Engineering Commons^™

Combined Forced And Free Convection On A Vertical Cylinder And Flat Plate, Aleksandros Mucoglu

Masters Theses

"In the study of fluid flow over heated surfaces, it is customary to neglect the effects of buoyancy force when the flow is horizontal. However, such a practice is not justified when the forced flow is along an inclined or a vertical surface, because under these conditions the buoyancy force modifies considerably the flow field and hence the heat transfer rate from the surface. Such a flow is termed combined forced and free convective flow.

The present study is concerned with the effects of buoyancy force on forced convection along an isothermal vertical cylinder and a flat plate. This type …

An Analytical And Experimental Study Of The Dynamic Response Of A Press, Woosoon Bai

Doctoral Dissertations

"This dissertation presents a simplified mathematical model and computer simulation of the vertical motion of a press. The model is verified by comparing simulation results with actual field measurements.

Using this model, the computer simulation is then extended to study the dynamic response of a bolted press, one with loosened anchor bolts, and one which is isolated. Press performance, in terms of acceleration of the press, velocity of its foundation, and forces transmitted to the foundation, is analyzed in relation to the foundation mass and the stiffness of the isolators, where applicable. Comparative performances of the presses secured by the …

The Effect Of Contact Angle, Surface Roughness, And Adsorption Of Heterogeneous Nucleation Of Condensing Water, Prafulla Chandra Mahata

Doctoral Dissertations

"Condensation of water vapor on various surfaces was studied experimentally. It was found that supersaturations as high as 25% were required to initiate condensation on hydrophobic surfaces. The supersaturation data agreed qualitatively with the Volmer theory of heterogeneous nucleation. The influence of adsorption of water vapor was found to be small. Surface roughness caused a little reduction in the critical supersaturation"--Abstract, page iii.

Measurements Of Condensation Coefficient Exhibited By Water Drops Grown On Rural Cloud Nuclei, Abbas M. Sinnarwalla

Doctoral Dissertations

"Values of condensation coefficient, ß, were experimentally determined for water drops grown on cloud nuclei in atmospheric air samples. The measured quantities were supersaturation, final drop size (6 to 7.5 µm radius), and time to grow from near dry radius to final radius. The drops were grown in a vertical-flow thermal diffusion chamber, at supersaturations near 0.5 and 1.0%. The final drop sizes were large enough so that ß did not depend upon the size of the nucleus producing a given drop. The average value of ß was 0.025 with a standard deviation of about 0.01"--Abstract, page 2.

Solid-Fluid Drag Reduction, Ian Radin

Doctoral Dissertations

"Pressure drop measurements were made on a variety of solid-liquid suspension systems in order to study the effects of particle shape and size, concentration, fluid viscosity and tube diameter on drag reduction. Measurements were made over a wide range of Reynolds numbers in two tubes: 1/4 inch and 1 inch in diameter.

Drag reduction could always be obtained with fibrous additives of length-to-diameter ratio greater than 25-35 if the concentration was sufficiently high. The drag reduction behavior of these suspensions is different from that of high polymer and soap solutions. Laminar flow behavior is stabilized giving lower than normal friction …

Numerical Modeling Of The Early Stage Of Cloud Formation In A Simulation Chamber, Adel Nassif Saad

Doctoral Dissertations

"A numerical model has been developed to simulate the growth of cloud droplets by condensation upon a spectrum of hygroscopic nuclei. The model is applicable to cloud simulation chamber conditions as well as to the study of the role of these nuclei on cloud base microstructure.

Equations are given for the growth by condensation of water vapor on a population of hygroscopic nuclei in a volume being cooled by expansion. The equations are integrated simultaneously, using Hamming's modified predictor-corrector method for given initial conditions, to obtain the droplet size distribution, temperature, pressure, supersaturation, and liquid water content. Temperature fluctuations, sedimentation …

Flow Field And Heat Transfer For Developing Flow Of Molten Glass In A Duct, Russell Ralph Beckmeyer

Masters Theses

"The molten glass flow (temperature range 1300 to 1500°C) in the entrance region of a duct was investigated with numerical methods. The mathematical model was restricted by assuming: (1) two dimensional, steady state, (2) Newtonian fluid, variable viscosity, and (3) Rosseland approximation. In addition, appropriate use was made of the fact that the Reynolds number is small and the Eckert number is very small. The inclusion of temperature dependent viscosity and a Rosseland approximation for radiation produced from the mass, momentum, and energy equations a system of coupled, nonlinear, partial differential equations which were solved by an iterative finite difference …

