The cooling correction

If we add heat to a perfectly insulated body at a steady rate then a graph of the temperature of the body against time will be a straight line (Figure 1(a)). However, if we now take into account the loss of heat a graph similar to Figure 1(b) will be obtained.





Clearly the final temperature in Figure 1(b) needs to be corrected for this loss of heat.




Figure 1(b) shows the cooling of the body after the supply of energy has been switched off at t_o. To enable us to correct the rise of temperature for heat loss we will assume forced convection and that Newton's law of cooling holds.

It can be shown that:

Δθ = φS₁/S₂

where Δθ is the cooling correction, and hence the true final temperature due to heating can be calculated.

The simplest way to allow for the cooling is to cool the object to a few degrees below room temperature before heating begins. The object therefore gains heat from the surroundings in the first part of the heating process and loses it in the second (see Figure 1(c)).