Behzad D. Mottahed

Design Considerations for Electronic Enclosures Utilizing Polymeric Materials

In this article, a comprehensive review of important enclosure design issues in electronic systems is given. Use of various polymer-based materials and materials selection criteria based on mechanical and electrical properties are reviewed. Structural design models for electronic enclosures are presented. Shielding effectiveness of a printed wiring board and gasketing are examined. A cost-estimation technique is summarized and future trends are discussed.

Material and geometry factors in joint design of electronic equipment to minimize electromagnetic interference

Reducing electromagnetic interference in electronic equipment is of great importance. This is normally accomplished by increasing the shielding effectiveness of the enclosure. In this study, shielding effectiveness is examined against enclosure material, joint geometry, and operating frequency. An experimental apparatus is designed and manufactured to aid in finding the suitable joint configurations and materials with high shielding effectiveness. Three groups of material, namely, metallic, filled polymers, and metalized filled polymers, are investigated. In addition to the choices of material, effect of joint configurations on shielding behavior are examined. Based on the experimental results, empirical relations are developed that relate shielding effectiveness to effective length, shape factor, and aperture dimensions ofthejoint structure. Finally, the best material and joint geometry among the investigated cases are presented.

Cooldown Simulation for the Compact Ignition Tokamak (CIT), Poloidal Field (PF) Coils

An experimental investigation was conducted to study the cooldown behavior of the Poloidal Field (PF) magnets. A full-scale model of a section of the cooling passages was built for this purpose. LN2 , was used as the coolant in the vertical passages at mass fluxes ranging between 42 to 140 Kg/m2 -s and heat fluxes from 17000 to 75000 W/m2 with nearly saturated liquid at the inlet. The heat flux was controlled with resistive heaters. Two distinct boiling regimes were observed. The first, Type I consists of film-boiling throughout the passage. Type II has nucleate boiling at the inlet, and is followed, in a short distance, to film-boiling. The equilibrium quality at the burnout point was calculated and was found to increase slightly with decreasing heat flux. The Leidenfrost temperature at which liquid Nitrogen wets the wall was measured to be about 180–200 K. Heat transfer coefficients in the order of 200–500 W/m2 -K for film boiling and 5000 to 10000 W/m2 -k for nucleate boiling in the type II regime were attained. Higher heat flux and mass flow rates resulted in higher heat transfer coefficients. Empirical correlations were obtained for the nucleate region of the type II regime.Copyright