# Simulate cooling of bread in ansys cfx

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 June 16, 2015, 04:58 Simulate cooling of bread in ansys cfx #1 Member   Sravan Kumar Join Date: May 2014 Posts: 57 Rep Power: 12 I wanted to simulate cooling process for a bread. Following is the test case: I have bread initially at 95 deg C, and it is cooled by passing air at 25 deg c with some flow velocity.I have to estimate the required time to cool the bread and observe the flow pattern around the bread at each time step. ( transient analysis ) However it is an initial phase of my work. Later I have to cool the bread by mixture of air and water droplets. ( mulitphase flow ) Can you guide me how I can go forward with the initial situation and simulate the initial case in Ansys CFX?

 June 16, 2015, 05:20 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,786 Rep Power: 143 Do you need the temperature profile inside the bread? Is the air cooling slow or high speed? In other words, is natural convection significant? What do you have to observe on the flow pattern? You can model this as a simple ODE with no need for CFD at all if you want. Just Newtons Law of cooling. And most importantly..... won't cooling the bread with water droplets make it go soggy? Yuk!

 June 16, 2015, 06:09 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,786 Rep Power: 143 The air cooling one is easy using CHT. Give the bread representative density, thermal conductivity and specific heat for material properties. Then give it an initial temperature. If natural convection is not significant that this simulation probably does not need CHT. You can do the air simulation to get the heat transfer coefficient, then just apply those heat transfer coefficients to a solid only thermal model. This will be much faster and easier than the CHT simulation.

 June 18, 2015, 09:39 #5 Member   Sravan Kumar Join Date: May 2014 Posts: 57 Rep Power: 12 I have not understood, natural convection is significant also. Here is what I have done: Inintially I have given the properties for bread as told and initialized its temperature with 95 deg c. And solved for heat transfer with thermal energy. However when I do this in around ten seconds the bread is getting cooled to 25 deg, which is not true. The problem was I was using steady type in analysis. Now I have initially simulating for steady state with heat transfer as isothermal for bread for some iterations then I am using this solution as a initialisation for transient analysis changing the heat transfer in bread to thermal energy for transient case. So now in steady state the bread doesnt cool down ( it is as expected ) but once it comes to transient case the temp of bread remains as same as before without drop in temperature.( which is expected to drop exponentially) Please guide me where I have went wrong.

 June 18, 2015, 18:52 #6 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,786 Rep Power: 143 Of course you need to model this transient. Don't be fooled by the time step size reported in steady state analysis - it is not "real" seconds. Make sure your CHT interfaces are correct, and the material properties of your bread are correct.

 Tags cfx, conjugate heat transfer, cooling, transient analysis