The Vaporization of Superheated Sodium in a Vertical Channel

1972 ◽  
Vol 94 (3) ◽  
pp. 300-304 ◽  
Author(s):  
Ralph M. Singer ◽  
Robert E. Holtz
Keyword(s):  
Cross Section ◽  
Thin Liquid Film ◽  
Rectangular Channel ◽  
Vertical Channel ◽  
Growth Patterns ◽  
Single Bubble ◽  
Bulk Liquid ◽  
Channel Cross Section ◽  
Channel Axis ◽  
Vapor Growth

Measurements of the vapor growth patterns and rates following the nucleation of superheated sodium in a vertical rectangular channel are presented and discussed. The vapor was found to grow as a single bubble for incipient bulk-liquid superheats greater than about 10 deg C, and this single bubble tended to completely fill the channel cross section (except for a thin liquid film on the walls) and to grow as a vapor slug for incipient bulk-liquid superheats greater than about 50 deg C. The temperature gradients in the liquid both normal and parallel to the channel axis prior to nucleation were found to have an important effect upon the dynamics of the vapor slug. Experimental data on the vapor growth and collapse rates and the associated pressure transients are presented for boiling pressures up to 1 atm and incipient superheats up to about 180 deg C.

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.

Velocity of a Large Bubble Rising in an Inclined Rectangular Channel

2003 ◽  
Author(s):  
Hachiro Hamaguchi
Keyword(s):  
Aspect Ratio ◽  
Cross Section ◽  
Inclination Angle ◽  
Circular Tube ◽  
Silicone Oil ◽  
Rectangular Channel ◽  
Large Bubble ◽  
Channel Axis ◽  
Test Channel ◽  
Bubble Rising

Velocity of a large single bubble rising in a stationary liquid in an inclined rectangular channel was measured using silicone oil having a kinematic viscosity of 1000mm2/s. The size of cross section of the test channel was 5mm × (5–40)mm, i.e., the aspect ratio was from 1 to 8. Experiments were carried out changing the aspect ratio of cross section of the channel, the inclination angle and “posture angle”, where the “posture angle” is an angel by which the channel is rotated around the channel axis. Movement of a large bubble in an inclined circular tube is determined by the inclination angle. On the other hand, it is shown that movement of a large bubble in an inclined channel is influenced also by the posture angle beside the inclination angel, i.e., the posture angle is an important parameter in an inclined rectangular channel. Relations among the rising velocity, the inclination angle, the posture angle and the aspect ratio were obtained by the experiments.

scholarly journals Analytical Solution of the Time-Dependent Microfluidic Poiseuille Flow in Rectangular Channel Cross-Sections and Its Numerical Implementation in Microsoft Excel

Biosensors ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 67
Author(s):  
Patrick Risch ◽  
Dorothea Helmer ◽  
Frederik Kotz ◽  
Bastian E. Rapp
Keyword(s):  
Analytical Solution ◽  
Cross Section ◽  
Poiseuille Flow ◽  
Exact Analytical Solution ◽  
Rectangular Channel ◽  
Channel Cross Section ◽  
Analysis Tool ◽  
Complex Flow ◽  
Microsoft Excel ◽  
Navier Stokes Equation

We recently demonstrated that the Navier–Stokes equation for pressure-driven laminar (Poiseuille) flow can be solved in any channel cross-section using a finite difference scheme implemented in a spreadsheet analysis tool such as Microsoft Excel. We also showed that implementing different boundary conditions (slip, no-slip) is straight-forward. The results obtained in such calculations only deviated by a few percent from the (exact) analytical solution. In this paper we demonstrate that these approaches extend to cases where time-dependency is of importance, e.g., during initiation or after removal of the driving pressure. As will be shown, the developed spread-sheet can be used conveniently for almost any cross-section for which analytical solutions are close-to-impossible to obtain. We believe that providing researchers with convenient tools to derive solutions to complex flow problems in a fast and intuitive way will significantly enhance the understanding of the flow conditions as well as mass and heat transfer kinetics in microfluidic systems.

Three-dimensional vapor growth mechanism of carbon microcoils

1999 ◽  
Vol 14 (11) ◽  
pp. 4329-4336 ◽  
Author(s):  
Xiuqin Chen ◽  
T. Saito ◽  
M. Kusunoki ◽  
S. Motojima
Keyword(s):  
Cross Section ◽  
Growth Mechanism ◽  
Driving Force ◽  
Carbon Deposition ◽  
Three Dimensional ◽  
Growth Patterns ◽  
Ni Catalyst ◽  
Initial Growth ◽  
Strong Anisotropy ◽  
Vapor Growth

