Influence of the main parameters of a parallel-plate dialyser under laminar flow conditions
A mathematical model describing the mass transfer in a parallel-plate dialyser with co-current laminar flow in both channels based on the Navier-Stokes equations and Fick's second law was developed. Numerical solutions are presented for pulse- and stepwise concentration changes of the solute in one of the channels using the Laplace transform technique. By simulation the influence of the main design and operational parameters of the dialyser and the most important physical constants for the mass transfer process were investigated. Conclusions with regard to optimum design and operation were drawn and some possibilities for simplifying the model were established
Analysis of transient laminar mass transfer in a parallel-plate dialyser
Mass transfer under laminar flow conditions is discussed on the basis of the Navier-Stokes equations and the axially dispersed plug-flow model. By fitting the results with these two approaches, relationships can be derived for predicting the mass-transfer coefficient and the Peclet number in a parallel-plate laminar flow system with on impermeable wall and an opposite wall at which the concentration is uniform. This single-stream relationship can be utilized for calculating the mass-transfer coefficients in both channels of a co-current parallel-plate dialyser. It is shown that the Peclet number in the axially dispersed plug-flow model derived for a parallel-plate flow where both sides are impermeable gives better results when applied to the co-current dialyser than the single-stream relationship. The results obtained allow the mathematical modelling of process and analytical flow-through manifolds incorporating a dialysis module.
Similarities in protozoan and flatworm habituation behavior.
ONE problem in the study of habituation in protozoa is that similar results, given the same experimental manipulations, may not be obtained in metazoa. I shall compare habituation behaviour in the protozoan Spirostomum with that in the micrometazoan Rhabdocoel flatworm Stenostomum; it remains to be shown whether there is a correspondence between protozoa and metazoa both in behaviour and in their underlying chemical processes. Both these organisms contract in response to mechanical and touch stimuli: when subjected to repeated stimulation, they habituate1. Furthermore, the more intense the stimulus, the longer it takes for habituation to occur1.