A thinwalled water tube has a 002m inside diamter at a mass

A thin-walled water tube has a 0.02m inside diamter at a mass flow rate of 0.01kg/s. THe outside of the tube is remained at constant temperature of 20C through an electric-heating element. Water at 10C entering a 1.5m long tube is to be heated to 40C. If the water property is Re=699.2, Pr-4.1, Kf=0.608W/mk, Cp=4.18 kj/kg-k, the innter tube surface temperature at outlet needs to be determined.

Which Nussult number correlation should be used to find the appropriate heat transfer coefficient?

Nu=0.023 Re^4/5Pr^1/3

Nu=3.66

Nu=3.66+(0.0668(D/L)Re*Pr)/(1+0.04(D/L*Re*Pr)^2/3)

Solution

since Re < 2000 this is a laminar flow

For a laminar flow through the pipe with constant wall temperature Nu = 3.66