Nonlinear Characteristics of a Sudden Expansion Followed by Sudden Contraction Channel

2016 ◽  
Author(s):  
Keyan Liu ◽  
Mo Yang ◽  
Yuwen Zhang ◽  
Chunyun Shen
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Temperature Field ◽  
Simple Algorithm ◽  
Sudden Expansion ◽  
Nonlinear Characteristics ◽  
Classic Problem ◽  
Flow And Heat Transfer ◽  
Quick Scheme ◽  
Sudden Contraction

The flow and heat transfer in a sudden expansion followed by sudden contraction channel are widely applied in industry, and it is also a classic problem for theoretical study. In this article, the SIMPLE algorithm with QUICK scheme were used to study the flow and heat transfer in a sudden expansion followed by sudden contraction channel. The nonlinear characteristics and temperature field were investigated for various Reynolds number and geometrical dimension. The results show that the temperature field evolves from symmetric to asymmetric state with the increasing Re. When Re ≥ Rec, the flow loses stability and from symmetric to asymmetric via a symmetry-breaking bifurcation; when the Reynolds number continues to increase, the fluid flow and heat transfer oscillation. The nonlinear characteristics of flow and heat transfer within the channel is further analyzed.

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.

Oscillation and Chaos in Combined Heat Transfer by Natural Convection, Conduction, and Surface Radiation in an Open Cavity

2012 ◽  
Vol 134 (9) ◽  
Author(s):  
Zhiyun Wang ◽  
Mo Yang ◽  
Ling Li ◽  
Yuwen Zhang
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Simple Algorithm ◽  
Open Cavity ◽  
Surface Radiation ◽  
Bottom Surface ◽  
Thermal Plumes ◽  
Flow And Heat Transfer ◽  
Quick Scheme ◽  
Combined Heat Transfer

Combined heat transfer by natural convection, conduction, and surface radiation in an open cavity is solved numerically by employing SIMPLE algorithm with QUICK scheme. The unsteady-state flow and heat transfer exhibited periodic oscillating or chaotic behaviors due to formation of the thermal plumes at the bottom wall. If the formation of thermal plumes is periodic, the oscillations of flow and heat transfer are also periodic. On the other hand, chaotic oscillations of flow and heat transfer can be observed when the formation of thermal plumes at the bottom surface is chaotic.

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 The Effect of Nanoparticle Shape and Microchannel Geometry on Fluid Flow and Heat Transfer in a Porous Microchannel

Symmetry ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 591 ◽  
Author(s):  
Zahra Abdelmalek ◽  
Annunziata D’Orazio ◽  
Arash Karimipour
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Cross Sections ◽  
Volume Fraction ◽  
Simple Algorithm ◽  
Maximum Heat ◽  
Nanoparticle Shape ◽  
Flow And Heat Transfer ◽  
Maximum Heat Transfer

Microchannels are widely used in electrical and medical industries to improve the heat transfer of the cooling devices. In this paper, the fluid flow and heat transfer of water–Al2O3 nanofluids (NF) were numerically investigated considering the nanoparticle shape and different cross-sections of a porous microchannel. Spherical, cubic, and cylindrical shapes of the nanoparticle as well as circular, square, and triangular cross-sections of the microchannel were considered in the simulation. The finite volume method and the SIMPLE algorithm have been employed to solve the conservation equations numerically, and the k-ε turbulence model has been used to simulate the turbulence fluid flow. The models were simulated at Reynolds number ranging from 3000 to 9000, the nanoparticle volume fraction ranging from 1 to 3, and a porosity coefficient of 0.7. The results indicate that the average Nusselt number (Nuave) increases and the friction coefficient decreases with an increment in the Re for all cases. In addition, the rate of heat transfer in microchannels with triangular and circular cross-sections is reduced with growing Re values and concentration. The spherical nanoparticle leads to maximum heat transfer in the circular and triangular cross-sections. The heat transfer growth for these two cases are about 102.5% and 162.7%, respectively, which were obtained at a Reynolds number and concentration of 9000 and 3%, respectively. However, in the square cross-section, the maximum heat transfer increment was obtained using cylindrical nanoparticles, and it is equal to 80.2%.

scholarly journals A detailed analysis of flow and heat transfer characteristics under a turbulent intermittent jet impingement on a concave surface

2021 ◽  
pp. 334-334
Author(s):  
Ali Hajimohammadi ◽  
Mehran Zargarabadi ◽  
Javad Mohammadpour
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Average Nusselt Number ◽  
Computational Study ◽  
Control Volume ◽  
Simple Algorithm ◽  
Jet Impingement ◽  
Concave Surface ◽  
Flow And Heat Transfer

A computational study is carried out of the three-dimensional flow field and heat transfer under a turbulent intermittent circular jet impingement on a concave surface. The control-volume procedure with the SIMPLE algorithm is employed to solve the unsteady RANS (use full form) equations. The RNG k-? model is implemented to simulate turbulence due to its success in predicting similar flows. The numerical results are validated by comparing them with the experimental data. The effects of jet Reynolds number and oscillation frequency on the flow and heat transfer are evaluated. The profiles of instantaneous and time-averaged Nusselt numbers exhibit different trends in axial (x) and circumferential (s) directions. It is found that increasing frequency from 50 to 200 Hz results in considerable time-averaged Nusselt number enhancement in both axial and curvature directions. The intermittent jet at a frequency of 200 Hz enhances the total average Nusselt number by 51.4%, 40%, and 33.7% compared to the steady jet values at jet Reynolds numbers of 10000, 23000, and 40000, respectively. In addition, a correlation for the average Nusselt number is proposed depending on the Reynolds number and the Strouhal number.

