Numerical Simulation of Heat and Flow of Liquid Through Minichannels

2006 ◽  
Author(s):  
Heming Yun ◽  
Lin Cheng ◽  
Liqiu Wang ◽  
Shusheng Zhang
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Region ◽  
Resistance Coefficient ◽  
Equivalent Diameter ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Simulation Results

In this paper the heat transfer and flow in minichannels was investigated by using CFD methods. The numerical simulation results show that the equivalent diameter has little influence on resistance coefficient in the laminar region. In the turbulent flow region, the resistance coefficient decreases with the increasing of the equivalent diameter. In all computation region, the friction factors increases with increasing of the aspect ratio, and the friction factors decreases obviously with increasing of Reynolds number. The numerical simulation results show that the equivalent diameter has little influence on heat transfer Nusselt number in laminar flow region. In turbulent region, the Nusselt numbers are larger than those in macro channels. The Nusselt numbers increase with decreasing of equivalent diameter and the aspect ratio for a given Reynolds number.

Spatially Resolved Heat Transfer and Friction Factors in a Rectangular Channel With 45-Deg Angled Crossed-Rib Turbulators

2003 ◽  
Vol 125 (3) ◽  
pp. 575-584 ◽  
Author(s):  
P. M. Ligrani ◽  
G. I. Mahmood
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Rectangular Channel ◽  
Test Surface ◽  
Spatially Resolved ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Smooth Channel ◽  
Rib Turbulators

Spatially resolved Nusselt numbers, spatially averaged Nusselt numbers, and friction factors are presented for a stationary channel with an aspect ratio of 4 and angled rib turbulators inclined at 45 deg with perpendicular orientations on two opposite surfaces. Results are given at different Reynolds numbers based on channel height from 10,000 to 83,700. The ratio of rib height to hydraulic diameter is .078, the rib pitch-to-height ratio is 10, and the blockage provided by the ribs is 25% of the channel cross-sectional area. Nusselt numbers are given both with and without three-dimensional conduction considered within the acrylic test surface. In both cases, spatially resolved local Nusselt numbers are highest on tops of the rib turbulators, with lower magnitudes on flat surfaces between the ribs, where regions of flow separation and shear layer reattachment have pronounced influences on local surface heat transfer behavior. The augmented local and spatially averaged Nusselt number ratios (rib turbulator Nusselt numbers normalized by values measured in a smooth channel) vary locally on the rib tops as Reynolds number increases. Nusselt number ratios decrease on the flat regions away from the ribs, especially at locations just downstream of the ribs, as Reynolds number increases. When adjusted to account for conduction along and within the test surface, Nusselt number ratios show different quantitative variations (with location along the test surface), compared to variations when no conduction is included. Changes include: (i) decreased local Nusselt number ratios along the central part of each rib top surface as heat transfer from the sides of each rib becomes larger, and (ii) Nusselt number ratio decreases near corners, where each rib joins the flat part of the test surface, especially on the downstream side of each rib. With no conduction along and within the test surface (and variable heat flux assumed into the air stream), globally-averaged Nusselt number ratios vary from 2.92 to 1.64 as Reynolds number increases from 10,000 to 83,700. Corresponding thermal performance parameters also decrease as Reynolds number increases over this range, with values in approximate agreement with data measured by other investigators in a square channel also with 45 deg oriented ribs.

Numerical Simulation of Nonlinear Flow and Heat Transfer in a Sudden Expansion and Contraction Channel

2016 ◽  
Author(s):  
M. Yang ◽  
L. Q. Yang ◽  
W. Lu ◽  
L. Li ◽  
Q. X. Liu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Reynolds Number ◽  
Rectangular Channel ◽  
Flow Region ◽  
Nonlinear Flow ◽  
Forced Flow ◽  
Sudden Expansion ◽  
Symmetric State ◽  
Flow And Heat Transfer

Numerical simulation of forced flow in sudden-expansion followed by sudden-contraction rectangular channel was presented for the whole flow region. The nonlinear flow and heat transfer characteristics were investigated by various Reynolds number and geometrical dimension and the critical Reynolds numbers under different conditions have been calculated. The results show flow and heat transfer from symmetric state to asymmetric state with the increase of Re. When Re<Rec (critical Reynolds number for flow transformation), the symmetric state is stable. On the other hand, when Re ≥Rec, the flow loses stability and from symmetric to asymmetric via a symmetry-breaking bifurcation. And the heat transfer performance have relevant characteristics as fluid flow.

