Flow Characteristics in a Curved Rectangular Channel With Variable Cross-Sectional Area

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
Avijit Bhunia ◽  
C. L. Chen
Keyword(s):  
Pressure Drop ◽  
Rectangular Channel ◽  
Variable Cross ◽  
Entry And Exit ◽  
Curved Channel ◽  
Dean Number ◽  
Cross Sectional ◽  
Dean Vortices ◽  
Area Expansion ◽  
Expansion Effect

Laminar air flow through a curved rectangular channel with a variable cross-sectional (c/s) area (diverging-converging channel) is computationally investigated. Such a flow passage is formed between the two fin walls of a 90 deg bend curved fin heat sink, used in avionics cooling. Simulations are carried out for two different configurations: (a) a curved channel with long, straight, constant c/s area inlet and outlet sections (entry and exit lengths); and (b) a short, curved channel with no entry and exit lengths. Formation of a complex 3D flow pattern and its evolution in space is studied through numerical flow visualization. Results show that a secondary motion sets in the radial direction of the curved section, which in combination with the axial (bulk) flow leads to the formation of a base vortex. In addition, under certain circumstances the axial and secondary flow separate from multiple locations on the channel walls, creating Dean vortices and separation bubbles. Velocity above which the Dean vortices appear is cast in dimensionless form as the critical Dean number, which is calculated to be 129. Investigation of the friction factor reveals that pressure drop in the channel is governed by both the curvature effect as well as the area expansion effect. For a short curved channel where area expansion effect dominates, pressure drop for developing flow can be even less than that of a straight channel. A comparison with the flow in a constant c/s area, curved channel shows that the variable c/s area channel geometry leads to a lower critical Dean number and friction factor.

Thermal Characteristics in a Curved Rectangular Channel With Variable Cross-Sectional Area

2011 ◽  
Vol 133 (12) ◽  
Author(s):  
Avijit Bhunia ◽  
C. L. Chen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Sink ◽  
Rectangular Channel ◽  
Variable Cross ◽  
Entry And Exit ◽  
Transfer Enhancement ◽  
Curved Channel ◽  
Dean Number ◽  
Cross Sectional

Heat transfer due to steady, laminar air flow through a curved rectangular channel with a variable cross-sectional (c/s) area is investigated computationally. Such a flow passage is formed between two fin walls of a curved fin heat sink with a 90 deg bend, used in avionics cooling. Simulations are carried out for two different configurations: (a) a variable c/s area curved channel with inlet and outlet sections (entry and exit lengths) that are straight and constant c/s area—termed as the long channel and (b) a variable c/s area curved channel with no entry and exit lengths—termed as the short channel. Multiple secondary flow patterns develop in the curved section of the channel, which in conjunction with the bulk axial flow, lead to the formation of multiple vortices and separation bubbles. The complex 3-D flow structures, as well as the variable c/s area of the curved channel (diverging–converging) significantly alter the heat transfer characteristics, compared to the straight fin heat sink. Secondary flow strengthens with increasing axial (bulk) flow velocity, or Dean number in dimensionless form. This in turn improves heat transfer from all walls, particularly, the outer curvature (concave) wall and the heat sink base. At the highest Dean number condition, the local heat transfer coefficient at certain locations of the outer curvature wall is augmented by as much as 3.5 times, compared to the straight fin walls. The overall channel average heat transfer coefficient is improved by about 40% for the long channels, and about 10% for the short ones. However, the heat transfer enhancement is associated with a penalty of higher pressure drop, compared to the straight channels. To quantify the effectiveness of thermal performance enhancement a system Figure of Merit (FOM) is defined. A greater than unity FOM value is observed for all curved channel geometries and flow rate conditions. This indicates that heat transfer enhancement in the variable c/s area curved channel outweighs the penalty of additional pressure drop, compared to a straight channel of similar length.

