Browsing by Author "Denny, Vernon E."
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Item Capillarity and bubble formation in one component liquid-vapor systems(1965) Hutten, Irwin M; Denny, Vernon E.An experimental technique is described whereby a wide variety of interfacial phenomena is observed. The system investigated is the one component carbon tetrachloride liquid-vapor system. The principal part of the apparatus is a vertical capillary which opens squarely at the top into a liquid reservoir. A vapor phase is created in the capillary so that it supports the liquid phase above it. Movie photography techniques are used to document the interfacial behavior in the capillary and also document the nature of bubble formation and detachment at the capillary mouth. Studies on very rapidly moving interfaces reveal that deformation of a bubble can be caused by inertial forces acting on it from the liquid phase above. Bubble deformation also occurs when rapidly growing bubbles reattach to the previously detached rising bubble. Movies of the action inside the capillary reveals phase fragmentation occurs in the nature of alternating but short-lived slugs of liquid and vapor. Phase fragmentation also occurs when vapor phase growth begins at a vapor nucleate entrapped in the liquid phase of the capillary. Experimental methods are employed to retard the interfacial movement so that its motion is not readily perceivable to the naked eye. Movie documentation reveals that the retarded interface responds to inherent fluctuations of the system. Fluctuations of a much higher frequency are also noted. Experiments are conducted whereby the retarded interface is slowly disturbed by increasing the heat input to the heat bath around the capillary. Studies of bubble detachment reveals that the bubble undergoes a necking action at the capillary mouth prior to detachment. For slowly forming bubbles, the surface force holding the neck to the capillary mouth can be equated to the buoyancy force acting on the detaching bubble.Item Coefficient of viscosity of superheated tetrachloride(1965) Ferenbaugh, Roger Willis; Denny, Vernon E.Measurements of the viscosity of superheated carbon tetrachloride were made at various superheats ranging from 0°C superheat to 37°C superheat. The measurements were made in three groups: two isotherms at 82.4°C and 88.3°C, and one isobar at 690 mm Hg. The three major drawbacks to attaining superheated conditions are vibrations (mechanical shock), impurities, and the maintenance of large volumes of superheated liquid. While the viscometer itself was a simple capillary viscometer, the special procedures and techniques required to attain the necessary superheats entailed the use of high vacuum equipment, liquid degassing systems, a vibration free table, and controlling systems to maintain the temperatures and pressures within the desired fluctuation limits. The results obtained show that the viscosity curve for carbon tetrachloride in the superheated regime appears to be a smooth continuation of the curve below the normal boiling point. A curve fit to the experimental data gave the following equation: This equation is valid over a temperature range of 70°C to 120°C. The standard deviation between the experimental data and values calculated from the given equation is ± 0.004, which is about 1%. The standard deviation between the fitted curve and previously reported data., which were obtained in a pressurized system, was ± 0.011, which is about 2.75%.Item Deformation and motion of a gas-liquid interface in a cylindrical capillary(1965) Chen, Jong Juh; Denny, Vernon E.The motion of a gas-liquid interface in a cylindrical capillary was studied. Stream function and vorticity equations were set up to describe a two dimensional flow in the liquid phase. Only momentum transfer is of interest; no heat transfer and mass transfer are involved. The driving force for flow is the pressure in gas phase; the surface tension is assumed negligible . Numerical solutions were obtained for a few time steps. The deformation of interface and the pattern of stream lines have been plotted.Item Density and compressibility of superheated carbon tetrachloride(1966) Smith, Ronald Lee; Denny, Vernon E.The effect of both pressure and temperature on the specific volume of carbon tetrachloride was determined using a new experimental technique. An apparatus, called a capillary pycnometer, was constructed which enabled extension of existing data on liquid densities into the superheated region. In brief, the apparatus consisted of a spherical quartz bulb attached to a long uniform section of capillary tubing in such manner as to enable superheating of the liquid contained in the bulb. Specific volume data were obtained by noting changes in level of the liquid meniscus in the (vertical) capillary caused by changes in either pressure or temperature in the bulb. Data were taken along four isotherms (69.83°C, 76.53°C, 82.23°C, and 88.03°C) under conditions of increasing pressure (falling meniscus) as well as decreasing pressure (rising meniscus). No hysteresis in the results was obtained for pressures ranging from 418 mm Hg to 1104 mm Hg. The maximum superheat reported in this study is 13.1°C (obtained at 88.03°C and 718 mm Hg), although values as high as 42°C were obtained during normal operation of the apparatus. Since the pycnometer system devised yielded only relative density values, it was necessary to obtain one absolute value to convert the other changes observed into absolute values. The data of Gibson and Loeffler were used for this purpose; in particular, a value of 1.49558 grams per cubic centimeter at 69.83°C was chosen. Thus, the data reported here can be no more accurate, on an absolute basis, than that reported by Gibson and Loeffler; however, an error analysis reveals that the data obtained here, treated on a relative basis, is superior to any yet reported.Item Experimental studies of nucleate pool boiling from artificial active sites(1963) Finlayson, Bruce A; Denny, Vernon E.Artificial active sites were studied during nucleate pool boiling of degassed carbon tetrachloride. The pressure of the system was controlled a t one and also at one and one-half atmospheres. Dynamic two phase behavior in a cylindrical cavity was investigated visually. A glass capillary was inserted through the heat transfer surface and the bore supported ebullition in the absence of naturally occurring nuclei. When ebullition occurred at the surface, a falling liquid film was observed on the cavity wall. Three cylindrical cavities with diameters ranging from 0.004 inches to 0.008 inches were formed in a stainless steel heat transfer surface. The surface superheat required for ebullition ranged from 1.5°F to 43.2°F. For an appreciable range of superheats, the cavities were armed with vapor but did not support ebullition. Bubble columns were photographed using a high-speed motion picture camera. The diameter of detaching bubbles increased with higher surface superheats. Bubbles generated from the glass capillary had lower frequencies than those generated from stainless steel heating surfaces. The liquid flow around a detaching bubble assumed two modes. Axially symmetric pulsating flow and flow by continuous rotation about an active site were recognized by their effects on bubble shape.Item Interaction of active sites in pool boiling heat transfer(1962) Baratz, Bernard; Denny, Vernon E.Heat transfer studies were performed on saturated carbon tetrachloride under natural convective and nucleate boiling conditions. A flat, polished, stainless steel plate was the heat source; and degassed, spectroscopic grade carbon tetrachloride was the heat transfer fluid. Tests were conducted at both one, and one and one-half atmospheres. Heat flux measurements were made for superheats ranging from 10 to 40°F, with corresponding heat fluxes ranging from 700 to 2500 Btu/hr-ft2. Two runs were performed. In the first run, seven equidistant cylindrical cavities, 0.006 inches in diameter and 0.010 - 0.012 inches deep, were drilled into the central portion of the heat transfer area. In the second run, additional holes with identical geometries were drilled halfway between the cavities studied in the first run. These artificial cavities served as active sites for the boiling studies. The purpose of the study was to investigate the nature of the interaction between these carefully positioned sites under nucleate boiling conditions. However, the drilling procedure created small protrusions around the mouths of the cavities. As a result, the bubbles obtained during nucleate boiling were smaller than would normally be expected, and no significant interaction between active sites was obtained for the site population densities studied. Nonetheless, the results provide useful information about the influence of cavity lip geometry on the heat transfer characteristics of an ebullating site. The boiling results obtained in this study reveal that the local heat transfer coefficient for the protruding lip case is an order of magnitude smaller than those obtained in other studies involving non-protruding lips.