Lecture 11 Examples

Lecture 11 Examples - effect of friction Plot the cycle in...

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Example 1: Air is contained in a piston-cylinder device fitted with stops. The piston initially rests on the stops and a pressure of 300 kPa is required to move the piston. Initially, the air is at 100 kPa and 27 °C and occupies a volume of 0.4 m 3 . Determine the amount of heat transferred to the air, while increasing the temperature to 1200 K. Assume air has constant specific heats evaluated at 300 K.

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Example 2: Carbon steel balls ( ρ = 7833 kg/m 3 and c p = 0.465 kJ/kg-°C) 8 mm in diameter are annealed by heated them first to 900 °C in a furnace, and then allowing them to cool slowly to 100 °C in ambient air at 35 °C. If 2500 balls are to be annealed per hour, determine the total rate of heat transfer from the balls to the ambient air.

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Example 3 : The gas inside a piston-cylinder device completes a four-step reverse cycle, called the reverse Stirling cycle, described as follows: 1-2: constant volume with V = 2 liter and p 1 = 1 bar 2-3: polytropic with pV = C and p 3 = 15 bar 3-4: constant volume with V = 0.2 liter 4-1: polytropic with pV = C Complete a thermodynamic analysis of this cyclic process defining the system as the gas and neglecting any

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Unformatted text preview: effect of friction. Plot the cycle in p-V coordinates. Determine the missing state variables p 2 and p 4 and the net work input W net (in joules). Example 4: The compound system in the sketch below contains a gas ( C v = 2.5 mR ) on both sides of an internal wall. As heat is transferred across the wall, the piston moves to the right until the gases obtain thermal equilibrium at T 2 . During this process the shaft force F shaft maintains the pressure for system B constant at 3 bar. Also, P A1 = 10 bar, T A1 = 1000 K, V A = 1 liter, and P B1 = 3 bar, T B1 = 300 K, and V B1 = 1 liter. Determine ( i ) the heat capacities at constant volume and at constant pressure for the gas: C v and C p ; ( ii ) the missing thermodynamic state properties: T 2 , P A2 , and V B2 ; ( iii ) the heat transferred from system A to B, Q A-B , the pressure work out of system B, W B and the shaft work, W S . Do not neglect the affects of atmospheric pressure, P = 1 bar. F shaft Q A-B A B...
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