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F2008-E234-S-Exam1

# F2008-E234-S-Exam1 - E234 THERMODYNAMICS Exam 1 Data R =...

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E234 THERMODYNAMICS Exam 1 – September 22, 2008 Data: R = 8.314 J/mol.K For air R = 0.287 kJ/kg.K M(air) = 29 kg/kmol 1. A tank has two rooms at 80.3 o F separated by a membrane. Room A has 1 kg air and pressure of 1 bar, room B has 750 L air with a specific volume of 0.83 m 3 /kg. The membrane is broken and the air comes to a uniform state. Determine a. The total mass of air b. The final density of the air c. The final pressure in bar and in mmHg T = 80.3 o F = 26.83 o C = 300 K 1 bar = 10 5 Pa Initial state: Tank A: P A = 1atm m A = 1kg T A = 300 K Ideal gas law: V A = m A R air T A /P A = 0.861 m 3 (watch your units) Tank B: V B = 0.75 m 3 v B = 0.83 m 3 /kg T B = 300 K m = V B /v B = 0.904 kg a. m = 0.904 + 1 =1.904 kg b. density = m/V = 1.904/(0.861 + 0.75) =1.18 kg/m 3 c. Ideal gas law: P = mR air T/V = 101.75 kPa 2. A water heater tank is cylindrical, 1 m tall, and diameter 0.5 m. It is made of a thin steel sheet covered by a 1.5 cm thick foam insulation with k = 0.025 W/m.K. The combined convection and radiation effects to the surrounding air are expressed in a convection coefficient of h = 12 W/m 2 .K. The hot water inside is at 72 o C and the

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F2008-E234-S-Exam1 - E234 THERMODYNAMICS Exam 1 Data R =...

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