scholarly journals Numerical Study on the Effect of the Pipe Groove Height and Pitch on the Flow Characteristics of Corrugated Pipe

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2614
Author(s):  
Ki-Bea Hong ◽  
Dong-Woo Kim ◽  
Jihyun Kwark ◽  
Jun-Seok Nam ◽  
Hong-Sun Ryou
Keyword(s):  
Aspect Ratio ◽  
Velocity Distribution ◽  
Friction Factor ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Main Flow ◽  
Secondary Vortex

For corrugated pipes with a square groove, it is known that there is no interaction between the main flow and groove flow when the aspect ratio is less than four. When the groove length and height are different, the interaction occurs in the pipe. In previous studies, it was investigated whether this interaction is dependent on groove length. However, when changing the groove height, the shape of the vortex generated inside the groove changes, which may cause the interaction to occur. Therefore, in this paper the interaction between the main and groove flow of corrugated pipes is investigated when changing both groove height as well as groove pitch, corresponding to an aspect ratio of less than four. For the groove height, the flow out of the groove after impingement changes with the shape of the secondary vortex in the groove. This flow deforms the velocity distribution in the main flow, and thus the friction factor is different. For the groove pitch, there is no difference in v-velocity distribution at the interface at the 5th and 20th groove. This means there is no interaction between the grooves, and, the friction factor differs as the number of grooves differs.

scholarly journals 2D Numerical Study of Heat Transfer Enhancement Using Fish-Tail Locomotion Vortex Generators

2021 ◽  
Vol 8 (3) ◽  
pp. 386-392
Author(s):  
Ahmed Hashim Yousif ◽  
Hakim T. Kadhim ◽  
Kadhim K. Idan Al-Chlaihawi
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Flow Characteristics ◽  
Vortex Generators ◽  
Transfer Enhancement ◽  
Number Range ◽  
Maximum Value ◽  
Fluid Flow Characteristics

In this paper, a numerical simulation is performed to study the effect of two types of concave vortex generators (VGs), arranged as fish-tail locomotion in a rectangular channel. The heat transfer and fluid flow characteristics with and without VGs are examined over the Reynolds number range 200≤Re≤2200.The two proposed types of the VGs are selected based on the speed of the fish movement which is arranged in different distances between them (d/H=0.6, 1, 1.3). The results show that the use of VGs can significantly enhance the heat transfer rate, but also increases the friction factor. The heat transfer performance is enhanced by (4-21.1%) reaching the maximum value by using the first type of the VGs at (d/H=1.3) due to better mixing of secondary flow and the new arrangement of the VGs which lead to decreasing the friction factor with an easy flow of fluid.

Bistability and hysteresis induced by form drag in nonlinear subcritical and supercritical double-diffusive Lapwood convection in shallow porous enclosures

2017 ◽  
Vol 812 ◽  
pp. 463-500 ◽  
Author(s):  
Redha Rebhi ◽  
Mahmoud Mamou ◽  
Patrick Vasseur
Keyword(s):  
Rayleigh Number ◽  
Aspect Ratio ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Lewis Number ◽  
Linear Stability Theory ◽  
Nonlinear Behaviour ◽  
Form Drag ◽  
Solute Fluxes ◽  
Double Diffusive

