In a refinery base oil comes out of a distillation unit and enters a tube at a bulk temperature of 400 K and mass flow r

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In a refinery base oil comes out of a distillation unit and
enters a tube at a bulk temperature of 400 K and mass flow rate of
20 kg/s. The surface of the tube is maintained at approximately
constant temperature of 300 K. What is the minimum length of the
tube so that the mean temperature at the outlet of tube does not
exceed 320 K? The inner dimeter of the tube is 10 cm. Calculate the
total convective heat transfer from the tube. Thermophysical
properties of base oil can be approximated by those of engine
oil