Unsteady state problem - draining from a tank

[_Greg_]

1. The problem statement, all variables and given/known data

http://www.physicsforums.com/attachment.php?attachmentid=24975&stc=1&d=1270737086

The flowrate leaving the tank is regulated by a partially open valve, You may assume that the pressure drop in the exit pipe system is across the valve itself.

The cross sectional area is 1m2. At steady state, the water level inside the tank is measured to be 1m for a feed stream flowrate of 0.5 m3/min.
Since the water into the tank has a temperature of 20*C, then the temperature out is also 20*C (assuming no heat losses)

Develop a MathCAD solution to find how the level and temperature changes when the flow and temperature of the feed stream changes

Question What equation do I need for this?

I have one for the liquid level but don't know how to combine it with temperature, some sort of energy balance.


2. Relevant equations

I have this, describing the liquid level in the tank

dh/dt = 1/A (F1+F2-k(sqrt h))

3. The attempt at a solution

I can't do it :frown:, all I could get is the above equation