Hot dry rock (HDR) is an important geothermal resource and the primary direction of future geothermal development. Granite is particularly rich in radiogenic heat-generating elements (e.g., U, Th, and K) and is thus the main target for HDR development worldwide. Southeastern China contains the most abundant granite distribution in the country and accounts for more than 40% of the total granite area. This paper analyzes the rock radiogenic heat production, geothermal flux, crustal thermal structure, and reservoir temperature in the key exploration areas based on a systematic investigation of the distribution of granite resources and their heat generation characteristics. A heat generation and accumulation model of HDR resources is proposed for southeastern China. The results show that southeastern China can be characterized by a quadratic heat gathering model that includes a mantle source heat supply, intracrustal heat generation, fracture heat transfer, and cover heat preservation. Among these, the radiogenic heat production of granite is one of the main factors that affects shallow geothermal fields in this region. Fracture structure and cover conditions also exert a strong control on the gathering and dissipation of underground heat. The widely distributed and high-heat-producing tuffs and fused tuffs in the Zhangzhou area offer promising heat-generating and heat-gathering conditions for future exploration and development of hot dry rock resources in the area. The results provide important insight on the genesis and heat control factors of HDR resources in southeastern China and a theoretical reference for future HDR resource exploration and development practices in the region.

Unraveling the seepage and heat transfer coupled process between the working fluid and the fractured rocks in geothermal reservoir is of great significance to the exploitation and utilization of geothermal resources. In this study, based on the numerical modeling of fracture flow in geothermal reservoirs, the seepage and convective heat transfer behavior of fractured granite during geothermal extraction were investigated, and the effects of different fracture patterns, fluid injection temperature, and injection velocity on the temperature evolution of rock mass were comparatively analyzed. The results clearly revealed the influence of five different fracture patterns, i.e., single fracture, echelon fracture, parallel fracture, Y-shaped fracture, and crossfracture, on heat transfer capacity. Generally, the echelon fracture has the highest fluid outlet temperature, while the crossfracture has the largest total heat and shows the strongest heat transfer capacity. Besides the fracture shape, the fluid injection temperature and injection velocity also play significant roles in the heat transfer performance. The increase of fluid injection temperature would improve the total outlet heat of the crossfracture system and also benefit the system life. When the fluid injection temperature raises from 20°C to 35°C, the system life and the total outlet heat would be increased by 58.76% and 22.42%, respectively. However, higher fluid injection velocity would damage the system life of the geothermal reservoir, which obviously results in a decrease in total outlet heat. With the fluid injection velocity increasing from 0.004 m/s to 0.006 m/s, the system life could drop by 72.47%, and the total outlet heat was reduced by 55.72%. This work contributes to the preliminary understanding of the coupled seepage and heat transfer behavior in rock mass with various fracture patterns, and it could provide some practical implications for the rational exploitation of geothermal resources.

The surface morphology of rough fractures significantly affects the fluid flow and heat transfer characteristics in the fractures. A thermal-flow coupling model with specific geometric fractures was established to investigate the influence of surface morphology on the heat transfer characteristics of a single fracture. The effect of temperature on the physical properties of rocks and fluids was included in the study to reflect the actual situation more realistically. The research results show that the temperature of the fluid in the rough fracture is nonlinearly distributed along the flow direction and the higher the flow velocity, the higher the heat transfer efficiency. The fracture surface morphology has a significant impact on the heat transfer characteristics, and the surface fluctuation will greatly affect the flow velocity, causing the fluid temperature to change abruptly at the fracture surface. Under the same flow rate, with the increase of the fluctuation degree of the fracture surface and the fluctuation frequency, the larger the heat exchange area of the fracture surface, the stronger the heat exchange performance. The heat transfer efficiency of the fracture is directly related to the heat transfer area of the fracture, so even with the same permeability, the heat transfer performance of fractures with different surface topography is different.

As lunar exploration missions advance, the need for safe and sustainable in situ energy systems has become increasingly critical. This study investigates the thermoelectric performance of Bi₂Te₃-based thermoelectric materials under the natural temperature variations on the lunar surface, aiming to illustrate the potential of thermoelectric generation technology in power supply for a crewed moon base. A numerical approach was employed to assess the energy conversion behavior and optimize the geometric design of a thermoelectric module couple consisting of a P-leg and N-leg. The results indicate that Bi₂Te₃-based modules exhibit promising functionality under cryogenic conditions, highlighting their potential as an in situ power source during the long lunar night. Furthermore, geometric optimization was shown to significantly enhance the overall thermoelectric performance. The present study illustrates that TEG technology offers a viable pathway toward reliable energy generation in extreme lunar environments, supporting future mission sustainability.