Fluidization, a relatively new unit operation by which a solid and gas or liquid may be contacted, is being widely developed in the field of catalytic cracking of petroleum because of its characteristic reduction of temperature gradients within the reaction mass. Basic research of the heat transfer properties of fluidized systems has lagged far behind industrial applications. It was the purpose of this investigation to evaluate the effect of temperature driving force and mass superficial air velocity on the coefficient of heat transfer at the bed wall of an externally heated, fluidized bed of Ottawa sand at wall temperature of 200, 400, and 600 °F , and average mass superficial air velocities of 82.5, 123.2, 170.3, and 217.5 pounds per hour-square foot. The tests were carried out under steady state conditions of air flow and bed wall temperature. A complete heat and material balance, including evaluation of heat losses, was made for each test. The boundary coefficients based on the internal area and temperature of the pipe wall were calculated. The effects of mass superficial air velocity and wall temperature on the boundary coefficient of heat transfer and on bed and bed wall temperature gradients were studied. From observations made it was noted that the fluidization range of the Ottowa sand bed began at a mass superficial air velocity of 91.0 pounds per hour-square foot and ended at 210.0 pounds per hour-square foot, the velocity at which slugging occurred throughout the bed. The horizontal temperature gradient across the bed increased with increasing bed wall temperature, increasing from a minimum of 0 °F at 200 °F wall temperature to 6 °F at 600 °F . The rate of heat flux to the air stream passing through the fluidized bed increased with mass air flow rate at constant bed wall temperature. The minimum heat flux was 84 Btu per hour and occurred at 200 °F and 82.5 pounds per hour-square foot, while the maximum was 1172 Btu per hour and occurred at 600 °F and 217.5 pounds per hour-square foot. The coefficient of heat transfer increased with bed wall temperature, reaching maximum values of 9.55, 13.40, 13.31, and 13.30 Btu per hour-square foot-°F at 600 °F and at mass superficial air velocities of 82.5, 123.2, 170.3, and 217.5 pounds per hour-square foot, respectively. / Master of Science

M. S.

The variation of the local coefficients of heat transfer with bed depth, particle density, and particle size were studied using a pyrex pipe four inches in diameter as the fluidizing vessel. The fluidized solids investigated were aerocat cracking catalyst, having a geometric-mean particle diameter of 0.00262 inch and an absolute density of 136.6 pounds per cubic foot; tabular alumina, having a geometric-mean particle diameter of 0.0138 inch and an absolute density of 238.8 pounds per cubic foot; silica gel, having a geometric-mean particle diameter of 0.0187 inch and an absolute density of 135.1 pounds per cubic foot; and superbrite glass beads, having a geometric-mean particle diameter of 0.0138 inch and an absolute particle density of 179.5 pounds per cubic foot. The heating element was a 230-vo1t, 1750-watt, copper-sheathed rod having a diameter of 0.25 inch. Temperature measurements were made with 20 B and S gage, iron-constantan thermocouples insulated with fiber-glass braid over glass wrap. Air varying in temperature from 80 to 85 °F and in humidity from 0.000 to 0.004 pound of water vapor per pound of dry air was used as the fluidizing medium. / Master of Science

After reviewing all available literature on heat transfer to superheated steam at high temperatures and pressures, it was concluded that further investigation of this problem would be of value. The thesis was concerned with the derivation of three heat transfer film coefficient equations and their related error equations. The three equations thus derived were not used to determine the value of the heat transfer film coefficient. No experimentation was performed to obtain the necessary data required by the three equations for calculating the heat transfer film coefficient value. Instead an error analysis was made of the film coefficient equations using the derived error equations. Prediction of the most accurate film coefficient equation was made based on results obtained from this analysis. Recommendations for the test apparatus and arrangement, test section design, and experimental procedure were advanced based on the error analysis results. No attempt was made in the thesis to develop an experimental heat transfer film coefficient similar to the equations found in the reviewed literature. / Master of Science

A study is presented to explore the suitability of CFD as a tool in the design and analysis of total temperature probes. Simulations were completed using 2D axisymmetric and 3D geometry of stagnation total temperature probes using ANSYS Fluent. The geometric effects explored include comparisons of shielded and unshielded probes, the effect of leading edge curvature on near-field flow, and the influence of freestream Mach number and pressure on probe performance. Data were compared to experimental results from the literature, with freestream conditions of M=0.3-0.9, p_t=0.2-1 atm, T_t=300-1111.1 K. It is shown that 2D axisymmetric geometry is ill-suited for analyses of unshielded probes with bare-wire thermocouples due to their dependence upon accurate geometric characterization of bare-wire thermocouples. It is also shown that shielded probes face additional challenges when modeled using 2D axisymmetric geometry, including vent area sizing inconsistencies. Analysis of shielded probes using both 2D axisymmetric and 3D geometry were able to produce aerodynamic recovery correction values similar to the experimental results from the literature. 2D axisymmetric geometry is shown to be sensitive to changes in freestream Mach number and pressure based upon the sizing of vent geometry, described in this report. Aerodynamic recovery correction values generated by 3D geometry do not show this sensitivity and very nearly match the results from the literature. A second study was completed of a cooled, shielded total temperature probe which was designed, manufactured, and tested at Virginia Tech to characterize conduction error. The probe was designed utilizing conventional total temperature design guidelines and modified with feedback from CFD analysis. This test case was used to validate the role of CFD in the design of total temperature probes and the fidelity of the solutions generated when compared to experimental results. A high level of agreement between CFD predictions and experimental results is shown, while simplified, low-order model results under predicted probe recovery. / Master of Science

