Calrods are tubular heating elements that convert electricity into heat via Joule heating. They are used in appliances because of their high power density. They are frequently modeled as uniform heating elements. This modeling approach cannot capture the temperature variations and the thermal stresses in the Calrod, which is necessary for predicting actual performance.
Veryst developed a detailed Calrod model that includes the helical heating element, the magnesium oxide insulation and the external steel tube. An electric potential difference was applied across the ends of the Calrod section. The resulting current generates heat which is transferred through the Calrod by conduction, and to the outside by convection and radiation.
We used the model to predict the transient and steady state thermal behavior of the Calrod, and identify local regions of high temperature and high thermal-induced stresses. We also calculated equivalent thermal and mechanical properties which can be used when the details of the Calrod are not modeled.
Calrod geometry Temperature distribution in Calrod after heating for 10 seconds