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 2500°F, at which temperature it has an emissivity of approximately 0.2. The water cooled walls and ends of the tube are maintained at 50°F. 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 70°F. 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

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Viewing port 12 in. Test specimen 4 in.