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We have investigated the physicochemical basis of electrokinetic charge separation in methanol using micron-sized channel diameters under both turbulent and laminar flow conditions. Turbulent flow studies were conducted using a 40 μm diameter stainless steel aperture which had a channel length of 0.5 mm. Under these conditions, electrokinetic streaming currents arose from a charge stripping process in the region close to the aperture channel wall. The moving liquid removed the relatively weakly held charges from the outer portion of the electrical double layer formed at the solid−liquid interface. Streaming currents were simultaneously measured at both the conducting aperture and a downstream copper plate. The magnitudes of the streaming currents were shown to be equal at the aperture and the plate; however, the sign of the current at each measurement location was opposite. The magnitude of the streaming currents varied quadratically with mean liquid flow velocity. Studies under laminar flow conditions were conducted using a 3 cm length of fused silica capillary which had an internal diameter of 25 μm. Under laminar flow conditions at higher flow velocities through the nonconducting fused silica channel, the extent of charge separation was ultimately limited by the extent to which excess charge built up within the capillary could be neutralized. We develop a simple model that shows how an interplay between fluid flow, ion mobility, and solid−liquid interfacial chemistry influences the extent of electrokinetic charging in the fused silica channels.

The purpose of this work is to validate, using numerical, finite element methods, the thermal assumptions made in the analytical analysis of a coupled thermistor probe-tissue model upon which a thermal conductivity measurement scheme has been based. Analytic, closed form temperature profiles generated by the self-heated thermistors can be found if three simplifying assumptions are made: 1)  the thermistor is spherical; 2)  heat is generated in all regions of the bead; and 3)  heat is generated uniformly in the bead. This analytic solution is used to derive a linear relationship between tissue thermal conductivity and the ratio of thermistor temperature rise over electrical power required to maintain that temperature rise. This derived, linear relationship is used to determine thermal conductivity from the observed experimental data. However, in reality, the thermistor bead is a prolate spheroid surrounded by a passive shell, and the heating pattern in the bead is highly nonuniform. In the physical system, the exact relationship between the tissue thermal conductivity and parameters measured by the thermistor is not known. The finite element method was used to calculate the steady-state temperature profiles generated by thermistor beads with realistic geometry and heating patterns. The results of the finite element analysis show that the empirical, linear relationship remains valid when all three simplifying assumptions are significantly relaxed.

A finite element model of the bioheat transfer equation has been developed to simulate the temperature distribution in the head of a subhuman primate. Simulations were made of the induction of deep hypothermia and of subsequent hypothermic circulatory arrest (HCA). Simulations of the circulatory arrest phase were performed with different values of surface heat transfer coefficient and tissue metabolic heat generation. Numerical results were compared with experimental data for the same procedure. The simulations indicate the brain cools rapidly to a near isothermal condition in response to an infusion of cold arterial blood. However, extracerebral structures cool much more slowly. The bulk of heat gain by the brain during HCA is due to heat transfer from these warmer extra-cerebral tissues. These results suggest extended cooling by cardiopulmonary bypass (CPB) combined with surface cooling pads should reduce or even prevent the rise of brain temperatures during HCA.

This paper investigates some of the numerical problems involved in simulating heat transfer in porous media in the presence of phase change. Applications of this type of simulation include modeling of certain metal forming processes, of biological tissues and organs during cryosurgery or cyropreservation, and of heat transfer in frozen soils subjected to transient environmental conditions. A two-dimensional finite element model was used in which the latent heat is treated directly as an energy source in the problem formulation. Several parameters addressed in this work are crucial to the successful implementation of numerical methods for nonlinear heat transport with phase change, including: the effect of nodal point spacing on the occurrence and magnitude of numerical oscillations in the temperature solution and the use of grid point spacing to control these oscillations; the limiting element size which should be used in order to insure stable temperature fields; and the effect which the range of temperatures over which latent heat is liberated has on the solution. The results indicate that numerical stability is achieved for combinations of the foregoing parameters which yield small values of the Stefan number.

The burn process resulting from the application of a hot, cylindrical source to the skin surface was modeled using the finite element technique. A rotationally symmetric 125-element mesh was defined within the tissue beneath and outlying to an applied heating disk. The disk temperature and duration of contact were varied, respectively, between 50 and 100°C for up to 30 s. Natural convection with ambient air was assumed for areas of skin surface not in direct contact with the disk. The simulated thermal history was used in a damage integral model to calculate the extent and severity of injury in the radial and axial dimensions.

Direct fluorination has been shown to impart moisture-transport, soil-release, and soil-antiredeposition properties to polyester material. These properties do not have the limitations associated with previous treatments such as stability, washfastness, and/or reproducibility. It is believed that the improved properties of polyester can be attributed to an increase in acidity and to the addition of fluorine to the polymer backbone. The direct fluorination treatment is unaffected by dyeing, heat setting, or ultraviolet light.