I have a 5th order polynomial of transient external wall temperature. I need to apply a transient wall temperature Boundary condition to Fluent. Please help me in applying it to apply it in fluent.
Starting with ANSYS Fluent 2020.R1 this polynomial can be implemented as a named expression in a few seconds. Just writing down the polynomial in dependence on time and assigning it to the wall temperature as an algebraic expression.
Regards,
Dr. Th. Frank.
Dr. T Frank - Could you please verify my expression for the equation I have attached, for your perusal, please.
My Equation from Excel:
y = 2E-22x5 - 5E-17x4 + 5E-12x3 - 2E-07x2 + 0.0045x + 294.32
My Expression:
2[K/s^5]*10**-22*t**5-5[K/s^4]*10**-17*t**4+5[K/s^3]*10**-12*t**3-2[K/s^2]*10**-7*t**2+0.0045[K/s]*t+294.32[K]
Without testing it in Fluent it seems Ok to me. Also for better readability I would have defined:
my_t = t / 1.0 [s]
Regards,
Dr. Th. Frank.
With the expression I defined earlier, I tried running it multiple times on student version. Everytime, after 10 - 12% in the run, it teminted with a unit type error.
Dr. Th. Frank - could you please share some tutorial which includes your previous suggestion of defining my_t and this expression.
Regards
Ali Hasan Khan
Defining several named expressions:
1) Making time a dimensionless number:
my_t = t / 1.0 [s]
2) Defining the polynom based on this dimensionless number:
polynom = f(my_t)
3) Assigning the desired dimension to the dimensionless polynom value:
temperature = polynom * 1.0 [K]
Regards,
Dr. Th. Frank.
Thank you Dr. Frank for your prompt responses. I have implemented your suggestions and it had been of great help.
Dear Dr. Frank
I did modify the 5D polynomial into a 6-Degree polynomial and ran it for 172,800s with 0.5 step size and 20 itterations per time step.
The properties of brick used are:
K = 0.7 W/m.K
Density = 0.7 Kg/m^3
Specific Heat = 840 J/Kg.K
Boundary Conditions:
1. Natural Convection on Internal (Room) Brick Wall:
- h = 15 W/m2K
- free stream Temp = 300K
2. Other 4 walls adjacent to other bricks: Adiabatic
3. Transient Temperature on Exposed Brick Wall:
- Equation =
y = 8E-27x6 - 2E-21x5 + 2E-16x4 - 5E-12x3 - 2E-08x2 + 0.0027x + 298.07
- Named Expression =
8[K/s^6]*10**-27*t**6-2[K/s^5]*10**-21*t**5+2[K/s^4]*10**-16*t**4- 5[K/s^3]*10**-12*t**3-2[K/s^2]*10**-8*t**2+0.0027[K/s]*t+298.07[K]
Dear Dr. Frank
With the above information, could you please suggest that what might be possibly wrong, considering the results obtained for an external temperature condition of Indian climatic condition between 14 May 08:00AM to 15 May 08:00 AM (I have attached an experimental graph in the following comments).
What I am trying to do is to validate an external temperature transient temperature between 08:00AM 14 May to 15 May 08:00 AM (24 hrs), for Indian climatic condition.
Thanks & Regards
Ali Hasan Khan, M.Tech. Research Scholar, IGBC AP, GRIHA CP
Center for Energy & Environment, MNIT Jaipur, Rajasthan 302022
Phone: +91-8299-493-050
E-mail: [email protected]
Have you placed temperature monitors on the inside and outside of the brick in order to verify, that the correct temperature bounds are assigned on both sides of the brick over time? That would be the easiest way to see, whether the applied boundary conditions are correct and leading to the desired near-wall temperatures (300 K on room side vs. agreement with polynomial value on the other side).
Regards,
Dr. Th. Frank.
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