[R] or [Ra]
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100[degC] is an expression that has temperature as the dimension. The COMSOL Multiphysics software interprets it as an absolute temperature and evaluates it as 373.15 K.
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373.15[1/K] is interpreted as an absolute inverse temperature (but no conversion is necessary from kelvin to kelvin).
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373.15[1/degC] evaluates to 100[1/K] using the offset of 273.15 degrees between kelvin and degrees Celsius.
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100[degC/K] is dimensionless, and the temperature is therefore a differential temperature; that is, the result is 100 because the conversion uses no offset.
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To make the COMSOL Multiphysics software interpret 100[degC/K] as an absolute temperature, split the expression using two separate expressions such as 100[degC][1/K], which equals 373.15. This is also what occurs when you use a variable (TC, for example) defined as 100[degC]. TC[1/K] is then also two expressions where both are interpreted as absolute temperature.
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For temperature units that require an offset and a scale factor to be converted to kelvin, it is not possible to convert them simply using a multiplication. While 293.15[K][1/degF] produces the expected output, 68 (68 degrees Fahrenheit corresponds to 293.15 kelvins), 293.15[K]*1[1/degF] evaluates to something completely different. As mentioned in the previous point, 293.15[K/degF] uses no offset and is also usually not the desired expression.
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