Showing papers by "Indian Institute of Technology Kharagpur published in 1978"

Minimum fluidization velocities in beds of mixed solids

Abstract: The fluidization behaviour of a bed of solids of mixed sizes and/or densities indicates that for a range of velocities between ubf (the velocity of beginning of fluidization) and utf (the velocity of complete fluidization), such a bed is only partially fluidized. The phase diagrams of these systems show that the phenomenon is analogous to the fractional crystallization of a multicomponent solution and it can find use in selective classification of solids. In the present work, data on ubf and utf for liquid fluidized beds of two, three, four and five component mixtures have been processed along with those reported earlier on gas-solid systems, to yield useful correlations for their prediction. Le comportement relatif a la fluidisation d'un lit forme de matieres solides de differentes dimensions et/ou densites indique que, pour des vitesses comprises entre ubf (vitesse au commencement de la fluidisation) et utf (vitesse lorsque la fluidisation est complete), un lit de ce genre n'est que partiellement fluidise. Les diagrammes des phases des systemes en question montrent que le phenomene est analogue a la cristallisation fractionnaire d'une solution a composants multiples et qu'il peut trouver une application dans la classification selective des matieres solides. On a traite, dans le present travail, les donnees relatives a ubf et utf, dans le cas de lits fluidises liquides qui comprenaient des melanges de 2, 3, 4 et 5 composants, ainsi que celles qui ont ete rapportees anterieurement sur les systemes formes de gaz et liquides; on en a deduit des correlations utiles pour leur prevision.

Long waves on a layer of a visco-elastic fluid down an inclined plane

Abstract: In this paper the finite amplitude stability of long waves on a layer of a second-order fluid flowing down an inclined plane is discussed. A systematic expansion procedure in terms of a parameterµ, which is the ratio of the undisturbed layer thickness to a representative length down the plane, is developed and solutions are obtained toO(µ3). It is found that weakly non-linear monochromatic waves tend to attain equilibrium states for Weber numbers ofO(µ−2). This equilibrium amplitude first increases with increase in the elastic parameterM, reaches a maximum and then decreases withM. It is also shown that the second fluid behaves like a Newtonian fluid with its viscosity reduced through division by the factor 1 + (5M/2).

Coupling of Waveguides through Large Apertures

Abstract: A closed form expression for the equivalent network of a narrow transverse slot in the common broadwall between two waveguides is derived in terms of self-reaction and discontinuity in modal voltage. The coupling is expressed in terms of equivalent circuit parameter. A comparison between theoretical results with those obtained from the results of Levinson and Fredberg (for slot length > 0.4a, where a is the broad dimension of the waveguide), the results obtained from the formula of Sangster and the experimental results are presented.

Electromagnetic Wave Propagation in a Rectangular Waveguide with Sinusoidally Varying Width

Abstract: Wave propagation along a rectangular waveguide with slowly varying width has been investigated with the help of field theory and approximate circuit theory. In the field theory approach, two different methods of analysis have been attempted. Many properties of the modulated periodic structure, e.g., the frequency dependence of the propagation constant group and phase velocities and the electric field axial variation for the fundamental space harmonic and its filter-like property have been investigated. The magnetic field lines on the H-plane for a typical case exhibit an expected configuration. Experimental results show close agreement with analysis. It is concluded that this structure supports the fast fundamental space harmonic.

Axisymmetric vibration of human skull-brain system

Abstract: Vibrations of the human head modelled as a prolate spheroidal shell are considered. The shell is assumed to be made of a linear viscoelastic solid containing a viscoelastic fluid representing the brain. Steady-state response of human-sized skull-brain system due to an axisymmetric load is analysed. The effect of the eccentricity of the shell on its stiffness is found to be quite significant.

Effect of particle size on the mechanical properties of poly(vinylchloride)-copper particulate composite

Abstract: The effect of particle size ratios on tensile strength, tensile modulus, impact strength, Vickers hardness and transverse rupture strength of particulate PVC-Cu composite has been studied. The strength values reach a maximum at a particular metal loading where the formation of a segregated network is believed to occur. This critical metal loading shifts towards lower values with increasing polymer-to-metal size ratios. The mean free path calculated from the proposed model is found to be same in all metal loadings, corresponding to strength maxima irrespective of the particle size ratios. A correlation between strength properties and the mean free path has been suggested.

