In a single-pass counterflow heat exchanger, 1.25 kg/s of water enter at 15°C and cools 2.5 kg/s of an oil having a specific heat of 2093 J/(kg K) from 95°C to 65°C. If the overall heat transfer coefficient is 280 W/(m2 K), determine the surface area required.
GIVEN
• Water cooling oil in a single-pass counterflow heat exchanger
• Water flow rate ( m w)= 1.25 kg/s
• Oil flow rate ( m o)= 2.5 kg/s
• Oil specific heat (cpo) = 2093 J/(kg K)
• Water inlet temperature (Tw, in) = 15°C
• Oil temperature
? To, in = 95°C
? To, out = 65°C
• Overall heat transfer coefficient (U) = 280 W/(m2 K)
FIND
• The surface area (A) required
SKETCH
PROPERTIES AND CONSTANTS
the specific heat of water (cpw) = 4187 J/(kg K)
The heat capacity rates are
Therefore, Cmin/Cmax = 1.0
The outlet temperature of the water can be determined from an energy balance
for counterflow
The rate of heat transfer is
Solving for the transfer area
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