3 replies to this topic

[trevortnt]

Hi my fluid mechanics exams is a few hours away and starting to panick a bit!

I have a question regarding the U-tube manometer:

A water-filled u-tube manometer is measuring the pressure drop upstream and downstream of a air flow in a pipe with the downstream point being 0.5m higher than the upstream. If the vertical height of the U tube manometer is 1.2m at the upstream point and 1.7m at the downstream point at what pressure drop would the manometer cease to work. Assume that the amount of water in the manometer enables the maximum pressure drop to be measured.



I'm really not sure what to do
please help
chris

[latexman]

The maximum pressure drop that manometer can read is 1.7 m of water column (the height of the downstream leg).

[katmar]

This is a strangely worded question. If the statement "If the vertical height of the U tube manometer is 1.2m at the upstream point and 1.7m at the downstream point" refers to the length of the glass tube then Latexman is correct with his answer. But if what is really meant is "If the vertical height of the water in the U tube manometer is 1.2m at the upstream point and 1.7m at the downstream point" then the meaning is different.

The fact that the given pressure differential corresponds to the difference between the two heights makes me think the question refers to the water in the manometer. If this is the case then the upstream leg can be depressed a further 1,2 m and the downstream leg can rise the same 1,2 m giving an additional differential of 2,4 m. Added to the existing 0,5 m differential this would make the maximum pressure differential 2,9 m.

[latexman]

Agreed, stangely worded.