Pulsatile flow of a dusty fluid through a constricted channel

Abstract: The problem of pulsatile flow of a fluid, containing small solid particles, through a two-dimensional constricted channel is studied in view of its importance in arteriosclerosis. A perturbation solution is sought in terms of the slope of the channel. The effects of mass concentration of dust particles on the streamline pattern, axial velocities of the fluid and solid particles, shear stress and pressure distribution are studied.

An Adjustable-Speed Induction Motor Drive with a Cycloconverter-Type Thyristor-Commutator in the Rotor

Abstract: An adjustable-speed drive comprising a slip-ring induction motor and a cycloconverter-type thyristor-commutator in its rotor circuit has been developed. The thyristor-commutator acts as a frequency-changer like a conventional commutator in a stator-fed ac commutator motor, converting line-frequency injected voltages directly to slip-frequency at the rotor terminals. The circuit permits a reversible power flow naturally, and speed-control is possible for subsynchronous as well as supersynchronous operation by controlling the injected secondary voltage. A rotor position-detector is used to switch the thyristor configuration in a sequential manner to generate an output voltage having a predominant slip-frequency component. The control logic and triggering circuit developed for the experimental drive are described in some detail. Experimental results as obtained with a laboratory model are presented together with some results of computer simulation of the drive system. Major limitations of the scheme and the scope for improvement are discussed.

Application of Gyarmati Principle to Boundary Layer Flow

Abstract: The paper deals with the development of a new variational method based on Gyarmati's principle for the solution of boundary layer flow along a flat plate. It is found that the variational solution differs by about 4% from exact result when a trial function of third degree is chosen for velocity profile. The results obtained with the help of the force representation of the principle are the same as obtained by the local potential method of Glansdorff and Prigogine. A polynomial of sixth degree with the help of universal form of the principle gives a result which differs by about 0.65% from the exact solution. The governing principle of dissipative processes, it seems, will prove itself quite satisfactory analytical method for the boundary layer flows.

Fluctuating boundary layer on a heated horizontal plate

Abstract: The paper deals with the boundary layer flow and heat transfer on a horizontal plate whose temperature differs from that of ambient fluid. The basic flow is purely induced by buoyancy which is caused by the difference of temperature in the plate and the fluid. The oscillation in the plate temperature causes a time dependent boundary layer flow and heat transfer. Two separate solutions for high and low frequency ranges are developed. The velocity and temperature fields are obtained with the help of Karman-Pohlhausen method in the low frequency range while for high frequencies we have employed a series expansion method in terms of frequency parameters. For very high frequencies, the oscillatory flow pattern is of ‘shear wave’ type unaffected by the mean flow and predicts a phase lead of π/4 in the local rate of heat transfer fluctuations while the skin friction has a phase lead of π/2.

Dynamics of rectangular footings by finite elements

Abstract: A finite element solution in three dimensions for rectangular footings resting on soil medium has been presented for the vertical mode of vibration. Soil medium has been idealized as an elastic half space. Both linear and nonlinear, as well as depth dependent, soil properties have been considered for analysis. For discretizing into a finite number of elements, the semi-infinite elastic medium is idealized as a bounded region by adopting appropriate boundary conditions. A simple hexadedron isoparametric element with eight nodes (ZIB8) has been taken as basic element. Experimental and analytical studies indicate that the nature of contact pressures at the footing-soil interface changes with the magnitudes of operational frequencies, thus all probable contact pressures have been incorporated in the analysis. Effects of embedment, static surcharge, nonhomogeneity, and nonlinear stress-strain characteristics are shown. Influences of the aforementioned factors on the resonant frequencies have been reported. Results are compared with the existing solutions and presented graphically.

Impedance of off-centered stripline fed series slot

Abstract: Theoretical and experimental results on the variation of the impedance characteristics of displaced series slots in the ground plane of a stripline are presented.

