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  3. 217 an apparatus for measuring thermal conductivity employs an electrical...

Question: 217 an apparatus for measuring thermal conductivity employs an electrical...

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2.17 An apparatus for measuring thermal conductivity employs an electrical heater sandwiched between two identical samples of diameter 30 mm and length 60 mm, which are pressed between plates maintained at a uniform temperature T,-77℃ by a circulating fluid. A conduct- ing grease is placed between all the surfaces to ensure good thermal contact. Differential thermocouples are imbedded in the samples with a spacing of 15 mm. The lateral sides of the samples are insulated to ensure one- dimensional heat transfer through the samples Plate, To AT Sample Heater leads Insulation Sample 2 Plate, To (a) With two samples of SS316 in the apparatus, the heater draws 0.353 A at 100V, and the differential thermocouples indicate ΔΤΙ ΞΔΙ2Ξ 25.0°C. What is the thermal conductivity of the stainless steel sam- ple material? What is the average temperature of the samples? Compare your result with the thermal con- ductivity value reported for this material in Table A.1 (b) By mistake, an Armco iron sample is placed in the lower position of the apparatus with one of the SS316 samples from part (a) in the upper portion. For this situation, the heater draws 0.601 A at 100V, and the differential thermocouples indicate ΔΤι ΔΤ, 15.0°C. What are the thermal conductivity and aver- age temperature of the Armco iron sample?

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