Effects of combined stressing on the electrical properties of film and ceramic capacitors
Advanced power systems which generate, control and distribute electrical power to many large loads are a requirement for future space exploration missions. The development of high temperature insulating materials and power components constitute a key element in systems which are lightweight, efficient, and are capable of surviving the hostile space environment. In previous work, experiments were carried out to evaluate film and ceramic capacitors for potential use in high temperature applications. The effects of thermal stressing, in air and without electrical bias, on the electrical properties of the capacitors as a function of thermal aging up to 12 weeks were determined. In this work, the combined effects of thermal aging and electrical stresses on the properties of teflon film and ceramic power capacitors were examined. The ceramic capacitors were thermally aged for 35 weeks and the teflon capacitors for 15 weeks at 200/spl deg/C under full electrical bias and were characterized, on a weekly basis, in terms of their capacitance stability and electrical loss in the frequency range of 50 Hz to 100 kHz. DC leakage current measurements were also obtained. The results obtained represent the influence that short-term thermal aging and electrical bias, have on the electrical properties of the power capacitors characterized.<<ETX>>
Electrical properties of Teflon and ceramic capacitors at high temperatures
Experiments were carried out to evaluate Teflon and ceramic capacitors for potential use in high-temperature applications. The capacitors were characterized in terms of their capacitance and dielectric loss as a function of temperature, up to 200 degrees C. At a given temperature, these properties were obtained in a frequency range of 50 Hz to 100 kHz, DC leakage current measurements were also performed in a temperature range from 25 to 200 degrees C. The experimental procedures and results are discussed.<<ETX>>
Laminar heat or mass transfer in rectangular channels and in cylindrical tubes for fully developed flow: comparison of solutions obtained for various boundary conditions
Abstract A comparison is made of results obtained with various boundary conditions at the wall of the channels. By comparing blood Sherwood numbers for finite wall resistance with those for constant concentration boundary condition only a small variation is found for various points along the blood channel.