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about heater simulation in the room
Posted 11 apr 2013, 11:31 GMT-4 Heat Transfer & Phase Change Version 4.3a 6 Replies
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Hello!
I am use comsol 4.3a , and use the non-isothermal flow physics to simulate the heater in the room.
And the room has a door , and I want to set the door is open, and it is connect to the enviroment. So the heat and air can go out through the opened door , also the air from enviroment can supply the room by the opened door.
So I select the open boundary to the door (I don not know it is correct or not correct),
1.if the heater is remove, the simulation can sucessful, but when I see the velocity field , the result the opened door have a very high velocity inlet to the room, and it is not resonable.
2.When the room has heater,and the simulation will fail , and the result is not convergence.
So anyone know how to set the open boundary for open door?
I am use comsol 4.3a , and use the non-isothermal flow physics to simulate the heater in the room.
And the room has a door , and I want to set the door is open, and it is connect to the enviroment. So the heat and air can go out through the opened door , also the air from enviroment can supply the room by the opened door.
So I select the open boundary to the door (I don not know it is correct or not correct),
1.if the heater is remove, the simulation can sucessful, but when I see the velocity field , the result the opened door have a very high velocity inlet to the room, and it is not resonable.
2.When the room has heater,and the simulation will fail , and the result is not convergence.
So anyone know how to set the open boundary for open door?
6 Replies Last Post 26 mag 2013, 21:05 GMT-4
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Posted:
1 decade ago
Hi
if you have no inlet or outlet boundariessuch defining any gauge "p", and only an "open one" you should set a pressure point (typically to a p=0 "gauge" pressure) somewhere in the room, else you do not define enough BC conditions for your "p" presusre variable
The do not forget boyancy forces that might be a major contributor to flow
This is a rather complex model, also non linear if you couple in temperature dependence on the material properties, so start simple check physics independetly first to be sure they are all coherent, and solve easily
--
Good luck
Ivar
if you have no inlet or outlet boundariessuch defining any gauge "p", and only an "open one" you should set a pressure point (typically to a p=0 "gauge" pressure) somewhere in the room, else you do not define enough BC conditions for your "p" presusre variable
The do not forget boyancy forces that might be a major contributor to flow
This is a rather complex model, also non linear if you couple in temperature dependence on the material properties, so start simple check physics independetly first to be sure they are all coherent, and solve easily
--
Good luck
Ivar
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Posted:
1 decade ago
Hi
Thank you for your answer, I have set pressure point constraint( 1 atm), but the simulation is still fail , it is not convergence.
1.And another thing is Non-isothermal flow' s open boundary setting.
The parameter just have exterior temperature and normal stress can be set , no exterior pressure can be set.
But in the real case, the door air flow is due to pressure difference for room and exterior.
So in non-isthermal flow physics module do not have this kind boundary setting?( or in noraml stress setting need input some relationship to the pressure by myself)
2.
For pressure point constraint, if set a pressure point (1 atm)set to the room corner,
If the room is been heat up, then the pressure will be change, but due to the pressure point (1 atm) constraint. around the pressure point ,the pressure will maintain 1 atm. so it is not same to the real case, since the room is been heat up, then the pressure around the corner also will be change.
Thank you for your answer, I have set pressure point constraint( 1 atm), but the simulation is still fail , it is not convergence.
1.And another thing is Non-isothermal flow' s open boundary setting.
The parameter just have exterior temperature and normal stress can be set , no exterior pressure can be set.
But in the real case, the door air flow is due to pressure difference for room and exterior.
So in non-isthermal flow physics module do not have this kind boundary setting?( or in noraml stress setting need input some relationship to the pressure by myself)
2.
For pressure point constraint, if set a pressure point (1 atm)set to the room corner,
If the room is been heat up, then the pressure will be change, but due to the pressure point (1 atm) constraint. around the pressure point ,the pressure will maintain 1 atm. so it is not same to the real case, since the room is been heat up, then the pressure around the corner also will be change.
