Fluid Mechanics (?)

This is the first time I had been 'conned' not by the question, but with the formulae given by our lecturer Dr. Siti. When we answer the question for our Test 2 this semester, I just answered the question like normal. Since the question needs us to find the Reynolds number, I put it as Re = ρVD/μ. In the middle of answering the question, Dr. Siti went and tell us that we should not use Re = ρVD/μ, but instead she asked us us to use Re = VD/μ. From there, when I calculated the Reynolds number for the flow of the fluid in pipes, I found that the number was too small to be with that liquid. I calculated around 400 for the pipe region.

For this case, in general
Re less than 2300 - laminar
Re more than 4000 - turbulent

Haha. I don't think the flow is laminar la. Coz liquid must always been turbulent. I think what she wanted to mention about the equation is Re = VD/v, since when we check for the dimension for VD/μ, it has dimensions since the Reynolds number is supposed to be dimensionless. I tried calculate for Re = VD/v and I found that the number is large, that is turbulent. And that must be logical. I think when I use back Re = ρVD/μ, can get the same answer like turbulent.

I don't know what will happen next after Dr. marked our test papers. I'm sure there will be arguments from us. Just watch out. Haha.


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