UNIFIED ENGINEERING Fall 2005

Ian A. Waitz

Problem T4. (Unified Thermodynamics)

A thermally-insulated piston-cylinder arrangement holds a thermally perfect gas at p₁ = 1MPa and T₁ = 300K. The piston is massless. The surroundings are p_atm = 0.1MPa and T_atm = 300K. Assume the weight of the piston is negligible and that c_p = 1.0035 kJ/kg-K, c_v = 0.7165 kJ/kg-K, and R = 0.287 kJ/kg-K.

a) What could you use this device for?

b) How much work (per kg) is done by the system if you pull the pin allowing the piston to move impulsively? What is the final state of the gas in the cylinder?

c) What is the maximum amount of work (per kg) you could extract from this system? How would you go about doing this? What is the final state of the gas in the cylinder?

d) Draw both processes on a p_ext-v diagram.

e) Conceptually, how would friction between the walls of the cylinder and the piston change the maximum amount of work you can do on the surroundings with this system? Why?

(LO#4, LO#5)