The temperature coefficient of resistivity of iron is 5.0 x 10–3/ºC; that of carbon is –0.50 x 10–3/ºC. When an iron wire and a carbon rod, each having the same 10 Ω resistance at 20ºC, are cooled from that temperature to –80ºC, the new ratio of the resistance of the carbon rod to the resistance of the iron wire at the lower temperature is Group of answer choices +1.9 –10 +2.1 –0.10 +10

Asteel tube (k=50 w/mk) of inner and outer diameter di = 20mm and do=26mm, respectively, is used to transfer heat from hot gases flowing over the tube (h-hot = 200w/m2k) to cold water flowing through the tube (h-cold = 8000 w/m2k). what is the cold-side overall heat transfer coefficient uc? to enhance heat transfer 16 straight fins of rectangular profile are installed longitudinally along the outer surface of the tube. the fins are equally spaced around the circumference of the tube, each having a thickness of 2mm and a length of 15mm. what is the corresponding overall heat transfer coefficient uc? *solve for uc in both cases*