Learning Forum

[Viktor Polášek]

Hi gents,
I'm dealing with water flow in the pipe and air flow around the pipe at the same time. Whether water or air is flowing is controlled by the following condition. If temperature of monitored point (tp) at tube is below 263K, the water is flowing. If temperature of tp is above 333K water is switched off and air starts flowing. Air flows until temperature of tp is below 263K. See behavior of flowing in graph below.I'm trying solve it through expressions at water/air velocity inlet.

Water:

IF(OR(AND(tp>=263.15[K],vc=0[m/s])(AND(tp<=333.15[K],vc=0.25[m/s]))), 0.25 [m/s], 0 [m/s])

Air:

IF(OR(AND(tp>=333.15[K],vair=0[m/s])(AND(tp>=263.15[K],vair=4[m/s]))), 4 [m/s], 0 [m/s])

where

tp - monitored temperature of point at tube wall

vc - monitored water velocity at inlet

vair - monitored air velocity at inlet

 

Unfortunatelly, it doesnt work. Any idea how to solve? Thanks in advance.

Greetings amd smooth convergence.

Viktor

 

[Rob]

Please can you expand on "doesn't work"? Ie is there an error, or the boundary isn't what you expect? 

[Viktor Polášek]

Hi Rob,

Thank you for your attention.

I mean the simulation is running, but it does not behave as I would expect. Once "tp" reaches 333.15 [K] both water and air are switched on/off so "tp" is oscillating around the peak temperature. Any idea or tip on how to describe the expression?

[Rob]

Do you need the OR & AND parts?  If tp then stuff, otherwise other stuff for both sides of the system. I assume you are running transient?