Learning Forum

[ESL]

I am a university student in Japan who uses ANSYS for research.

I am doing a research on heat transfer when a fluid flows through a packed layer.

In my simulation, the temperature of the solid in the packed layer increases when the fluid flows in the positive direction and decreases when it flows in the negative direction.　This temperature rise and fall is set by the energy of the source term in the porous zone.

However, the simulation does not work well with the following message

• Message: Error at Node 0: Invalid expression : energy_profile/1[s].

Please help me with my research, I would appreciate it.

The expression I set for the energy term is as follows

• IF(u_profile/1[m/s]>0,energy,-energy) 

where u_profile is the flow velocity and energy is the temperature rise and fall.

The equations for u_profile and energy are as follows

• u_profile = 0.9*sin(omega*Time)
• energy = entoropy_change*mass(['porous_zone'])*T(['porous_zone'])/(3.0[m^3]*10^-6)
• entoropy_change = 5.3[J/(kg*K)]*exp(-(T/1[K]-110)^2/5.0^2)

A simple model diagram is shown below.

I am looking forward to your advice.

[Rob]

If you don't hook up the expression what value does each part return after you initialise the model but before you start iterating?

[ESL]

[ESL]

Thank you for your message.
Are you sure you are asking what the initial conditions are?
I'm sorry, I'm not familiar with ANSYS, so I can't see a list of what the initial values are.
Just in case you are wondering, the temperature conditions and pressures I have set are 110K (=-160┬░C) and atmospheric pressure as the initial values for all zones.
I hope I have answered your question.

[DrAmine]

If you compute the expression does it work and return proper values? Your velocity expression is missing dimension.

[ESL]

Thank you for your comment.
I think the expression you defined returns the appropriate value.
(Please refer to the figure below. The velocity is a sin function with period 1, so the output will vary with time)

Also, thank you for pointing out the dimensions.ÒÇÇThe above equation was missing the units.
The units are set in ANSYS, and the unit of velocity is m/s.

[Rob]

If you don't hook the expressions up and initialise the model you can then evaluate the expressions: what values do they return?