# Numerical Heat Transfer Simulation of Oil Shale Large-Size Downhole Heater
## 5 Conclusions  
The numerical heat transfer simulation of a large-size downhole heater was performed under a number of parameter settings, and the simulation findings essentially met the research target of injecting a huge flow of high-temperature gas into the well. As a result, only the conditions simulated in this research can yield the following conclusions:Upon injecting gas into the heater, the gas temperature rapidly increases due to the absence of helical baffle constraints at the gas input, leading to enhanced heat transmission. As the gas temperature rises, it essentially reaches the temperature required for oil shale maturation at the output. Heat accumulates on the surface of the heating rod as the temperature gradient with the gas decreases. Lowering the heating power while increasing the injected gas flow rate can reduce the distribution area and density of high-temperature hot spots on the heating rod's surface. In practical working conditions, the authors believe that reducing the heating power of the heating rod is more feasible.
2. The gas heating rate at the outlet exhibits two stages, with a diminished temperature rise as the shell length increases and a theoretical maximum value for the heater's outlet temperature. An energy exchange balance between heating power and injected gas flow rate ensures more efficient energy utilization and extends the heater's service life. As a result, the outlet temperature, also referred to as the actual temperature, cannot surpass the theoretical temperature in this operational situation.
3. The pressure distribution in the shell decreases linearly. Gas viscosity gradually increases as the gas flow channel lengthens. Simultaneously, the local differential pressure resistance and frictional resistance of the heater in the well increase, causing a further decline in the flow rate of the injected gas. Adopting \(h/\Delta p^{\frac{1}{3}}\) as the heat transfer performance evaluation index, it was found that the optimal heat transfer performance was attained at 100 m\({}^{3}\)/h. However, heat transfer performance was notably impacted by heating power at 200 m\({}^{3}\)/h, with the former surpassing the latter by approximately 6%. Moreover, heat transfer performance was most stable at 160 m\({}^{3}\)/h.
4. The gas heating stage of the heater was characterized by a rapid warming stage, a steady warming stage, and an over-heating stage, determined by the temperature distribution and temperature change on the surface of the heating rods. Due to the larger size of the heater, a greater volume and area can be utilized for the heating rods, enhancing the heater's heating performance. Controlling the flow rate of the injected gas and the heating power enables efficient in situ heating of the oil shale.  
Conceptualization, Q.B. and Q.L.; software, Q.L.; validation, X.L., Q.L. and Q.B.; formal analysis, X.L.; investigation, Q.L.; resources, Q.L.; data curation, Q.B.; writing--original draft preparation, Q.B.; writing--review and editing, Q.B.; supervision, X.L.; project administration, X.L.; funding acquisition, Q.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Key R&D Program of China (Grant No.2019 YFA0705502, Grant No.2019 YFA0705501), the Young and Middle-aged Excellent Team Project for Scientific and Technological Innovation of Jilin Province of China (Grant No.20220508135 RC), the Independent Innovation Capacity Project of Jilin Province Development and Reform Commission (Grant No.2022C021) the Program for JLU Science and Technology Innovative Research Team (Grant No.2020 TD-05), and the Fundamental Research Funds for the Central Universities.  
Not applicable.  
The data provided in this study can be provided at the request of the corresponding author. Due to the involvement of subsequent research progress, the data has not been made public.  
The authors declare no conflicts of interest.