Steam Flow And Heating Time In Batch Reactor

[seagal3232]

Hello everyone,

I'm trying to calculate the following:

a- Saturated steam flow required to heat a liquid inside a reactor (steam flows through half pipe)
b- Time required to heat up the liquid to a certain temperature

For a) I'm using the example provided by Spirax Sarco (https://www.spiraxsa...ets#article-top)



As for b, I'm using an equation from the following page (https://www.thermope...de/content/547/)


Let's assume I know U and A,

My question is the following. How are steam flow and time required related? I don't immediately see how raising or lowering the steam flow would affect the time it takes to heat up the vessel. My only guess is that changing the flow affects the velocity which in turns affect U and every other term related to that,

Thanks in advance,

 

[LittleInch]

What's the final temp of the liquid?

The issue you're missing is that as the temperature of the liquid in the reactor rises, heat transfer decreases and heat losses increase so the temp versus time of the liquid is not a straight line. How curved that line is depends on many things. Such as mass of thr liquid, its heat capacity, losses from the tractor etc.

Raising steam flow might decrease the time but equally might not.

 

[Latexman]

Do you have Kern’s Process Heat Transfer? His book shows the derivation of several equations for the solution of unsteady-state heat transfer differential equations. IIRC, your problem is documented there.

 

[EdStainless]

If you raise steam flow it will usually slightly increase the average temp of the steam by raising the outlet temp.
Of course this is wasting energy in exchange for time.
I have seen this done in steps.
When the system is cold start with a fairly low steam temp, and then as the system gets hotter increase steam flow.
Yes the actual solution for this requires real calculus.

 

[pierreick]

On top of what Latexman is suggesting, consider taking a look a Perry's chemical engineer's handbook.
Pierre