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Circular polarization in pulsar integrated profiles  [PDF]
J. L. Han,R. N. Manchester,R. X. Xu,G. J. Qiao
Physics , 1998, DOI: 10.1046/j.1365-8711.1998.01869.x
Abstract: We present a systematic study of the circular polarization in pulsar integrated profiles, based on published polarization data. For core components, we find no significant correlation between the sense-change of circular polarization and the sense of linear position angle variation. Circular polarization is not restricted to core components and, in some cases, reversals of circular polarization sense are observed across the conal emission. In conal double profiles, the sense of circular polarization is found to be correlated with the sense of position-angle variation. Pulsars with a high degree of linear polarization often have one hand of circular polarization across the whole profile. For most pulsars, the sign of circular polarization is the same at 50-cm and 20-cm wavelength, and the degree of polarization is similar, albeit with a wide scatter. However, at least two cases of frequency-dependent sign reversals are known. This diverse behaviour may require more than one mechanism to generate circular polarization.
Forced convection to laminar flow of liquid egg yolk in circular and annular ducts
Bernardi, M.;Silveira Jr., V.;Telis, V. R. N.;Gabas, A. L.;Telis-Romero, J.;
Brazilian Journal of Chemical Engineering , 2009, DOI: 10.1590/S0104-66322009000200006
Abstract: the steady-state heat transfer in laminar flow of liquid egg yolk - an important pseudoplastic fluid food - in circular and concentric annular ducts was experimentally investigated. the average convection heat transfer coefficients, determined by measuring temperatures before and after heating sections with constant temperatures at the tube wall, were used to obtain simple new empirical expressions to estimate the nusselt numbers for fully established flows at the thermal entrance of the considered geometries. the comparisons with existing correlations for newtonian and non-newtonian fluids resulted in excellent agreement. the main contribution of this work is to supply practical and easily applicable correlations, which are, especially for the case of annulus, rather scarce and extensively required in the design of heat transfer operations dealing with similar shear-thinning products. in addition, the experimental results may support existing theoretical analyses.
Two Dimensional Laminar Flow of a Liquid with Circular Hydraulic Jump  [cached]
Asuquo Essien Eyo,Enobong E. Joshua,Paul J. Udoh
Modern Applied Science , 2011, DOI: 10.5539/mas.v5n3p56
Abstract: We examine two-dimensional laminar flow of a liquid with circular hydraulic jump using boundary layer approach, but with the inclusion of a velocity profile approximated by a quadratic function. Our motivation is due to an earlier work of * on radial spread of a liquid over a horizontal plate. We obtain a new relation for the displacement thickness, momentum thickness and position of the jump. Our approximate values based on ** are compared with the exact values due to ***. The comparison shows the error of about 9% in the shear rate relation on the plate and the error of about 3.5% in the thickness ratio. Our values agree to a large extent with the exact values and also show improvement of our work upon that of * with respect to the thickness ratio.
Circular, stationary profiles emerging in unidirectional abrasion  [PDF]
G. Domokos,G. W. Gibbons,A. A. Sipos
Physics , 2012,
Abstract: We describe a PDE model of bedrock abrasion by impact of moving particles and show that by assuming unidirectional impacts the modification of a geometrical PDE due to Bloore exhibits circular arcs as solitary profiles. We demonstrate the existence and stability of these stationary, travelling shapes by numerical experiments based on finite difference approximations. Our simulations show that, depending on initial profile shape and other parameters, these circular profiles may evolve via long transients which, in a geological setting, may appear as non-circular stationary profiles.
Irreversibilities in Duct Geometries of Rhombic and Circular with Constant Wall Heat Flux and Laminar Flow  [PDF]
H. Taherian,H. Mirgolbabaei
Journal of Applied Sciences , 2009,
Abstract: In this study, a second law comparison of irreversibility is used to determine the optimum duct geometry which minimizes losses for a range of laminar flows with constant wall heat flux condition. Water as a working fluid is considered. The duct geometries used are rhombic with various angle of bevel and circular. Hydraulic diameters are used for the different geometries. The rhombic geometry with the angle of 90°, when the frictional contributions of entropy generation become important is the best. Also power required to overcome fluid friction in the mentioned duct is smallest.
Onset of Turbulence in Planar and Circular Pipe  [cached]
L. Jirkovsky,L. Bo-ot
Science Diliman , 2003,
Abstract: A third-order hydrodynamic equation with a molecular structure parameter, obtained through a projection and perturbationformalism from the Liouville equation is applied to circular and planar Poisseuille-Hagen flow. It is shown that there is noprincipal difference in the resulting parabolic velocity profiles as long as the flows remain laminar. However, a difference isnoted in the onset of turbulence in consistency with observations, showing larger stability of the parabolic velocity profilein circular pipe.