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Posted:
1 decade ago
Hi
a few things:
a) normally the pressure point is a gauge pressure, typically "0[Pa]", and you solve for "delta p", now COMSOL has another pA absolute pressure in the physics node to take the absolute pressure (by default also 1[atm]). But by adding 1[atm] at your point you might be using 2[atm] absolute for your air pressure property reference, pls check.
b) reread carefully the doc about open boundary and outlet, they are not that different, it is on purpouse that p is not defined for the open boundary (as I understood). But I believe you could also use the "outlet" instead if the "open boundary" and use the pressure outlet. And do not forget tat an outlet is not blocking any "inlet"
c) you can also decide to use a field instead of a scalar, for the pressure, it's changing at some 12[Pa/m] elevation at sea level, if your door is 2 m heigh it has also a pressure change across its height too ;)
And you might add too a T dependence to the pressure change
--
Good luck
Ivar
a few things:
a) normally the pressure point is a gauge pressure, typically "0[Pa]", and you solve for "delta p", now COMSOL has another pA absolute pressure in the physics node to take the absolute pressure (by default also 1[atm]). But by adding 1[atm] at your point you might be using 2[atm] absolute for your air pressure property reference, pls check.
b) reread carefully the doc about open boundary and outlet, they are not that different, it is on purpouse that p is not defined for the open boundary (as I understood). But I believe you could also use the "outlet" instead if the "open boundary" and use the pressure outlet. And do not forget tat an outlet is not blocking any "inlet"
c) you can also decide to use a field instead of a scalar, for the pressure, it's changing at some 12[Pa/m] elevation at sea level, if your door is 2 m heigh it has also a pressure change across its height too ;)
And you might add too a T dependence to the pressure change
--
Good luck
Ivar
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Posted:
1 decade ago
Thank you for your response!
For
(a) I am checked, and set the pressure point to 0[Pa], however when add some boundary (such as inlet , outlet ,or open boundary condition) it is still not convergence.
(b)I am look the doc about open boundary setting and the equation , so open boundary setting is depent on the temperature difference and not depent on the pressure, is it right?
(c)How add T dependence to the pressure change?
Thank you very much!
For
(a) I am checked, and set the pressure point to 0[Pa], however when add some boundary (such as inlet , outlet ,or open boundary condition) it is still not convergence.
(b)I am look the doc about open boundary setting and the equation , so open boundary setting is depent on the temperature difference and not depent on the pressure, is it right?
(c)How add T dependence to the pressure change?
Thank you very much!
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Posted:
1 decade ago
Hi
add the p=0 only if you have no tother P= something BC already defined
The open boundary (see the help) does not define p, neither an nlet or outlet, except if you use the P= something setting (pls re-check last statement, but I believe it's s,o use the equation view to check the BC equations see options preferences show equation view)
Mostly the T dependence arrive via the T value of the material properties, so either you define a parameter with T= constant, or you define a T via some physics (but not necesarily both ;)
--
Good luck
Ivar
add the p=0 only if you have no tother P= something BC already defined
The open boundary (see the help) does not define p, neither an nlet or outlet, except if you use the P= something setting (pls re-check last statement, but I believe it's s,o use the equation view to check the BC equations see options preferences show equation view)
Mostly the T dependence arrive via the T value of the material properties, so either you define a parameter with T= constant, or you define a T via some physics (but not necesarily both ;)
--
Good luck
Ivar
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Posted:
1 decade ago
Hello,
In the same subject, about heat simulation of the room, i just begin my model in 2D, and i have some questions:
1) I can not yet to obtain my variables (Temperature and Velocity) depends on time knowing that i have chosen the time dependent condition of my study.
2) I want to add of my output variables, in addition to Temperature, Pressure and velocity, the heat.
3) Thank you very much for your answers
Best regards
Lahoucine
In the same subject, about heat simulation of the room, i just begin my model in 2D, and i have some questions:
1) I can not yet to obtain my variables (Temperature and Velocity) depends on time knowing that i have chosen the time dependent condition of my study.
2) I want to add of my output variables, in addition to Temperature, Pressure and velocity, the heat.
3) Thank you very much for your answers
Best regards
Lahoucine