A small (1/4 in. diameter 1 in. long) metal test specimen is suspended by very fine wires in a large evacuated tube. The metal is maintained at a temperature of 2500F, at which temperature it has an...

A small (1/4 in. diameter

1 in. long) metal test specimen is suspended by very fine wires in a large evacuated tube. The metal is maintained at a temperature of 2500F, at which temperature it has an emissivity of approximately 0.2. The water-cooled walls and ends of the tube are maintained at 50F. In the upper end is a small (1/4-in.-diameter) silica glass viewing port. The inside surfaces of the steel tube are newly galvanized. Room temperature is 70F. Estimate

a. the view factor from the specimen to the window;

b. the total net heat-transfer rate by radiation from the test specimen;

c. the energy radiated through the viewing port.