## Sunday, December 6, 2009

### PAST BOARD EXAM QUESTION:POWER SET-I (ANSWERS)

Below are the answers to the question on the POWER Set-I Questions taken from prevous engineering board examination.

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)
a. 34.3psig

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)
c. 365 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)
c. Vd=1.03 cu.ft/cycle, Power=96 hp

4. Steam enters turbine stage with an enthalpy of 3628 kJ/kg at 70m/s and leaves the same stage with an enthalpy of 2846 kJ/kg and velocity of 124 m/s. calculate the work done by the steam. (Mechanical Engineering Board Exam 1986)
b. 776.8 kJ/kg

5. In an air standard Otto cycle, the clearance volume is 18% of the displacement volume. Find the thermal efficiency? (Mechanical Engineering Board Exam 1993)
d. 53%

6. A reversed Carnot cycle is used for cooling. The input work is 12kW, while the COP is 3.8. Calculate the refrigerating effect in TOR. (Mechanical Engineering Board Exam)
b. 12.97

7. The compression ratio of a standard gasoline engine is 8. The heat added is 1850kJ/kg. If the initial pressure and temperature are 100Kpa and 25 degrees C respectively, determine the temperature at the end of isentropic expansion. (Mechanical Engineering Board Exam)
d. 1147

8. What is the logarithmic mean temperature difference (LMTD) of a double pipe counterflow heat exchanger if the fluid enters at 90 degrees C and exits at 50 degrees C. Inside the inner pipe, another fluid enters at 20 degrees C and exits at 60 degrees C. (Mechanical Engineering Board Exam)
b. 30

9. The volume of concrete needed for the foundation of an engine is 12 cubic meters. The concrete mixture is 1:3:5 by volume. Calculate the number of 40 kg bags of cement needed considering the density of cement to be 1500kg/cu.m. (Mechanical Engineering Board Exam)
d. 50

10. A 305mm x 457mm four stroke single acting diesel engine is rated at 150 kW at 260 rpm. Fuel consumption at rated load of 0.26 kg/kw-hr with a heating value of 43912 KJ/kg. Calculate the brake thermal efficiency. (Mechanical Engineering Board Exam 1990)
a. 31.63%
Solutions will be posted this coming week!

Do you want to be notified if new articles are posted here? There are three ways:
1. Subscribe via email.