|Oct12-10, 12:19 AM||#1|
Flow rate depending on pressure with constant inlet rate.
A 10 m high, 5 diameter cylindrical water tank has an inlet at the top and a drain at the bottom. The flow rate out of the tank depends on the pressure at the bottom of the tank via the following:
dm/dt = (10^-4)*(P_bot)
where P_bot is the absolute pressure in Pascal at the bottom of the tank. The tank is open to atmosphere at the top (P_atm) The density of water is 1000kg/m^3
a. What are the units of 10^-4
- If P_bot is in Pascals then it should just be [meter*second]
b.What is the absolute pressure at the bottom of the tank is psia when the tank is 50% full?
- P = P_atm + (density*g*h)
= 14.7 psi + (49000*145.04*10^-6) psi = 21.8 psi
c.What is the gauge pressure at the bottom of the tank is psig when the tank is 50% full?
- P_gauge = P_abs -P_atm
= 21.8-14.7 = 7.1 psi
d. At steady state, there is a specific inlet flow rate required to maintain a given water level in the tank.
Derive an equation that gives the inlet flow rate (in [kg/s]) required to maintain the water height (h) at a given level, where h [m] is measured from the bottom of the tank upwards.
inlet flow rate[kg/s] = outlet flow rate = F(h) = (10^-4)(P_atm + density*g*h)
I'm not sure about this one.
e. Determine the inlet flow rate needed to keep the water level at 50% full.
10^-4(101325 Pa + 1000(9.8)(5m) = 15.03 kg/s
f. Assume that the tank is initially empty. At time t=0, the inlet is turned on at the flow rate you found in part (e). How long does it take the tank to reach 30% full.
This is where I got stuck.
I would assume inlet rate is constant at 15.03 kg/s. But I have no idea how to calculate the out flow rate.
g. How long does it take for the initially empty tank from part (f) to reach 50% full?
And I guess this is exactly like f.
|Oct14-10, 07:11 PM||#2|
blehxpo: Your answers are correct on items (a) through (e). On item (d), you might want to fill in the known numeric constants, but your choice.
(f) Hint 1: qout(h) = (1/rho)*Fout(h), where Fout(h) is the function you derived in item (d).
dV/dt = qin - qout(h).
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