A high temperature fuel cell uses a cylindrical copper busbar of diameter d = 8mm to maintain electrical connection to a programmable load. The electrical connections at the load must be kept below 70C to avoid electrical fault, and the busbar emerges from a furnace which is maintained at 850C. The ambient temperature in the workshop is 25C.

c) . Now, in order to conserve expensive copper, estimate the minimum length of the fin required in order to ensure the fin temperature will drop to the load allowance of 70C. Assume that no heat is lost from the tip of the fin.

The properties of air at 210C are: = 0.73 kg.m-3 cP = 1029 J.kg-1.K-1 = 2.61x10-5 kg.m-1.s = 3.57x10-5 m.s-1 kair= 0.03888 W.m-1.K-1