Kamalesh K. Sirkar

Creeping flow mass transfer to a single active sphere in a random spherical inactive particle cloud at high schmidt numbers

Using the solution by Tam of Navier-Stokes equations for creeping flow around an active sphere surrounded by a random cloud of inactive spheres, an asymptotic solution of the convective diffusion equation is obtained for high Schmidt numbers. The Sherwood number for the overall mass transfer coefficient to the active sphere has been analytically related to the Peclet number as It agrees very well with the experimental mass transfer data on single active spheres for σ = 0476, Re < 10 and large Sc. This analytical result becomes invalid as σ decreases to 0.33. Pfeffers model for the same problem has excellent agreement with the mass transfer data on single active spheres for σ = 026, Re < 10 and Sc = 1600. Pfeffers model seems to be quite satisfactory for the usual range of void volume fractions in packed beds. The present model seems to be more accurate at higher values of void volume fractions in packed and distended beds.

Separation of gaseous mixtures with asymmetric dense polymeric membranes

Abstract The advantages of using asymmetric polymeric membranes with a dense skin and a microporous backing for separation of permanent gas mixtures have been p

Explicit flux expressions in tubular reverse osmosis desalination

Abstract Calculation of actual fluxes in reverse osmosis desalination through membrane tubes involves considerable iteration due to the existence of concentration polarization. Explicit flux expressions have been developed for such cases on the basis of the flux expressions of Lonsdale , Sourirajan, and Johnson to eliminate iteration. Low levels of solvent flux in existing membranes allow approximations leading to such explicit expressions. The computer flow diagram for reverse osmosis plant design with membrane tubes in series has been simplified by means of the explicit flux expressions.

On the Composite Nature of the Extent of Separation

Abstract The fundamental expression for Ronys extent of separation in a 2-component system has been reexamined for any separation stage with respect to its relation with the traditional stage separation factor for a wide variety of separation processes. It has been shown that for a single entry or double entry rate governed barrier separation stage, the extent of separation is a composite index consisting of a stage capacity factor proportional to the barrier area and a stage enrichment factor (α − 1) or (β1 1). The latter-need not be close to zero. For a reverse osmosis and a gaseous diffusion stage, the extent of separation has been expressed in terms commonly used for these processes. The composite nature of the extent of separation has been also determined for batch dialysis, batch thermal diffusion, as well as for a single equilibrium stage, and related to known features of these separation processes in terms of stage capacity and stage enrichment.

A preliminary investigation of the permeation of some permanent gases through foam membranes

Abstract To evaluate gas permeation properties of foam membranes, a preliminary investigation of the permeation of O2, N2, and CO2 through a monolayer of foam bubbles formed on an aqueous glycerol solution with saponin as surfactant was carried out in a new static foam membrane test cell. Foam stability, a prerequisite to meaningful measurement, was highest with a 70% glycerol solution. Using the notion of an average foam bubble, time-dependent measurements of gas composition above foam bubbles and foam bubble height reduction yielded values of permeation parameters from the solution of appropriate mass balance equations. The O2 permeation parameter defined by the ratio of the O2 permeability coefficient and the foam bubble wall thickness was found to have a value comparable to that of a 1-mil-thick silicone rubber film. The O2N2 separation factor, found to be around 2 for the same system, is comparable also to that of a silicone rubber film. Significant absorption of CO2 in the surfactant liquid solution suggests limitations of this new foam permeation cell to gases with extremely limited solubility.

Skin Thickness of Dense Asymmetric or Composite Membranes for Maximum Extent of Separation of Permanent Gas Mixtures

Abstract The dense skin thickness in a dense asymmetric polymeric membrane of the Loeb-Sourirajan type has been optimized for achieving the maximum extent of separation of a binary mixture of permanent gases with the help of Sirkars expression for the extent of separation in a single entry barrier separation stage. The expression for fluxes and separation factor through the dense asymmetric membrane were obtained from a recent analysis by Sirkar. The dense skin thickness on the microporous support in a composite membrane has also been optimized.

Creeping flow in a cloud of round drops having an arbitrary size distribution

Abstract Point force approximation has been used to determine the expected velocity and pressure field in creeping flow around a test drop or bubble placed in a

Stage and point efficiencies in barrier separation processes

Abstract The Murphree type stage and point efficiencies for any rate governed barrier separation process have been critically examined. Standarts plate efficiency definition and the concept of the rate of enriching mass transfer through the barrier have been utilised to propose new definitions of stage and point efficiencies in barrier separation processes with single entry separating elements. Expressions have been derived for the proposed point efficiency for various nonidealities encountered in some common barrier separation processes. An analytical relation between the proposed stage and point efficiencies has been developed for an ideal cross flow stage in a close separation barrier separation process. The procedure for estimating the proposed stage efficiency has been indicated also for a cross flow stage when the flux expressions through an ideal and a real barrier are known.

Point and Stage Efficiencies in Distillation

Abstract The definition of Murphree point efficiency in distillation is critically examined. Characteristics of Standarts stage efficiency definition are utilized to define a new point efficiency on a plate in a column. This new definition was shown to be consistent and symmetrical. For crossflow on a plate, the proposed point efficiency was found to be equal to Standart stage efficiency subject to only the assumption of a uniform value of the proposed point efficiency over the whole plate.