DESIGN OF A HELICAL COIL HEAT EXCHANGER FOR COOLING OF SUPERCRITICAL HELIUM
For operation of NbTi-based superconducting magnet, it is required to maintain at temperature about 5 K. To have efficient cooling of these magnet coils, supercritical helium (SHe) at operating temperature of ~5 K and pressure ~4 bar is required. SHe passes through the cables of magnets and removes heat loads which is carried through this SHe to the bath of liquid helium (LHe). The vapour generated in the LHe bath due to the heat loads of magnet system goes to the helium plant which further gets liquefied. The fluid properties at supercritical state vary with change in temperature and pressure which should be taken care during design of heat exchanger. To retrieve and reuse, the heat load carried by the supercritical Helium needs to be exchanged with the liquid Helium, resulting in boiling of LHe. A suitable heat exchanger would help to achieve the heat transfer between supercritical Helium and liquid Helium. A cold circulator is used for recirculation of SHe. Since the heat exchanger is kept inside a liquid Helium container housed in a cold box belonging to a Helium refrigeration and liquefaction plant, there are certain dimensional constraints involved in the design of required heat exchanger. Compact heat exchangers with less space consumption along with higher heat transfer surface area are preferred in such situations.
Helical coil heat exchangers falling under the category of compact exchangers are found to suit the purpose of cooling supercritical Helium at 4 bar from a proposed temperature of 5.2 K to 4.6 K using liquid Helium at 4.5 K and 1.2 bar