Hi everyone. I am not sure if this is the best place for this question but here it goes.(adsbygoogle = window.adsbygoogle || []).push({});

I am looking to build a small heating element to position in the base of a tank of water. I want to avoid any boiling of the water so want to keep the temperature of the wire at around 90 degrees C. The calculation I have used is as follows:

Assume the heating element is a circular horizontal flat disc so the length scale is L=A/P where A is the surface area and P is the perimeter (as detailed in Fundamentals of Heat Transfer). (The design doesn't have to be a circular disc although it would be preferred).

Calculate the averages Nusselt number as: Nu=0.54Ra^(1/4) which yields 13.62 assuming an ambient temperature of the water of 20 degrees C and all properties in the calculation taken at the average temperature of the setup (90+20)/2=55 degrees C.

Then calculate an average heat transfer coefficient from h=(Nu kappa)/L, where the conductivity of nichrome was taken as 11.3.

Assuming that the majority of heat loss will be due to convection away from the surface I then calculated the required power from Q=hA(90-20).

Does this calculation seem reasonable? I anticipate I am doing something hideously wrong as keep getting power ratings of around 300W and I was expecting it to be much less for such a modest temperature. My naivety may be in the picking of the conductivity of the element: is there a better way to get an approximate rating of this value?

Regards

Smithy

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# Heating element temperature - correct calculation?

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