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.

Experimental Investigation of Flow Characteristics in a Square Duct With Delta-Wing Vortex Generators

2013 ◽  
Author(s):  
Vadiraj V. Katti ◽  
Anandkumar S. Malipatil ◽  
Mahesh R. Ingalagi
Keyword(s):  
Aspect Ratio ◽  
Friction Factor ◽  
Delta Wing ◽  
Flow Characteristics ◽  
Vortex Generator ◽  
Hydraulic Diameter ◽  
Vortex Generators ◽  
Geometrical Parameters ◽  
Square Duct ◽  
Factor Ratios

The influence of delta wing vortex generators on the wall of square duct and the pressure loss penalty has been experimentally investigated in this study. The combined effects of geometrical parameters of delta wing vortex generators on friction factor ratios are reported for the Reynolds number based on the duct hydraulic diameter in the range of 8000–24000. The geometrical parameters of vortex generators systematically varied in this study are the pitch to vortex generator height ratio (p/e), vortex generator height to duct hydraulic diameter ratio (e/Dh), aspect ratio of vortex generator (ar). Results are reported for 0.1 ≤ e/Dh ≤ 0.5, 1.6 ≤ p/e ≤ 16, 1.6 ≤ ar ≤ 14.9, in duct having aspect ratio AR = 1. The experimental results of the present study for friction factor in smooth square duct agree well with values estimated from correlations proposed by Blasius.

Heat Transfer for High Aspect Ratio Rectangular Channels in a Stationary Serpentine Passage With Turbulated and Smooth Surfaces

2013 ◽  
Author(s):  
Matthew A. Smith ◽  
Randall M. Mathison ◽  
Michael G. Dunn
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Hydraulic Diameter ◽  
Internal Cooling ◽  
Number Range ◽  
Aspect Ratios ◽  
Parallel Configuration

Heat transfer distributions are presented for a stationary three passage serpentine internal cooling channel for a range of engine representative Reynolds numbers. The spacing between the sidewalls of the serpentine passage is fixed and the aspect ratio (AR) is adjusted to 1:1, 1:2, and 1:6 by changing the distance between the top and bottom walls. Data are presented for aspect ratios of 1:1 and 1:6 for smooth passage walls and for aspect ratios of 1:1, 1:2, and 1:6 for passages with two surfaces turbulated. For the turbulated cases, turbulators skewed 45° to the flow are installed on the top and bottom walls. The square turbulators are arranged in an offset parallel configuration with a fixed rib pitch-to-height ratio (P/e) of 10 and a rib height-to-hydraulic diameter ratio (e/Dh) range of 0.100 to 0.058 for AR 1:1 to 1:6, respectively. The experiments span a Reynolds number range of 4,000 to 130,000 based on the passage hydraulic diameter. While this experiment utilizes a basic layout similar to previous research, it is the first to run an aspect ratio as large as 1:6, and it also pushes the Reynolds number to higher values than were previously available for the 1:2 aspect ratio. The results demonstrate that while the normalized Nusselt number for the AR 1:2 configuration changes linearly with Reynolds number up to 130,000, there is a significant change in flow behavior between Re = 25,000 and Re = 50,000 for the aspect ratio 1:6 case. This suggests that while it may be possible to interpolate between points for different flow conditions, each geometric configuration must be investigated independently. The results show the highest heat transfer and the greatest heat transfer enhancement are obtained with the AR 1:6 configuration due to greater secondary flow development for both the smooth and turbulated cases. This enhancement was particularly notable for the AR 1:6 case for Reynolds numbers at or above 50,000.

Extended Thermodynamic Approach for Non-Equilibrium Gas Flow

2013 ◽  
Vol 13 (5) ◽  
pp. 1330-1356 ◽  
Author(s):  
G. H. Tang ◽  
G. X. Zhai ◽  
W. Q. Tao ◽  
X. J. Gu ◽  
D. R. Emerson
Keyword(s):  
Heat Transfer ◽  
Equilibrium State ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Flow Characteristics ◽  
Bimodal Distribution ◽  
Thermodynamic Approach ◽  
Navier Stokes ◽  
Extended Thermodynamic ◽  
Non Equilibrium

AbstractGases in microfluidic structures or devices are often in a non-equilibrium state. The conventional thermodynamic models for fluids and heat transfer break down and the Navier-Stokes-Fourier equations are no longer accurate or valid. In this paper, the extended thermodynamic approach is employed to study the rarefied gas flow in microstructures, including the heat transfer between a parallel channel andpressure-driven Poiseuille flows through a parallel microchannel andcircular microtube. The gas flow characteristics are studied and it is shown that the heat transfer in the non-equilibrium state no longer obeys the Fourier gradient transport law. In addition, the bimodal distribution of streamwise and spanwise velocity and temperature through a long circular microtube is captured for the first time.