Flow in a Curved Rectangular Channel With Variable Cross-Section Area

2008 ◽  
Author(s):  
Avijit Bhunia ◽  
C. L. Chen
Keyword(s):  
Pressure Drop ◽  
Cross Section ◽  
Rectangular Channel ◽  
Variable Cross Section ◽  
Variable Cross ◽  
Entry And Exit ◽  
Curved Channel ◽  
Cross Section Area ◽  
Secondary Motion ◽  
Curved Section

Laminar air flow through a curved rectangular channel with a variable cross-section (c/s) area (diverging-converging) is numerically investigated. Such a flow passage is formed between the two fin walls of a 90° bend curved fin heat sink, used in avionics cooling. Simulations are carried out for two different configurations — (a) a curved channel with long, straight, constant c/s area inlet and outlet sections (entry and exit lengths), and (b) a short, curved channel with no entry and exit lengths. Formation of a complex, 3-D flow pattern and its evolution in space is studied through numerical flow visualization. Results show that a secondary motion sets in the radial direction in the curved section, which in combination with the axial (bulk) flow leads to the formation of a base vortex. In addition, under certain circumstances the axial and secondary flow separate from multiple locations on the channel walls, and create Dean vortices and separation bubbles. The role of variable c/s geometry is elucidated by comparing the results with those of a constant c/s area, curved channel. Investigation of the dimensionless friction factor reveals that the overall channel pressure drop is governed by both the curvature effect as well as the area expansion effect. Due to the combined effect pressure drop for developing flow in a short, curved channel can be even less than that of a straight channel.

Mixing Enhancement in Spiral Microchannels

2016 ◽  
Author(s):  
Lakshmi Balasubramaniam ◽  
Rerngchai Arayanarakool ◽  
Samuel D. Marshall ◽  
Bing Li ◽  
Poh Seng Lee ◽  
...  
Keyword(s):  
Industrial Applications ◽  
Secondary Flows ◽  
Experimental Investigations ◽  
Mixing Enhancement ◽  
Curved Channel ◽  
Cross Sectional ◽  
Mixing Performance ◽  
Dean Vortices ◽  
Potential Applications ◽  
Sectional Shape

Advancements in the field of microfluidics has led to an increasing interest to study laminar flow in microchannel and its potential applications. Understanding mixing at a microscale can be useful in various biological, heating and industrial applications due to the space and time reduction that micro mixing permits. This work aims to study mixing enhancement due to curved microchannel and the influence of varying microchannel cross sectional shape through numerical and experimental investigations. Unlike prior studies which use channel dimensions in the lower microscale range, this work has been conducted on channels with dimensions in the higher end of micrometer range. Using a cross sectional hydraulic diameter of 600 μm enables introduction of flow into the curved channel at a Reynolds Number ranging from 0.15 to 75, the findings of which show considerable improvement in the mixing performance as compared to that of equivalent straight channels, due to the development of secondary flows known as Dean Vortices.

Dean vortices in finite-aspect-ratio ducts

2013 ◽  
Vol 716 ◽  
Author(s):  
Philip E. Haines ◽  
James P. Denier ◽  
Andrew P. Bassom
Keyword(s):  
Aspect Ratio ◽  
Stokes Equations ◽  
Finite Amplitude ◽  
Navier Stokes ◽  
Curved Channel ◽  
Dean Number ◽  
Element Analysis ◽  
Navier Stokes Equations ◽  
New Class ◽  
Dean Vortices

AbstractWe consider the development of Dean vortices in a curved channel of finite aspect ratio. Solutions to the axisymmetric Navier–Stokes equations are obtained through a finite-element analysis, allowing us to explore the complex and rich bifurcation pattern of the flow as the aspect ratio and Dean number vary. We demonstrate a new class of finite-amplitude vortices and discuss their relationship to similar structures seen in finite-length Taylor–Couette flow.

DETERMINATION OF THE FUNCTION OF THE ROD’S CROSS-SECTIONAL AREA USING VIBRATION EIGENFREQUENCIES

2020 ◽  
Vol 0 (4) ◽  
pp. 19-24
Author(s):  
I.M. UTYASHEV ◽  
◽  
A.A. AITBAEVA ◽  
A.A. YULMUKHAMETOV ◽  
◽  
...  
Keyword(s):  
Cross Sectional Area ◽  
Variable Cross ◽  
Sectional Area ◽  
Longitudinal Vibrations ◽  
Cross Sectional ◽  
Method Error ◽  
Various Boundary Conditions ◽  
Elastic Fixation ◽  
Crosssectional Area

