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temperature
Posted 24.05.2011, 14:32 GMT-4 Version 3.5a 1 Reply
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Hello,
I would like to calculate the temperature in a fluid (water), and there are two hot spots PT1 and PT2. However I can not define the value ??of temperatures for points (PT1 and PT2). I'm using Navier-Stokes and convection and conduction modes.
The Point Setting is inactive. How can I solve this problem?
I would like to calculate the temperature in a fluid (water), and there are two hot spots PT1 and PT2. However I can not define the value ??of temperatures for points (PT1 and PT2). I'm using Navier-Stokes and convection and conduction modes.
The Point Setting is inactive. How can I solve this problem?
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1 Reply Last Post 25.05.2011, 01:50 GMT-4
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Posted:
1 decade ago
Hi
I believe you cannot define a fixed temperature on a "point", as a point has no area, and a fixed temperature means you need to extract or insert a certain thermal flux = W/m^2 over that undefined area.
Try to replace your two "points" by two small circles = boundaries in 2D, then it should work
A general rule in COMSOL: try to stick to Domain and Boundary BC only and do not use lower level entities (= Edges or Points in 3D, or Points in 2D) as these represent singularities.
Think it over:
in 3D for a given domain = volume, you have surface = boundaries that are unique (they may be split between at most 2 domains (hence the "up" and "down" normals depending on which side you are).
But still in 3D, an EDGE is shared by 2 or more boundaries. So a mesh node point on an Edge, how to define a dependent variable on that point ? is it the average value along the adjacent boundaries ? and the derivatives = gradients how do you define them ?.
For Point Entities it is even worse, no area => no flux ?
For these lower level Entities you must make too many hypothesis, so COMSOL states => it cannot decide for you.
--
Good luck
Ivar
I believe you cannot define a fixed temperature on a "point", as a point has no area, and a fixed temperature means you need to extract or insert a certain thermal flux = W/m^2 over that undefined area.
Try to replace your two "points" by two small circles = boundaries in 2D, then it should work
A general rule in COMSOL: try to stick to Domain and Boundary BC only and do not use lower level entities (= Edges or Points in 3D, or Points in 2D) as these represent singularities.
Think it over:
in 3D for a given domain = volume, you have surface = boundaries that are unique (they may be split between at most 2 domains (hence the "up" and "down" normals depending on which side you are).
But still in 3D, an EDGE is shared by 2 or more boundaries. So a mesh node point on an Edge, how to define a dependent variable on that point ? is it the average value along the adjacent boundaries ? and the derivatives = gradients how do you define them ?.
For Point Entities it is even worse, no area => no flux ?
For these lower level Entities you must make too many hypothesis, so COMSOL states => it cannot decide for you.
--
Good luck
Ivar