Light microscopic investigation of the effect of the freezing process on mass transfer during sublimation

582

26th

ABSTRACTS,

gical Research, MRC Clinical Research Centre, Northwick Park Hospital, Harrow, Middlesex HA1 3UJ, United Kingdom). Nonfreezing cold injury (NFCI) results from cooling at temperatures between + 15 and - 1°C for prolonged (>6 hr) periods. The condition affects the foot primarily and produces acute pain, paraesthesia, and vascular failure: this may in time lead to gangrene necessitating amputation. The etiology is still poorly defined. Using an anesthetized rabbit hind limb model immersed in cold water for 12 or 16 hr, we have investigated the relative importance of temperature, immersion, and ischemia and studied the development of a neuropathy and myopathy. EMG and nerve conduction studies and light and electron microscopy revealed that after 12 hr cold immersion, axonal degeneration occurs with large myelinated axons the most susceptible; there is also some evidence of nonmyelinated axonal degeneration and regeneration. No comparable damage could be detected in other tissues which suggests that NFCI is primarily a neuropathy with secondary vascular and ischemic sequelae. 134. A Clinical Hypothermal

Use of Peripheral Nerve Technique. Xu BAODE

Repair

by

ET AL.

(89

Hospital, Weifang, Shantung, People’s Republic of China). 135. Light Microscopic Investigation of the Effect of the Freezing Process on Mass Transfer during Sublimation. M. KOCHS AND C. K~RBER

(Helmholtz-Institut fiir Biomedizinische Technik an der RWTH Aachen, D-5100 Aachen, West Germany). Two different experimental setups were constructed for the observation of the processes during defined freezing and subsequent drying. Both were used to correlate the sublimation kinetics to the morphology of the ice crystals formed during freezing. The first apparatus was designed to simulate the thermal conditions typical for bulk samples, with the consequence that the ice matrix morphology changes during the progressing solidification process. The phenomena during freezing and subsequent drying, qualitatively similar to those occurring in a bulk sample, could be investigated in that way. The second apparatus, utilizing a gradient stage for directional solidification (the sample is frozen with a constant interface velocity and a constant temperature and concentration gradient at the phase boundary), creates an ice matrix of regular morphology. With this setup mass transport through the partially dry ice matrix could be investigated and correlated to the characteristic size of the crystals. The model solution used in the experiments was an aqueous hydroxyethyl starch solution (10 wt%). Two important preliminary results of the experiments are: (i)

ANNUAL

MEETING

During freezing a layer of highly concentrated solution is formed on the surface of the sample, which forms a significant barrier for vapor transport during drying. (ii) Some ice crystals may not have proceeded to the outer surface of the sample during freezing. These do not dry as rapidly as the surrounding crystals, and mass transfer has to be performed through the highly concentrated amorphous intercrystalline solution. Applying the theory for mass transfer in capillary porous bodies, mass transfer coefficients are calculated from the experiments. 136. Cryopreservation ing Navier-Stokes AND

GEORGE

Perfusion Flow Simulation UsEquations. LEE SEUNGSOO S. DULIKRAVICH

(Penn

State

Uni-

versity, University Park, Pennsylvania 16802). During perfusion of tissues with cooling liquids, flow pattern inside the flow passages influences convective heat transfer process. We have developed a computer software package capable of accurately predicting detailed temperature or heat flux distribution on the walls of two dimensional and three dimensional flow passages of varying cross-sectional shapes and sizes. The analytic model consists of complete NavierStokes equations for incompressible, steady, laminar flow of Newtonian fluids. Computational grids used to discretize realistic flow passage configurations were developed on the basis of our previous work on boundary-conforming grids using efficient optimization. Our flow analysis iterative algorithm is computationally efficient since it incorporates our new method for acceleration of iterative algorithms. We have obtained detailed computational prediction of flowfield velocity vectors, pressures, local stresses, wall friction, and convective heat transfer coefficients in small passages having varying cross sections including strongly stenosed blood vessels. Results were obtained for cooling fluids at different bulk temperatures and for the passage walls at different temperatures. Various perfusion speeds and cooling liquid viscosity and density variation were studied by computing flows at different Reynolds numbers with the capability of numerically predicting strong recirculation regions. In the future we plan to include turbulence modeling so that we can simulate perfusion in large vessels at higher Reynolds numbers. We also plan to couple our heat conduction prediction computer code with this software package in order to get a time-accurate prediction capability for the combined convective/conductive heat transfer in a perfused tissue. 137.

The

Theory

BRONSHTEYN

of Crystallization (Department

Hydrolysis. of Agronomy,

V. Cor-

nell University, Ithaca, New York 14853). As an example of the phenomenon of crystallization hydrolysis, let us consider hydrolysis in the case of