Carbon microcoils were grown by the Ni-catalyzed pyrolysis of acetylene. The growth patterns and the tip morphologies of the carbon coils are examined in detail, and a growth mechanism is proposed. Basically, six thin fibers grew from a Ni catalyst grain during the initial growth stage immediately followed by the coalescence of the four fibers to form two fibers and then forming double-helixed carbon coils. A small amount of S and O, as well as C and Ni, was observed on the periphery of the cross section of the Ni catalyst grain. On the other hand, S and O were not observed in the central part. The driving force of the coiling of the straight fibers to form carbon coils is considered to be the strong anisotropy of the carbon deposition between different crystal faces.

scholarly journals Stability of convection in a horizontal channel subjected to a longitudinal temperature gradient. Part 1. Effect of aspect ratio and Prandtl number

2009 ◽  
Vol 635 ◽  
pp. 275-295 ◽  
Author(s):  
T. P. LYUBIMOVA ◽  
D. V. LYUBIMOV ◽  
V. A. MOROZOV ◽  
R. V. SCURIDIN ◽  
H. BEN HADID ◽  
...  
Keyword(s):  
Temperature Gradient ◽  
Aspect Ratio ◽  
Prandtl Number ◽  
Cross Section ◽  
Horizontal Channel ◽  
Channel Cross Section ◽  
Instability Mode ◽  
Channel Axis ◽  
Longitudinal Temperature Gradient ◽  
Longitudinal Temperature

The paper deals with the numerical investigation of the steady convective flow in a horizontal channel of rectangular cross-section subjected to a uniform longitudinal temperature gradient imposed at the walls. It is shown that at zero Prandtl number the solution of the problem corresponds to a plane-parallel flow along the channel axis. In this case, the fluid moves in the direction of the imposed temperature gradient in the upper part of the channel and in the opposite direction in the lower part. At non-zero values of the Prandtl number, such solution does not exist. At any small values of Pr all three components of the flow velocity differ from zero and in the channel cross-section four vortices develop. The direction of these vortices is such that the fluid moves from the centre to the periphery in the vertical direction and returns to the centre in the horizontal direction. The stability of these convective flows (uniform along the channel axis) with regard to small three-dimensional perturbations periodical in the direction of the channel axis is studied. It is shown that at low values of the Prandtl number the basic state loses its stability due to the steady hydrodynamic mode related to the development of vortices at the boundary of the counter flows. The growth of the Prandtl number results in the strong stabilization of this instability mode and, beyond a certain value of the Prandtl number depending on the cross-section aspect ratio, a new steady hydrodynamic instability mode becomes the most dangerous. This mode is characterized by the localization of the perturbations near the sidewalls of the channel. At still higher values of the Prandtl number, the spiral perturbations (rolls with axis parallel to the temperature gradient) become the most dangerous modes, at first the oscillatory spiral perturbations and then the Rayleigh-type steady spiral perturbations. The influence of the channel width on these different instabilities is also emphasized.

Asymptotic and Exact Analysis for Constructal Optimization of Microchannel Heat Sink

2008 ◽  
Author(s):  
Omid Asgari ◽  
Mohammad Hassan Saidi
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Cross Sections ◽  
Rectangular Channel ◽  
Channel Cross Section ◽  
Geometrical Parameters ◽  
Approximate Methods ◽  
Maximum Heat ◽  
Circular Duct ◽  
Maximum Heat Transfer

Microchannel are at the fore front of today’s cooling technologies. They are widely being considered for cooling of electronic devices and in micro heat exchanger systems due to their ease of manufacture. One issue which arises in the use of microchannels is related to the small length scale of the channel or channel cross-section. In this work, the maximum heat transfer and the optimum geometry for a given pressure loss have been calculated for forced convective heat transfer in microchannels of various cross-section having finite volume for laminar flow conditions. Solutions are presented for 10 different channel cross sections, namely parallel plate channel, circular duct, rectangular channel, elliptical duct, polygonal ducts, equilateral triangular duct, isosceles triangular duct, right triangular duct, rhombic duct and trapezoidal duct. The model is only a function of Prandtl number and geometrical parameters of the cross-section, i.e., area and perimeter. This solution is performed with two exact and approximate methods. Finally, in addition to comparison and discussion about these two methods, validation of the relationship is provided using results from the open literature.

scholarly journals Flexural bearing capacity and failure mechanism of CFRP-aluminum laminate beam with double-channel cross-section

2021 ◽  
Vol 28 (1) ◽  
pp. 139-152
Author(s):  
Teng Huang ◽  
Dongdong Zhang ◽  
Yaxin Huang ◽  
Chengfei Fan ◽  
Yuan Lin ◽  
...  
Keyword(s):  
Carbon Fiber ◽  
Bearing Capacity ◽  
Failure Mechanism ◽  
Cross Section ◽  
Failure Criterion ◽  
Failure Modes ◽  
Channel Cross Section ◽  
Fiber Layer ◽  
Flexural Bearing Capacity ◽  
Double Channel

