Numerical Simulation of the Thermal and Fluid-Dynamic Behavior of a Cryogenic Capillary Tube

Abstract A 2D numerical model based on an axisymmetric geometry has been developed to simulate the behavior of the two-phase working fluid in a horizontal capillary tube. Numerical results have been compared with experimental results to validate the model. Fluid flow characteristics related to the liquid film and the bubbles shape have been reproduced and evaporation and condensation processes in the liquid film have been simulated. Furthermore, the heat transfer from the evaporator to the condenser through fluid oscillations has been verified and specific thermodynamic instabilities of the working fluid in pulsating heat pipes have been reproduced. Conversely, it appears that only thermal instabilities are not sufficient to maintain an oscillating two-phase flow in horizontal capillary tubes. Nevertheless, the model represents accurately the overall heat transfer phenomena and constitutes a first step for future 2D numerical simulations of horizontal pulsating heat pipes.