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

Physics & Space Science

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