Does anybody know why pressure is not one of parameter that would give impact to reynold number calculation? I don’t know exactly the answer and what the explanation is. If you read the reynold number formula you would only find that the turbulent flow is only affected by internal diameter, viscosity, and flowrate. If I imagine myself one occassion we hold pressure in a line, and pressure raise up to high value and suddenly we release the pressure so then we will see the horrible fluid flowrate come out from the line. It is turbulent, isn’t it? So high pressure will create high reynold number, is it right?

Turbulent flow for hydraulic filtering is a must, it is mandatory in every project. The question then how to make the flow that will be always turbulent in whole length at anywhere and anytime. I will close my eyes on what my curiousity about pressure effect and what I guess. In order to make a turbulent flow as per reynold theory we just need to produce a specific flowrate to get reynold number in the observed line is more than 4000. In my case I have fluid Macdermid Oceannice HW540E which has kinematic viscosity 2 Centistoke at 30-40 degC. I have hydraulic line with inside diameter 10.35 mm. How much minimum of my flowrate? Using Reynold formula I will get value at least 4 Litre/minutes, I will get Re 4000. How about the length? How about the line goes up and goes down? Why don’t we consider that?. Mmmm..it will have effect somewhere. But where? why Mr. Reynold did not capture this during his research on turbulent formula. I don’t know.

Wherever and whenever the effect of line elevation we don’t give care so much as we follow the formula of Mr. Reynold. To get the turbulent flow I just need to ensure that wherever the line as long it is 10.35 mm and the fluid has viscosity 2 Centistoke and my flowrate is more than 4 Litre/minute, I can prove that my flowrate is turbulent more than Re 4000. And the flushing / filtering requirement can be achieved.

Then how to ensure that the flowrate at least 4 Litre/minute in all length of the line. The discussion come to the pump theory. How much pressure and flowrate shall be delivered by pump to ensure that all length have at least 4 litre/minutes. The discussion about pressure shall be produced by pump shall have interface with bernoulli equation. The pump shall have enough pressure from the pump discharge to bring the fluid raise up to elevation. The minimum pressure shall be produced by pump againts elevation, friction loss, and length was called as Head. If the pump can produce the pressure more than the head so then the pump will deliver designated flowrate at specific rotation RPM. If the flowrate produced in discharge of the pump is more than 4 litre/minute, let say I will use 10 liter/minute, so wherever the point, the flowrate will be the same (if no branch). The flowrate attitude is like current in electricity, they will be the same in a loop without branch-parallel. When the head pressure produced by pump is not enough then the flowrate will not fully occupy cross sectional area of the line, so then the flowrate is coming down and they will only flow in half of pipe so then fluid mechanic calcalution no longer applicable.

Please advise me friend! Thank You

Nova Kurniawan

Instrument Engineer, I am working at J Ray McDermott, Indonesia

Filed under: Engineering

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