Thermal fluid coupling simulation and optimization of downhole baffle heater adapted to Tar-rich Coal in-situ...

The downhole heater is a crucial equipment for realizing the in-situ pyrolysis process of Tar-rich Coal. The different structural performances of heaters can also affect the heat transfer effect underground. The article investigates the comprehensive heat transfer performance of circular horizontal baffle and spiral baffle heaters through digital modeling and simulation. The distribution characteristics of flow velocity, heat transfer coefficient and wall temperature of the heating tube, as well as the pressure drop in the shell side, were investigated for two types of heaters within a mass flow rate of 0.00693-0.05542 kg s^-1. The variation patterns of the Nusselt number and thermal resistance coefficient of the two type heaters under different mass flow rates were analyzed. The results showed that compared to the spiral baffle heater, the Nusselt coefficient of the circular baffle heater decreased by 3.82%, 10.75%, 0.73%, and 8.45%, respectively, at mass flow rates of 0.00693 kg s^-1, 0.01386 kg s^-1, 0.02078 kg s^-1, and 0.03464 kg s^-1, while the thermal resistance coefficient increased by 2.33%, 10.62%, 0.98%, and 7.59%. This indicates that the helical baffle heater is more suitable for the process parameters of in-situ pyrolysis of Tar-rich Coal. Based on numerical simulation results, a prototype of a spiral baffle heater with a pitch of 110 mm was fabricated. Gas heating experiments were conducted at corresponding mass flow rates of 0.00693 kg s^-1, 0.01039 kg s^-1, and 0.01386 kg s^-1. The results indicate that the temperature values obtained from numerical simulation analysis are essentially identical to the actual experimental temperature data, with an average error of <  ± 7% for the heater outlet temperature. This proves the accuracy and reliability of the numerical simulation analysis.