Direct Numerical Simulation of Forced Convective Heat Transfer From a Heated Rotating Sphere in Laminar Flows

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Zhi-Gang Feng
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Direct Numerical Simulation ◽  
Density Function ◽  
Heat Diffusion ◽  
Rotating Sphere ◽  
Nusselt Numbers ◽  
Flow Reynolds Number ◽  
The Mean ◽  
Simulation Results

The laminar forced convection of a heated rotating sphere in air has been studied using a three-dimensional immersed boundary based direct numerical simulation method. A regular Eulerian grid is used to solve the modified momentum and energy equations for the entire flow region simultaneously. In the region that is occupied by the rotating sphere, a moving Lagrangian grid is used, which tracks the rotational motion of the particle. A force density function or an energy density function is introduced to represent the momentum interaction or thermal interaction between the sphere and fluid. This numerical method is validated by comparing simulation results with analytical solutions of heat diffusion problem and other published experimental data. The flow structures and the mean Nusselt numbers for flow Reynolds number ranging from 0 to 1000 are obtained. We compared our simulation results of the mean Nusselt numbers with the correlations from the literature and found a good agreement for flow Reynolds number greater than 500; however, a significant discrepancy arises at flow Reynolds number below 500. This leads us to develop a new equation that correlates the mean Nusselt number of a heated rotating sphere for flows of 0≤Re≤500.

Numerical Simulation and Optimization of Heat Transfer in Microchannel by Implementing Nonuniform Electrokinetic Forces

2008 ◽  
Author(s):  
V. Esfahanian ◽  
F. Kowsary ◽  
N. Noroozi ◽  
M. Rezaei Barmi
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Reynolds Number ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Flux Boundary Condition ◽  
Simulation And Optimization ◽  
Nusselt Numbers ◽  
Wall Potential ◽  
Uniform Wall

The increasing power dissipation and decreasing dimensions of microelectronic devices have emphasized the demand for extremely efficient compact cooling technology. Microchannel heat sinks are of particular interest due to high rates of heat transfer, which have become known as one of the effective cooling technologies. In the present work, numerical simulation of incompressible flow in two dimensional microchannels by implementing nonuniform electrokinetic forces is performed using finite volume method. The velocity field and the heat transfer rate are influenced by the wall potential variations through the microchannel. Nondimensional parameters of heat transfer and fluid flows, Debay Huckel length, microchannel size and wall charge potential distribution, have major roles in this investigation. For fixed values of Reynolds number and microchannel size, the patterns of wall potentials are optimized to enhance the heat transfer rate. Velocity profiles are computed and temperature distribution and Nusselt number are obtained for uniform wall heat flux boundary condition. Average and local Nusselt numbers are illustrated for different wall potential configurations and Reynolds number. Velocity vectors and pressure drop are presented for different zeta potentials and Reynolds numbers. Finally, results of nonuniform electrical force are compared to uniform ones.

Periodic Fluid Flow and Heat Transfer in a Square Cavity Due to an Insulated or Isothermal Rotating Rectangular Object

2009 ◽  
Author(s):  
Y.-C. Shih ◽  
J. M. Khodadadi ◽  
H.-W. Dai ◽  
Liwu Fan
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Angular Velocity ◽  
Aspect Ratio ◽  
Reynolds Numbers ◽  
Constant Angular Velocity ◽  
Square Cavity ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Aspect Ratios

