Learning Forum

[Lia93]

Hola a todos, estoy realizando la simulaci?n de un reactor batch cil?ndrico que este lleno de agua en su interior y est? cerrado completamente. Debo poner como condiciones de frontera un flujo de calor que incide en la pared del cilindro, p?rdidas convectivas y radiativas; pero el Software no me permite poner las tres a la vez, c?mo podr?a introducir el flujo de calor en la mitad del cilindro que es donde incide utilizando una UDF???.Tambi?n tengo otra duda, deseo que mi agua se mantenga en estado l?quido todo el tiempo, utilizo un presi?n inicial de 20 bar ya que mi proceso para que se realice debe estar a altos valores de presi?n y temperatura y el volumen del agua no var?a, pero cuando hago la simulaci?n el valor de la temperatura no var?a significativamente y en la pr?ctica no ocurre as?, como podr?a ver esos cambios de presi?n en funci?n de la temperatura???n

[Rob]

Hello everyone, I am simulating a cylindrical batch reactor that is filled with watern inside and is completely closed. nI must put as boundary conditions a heat flux that affects the cylinder wall, convectiven and radiative losses; But the Software ndoes not allow me to put all three at the same time, how could I introduce the heat flown in the middle of the cylinder that is where it affects using a UDF ???I also have another question, I want my water to remain in a liquid state all the time, nI use an initial pressure of 20 bar since my process nmust be at high pressure and temperature values ??and the volume of the water does not vary,n But when I do the simulation, the temperature value ndoes not vary significantly and in practice it does not, how could I see these pressure nchanges as a function of temperature ???nn

[Amine Ben Hadj Ali]

1/Mixed (Robin) Wall BC allowes you to provide convective and radiative tranfer from outside to your domainn2/Also use transient solver to keep track of pressure build up. For water uses Boussinesq Density formulation to account for buoyancy effects (only viable if temperature differences are low: isobaric thermal expansin coefficient times Temperature difference <<1.n

[Rob]

Have a careful look at the wall boundary conditions in Fluent. They're set to allow you to add/remove heat from the computed domain and means you don't always need to model the outside. So, in your case it sounds like you want to over constrain the boundary:review what you actually want/know and see how that compares to the options. Note, radiation can often be neglected. nUnless you tell Fluent how to include phase change (multiphase models) the process fluid will remain as water. If you're wanting natural convection look for buoyancy and Boussinesq Approximation (including limitations) on here and in the documentation. n