Heat exchangers are key components of most power conversion systems, a few industrial sectors can particularly benefit from high temperature heat exchangers. Examples include conventional aerospace applications, advanced nuclear power generation systems, and high efficiency stationary and mobile modular fossil fuel to shaft power/electricity conversion systems. This paper provides a review of high temperature heat exchangers in terms of build materials, general design, manufacturing techniques, and operating parameters for the selected applications. Challenges associated with conventional and advanced fabrication technologies of high temperature heat exchangers are discussed. Finally, the paper outlines future research needs of high temperature heat exchangers.

Background: Although previous researches have examined the direct effects of the personality trait of grit in predicting students' procrastination and engagement, its indirect effects have been less studied. Aims:The general purpose of this study is to investigate the role of grit that directly or indirectly increases academic engagement and decreases academic procrastination. Methods: The present study was descriptive and of correlation and structural equations. The statistical population of the study included all non-profit high school male students in Hamadan city in the academic year 1398-99. Based on the two-stage cluster sampling method, 500 students were selected and completed Duckworth and Quinn's (2007) Grit scale, Reeve's (2013) academic engagement scale, Solomon & Rothblum's (1984) academic procrastination, and Elliot, Murayama's, and Pekrun's (2011) achievement goal questionnaire. Data were analyzed using the structural equation statistical method and Spss24 and AMOS-26 software. Results: The results showed that grit had a positive and significant effect on academic engagement with the mediating role of self-based and task-based development goals (β= 0.05, p<0.01). But grit did not have a negative and significant effect on academic procrastination with the mediating role of self-based and task-based achievement goals (β= 0.06, P= 0.68). Conclusion: Self-based and task-based competencies can increase behavioral, cognitional, emotional, and agentic engagement in grittier students. But these competencies can't play a significant role in reducing procrastination.