This paper considers natural Lapwood convection in a shallow porous cavity filled with a binary fluid. The investigation is mainly focused on the nonlinear behaviour of subcritical convection and the bistability phenomenon caused by the combined effects of porous medium form drag and double-diffusive convection. The Dupuit–Darcy model, which includes the effect of the form drag at high Reynolds flow, is used to describe the convective flow in the porous matrix. The enclosure is subject to vertical temperature and concentration gradients. The governing parameters of the problem under study are the Rayleigh number, $R_{T}$, the buoyancy ratio, $\unicode[STIX]{x1D711}$, the Lewis number, $Le$, the form drag coefficient, ($1/P_{r}^{\ast }$), where $P_{r}^{\ast }$ is a modified Prandtl number, and the aspect ratio of the cavity, $A$. An analytical solution, valid for shallow enclosures ($A\gg 1$), is derived on the basis of the parallel flow approximation. Among other things, this work focuses on the effects of the form drag parameter on the convective flows that occur when the thermal and solutal buoyancy forces are opposing each other. For this situation, in the absence of the form drag effect, the onset of motion is known to occur at a subcritical Rayleigh number, $R_{TC}^{sub}$, which depends upon $\unicode[STIX]{x1D711}$ and $Le$ only. The effects of $P_{r}^{\ast }$ on $R_{TC}^{sub}$ and on the subsequent convective heat and mass transfer rates are found to be significant. A new bistability phenomenon arises when the onset of subcritical convection is shifted close to or beyond the threshold of supercritical convection, whether heating or cooling isothermally or upon applying constant heat and solute fluxes, regardless of the enclosure aspect ratio value. It is demonstrated, on the basis of linear stability theory, that the form drag parameter has a stabilizing effect and considerably affects the threshold for Hopf bifurcation, $R_{TC}^{Hopf}$, which characterizes the transition from steady to unsteady convection. In the range of governing parameters considered in this study, the heat, solute and flow characteristics predicted by the analytical model are found to agree well with the numerical study of the full governing equations.

Numerical study on significance of wave amplitude, wavelength and aspect ratio on heat transfer and fluid flow characteristics in circular wavy MC heat sink design

2021 ◽  
pp. 095440622198937
Author(s):  
Valaparla Ranjith Kumar ◽  
Karthik Balasubramanian ◽  
K Kiran Kumar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fluid Flow ◽  
Aspect Ratio ◽  
Wave Amplitude ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Uniform Heat Flux ◽  
Uniform Heat ◽  
Fluid Flow Characteristics

In this study, hydrothermal characteristics in a circular wavy microchannel (CWMC) design under laminar flow conditions with uniform heat flux is numerically studied. Parametric studies in an innovative CWMC design were carried out at various wave amplitudes, wavelengths and aspect ratios. Three dimensional numerical study was performed in the Reynolds number (Re) range from 100 to 300 with uniform heat flux (50 W/cm2) applied at bottom of the channel, treating copper as channel material and water as working fluid. The obtained results were compared to sinusoidal wavy microchannel (SWMC).The results showed that heat transfer and fluid flow characteristics were significantly influenced by wave amplitude, wavelength and aspect ratio. Velocity vectors and contours were presented to understand the heat transfer and fluid flow characteristics. Stream-wise local Nusselt number, overall performance factor, span-wise velocity and temperature variation are also presented. It is concluded that CWMC with higher wave amplitude, smaller wave length and smaller aspect ratio gives higher heat transfer augmentation with corresponding pressure drop penalty.

Frictional Characteristics of Microchannel Gas Flow

2003 ◽  
Author(s):  
Abdullahel Bari ◽  
Jae-Mo Koo ◽  
Linan Jiang ◽  
Jay Paidipati ◽  
Kenneth E. Goodson
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Friction Factor ◽  
Gas Flow ◽  
Flow Characteristics ◽  
Hydraulic Diameter ◽  
Transition To Turbulence ◽  
Gas Flows ◽  
Design And Development ◽  
Predicted Values

The improved rates of heat transfer in microchannel gas flows are promising for the design and development of microfluidic systems. This research focuses on the flow characteristics of air in rectangular micro/minichannels at moderate velocities (∼100 m/sec). The 50.8 mm long channels vary from approximately 266 μm to 1090 μm in hydraulic diameter, and the aspect ratio ranges from 0.1 to 0.75. The value of Re ranged from 250 to 4300, with the intention of studying the transition to turbulence. The friction factor is found to be higher than predicted values for Re < 1400 and lower when Re > 1400 suggesting earlier transition to turbulence.

