An analytical and experimental study was done to determine the effect of entrainment on the heat transfer to a single, plane, turbulent impinging jet. Solutions to the momentum and energy equations were obtained with similarity and series analyses. The analytical model is compared with measured heat transfer rates to single air jets impinging normally on an isothermal heated surface. To determine the effect of entrainment, the temperature of the environment surrounding the jet was varied between the initial temperature of the jet and the plate temperature. Results obtained for jet arrays show that entrainment of air in the recirculation region between the jets can significantly affect the heat transfer rates. Comparison of the analytical model to the measured heat transfer rates for jet arrays shows that the single jet model can be successfully applied to jet arrays when the effect of entrainment is considered. / Master of Science

The behavior of aluminum alloy ship deck panels under the thermal loads of Vertical Take-off-and Landing (VTOL) capable aircraft has become a question of interest with the introduction of new primarily aluminum alloy ships to the U.S. Naval Fleet. This study seeks to provide an initial investigation of this question by examining the transient transfer of heat through aluminum alloy ship deck panels under application of the local heat transfer similar to that of a VTOL aircraft exhaust plume core in typical operation. In this study, a jet stream intended to replicate the key physics of the core of a VTOL aircraft plume was impinged onto the upper surface of aluminum alloy corrugated deck panel test specimen. Temperature measurements are taken via thermocouples on the face of the specimen opposite the impingement to evaluate heat transfer through the specimen. This data is used to assess the effects of variation in the geometry of the corrugation between specimen. Qualitative temperature distributions were also gathered on the impingement surface via thermal imaging. A quantitative assessment of the heat paths for transverse and vertical heat transfer was made based on a thermal resistance model, leading to a conceptual description of predominant heat flow paths in the specimen, specifically weld lines between the corrugation and the flat plate surfaces. In support of this, thermal images indicated that the weld lines provided paths for heat to be pulled away from the center of heat application more rapidly than over the rest of the surface. Ultimately, heat transfer through the specimen was found to be more dependent on the flow conditions than the variations in geometry of the deck panels due to the low variation in thermal resistance across the plate. A recommendation is made based upon this observation to use the deck panels similarly to heat exchanges by adding a small amount of through-deck airflow in the areas of high heat load. / Master of Science

The goal of this thesis is to develop a set of standards for use in calibrating heat flux gages at elevated temperatures in a radiant heat transfer environment by comparing several "trial" standards. Ideally, the same incident heat flux is derived from each standard when exposed to the same heat source. Three heat flux standards are proposed and evaluated. The standards are based on temperature measurements, material properties, and electrical measurements. The theory and design of each standard are described, as are the calibration procedures used. For experimental comparisons, two standards are simultaneously exposed to heat fluxes of up to 220 W/cm² by placing one standard on each side of a graphite flat plate heater. The temperature measurement based standard derives incident heat flux from the temperature of a blackbody heat source and the Stefan-Boltzmann law. The heat flux gage employed in this standard is a water-cooled Gardon gage. This standard does not operate at high temperatures. The calibration of this standard produced highly repeatable results. / Master of Science

This study is an investigation of the film cooling effectiveness and heat transfer coefficient of a two-dimensional turbine rotor blade in a linear transonic cascade. Experiments were performed in Virginia Tech's Transonic Cascade Wind Tunnel with an exit Mach number 0f 1.2 and an exit Reynolds numbers of 5x106 to simulate real engine flow conditions. The freestream and coolant flows were maintained at a total temperature ratio of 2(+,-)0.4 and a total pressure ratio of 1.04. The freestream turbulence was approximately 1%. There are six rows of staggered, discrete cooling holes on and near the leading edge of the blade in a showerhead configuration. Cooled air was used as the coolant. Experiments were performed with and without film cooling on the surface of the blade. The heat transfer coefficient was found to increase with the addition of film cooling an average of 14% overall and to a maximum of 26% at the first gauge location. The average film cooling effectiveness along the chord-wise direction of the blade is 25%. Trends were found in both the uncooled and the film-cooled experiments that suggest either a transition from a laminar to a turbulent film regime or the existence of three-dimensionality in the flow-field over the gauges. / Master of Science

The concept, design, fabrication, and calibration of a new type of layered heat flux gage is described. Using thin-film microfabrication techniques the gage design is able to combine many of the desirable characteristics of other previous gage designs to produce a gage that has a very small size, high frequency response, and the ability to measure very high heat flux rates. The heat flux microsensor incorporates a differential thermopile, a set of 100 differential thermocouple pairs connected in series across a thin thermal resistance layer. The gage is fabricated on a model surface without the need for additional adhesives. The design configuration allows the thermal insulating layer to remain very thin, while still retaining the high output typical of much thicker gages. The small overall thickness of the gage, less than 2 µm, gives it a fast time response with the capability of measuring heat transfer in transient flow conditions. The combination of small thickness and small surface dimensions, 1 mm by 1 cm, gives the microsensor negligible flow and thermal disruption. The performance of a prototype microsensor deposited on Corning 7059 glass was measured. Steady-state calibrations were done using a convection calibration apparatus. The measured sensitivity (before amplification) was 0.164 mV per watt/cm². The output was linear over the range tested from 800 to 9000 watts/m². The unsteady response was tested using a continuous laser beam directed through a variable speed chopper wheel onto the gage surface. Results showed a frequency response of at least 1 kHz. / Master of Science

