Search Results

Renewal theory concerns itself with the replacement of randomly failing parts. In the simplest case we have a one component system which is kept running continuously by replacing a failed component at the instant of failure with an identical “new” component. The random variable N(t) = the number of failures (or replacements) to time t is then of interest in many types of reliability analysis. In this paper the distribution of N(t) is considered when the underlying failure law is a Weibull distribution. Tables of the mean and standard deviation of N(t) for various values of the Weibull slope parameter are presented. Applications to warranty and spare parts analyses are also noted.

Convective heat transfer coefficients were determined for thermocouple junctions oriented parallel to the gas flow for Reynolds numbers (based on wire diameter) from 163 to 17,500. Chromel-alumel wires of 0.013-0.051 in. diameter were tested in air and products of natural gas combustion at temperatures of 60, 500, and 1000 F. Transient response was used to determine the heat transfer coefficient, and all data were corrected for variation of metal specific heat and radiant heat transfer. The affect on apparent heat transfer coefficient was determined for variations in junction weld-bead size, junction length, and wire separation. An empirical equation has been derived relating Nusselt number and Reynolds number that fits 92% of the test data within ± 10%.