Wednesday, December 30, 2009

ANSWERS TO BOARD EXAM REVIEWER: POWER ELEMENTS








Here's the answers to the questions posted on the last article.
1. The measure of how effective a boiler is in transferring heat from furnace to the water and steam.
Answer: C. Boiler efficiency

2. A heat exchanger used to remove dissolved air in water?
Answer:b. Deaerator

3. A state of water where the quantity of steam and liquid water is indistinguishable.
Answer: a. Critical point
Reference: p.62, Thermodynamics 6th.Ed., Faires and Simmang

Friday, December 25, 2009

BOARD EXAM REVIEWER: POWER ELEMENTS






I have here some of the most frequently appearing types of "elements" on the subject of power and industrial plant engineering. Answers will be provided after a week.
These questions were based on previous board examination and was reworded and modified but it carries the same thought as the actual questions.


Instruction: Choose the BEST answer.

1. The measure of how effective a boiler is in transferring heat from furnace to the water and steam.
A. Coefficient of heat transfer
B. Boiler conductivity
C. Boiler efficiency
D. Furnace efficiency

2. A heat exchanger used to remove dissolved air in water?
a. Condenser
b. Deaerator
c. Reheater
d. Boiler

3. A state of water where the quantity of steam and liquid water is indistinguishable.
a. Critical point
b. Absolute zero
c. Boiling point
d. Freezing point

4. A power plant that harness energy from the difference in temperature between the depths of the ocean.
a. OTEC
b. Geothermal plant
c. Hydroelectric plant
d. Wave power plant


5. The most efficient thermal cycle.
a. Rankine cycle
b. Otto Cycle
c. Diesel Cycle
d. Carnot Cycle

Wednesday, December 23, 2009

SOLUTION TO MECHANICAL BOARD EXAM PROBLEMS: Power Set-1






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)

Tuesday, December 8, 2009

IMPORTANT: Email Subscriptions






I'm very glad about the response of the visitors of this blog. In it's 7th Month now, Mechanical Engineering Blog Site already have 96 email subscription requests! This can only mean one thing--that the visitors are interested on the future contents of this site. The sad news though is that only 64 out of those 96 subscriptions (67 percent) are active. The remaining 32 requests are in the state of "pending confirmation".



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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