problem 1: A pressurized water tank is used as a source of water for a fire hose. The pressure of the air in the top of the tank is 20 atm (gauge). To be effective, the minimum exit velocity (Vexit) of the water from the hose must be at least 20 m/s. The water supply pipe and hose consist of 10 metres of 50 mm inside-diameter pipe and hose. The average roughness height inside the pipe and hose is 0.05 mm. The system contains one 90° elbow and one flow control valve. The valve’s K vs Closure % calibration curve is given in figure below.
a) State any assumptions associated with this problem.
b) Determine the valve closure (in %) to achieve a water exit velocity of 20 m/s.
c) Determine the exit velocity when the valve is fully open.
The properties of water are: ρ = 1000 kg/m3 and µ = 1.00 x 10-3 N.s/m2.
Figure: (a) Water tank and fire hose and (b) the K-vs-Closure graph.