LES Simulations of Rotating Two-Pass Ribbed Duct With Coriolis and Centrifugal Buoyancy Forces at Re=100,000

2016 ◽  
Author(s):  
Cody Dowd ◽  
Danesh Tafti
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Large Eddy Simulations ◽  
The Other ◽  
Coriolis Forces ◽  
Flow And Heat Transfer ◽  
Large Eddy ◽  
Buoyancy Forces ◽  
First Pass ◽  
Duct Geometry

The focus of this research is to predict the flow and heat transfer in a rotating two-pass duct geometry with staggered ribs using Large-Eddy Simulations (LES). The geometry consists of a U-Bend with 17 ribs in each pass. The ribs are staggered with an e/Dh = 0.1 and P/e = 10. LES is performed at a Reynolds number of 100,000, a rotation number of 0.2 and buoyancy parameters (Bo) of 0.5 and 1.0. The effects of Coriolis forces and centrifugal buoyancy are isolated and studied individually. In all cases it is found that increasing Bo from 0.5 to 1.0 at Ro = 0.2 has little impact on heat transfer. It is found that in the first pass, the heat transfer is quite receptive to Coriolis forces which augment and attenuate heat transfer at the trailing and leading walls, respectively. Centrifugal buoyancy, on the other hand has a bigger effect in augmenting heat transfer at the trailing wall than in attenuating heat transfer at the leading wall. On contrary, it aids heat transfer in the second half of the first pass at the leading wall by energizing the flow near the wall. The heat transfer in the second pass is dominated by the highly turbulent flow exiting the bend. Coriolis forces have no impact on the augmentation of heat transfer on the leading wall till the second half of the passage whereas it attenuates heat transfer at the trailing wall as soon as the flow exits the bend. Contrary to phenomenological arguments, inclusion of centrifugal buoyancy augments heat transfer over Coriolis forces alone on both the leading and trailing walls of the second pass.

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.

scholarly journals Effect of the size of graded baffles on the performance of channel heat exchangers

2020 ◽  
Vol 24 (2 Part A) ◽  
pp. 767-775 ◽  
Author(s):  
Djamel Sahel ◽  
Houari Ameur ◽  
Touhami Baki
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Exchangers ◽  
Computer Code ◽  
Channel Length ◽  
Heat Transfer Characteristics ◽  
Enhancement Of Heat Transfer ◽  
Transfer Rates ◽  
Flow And Heat Transfer ◽  
Friction Factors

The baffling technique is well-known for its efficiency in terms of enhancement of heat transfer rates throught channels. However, the baffles insert is accompanied by an increase in the friction factor. This issue remains a great challenge for the designers of heat exchangers. To overcome this issue, we suggest in the present paper a new design of baffles which is here called graded baffle-design. The baffles have an up- or down-graded height along the channel length. This geometry is characterized by two ratios: up-graded baffle ratio and down-graded baffle ratio which are varied from 0-0.08. For a range of Reynolds number varying from 104 to 2 ? 104, the turbulent flow and heat transfer characteristics of a heat exchanger channel are numerically studied by the computer code FLUENT. The obtained results revealed an enhancement in the thermohydraulic performance offered by the new suggested design. For the channel with a down-graded baffle ratio equal to 0.08, the friction factors decreased by 4-8%

scholarly journals Discussion on improved method of turbulence model for supercritical water flow and heat transfer

2020 ◽  
Vol 24 (5 Part A) ◽  
pp. 2729-2741
Author(s):  
Zhenchuan Wang ◽  
Guoli Qi ◽  
Meijun Li
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Turbulence Model ◽  
Buoyancy Effect ◽  
Improved Method ◽  
Production Term ◽  
Flow And Heat Transfer ◽  
Effect Model

The turbulence model fails in supercritical fluid-flow and heat transfer simulation, owing to the drastic change of thermal properties. The inappropriate buoyancy effect model and the improper turbulent Prandtl number model are several of these factors lead to the original low-Reynolds number turbulence model unable to predict the wall temperature for vertically heated tubes under the deteriorate heat transfer conditions. This paper proposed a simplified improved method to modify the turbulence model, using the generalized gradient diffusion hypothesis approximation model for the production term of the turbulent kinetic energy due to the buoyancy effect, using a turbulence Prandtl number model for the turbulent thermal diffusivity instead of the constant number. A better agreement was accomplished by the improved turbulence model compared with the experimental data. The main reason for the over-predicted wall temperature by the original turbulence model is the misuse of the buoyancy effect model. In the improved model, the production term of the turbulent kinetic energy is much higher than the results calculated by the original turbulence model, especially in the boundary-layer. A more accurate model for the production term of the turbulent kinetic energy is the main direction of further modification for the low Reynolds number turbulence model.

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