Showing papers by "Indian Institute of Technology Madras published in 1983"

Hydrodynamics of two-phase cocurrent downflow through packed beds. Part I. Macroscopic model

Abstract: Pressure drop and liquid saturation are two important design parameters in cocurrent gas-liquid downflow through packed beds. A macroscopic model based on momentum balance is formulated for the condition of no radial pressure gradients. The model includes the effect of bubble formation on the pressure drop and holdup and is compared with the experimental data of the earlier investigators and of the present study. The model provides a functional form for correlating pressure drop and liquid saturation but some parameters have to be determined by fitting the experimental data.

Linear electrooptic effect in doped KDP crystals

Abstract: The dispersion of half wave voltages with wave length and temperature of potassium dihydrogen ortho phosphate (KDP) crystals with additives and dopants like borax, nickel phosphate, manganese phosphate, sodium dihydrogen orthophosphate and potassium arsenate were determined. The refractive index for all the above crystals were found by the modified Rayleigh’s refractometer method. The linear electrooptic coefficients were calculated at various wavelengths of light. The variation of half wave voltage was also studied as a function of concentration of the dopant.

Active compensation in the switched-capacitor biquad

Abstract: One of the limiting factors in the performance of high-ω p and high-Q p active filters is the finite frequency-dependent gain characteristics of operational amplifiers (op-amps). Investigated here is a simple compensation scheme to reduce the sensitivity of the performance of a switched-capacitor biquad to the finite gain-bandwidth product of the op-amps. Theoretical and experimental results show that the scheme is very useful.

Dispersed phase holdup and drop size distributions in reciprocating plate columns

Abstract: The paper covers an experimental and theoretical investigation of the dispersed phase holdup and drop size distribution for gas-liquid and liquid-liquid counter-current flow in reciprocating plate columns provided with plates having small hole size and free area. The response of the reciprocating plate column is similar to that of liquid-pulsed columns exhibiting mixer-settler and emulsion regions. The dispersed phase holdup depends on the dispersed phase flow rate, the vibrating speed of the plate stack, the plate geometry and the number of plates: it was found to be minimum at the transition between the mixer-settler and emulsion regions. The dispersed phase holdup is modeled incorporating apparent interstitial liquid velocity and the slip velocity to account for the non-descriptive flow pattern between the phases. The drop size distribution is satisfactorily represented on a Rosin–Rammler Chart. Sauter mean diameter, calculated from the distributions, indicated an advantage in the drop size-power consumption relation when plates having small hole size and free area are used. Equipment used for fluid-fluid contacting is often broadly classified as either stagewise or differential contactors. The classification is further sub-divided as gravity, mechanically-agitated and pulse-agitated, depending on the method adopted for interdispersing the phases. Pulse-agitation involves the use of either reciprocating perforated plates moving vertically up and down the column, or pulsing a phase hydraulically keeping the internal structure of the column stationary. The literature on reciprocating plate columns (RPC) primarily is concerned with the study of liquid-liquid systems using perforated plates having large hole size and free area. This paper presents the dispersed phase holdup and drop size distributions for gas-liquid and liquid-liquid systems in reciprocating plate columns with small perforation diameter and free area for the plate.

First passage time distributions for finite one-dimensional random walks

Abstract: We present closed expressions for the characteristic function of the first passage time distribution for biased and unbiased random walks on finite chains and continuous segments with reflecting boundary conditions. Earlier results on mean first passage times for one-dimensional random walks emerge as special cases. The divergences that result as the boundary is moved out to infinity are exhibited explicitly. For a symmetric random walk on a line, the distribution is an elliptic theta function that goes over into the known Levy distribution with exponent 1/2 as the boundary tends to ∞.

