Temporal and Spatial Evolution Laws of Temperature Effects in High-Velocity Liquid Nitrogen Jet Rock Breaking

Abstract

The high-velocity liquid nitrogen jet exhibits promising potential in the exploration and development of geothermal reservoirs, primarily attributed to its unique cryogenic properties. To investigate the temporal and spatial evolution laws of temperature effects in liquid nitrogen jet rock breaking, we formulate a three-dimensional numerical model employing coupled heat-fluid-solid theory. The simulation of the fluid and solid domains is conducted using Fluent and Structural, respectively. The influence of temperature variations on the thermo-physical properties of fluids and solids is considered. The flow field characteristics of water jets and liquid nitrogen jets are compared. Analysis focuses on the dynamic evolution of temperature gradients in rocks. The distribution characteristics of stress fields within the rock are further recognized. Moreover, a stress distribution volume ratio is introduced as an objective evaluation index to compare the areas of rock damage when subjected to cryogenic jets. Results indicate that the flow field of the liquid nitrogen jet exhibits a widespread distribution of high turbulent kinetic energy and a distinctive vortex ring structure. The former augments the heat transfer rate between liquid nitrogen and rock, while the latter disturbs the flow field. Under the influence of cryogenic jets, the temperature gradient of the rock displays significant non-uniformity. Maximum temperature gradients induced in rocks by liquid nitrogen and water jets are 185500 K/m and 33980 K/m, respectively. The temperature effect during rock breaking by liquid nitrogen jets emerges as a dominant factor in the distribution and evolution of the rock stress field. In comparison to water jets, liquid nitrogen jets exhibit a larger stress distribution volume ratio with a maximum value of 0.159, thereby demonstrating superior rock breaking performance. The key findings are expected to provide the mechanism of liquid nitrogen jet rock breaking more comprehensively, as well as theoretical guidance for engineering applications.

Keywords: Geothermal energy, Liquid nitrogen jet, Heat-fluid-solid coupling, Temperature gradient, Thermal stress