Enumerate the three modes by which heat can be transferred from one place to another

Enumerate the three modes by which heat can be transferred from one place to another. Which is the
slowest of all ?
How do you define the thermal conductivity of a material ?
What do you understand by the terms ‘convective heat transfer co-efficient’ and ‘overall heat transfer
co-efficient’.
Derive an expression for heat loss in kJ/m 2 -hr through a composite wall of layers (i) without considering
convective heat transfer co-efficients and (ii) considering the convective heat transfer co-efficients.
Classify the heat exchangers according to the flow directions of fluid and give few examples of each in
actual field of application.