Aakash:
If you are telling us the truth about your prof ridiculing you because of a misconception on your part regarding fluid flow, then you, unfortunately, have a bad teacher. No student should be ridiculed about having a lack of knowledge or proper prior teachings. A student, by definition, is supposed to be ignorant and lacking in knowledge. That is why he is in school: to obtain that knowledge. Instead of making fun of your ignorance on the subject, the prof should make it his/her job to teach you where you are going wrong and how to remedy your lack of knowledge on the subject. That is what the prof is being paid to do.
By being candid and admitting your lack of knowledge, you have come to the right place. This is why Chris Haslego started this Student Forum in order to concentrate specifically on student problems. Here, you will receive some advice and key learnings from experienced engineers who have gone through the same learning cycle.
You are wrong in your concept of fluid flow - but not because “it's a continuous pipeline and not a closed box, the gas law isn't valid and the pressure will remain the same and a drop will be experience throughout the pipeline only because of friction or elevation.” There is no reason to apply the gas law as you have indicated because, as stated, this is not a static gas problem - although the principles supporting the gas law DO apply to the gas flow because as the gas is reduced in pressure due to pressure drop, it will expand. Therefore, the compressibility factor does play a role in gas pipeline calculations. This is where I think you are having difficulty understanding the unit operation of gas flow. There are many fluid flow texts in existence that explain the principles involving both liquids and gases (gases being the most difficult).
All fluid flow - whether liquid or gas - takes place under the influence of a DRIVING FORCE. Once the fluid flows, it is subjected to a pressure loss as it proceeds downstream in its conduit. This pressure loss is due to conduit wall friction (as told to you) but also to directional turns, conduit fittings (valves, elbows, Tees, etc.), and fluid turbulence. It is important to understand this principle and dominate it. Many students confuse this topic by believing that pumps and compressors are the cause of pressure build-up. Actually, neither pumps nor compressors create a pressure. It is THE RESISTANCE that the fluid has to confront and overcome in its flow path that actually causes the original source to develop a pressure. Without a flow resistance, there would be no pressure drop and consequently no pressure developed at the source.
What is definitely important here is your cooperation in fully studying and understanding the basic Darcy Equation for liquid flow. It is important that you know the basis and the assumptions taken for the development of this equation. Once you have grasped this, you will be prepared to tackle the more difficult subject of compressible flow.
I am confident that some of our experienced engineers will join in this thread with helpful and constructive advice regarding gas flow in pipelines and how to develop the correct relationship regarding pressure drop in a pipeline. This topic should be of great interest and value to all chemical engineering students because it will not go away after college. It will continue to be a subject to resolve through your future career.
I will be submitting some documents later from personal notes that I have accumulated through the years that may be of interest and help to you. Right now, I’m on my way out on personal business.
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