Extensive investigations employing fins as extended surfaces have been conducted, but relatively little experimental work has been conducted with pins, no information is available on the heat transfer characteristics of a pin and annular fin combination, i.e., a finned pin. The increased surface area of a finned pin would promote more heat transfer. In this thesis a theoretical investigation of the basic heat transfer characteristics of a finned pin, and an experimental investigation to verify the theoretical result were conducted. 1. Theoretical investigation consists of: (1) Optimum dimensions (2) Sample calculation of optimum dimensions (3) Derivation of heat transfer equations (4) Sample calculations of heat flow-rate and temperature distribution 2. Experimental investigation consists of: (1) Set-up of experimental equipment (2) Measurements of heat flow-rate and temperature distribution (3) Comparison of theoretical results with measured results 3. Conclusions: The conclusions were based on the comparison of the two-disc finned pin with the plain pin. (1) For the two-disc finned pin employed in this thesis: Increase in heat-flow-rate: 85% Increase of effectiveness: 61% (2) In general, the increase in heat flow-rate depends on the material, dimensions, temperature difference and spacing of annular fins. / Master of Science

The determination of the heat transfer through a flat wall of which one surface is isothermal at a temperature of t_a and the other surface is isothermal at a temperature t_b is the simple problem of heat transfer. The equation: Q= (kA(t_a - t_b))/L Permits an easy solution of the problem where Q is the heat transfer, k is the thermal conductivity, A is the area through which the heat is transferred, and L is the distance between the two surfaces. The equation is only applicable where the area A is constant. This equation may be used without appreciable error for insulated enclosures such as furnaces where the insulation thickness is very small in comparison with the dimensions of the enclosure. Shape factors have been applied to this basic equation so the equation may be used in the determination of heat transfer where the area A is not constant and the effect of corners can not be neglected. The equation then becomes Q= (fkA((t_a - t_b))/L Where f is the shape factor. In 1947, T. S. Nickerson for a Master’s thesis at V.P.I. determined the values of the shape factor where the above equation is applied to cylindrical enclosures having flat ends and relatively thick walls of uniform thickness. Mr. Nickerson solved this problem analytically by the relaxation method. His solution depended upon the inside and outside surfaces of the insulation about the enclosure being isothermal surfaces. The values were calculated for combinations of ratios of insulation thickness to length of enclosure and length of enclosure to diameter of enclosure. This investigation is an experimental determination of these values using gypsum plaster cylinders of different combinations of ratios of length to diameter. However, before tests could be conducted on the cylindrical enclosures, the conductivity of gypsum plaster, the insulation about the cylindrical enclosure, had to be found. The method of determination of the conductivity and the values are given in Appendix A. / Master of Science

In a bid to reduce vehicular emissions, automobile manufacturers are moving towards elec- tric and hybrid vehicles. Most hybrid vehicles use Lithium-ion batteries as energy storage systems. Lithium-ion batteries have a narrow range of temperature within which they can be operated efficiently. Operation of Lithium-ion batteries outside this range decreases the life of batteries and reduces performance of the vehicle. Due to this limitation, it is important to prevent overheating of Lithium-ion batteries. Battery pack studied in this work has a fan system for air-cooling the cells. The battery management system (BMS) in the battery pack functions to keep the temperature of the cells within allowable limits by either regulating the fan speed or communicating with the vehicle controller to adjust magnitude of applied current. BMS used in the work is equipped with limited number of temperature sensors that can measure surface temperature of few cells in the battery pack. Additional temper- ature information can be used for better thermal control of the cells in the battery pack. Lithium-ion cells are known to have a measurable temperature gradient when operating un- der extreme conditions. As a result, the surface temperature of cells as measured by the temperature sensors in BMS is not always representative of the maximum cell temperature. To overcome these limitations, a simplified transient thermal model predicting core and sur- face temperature of cell is presented in this work. This model can be implemented in a BMS for real-time control of cell temperature. The thermal model is validated against data avail- able from testing the battery pack. Different current profiles, representative of real-world driving scenarios, are applied to the thermal model and the temperature rise of cells under those conditions is studied. For an array of cells, the thermal model predicts significant temperature rise along the airflow direction, suggesting the use of last cell temperature for thermal control. For short duration, high magnitude of current pulses, temperature rise is shown to be similar for same thermal energy deposited by different current pulses. The maximum thermal energy that can be deposited in the battery by a current pulse can be determined for given conditions of airflow rate, continuous current and air inlet temperature. The maximum magnitude of thermal energy that can be deposited by a peak current pulse to limit cell temperature is shown to be a function of current magnitude squared and the pulse duration time. For multiple current pulses applied to the battery pack, the model can evaluate the minimum time interval between current pulses to keep the temperature of cells within prescribed limits. The minimum time required between two current pulses is shown to decrease by increasing the airflow rate through the battery pack. By increasing the airflow rate, the battery pack is able to operate at a higher continuous current without exceeding the temperature limit. / Master of Science / In a bid to reduce vehicular emissions, automobile manufacturers are moving towards electric and hybrid vehicles. Most hybrid vehicles have an energy storage system in addition to the conventional Internal Combustion (I.C.) engine. Lithium-ion batteries are used as energy storage systems in most hybrid vehicles due to their high energy density, long life and low self discharge rate. Lithium-ion batteries can be operated efficiently only in a narrow range of temperature. Operating these batteries outside of this temperature range results in their faster degradation which results in lower performance of hybrid vehicle. Due to this limi- tation, prevention of overheating in Lithium-ion batteries is extremely important. To keep the operation of Lithium-ion batteries within specified temperature limits, most batteries in hybrid vehicles are equipped with battery management systems (BMS). The BMS monitors cell voltage, cell temperature and applied current and keeps the temperature of cells within allowable limits. BMS of the battery pack used in this work has fan system for air-cooling the individual cells, and can lower the temperature rise of the cells by varying the fan speed. This BMS has limited temperature sensors that can predict surface temperature of few cells of the battery pack. Additional temperature information can be used to improve thermal control of the battery pack. This work presents a simplified thermal model that can be used in controller of a BMS to improve thermal control of cells and keep the temperature of cells within specified limits.

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