The paper presents solutions to the direct and inverse problems on longitudinal vibrations of a rod with a variable cross-sectional area. The law of variation of the cross-sectional area is modeled as an exponential function of a polynomial of degree n . The method for reconstructing this function is based on representing the fundamental system of solutions of the direct problem in the form of a Maclaurin series in the variables x and λ. Examples of solutions for various section functions and various boundary conditions are given. It is shown that to recover n unknown coefficients of a polynomial, n eigenvalues are required, and the solution is dual. An unambiguous solution was obtained only for the case of elastic fixation at one of the rod’s ends. The numerical estimation of the method error was made using input data noise. It is shown that the error in finding the variable crosssectional area is less than 1% with the error in the eigenvalues of longitudinal vibrations not exceeding 0.0001.

Longitudinal oscillation of a rod with a variable cross section

2019 ◽  
Vol 14 (2) ◽  
pp. 138-141
Author(s):  
I.M. Utyashev
Keyword(s):  
Cross Section ◽  
Natural Frequencies ◽  
Liouville Problem ◽  
Variable Cross Section ◽  
Variable Cross ◽  
Longitudinal Vibrations ◽  
Cross Sectional ◽  
Independent Functions ◽  
The Cross ◽  
The Right

Variable cross-section rods are used in many parts and mechanisms. For example, conical rods are widely used in percussion mechanisms. The strength of such parts directly depends on the natural frequencies of longitudinal vibrations. The paper presents a method that allows numerically finding the natural frequencies of longitudinal vibrations of an elastic rod with a variable cross section. This method is based on representing the cross-sectional area as an exponential function of a polynomial of degree n. Based on this idea, it was possible to formulate the Sturm-Liouville problem with boundary conditions of the third kind. The linearly independent functions of the general solution have the form of a power series in the variables x and λ, as a result of which the order of the characteristic equation depends on the choice of the number of terms in the series. The presented approach differs from the works of other authors both in the formulation and in the solution method. In the work, a rod with a rigidly fixed left end is considered, fixing on the right end can be either free, or elastic or rigid. The first three natural frequencies for various cross-sectional profiles are given. From the analysis of the numerical results it follows that in a rigidly fixed rod with thinning in the middle part, the first natural frequency is noticeably higher than that of a conical rod. It is shown that with an increase in the rigidity of fixation at the right end, the natural frequencies increase for all cross section profiles. The results of the study can be used to solve inverse problems of restoring the cross-sectional profile from a finite set of natural frequencies.

scholarly journals Numerical and Theoretical Study of Performance and Mechanical Behavior of PEM-FC Using Innovative Channel Geometrical Configurations

2021 ◽  
Vol 11 (12) ◽  
pp. 5597
Author(s):  
Hussein A. Z. AL-bonsrulah ◽  
Mohammed J. Alshukri ◽  
Ammar I. Alsabery ◽  
Ishak Hashim
Keyword(s):  
Fuel Cell ◽  
Cross Section ◽  
Rectangular Channel ◽  
Compressive Load ◽  
Proton Exchange ◽  
Channel Cross Section ◽  
Channel Height ◽  
Cross Sectional ◽  
Triangular Channel ◽  
Higher Power

Proton exchange membrane fuel cell (PEM-FC) aggregation pressure causes extensive strains in cell segments. The compression of each segment takes place through the cell modeling method. In addition, a very heterogeneous compressive load is produced because of the recurrent channel rib design of the dipole plates, so that while high strains are provided below the rib, the domain continues in its initial uncompressed case under the ducts approximate to it. This leads to significant spatial variations in thermal and electrical connections and contact resistances (both in rib–GDL and membrane–GDL interfaces). Variations in heat, charge, and mass transfer rates within the GDL can affect the performance of the fuel cell (FC) and its lifetime. In this paper, two scenarios are considered to verify the performance and lifetime of the PEM-FC using different innovative channel geometries. The first scenario is conducted by adopting a constant channel height (H = 1 mm) for all the differently shaped channels studied. In contrast, the second scenario is conducted by taking a constant channel cross-sectional area (A = 1 mm2) for all the studied channels. Therefore, a computational fluid dynamics model (CFD) for a PEM fuel cell is formed through the assembly of FC to simulate the pressure variations inside it. The simulation results showed that a triangular cross-section channel provided the uniformity of the pressure distribution, with lower deformations and lower mechanical stresses. The analysis helped gain insights into the physical mechanisms that lead to the FC’s durability and identify important parameters under different conditions. The model shows that it can assume the intracellular pressure configuration toward durability and appearance containing limited experimental data. The results also proved that the better cell voltage occurs in the case of the rectangular channel cross-section, and therefore, higher power from the FC, although its durability is much lower compared to the durability of the triangular channel. The results also showed that the rectangular channel cross-section gave higher cell voltages, and therefore, higher power (0.63 W) from the fuel cell, although its durability is much lower compared to the durability of the triangular channel. Therefore, the triangular channel gives better performance compared to other innovative channels.

