Design of Finned-Tube Assembly for Frozen Seal Valve

摘要

Special type of Valves are used to control High temperature sodium flow in secondary sodium system of FBR (i.e.) to isolate steam generators from sodium flow during its maintenance. These valves are known as frozen seal butterfly valves. A circular disc perfectly fitted in the valve seat provided in sodium pipes. The disc is attached to a cylindrical stem to provide stroke. The stem is covered by a sheath which itself attached to the sodium pipe line. There is an annular gap provided between the stem and sheath. Due to the pressure of secondary sodium line, sodium raises through this annular path. To avoid sodium leak through the gland of the valve, liquid is forced to freeze the annular path while it's raising. To promote this phenomena, heat transfer through the sheath needed to the augmented. This is achieved by providing the circular fins attached to the outer surface of the sheath. However large number of fins are uneconomical, fins of larger diameter reduce its efficiency. Hence the number of fins, geometry and its spacing should be optimum to freeze the sodium in the annular path while it's raising but before to reach the gland of the valve. This paper explains the mathematical modelling of the fins and its optimization to obtain better thermo-dynamical efficiency.