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The boiling models use departure diameter and frequency in closure relations for the calculation of nucleate boiling heat flux. These parameters are normally derived from empirical correlations which depend heavily on experiments. While these parameters are studied mostly for saturated conditions, there is not sufficient data for the values of departure diameter and frequency in subcooled boiling. In this work, the bubble departure characteristics, i.e. the departure diameters and frequency have been measured using high speed visualization experiments with subcooled demineralized water at atmospheric pressure for nucleate pool boiling conditions. The water pool dimensions were 300  mm × 135  mm × 250  mm with four different heating elements to carry out the parametric studies of bubble departure behavior. The considered parameters were heater surface roughness, heater geometry and heater inclination along with the experimental conditions like degree of subcooling (Δ T sub = 5−20 K), superheat (Δ T sat = 1−10 K) and the heat flux. The departure diameters and frequencies were directly measured from the images captured. It was intended to generate the subcooled nucleate pool boiling data under a wide range of conditions which are not present in the literature. The departure diameter was found to increase with the wall superheat, heater size and the inclination angle while the liquid subcooling and surface roughness produced a damping effect on the diameter. The departure frequency was found to increase with the wall superheat and the inclination angle, but decreases with an increase in the heater size. The frequency increases with the degree of subcooling except very close to the saturation, and is unaffected by the surface roughness beyond a certain superheat value. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this study was to determine the sphingolipid (SL) profile in cells defective in autophagy protein ATG-7 and overall cell death after photodynamic therapy (PDT) with the photosensitizer Pc 4. MCF-7 human breast cancer cells with downregulated ATG-7 and their scrambled controls (Scr) were used. Exposure of ATG-7 knockdown cells to PDT led to increased cell killing. PDT evoked an early (2h) greater global increase in ceramides in ATG-7 defective cells compared to Scr cells. The total increases in dihydroceramide (DHceramide) were significant at 2 and 24h in both cell types post-PDT. The levels of sphingosine-1-phosphate (S1P) and sphingosine were decreased below resting levels at both time points irrespective of the cell type. The data imply that ceramide might be a marker of ATG-7 deficiency in cells sensitized to PDT. [Copyright &y& Elsevier]