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Pipe Heating Control HELP!!!

Posted 12.06.2012, 15:26 GMT-4 Fluid & Heat, Chemical Reaction Engineering Version 4.2a 3 Replies

Nicholas Medeiros
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Hey everyone,

Attached is a model I have of air being heating as it passes throug a pipe.

Right now the Q (heat source term) was calculated to raise the temperature of the pipe from the inlet temp of ~290 K to the desired temp of ~350. The Q is a parameter that I put in based on my calculations.

I want implement P-control (proportional control) so I added a variable that says

Qcontrolled = kP(Tmeasured-Tsetpoint), where my set point temp is 70C, kP is my proportional parameter, and Tmeasured SHOULD be the temp of the air at a point in the pipe in the heated section.

Basically, I want to add P control. I don't want to have to calculate a Q and then add it as a parameter. I want to have Q be a calculated number based on the required set point of 70 C.

Any thoughts on how to do this? Help is greatly appreciated!

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3 Replies Last Post 27.02.2013, 05:26 GMT-5
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago 12.06.2012, 16:16 GMT-4
You can set the heat source to kP*(Tsetpoint-T). T is the current temperature variable which will be automatically evaluated at each point.

Nagi Elabbasi
Veryst Engineering
You can set the heat source to kP*(Tsetpoint-T). T is the current temperature variable which will be automatically evaluated at each point. Nagi Elabbasi Veryst Engineering
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 13.06.2012, 04:04 GMT-4
Hi

You can also add an ODE with the heat density value Qode driven by (Tmeasured - Tset), define Tmeasured as the average over boundary "6"

But use a physics controlled mesh with boundary layers, yours is too coarse. not to say you are in a highly turbulent regime,

I would further suggest to start to reduce the velocity and make it work correctly in laminar, then increase the velocity and run in turbulent mode

--
Good luck
Ivar
Hi You can also add an ODE with the heat density value Qode driven by (Tmeasured - Tset), define Tmeasured as the average over boundary "6" But use a physics controlled mesh with boundary layers, yours is too coarse. not to say you are in a highly turbulent regime, I would further suggest to start to reduce the velocity and make it work correctly in laminar, then increase the velocity and run in turbulent mode -- Good luck Ivar
Jasmine poil
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Posted: 1 decade ago 27.02.2013, 05:26 GMT-5
Hi All,
I'm building my own house and I'm coming near the stage where I need to lay pipes for rads.
I'm not a plumber, so any tips welcome, I'd like to route the pipes myself as I know the house,
and there are a few tricky sections where I must be careful to maintain a steady fall to a drainpoint.
Here's a rough idea of my system plans,
I'm going with plastic pipe, 1/2" copper (irish) tee-d to rads.
3 zone sytem (maybe 4,see below),
DHW,
upstairs rads,
downstairs rads,
from a sealed system, hot press downstairs in utility room.
2 heating thermostats (up/downstairs), TRVs on nearly all rads.
Solid fuel boiler and large buffer tank in outhouse, ( a few metres underground piped from hotpress)
hot water from buffer tank as required to zones.
My query for now is downstairs loop:
I've did the calcs for space heating hope I've got them right, but my rads are coming in around 25KW downstairs only.
Physically this zone run is around 60metres long.
I'm thinking a 3/4" diameter pipe may be too small for this as one zone, I may have to split into 2 zones downstairs?.
Is there a way I can figure out the size of pipe required, do I need to factor in area rather than run length.
thanks for reading.....London-boiler-repair.co.UK/



Hi All, I'm building my own house and I'm coming near the stage where I need to lay pipes for rads. I'm not a plumber, so any tips welcome, I'd like to route the pipes myself as I know the house, and there are a few tricky sections where I must be careful to maintain a steady fall to a drainpoint. Here's a rough idea of my system plans, I'm going with plastic pipe, 1/2" copper (irish) tee-d to rads. 3 zone sytem (maybe 4,see below), DHW, upstairs rads, downstairs rads, from a sealed system, hot press downstairs in utility room. 2 heating thermostats (up/downstairs), TRVs on nearly all rads. Solid fuel boiler and large buffer tank in outhouse, ( a few metres underground piped from hotpress) hot water from buffer tank as required to zones. My query for now is downstairs loop: I've did the calcs for space heating hope I've got them right, but my rads are coming in around 25KW downstairs only. Physically this zone run is around 60metres long. I'm thinking a 3/4" diameter pipe may be too small for this as one zone, I may have to split into 2 zones downstairs?. Is there a way I can figure out the size of pipe required, do I need to factor in area rather than run length. thanks for reading.....London-boiler-repair.co.UK/

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