Papers by Author: T.Y. Yeh

Abstract: The manufacturing of plate heat exchangers is much more difficult than that of making traditional heat exchangers. The demand of increased corrosion resistance, avoiding Cu ion contamination, resisting to high-temperature resulting from various applied environments makes the traditional Cu brazed 316 stainless steel (316SS) plate heat exchanger fail to satisfy certain applications. Corrosion-resistant brazed 316SS plate heat exchangers are successfully developed using two commercially available Ni-based brazing foils, and they are valuable for industrial applications.

Abstract: Infrared heating is featured with a high heating rate up to 50oC/s. It is a very powerful tool applied in brazing application, so infrared heating has been used to study the kinetics of brazing process in recent years. The importance of brazing Ti alloys has been increased in past twenty years due to the strong demand from chemical and aerospace industry. Based on the previous studies, the use of Ti-based brazes alloyed with Cu and Ni contents is considered as one of the best alloys in brazing Ti and its alloys due to their high bonding strength. However, the presence of Ti-Cu-Ni intermetallics in the brazed joint has a strong effect on the joint strength, and the reaction kinetics of the joint is still unclear. The purpose of this investigation is concentrated on transmission electron microscopy (TEM) study of the infrared brazed CP-Ti using Ti-15Cu-15Ni filler, and microstructural evolution of the infrared brazed joint is unveiled. It is helpful for industrial applications of Ti-based alloys.

Abstract: Functionally gradient materials (FGMs) composed of 3YSZ and IN713LC were developed in three different configurations. A linear-mode FGM had its compositions with a monotonic change in coefficient of thermal expansion (CTE). Negative- and positive-deviated FGMs had their compositions with lower and higher CTEs, respectively, on the ceramic sides. Fracture behaviors of these three types of FGMs were evaluated with aids of residual stress analyses. FGMs with a positive CTE deviation demonstrated the best performance in the experiment. The brittle ceramic side was under high compressive stress, and high tensile stresses were primarily initiated in the metal-rich gradient layers.

Abstract: The compatibility of various electrolyte and electrode combinations has been assessed based on viewpoints of mechanics. The membrane-electrode assembly (MEA) was mainly comprised of traditional ceramic-metal materials as well as solid electrolytes. Variations of key variables such as size and coefficient of thermal expansion were incorporated into ABAQUS sensitivity analyses. Accordingly, general design rules in manufacturing solid oxide fuel cell (SOFC) were proposed, and these rules were beneficial to produce multilayer MEA in the future.