Fluid and Thermal Analysis of LN2 Flowing Through Tubes of Cryostat System

Abstract

The steady state superconducting Tokamak (SST-1) is a medium size tokamak with super conducting magnet. The vacuum system is put for isolating superconducting coils from the ambient temperature and pressure. The vacuum system is called Cryostat. The cryostat is made up of SS 304 L materials in sixteen sectors with four panels of each sector. LN2 at 80 K is used to remove heat from these panels. Three out of four panels are maintained at 80 K temperatures. However, on inner cylinder panel 80 K temperature is not achieved. Design of system is precise for which 80 K temperature is mandatory at all panels for steady state operation.

This report is prepared for analysis of LN2 at 80 K flowing through tubes of 8 mm diameter. The panels on which tubes are mounted are trapezoidal, rectangle and cylindrical shapes. Heat fluxes are imparted on these panels. In this analysis heat radiated to each panel is estimated. Mass and velocity of flow at each panel is also estimated.

Pressure drop of LN2 flow on each panel is estimated. Two phase and single phase flow of LN2 are considered while estimating pressure drop. Pressure drop for two phase flow is calculated by homogeneous model. Along with two phase and single phase flow different layout are also considered for pressure drop estimation. Different layout which are required to consider are horizontal, vertical and bends.

Finite element analysis is done in Ansys CFD. Fluid flow and thermal analysis is done for this project. Initially analysis is carried out for 2.1 bars pressure and 80 K temperature at inlet of each panel. Analysis is done by varying properties of LN2 with temperatures. Properties of LN2 which vary with temperatures are density, viscosity, specific heat and conductivity. Inner cylinder panels are analyzed for different pressure starting from 2.1 bars and 80 K temperature to 4.1 bars pressure and temperatures remain same at inlet.

This report is also covered finite element analysis and it’s general features with capabilities of Ansys.