A heat exchanger for heating liquid mercury is under development. The exchanger is visualized as a 15cm-long and 0.3m-wide flat plate. The plate is maintained at 70 °C and the mercury flows parallel to the short side at 15 °C with a velocity of 0.3 m/s. a) Find the local drag (in N/m2 ) at the midpoint of the plate. b) Find the total drag force (in N) on the plate. c) Find the local heat transfer rate (in W/m2 ) at the midpoint of the plate. d) Find the total heat transfer rate (in W) on the plate.

a) The local drag at the midpoint is 0.921 N/m²

b) The drag force is 0.059 N

c) The local heat transfer is 27158.6 W/m²

d) The total heat transfer is 17282.5 W

Explanation:

Given:

ρ = 13557.5 kg/m³

v = 0.1165x10⁻⁶m²/s

Pr = 0.026

k = 8.5675 W/m K

vα = 0.3 m/s

Tα = 15°C

a) The Reynold´s number is:

The flow is laminar. The drag coefficient at the midpoint is:

The local drag at the midpoint is equal:

b) The average coefficient for the plate is:

The total drag force is:

c) The equation:

at midpoint n = 0.075 m

The local heat transfer is:

d) The average heat coefficient is:

The average Nussele:

it would be c. predictability