Publications

Electrothermal actuation has been used in microelectromechanical systems where low actuation voltage and high contact force are required. Power consumption to operate electrothermal actuators has typically been higher than with electrostatic actuation. A method of designing and processing electrothermal actuators is presented that leads to an order of magnitude reduction in required power while maintaining the low voltage, high force advantages. The substrate was removed beneath the actuator beams, thereby discarding the predominant power loss mechanism and reducing the required actuation power by an order of magnitude. Measured data and theoretical results from electrothermally actuated switches are presented to confirm the method. © 2008 Society of Photo-Optical Instrumentation Engineers.

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A model is developed to predict the thermal response of real electronic devices during pulsed Nd:YAG laser welding. Modeling laser-part interaction requires incorporation of weld pool hydrodynamics, and laser-metal vapor and laser-surface interactions. Although important information can be obtained from these models, they are not appropriate for use in design of actual components due to computational limitations. In lieu of solving for these detailed physics, a simple model is constructed. In this model, laser-part interactions are accounted for through an empirically determined energy transfer efficiency which is developed through the use of modeling and experiments. This engineering model is appropriate since part thermal response near the weld pool and weld pool shape is not of interest here. Reasonable agreement between predictions and experimental measurements for welding of real components are indicated.

A numerical solution for buoyant natural convection within a square enclosure containing a fluid with highly temperature dependent viscosity is presented. Although the fluid properties employed do not represent any real fluid, the large variation in the fluid viscosity with temperature is characteristic of turbulent flow modeling with eddy-viscosity concepts. Results are obtained using a primitive variable formulation and the resistor method. The results presented include velocity, temperature and pressure distributions within the enclosure as well as shear stress and heat flux distributions along the enclosure walls. Three mesh refinements were employed and uncertainty values are suggested for the final mesh refinement. These solutions are part of a contributed benchmark solution set for the subject problem.

A comprehensive three-dimensional numerical investigation of the effect of beat source travel speed on temperatures and resulting thermal stresses was performed for CO{sub 2}-laser welding. The test specimen was a small thermal battery header containing several stress-sensitive glass-to-metal seals surrounding the electrical connections and a temperature sensitive ignitor located under the header near the center. Predictions of the thermal stresses and temperatures in the battery header were made for several travel speeds of the laser. The travel speeds examined ranged from 10mm/sec to 50mm/sec. The results indicate that faster weld speeds result in lower temperatures and stresses for the same size weld. This is because the higher speed welds are more efficient, requiring less energy to produce a given weld. Less energy absorbed by the workpiece results in lower temperatures, which results in lower stresses.

An examination of the effect of a realistic (though conservative) hot day environment on the thermal transient behavior of spent fuel shipping casks is made. These results are compared to those that develop under the prescribed normal thermal condition of 10 CFR 71. Of specific concern are the characteristics of propagating thermal waves, which are set up by diurnal variations of temperature and insolation in the outdoor environment. In order to arrive at a realistic approximation of these variations on a conservative hot day, actual temperature and insolation measurements have been obtained from the National Climatic Data Center (NCDC) for representatively hot and high heat flux days. Thus, the use of authentic meteorological data ensures the realistic approach sought. Further supporting the desired realism of the modeling effort is the use of realistic cask configurations in which multiple laminations of structural, shielding, and other materials are expected to attenuate the propagating thermal waves. The completed analysis revealed that the majority of wall temperatures, for a wide variety of spent fuel shipping cask configurations, fall well below those predicted by enforcement of the regulatory environmental conditions of 10 CFR 71. It was found that maximum temperatures at the cask surface occasionally lie above temperatures predicted under the prescribed regulatory conditions. However, the temperature differences are small enough that the normal conservative assumptions that are made in the course of typical cask evaluations should correct for any potential violations. The analysis demonstrates that diurnal temperature variations that penetrate the cask wall all have maxima substantially less than the corresponding regulatory solutions. Therefore it is certain that vital cask components and the spent fuel itself will not exceed the temperatures calculated by use of the conditions of 10 CFR 71.

The structural properties of spent nuclear fuel shipping containers vary as a function of the cask wall temperature. An analysis is performed to determine the effect of a realistic, though bounding, hot day environment on the thermal behavior of spent fuel shipping casks. These results are compared to those which develop under a steady-state application of the prescribed normal thermal conditions of 10CFR71. The completed analysis revealed that the majority of wall temperatures, for a wide variety of spent fuel shipping cask configurations, fall well below those predicted by using the steady-state application of the regulatory boundary conditions. It was found that maximum temperatures at the cask surface occasionally lie above temperatures predicted under the regulatory condition. This is due to the conservative assumptions present in the ambient conditions used. The analysis demonstrates that diurnal temperature variations which penetrate the cask wall have maxima substantially less than the corresponding temperatures obtained when applying the steady-state regulatory boundary conditions. Therefore, it is certain that vital cask components and the spent fuel itself will not exceed the temperatures calculated by use of the steady-state interpretation of the 10CFR71 normal conditions.