Numerical investigation of heat transfer in the vertical annulus between pressure tube and calandria tube of the advanced heavy water reactor

In AHWR, calandria tube surrounds the pressure tubes. An annular gap exists between pressure tube and calandria tube. The gap is closed from top but is open from bottom. Due to differential temperature between pressure tube and calandria tube, air flow induced by natural convection may exist. The flow of air may lead to heat transfer from pressure tube (which is at high temperature due to contact with coolant) to calandria tube (which is at lower temperature due to contact with moderator). The quantification of heat transfer between pressure tube and calandria tube is numerically carried out with the help of CFD code - PHOENICS. CFD simulation involves numerical solution of the Navier-Stokes and energy equation. Validation of the CFD code with experimental results and some established computational work from the literature has been done in order to verify accuracy of the code. The natural convection phenomenon in the annular gap is then simulated. The velocity and temperature fields obtained from the CFD simulation are used to computed local and average heat transfer coefficients. Heat transfer coefficient for various pressure tube temperatures is computed. The effect of presence of water on heat transfer in the annular gas is also studied. (author)