Question

2. A piston-cylinder device maintain a constant pressure of 800 kPa while containing 20 kg of saturated water vapor. The system is heated with a resistance heater for 10 min at a current of 8 A at the standard wall voltage of 120 V. In that time, 3.2 kJ of heat is lost through the walls. What is the temperature at the heated state? 3 5-18E Hydrogen is contained in a piston-cylinder device at 14.7 psia and 15 ft. At this state, a linear spring ( F X) with a spring constant of 15,000 lbf/ft is touching the piston but exerts no force on it. The cross-sectional area of the piston is 3 it?. Heat is transferred to the hydrogen, causing it to expand until its vol- ume doubles. Determine (a) the final pressure, (b) the total work done by the hydrogen, and (c) the fraction of this work done against the spring. Also, show the process on a P-V diagram.

Answer 1

Solutions Www State 1 state 2 Given, P = pressure at state 1. = 14.7 psia - 15 ft² Po= pressure at state 2 V = 2V, = 30 ft? Spring constant of Springkä = 15000 lb/t. Cross-sectional aula of the piston - 34+? The distance moved by piston ''= V-VI A = 5 ft. force exeitted by spring of piston on Spring is F = k. x = 15000 dbf x 5ft = 750001 bt

Presque force by spring final pressure , Pg = P, & f Pressure force by spring = F = 75000 aff 2 3x144 inch = 173.61 psi Py = 14.7 + 173,61 = 188.31 psi. total work done by hydrogen is W = kx2 + P, CU,U) The 14.7 x 15 x1728 inch 3 = I x 15000 lbf x 5 + + 381024 2250000 lbf inch = 263102 4 ebf inch 219252 lbf ft.

@ fraction of this work done against the spring 2250000 = .85 SIB 26310 24 It means work done against the spring is 85.518% of the total work. (P2, ve) ( ( 173.61,50) CP,V) gives the curre also The area under the pv total work done.