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Q9.A horizontal section of fire main is made from a 100 mm internal diameter rigid steel pipe and is terminated by a 40 mm diameter nozzle, open to the atmosphere.

The flow through the nozzle is controlled by a valve with an on/off action.

The fire main contains sea water maintained at a pressure of 7 bar(gauge).

(a) Calculate EACH Of the following when the valve is fully open:

(i) the mass through the nozzle; (6)

(ii) the force exerted on the fire main by the nozzle. (6)

(b) Calculate the instantaneous pressure in the fire main when the valve switches from fully to fully closed. (4)

Note: for Sea water density ρ=1025  kg⁄m³ . Bulk modules K=2.34×  N⁄m²

For the pipe  C²/2 = (δp)²/2Kρ

c = Fluid velocity, K = Bulk modules, ρ = Fluid density, δp = Change of pressure.