Abstract
The high-velocity liquid nitrogen jet exhibits promising potential in the exploration and development of geothermal reservoirs, primarily attributed to its unique temperature effect. However, the mechanism of the temperature effect in the rock breaking process of liquid nitrogen jets remains unclear. To address this issue, we develop a three-dimensional numerical model of jet rock breaking based on the coupled heat-fluid–solid theory. The simulation of the fluid and solid domains is conducted using Fluent and Structural, respectively. Using the multi-physics coupling interface of the Workbench platform, the flow field data are mapped to the solid domain to simulate the effect of liquid nitrogen on the rock. The characteristics of the flow field, the dynamic evolution of the temperature gradient, and the distribution of the stress field for water and liquid nitrogen jets are compared. A stress distribution volume ratio is introduced as an evaluation index for the rock damage area. 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 enhances heat exchange between liquid nitrogen and rock, while the latter disturbs the flow field. The temperature gradient of the rock under the cryogenic jet exhibits significant inhomogeneity and decreases continuously with increasing impact time. Maximum temperature gradients induced in rocks by liquid nitrogen and water jets are 185500 K/m and 33980 K/m, respectively. The temperature effect is the dominant factor in the stress field of rocks subjected to liquid nitrogen jets. 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. These key findings provide new insights into determining the effective range of temperature effects and evaluating rock damage.
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