In order to achieve the best performance of a thermal system, two major analyses must be carried out on the system: energy and entropy generation. The best scenario is a mechanism in which the system has minimum entropy generation and the highest Nu number. In this regard, we investigated entropy generation and Nu number of fluid flow through tubes of various cross-sections, namely circular tubes, square channels, and rectangular ducts. Additionally, the addition of nanoparticles was tested, and both analyses were carried out. The results reveal that using nanoparticles could significantly increase Nu number and, at the same time, decrease entropy generation. The results showed that the circular cross-section performs better in Nu number and entropy generation. In most cases, the rectangular cross-section performed better than the square one in terms of energy and entropy. In the best case, the average Nu for the circular cross-section was 26% greater than that of the square. The average Nu of the rectangular cross-section showed that this value is 5% greater than that of the square cross-section. Additionally, the total entropy generation of circular cross-sections, which is the minimum, was 44% and 38% lower than rectangular and square cross-sections, respectively.
Summary
The main aim of this chapter is to make a brief and comprehensive overview of various events of crises across the EU member states that arose in the period from the adoption of the Lisbon Treaty until the end of year 2020. The chapter first, examines the period of crisis in the EU after the adoption of Lisbon Treaty and before BREXIT which includes: economic and debt crisis, euro-zone crisis, Ukrainian crisis and migration crisis. The next part of the chapter looks at BREXIT as “another serious test for the EU”. In the third stage, the chapter looks at the most recent crisis the EU is facing as a consequence of global spread of COVID19 virus in the world and examines various options for further potential cooperation of member states in this new area. In this part chapter looks at the scope of EU competences and explores measures adopted by the EU since the beginning of the pandemic. In its conclusions the chapter looks at various options and scenarios of further potential developments the “European union on crossroads” at the end of year 2020. This includes reflections on various (and often contradictory) views and arguments on the shape of future euro integration process.
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