5000 kg/hr of oil is to be cooled from 70°C to 50°C in counter flow double pipe heat exchanger by using water at 20°C flowing at a velocity of 8.0 m/sec. The size of the inner copper pipe is 1.8 cm ID and 2.1 cm OD, oil flows through the annulus between this pipe and a 3 cm ID steel pipe. Thermal conductivity of copper is 330 kcal/hr-m°C. Find (i) LMTD, (ii) heat transfer coefficients on water and oil sides, (iii) overall heat transfer coefficient and (iv) length of pipe required. Assume the following data for oil and water at their mean temperatures:
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Property (Units)
|
Oil
|
Water
|
|
r(kg/m3)
|
864
|
998.2
|
|
Cp(kcal/kg°C)
|
0.489
|
1.0
|
|
k(kcal/kg°C)
|
0.126
|
0.515
|
|
m(kgf-sec/m2)
|
152 ´ 10–6
|
102.4 ´ 10–6
|
|
n (m2/sec)
|
1.726 ´ 10–6
|
1.006 ´ 10–6
|