In the second experiment, the measurements are carried out at steady state by continuously heating the cylinder. This can be accomplished by directly passing current through the cylinder, or by using electric rod heaters, held concentrically within the cylinder. Depending on the air velocity the cylinder will attain a temperature . From energy balance, one can write

where is the electrical heater input to the cylinder.

The question here is: Of the transient and steady state experiments identify the method to be preferred for obtaining the heat transfer coefficient. To answer this question, one needs to realize that the transient method relies on measurement of time while the steady state method relies on the measurement of electrical power . Assuming fixed uncertainties in time and electrical power ( and respectively), it is clear that the transient method is preferable if

and the steady state method should be adopted if