Asingle-pass, cross-flow heat exchanger uses hot exhaust gases (mixed) to heat water (unmixed) from 30 to 80c at a rate of 3 kg/s. the exhaust gases, having thermophysical properties similar to air, enter and exit the exchanger at 225 and 100c, respectively. if the overall heat transfer coefficient is 200 w/m2 k, estimate the required surface area.

47.4889 m^2

Explanation:

Calculate the total heat transfer as

= 3×4184(80-30)= 627600 J/s

Now calculating logarithmic mean temp. difference

soloving we get

LMTD= 103°C

To calculate the effectiveness we use

ε=

=0.641

Now we know that

Q= εAsU LMTD

627600 = 0.641×A_s×200×103

putting values and calculating we get

As= 47.4889 m^2

The required surface area is

= 47.4889 m^2