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755 assumptions 1 steady operating conditions exist 2

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Unformatted text preview: = 0.92 P2 = 80 kPa a 80 kP T2a 2s T2s FIGURE 7–55 Schematic and T-s diagram for Example 7–16. 2a s s2s = s1 SOLUTION A sketch of the system and the T-s diagram of the process are given in Fig. 7–55. Assumptions 1 Steady operating conditions exist. 2 Air is an ideal gas. 3 The inlet kinetic energy is negligible. 4 The nozzle is adiabatic. Analysis The temperature of air will drop during this acceleration process because some of its internal energy is converted to kinetic energy. This problem can be solved accurately by using property data from the air table. But we will assume constant specific heats (thus sacrifice some accuracy) to demonstrate their use. Let us guess that the average temperature of the air will be about 800 K. Then the average values of Cp and k at this anticipated average temperature are determined from Table A–2b to be Cp 1.099 kJ/kg · K and k 1.354. (a) The exit velocity of the air will be a maximum when the process in the nozzle involves no irreversibilities. The exit velocity in this case is determined from the st...
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