Structural and magnetic investigations on the CT ion-radical salt [p-(dimethylamino)phenyl]dimethylammonium bis(maleonitriledithiolato)nickelate(III)

Abstract: Etude du compose du titre par diffraction RX, spectrometrie d'absorption electronique, mesures des susceptibilite magnetique et conductivite electrique, spectrometrie RPE. Les ions Ni(mnt) 2 − et TMPD + forment des strates le long de l'axe a d'une maille triclinique, avec de courts contacts entre les unites facilitant les transferts de charge entre anions et cations. Les mesures de susceptibilite et la spectrometrie RPE mettent en evidence deux domaines de temperature T 100 K. Pour T<100 K, comportement de type Curie-Weiss

Noniterative techniques for minimum phase signal reconstruction from phase or magnitude

Abstract: New noniterative techniques are proposed for reconstruction of signal from samples of magnitude or phase of the Fourier transform of the signal. The only condition for reconstruction is that the signal is a minimum phase one. The basis for these new techniques is the relation between the magnitude and phase functions through cepstral coefficients The techniques are illustrated through several examples. In all the cases we find that phase from magnitude can be obtained exactly and magnitude from phase can be obtained to within a scale factor. Effects of truncation of minimum phase signals and aliasing due to sampling in the frequency domain are discussed. These studies show that effective noniterative techniques can be evolved for signal reconstruction instead of cumbersome iterative procedures suggested in literature recently.

Three-dimensional finite element analysis of cracked thick plates in bending

Abstract: By using the finite element technique, stress intensity factors have been obtained for finite rectangular plates and the results have been given for various h/a, W/a and L/W ratios. By using a three-dimensional isoparametric element, the problem has been considered as a three-dimensional one and the variation of stress intensity factor across the plate thickness has been found to be nonlinear.

Minimal delay realization of first order 2-D all-pass digital filters

Abstract: A method is proposed to realize a first-order 2-D all-pass transfer function with two delays and six multipliers. Stability constraints on the coefficients of first-order 2-D filters are used to guarantee the existence of real-gain multipliers for the realized filter.

First passage time and escape time distributions for continuous time random walks

Abstract: We consider an arbitrary continuous time random walk (ctrw)via unbiased nearest-neighbour jumps on a linear lattice. Solutions are presented for the distributions of the first passage time and the time of escape from a bounded region. A simple relation between the conditional probability function and the first passage time distribution is analysed. So is the structure of the relation between the characteristic functions of the first passage time and escape time distributions. The mean first passage time is shown to diverge for all (unbiased)ctrw’s. The divergence of the mean escape time is related to that of the mean time between jumps. A class ofctrw’s displaying a self-similar clustering behaviour in time is considered. The exponent characterising the divergence of the mean escape time is shown to be (1−H), whereH(0

Competing oxygen migrations in ortho nitro aromatic thioamides on electron impact

Abstract: Interesting competitive oxygen migrations from the nitro group to the nitrogen and to the sulfur have been noticed during the mass spectral decomposition of ortho nitro aromatic thioamides on electron impact. The migration of the oxygen to the nitrogen of the thioamide function results in the formation of stable o-nitrosothiobenzoyl cation. The other novel ortho effect noticed in the ortho isomers is the transfer of an oxygen from the nitro group to the sulfur followed by the ejection of SO from the molecular ions. A mechanism involving the initial oxygen migration to the sulfur through a favourable 6-membered transition state followed by cyclization with the concomitant expulsion of SO is proposed for this process. Other interesting decomposition processes occurring as a consequence of this ortho effect have also been noticed. The proposed mechanisms for these processes are supported by mass analysed ion kinetic energy spectra and high voltage scans.

Hydrodynamics of two‐phase cocurrent downflow through packed beds. Part II: Experiment and correlations

Abstract: Two-phase pressure drop and dynamic and total liquid saturation are experimentally determined for air-water system under cocurrent downflow through packed beds using packing differing widely in geometry The experimental data of the present study as well as that available in literature is satisfactorily correlated in terms of: (a) Lockhart-Martinelli parameters; and (b) the Reynolds numbers defined for the respective phases and the bed porosity, taking into account the flow behavior of the phases through the packed bed