Phase change effects in parallel and tapered liquid face seals are studied analytically. Both an isothermal and adiabatic model of low Reynolds number flow are considered by numerical integration of the descriptive equations for a real fluid. Real fluid thermodynamic properties are calculated for each step, using a computer program for the steam tables or thermodynamic properties of the fluid considered. Examples are presented for water. The general conclusions are: 1. For low leakage rate the isothermal model is more accurate and for high leakage rates the adiabatic model is more accurate. 2. Both parallel models, ordinarily neutrally stable with a liquid, yield the same general conclusions about stability. If the sealed fluid is near enough to saturation conditions, there will exist generally two values of the film gap, h, which yield the same separating force under a given set of operating conditions. For a given speed, face excursions about the larger value are stable, but excursions about the lower value are unstable, either growing to the larger h if displaced apart or collapsing if displaced together. 3. The transient of collapse is described by the adiabatic model which predicts a catastrophic collapse and then either failure or explosive return to a larger value of h. 4. Converging seals (ordinarily stable with a liquid at some given value of h) may become unstable, the phase change effect dominating the behavior and giving rise to collapse as described above. 5. The mass leakage rate is reduced significantly below the all liquid value when boiling occurs.

Potted electronics are becoming more common in precision-guided artillery due to demands for increased structural-robustness. In field artillery applications, the potted electronics are inactive for most of their lifetime. Projectiles may be stored in a bunker without environmental (temperature and humidity) controls for up to 20 years. In contrast, the electronics for most commercial applications tend to be active for most of their lifetime and the operating environment is more predictable. This difference makes the thermal management task for the artillery application challenging. The ability to accurately analyze these designs requires the use of fully coupled thermal-stress transient-analysis with accurate material properties over the full temperature range. To highlight the thermal-stress transient effects, the potted configuration of a typical electronics assembly is analyzed. The thermal analysis indicates that significant stresses can develop in critical locations as a result of temperature cycles. The structural dynamic responses of unpotted and potted assemblies, subjected to gun-launch environments, are also compared. The results indicate that for the potted design, the dynamic response of the processor board is attenuated by the potting material.

Potted electronics are becoming more common in precision-guided artillery-launched munitions and also missile systems due to the requirements for miniaturization and structural-robustness. In this paper we have presented a methodology for encapsulating circuit board assemblies (CBA) with a thin polymer layer. The protective polymer layer is both flexible and soft enough to protect the CBA from damage caused by CTE mismatches, and without any appreciable degradation in the structural support during the high-g forces of projectile launch. The application process described here allows for the use of a broad range of polymer materials including those that may not be formed directly against an actual CBA. Proof-of-concept experimental tests and finite-element simulations have been performed and the tests and simulation results are shared in this paper. In addition, the protective polymer layer can also be used to improve in-circuit board crosstalk and RF interference shielding, tin-whisker growth control, moisture barrier properties, and thermal management for un-potted and potted CBAs.

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The steady and dynamic behavior of thin film evaporators and condensers are simulated with a general thin film heat exchanger model. The dynamics of the gravity-controlled falling laminar film on horizontal and vertical tubes are studied in detail. For a first approximation or for a slow transient a single-lumped model can be used. For a refined simulation or for a severe transient a grouped model is proposed. The grouped model preserves the important feature of delay-time and wave-distortion of a transient, which was observed in a separate precise analysis [9]. The thin film heat exchanger models are used in the dynamic simulation computer programs ODSP3 and OSCAR which were established for OTEC systems. Typical results are presented to demonstrate the capability of the model.