Comparative Thermal Analysis of Circular and Profiled Cooling Channels for Injection Mold Tools
K. Altaf,V.R. Raghavan,A.M.A. Rani
Journal of Applied Sciences , 2011,
Abstract: Injection Mold Thermal Management is a critical issue in plastic injection molding process and has major effects on production cycle times that is directly linked with cost and also has effects on part quality. For this reason, cooling system design has great significance for plastic products industry by injection molding. It is crucial not only to reduce molding cycle time but also it considerably affects the productivity and quality of the product. The cooling channels in injection molding have circular cross section due to the conventional manufacturing technique of drilling. In Rapid Prototyping and Tooling techniques of fabricating conformal cooling channels, the channel cross section is again circular. In circular channel, there can be a problem that the distance from the edges of channel to the cavity is not constant and it is variable even for conformal channels. This can give problem of not having even heat dissipation. In this study, injection mold designing and thermal simulations were performed and comparison is presented between molds having cooling channels of circular cross section with mold with profiled cross section channels. Thermal analysis and simulations can effectively predict the performance of circular channels as compared to profiled channels. Some concepts are also presented for the manufacturing of molds with circular and profiled channels with the use of metal filled epoxies.
Entropy Generation in Laminar Fluid Flow through a Circular Pipe  [PDF]
Ahmet Z. Sahin,Rached Ben-Mansour
Entropy , 2003, DOI: 10.3390/e5050404
Abstract: A numerical solution to the entropy generation in a circular pipe is made. Radial and axial variations are considered. Navier-Stokes equations in cylindrical coordinates are used to solve the velocity and temperature fields. Uniform wall heat flux is considered as the thermal boundary condition. The distribution of the entropy generation rate is investigated throughout the volume of the fluid as it flows through the pipe. Engine oil is selected as the working fluid. In addition, water and Freon are used in a parametric study. The total entropy generation rate is calculated by integration over the various cross-sections as well as over the entire volume.
Comparison of the Exact and Approximate Values of Certain Parameters in Laminar Boundary Layer Flow Using Some Velocity Profiles  [cached]
Asuquo Essien Eyo,Nkem Ogbonna,Moses Effiong Ekpenyong
Journal of Mathematics Research , 2012, DOI: 10.5539/jmr.v4n5p17
Abstract: We apply second, third, fourth, fifth and sixth order velocity profiles to discuss laminar boundary layer flow over a flat plate. Inclusion of these velocity profiles in Von Karman-Pohlhausen (1921) momentum integral equation enables us to determine the approximate values of the parameters namely, (i) boundary layer thickness, (ii) displacement thickness, (iii) momentum thickness, (iv) thickness ratio, (v) skin friction coefficient, (vi) drag coefficient and (vii) the shear rate relation on the plate. Comparison of the approximate values with the exact Blasius (1908) values leads to the determination of the percentage error for each of the above parameters for the different velocity profiles. From the sixth order velocity profile we can predict that higher order velocity profiles will yield greater percentage errors and hence worse and worse results for these parameters except displacement thickness.
Second Law Analysis of Laminar Flow in a Circular Pipe Immersed in an Isothermal Fluid  [PDF]
Vishal Anand,Krishna Nelanti
Journal of Thermodynamics , 2013, DOI: 10.1155/2013/234264
Abstract: Entropy generation and pumping power to heat transfer ratio (PPR) of a laminar flow, for a circular tube immersed in an isothermal fluid, are studied analytically in this paper. Two different fluids, namely, water and ethylene glycol, are chosen to study the influence of fluid properties on entropy generation and PPR. The expressions for dimensionless entropy generation, Bejan number and PPR are derived in a detailed way and their variations with Reynolds number, external Biot number, and the dimensionless temperature difference are illustrated. The results of the analysis are compared with those for a laminar flow in a circular tube with uniform wall temperature boundary condition. Finally, a criterion is established to determine which type of thermal boundary conditions is more suitable for a particular fluid, with respect to its influence on entropy generation. 1. Introduction Heat transfer is a fundamental source of thermodynamic irreversibility in all real engineering devices. When heat is transferred across a finite temperature difference, some capacity to do work is lost. In convection, apart from heat transfer, fluid friction is the other source of loss of available work. Both heat transfer and fluid friction generate entropy. This entropy generation must be minimized to reduce the loss of available work. Entropy generation minimization is no longer an avant-garde philosophy but a mainstream one in the design of thermal systems. In the past, many researchers have studied the problem of entropy generation minimization in fluid flow with heat transfer. Bejan [1, 2] outlined the method for evaluating the entropy generation in fluid flow with heat transfer. He found out the entropy generated in fluid flow with heat transfer over a flat plate, in a duct, for cylinders in cross flow and in various other geometrical configurations. ?ahin [3] studied the entropy generated in a circular duct with uniform wall temperature for two fluids, namely, water and glycerol. The effect of temperature on viscosity was taken into account in that study. He found out that the total energy loss (due to pumping process and entropy generation) can be minimized with respect to the duct length for viscous fluids with temperature dependent viscosity. ?ahin [4, 5] also considered the effect of duct geometries on the entropy generation, both for uniform wall temperature and for uniform heat flux boundary conditions. The various duct geometries like circular, square, rectangular, equilateral triangle, and sinusoidal were considered. In general, circular geometry was found to be
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