Effects of Al2O3–Cu/water hybrid nanofluid on heat transfer and flow characteristics in turbulent regime

2015 ◽  
Vol 26 (04) ◽  
pp. 1550047 ◽  
Author(s):  
Behrouz Takabi ◽  
Hossein Shokouhmand
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Pure Water ◽  
Flow Characteristics ◽  
Hydrodynamic Performance ◽  
Hybrid Nanofluid ◽  
Turbulent Regime ◽  
Average Increase ◽  
Finite Volume Discretization ◽  
Wide Range

In this paper, forced convection of a turbulent flow of pure water, Al 2 O 3/water nanofluid and Al 2 O 3– Cu /water hybrid nanofluid (a new advanced nanofluid composited of Cu and Al 2 O 3 nanoparticles) through a uniform heated circular tube is numerically analyzed. This paper examines the effects of these three fluids as the working fluids, a wide range of Reynolds number (10 000 ≤ Re ≤ 10 0000) and also the volume concentration (0% ≤ ϕ ≤ 2%) on heat transfer and hydrodynamic performance. The finite volume discretization method is employed to solve the set of the governing equations. The results indicate that employing hybrid nanofluid improves the heat transfer rate with respect to pure water and nanofluid, yet it reveals an adverse effect on friction factor and appears severely outweighed by pressure drop penalty. However, the average increase of the average Nusselt number (when compared to pure water) in Al 2 O 3– Cu /water hybrid nanofluid is 32.07% and the amount for the average increase of friction factor would be 13.76%.

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.

A General Approach to Analysis of Flow and Heat Transfer in Packed Beds

2008 ◽  
Author(s):  
Aleksander Vadnjal ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
Surface Area ◽  
Hydraulic Diameter ◽  
Experimental Results ◽  
Transfer Coefficients ◽  
Internal Surface Area ◽  
The Media

It is postulated that proper scaling will collapse the multiplicity of data for friction and heat transfer coefficient to a usable reasonably general formulation by choosing the hydraulic diameter as Dh=4·〈m〉Sw where &lt;m&gt; is the average porosity and Sw is the surface area per unit volume. The chosen hydraulic diameter allows the transformation and comparison of correlation equations and experimental results obtained for diverse media morphologies. Also, it allows experimentally-determined characteristics of the media to be related to the closure relationship derived from the VAT analysis. The numerical results of closure are presented and are compared to various experimental results. The Nusselt number is based on the media internal local surface average transfer coefficient and the friction factor is the local internal value. Results obtained by VAT closure using direct numerical simulation show reasonable agreement between calculated local friction factors and local heat transfer coefficients and data confirming that the friction factor and heat transfer coefficient when correctly scaled can be computed numerically with satisfactory results. This conclusion will enable one to optimize the effectiveness of a compact heat exchanger in terms of porosity and internal surface area.

Heat Transfer and Pressure Drop Correlation for Helicoidal Pipes of Rectangular Cross Section

2009 ◽  
Author(s):  
Christopher Katinas ◽  
Ahmad Fakheri
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Aspect Ratio ◽  
Friction Factor ◽  
Cross Section ◽  
Numerical Solutions ◽  
Rectangular Cross Section ◽  
Dean Number ◽  
Curvature Effects ◽  
The Impact

In this study, flow and heat transfer for laminar flow in curved channels of rectangular cross section is examined. The focus of the numerical solutions is on rectangular cross sections with an aspect ratio less than one, since little information is available for heat transfer in curved rectangular pipes whose width is greater than height. The study examines the impact of the aspect ratio and Dean number on both friction factor and Nusselt number. The results show that although both friction factor and Nusselt number increase as a result of curvature effects, the heat transfer enhancements significantly outweigh the friction factor penalty. Numerical solutions in this study consider the more realistic case of hydrodynamically developed and thermally developing flow.

