Question

A small distiller evaporates 10 L of water per half hour. Alloy tubing exposed to the air serves a condenser to recover steam. The outside surface of the tubing is at 99C. The ambient temperature is 20C. The inside diameter of the tube is 0.85 cm, and the outside diameter is 1.2 cm. The thermal conductivity of copper is 388W/m.K, latent heat of condensation (hfg) for saturated steam at 100C is 2257kJ/kg. In order to condense all the steam, the tube length in meters is most nearly. How long must the tube be to condense all of the steam?
a) 0.3 nm
b) .2 m
c) 2.4 m
d) 8.3 mm
e) 10.8 m

Answer 1

Answer:

c) 2.4m

Explanation:

1 liter of water evaporates in 30 minutes, Mass of water evaporation is :

1 / (30 * 60) = 5.55 * $10^{-4}$

The diameter of the tube is 0.85 cm inside and 1.2 cm outside

L = 1253 / 518.434 = 2.416

The length of the copper tube must be 2.4 m long.