A N experimental investigation of the extinction behavior of solid composite propellants (PBAN + AP) by rapid depressurization is made. An analytic procedure by an adiabatic process (or isentropic process) and Summerfield's burning rate law is taken to predict pressure decay. The vents' opening rate is assumed to be a parabolic function of time; also, a model of "adiabatic-isentropic combined process" is proposed for improving the predictions.
ContentsCiepluch concluded that there was a minimum depressurization rate (dP/dO c required to extinguish combustion, * that many solid propellant compositions might be susceptible to the reignition phenomenon, and that the residual chamber gas and the residual heat in the propellant surface were the primary sources of ignition energy. 2 Jensen and Brown 3 found that the exhaust pressure level could influence extinction and reignition behavior.Experimental investigation of this study is achieved by using a test motor shown schematically in Fig. 1.As shown, two additional vents on the head of the motor were blocked up with vent covers that were held in position with two U-clamp bends and two explosive bolts. The motor was depressurized rapidly by initiating the explosive bolts and opening the vents. A pressure transducer and a high-speed camera were used to record the pressure variation and extinction phenomena, respectively. The results are listed in Table 1.It is found that the combustion of PBAN propellants was extinguished temporarily by opening suitable venting ratio ports on the motor head, but that reignition occurred because of residual heat feeding back to the propellant grain under the test environment of 1 atm. Furthermore, the reignition could be delayed by inserting vulcanized fiber between the freestanding grain and the motor case (with motors 2 and 4) because of the effects of reducing residual heat transfer from the motor case and hot gases.In this investigation either an isentropic or an adiabatic process is assumed, and Summerfield's burning rate law is used to predict pressure decay. Besides, the venting ratio is assumed as a parabolic function of time 4 during the period of delayed time t d before full opening of the vents.The main assumption of isentropic pressure decay is that the extinction occurs immediately upon opening of the vents without time delay. For the case of adiabatic pressure decay,
Out-of-plane magnetic anisotropy (OMA) of FeCoNbB amorphous films has been studied. The OMA is abnormally enhanced by elevating the substrate temperature from room-temperature to 500 °C, being much different from most soft-magnetic amorphous films. Furthermore, the films show a slightly decay in the OMA when annealed at a temperature lower than the respective deposition temperature. But when annealed at a temperature 50 °C higher than the respective deposition temperature, the OMA suddenly disappears. Such results indicate a distinguishing mechanism of non-magnetoelastic-anisotropy dominated OMA. A model of co-effects of magnetoelastic anisotropy and microshape anisotropy is proposed.
The thermal management systems or heat sinks are an integral part of electronic devices for aerospace applications. The heat transfer characteristics of the widely used phase change material (PCM)-based heat sinks under hypergravity conditions are essential in the designation of the heat sink. The current study conducts a systematic evaluation on the thermal characteristics of PCM coupled with hybrid fin-metal foam (FMF) structure under variable hypergravity conditions. A validated two-dimensional transient melting heat transfer model of the designed system is proposed, and the influences of enclosure orientation, fin height, PCM slab thickness, and the distribution of fin and metal foam under different hypergravity conditions are investigated. Results show that with the decrease in inclination angle, the melting time and the heating wall temperature become lower, and the optimal inclination angle is 0 . As the PCM slab thickness gets larger, natural convection is enhanced, while the heating wall temperature and melting time become larger. With the rise of hypergravity value, the effect of inclination angle strengthens, while the influence of PCM slab thickness weakens. Furthermore, with the rise of the copper foam fraction in the hybrid FMF structure, the melting time and the heating wall temperature firstly decrease and increase afterward. The optimal copper foam fraction is 58.62%. This study guides the optimal design of the PCMbased heat sink in aerospace applications.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.