Features of thermomechanics of pulsating gas flows in inlet systems with grooves applicable to automotive engines

2021 ◽  
pp. 85-89
Author(s):  
L. V. Plotnikov ◽  
◽  
N. I. Grigoryev ◽  
L. E. Osipov ◽  
O. A. Plotnikov ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Internal Combustion Engines ◽  
Gas Flow ◽  
Primary Data ◽  
Gas Flows ◽  
Inlet System ◽  
Heat Engines ◽  
System A ◽  
High Dynamics ◽  
Secondary Vortices

Reciprocating internal combustion engines (RICE) are widely used as heat engines for converting the chemical energy of a fuel into mechanical work on the crankshaft. Aerodynamic and thermophysical processes in gas exchange systems significantly affect the efficiency of the RICE. This paper examines the possibility of influencing the gas dynamics and heat transfer of pulsating gas flows in the inlet system by placing a channel with grooves. It is known that the presence of grooves in the channel leads to the formation of significant secondary vortices, which radically change the physical picture of the gas flow. The studies were carried out on a laboratory bench, which was a singlecylinder model of a turbocharged RICE. A system of measurements of basic physical quantities is described, taking into account their high dynamics. Techniques for processing experimental data are presented. Primary data on instantaneous values of gas-dynamic and heatexchange characteristics of pulsating flows are presented. It was found that the presence of a channel with grooves in the inlet system leads to a decrease in the degree of turbulence to 40 % and an intensification of heat transfer in the range of 5–50 % compared to the basic inlet system. A positive effect is shown in the form of an increase in engine power by 3 % when using the modernized system.

A Comprehensive Model for Simulating Supercritical-Water Flow in a Vertical Heavy-Oil Well

SPE Journal ◽  
2021 ◽  
pp. 1-16
Author(s):  
Jiaxi Gao ◽  
Yuedong Yao ◽  
Dawen Wang ◽  
Hang Tong
Keyword(s):  
Heat Transfer ◽  
Supercritical Water ◽  
Oil Recovery ◽  
Heavy Oil ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Transfer Model ◽  
Oil Well ◽  
Horizontal Wellbore ◽  
Predicted Values

Summary Supercritical water has been proved effective in heavy-oil recovery. However, understanding the flow characteristics of supercritical water in the wellbore is still in the early stages. In this paper, using the theory of heat transfer and fluid mechanics and combining that with the physical properties of supercritical water, a heat-transfer model for vertical wellbore injection with supercritical water is established. The influence of heat transfer and the Joule-Thomson effect on the temperature of supercritical water are considered. Results show the following: The predicted values of pressure and temperature are in good agreement with the test values. The apparent pressure of supercritical water at the upper end of the wellbore is lower than the apparent pressure at the lower end. However, the equivalent pressure of supercritical water at the upper end of the wellbore is higher than the equivalent pressure at the lower end. The apparent pressure of supercritical water is affected by three factors: flow direction, overlying pressure, and Joule-Thomsoneffect. The closer to the bottom of the well, the greater the overlying pressure of the supercritical water, resulting in an increase in apparent pressure and the density of the supercritical water. As the injection time for supercritical water increases, the temperature around the upper horizontal wellbore increases.

Numerical investigation on turbulent convective heat transfer of nanofluid flow in a square cross-sectioned duct

2019 ◽  
Vol 29 (4) ◽  
pp. 1432-1447 ◽  
Author(s):  
Gülbanu Şenay ◽  
Metin Kaya ◽  
Engin Gedik ◽  
Muhammet Kayfeci
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Friction Factor ◽  
Flow Characteristics ◽  
Constant Heat Flux ◽  
Ansys Fluent ◽  
Square Duct ◽  
Content Type ◽  
Volume Fractions ◽  
Darcy Friction Factor

Purpose The purpose of this study is to numerically investigate the heat transfer enhancement by using two different nanofluids flow throughout the square duct under a constant heat flux (500 × 103 W/m2). Design/methodology/approach In numerical computations, ANSYS Fluent code based on the finite volume method was used to solve governing equations by iteratively. Water, Al2O3-water and TiO2-water nanofluids were used for different flow velocities changing 1 m/s to 8 m/s (i.e. Reynolds number varying from 3,000 to 100,000). Findings The results were compared with results published previously in the literature and close agreement was observed especially considering Dittus and Boelter correlation for water. It was found that from the obtained results, increasing flow velocity and volume fractions of nanoparticles has caused to increase Nu number for all cases. Besides, variations of pressure drop, Darcy friction factor are presented graphically and discussed in detail. The results are consistent with a deviation of 1.3 to 15 per cent with the results of other researchers. Originality/value The effects of the Re numbers and volume fractions of nanoparticles (0.01 ≤ Φ ≤ 0.04) on the heat transfer and fluid flow characteristics such as average Nu number, pressure drop (ΔP) and Darcy friction factor (f) were investigated.

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