ME 324 HW #6 15.04.2015 1. Suppose an experiment is conducted

ME 324
HW #6
15.04.2015
1. Suppose an experiment is conducted as follows: Air at 300 K enters a smooth tube of 0.1 m in
(inner) diameter and 6 m in length with the mass flow rate of 0.002 kg/s. A constant heat flux is
imposed and the outside tube wall is thermally insulated from the atmosphere. The exit air
temperature is measured to be 350 K.
(1) Find the total heat flux from the tube to the air.
(2) Find the heat transfer coefficient at the exit.
(3) Estimate the wall temperature at the exit.
2. An oil with Pr = 1960, ρ = 860 kg/m3, ν = 0.00016 m2/s and k = 0.14 W/m°C enters a tube, 2.5
mm in diameter and 0.6 m in length. The oil entrance temperature is 20°C and the tube wall
temperature is 120°C. The mean flow velocity is 0.3 m/s. As a first approximation, the properties
are assumed to be constant. Calculate (1) the oil temperature at the exit and (2) the total heat
transfer rate from the tube to the oil. (Note that the thermal entry length may be assumed because
it is an oil flow with high Pr.)