[EngineeringAlex]

Hi all!

I'm a bit stuck on doing an energy balance for an unsteady state. Haven't been taught it and its cropped up in a past exam paper for engineering thermodynamics!

So I've got 4 streams (data seen below) going into a tank that's filling at 0.5m/h (Tank D=2m and H=2m).
        _______
s1 |          |
s2 |          | s4
s3 |______|

s1: T=90°c , m=1 Kg/s
s2: T=50°c , m=2 Kg/s
s3: T=30°c , m=? Kg/s
s4: T=?°c , m=6 Kg/s

I had to find the mass flow rate of stream 3 based on the above and have found it to be 3.436 Kg/s (Hope that's correct  )

Next question is find the outlet temperature... I know you have to use an energy balance as in part one the same tank was steady state. But now its unsteady it's apparently:
Eacc = Ein - Eout

What is Eacc and how do i use it!

Hope I've been clear, first time posting!

Thanks!
Alex