CFX Air conditioning Simulation_expression help!!!! Urgen!!!

yin2 · March 28, 2009, 05:02

hai,
I am new learner about CFX.
can any one help me to solve my problem? it is quite urgen for me...!!!

I am doing an experiment about the condition of air at an Air conditioning Unit.
Is a DOE (design of experiment) for getting the thermal comfort setting of an Air Conditioning Unit.

So, i need to set the inlet properties at my inlet to get the outlet result for validate by the experiment data.
The result i need is the air velocity, air temperature and the pressure.

do any one know how to write the expression of this condition??

The attachment is the print screen of my problem.
hope anyone can help me!!!

Thanks!!

rikio · March 28, 2009, 21:42

Hi,

Could you describe your problem more detail? What are known from test? and what boundary conditions have you employed? You need to set a nonconstant BC for it such that expression have to be used?
Experimental data of the outlet profile have been obtained, and you have to get a solution by setting inlet properties to match outlet profile?

yin2 · March 29, 2009, 06:08

Hai,
Thanks for reply...

for my experiment, the data i took is the air velocity and air temperature of at the inlet and outlet of the chamber.

So, now i want to do a simulation for comparing the data with my experimental data. got a part is writing the expression for the thermal rountine. That part i not so understand and i feel that the error will occur is cause of that part.

is that really need to write an expression?
or i can ignored it, just done until the boundary condition there?

i set my chamber as adiabatic. set the normal speed of flow for me to set the air flow that i get from my experiment. also the temperature setting. just this two setting i set for inlet. For outlet, i set the pressure as 0 Pa.

rikio · March 29, 2009, 07:47

Hi,

Just set velocity or mass flow at inlet, and pressure at outlet. Of course, other boundary conditions can be used.
Regarding the expression, the temperature is supposed to change in the chamber, right? So you want to define an expression to get the thermal field? Why not giving a heat flux, or something like that, at walls.

yin2 · March 30, 2009, 06:22

Thanks rikio,

so, you means that, i can skip the expression part for the setting at the boundary condition there?

so just set the temperature and air speed at inlet, 0Pa at outlet..then just simulate it at solver...

ok, thanks yah...i try it first!!

pratikmehta · March 30, 2009, 08:06

Hi,

Could you please explain , when you are having the boundary conditions at the inlet , wall and the outlet, what is the expression that you want to insert . Is it to do with the fluid properties dependent on temp , viscosity or some other variables ??,

What is the goal of your simulation ?. apart from it being a DOE

Best of luck

yin2 · March 30, 2009, 23:34

hai,
now i'm doing it without insert any expression. I just set the boundary condition at inlet, outlet and the room (wall of room). Then, the simulation work!!

Since i now ran out of time, so i just try to get the simulation first.
Actually for mine simulation, the expression is needed to get the thermal field, but i ignored it first...
hehe...

my goal of the simulation is to get the temperature profile and velocity profile at the chamber.

March 29, 2009, 06:08	Re:	#3
yin2 New Member yinyin Join Date: Mar 2009 Posts: 4 Rep Power: 17	Hai, Thanks for reply... for my experiment, the data i took is the air velocity and air temperature of at the inlet and outlet of the chamber. So, now i want to do a simulation for comparing the data with my experimental data. got a part is writing the expression for the thermal rountine. That part i not so understand and i feel that the error will occur is cause of that part. is that really need to write an expression? or i can ignored it, just done until the boundary condition there? i set my chamber as adiabatic. set the normal speed of flow for me to set the air flow that i get from my experiment. also the temperature setting. just this two setting i set for inlet. For outlet, i set the pressure as 0 Pa.

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March 28, 2009, 21:42		#2
rikio Senior Member Rikio Join Date: Mar 2009 Location: SH, China Posts: 182 Blog Entries: 1 Rep Power: 17	Hi, Could you describe your problem more detail? What are known from test? and what boundary conditions have you employed? You need to set a nonconstant BC for it such that expression have to be used? Experimental data of the outlet profile have been obtained, and you have to get a solution by setting inlet properties to match outlet profile?

March 29, 2009, 07:47		#4
rikio Senior Member Rikio Join Date: Mar 2009 Location: SH, China Posts: 182 Blog Entries: 1 Rep Power: 17	Hi, Just set velocity or mass flow at inlet, and pressure at outlet. Of course, other boundary conditions can be used. Regarding the expression, the temperature is supposed to change in the chamber, right? So you want to define an expression to get the thermal field? Why not giving a heat flux, or something like that, at walls.

March 30, 2009, 06:22	Re	#5
yin2 New Member yinyin Join Date: Mar 2009 Posts: 4 Rep Power: 17	Thanks rikio, so, you means that, i can skip the expression part for the setting at the boundary condition there? so just set the temperature and air speed at inlet, 0Pa at outlet..then just simulate it at solver... ok, thanks yah...i try it first!!

March 30, 2009, 08:06		#6
pratikmehta Member Pratik Mehta Join Date: Mar 2009 Posts: 32 Rep Power: 17	Hi, Could you please explain , when you are having the boundary conditions at the inlet , wall and the outlet, what is the expression that you want to insert . Is it to do with the fluid properties dependent on temp , viscosity or some other variables ??, What is the goal of your simulation ?. apart from it being a DOE Best of luck

March 30, 2009, 23:34		#7
yin2 New Member yinyin Join Date: Mar 2009 Posts: 4 Rep Power: 17	hai, now i'm doing it without insert any expression. I just set the boundary condition at inlet, outlet and the room (wall of room). Then, the simulation work!! Since i now ran out of time, so i just try to get the simulation first. Actually for mine simulation, the expression is needed to get the thermal field, but i ignored it first... hehe... my goal of the simulation is to get the temperature profile and velocity profile at the chamber.