) A simple, vertical U-tube manometer is used to measure the difference between two gas pressures. Write down an equation for the pressure difference in terms of the difference in the level of the fluid in the manometer. Describe briefly, with the help of diagrams, two modifications to the basic design which offer greater sensitivity to small pressure differences. Give equations for their use.
(1) A simple, vertical U-tube manometer is used to measure the difference
between two gas pressures.
Write down an equation for the pressure difference in terms of the difference in
the level of the fluid in the manometer. Describe briefly, with the help of
diagrams, two modifications to the basic design which offer greater sensitivity to
small pressure differences. Give equations for their use.
ii) An extractor fan draws air from a room and delivers it to the surroundings
through a 5m long circular duct of diameter 0.1m. The friction coefficient
for the duct flow is 0.002. The fan characteristic, relating its total pressure
rise, ∆P (Nm-2) to the volume flow rate is: ∆P = 103−7x104Q 2
. What is the
rate of flow through the duct?
You may assume that the room and surroundings are both at atmospheric
pressure; state and justify any other assumptions you make.
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