A transient fluid-thermo-structural coupling study of high-velocity LN2 jet impingement on rocks

Abstract The high-velocity liquid nitrogen (LN2) jet is an efficient rock breaking method that can be applied in improving drilling rate and enhancing stimulation performances of fossil fuel and geothermal reservoirs. To determine the cooling effect during LN2 jet impingement, a transient fluid-thermo-structural coupling study was conducted in this paper. We adopted a loose coupling method in which the fluid domain and the structure domain are simulated by FLUENT and ABAQUS, respectively, and coupling quantities were exchanged across the fluid-structural interface in every real time increment through the Mesh-based Parallel Code Coupling Interface (MpCCI) server. The v2-f model was employed to calculate the flow field and heat transfer in the fluid domain, and changes of thermo-physical properties of fluid and solid with temperature were considered in the calculation. This model was validated by comparing the simulation results with previous experimental data. According to our simulation results, the velocity and turbulence intensity of LN2 jet are significantly greater than those of water jet under the same conditions. The process of high-velocity LN2 jet impingement can be divided into two stages: (1) the jet impact dominated stage and (2) the thermal dominated stage. In the former stage, stress distributions under the impacts of water jet and LN2 jet are similar. A compressive zone surrounded by a ring tensile stress zone is generated on the impact surface. In the latter stage, the compressive stress near the stagnation point transfers to tensile stress gradually under the effect of LN2 cooling. The LN2 jet induces higher tensile and shear stress in rock, and thus can achieve better rock-breaking performances than water jet. Increasing the rock temperature can further improve the stress magnitude in rock, which makes the rock-breaking performances of LN2 jet more significant.