David P. Kessler

Momentum, heat, and mass transfer fundamentals

Essentials the mass balances the energy balances the momentum balances application of dimensional analysis momentum transfer in fluids heat transfer models mass transfer model. Appendices: vector and tensor operations error function nomenclature.

The permeability tensor for anisotropic nonuniform porous media

Abstract This paper describes a study of the permeability of anisotropic, nonuniform porous media. The approach is through a statistical model of the microstructure of the porous media. Using a capillary-type model with a distribution of pore sizes and orientations, we show that the permeability can be described by a second-order symmetric tensor regardless of the preferential orientation of the pores in the microstructure. We also show that an ergodic assumptions is not always true—spatial averages cannot generally be interchanged with mathematical expectations.

Average Pore Velocities in Porous Media

It is shown that for a statistical model of a porous medium with nonuniform pores, the number average pore velocity and the velocity given by the Dupuit‐Forcheimer relation are equivalent only in certain limiting cases.

A kinetic analysis of the acidic degradation of penicillin G and confirmation of penicillamine as a degradation product

Two recently proposed degradation pathways for the acidic degradation of pencillin G were examined by calculating the theoretical time course based on each pathway and examining the fit of the theoretical predictions to the experimental data. A substantial difference in the goodness of fit was observed. The degradation pathway which provided the best fit included penicillamine as a terminal degradation product. This pathway is therefore favoured since penicillamine was also identified as a degradation product of penicillin G by both reversed-phase high pressure liquid chromatography and differential pulse polarography.

Investigation of a proposed penicillin G acidic degradation scheme using high-pressure liquid chromatography and optimization techniques and mechanistic considerations

Optimization techniques were used to fit a recently proposed degradation scheme to recently published n.m.r. data for the time course of penicillin G and four degradation products at pH 2.5 and 37°C. Several conclusions arising from the n.m.r. analysis which were originally associated with the degradation scheme were not compatible with the optimized rate constants. It was necessary to change substantially the proportion of penicillin G degrading through benzylpenicillenic acid, benzylpenillic acid, and benzyl-penicilloic acid in order for the degradation scheme to fit the n.m.r. data. Benzylpenillic acid replaced benzylpenicillenic acid as the major product. The rate constants best describing the n.m.r. data showed benzylpenicillenic acid proceeding almost exclusively through benzylpenamaldic acid. Such optimization implied that the scheme could be simplified to three parallel reaction pathways, the dominant reaction occurring through benzylpenillic acid. However, mechanistic considerations indicate that the direct conversion of penicillin G into benzylpenillic acid is not possible and that a likely intermediate is benzyl-penicilloic acid. The degradation of benzylpenicilloic acid at pH 2.5 was consequently monitored by ionpair reversed-phase high-pressure liquid chromatography and rapid formation of benzylpenillic acid was detected. This observation is inconsistent with the recently proposed degradation scheme, even though the scheme can be made to fit the n.m.r. kinetic data.

MASS TRANSFER CHARACTERISTICS OF A SORBENT-BASED RECIPROCATING DIALYZER

Theoretical analysis of solute transfer in a dialyzer with ideal periodic flow patterns provides a quantitative basis of evaluating designs and interpreting data. For constant volumetric flow rate of blood in each half cycle, two mass transfer models have been developed: one with fixed thickness of the blood film and changing transfer area and another with changing thickness and fixed transfer area. Fractional solute removal is calculated for membrane-Sherwood number ranging from 0.01 to infinity and dimensionless cycle time from 0.01 to 70. The theoretical efficiency of the second model is about twice that of the first, and within 20% of that of a flow-through parallel plate dialyzer with the same blood film thickness and membrane area, In-vitro experiments of creatinine transfer agree with the first model within experimental accuracy.