Learning Forum

[geojacob]

I have the problem of a reactor that has heat exchanging pipes through it. Biomass is placed in the reactor and with the flow of air combustion starts and air exits through the chimney transfering heat to the heat exchange pipes.

 

My question is, is there a possibility to simulate biomass combustion and associated chemical reaction in ANSYS. What are some good method to understand the way this simulation has to be done.

[Rob]

You can model biomass combustion. Before trying to explain the best approach, what do you need to know, and what design are you looking at?

[geojacob]

As I am a student and new in this field, I could explan it briefly.

 

The boiler has heat exchangers and the heat carried away by heat exchangers must be studied. The biomass in the boiler burns out and thus a simulation model has to be made. As I understand the the following are the steps to be followed.

A 3D or 2D model has to be made in design modeler, The heat exchanger or the heat sink carry some heat outside, while the combustion products rexit through the outlet pipe.

 

Since biomass combustion happens and the chemical reactions are known how is it possible to simulate the chemical reaction and correspoding heat increase and heat carried away by the heat exchanger.

 

How is it possible to develop a mathematical formulation for this and based on this what must be the approach to develop a model.

[Rob]

OK, to start with I'd consider a system where you add heat/temperature into the domain without using combustion models. You can then model the HX unit, and focus your attention there. 

Model simplification is one of the most overlooked skills in simulation: the aim is to get the most information out of a model using the least amount of effort & resource. That way you can model many different geometries to find the optimum solution. 

[geojacob]

How do we add heat in the domain without combustion model?

 

I have to consider the flow of air in and out of the geometry.

 

[Amine Ben Hadj Ali]

By providing an energy source term.

[geojacob]

Could you please say where could I find an example or a tutorial withprovidign energy source

[Amine Ben Hadj Ali]

https://youtu.be/1Dk5pMryybM

[geojacob]

Thanks for your reply.

 

Given the chemical reaction causes the temperature rise in the chamber. IS it possible to simulate that too for a given period of time?

The watervapour condenses on the heat exchanger pipes and could this to be simulated

 

Also, since this has a porous bed and combustion takes place, how do  I make the hand calculations and governing equations for the same.

 

[Rob]

You will need to work out the source terms based on the reaction scheme, either by hand or using some code. We can model all of the combustion, but if you're wanting to focus on the heat exchanger you'll finish up spending most of the cpu & mesh on the combustion zone rather than the area of interest. 

Re condensation, yes we can do that. However, if you have a gas mixture containing water vapour you can (initially) look at the relative humidity to see if condensation is likely. From there we'd probably look at the wall film models (read the documentation). 

 

[geojacob]

 

In this case, what procedure must be followed.

To consider two cases as told before,

 First consider the heat generation take place by giving the heat flux value and applying it to the whole surface as shown in the tutorial and simultaneously modeling the heat extracted by the heat sink?

 

[Rob]

Source to add the heat. Sink to remove, or conduction/convection. It's not clear how air gets from the combustion zone into the chimney so you'll need to explain in more details.