To study the influence of hydrogen mixing ratio on the leakage of natural gas pipelines, a mathematical model for the leakage and diffusion of directly buried high?pressure hydrogen mixed natural gas pipelines was established based on computational fluid dynamics theory and numerical simulation method.The leakage status, volume fraction distribution of hydrogen mixed gas,and the distribution of soil pressure and gas velocity around the pipeline were analyzed under different hydrogen mixing ratios.The results show that with the increase of hydrogen mixing ratio, the explosion radius of hydrogen mixed gas in the atmosphere will gradually decrease,and the range of high?pressure area around the pipeline will gradually decrease,and the gas flow rate at the leakage port will gradually increase.When the hydrogen mixing ratio is 30%,the explosion radius in the atmosphere is reduced by 43%,and the gas flow rate at the leakage port is increased by 68%.This provides a theoretical reference for the safety and emergency repair of hydrogen?doped natural gas pipelines and has important practical significance for promoting the large?scale application of hydrogen?doped natural gas.

This paper proposed a method to improve the safety of shell and tube heat exchangers by adding a heat insulation layer at the inlet end of the heat exchange tube. Based on the SIMPLE algorithm, the transient change model of end temperature difference of three?dimensional shell and tube heat exchanger was established, and the effects of the changes of insulation thickness and insulation material on the safety of heat exchanger were compared. The results show that the temperature difference between the two sides of the heat exchange tube is significantly reduced when the pipe end insulation layer is installed, regardless of the material of the pipe end insulation layer; The greater the thickness of the insulation layer at the pipe end and the thermal conductivity of the insulation material, the greater the reduction of temperature difference, instantaneous thermal shock stress and temperature difference thermal stress on both sides of the heat exchange tube, and the higher the safety of the heat exchanger; When the thickness of the pipe end insulation layer is 247.5 mm and the thermal conductivity is 2.090 0 W/(m?K), the maximum instantaneous temperature difference on both sides of the heat exchange pipe can be reduced by 10.1%, the maximum temperature difference can be reduced by 12.5% during stable operation, and the instantaneous thermal shock stress and temperature difference thermal stress can be reduced by 10.1% and 12.5%.