No description available.

Thesis--Wisconsin. / Includes bibliographical references (leaves 29-30).

The local and macroscopic wet-bulb temperature depressions have been measured for naphthalene, p-dichlorobenzene and d-camphor particles sublimating into an air or helium gas stream. The organic chemicals were moulded into cylindrical, spherical and flat plate 'wet-bulbs'. A simple model based on the analogy between heat and mass transport postulates the dependence of the macroscopic psychrometric ratio of a cylinder in crossflow, a sphere or a flat plate, and the local psychrometric ratio of a plate, on the Lewis number of the system. A second model is developed which enables the calculation, by means of a Biot number correction, of the local psychrometric ratio of a cylinder or a sphere when heat is conducted internally through the body. This local psychrometric ratio can also be related to the system Lewis number. Two models are also developed to predict the 'limiting' wet-bulb temperature depression for a cylinder, sphere or flat plate under conditions of pure molecular diffusion of heat and mass. The measured local and macroscopic psychrometric ratios for all wet-bulb shapes studied were found to be independent of the gas temperature level, gas velocity, free stream turbulence intensity and integral scale of turbulence, in accordance with the models. For spheres and cylinders, the particle diameter did not affect the measured local and macroscopic psychrometric ratios. The experimental wet-bulb temperature depressions were found to vary linearly with the measuring thermocouple wire diameter to the three-halves power. The macroscopic psychrometric ratio, β₀, of spheres and cylinders has been correlated with the film Lewis No., Le[subscript f] , for eighteen gas-vapor systems by β₀= Le[subscript f] ⁻º‧⁵⁷. The author's data have extended the upper limit of Lewis number for correlation of macroscopic psychrometric ratio from 3.7 to 7.2. The author's measurements in helium indicate that the semiempirical correlation of Bedingfield and Drew is the best previous relationship for predicting the macroscopic psychrometric ratio for a cylinder. Under conditions of forced convection, the local psychrometric ratio, ββ, at the front stagnation point of spheres and cylinders can be correlated by ββ = Le[subscript f]⁻º‧⁶⁹ This result verifies the Chilton - Colburn analogy for attached laminar boundary layer flow. The local psychrometric ratio at the rear stagnation point of spheres and cylinders can be predicted by ββ = Le[subscript f]⁻º‧⁴⁶ when a wake exists behind the particle. This result is suggestive that a transport mechanism such as that proposed by Danckwerts may be controlling the transport processes in the wake. The local psychrometric ratios on a flat plate under conditions of laminar boundary layer flow are in close agreement with the Chilton - Colburn analogy. The intensity and longitudinal scale of turbulence down stream of screens in a four-inch square wind tunnel are presented. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

No description available.

Call number: LD2668 .T4 1951 D3 / Master of Science

Thesis (M. Sc.(Eng.))--University of Hong Kong, 1970. / Mimeographed.

Thesis (Ph. D. - Hydrology and Water Resources)--University of Arizona. / Includes bibliographical references.

Humidity measurement in industries is a critical factor, since it may affect the business cost of the product, end product quality, optimal functioning of equipment, and the health and safety of the personnel. Hence, humidity sensing is becoming very important, especially in the control systems for industrial processes. Since humidity is expressed in different ways, it is very difficult to come up with a reliable, consistent, and repeatable humidity measurement approach. In contrast to other sensors employed for measuring other parameters like temperature and pressure, a humidity sensor has to be in contact with the process environment and hence is difficult to implement. This research was initiated at the Diagnostic Instrumentation and Analysis Laboratory (DIAL) for the requirement from the DOE to monitor the moisture in the soil at the nuclear waste storage facility. The idea was to monitor the leakage, if any, in the storage cylinders to avoid any hazard that may come up. The humidity sensor in this case had to be able to transmit the measurement over a distance far away from the actual measurement site. Keeping all these factors in mind, a chemically deposited optical fiber humidity sensor was developed. It was based on the evanescent tail absorption of light passing through an optical fiber due to hygroscopic material deposited on it. The hygroscopic material used was an aqueous solution of Poly-vinyl-acetate (PVA) and Cobalt Chloride (COCl2). The sensor yielded a consistent humidity measurement from 75% to 95%. Based on the above research, research is currently in progress to bring up a commercial prototype of the sensor.

published_or_final_version / Civil Engineering / Master / Master of Science in Engineering

The recent development of the peltier-type thermocouple psychrometer has made possible the measurement of soil moisture potentials to values as low as -80 bars. The applicability of this type of psychrometer to "in situ" measurements of moisture potential at a Sonoran desert field site is investigated. An evaluation is made of the effect of variations in soil temperature, moisture content, and solute concentrations on the psychrometric measurements. Moisture potential measurements with the psychrometer are shown to be limited to a moisture content range composing approximately 50 per cent of the total variation in soil moisture observed during the study. A significant quantity of moisture is transferred across the soilatmosphere interface at moisture contents both above and below the measurement range of the psychrometer. Psychrometric measurements cannot be used to determine the total moisture flux into or out of the soil horizon. The temperature component of the total soil moisture potential is not measurable with the thermocouple psychrometer. Under conditions occurring frequently within the study period, this component is shown to be of equivalent or greater magnitude than the components measured with psychrometric techniques. Laboratory measurements of the sorption-desorption isotherms for the field soils were made using thermocouple psychrometers. The isotherms vary significantly among samples, as a function of soil composition. This variation prevents the determination of absolute values of soil moisture content from measurements of soil moisture potential. However, for the soils at the field site, the slope of the moisture isotherms at a given potential does not vary significantly among samples. Psychrometric measurements can be used to determine moisture content changes at the study site, within the measurement range of the psychrometers. The variation in moisture isotherms, the significance of temperature induced moisture flux, and the limited moisture range of psychrometric measurements prevents the construction of a quantitative model of soil moisture movement from potential measurements made with thermocouple psychrometers. The effect of Celtis pallida (desert hackberry), a native plant species, on the soil moisture regime is described. Moisture uptake by the plant, and precipitation input to the soil near the plant are described in terms of the potential variations they produce. The particular hackberry plant studied is shown to be removing moisture from the soil at potential values as low as -30 atmospheres. Moisture potentials in the root zone were within the measurement range of the psychrometers throughout most of the year. The measurement of soil moisture potentials with the thermocouple psychrometer is shown to be an effective means of studying moisture content variations in the root zone of desert plant species.