Abstract In this study, the flexural bearing capacity and failure mechanism of carbon fiber-reinforced aluminum laminate (CARALL) beams with a double-channel cross-section and a 3/2 laminated configuration were experimentally and numerically studied. Two types of specimens using different carbon fiber layup configurations ([0°/90°/0°]3 and [45°/0°/−45°]3) were fabricated using the pressure molding thermal curing forming process. The double-channel CARALL beams were subjected to static three-point bending tests to determine their failure behaviors in terms of ultimate bearing capacity and failure modes. Owing to the shortcomings of the two-dimensional Hashin failure criterion, the user-defined FORTRAN subroutine VUMAT suitable for the ABAQUS/Explicit solver and an analysis algorithm were established to obtain a progressive damage prediction of the CFRP layer using the three-dimensional Hashin failure criterion. Various failure behaviors and mechanisms of the CARALL beams were numerically analyzed. The results indicated that the numerical simulation was consistent with the experimental results for the ultimate bearing capacity and final failure modes, and the failure process of the double-channel CARALL beams could be revealed. The ultimate failure modes of both types of double-channel CARALL beams were local buckling deformation at the intersection of the upper flange and web near the concentrated loading position, which was mainly caused by the delamination failure among different unidirectional plates, tension and compression failure of the matrix, and shear failure of the fiber layers. The ability of each fiber layer to resist damage decreased in the order of 90° fiber layer > 0° fiber layer > 45° fiber layer. Thus, it is suggested that 90°, 0°, and 45° fiber layers should be stacked for double-channel CARALL beams.

scholarly journals Fractal-induced 2D flexible net undulation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Michael Joon Seng Goh ◽  
Yeong Shiong Chiew ◽  
Ji Jinn Foo
Keyword(s):  
3D Reconstruction ◽  
Cross Section ◽  
Channel Cross Section ◽  
Time Varying ◽  
Blockage Ratio ◽  
Transient Time ◽  
Cross Sectional ◽  
Velocity Fluctuations ◽  
Square Grid ◽  
Multilength Scale

AbstractA net immersed in fractal-induced turbulence exhibit a transient time-varying deformation. The anisotropic, inhomogeneous square fractal grid (SFG) generated flow interacts with the flexible net to manifest as visible cross-sectional undulations. We hypothesize that the net’s response may provide a surrogate in expressing local turbulent strength. This is analysed as root-mean-squared velocity fluctuations in the net, displaying intensity patterns dependent on the grid conformation and grid-net separation. The net’s fluctuation strength is found to increase closer to the turbulator with higher thickness ratio while presenting stronger fluctuations compared to regular-square-grid (RSG) of equivalent blockage-ratio, σ. Our findings demonstrate a novel application where 3D-reconstruction of submerged nets is used to experimentally contrast the turbulence generated by RSG and multilength scale SFGs across the channel cross-section. The net’s response shows the unique turbulence developed from SFGs can induce 9 × higher average excitation to a net when compared against RSG of similar σ.

Long waves in a straight channel with non-uniform cross-section

2015 ◽  
Vol 770 ◽  
pp. 156-188 ◽  
Author(s):  
Patricio Winckler ◽  
Philip L.-F. Liu
Keyword(s):  
Boundary Layer ◽  
Wave Propagation ◽  
Cross Section ◽  
Three Dimensional ◽  
Channel Cross Section ◽  
Cross Sectional ◽  
New Model ◽  
One Dimensional ◽  
Uniform Channel ◽  
The Cross

A cross-sectionally averaged one-dimensional long-wave model is developed. Three-dimensional equations of motion for inviscid and incompressible fluid are first integrated over a channel cross-section. To express the resulting one-dimensional equations in terms of the cross-sectional-averaged longitudinal velocity and spanwise-averaged free-surface elevation, the characteristic depth and width of the channel cross-section are assumed to be smaller than the typical wavelength, resulting in Boussinesq-type equations. Viscous effects are also considered. The new model is, therefore, adequate for describing weakly nonlinear and weakly dispersive wave propagation along a non-uniform channel with arbitrary cross-section. More specifically, the new model has the following new properties: (i) the arbitrary channel cross-section can be asymmetric with respect to the direction of wave propagation, (ii) the channel cross-section can change appreciably within a wavelength, (iii) the effects of viscosity inside the bottom boundary layer can be considered, and (iv) the three-dimensional flow features can be recovered from the perturbation solutions. Analytical and numerical examples for uniform channels, channels where the cross-sectional geometry changes slowly and channels where the depth and width variation is appreciable within the wavelength scale are discussed to illustrate the validity and capability of the present model. With the consideration of viscous boundary layer effects, the present theory agrees reasonably well with experimental results presented by Chang et al. (J. Fluid Mech., vol. 95, 1979, pp. 401–414) for converging/diverging channels and those of Liu et al. (Coast. Engng, vol. 53, 2006, pp. 181–190) for a uniform channel with a sloping beach. The numerical results for a solitary wave propagating in a channel where the width variation is appreciable within a wavelength are discussed.

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