Study on characteristics of temperature variation of coring tube wall during gas content determination process

In order to determine the reasonable dosage of freezing required in the process of coal mine freezing and coring, the key to solve the problem is to study the temperature characteristics of the tube wall during the coring process. Based on the self-developed automatic temperature measuring device for coring tube,the coring tube wall temperature test was carried out at the coring depth of 5, 20 and 40 m (lower tube stage, cutting stage, and retraction stage). By establishing the heat transfer model of the tube wall of the coring tube, the inverse problem of two-dimensional unsteady heat conduction was solved based on the sequential function method, and the temperature change law of the tube wall during the coring process was verified and analyzed. The results showed that in the tube lowering stage, when the coring depth was larger (40 m), the temperature of coring tube rose rapidly. In the cutting stage, at different coring depths, the temperature of the coring tube began to rise rapidly after a period of cutting, and reached the highest value at the end of the cutting. In the withdrawal stage, the temperature drop rate of coring tube was basically the same, and it was in a slow cooling state. The simulated temperature of the reconstructed core tube wall by using sequential function specification method was in good agreement with the field measured temperature, and the error was small.The research results can provide a reference for the development of low-temperature freezing and coring device for the determination of coal seam gas content.