1.Water flows at 50oC inside a 2.5-cm-inside-diameter tube such that hi= 3500 W/m2 oC. The tube has a wall thickness of 0.8 mm with a thermal conductivity of 16 W/m2 oC. The outside of the tube loses heat by free convection with ho = 7.6 W/m2 oC. Calculate the overall heat-transfer coefficient and heat loss per unit length to surrounding air at 20oC.
2. Two 3.0-cm-diameter 304 stainless-still bars, 10 cm long, have ground surfaces and are exposed to air with a surface roughness of about 1 ?m. If the surfaces are pressed together with a pressure of 50 atm and the two-bar combination is exposed to overall temperature difference of 100oC, calculate the axial heat flow and temperature drop across the contact surface.