Numerical Study of Friction Factor and Heat Transfer Characteristics for Single-Phase Turbulent Flow in Tubes with Helical Micro-Fins

2012 ◽  
Vol 59 (4) ◽  
pp. 469-485 ◽  
Author(s):  
Piotr Jasiński
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Numerical Simulations ◽  
Friction Factor ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Thermal Characteristics ◽  
Pressure Drops ◽  
Experimental Stand ◽  
Helical Angle

The paper presents a numerical study on the heat transfer and pressure drop, related to flow in pipes with helical micro-fins. For all tested geometries, one applied a constant wall heat flux and fully developed 3D turbulent flow conditions. The influence of the angle of micro fins (referred to the tube axis) on thermal-flow characteristics were tested. The value of this angle was varied - with a step of 10 degrees - from 0 to 90 degrees (representing grooves parallel and perpendicular to the axis, respectively). Before numerical investigation, the pipe with helical angle of 30 degree was tested on an experimental stand. The results obtained from experiment and numerical simulations were compared and presented on the charts. As an effect of the numerical simulations, the friction factor f and Nusselt number characteristics was determined for the range of Re=104 ÷ 1.6 × 106. The analysis of the results showed high, irregular influence of the helical angle on thermal characteristics and pressure drops. Additionally, the ratios: f / fplain, Nu/Nuplain and efficiency indexes (Nu/Nuplain)/( f / fplain) as a function of the Reynolds number for every helical angle were shown on the charts.

A Numerical Study on the Influence of Hole Aspect Ratio on the Performance Characteristics of a Hole-Pattern Seal

2014 ◽  
Author(s):  
Patrick J. Migliorini ◽  
Alexandrina Untaroiu ◽  
Houston G. Wood
Keyword(s):  
Aspect Ratio ◽  
Friction Factor ◽  
Numerical Study ◽  
Vortex Formation ◽  
Experimental Studies ◽  
Jet Flow ◽  
Bulk Flow ◽  
Hole Depth ◽  
Friction Factors ◽  
Annular Seals

In turbomachinery, annular seals are used to reduce leakage between regions of high and low pressure. Many configurations of annular seals have been developed and studied in the literature including plain, labyrinth, pocket-damper, honeycomb, and hole-pattern. In machines experiencing stability issues, honeycomb and hole-pattern type seals have been used to replace labyrinth seals. Bulk-flow models are typically used to predict the leakage and dynamic coefficients of hole-pattern seals, relying on empirically derived friction factor coefficients. Previous experimental studies have shown that, for hole-pattern seals, the leakage and stator friction factor are strongly influenced by hole-depth. However, this behavior is not a monotonic function of hole-depth, a fact that might reduce confidence in future bulk-flow model predictions if not properly accounted for. A recent numerical study has highlighted the role of vortex formation in the holes which has a strong influence on the flow in the clearance region. Depending on the shape of the vortex, the flow in the hole can act much like a pinch valve, reducing the effective clearance of the jet flow. In this paper, computational fluid dynamics simulations of several hole-pattern seal configurations have been performed to study the effect of hole-aspect ratio (depth versus diameter) on the leakage and friction factors. The Reynolds Averaged Navier Stokes (RANS) equations with k-ε turbulence model were solved using ANSYS CFX. It was found that the shape of the hole influences the vortex formation within the hole, effecting the jet flow in the clearance region and the seal leakage. The results show that the leakage is heavily dependent on the hole diameter in addition to the hole depth. The relationship between the friction factors and the geometry of the seal was found to be non-monotonic. It is therefore difficult to develop a friction factor model that will accurately encompass all configurations and it is recommended that friction factor data be interpolated from experimental or numerical results.