Computational analysis of transient phenomenon followed by the periodic state of laminar flow and heat transfer due to a rectangular rotating object in a square cavity is investigated. A finite-volume-based fixed-grid/sliding mesh computational methodology utilizing primitive variables is used. Rectangular rotating objects with different aspect ratios (AR = 1, 2, 3, 4) are placed in the middle of a square cavity. The motionless object is set in rotation at time t = 0 with a constant angular velocity. For the insulated and isothermal objects, the cavity is maintained as differentially-heated and isothermal enclosures, respectively. Natural convection heat transfer is neglected. For a given shape of the object and a constant angular velocity, a range of rotating Reynolds numbers are covered for a Pr = 5 fluid. The Reynolds numbers were selected so that the flow field is not affected by the Taylor instabilities (Ta &lt; 1750). The periodic flow field, the interaction of the rotating objects with the recirculating vortices at the four corners and the periodic channelling effect of the traversing vertices are clearly elucidated. The corresponding thermal fields in relation to the evolving flow patterns and the skewness of the temperature contours in comparison to conduction-only case were discussed. The skewness is observed to become more marked as the Reynolds number is lowered. Transient variations of the average Nusselt numbers of the respective systems show that for high Re numbers, a quasi-periodic behavior due to the onset of the Taylor instabilities is dominant, whereas for low Re numbers, periodicity of the system is clearly observed. Time-integrated average Nusselt numbers of the insulated and isothermal object systems were correlated to the rotational Reynolds number and the aspect ratio of the rectangle. For high Re numbers, the performance of the system is independent of the aspect ratio. On the other hand, with lowering of the hydraulic diameter (i.e. bigger objects), objects with the highest and lowest aspect ratios exhibit the highest and lowest heat transfer, respectively. High intensity of the periodic channelling and not its frequency are identified as the cause of the observed enhancement.

scholarly journals HEAT EXCHANGE OF ELECTRIC CONDUCTIVE LIQUID AT LARGE VALUES OF THE REYNOLD'S MAGNETIC NUMBER

2021 ◽  
pp. 12-22
Author(s):  
С.В. Соловьев ◽  
Т.С. Соловьева
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Heat Exchange ◽  
Spherical Layer ◽  
Magnetic Reynolds Number ◽  
Electrically Conductive ◽  
Conductive Liquid ◽  
Nusselt Numbers

Представлены результаты численного моделирования нестационарного конвективного теплообмена и магнитной гидродинамики электропроводной жидкости в сферическом слое при граничных условиях для температуры первого рода. Исследовано влияние величины магнитного числа Рейнольдса на эволюцию структуры течения жидкости, поле температуры, магнитной индукции и распределение чисел Нуссельта. The results of numerical simulation of unsteady convective heat transfer and magneto hydrodynamics of an electrically conductive fluid in a spherical layer under boundary conditions for a temperature of the first kind are presented. The influence of the value of the magnetic Reynolds number on the evolution of the structure of the fluid flow, the field of temperature, magnetic induction and the distribution of Nusselt numbers is investigated.

scholarly journals HEAT EXCHANGE OF ELECTRIC CONDUCTIVE LIQUID WHEN DEPLOYING THE HEAT FROM THE INNER SURFACE OF THE SPHERICAL LAYER AT SMALL VALUES OF THE REYNOLD'S MAGNETIC NUMBER

2021 ◽  
pp. 212-219
Author(s):  
С.В. Соловьев
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Reynolds Number ◽  
Spherical Layer ◽  
Magnetic Reynolds Number ◽  
Unsteady Heat Transfer ◽  
Electrically Conductive ◽  
Conductive Liquid ◽  
Nusselt Numbers ◽  
Inner Surface

Представлены результаты численного моделирования нестационарного теплообмена и магнитной гидродинамики электропроводной жидкости в сферическом слое. Исследовано влияние малых значений магнитного числа Рейнольдса и диссипации джоулевой теплоты на эволюцию структуры течения жидкости, поле температуры, магнитной индукции и распределение чисел Нуссельта. The results of numerical simulation of unsteady heat transfer and magneto hydrodynamics of an electrically conductive fluid in a spherical layer are presented. The influence of small values ​​of the magnetic Reynolds number and dissipation of Joule heat on the evolution of the structure of the fluid flow, the field of temperature, magnetic induction and the distribution of Nusselt numbers is investigated.

scholarly journals Convective Heat Transfer in a High Aspect Ratio Minichannel Heated on One Side

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Eric C. Forrest ◽  
Lin-Wen Hu ◽  
Jacopo Buongiorno ◽  
Thomas J. McKrell
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Prandtl Number ◽  
High Aspect Ratio ◽  
Nusselt Numbers ◽  
Friction Pressure ◽  
Friction Pressure Drop ◽  
Asymmetric Heating

