Question

Thermal energy generated by the electrical resistance of a 5-mm-diameter and 4-m-long bare cable is dissipated to the surrounding air at 20°C. The voltage drop and the electric current across the cable in steady operation are measured to be 60 V and 1.5 A, respectively. Disregarding radiation, estimate the surface temperature of the cable. Evaluate air properties at a film temperature of 60°C and 1 atm pressure. Is this a good assumption?

Answer 1

Answer:

surface temperature = 128.74⁰c

Explanation:

Given data

diameter of cable = 5 mm = 0.005 m

length of cable = 4 m

T∞ ( surrounding temperature ) = 20⁰c

voltage drop across cable ( dv )= 60 V

current across cable = 1.5 A

attached to this answer is the comprehensive analysis and solution to the problem.

The assumption made is not a good one since the calculated Ts ( surface temperature ) is very much different from the assumed Ts