# Thermal Unit Operations

1CHEE 3601 Assignment 5
Question 1
You would like to use a plate heat exchanger to cool 45,000 kg/h of alcohol from 55.4°C to 43°C.
Cooling water at 25°C will be used. The water outlet temperature should not be higher than
40°C.
The channels created by the plates are 0.360 m deep and 0.005 m wide, with a effective plate area of
0.319 m2.
The plates are stainless steel with a thickness 10 mm.
If your initial estimate for U is 2000 W/m2 K, what is the number of plates required? Calculate the heat
transfer coefficients for each fluid, and the overall U. Compare that to your initial estimate of U.
Question 2
A 2.5 cm OD tube is fitted with 5 cm OD annular fins spaced every 0.5 cm, from fin centre to fin centre.
The fins are an aluminum alloy (k=161 W/mK) and are of constant thickness 0.0229 cm. The external
free convection coefficient is 8.5 W/m2K/. For a tube wall temperature of 165 oC and ambient air
temperature of 27 oC, determine the heat loss per meter length of finned tube.
2
Question 3
If I want to add fins to a bare wall, how much will it increase the heat transfer from that wall?
Bare wall: h=40 W/m2K
With fins: h= 30 W/m2K
Fins are rectangular aluminum fins with a length of 50 mm, thickness of 0.5 mm and spaced equally at a
distance of 4 mm (making 250 fins/m).
a) bare wall
b) fins (example – use numbers above)/

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