Experimental results are presented for single-phase heat transfer in a narrow rectangular minichannel heated on one side. The aspect ratio and gap thickness of the test channel were 29:1 and 1.96 mm, respectively. Friction pressure drop and Nusselt numbers are reported for the transition and fully turbulent flow regimes, with Prandtl numbers ranging from 2.2 to 5.4. Turbulent friction pressure drop for the high aspect ratio channel is well-correlated by the Blasius solution when a modified Reynolds number, based upon a laminar equivalent diameter, is utilized. The critical Reynolds number for the channel falls between 3500 and 4000, with Nusselt numbers in the transition regime being reasonably predicted by Gnielinski's correlation. The dependence of the heat transfer coefficient on the Prandtl number is larger than that predicted by circular tube correlations, and is likely a result of the asymmetric heating. The problem of asymmetric heating condition is approached theoretically using a boundary layer analysis with a two-region wall layer model, similar to that originally proposed by Prandtl. The analysis clarifies the influence of asymmetric heating on the Nusselt number and correctly predicts the experimentally observed trend with Prandtl number. A semi-analytic correlation is derived from the analysis that accounts for the effect of aspect ratio and asymmetric heating, and is shown to predict the experimental results of this study with a mean absolute error (MAE) of less than 5% for 4000 < Re < 70,000.

Corrugated-Duct Heat Transfer, Pressure Drop, and Flow Visualization

1982 ◽  
Vol 104 (3) ◽  
pp. 410-416 ◽  
Author(s):  
J. E. O’Brien ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Prandtl Number ◽  
Flow Visualization ◽  
Convection Heat Transfer ◽  
Transfer Coefficients ◽  
Complex Flow ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Corrugated Duct

Experiments were performed to determine forced convection heat-transfer coefficients and friction factors for flow in a corrugated duct. The corrugation angle was 30 deg and the interwall spacing was equal to the corrugation height. The Reynolds number, based on the duct hydraulic diameter, ranged from 1500 to 25,000, and the Prandtl number ranged from 4 to 8 (water). Flow visualization, using the oil-lampblack technique, revealed a highly complex flow pattern, including large zones of recirculation adjacent to the rearward-facing corrugation facets. Nusselt numbers in the periodic fully developed regime, when correlated, resulted in a Reynolds-number dependence of Re0.614 and a Prandtl-number dependence of Pr0.34. The enhancement of heat transfer as compared to a conventional parallel-plate channel was about a factor of 2.5. Friction factors obtained from measured axial pressure distributions were virtually independent of the Reynolds number and equal to 0.57, a value appreciably greater than that for unidirectional duct flows.

Influence of Rotating Directions on Hydrothermal Characteristics of a Two-Pass Parallelogram Channel With Detached Transverse Ribs

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Tong Miin Liou ◽  
Shyy Woei Chang ◽  
Chih Yung Huang ◽  
I An Lan ◽  
Shu Po Chan
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Density Ratio ◽  
Number Density ◽  
Performance Factors ◽  
Ribbed Channel ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Static Channel

The detailed Nusselt number distributions on leading and trailing endwalls together with the Fanning friction factors of a rotating two-pass parallelogram ribbed channel are simultaneously measured under forward and backward rotations. The tested Reynolds number, rotation number, density ratio, and buoyancy number are respectively in the ranges of 5000 < Re < 15,000, 0 < Ro < 0.3, 0.044<Δρ/ρ < 0.2, and 0 < Bu < 0.142. The area-averaged leading and trailing Nusselt numbers at forward rotations are 0.69–1.77 and 0.85–1.98 relative to the static-channel Nusselt number references, respectively. With backward rotations, the ratios of regionally averaged Nusselt numbers between rotating and static channels for leading and trailing endwalls fall in the respective range to 0.86–2 and 0.91–1.76. At both forward and backward rotations, all the f factors over leading endwall (LE) and trailing endwall (TE) are elevated from the static-channel levels and increased by increasing Ro. Channel averaged f/f0 ratios are respectively raised to 1.21–2.21 and 1.21–2.1 at forward and backward rotations. As the heat transfer enhancements (HTE) attributed to the presence of detached transverse ribs taking precedence of the accompanying f augmentations, all the thermal performance factors are above unity in the range of 1.26–2.94. Relative to the similar rotating two-pass parallelogram channel with attached 90 deg ribs, the detached ribs generate the higher degrees of heat transfer enhancements with the larger extents of f augmentations.

Sign in / Sign up

Export Citation Format

Share Document