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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Liquid Crystal Thermography Studies In Water Pool Boiling At Subatmospheric Pressures

Talari, Kiran 01 January 2007 (has links)
A pool boiling experimental facility has been designed and built to investigate nucleate pool boiling in water under sub atmospheric pressure. Liquid crystal thermography, a non intrusive technique, is used for the determination of surface temperature distributions. This technique uses encapsulated liquid crystals that reflect definite colors at specific temperatures and viewing angle. Design of the test section is important in this experimental study. Since a new TLC is required for every new set of test conditions, a permanently sealed test section is not an option. The real challenge is to design a leak proof test section which is flexible so that it can be taken apart easily. A plexiglass test section, including a top chamber with an internal volume of 60.9 x 60.9 x 66.4 mm and a bottom plate of 5.5mm thickness is designed and assembled together using quick grips. In the test section, water is boiled using 85.0mm x 16.0mm and 0.050mm thick Fecralloy® as the heating element. The TLC sheet is attached to the bottom plate and the heating element is placed on top of TLC so that the temperature distribution of the heating element during boiling can be interpreted from TLC. A camera system fast enough to capture the thermal response of the TLC and an arrangement to capture both hue of the TLC and growth of the bubble on the same frame has been designed and successfully used. This system allowed recording of position, size and shape of the bubble with synchronized surface temperature. In order to get hue vs. temperature relation, in-situ calibration of the TLC is performed for each test condition with the present experimental setup and lighting conditions. It is found that the calibration curve of the TLC at atmospheric pressure is different from the calibration curve of the same TLC at subatmospheric pressures. The maximum temperature difference between the two curves for the same hue is found to be only 0.6°C. The experiment is run at four different test conditions of subatmospheric pressure and low heat flux. It is run at system pressures of 6.2kPa (0.89Psi) and 8.0kPa (1.16Psi) with a constant heat flux of 1.88kW/m2 and 2.70kW/m2, and a constant heat flux of 2.70kW/m2, 3.662kW/m2 and 4.50 kW/m2 respectively. Analysis of nucleating surface temperatures using thermochromic liquid crystal technique is performed for these test conditions and the bubble dynamics is studied. The temperature distribution is quite varied in each case and the temperature is at its maximum value at the center of the bubble and it decreases radially from the center. The dry spot observed during the experiments indicates that the process of evaporation of the microlayer is dominant at subatmospheric pressures. It is observed that at very low pressure and heat flux the bubble growth is accompanied by the neck formation. Boiling parameters such as bubble frequency, bubble size and contact are also analyzed and a summary of these results for four different test conditions is presented and the relevant differences between the cases are discussed and the effect of increase in pressure and heat flux is noted.
2

The Effects of Gamma Irradiation, Color Mutation and Various Subatmospheric Pressures on the Growth and Patulin Production by Penicillium Expansum and Penicillium Patulum

Adams, Karl B. 01 May 1975 (has links)
To assess the effects of gamma radiation at low doses, spores of Penicillium expansum NRRL 971 and Penicillium patulum NRRL 989 were exposed to doses of 0, 50, 100, 150, and 200 krads. The amount of patulin for each culture was quantitatively determined and growth at each dose was evaluated. The results showed a 31% increase in the amount of patulin synthesis after a dose of 150 krads for Penicillium expansum At 200 krads, both fungi showed low levels of patulin production and inhibited growth. Eight color mutants of P. expansum and eight color mutants of P. patulum were produced by exposing spores of each fungus to doses of 150 and 200 krads of gamma radiation. An evaluation of patulin production and growth for each mutant showed that color mutation could result in mutants with an enhanced ability to grow or produce increased levels of patulin. When grown at a subatmospheric pressure of 320 mm Hg, P. expansum produced 30% more patulin per flask, when compared to control cultures. At 160 mm Hg, P. expansum showed a 75% decrease over the control cultures. P. patulum was greatly affected by the temperature of 15℃ and showed decreases both in growth and patulin production. Effective control of growth and patulin synthesis was found for these fungi at 160 mm Hg.

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