on August 9th, 2012

Dear Colleagues

An interesting little (simple) brain teaser for you – no matter whether what discipline or type of engineering professional you are.

The Challenge
A tank at atmospheric pressure contains 1 kg of air. The tank is then pressurized with an additional 3 kgs of air. What is the resultant gauge pressure (in bars) in the tank after this 3kgs of air has been added? Absolute pressure = gauge pressure + atmospheric pressure

A. 1 bar
B. 3 bar
C. 4 bar

You could use the Universal Gas Law in your deliberations:

PV = nRT

Where V is volume; P is absolute pressure; n is the number of moles (‘molecules’); R is a constant and T is the temperature.

Assume atmospheric pressure is 1 bar (the initial pressure) – naturally this is a number which could change depending on what altitude you are at.

Solution (suggested – you could do it in a myriad of different ways)
There is initially 1kg of air occupying V0 initial volume.

With 3kgs of air added; there is now a total of 4kg of air in the tank (thus the final number of moles or particles is effectively 4 times that of the initial number).

The volume (V0) and temperature (TO) of the tank still stays the same.

Thus:

P0 V0  = n0 R T0 (initial state)
P1  V0  =  n1 R T0  (final state where n1 = 4 x n0)
Thus – dividing each side of equation 1 and 2 we get:

P1  V0 / P0 V0  =  4 x n0 R T0  /  n0 R T0

P1  V0 / P0 V0  =  4 x n0 R T0  /  n0 R T0

Thus P1 = 4 P0

Hence, the final pressure P1 = 4 bar absolute or 3 bar gauge pressure (thus answer B above)

Do you agree?

My humble appreciation to Dr Rodney Jacobs and David Spitzer (the flow guru) for their contributions and critique.

Albert Einstein remarked: I never teach my pupils. I only attempt to provide the conditions in which they can learn.

Yours in engineering learning

Steve


The latest news

The Next Big Driver for Instrumentation and Control: The ESG Criteria in Engineering 

The Next Big Driver for Instrumentation and Control: The ESG Criteria in Engineering 

The post The Next Big Driver for Instrumentation and Control: The ESG Criteria in Engineering  appeared first on EIT | Engineering Institute of Technology. Continue reading The Next Big Driver for... Read more
Why Earthing and Lightning Protection is important

Why Earthing and Lightning Protection is important

The post Why Earthing and Lightning Protection is important appeared first on EIT | Engineering Institute of Technology. Continue reading Why Earthing and Lightning Protection is important at EIT |... Read more
EIT students go exploring

EIT students go exploring

The post EIT students go exploring appeared first on EIT | Engineering Institute of Technology. Continue reading EIT students go exploring at EIT | Engineering Institute of Technology.EIT, Campus and... Read more
EIT - South Africa