A solution with a boiling point of 82°C boils on the outside of a 2.5 cm tube with a No. 14 BWG gauge wall. On the inside of the tube flows saturated steam at 40 kPa(abs). The convection heat transfer coefficients are 8.5 kW/(m2 K) on the steam side and 6.2 kW/(m2 K) on the exterior surface. Calculate the increase in the rate of heat transfer if a copper tube is used instead of a steel tube

Question

GIVEN

• Tube with saturated steam on the inside and solution boiling at 82°C outside

• Tube specification: 1 in. No. 14 BWG gauge wall

• Saturated steam in the pipe is at 40 kPa(abs)

• Convective heat transfer coefficients

? Steam side ( ci h ) : 8.5 kW/(m2 K)

? Exterior surface ( co h ) : 6.2 kW/(m2 K)

FIND

• The increase in the rate of heat transfer for a copper over a steel tube

ASSUMPTIONS

• The system is in steady state

• Constant thermal conductivities

SKETCH

Answer 1

The thermal circuit for the tube is shown below



The individual resistances are



The rate of heat transfer is



For the copper tube



For the steel tube



The increase in the rate of heat transfer per unit length with the copper tube is