Answer to Question #173960 in Mechanical Engineering for Randal Rodriguez

Question #173960

Note: Draw the P-V, T-S diagrams for all problems

1. A reversible nonflow constant volume process increases the internal energy by 316.5 kJ for 2.268 kg m of a gas for which R = 430 J/kg m -K and k = 1.35. For the process, determine a) Work, b) heat

transferred c) change in enthalpy d) change in entropy if the initial temperature is 204.4 o C..

2. A certain ideal gas has a constant R = 38.9 ft-lf f /lb m -R with k = 1.4. a) If 3 lb m of this gas undergoes a reversible nonflow constant volume process from 120 psia,740 o F to 140 o F find P 2 , ∆U, ∆H, Q, Work. b) If the process in “a” had been steady flow find work and ∆S.

3. A group of 50 persons attended a secret meeting in a room 14 m x 10 m x 3.5 m high. The room is

completely sealed off and insulated. Each person gives off 150 kCal/hr of heat and occupies a volume

of 0.2 m 3 . The room has an initial pressure 101.3 kPaa and temperature of 16 o C. Calculate the room

temperature after 10 min. NOTE: (4.187 kJ = 1 kCal)

Expert's answer


The change in entropy,

Specific heat at constant volume,

Final temperature,

Entropy change,


Heat released after 10 minutes is therefore 18.84 MJ.

n = 20236.8 moles of air

but, 1 mole of air = 29

the mass of air in the room = 586kg

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