Control of dehumidifier with system level heat exchanger

Hey guys,

i'm trying to add controls to the attached model. I'd like to control the flow-rate of the 2 flow-rate-sources in order to change the heat/cold transfered to the MA-Network. When doing so manually there's not the change i expected, so i figured, that i also need to change the nominal rate of heat-transfer of the system-level-heat-exchanger accordingly to the flow-rate. Also when the flow-rate is too low, i get an error. I assume it's because the model thinks of the rate of heat-transfer as constant, so by chaning the flow-rate deltaT becomes incredibly high.

I tried to do so with a Matlab script, that influenced the parameters over time. But the graphs showed me this doesn't work like inteded. And i've found this, saying basicly it's not possible to add the controls i had in mind, am i wrong?

https://de.mathworks.com/help/simscape/ug/how-simscape-run-time-parameters-differs-from-simulink.html

Can somebody help me please? Maybe i'm just not seeing the obvious solution here :D

Cheers,

[Yifeng Tang]

Could you please clarify on what you mean by "When doing so manually there's not the change i expected"? Like:

(1) what change are you expecting?

(2) what did you control manually, which flow sources (MA or TL)? by how much?

(3) what did you observe when doing (2)? And why that's not what you expected?

Basically trying to help the community understand and reproduce your observations.

Changing the "nominal rate of heat-transfer" is like change the heat exchanger itself. It's not "control". You should parametrize the heat exchanger to the best of your knowledge and then keep it unchanged when you run different conditions (temperature and flow rates, for instances).

[Moritz]

Sorry for not elaborating explicitly.

By manually changing i mean increasing or decreasing the mass flow rate of the flow-rate-source(TL) as well as the nominal mass flow rate of the system-level heat exchanger (TL-MA).

If i decrease the mass flow rate of both, i expect the heat exchanger to cool/heat less, because Q = m'*cp * ΔT by decreasing m', Q must decrease as well if ΔT is constant.

I changed the mass flow rate(flow rate source(TL) and system-level heat exchanger(TL-MA)) from 0.1 to 5 kg/s in different intervals and it had no effect at all.

I observed the temperature and humidity inside my constant volume chamber (MA). I expect the temperature and humidity to change if i increase of decrease the mass flow rate.

While i wrote this, i was thinking: maybe it's the wrong approach to change the nominal mass flow rate of the systemlevel heat exchanger(TL-MA), maybe i should keep that constant and just change the mass flow rate of the flow rate source (TL).

And indeed that was my mistake. Ups, yeah i'm not that familiar with simscape yet.

Thanks a lot for asking the right questions to help me understand the problem :)

Cheers for helping me out :)

Answer 1

[Yifeng Tang]

Summarize the information exchange in the "Comments":

Changing the "nominal rate of heat-transfer" is like change the heat exchanger itself. It's not "control". You should parametrize the heat exchanger to the best of your knowledge and then keep it unchanged when you run different conditions (temperature and flow rates, for instances).

Manually increasing or decreasing the mass flow rate of the flow-rate-source(TL) as well as the nominal mass flow rate of the system-level heat exchanger (TL-MA), from 0.1 to 5 kg/s in different intervals, it had no effect at all, while the expectation was that the temperature and humidity inside the volume chamber (MA) would change if the mass flow rate increases or decreases.

Instead, one should keep that constant and just change the mass flow rate of the flow rate source (TL).

[Moritz]

Yes exactly, i didn't know. Makes sense though, but somehow it didn't accure to me.

Just to prevent future problems, where could i find such information?

Thanks for the help :)