## Saturday, February 13, 2010

### ANSWERS to Mechanical Engineering Board Exam Questions in FLUID MECHANICS

Here is the answer to the questions posted last week. Please let me know if you have additional concerns by commenting.

1. In fluid mechanics, it is the ratio of the area of the vena contracta to the area of the smaller pipe.

2. When the Reynolds number of a fluid flow is 3500, the flow is…
Answer: C. Intermediate between turbulent or laminar (corrected)

3. What will happen if the pressure of water flowing in a pipe dropped below its vapor pressure?
Answer: C. bubbles will form inside the pipe

4. It is the common name for the rattling noise heard inside the pipe as a result the instantaneous rise in the fluid pressure.

5. It is flow pattern where a fluid flows in concentric circles with no radial flow.

6. In an open channel flow (open channel refers to flows with free surface), what is the optimum channel shape for maximum flow rate?

7. Which factor(s) affects the flow regime (laminar or turbulent) of a fluid in a pipe?
Answer: D. Both a and b

8. The greatest contributor to the head losses in pipes is…

9. What will happen to the buoyant force if the density of the liquid is decreased?

10. For a partially immersed body, the point at which the line of action of the buoyancy force cuts the vertical centre line of the floating body in the displaced position is known as the…

1. sana maraming panga mga review question na post lalu na yung mga latest question sa board exam

2. sure! I'll try to make more and better review questions.

3. good day...we have a question about Reynolds Number, because in my research from Engineering Toolbox LAMINAR when RE < 2300, TRANSIENT when 2300 < RE <4000 TURBULENT when RE > 4000 Thanks for your advice....

4. You are correct! My reference is wrong. It is OUTDATED.
When RE >4000 flow is turbulent
When RE <2300 flow is laminar
In between those values is the transition range.

Thanks for the input and my apologies for giving an incorrect answer.

The answer above has been corrected accordingly.

5. Greetings......
i will be take examination this coming October... i need more elements specially in Machine Design.. what are the best book and author should be...
i appreciate for all your help....... thank you for your blog site so helpful.. Good luck to all of us..

7. for those about to take the licensure exam enrolled in a review that has the highest passing rate they have some bonuses before the exam,good luck

8. question 8. hindi po tama ang question. ang question dapat ay "the head losses in pipes is equivalent to? pipe length

if your pertaining to "piping" and not "pipe", then the answer should be indeterminate. a lot of factors contribute to the whole piping system. not only the pipes but the whole system should be considered. Do you know that the equivalent length of a 4inch flanged steel globe valve is 120 ft? it means that the pressure drop across this specific fitting is equivalent to the pressure drop across the 120 ft steel pipe. what if ang system is positive suction while discharge 50ft length is along pump center line but is connected with 2 swing check and 1 globe valve? fitting head loss is way greater that the total pipe loss. we should always consider if the system is closed or open, saturation pressure of the fluid at certain temperature for closed systems, the relative roughness of materials being used and the kinematic viscosity to calculate the friction factor f in formula hf=fLv^2/2dg.

therefore, question 8 is indeterminate.

wag po tayo basta basta maniniwala sa sabi ng review center or sabi ni professor. magbasa po tayo ng libro at hindi reviewer lang. lahat ng review center ay bumibili lang ng tanong sa examiner at yan ang totoo. buti sana kung ang tanong at ang answer ay tama. email me if you have question regarding general engineering at thermal-fluids engineering.

gonzalesij@yahoo.com

9. Reynolds number for Laminar flow is less than (approx) 2100 and not 2300. Mali ang engg toolbox.

10. in question 1 is contraction coefficient similar to orifice sizing, beta ratio= d1/d2, where d1 is the orifice while d2 is the internal pipe diameter?