[kelly1]

Hello,

My textbook - McCabe - is not very helpful in helping me solve part (ii) & (iv) of the following:

A 1:1 shell & tube heat exchanger is required to cool 10,000 kg/h of light oil from 105°C to 20°C using cooling water which is available at 15°C and leaves at 30°C. The light oil flows inside the tubes and the water is on the shell side.

(i) Based on the stated temperatures, show whether the flow configuration concurrent or countercurrent. What is the log mean temperature difference?
(ii) Calculate the number of tubes for a linear velocity of the oil of 0.8 m/s.
(iii) Calculate the film coefficient for the oil on the inside of the tubes.
(iv) Determine whether the number of tubes calculated in (ii) is sufficient to perform the required duty.

Data
Specification of Heat Exchanger tubes:
Stainless steel, 12.5 mm ID, 16.0 mm OD, 4.0 m length.
Thermal conductivity of stainless steel: 16 W/m °C
Heat transfer coefficient for water on outside tubes: 900 W/ m2 °C
Properties of Oil:
Density: 850 kg/m3
Viscosity: 1.6 x 10-3 Pa.s
Thermal conductivity: 0.15 W/m °C
Specific heat: 1900 J / kg °C

The only formula I've come across so far is:

Hn = 0.725[(k^3*rho^2*h*lamda)/N*deltaT*Do*viscosity)]^(1/4)

But since I can't find the - average coefficient for the entire stack (Hn), I cannot solve for N.

Could someone please offer ANY suggestions?

Kind regards,
Kelly