Give a short written answer for these three questions Why do

Give a short written answer for these three questions: Why do we use the logarithmic mean temperature instead of the arithmetic mean temperature for a flow in a tube whose surface temperature is constant? What does the view factor represent? When is the view factor from a surface to itself not zero?

Solution

A) Logarithmic mean temp. makes it more easy manual calculations as comare to airthmetic mean temprature and also airthmetic mean temp.  give a approximation for the mean temperature difference when the smallest of the inlet or outlet temperature differences is more than half the greatest of the inlet or outlet temperature differences.

B) View factor is the proportion of the radiation which leaves surface from A and strike to  surfaceB.View factor from a surface to itself not zero when the other surface is concave in nature.