Effect of re-irradiation on Z1 centres

Abstract: Thermoluminescence (TL) is used to study the effect of re-irradiation on Z1 centres in Ca-doped KBr crystals. The results show that re-irradiation with X-rays of F bleached crystal destroys the Z1 centres in agreement with the observations made by earlier workers based on purely optical absorption studies. However, the present investigation clearly shows that during re-irradiation Z1 V recombination takes place instead of Z1 F conversion as suggested by earlier workers. Mittels Thermolumineszenz (TL) wird der Einflus einer Bestrahlung von Z1-Zentren in Cadotierten KBr-Kristallen untersucht. Die Ergebnisse zeigen, das die erneute Bestrahlung eines Kristalls mit gebleichten F-Zentren mittels Rontgenstrahlen die Z1-Zentren zerstort in Ubereinstimmung mit den fruher von anderen Autoren gemachten Beobachtungen bei rein optischen Absorptionsuntersuchungen. Jedoch zeigt die vorgelegte Untersuchung deutlich, das wahrend der wiederholten Bestrahlung, anstatt der von den fruheren Autoren vorgeschlagenen Z1 F-Konversion, Z1 V-Rekombination stattfindet.

A cation exchange resin from poly(N‐vinyl carbazole)

Abstract: Poly(N-vinyl carbazole) was sulfonated with different sulfonating agents and ion exchange capacities of the resins produced were evaluated. A maximum capacity of 4.5 meq · g−1 of dry resin was realized when sulfonation was done with 98.8% H2SO4 at 30°C for 10 h. The pH titration curves reveal the nature of a strong monofunctional cation exchanger with a pK value of 2.2. The resin exhibits a moderate rate of exchange with NaCl and is thermally stable up to ca. 250°C. Poly(N-vinylcarbazol) wurde mit verschiedenen Reagenzien sulfoniert und die Ionenaustauschkapazitat der erhaltenen Harze bestimmt. Eine maximale Kapazitat von 4,5 meq · g−1 des trockenen Harzes wurde durch 10stundige Reaktion mit 98,8proz. H2SO4 bei 30°C erhalten. Die pH-Titrationskurven lassen einen starken monofunktionellen Kationenaustauscher mit einem pK-Wert von 2,2 erkennen. Das Harz zeigt eine masige Austauschgeschwindigkeit mit NaCl und ist bis zu 250°C thermisch stabil.

Laminar free convection heat transfer of a viscous incompressible heat generating fluid-flow past a vertical porous plate in the presence of free-stream oscillations. I

Abstract: The title problem has been analysed with a view to estimate the effect of the temperature dependent heat sources (sinks) on the oscillatory flow and heat transfer. The governing equations have been reduced to two non-linear ordinary differential equations which have been solved approximately subject to the relevant boundary conditions. The flow- and heat-transfer characteristics have been found to depend on the heat source parameter α besides the usual free convection parameterG, the wall temperature-ratio parameterm, the Prandtl numberP and the Eckert numberE. For convenience the work has been divided into two parts, Part I dealing with the mean flow and heat transfer and the Part II with the unsteady flow and heat transfer. Several qualitatively interesting results concerning the effect of heat sources (sinks) on the mean flow and heat transfer have been pointed out clearly in Section 3.

Effect of Elevated Temperature on the Unaccelerated and Accelerated Sulfur Vulcanization of Natural Rubber

Abstract: High cure temperature up to 180°C seems to have no significant effect on the mechanism of unaccelerated sulfur vulcanization of natural rubber. In the case of accelerated systems, the conventional ones undergo more desulfurization and decomposition of the initially formed polysulfidic crosslinks at higher cure temperature. The EV systems show less dependence on cure temperature, and the main maturing reaction seems to be desulfurization of the polysulfidic crosslinks. The semi-EV system shows behavior intermediate between the conventional system and the EV one. Expectedly, the EV systems show better resistance to reversion at high cure temperature than the conventional and semi-EV systems.

Co-current flow liquid-liquid binary mass transfer in ejectors

Abstract: Liquid-liquid binary mass transfer involving simultaneous transfer of an organic phase component to the aqueous phase and an aqueous phase component to the organic phase in water-n butanol and water-methyl ethyl ketone systems has been studied in a vertical ejector system. Correlations have been developed to predict both dispersed and continuous phase film capacity coefficients as function of various physical and dynamic variables of the system. On a etudie, dans un dispositif d'ejecteur vertical, le transfert de masse d'un liquide a un autre; il s'agissait du transfert simultane d'un composant d'une phase organique a une phase aqueuse et du composant d'une phase aqueuse a une phase organique dans les systemes eau-butane normal et eau-cetone methylee et ethylee. On a mis au point des correlations qui permettent de prevoir les coefficients de capacite de transmission superficielle, a la fois en phase dispersee et en phase continue, en fonction des diverses variables physiques et dynamiques du systeme.