## Fluids

#### The NTGK model constants

• alluch94
Subscriber

Hello i am working on the ntgk model of a battery and i a m realy stuck in the documentations conerning C1 and C2 constants how we can calculate them or how the calculation is done by ansys if we used several volatge curve

• wcao
Ansys Employee
Hello First of all, C1 and C2 are coefficient for the influence of temperature only, as you can see from the formulas. The data you provided to Fluent for parameter estimation includes the information containing discharging rate (C-rate), time, voltage and temperature. The integral of discharging rate over time is the DoD. So the voltage-time curve you are suppling is also a kind of voltage-DoD curve. From the formula below
At each time, Y and U are function of U and hence function of DoD.
If you have supplied the curve at multiple temperature point, you can then easily represent Y and U as function of both DoD and temperature. Based on that, simply regression can calculate out the coefficient a_n, b_n, C_1 and C_2 in the formulas you showed. Thank you.

• alluch94
Subscriber
Hello Thank you for your answer. Honestly i am still having a problem with these two constants. If i use the table method instead of polynomial i am getting different temperature value and also different values for the voltage in the voltag time cuve that i plot.
Add to that if i used the polynomial method and with the estimation tool i provided Data of 3 voltage curve, automatically the c1 and c2 are et to zero which makes no inluence of the temperature on these constants.
Regards