Liquid nitrogen freezing reduces the temperature of environmental soil layer by boiling heat absorption and convection heat transfer of liquid nitrogen in the freezing pipe, and quickly freezes the water in the soil to form a freezing curtain with supporting effect. Compared with the traditional brine freezing technology, the freezing temperature of liquid nitrogen is extremely low, the temperature field is not uniformly distributed, and there are more factors affecting the freezing effect, while the heat exchange of liquid nitrogen freezing process lacks of study. Based on the theory of convective heat transfer, the freezing energy exchange process in the pipe is analyzed, the convection heat transfer coefficient of liquid nitrogen heat absorption is calculated, and the characteristics of the freezing temperature field of liquid nitrogen is simulated. Combined with the field measured data, the reverse heat transfer analysis of the liquid nitrogen convective heat transfer coefficient is carried out, which reduces the calculation error of the convective heat transfer coefficient. The study results show that the liquid nitrogen absorbs heat mainly by boiling heat absorption of liquid nitrogen and convective heat transfer of low-temperature nitrogen. The simulation of the freezing temperature field of liquid nitrogen based on convective heat transfer theory and its heat transfer coefficient needs to consider the change of heat transfer coefficient with freezing time and freezing depth, and a constant heat transfer coefficient cannot accurately reflect the whole process of convective heat transfer, which will lead to the difference between the temperature decline trend and actual measurement during the active freezing period and maintenance freezing period, and between the simulated temperature and actual temperature, the temperature obtained by calculation is relatively low. The freezing time is divided into 16 time periods and the freezing space is divided into 4 areas. The non-uniformity correction of the heat transfer coefficient is carried out to make the heat transfer coefficient a variable that changes with the freezing time and space, which not only conforms to the reality but also reduces the error, and it is more consistent with the practical engineering measured data. The research results can provide theoretical basis and technical reference for similar liquid nitrogen freezing projects.
