When setting the boundary condition for the external wall of a cooling channel that contains hot and cold fluids between them a plate, what is the best condition for calculating the Nusselt number in ANSYS fluent? is it the setting of a constant temperature or a constant heat flux or a thermal insulation condition and how much does each of these conditions affect the value of Nusselt number and which gives us Better accuracy results if the channel is part of a multi-channel exchanger. Thank you in advance
https://www.sciencedirect.com/topics/engineering/cooling-channel
Dear Ahmad Aboulkhail ,
The Nusselt number should be calculated separately for both sides. In fact, all parameters involved in Nu calculation such as local surface and bulk temperatures, area, and q" are different for both hot and cold surface. Please set the boundary condition as "interface" and "coupled" to obtain the best answer. You can also calculate U as the overall heat transfer coefficient from convective heat transfer coefficients at the hot and cold sides as indicated in the attached image.
More information can be found in one of our published article as addressed follow:
Article Convective heat transfer enhancement in a double pipe mini h...
Thank you for your answer, Mr. Mojtaba, but to mean the boundary condition on the outer walls and not on the surface separating the two fluids, what should be put in order to obtain the best answer (insulated wall, constant temperature or constant heat flux ...)
Mojtaba Bezaatpour
It depends on ur condition. If u want heat dissipation to be zero, set the outer wall insulated (heat flux =0) , or if the heat exchanger is exposed to the ambient, set mixed or convective on outer wall. In such case, u should know the ambient temperature and free convection coefficient.
Dear Ahmad Aboulkhail
please see the following links:
https://www.comsol.com/blogs/using-the-inflow-boundary-condition-in-nonisothermal-flow-simulations
https://www.comsol.com/blogs/introduction-to-modeling-natural-convection-in-comsol-multiphysics
https://www.afs.enea.it/fluent/Public/Fluent-Doc/PDF/chp06.pdf
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