Numerical Investigation of 3-D Turbulent Flow in Orifice Plate within a Pipe

2015 ◽  
Vol 761 ◽  
pp. 27-31
Author(s):  
Mohamed Abed Alabas Siba ◽  
Wan Mohd Faizal Wan Mahmood ◽  
Mohd Zaki Nuawi ◽  
Rasidi Rasani
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Turbulent Flow ◽  
Finite Volume ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Orifice Plate ◽  
Navier Stokes ◽  
Volume Method

A numerical study of the turbulent flow in an orifice plate within a pipe is carried out by utilizing the Navier-Stokes (N-S) equations. The governing equations are solved using primitive variables with a finite volume method (FVM) and simulated using the finite volume based commercial CFD code ANSYS. The study investigates the influences of Reynolds numbers (Re = 5000, 10000, and 15000) and aspect ratio (β = 0.2, 0.3, and 0.5), on the flow characteristics, i.e. the velocity profile, the differential pressure, and the vorticity, and on the mechanical properties, i.e. the strain, the stress, and the total deformation of the flow around and beyond the orifice. It is found that as the Reynolds number increases, the flow velocity and the pressure increase. The vorticity images show a slightly different behavior. As the Reynolds number has its own effect on the results, it is also found that the aspect ratio affects the results more significantly. The flow patterns are presented for unsteady flow throughout the orifice plate at different values of the Reynolds number.

Numerical Study on Effect of Volume Fraction of Nanoparticles on Rayleigh-Bernard Convection in Different Enclosures

2014 ◽  
Vol 592-594 ◽  
pp. 945-950 ◽  
Author(s):  
S. Senthil Kumar ◽  
S. Karthikeyan
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Volume Fraction ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Boussinesq Approximation ◽  
Working Fluid ◽  
Volume Fractions ◽  
Aspect Ratios ◽  
Fluid Flow Characteristics

Numerical investigations of Rayleigh-Bernard convection in enclosures of different modified bottom and top surfaces filled with Au-Water Nanofluid with different volume fractions are presented. This paper describes a numerical predication of heat transfer and fluid flow characteristics inside enclosures bounded by modified bottom and top surfaces and two periodic straight vertical walls. Simulations are carried out for a Rayleigh number of 6×104 and two aspect ratios (0.25 & 0.5) with working fluid as Au-Water Nanofluid and The same analyses are performed with the Nanofluid having Au nanoparticles of same size and different volume fraction of φ = 5%, 10%, 15% and 20 % in order to see the effect of Nanofluid volume fraction on heat transfer. The Boussinesq approximation is used in order to take density change effect in the governing equations. The study investigates the effect of the nanoparticles volume fraction, and the aspect ratio on the heat transfer. The results are presented in terms of isotherms, streamlines local and average surface Nusselt numbers. Results show that the flow and isotherms are affected by the geometry shape and by the presence of nanoparticles with different volume fractions. It is also shown that for a fixed value of aspect ratio, the convective heat transfer is decreased for the increase in volume fraction of Nanofluid.

scholarly journals Numerical study on heat transfer and flow characteristics of nanofluids in a circular tube with trapezoid ribs

Open Physics ◽  
2021 ◽  
Vol 19 (1) ◽  
pp. 224-233
Author(s):  
Wei Wang ◽  
Bo Zhang ◽  
Lanhua Cui ◽  
Hongwei Zheng ◽  
Jiří Jaromír Klemeš ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Base Fluid ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Constant Heat Flux ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Convective Heat Transfer Coefficients

Abstract This study aims to investigate heat transfer and flow characteristics of ethylene glycol/water (EGW) and CuO–EGW nanofluids in circular tubes with and without trapezoid ribs. Nusselt number and friction factor in tubes with trapezoid ribs are analysed under a constant heat flux by changing rib bottom angles. This study compares the convective heat transfer coefficients of 6 vol.% CuO–EGW nanofluid and base fluid. It is found that under a constant Reynolds number, the Nusselt number and friction factor for CuO–EGW nanofluid and base fluid increase with an increase in the inclination angle. The Nusselt number for the CuO–EGW nanofluid in the tube with 75° rib bottom angle averagely increases by 135.8% compared to that in the smooth tube, and the performance evaluation criterion is 1.64.

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