Thermal-Transient Analysis of the Brayton Isotope Power System (BIPS) Recuperator

摘要

The purpose of this study was to: examine the proposed Brayton Isotope Power System (BIPS) startup model; select the most favorable condition with regard to a recuperator cyclic life; perform a detailed transient heat transfer analysis; and compute the resultant thermal stresses and low cycle fatigue life. In addition, a study was performed to compare the predicted metal temperature transients with experimental data. Proposed system startup modes were examined and the most favorable method was selected. Detailed transient temperature analyses were performed for the selected startup sequence and temperature maps were developed for the response of the heat exchanger elements, bars, plates, fins, and manifolds. This data was the basis for subsequent structural analysis. Recommendations for heat exchanger modifications to obtain a more uniform thermal response throughout the structure are proposed. These changes would result in reduced thermal stresses and should be considered for follow-on, advanced recuperator designs. Good agreement between experimental data and transient temperature predictions is shown; the analytical techniques are verified. The structural analysis identified certain critical areas within the core assembly where a high thermal stress is developed. Low cycle fatigue cracks could develop in some of the critical areas after accumulating less than 100 startup cycles (design life). These cracks, if they propagate through the structure, would result in an internal bypass leak that would degrade system performance; however, no external leakage with loss of working fluid would occur. It is concluded that the recuperator low cycle fatigue life is adequate for the BIPS applications. Additional analyses are proposed to more rigorously define the three-dimensional thermal stresses and the resultant cyclic life. These results will increase the confidence level in the present recuperator structural design. (ERA citation 06:028349)