5 Replies Latest reply on Nov 15, 2016 4:59 PM by Amit Katz

    Furnace Flow Simulation Issue

    Austin Smith

      Hello,

       

      So I am new to flow simulation, just started to use the program roughly a little over 3 weeks ago and I am trying to simulate the flow of gases from a combustion reaction of propane with air as well as heat conduction throughout the furnace model. For the simulation I am taking into account both conduction and radiation. The products of a combustion reaction of propane come from a burner inside the model and have been defined as an inlet mass flow with a flow rate of 0.016 kg/s and I have identified a heat source of 295kW on the same face of the burner. There are two vents in the furnace model, both defined as open to the environment for boundary conditions. I have defined the outside walls of the furnace as Stainless Steel 321 and the inside walls as Brick, fireclay, glazed (to mimic the insulation we plan to use for the actual furnace). For the default wall thermal condition, I am not exactly sure what option to select. For most of the simulations I have run I've used adiabatic wall. I have calculations that say the average inside wall temperature should reach roughly 479 K. I have also tried to set the initial and ambient temperature of the environment to reach around 1470 K after a certain amount of time (through the setup wizard) using the dependency option with an initial temperature of 293 K and after running the simulation, the furnace stays at the indicated 293 K and does not reach anywhere near the specified 1470 K. I have multiple projects in the file below from trying various options for the simulation to no avail.

       

      I am not sure what I am doing wrong and would greatly appreciate help with this. My major issue currently is the temperature distribution through the furnace. The furnace walls do not display they are changing in temperature. When I put a Cut Plot inside the furnace to displace the temperature, the inside of the furnace is not affected whatsoever. Again any input is greatly appreciated! If anything needs to be clarified feel free to ask! I also attached the most recent cut plot I was able to obtain from inside the furnace.

       

      Message was edited by: Austin Smith

        • Re: Furnace Flow Simulation Issue
          Amit Katz

          Instead of trying to define wall conditions, I would recommend you model the thickness of the insulation and the walls you plan to use, then apply material conditions to them. The outside wall condition is tricky. Try starting out with adiabatic walls and see how that goes.

          Also, in addition to defining the heat flux at the gas inlet I would recommend defining the temperature of the fluid as well.

            • Re: Furnace Flow Simulation Issue
              Austin Smith

              Originally I specified the inlet mass flow temperature in my past simulations at 1493 K and I've been using the Adiabatic wall for the Outside Wall condition as well. This time I did what you suggested and applied a radiative surface to the inner walls of the furnace to resemble one of the insulation types we plan to use (Fire Brick). As you can see from the image below I also changed the burner shape to actually resemble the flame length and diameter. Overall our results greatly improved, there was a temperature distribution in the walls of the furnace as seen in the attached image below. The temperature distribution of the fluid inside the furnace remains ambient though

               

              Cut Plot - Temperature.PNG

                • Re: Furnace Flow Simulation Issue
                  Amit Katz

                  Two notes:

                  What does your mesh look like? It's hard to tell exactly, but judging from the rough nature of your contour plot it seems to me to be very coarse.

                  What material are you using for the solid geometry (not the wall conditions) in this model? I see several types of geometry here but no materials set in your project tree.

              • Re: Furnace Flow Simulation Issue
                Bill McEachern

                Without sounding paternalistic: have you done some of the thermal problems in the tutorial manual? It sounds like you are missing something very basic. Your description seems pretty sensible but not enough detail to help you out. I have done quite a few furnaces and it should not be overly difficult to get something reasonable. Your general approach seems pretty sound but the devil is in the details. If I were you I would start with a steady state analysis of a box with an inlet and an out let and get that working and them complicate from their. Teh BC I would use on the outside is adiabatic or a convection coefficient and ambient temp but it seems the least of your problems.

                  • Re: Furnace Flow Simulation Issue
                    Austin Smith

                    So turns out our dimensions were wrong for the furnace. We had a 5m x 5m x 5m furnace when it was suppose to be 5 ft x 5 ft x 5 ft. I then changed the shape of the burner in the furnace model to a cylinder to resemble the actual flame length and diameter and used the faces of the cylinder as the heat source. I also specified the inner walls of the furnace as a radiative surface to mimic the type of insulation we plan on using, Fire Brick, instead of specifying it in the general settings. Overall our results greatly improved, there was a temperature distribution in the walls of the furnace as seen in the attached image below. The temperature distribution of the fluid inside the furnace remains ambient though. The temperature of the inlet mass flow is specified at 1493 K so I am not sure what the problem is.

                     

                    I plan on doing simpler cases like you suggested and I actually talked to a professor and he suggested the same thing.Cut Plot - Temperature.PNG