Cooling time of Anhydrous Ammonia

[droctagon]

Hello Everyone! I have a problem that I am having trouble solving. I have a 30000 gallon tank of anhydrous ammonia at room temperature. The tank is 11 feet in diameter, horizontally oriented in a warehouse. The tank is made from 3/8" thick carbon steel and is not insulated. There is no direct heat on the tank. The tank initially contains 5,000 gallons of NH3 at room temperature. 5,000 more gallons of NH3 at -20 F is added to the tank. We can assume perfect mixing and for purpose of calculation, neglect radiation effects. I am pretty sure an iterative solution is needed but I am having trouble coming up with one. The method I used to solve the problem was find the heat required heat the mixture to room temperature and divide it by the heat coming into the tank. The problem is that my delta T cancels out! If anyone as any insight to a problem such as this please let me know as soon as possible. Thank you all very very much.

- Aaron

 

[droctagon]

I am looking for the time it will take for the mixture to warm back up to 70 F. I know there is convection from the outside of the tank to the tank surface, then conduction through the tank, thn convection from the inner tank surface to the fluid, then conduction through the fluid. Does anyone have any thoughts?

 

[mbeychok]

More information please. I assume that you are talking about liquid ammonia since you refer to gallons. If so, what is the pressure inside the tank? Is it high enough to maintain the ammonia as a lquid at room temperature?

At 70 degrees F, the pressure required would be about 130 psia.

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[droctagon]

This is anhydrous ammonia. We will assume that the pressure you have provided is correct and that it is going to be a liquid.