Master of Science

Since the turn of the twentieth century, many investigations have been made in the field of heat-transfer from finned cylinders in an air-stream with the fin-plane parallel to the air-stream. Most of these investigations have been made by the National Advisory Committee on Aeronautics (NACA) at Langely Memorial Aeronautical Laboratory, Langely Field, Virginia. The problem of determining the rate of heat-transfer from finned cylinders is extremely complex due to many variables such as fin space; fin width; fin thickness; cylinder diameter; and cooling air conductivity, viscosity, turbulence, and velocity. In the literature reviewed, there have been no successful theoretical equations for the determination of the rate of heat—transfer. Therefore, all information on the rate of heat-transfer must be based on experimental results or on empirical relationships which closely approximate the experimental values. The rate of heat-transfer from finned cylinders is a very important factor in the design of air-cooled internal combustion engines and high rate heat-exchangers. It is known that the rate of heat-transfer for the range of fin-plane/air-stream angles between 30 and 60 degrees is nearly twice that of a zero fin-plane/air-stream angle, Since the subject of heat-transfer from finned cylinders in an air-stream with the fin-plane parallel to the air-stream has been thoroughly investigated by the NACA, the author decided to conduct this investigation on finned cylinders in an air—stream with varying fin-plane/air-stream angles. Due to the limiting size of equipment available, this investigation was conducted on finned cylinders with a cylinder diameter of about one inch, while the test carried on by the NACA covered a range of cylinder diameters from 3.66 to 6.34 inches.⁵ The difference in the cylinder diameters may provide a valuable correlation for the variation of the rate of heat-transfer due to cylinder diameter. / Master of Science

Temperature is a parameter which is important because of its influence on other material properties. Many temperature measurement techniques are available but few of them permit a direct visualization of surface temperature Variation. The Liquid crystal method is one of the rare methods that permits a complete color mapping of surface temperature and that is also fast enough to respond to surface temperature Variation on plates heated by cyclic bending. A mathematical model for irreversible mechanical heating of plates is developed to support the experimental investigation. The results, which include comparison of the theory and the experiment, show that liquid crystals allow good qualitative measurements and can lead, with certain precautions, to quantitative results. / Master of Science

The requirement for accurate total temperature measurements in gaseous flows was first recognized many years ago by engineers working on the development of superchargers and combustion diagnostics. A standard temperature sensor for high temperature applications was and remains to be the thermocouple. However, this sensor is characterized by errors due to conduction heat transfer from the sensing element, as well as errors associated with the flow over it. In particular in high temperature flows, the sensing element of the thermocouple will be much hotter than its surroundings, leading to radiation heat losses. This in turn will lead to large errors in the temperature indicated by the thermocouple. Because the design and testing of thermocouple sensors can be time consuming and costly due to the many parameters that can be varied and because of the high level of detail attainable from computational studies, the use of advanced computational simulations is ideally suited to the study of thermocouple performance. This work sought to investigate the errors associated with the use of total temperature thermocouple probes and to assess the ability to predict the performance of such probes using coupled fluid-heat transfer simulations. This was done for a wide range of flow temperatures and subsonic velocities. Simulations were undertaken for three total temperature thermocouple probe designs. The first two probes were legacy probes developed by Glawe, Simmons, and Stickney in the 1950's and were used as a validation case since these probes were extensively documented in a National Advisory Committee for Aeronautics (NACA) technical report. The third probe studied was developed at Virginia Tech which was used to investigate conduction errors experimentally. In all cases, the results of the computational simulations were compared to the experimental results to assess their applicability. In the case of the legacy NACA probes, it was shown that the predicted radiation correction compared well with the documented values. This served as a validation of the computational method. Next the procedure was extended to the conduction error case, where the recovery factor, a metric used to relate the total temperature of the flow to the total temperature indicated by the sensor, was compared. Good agreement between the experimental results was found. The effects of radiation were quantified and shown to be small. It was also demonstrated that computational simulations can be used to obtain quantities that are not easily measured experimentally. Specifically, the heat transfer coefficients and the flow through the vented shield were investigated. The heat transfer coefficients were tabulated as Nusselt numbers and were compared to a legacy correlation. It was found that although the legacy correlation under-predicted the Nusselt number, the predicted results did follow the same trend. A new correlation of the same functional form was therefore suggested. Finally, it was found that the mounting strut had a large effect on the internal flow patterns and therefore the heat transfer to the thermocouple. Overall, this work highlights the usefulness of computational simulations in the design and analysis of total temperature thermocouple sensors. / Master of Science

The primary objective of this Investigation was to determine the heat transfer rate and characteristics of three vibrated wires In a parallel flow. A simple experimental apparatus was constructed with which to pursue the investigation, and various results were obtained. Three wires of different diameters were individually tested in two configurations. One configuration consisted of electrically heated stationary wires which transferred heat to air flowing at various velocities and parallel to the wires. This was investigated to compare the results with previously reported investigations of small cylinders in parallel flow. The second configuration consisted of vibrating wires at various air velocities In parallel flow and at various frequencies and amplitudes. The results show that for the stationary wires the heat transfer characteristics are In accord In principle with the results of similar investigations. The results obtained when the wires were vibrated show that vibration in forced convection Increased heat transfer rate up to a certain value of flow Reynolds number after which the effect of vibration on heat transfer was negligible. The effect of amplitude and frequency on the Improvement of heat transfer rate was greater at a particular range of values of frequency and amplitude. As both frequency and amplitude were Increased above this range, the rate of Improvement In heat transfer was not as great. / Master of Science