A 1 inch diameter tube at 922 K is used in nuclear reactor a

A 1 inch diameter tube at 922 K is used in nuclear reactor as part of a heat exchanger. It is exposed on the outside to liquid sodium with a temperature of 366 K at a velocity of 5 m/s. See the Appendix for properties of liquid metals. The tube is removed for inspection and you need to perform a microscopic analysis on the tube to look for signs of overheating the tube wall. At what angles around the tube relative to the oncoming flow would you concentrate your inspection? What is the worst-case local heat transfer coefficient you would expect for these conditions? What is the average heat transfer coefficient for the exterior of the tube?

Solution

Assume this is a system with steam passing inside the tube and sodium outside?

1) Sodium has to be pure otherwise if water, hydorgen or oxygen, carbon from graphite electrodes used to prepare sodium and other trace impurites enter then there could be problems.

Major cause of corrosion is due to leaching of alloying elements, like Cr, Ni, Mn etc from the tubing at sustained high temperatures due to phase diagram considerations.

a) cannot predict any angle for corrosion, unless the sodium is coming in at an angle, say at a bend or other geometry change.

b) the planar or cylindrical heat transfar coefficient may have to be changed to account for piting--depends on the concentration of pits and depth, radii etc.

c) use the log form for the cylinder ( must know the thickness)