How can I apply the feature of 'Enclosed cavity' for expansion air by heating?

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Hello, I'm trying to make a model of sealed crucible filed with air. I set the heat flux on the top of the crucible to heat it and so does the air which is in the crucible. The air get expansion, and the inside wall of the crucible get pressure as load. So I choose the physics :

Heat transfer in solids and fluids --> about the crucible and air / Structure mechanics --> about the crucible / -->Multiphysics - Thermal expansion --> about the crucible

In Structure mechanics, I set the "Boundary load" = P1(T/T1)/(1+3alpha*(T-T1)) T1 = initial temperature / P1 = initial pressure / alpha = coefficient of thermal expansion of crucible The equation of boundary load means the pressure load considered the thermal expansion of the crucible.

COMSOL 6.2 released the feature of "Enclosed Cavity" which can simulate the volume change by pressure load. But when I apply this feature, it doesn't work. I saw some examples about 'enclosed cavity' (Hyperelastic Seal & Biventricular Cardiac Model tutorial models), they have something in common that the volume changes by force but not the air expansion.

How can I apply the 'enclosed cavity' to simulate the pressure load by air expansion? Would it be accurate to proceed the way I originally did?

Best,

Hyeontak Kim


1 Reply Last Post 2024年7月15日 GMT-4 04:56
Aaron Dettmann COMSOL Employee

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Posted: 2 hours ago 2024年7月15日 GMT-4 04:56

If I understand your model correctly, I believe the Enclosed Cavity feature might still suited for solving your problem.

Note, however, that the Enclosed Cavity feature assumes that the entrapped air inside the cavity has a uniform pressure and temperature in the fluid domain, and that the gas state is governed by a global equation of state. In other words, temperature or pressure gradients cannot be resolved.

Assuming that you know the air temperature (e.g. assuming thermal equilibrium between wall and gas, or solve for a heat transfer equation), you can define your equation of state for the air (e.g. ideal gas).

You can then enter this equation of state either in the Fluid subnode, if you choose User defined from the Compressibility list. Alternatively, you could use the Prescribed Pressure subnode (and delete the Fluid subnode).

If you have any further questions, please don't hesitate to elaborate or share more details about what specifically does not work as expected.

If I understand your model correctly, I believe the Enclosed Cavity feature might still suited for solving your problem. Note, however, that the Enclosed Cavity feature assumes that the entrapped air inside the cavity has a uniform pressure and temperature in the fluid domain, and that the gas state is governed by a global equation of state. In other words, temperature or pressure gradients cannot be resolved. Assuming that you know the air temperature (e.g. assuming thermal equilibrium between wall and gas, or solve for a heat transfer equation), you can define your equation of state for the air (e.g. ideal gas). You can then enter this equation of state either in the Fluid subnode, if you choose *User defined* from the *Compressibility* list. Alternatively, you could use the *Prescribed Pressure* subnode (and delete the *Fluid* subnode). If you have any further questions, please don't hesitate to elaborate or share more details about what specifically does not work as expected.

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