Hydro dynamics question

The first problem is:

What is intended to be achieved, and why has the different-shaped tank been pre-selected to achieve it?

The second problem is:

What's in the tank, and at what temperature?

Based on the description you gave, the flow rate of liquid and time required to discharge the tank is dependent on the pressure inside the tank and the size of the discharge pipe. Tank geometry is irrelevent. If the tank volume affects your pressure because you initially pressurize and let the pressure decline as it drains, you will see some impact from a larger or smaller gas volume in the tank.

The liquid consists of a mixture: 65% water and 35% coarse sand. Will this mixture impede the flow through a 1- 1/2 inch exhaust pipe?

The time of purging depends mainly on the how much the pressure at the nozzle of discharging. This pressure equals to the internal pressure of tank (55 psi) plus the pressure due to height of liquid column above the discharging nozzle. Therefore changing the physical dimensions of tank shall have such an effect at the hydrodynamics if you handle the same fluid at the same pressure and same temperature.

This depends on how much the change in liquid height above the discharging nozzle.

So, if the liquid height is increased, this height shall have an additional pressure equal to the weight of the increased column of liquid to be added to 55 psi, in this case the mass flow rate may be increased, i.e the purging time 15 seconds may be be minimized to become 14 seconds or less to discharge the same quantity of 25 gallons.

Note. May be the increasing of pressure due to increasing of height of liquid is very small, anyway it must be calculated to see its effects.

That is the only light change in pressure at the nozzle of discharging, and you can use the new vessel without any problem nor expecting any more.

We have a pressurized tank that is 18'' diameter and 24'' long. It holds approximately 25 gallons of liquid. It takes about 15 seconds to purge the tank at 55 psi. We would like to use a 12'' diameter by 50'' long tank instead. We are currently using a 1-1/2'' diameter discharge pipe.What problems could we expect to encounter? ADDITIONAL INFORMATION: Although the tank capacity is 25 gallons; there is never more than 10 - 15 gallons liquid emptying into the tank, a mixture of water, sand & concrete. The intent is to pressurize the tank to 55 psi, then discharge the entire contents of the tank. It is imperative that all of the fluid is completely discharged. The discharged fluid is discharged into another tank located 10' above the 25 gallon tank, through a 1 -1/2 inch pipe. It is imperative that no fluid remains in the tank, because it will harden and be impossible to dislodge.Need recommendation, suggestion for insuring the tank is completely emptied. The tank is on a horizontal plane.