<P> For example, consider a pipe with a fluid flowing inside . The approximate rate of heat transfer between the bulk of the fluid inside the pipe and the pipe external surface is: </P> <Dl> <Dd> q = (1 1 h + t k) ⋅ A ⋅ Δ T (\ displaystyle q = \ left ((1 \ over ((1 \ over h) + (t \ over k))) \ right) \ cdot A \ cdot \ Delta T) </Dd> </Dl> <Dd> q = (1 1 h + t k) ⋅ A ⋅ Δ T (\ displaystyle q = \ left ((1 \ over ((1 \ over h) + (t \ over k))) \ right) \ cdot A \ cdot \ Delta T) </Dd> <Dl> <Dd> q = heat transfer rate (W) </Dd> <Dd> h = convective heat transfer coefficient (W / (m K)) </Dd> <Dd> t = wall thickness (m) </Dd> <Dd> k = wall thermal conductivity (W / m K) </Dd> <Dd> A = area (m) </Dd> <Dd> Δ T (\ displaystyle \ Delta T) = difference in temperature . </Dd> </Dl>

Overall heat transfer coefficient of a heat exchanger