In an oil cooler the oil enters 10 mm diameter tubes at 160°C and is cooled to 40°C. The mean velocity of oil in the tubes is 1.5 m/s. Calculate the mean heat transfer coefficient. For turbulent flow of liquid being cooled take Nu=0.0265 Re0.8Pr0.3 and for laminar flow Nu = 3.65. Take all properties at bulk mean temperature and the properties are listed below:
|
t
°C
|
r
kg/m3
|
v
centi stokes
|
k
W/m K
|
c
kJ/kg K
|
|
40
|
878
|
251.0
|
0.144
|
1.96
|
|
100
|
839
|
20.4
|
0.137
|
2.22
|
|
160
|
806
|
5.7
|
0.131
|
2.48
|
1 centi stoke = 10–6 m2/s