ABSTRACT
Recent progress in modeling pure liquid and dendritic alloy solidification is reviewed to lay the groundwork for freezing of solutions relevant to cryopreservation of biological materials. The classical Stefan problem of freezing/melting a pure substance is discussed first to introduce some of the fundamental concepts, and then the framework for modeling the freezing of solutions is reviewed. The formalism is extended to the freezing of a solution-saturated porous media. As an application of the methodologies developed by engineers, freezing of a sodium chloride solution in a flat bag is simulated, and then using the temperature and salt concentration data calculated the kinetics of water loss from a model cell is predicted.
ABSTRACT
Approximate methods for calculating the error introduced by the deflection of the light beam or refractive error in schlieren, shadowgraph, interferometric, and holographic measurements of transport phenomena are investigated. Relative error is reported for the well-known correction parabola and paraxial approximations as well as for a new first-order approximation in both a linear and nonlinear refractive index field. The first-order approximation is exact in a linear field but is in about the same error as the other approximations in the nonlinear field of a boundary layer. In many cases, actual optical data can be corrected for refractive errors by using the results presented.
ABSTRACT
A spectral remote sensing method for recovering the temperature distribution in semitransparent solids from remotely sensed spectral emission data is studied. An analytical model that relates the emerging spectral intensity from a plane layer of solid heated by an external radiation source to the temperature distribution, spectral radiation properties, radiation characteristics of the interfaces of the solid, and the source is formulated. The temperature profile is expressed in the form of a finite series of Legendre polynomials; and the coefficients are obtained using an optimization scheme that, by iteratively solving the expressions for emerging intensity, reconstructs the distribution that best fits the spectral emission data. The validity and accuracy of the remote sensing method is evaluated by comparing the recovered temperature with independent measurements in two different experiments; one using surface thermocouples only and the other a Mach-Zehnder interferometer. Experimental results are reported for PPG clear float glass and Corning Code 7940 fused silica using a Perkin-Elmer spectrometer and Barnes Spectralmaster radiometer to measure the emerging spectral radiant energy. For clear float glass, the recovered temperatures were a maximum of 1.5% higher than those measured with surface thermocouples. For fused silica, the linear recovered and interferometrically measured temperature profiles agreed well, with the maximum deviation never exceeding approximately 2% up to about 1000 K.
ABSTRACT
The mutual diffusional interference between adjacent stomata in laminar flow over a leaf is shown to play a decisive role in determining overall transpiration. The magnitude of this interference varies with the interaction of the vapor diffusional shells forming above each stoma and the air flow over the leaf. The interference decreases with increasing incident radiation and wind velocity. The effect of interference on the stomatal resistance to diffusion plays a major role in the overall variations in transpiration.
