditions imposed on the instantaneous velocity and temperature fields in both the streamwise and the lateral directions. The following geometrical parameters, normalized with respect to a representative module height, were studied: a dimensionless plate length equal to 1, and a dimensionless plate thickness of 0.250. This relatively high value of dimensionless plate thickness, compared to those commonly encountered in rectangular offset-fin cores of compact heat exchangers, was deliberately chosen to induce and enhance the unsteady features of the fluid flow and heat transfer phenomena. Different specified values of the time-mean modular streamwise gradient of the reduced pressure were investigated, yielding values of Reynolds number (Kays and London definition) in the range of 100 to 625. The Prandtl number was fixed at 0.7. In the multiple-module simulations, for Reynolds number values exceeding 400, it was found that multiple solutions are possible: the particular solution which is obtained in any one simulation depends on the specified initial conditions. The results presented include time-mean modular friction factors, modular Colburn factors, and Strouhal numbers.

Developing Fluid Flow and Heat Transfer in a Semi-Porous Square Channel

2003 ◽  
Author(s):  
Tien-Chien Jen ◽  
Tuan-Zhou Yan ◽  
S. H. Chan
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Fluid Flow ◽  
Stokes Equations ◽  
Temperature Fields ◽  
Porous Channel ◽  
Navier Stokes ◽  
Axial Position ◽  
Navier Stokes Equations ◽  
Flow And Heat Transfer

A three-dimensional computational model is developed to analyze fluid flow in a semi-porous channel. In order to understand the developing fluid flow and heat transfer process inside the semi-porous channels, the conventional Navier-Stokes equations for gas channel, and volume-averaged Navier-Stokes equations for porous media layer are adopted individually in this study. Conservation of mass, momentum and energy equations are solved numerically in a coupled gas and porous media domain in a channel using the vorticity-velocity method with power law scheme. Detailed development of axial velocity, secondary flow and temperature fields at various axial positions in the entrance region are presented. The friction factor and Nusselt number are presented as a function of axial position, and the effects of the size of porous media inside semi-porous channel are also analyzed in the present study.

scholarly journals HEAT TRANSFER AND FLUID FLOW INSIDE DUCT WITH USING FAN-SHAPE RIBS

2021 ◽  
pp. 1-7
Author(s):  
Ahmed Yousif
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Ansys Fluent ◽  
Flow And Heat Transfer ◽  
Pitch Ratio ◽  
Flow Through ◽  
Energy Equations ◽  
Heat Transfers ◽  
Meshing Process

A 2-D computational analysis is carried out to calculate heat transfer and friction factor for laminar flow through a rectangular duct with using fan–shape ribs as a turbulator. The types of rib shapes are imported on the heat transfer rate and fluid flow in heat exchangers. The present study makes use of fan-shaped ribs with two arrangements. The first arrangement was downstream fan–shape ribs (case 1) and upstream fan–shape ribs (case 2) is investigated. A commercial finite volume package ANSYS FLUENT 16.1 is used for solving the meshing process with continuity, momentum, and energy equations respectively to investigate fluid flow and heat transfer across the ribs surface. The Reynolds number (Re) range of (400 – 2250) with different relative roughness pitch (p/H= 0.17, 0.22, 0.27 and 0.32) at constant rib high (e/H). The results show that the heat transfers and friction increase with using ribs also, the results show that heat transfer Directly proportional to pitch ratio and Reynolds number. The Nusselt number enhancement by (12% -29%).    

Numerical and Experimental Prediction of Transitional Characteristics of Flow and Heat Transfer in an Array of Heated Blocks

1999 ◽  
Vol 121 (3) ◽  
pp. 202-208 ◽  
Author(s):  
Y. Asako ◽  
Y. Yamaguchi ◽  
M. Faghri
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Parallel Plate ◽  
Three Dimensional ◽  
Parallel Plates ◽  
Number Range ◽  
Flow And Heat Transfer ◽  
Numerical Predictions ◽  
Experimental Prediction

Three-dimensional numerical analysis, for transitional characteristics of fluid flow and heat transfer in periodic fully developed region of an array of the heated square blocks deployed along one wall of the parallel plates duct, is carried out by using Lam-Bremhorst low-Reynolds-number two equation turbulence model. Computations were performed for Prandtl number of 0.7, in the Reynolds number range of 200 to 2000 and for two sets of geometric parameters characterizing the array. The predicted transitional Reynolds number is lower than the value for the parallel plate duct and it decreases with increasing the height above the module. Experiments were also performed for pressure drop measurements and for flow visualization and the results were compared with the numerical predictions.