A Finite Element Method For Three-Dimensional Analysis Of Metal Forming, Nguyen Don Phu

Doctoral Dissertations

"The importance of metal forming by extrusion was reviewed. A Finite Element Approach was developed to analyze extrusion processes. A brick type linear element and the Upper Bound theorem were used to analyze the extrusion of a cylindrical billet into a square cross-section prism. A minimization technique for a non-linear functional with linear constraints was developed. Different types of boundary conditions were also formulated. A frictionless extrusion was simulated using the computer program developed. Velocity profiles at different sections of the deforming solid were obtained and an average extrusion pressure was predicted for a given area reduction ratio.

Extrusions from …

Direct And Inverse Heat Conduction In Rock Materials Using The Finite Element Method, Vernon Dale Allen

Doctoral Dissertations

"A finite element method is presented for solution of direct and inverse heat conduction problems in rock materials. Finite element programs for direct and inverse heat conduction problems were developed and demonstrated. Flow charts are given for the finite element programs.

The direct finite element heat conduction program changes material properties with temperature to approximate the temperature dependent properties of rock materials. An example problem was solved by the finite element method and also using Kirchoff's transformation. The finite element solution compared quite well with the Kirchoff transformation solution.

The inverse method utilizes the direct finite element heat conduction program …

Dropwise Condensation As Affected By Vapor Diffusion And Molecular Sticking, Salil K. Banerjee

Doctoral Dissertations

"Experimental values of heat flux in dropwise condensation on a gold plated vertical copper surface were determined in presence and absence of (or minute traces of) noncondensable gas. The noncondensable gas concentration varied from 0.0045% to 7.5% over a range of subcooling from 2.155 to 17.13°F and system pressure of 4.124 to 16.67 psia. The calculated heat transfer coefficient ranged from 1,545 to 11,135 Btu/hr-ft²-°F. In the part of the experiment where precautions were taken to avoid the presence of noncondensable gas in the water vapor, much higher values of heat flux were observed. Values of heat transfer coefficient ranging …

Two-Dimensional Radiative Transfer In A Finite Scattering Mediu, James Warren Koewing

Masters Theses

"Exact formulations are presented for the source function, intensity and flux for a two-dimensional, isotropically scattering medium of finite thickness. Spatially varying collimated and diffuse radiation of the following types are incident on the medium: (1) cosine varying, (2) semi-infinite step, (3) step at the origin, and (4) finite strip. The solutions for the cosine varying collimated boundary condition are used to construct solutions for the other boundary conditions. The two-dimensional integral equations are reduced to one-dimensional equations by separating variables. Through a series of transformations, the one-dimensional equations are put into a form in which the source function, intensity …

Laser Holographic Interferometric Investigation Of Heat Transfer About An Isothermal Vertical Flat Plate, Richard Michael Quinlisk

Masters Theses

"A study of the laser holographic interferometer was conducted to compare heat transfer data obtained with the device to standard free convection boundary layer theory. The system studied was an isothermal vertical flat plate. The interferometer was used to obtain fringe patterns of the boundary layer at the plate surface.

Data from the holographic interferograms were recorded by making conventional two-dimensional photographs of the holographic images.

The optical data are shown to have a good correlation to Von-Karman theory. Values of the boundary layer thickness, temperature distribution, and heat transfer were compared. An attempt was made to probe the boundary …

Diurnal Solar Heating And Cooling Of A Water Reservoir, Stephen Patrick Lepper

Masters Theses

"The transient diurnal heating of a water reservoir by solar radiation; and its cooling by surface convection, evaporation, and radiation emission was analytically modeled. The directional and spectral properties of the incident solar radiation, the air-water interface, and the selective attenuation of radiant energy by the water were properly included in the analysis. The diurnal vertical temperature distribution was predicted by numerically solving the energy equation using a finite difference technique. It was determined that the surface boundary conditions and the selective absorption of radiant energy by the water strongly influence the thermal stratification of stagnant water.

The diurnal compensating …