Hi,
From the code you provided, it seems that you are using the `ode23` function to solve a system of ordinary differential equations (ODEs) representing the molar flow rates and temperature in a plug flow reactor (PFR). However, there are a few issues in your code that might be causing unexpected results in the plotted graphs.
1. Initial conditions: The initial condition for species B (`Fb`) is set to 0, which might be causing the decrease in `Fb` right away. If you expect `Fb` to have a non-zero initial value, you should adjust the `Y0` vector accordingly.
2. Temperature calculation: In the `dTdV` equation, the term `2*rc*(dH2)` seems to be incorrect. It should be `rc*(dH2)`. Additionally, make sure that the signs and units of the terms in the equation are correct. Double-check the heat of reaction values (`dH1` and `dH2`) and the heat capacity values (`Cpa`, `Cpb`, `Cpc`, and `Cpi`) to ensure they are consistent.
3. Reaction rates: The calculation of the reaction rates `ra`, `rb`, and `rc` seems correct based on the given reaction equations. However, check that the stoichiometric coefficients and rate constants are accurate for the specific reaction you are modeling.
4. Volume range: The `Vspan` variable is set to `[0 1]`, representing the volume range for the PFR. Ensure that this range is appropriate for your system and that the simulation covers the desired volume range.
Make sure to review and verify these aspects of your code to ensure that the equations, initial conditions, and parameters are correctly implemented. Additionally, consider using the `ode45` function instead of `ode23` for better accuracy, especially if the solution involves steep changes or stiff ODEs.
