When the properties of the mass change during the

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Unformatted text preview: system increases by ms when mass in the amount of m enters and decreases by the same amount when the same amount of mass at the same state leaves the system. When the properties of the mass change during the process, the entropy transfer by mass flow can be determined by integration from · Smass sr Ac n dAc and Smass sdm where Ac is the cross-sectional area of the flow and normal to dAc. t n · Smass dt (7–75) is the local velocity Entropy is not transferred with work Entropy generation via friction FIGURE 7–59 No entropy accompanies work as it crosses the system boundary. But entropy may be generated within the system as work is dissipated into a less useful form of energy. hm s Control volume mh ms FIGURE 7–60 Mass contains entropy as well as energy, and thus mass flow into or out of system is always accompanied by energy and entropy transfer. cen54261_ch07.qxd 11/18/03 9:57 AM Page 322 322 FUNDAMENTALS OF THERMAL-FLUID SCIENCES Entropy Generation, Sgen Irreversibilities such as friction, mixing, chemical reactions, heat transfer through a finite temperature difference, unrestrained expansion, nonquasiequilibrium compression, or expans...
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