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<br />. <br /> <br />20 <br /> <br />. <br /> <br />After leaving the control valve, the flow entered into the vacuum <br />cleaner. The 16 gallon (60.6 liters) Wet - Dry Shop Vac, with a variac attached <br />to the motor to reduce the voltage supply to a constant 60 volts, provided the <br />necessary suction force despite the long periods of low temperature. <br />Ice crystal nucleation took place by using the popping bubble technique <br />(Ryan et aI., 1976) in a 20-liter jug filled with fog produced by breathing into <br />the container. A cooking baster, with inside walls coated with ice to prevent <br />nucleated crystals from subliming, carried and injected a controlled number <br />of ice crystals through a hole and into the ice crystal suspension tunnel. The <br />growth period began with the injection of the crystals into the tunnel that was <br />allowed to reach thermal equilibrium. The thermocouples ensured that the <br />tunnel temperatures were held constant in the range of -4 to -22oe to within <br />one degree during the entire growth period, which lasted from 4 to 10 <br />minutes. When the experimental period ended at the predetermined <br />moment, the crystals were captured with a cover glass coated with motor oil <br />and placed upside down on a glass slide with depression holding silicon oil to <br />preserve the crystal (Fukuta et aI., 1979). This arrangement provided the <br />means for obtaining a side view by horizontally moving the cover glass and <br />rotating the crystal. These methods of ice crystal preservation and movement <br />helped measure the a- and c-axial lengths after 4, 6, 8, or 10 minutes of <br />growth. Hot air then melted the ice crystal to determine the ice crystal mass <br />through the diameter measurement under the microscope after the growth <br />period. <br />Improvements in the experimental designs made in this study greatly <br />increased the usefulness of the measured data set, which consisted of liquid <br />water content, ice crystal mass, a- and c-axiallengths and fall velocity. The <br /> <br />e) <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />e <br /> <br />. <br /> <br />. <br />