Negative thermal resistance in SimScape

Question

Richard 2020-1-28

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/502412-negative-thermal-resistance-in-simscape

回答： Kumar Bhivesh Sharma 2022-3-19

Hi,

I'm trying to build a lumped parameter thermal model of a permanent magnet synchronous machine in SimScape. By doing so, I need to implement some negative thermal resistances. (For reasons, see below). Unfortunately, SimScape does not allow thermal resistances to be negative. So does anybody of you has an idea how to handle this (or had this problem himself)?

The problem background is the following: If we, for example, consider radial heat flow through a hollow cylinder with internal heat generation, it is generally acknowledged in related research that one should not apply the heat flow directly between the two nodes each representing half of the wall thickness of a hollow cylinder but instead include a negative thermal resistance connected to the aforementioned resistances in "T-configuration".

A short and comprehensive overview about the necessity of negative resistances is e.g. given in "Thermal modelling of a high speed permanent magnet synchronous machine, PhD, Grobler A.J, May 2011" (Chapter 3). The relevant chapter is freely accessable via: http://dspace.nwu.ac.za/bitstream/handle/10394/6528/Grobler_AJ_Chapter3.pdf?sequence=4&isAllowed=y

Thanks in advance for your help!

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Jonas 2020-2-17

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/502412-negative-thermal-resistance-in-simscape#answer_415915

在 MATLAB Online 中打开

When you check the source code of the Thermal Resistance block, it is indeed hard-coded that the thermal resistance is larger or equal than zero.

component resistance < foundation.thermal.branch
% Thermal Resistance
% This block represents a generic resistance in a thermal network. The heat
% flow rate is proportional to the temperature difference and inversely
% proportional to the resistance.
% Copyright 2016 The MathWorks, Inc.
parameters
    resistance = {1, 'K/W'}; % Thermal resistance
end
equations
    assert(resistance >= 0)
    if isfinite(resistance)
        T == resistance * Q;
    else
        Q == 0;
    end
end
end