Browsing by Author "Kingrea, Charles Leo"

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    Chemical treatment of bread corn during milling process to eliminate insect contamination
    Kingrea, Charles Leo (Virginia Polytechnic Institute, 1951)
    The problem of this investigation was to develop a satisfactory method by which insect infested corn could be treated continuously to eliminate the contamination normally found in the corn meal produced from the corn. An extensive literature review was compiled covering the processing of corn, the description of insects infesting stored corn, the sources of insect contamination, the tests for contamination in the corn meal, and the methods now employed or proposed for the reduction of this contamination. In connection with the fumigation of stored grain, tables were prepared showing the results of fumigations of grain insects with more than 400 chemical compounds. Those compounds which appeared to be best suited for this type of treatment of the corn, were then listed in a separate table and the properties of the compounds detailed so that a selection of the optimum compounds for experimental testing could be made. In addition to fumigation procedures, thermal procedures employing infrared radiation and dielectric heating were possible methods for killing the insects in the corn. Another procedure recommended for this purpose was the use of the mechanical force to kill the insect by means of high speed centrifugal machines called "Entoleter" Infestation Destroyers. By means of fragment analyses of samples of corn meal, it was found that the source of the corn and the care which it received during storage and handling were of primary importance in producing corn meal free from contamination by the present milling procedures. As a result of similar analyses it was found that precracking and aspirating of the corn on certain types of equipment prior to the normal grinding of the meal did not result in a reduction in the quantity of fragments present in the meal. Carbon tetrachloride and trichloroethylene were selected for possible utilization in very rapid fumigation of the infested corn. Laboratory apparatus based on the operation of the solvent-vapor degreaser for metal parts was constructed. In the resulting tests, it was found that with infested corn suspended in the vapor of boiling carbon tetrachloride or trichloroethylene the mortality of all stages of the rise weevil was 100 per cent after an exposure period of only one minute. Other tests indicated that after air drying of the grain the carbon tetrachloride did not have any deleterious effect on the baking properties of the corn. In connection with heat sterilization methods, tests were conducted which indicated that the baking properties of corn heated to temperatures below 160 °F were not impaired. Further tests were conducted which indicated that both infrared heating and dielectric heating were 100 per cent effective in killing all stages of rice weevil in infested com after an exposure period of two minutes to infrared radiation or one minute to dielectric heating. In both cases the temperature of the com did not reach 160 °F. Tests conducted with the "Entoleter” centrifugal machine indicated that the damage to the whole grain com by the action of the machine was excessive and all of the rise weevil were not killed. After due consideration of the experimental results it was decided that the system of rapid fumigation of the infested corn was the most reasonable solution to the problem of killing the insect infestation in the corn, The equipment necessary for the proposed system can be assembled with a few modifications of solvent-vapor, metal-degreasing equipment and with a suitable solvent recovery system. It is anticipated that the removal of the dead insects, larvae, eggs, and pupae can be accomplished on commercial milling equipment now available if the insects are killed prior to the processing and the reinfestation of the product is not an important factor during the processing.
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    The effects of the major design and operation variables on the enrichment by thermal diffusion of aqueous sugar solutions
    Kingrea, Charles Leo (Virginia Polytechnic Institute, 1953)
    Continuous, liquid, thermal diffusion is a useful separation method which heretofore has been utilized primarily on a laboratory scale for accomplishing the separation of isotopes, azeotropes, and hydrocarbons of a particular series. Although the thermal diffusion effect, wherein a gradient of temperature in a body of fluid gives rise to a gradient of concentration, was discovered in 1856, it did not become commercially feasible until 1939 when Clusius and Dickel developed the thermogravitational procedure. In this method, the temperature gradient is applied in a horizontal direction to a vertical layer of liquid, and the convection currents set up by the concentration gradient thus established move the fluids of different concentrations in opposite directions; streams of different concentrations are continuously drawn off from the top and from the bottom of the apparatus. The important commercial application has been the separation of uranium isotopes contained in liquid uranium hexafluoride. This work was part of the Atomic Energy program; the results have not been published. One major oil company has carried out a detailed research and development program on the separation of petroleum fractions by liquid thermal diffusion. This investigation was concerned with developing formulae, methods of calculation, and empirical data necessary for designing commercial equipment utilizing liquid thermal diffusion. Vertical, concentric-tube, thermal diffusion columns were constructed which could be operated with a continuous feed and draw-off of liquid from the diffusion annulus. Steam or hot water was used as the heating medium and tap water was used for cooling purposes. The columns were assembled with a copper center tube through which the cooling water flowed, and a concentric glass tube which formed the hot wall of the diffusion annulus. This set of tubes was jacketed with a pyrex pipe to form a steam or hot water reservoir about the hot wall of the diffusion annulus. Aqueous solutions of sugar were used as the test liquid. Separation effects were observed in solutions where the initial concentration was between 0.5 and 2.0 gram mols of sugar per liter. All tests were made under steady-state conditions and differences observed between the concentration of the bottom product and that of the top product varied from 0 to 28.3 weight per cent sugar. Curves, together with specific and generalized formulae, were presented to indicate the effect of each of seven variables on the separation ratio. The feed concentration was varied between 15 and 55 weight per cent sugar, and the separation ration reached a maximum between 26.6 and 44.2 weight per cent sugar. Heating fluid temperatures varying from 77 to 124 degrees centigrade were employed and the separation ratio increased linearly with the heating fluid temperature. Annulus width varying from 3.1 to 19. 7 millimeters were studied and the separation ration reached a maximum for widths between 13.0 and 16. 7 millimeters. The separation ratio decreased as the feed rate was increased from 3.0 to 248 milliliters per hour; however, it increased as the ratio of the bottom draw-off rate to the feed rate was increased from 0.047 to 0.916. The separation ratio reached a maximum when the feed port was located near the middle of the column. Maximum separations were obtained with a column length of only 24.1 centimeters; however, for other column lengths from 54.2 to 114.3 centimeters, the separation ratio increased slightly as the column length was increased. In addition to the desired temperature gradient across the liquid in the diffusion annulus, large temperature drops occurred in the glass wall of the diffusion annulus (19 to 23 degrees centigrade), and in the water film inside the copper, center tube (8 to 16 degrees centigrade). Certain fundamental factors relative to continuous, liquid, thermal diffusion have been developed in this investigation. Further research should provide similar data for other liquid systems and for other column designs. This will enable the chemical engineer to design commercial apparatus for specific applications.