3. CALCULATION OF CONCENTRIC TUBES HEAT EXCHANGERS
3. 8. Example 2
To heat 10000 kg/h of oil from 35 ºC to 85 ºC is used a concentric tubes heat exchanger. The heating agent is water steam saturated that condenses to 104 ºC in the space between the tubes.
Due to a malfunction in the boiler producing steam, this flow decreases, so maintaining a constant temperature of the condensation, the global heat transfer coefficient decreases to 42% compared to initial value.Calculate:
a) Mass flow rate of water steam (W1).
b) Global coefficient of heat transmission referred to the area outside the inner tube (U0).
c) Area of the inner tube (A0).
d) New heat transfer coefficient referred to the area outside the inner tube (U'0) after the malfunction.
e) New oil outlet temperature (t'20).
Information:
Average specific heat of oil = 2.5 KJ/kgK
Convection coefficient for oil = 2510 KJ/hm2K
Convection coefficient for steam = 4200 KJ/hm2K
The wall thickness of the inner tube can be considered negligible.