Learning Forum

[Wasim]

Hi i m doing multiphase fluidized bed reactor simulation with time. Primary phase is gas and secondary phase is solid, both phase reacting with each other according to heterogeneous reaction provided through udf for calculating reaction rate. I am facing floating exception error with warning that cp of solid is zero at specified temperature, whether cp of solid affect calculation or any value creating problem. My stepsize is of the order of 1e-7 and no of step 6e7 with 80 iteration per stepsize. Thanks in advance frustrated with this type of errorn

[Rob]

Check the temperature field, and the material properties. If you're using polynomial fits plot what you put into Fluent to see how it looks. If you have a packed/fluidised bed what volume fraction did you initialise at compared to the packing limit? n

[Wasim]

i used volume fraction of solid 0.48 and packing limit of 0.6n

[Rob]

OK, and if you monitor the reaction rate how does that look? Any time the solver gives a weird data value (eg hits the temperature or pressure limits) check to see what's going on. nThe particle spacing is because as the particle loading nears the packing limit Fluent bounces the particles apart, if you initialise at or above the packing limit this all happens in the first time step:particles have been known to exceed the speed of light..... n

[Wasim]

My simulation run firstly but after 2000 iteration it gives a error massage as floating point exceptionn

[Wasim]

Hi Rob, again i am facing problem of floating point exception if i decreased steps size to e-7 and number of iteration to 40 then after 15000 iteration my heterogeneous rkn seen not working because mole of product not increasing as well as mole of reactant not decreasing. can you please tell me why this is happening, initially rkn working fine but aftr 15000 this type of problem occur. please reply soon because i stuck here since last 2 months n

[Rob]

Assuming the model is converging and you still have reactants in the system do you have enough energy to trigger the reaction? n

[Wasim]

As i think there is continuous supply of reactant from inlet, so reaction should be there if not then how we can sustain reaction because it complete within fraction of second. after that flat line then how can be plot that reactants and products plots against time duration of few seconds say 6 sec. n

[Rob]

Look at the real system: how does it sustain the reaction? Ie in burners there's a very carefully designed way of anchoring the flame where you want it. n