A Numerical Study of Flow and Heat Transfer in a Smooth and Ribbed U-Duct With and Without Rotation

2000 ◽  
Vol 123 (2) ◽  
pp. 219-232 ◽  
Author(s):  
Y.-L. Lin ◽  
T. I.-P. Shih ◽  
M. A. Stephens ◽  
M. K. Chyu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Mach Number ◽  
Vector Fields ◽  
Numerical Study ◽  
Density Ratio ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Flow And Heat Transfer

Computations were performed to study the three-dimensional flow and heat transfer in a U-shaped duct of square cross section under rotating and non-rotating conditions. The parameters investigated were two rotation numbers (0, 0.24) and smooth versus ribbed walls at a Reynolds number of 25,000, a density ratio of 0.13, and an inlet Mach number of 0.05. Results are presented for streamlines, velocity vector fields, and contours of Mach number, pressure, temperature, and Nusselt numbers. These results show how fluid flow in a U-duct evolves from a unidirectional one to one with convoluted secondary flows because of Coriolis force, centrifugal buoyancy, staggered inclined ribs, and a 180 deg bend. These results also show how the nature of the fluid flow affects surface heat transfer. The computations are based on the ensemble-averaged conservation equations of mass, momentum (compressible Navier-Stokes), and energy closed by the low Reynolds number SST turbulence model. Solutions were generated by a cell-centered finite-volume method that uses second-order flux-difference splitting and a diagonalized alternating-direction implicit scheme with local time stepping and V-cycle multigrid.

Numerical investigation of fluid flow structure and heat transfer in a passage with continuous and truncated V-shaped ribs

2015 ◽  
Vol 25 (1) ◽  
pp. 171-189 ◽  
Author(s):  
Shian Li ◽  
Gongnan Xie ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Content Type ◽  
Flow And Heat Transfer

Purpose – The employment of continuous ribs in a passage involves a noticeable pressure drop penalty, while other studies have shown that truncated ribs may provide a potential to reduce the pressure drop while keeping a significant heat transfer enhancement. The purpose of this paper is to perform computer-aided simulations of turbulent flow and heat transfer of a rectangular cooling passage with continuous or truncated 45-deg V-shaped ribs on opposite walls. Design/methodology/approach – Computational fluid dynamics technique is used to study the fluid flow and heat transfer characteristics in a three-dimensional rectangular passage with continuous and truncated V-shaped ribs. Findings – The inlet Reynolds number, based on the hydraulic diameter, is ranged from 12,000 to 60,000 and a low-Re k-e model is selected for the turbulent computations. The local flow structure and heat transfer in the internal cooling passages are presented and the thermal performances of the ribbed passages are compared. It is found that the passage with truncated V-shaped ribs on opposite walls provides nearly equivalent heat transfer enhancement with a lower (about 17 percent at high Reynolds number of 60,000) pressure loss compared to a passage with continuous V-shaped ribs or continuous transversal ribs. Research limitations/implications – The fluid is incompressible with constant thermophysical properties and the flow is steady. The passage is stationary. Practical implications – New and additional data will be helpful in the design of ribbed passages to achieve a good thermal performance. Originality/value – The results imply that truncated V-shaped ribs are very effective in improving the thermal performance and thus are suggested to be applied in gas turbine blade internal cooling, especially at high velocity or Reynolds number.

Heat and Fluid Flow Within an Anisotropic Porous Medium

2002 ◽  
Vol 124 (4) ◽  
pp. 746-753 ◽  
Author(s):  
A. Nakayama ◽  
F. Kuwahara ◽  
T. Umemoto ◽  
T. Hayashi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Permeability Tensor ◽  
Interfacial Heat Transfer Coefficient ◽  
Flow Angle ◽  
Number Range ◽  
Flow And Heat Transfer ◽  
Degree Of Anisotropy ◽  
Anisotropic Porous Medium

A numerical experiment at a pore scale using a full set of Navier-Stokes and energy equations has been conducted to simulate laminar fluid flow and heat transfer through an anisotropic porous medium. A collection of square rods placed in an infinite two-dimensional space has been proposed as a numerical model of microscopic porous structure. The degree of anisotropy was varied by changing the transverse center-to-center distance with the longitudinal center-to-center distance being fixed. Extensive calculations were carried out for various sets of the macroscopic flow angle, Reynolds number and degree of anisotropy. The numerical results thus obtained were integrated over a space to determine the permeability tensor, Forchheimer tensor and directional interfacial heat transfer coefficient. It has been found that the principal axes of the permeability tensor (which controls the viscous drag in the low Reynolds number range) differ significantly from those of the Forchheimer tensor (which controls the form drag in the high Reynolds number range), The study also reveals that the variation of the directional interfacial heat transfer coefficient with respect to the macroscopic flow angle is analogous to that of the directional permeability. Simple subscale model equations for the permeability tensor, Forchheimer tensor and directional Nusselt number have been proposed for possible applications of VAT to investigate flow and heat transfer within complex heat and fluid flow equipment consisting of small scale elements.

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