Here are the solutions to board problems given at Power Subject Set-1. If you do not understand anything, feel free to write a comment voicing out your concern. I'm still looking for better ways to present my solution. I still don't know how to present equations and mathematical symbols with blogger. Please bear with me.

1. An automobile tire is inflated to 32psig pressure at 50 degree F. After being driven, the temperature rises to 75 degree F. Determine the final gage pressure assuming the volume remains constant. (Electrical Engineering Board Exam Problem)

Solution:

Since volume is constant, use Charles’ Law on constant volume processes.

P1/T1=P2/T2

Note: P and T should be absolute.

(32+14.7)/ (50+460) =P2/ (75+460)

P2=48.99 psia

Converting back to gage pressure,

P2g=48.99-14.7

P2g=34.29 psig

2. Four hundred cubic centimeters of gas at a pressure of 740 mmHg absolute and temperature of 18 degree C undergoes a process until the pressure and temperature becomes 760 mmHg absolute and 0 degrees C respectively. Calculate the final volume of the gas. (Electrical Engineering Board Exam Problem)

Since all the parameters (temperature, pressure and volume) changes, use combined gas law

PV/T=constant

P1V1/T1=P2V2/T2

(740)(400)/(18+273)=(760)V2/(0+273)

V2=365.3 cc

3. A single acting air compressor with a clearance of 6% took air at atmospheric pressure and temperature of 85 degrees F, discharges it at a pressure of 85 psia. Assuming that the compression is isentropic, find the piston displacement per cycle and the air power (hp) of the compressor if the RPM is 750. (Mechanical Engineering Board Exam 1978)

(I haven't got this correct yet, LOL)