3.50 A stainless steel (AISI 304) tube used to transport a chilled pharmaceutical has an inner diameter of 36 mm and a wall thickness of 2 mm. The pharma- ceutical and ambient air are at temperatures of 6°C and 23°C, respectively, while the corresponding inner and outer convection coefficients are 400 W/m2 · K and 6 W/m2 · K, respectively.
(a) What is the heat gain per unit tube length?
(b) What is the heat gain per unit length if a 10-mm-
conductivity of kB = 1.5 W/m · K and its outer surface
is subjected to convection with a fluid of temperature Too= -15°C and heat transfer coefficient 50 W/m2· K. The thermal contact resistance between the cylinder surfaces and the heater is negligible.
(a) Determine the electrical power per unit length of the cylinders (W/m) that is required to maintain the outer surface of cylinder B at 5°C.
(b) What is the temperature at the center of cylinder A?