Heat Transfer And Pressure Drop Of An Angled Discrete Turbulator At Elevated Reynolds Numbers Up To 900,000

2021 ◽  
pp. 1-29
Author(s):  
Sam Ghazi-Hesami ◽  
Dylan Wise ◽  
Keith Taylor ◽  
Peter Ireland ◽  
Étienne Robert
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Enhance Heat Transfer ◽  
Near Surface ◽  
Number Range ◽  
Smooth Channel

Abstract Turbulators are a promising avenue to enhance heat transfer in a wide variety of applications. An experimental and numerical investigation of heat transfer and pressure drop of a broken V (chevron) turbulator is presented at Reynolds numbers ranging from approximately 300,000 to 900,000 in a rectangular channel with an aspect ratio (width/height) of 1.29. The rib height is 3% of the channel hydraulic diameter while the rib spacing to rib height ratio is fixed at 10. Heat transfer measurements are performed on the flat surface between ribs using transient liquid crystal thermography. The experimental results reveal a significant increase of the heat transfer and friction factor of the ribbed surface compared to a smooth channel. Both parameters increase with Reynolds number, with a heat transfer enhancement ratio of up to 2.15 (relative to a smooth channel) and a friction factor ratio of up to 6.32 over the investigated Reynolds number range. Complementary CFD RANS (Reynolds-Averaged Navier-Stokes) simulations are performed with the κ-ω SST turbulence model in ANSYS Fluent® 17.1, and the numerical estimates are compared against the experimental data. The results reveal that the discrepancy between the experimentally measured area averaged Nusselt number and the numerical estimates increases from approximately 3% to 13% with increasing Reynolds number from 339,000 to 917,000. The numerical estimates indicate turbulators enhance heat transfer by interrupting the boundary layer as well as increasing near surface turbulent kinetic energy and mixing.

scholarly journals Effect of Metal Foam Insert Configurations on Flow Boiling Heat Transfer and Pressure Drop in a Rectangular Channel

Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4617
Author(s):  
Sanghyun Nam ◽  
Dae Yeon Kim ◽  
Youngwoo Kim ◽  
Kyung Chun Kim
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Mass Flux ◽  
Test Section ◽  
Boiling Heat Transfer ◽  
Metal Foam ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Saturation Pressure ◽  
Two Phase

Heat transfer under flow boiling is better in a rectangular channel filled with open-cell metal foam than in an empty channel, but the high pressure drop is a drawback of the empty channel method. In this study, various types of metal foam insert configurations were tested to reduce the pressure drop while maintaining high heat transfer. Specifically, we measured the boiling heat transfer and pressure drop of a two-phase vertical upward flow of R245fa inside a channel. To measure the pressure and temperature differences of the metal foam, differential pressure transducers and T-type thermocouples were used at both ends of the test section. While the saturation pressure was kept constant at 5.9 bar, the steam quality at the inlet of the test section was changed from 0.05 to 0.99. The channel height, moreover, was 3 mm, and the mass flux ranged from 133 to 300 kg/m2s. The two-phase flow characteristics were observed through a high-speed visualization experiment. Heat transfer tended to increase with the mean vapor quality, and, as expected, the fully filled metal foam channel offered the highest thermal performance. The streamwise insert pattern model had the lowest heat transfer at a low mass flux. However, at a higher mass flux, the three different insert models presented almost the same heat transfer coefficients. We found that the streamwise pattern model had a very low pressure drop compared to that of the spanwise pattern models. The goodness factors of the flow area and the core volume of the streamwise patterned model were higher than those of the full-filled metal foam channel.

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