Multilayer structure is one of the research focuses of thermoelectric (TE) material in recent years. In this work, n-type 800 nm Bi₂Te₃/(Pt, Au) multilayers are designed with p-type Sb₂Te₃ legs to fabricate ultrathin microelectromechanical systems (MEMS) TE devices. The power factor of the annealed Bi₂Te₃/Pt multilayer reaches 46.5 μW cm⁻¹ K⁻² at 303 K, which corresponds to more than a 350% enhancement when compared to pristine Bi₂Te₃. The annealed Bi₂Te₃/Au multilayers have a lower power factor than pristine Bi₂Te₃. The power of the device with Sb₂Te₃ and Bi₂Te₃/Pt multilayers measures 20.9 nW at 463 K and the calculated maximum output power reaches 10.5 nW, which is 39.5% higher than the device based on Sb₂Te₃ and Bi₂Te₃, and 96.7% higher than the Sb₂Te₃ and Bi₂Te₃/Au multilayers one. This work can provide an opportunity to improve TE properties by using multilayer structures and novel ultrathin MEMS TE devices in a wide variety of applications.

This research seeks to investigate extremely efficient catalysts for the nitrogen reduction process (NRR), utilizing machine learning (ML)-aided density functional theory (DFT) computations. Specifically, we investigate dual transition metal atoms anchored on hexagonal nitrogen-doped graphene (TM₁-TM₂@N₆G) as prospective high-activity catalysts for the NRR. The findings indicate that the synergistic effect of dual transition metal atoms in the TM₁-TM₂@N₆G catalyst overcomes the intrinsic constraints of the linear relationship among intermediates, facilitating the activation and adsorption of N₂, thereby exhibiting significant potential for ammonia synthesis through N₂ reduction. Particularly, four catalysts screened by ML and DFT exhibit good stability and excellent selectivity and activation towards N₂. Among them, the catalysts Ti-Cr@N₆G, Ti-Mo@N₆G, and Ti-Pd@N₆G possess two reaction pathways with minimum reaction energies of 0.55 eV, 0.50 eV, and 0.40 eV, respectively. Remarkably, Ti-Co@N₆G, which features a single reaction pathway, exhibits a reaction energy lower than 0.05 eV, allowing the NRR to proceed spontaneously. It is noteworthy that incorporating ML into DFT calculations facilitates the rapid screening of all transition metal combinations, significantly accelerating the research on catalytic performance and optimizing the selection of catalysts.

Energy storage is essential for solar energy utilization, and thermocline storage tanks are commonly used. To improve temperature stratification and storage efficiency, we investigated the effect of different water distributor configurations on tank stratification. We numerically analyzed the heat storage processes in hot water tanks with three water distribution configurations: star, antenna, and octagonal. Temperature stratification was evaluated based on thermocline thickness and storage efficiency. Thermal storage efficiency improves by 0.45% when the outlet direction of the water distributor matches the fluid’s motion direction during natural stratification. The energy storage process is categorized into three stages based on efficiency changes, with different factors affecting efficiency at each stage. In the initial stage, antenna-type and octagonal water distribution improve temperature uniformity along the axial section, reduce thermocline thickness, and enhance stratification. Final efficiency during this stage is primarily influenced by energy loss resulting from the mixing of hot and cold water. In the development stage, energy storage efficiency decreases mainly because the lower boundary of the thermocline reaches the exit, causing partial discharge of hot water. Among the three configurations, the octagonal water distribution exhibits the lowest energy loss, 6.4% lower than that of the star-type distribution.

As one of the methods to extract geothermal energy, downhole coaxial heat exchanger is widely concerned because of its high heat extraction rate and no need of re injection. However, there are few studies on the extraction of open-loop heat from a single deep geothermal shaft, and there is a lack of detailed inlet and outlet transient temperature data. In this study, the downhole coaxial open-loop heat collector is improved, and the slotted liner at the bottom of the well is used to form a free open space to improve the heat exchange. Using the improved experimental device design, the field thermal recovery test was carried out in deep geothermal well of Shengli Oilfield, Dongying, China. According to the field test results, the control equation was established, and the influence of parameters on the thermal recovery rate was studied. It is found that the improved heat output is greater than the reported value of the downhole heat exchanger with the traditional structure. After about eight days, the heat extraction rate reached a gradually stable stage. After 15 days of continuous operation, the heat output is stable at 200 kW, and the water temperature at the water outlet is 34.6 °C.

Heat loss in steam injection pipelines is one of the primary causes of low thermal efficiency in heavy oil steam injection. To investigate the heat loss and heat transfer variation patterns in steam injection pipelines, a three-dimensional numerical model was established using Fluent software. The effects of overhead pipeline insulation parameters and environmental factors on heat loss and radial temperature distribution were analyzed. This study systematically quantifies the effects of sunlight radiation for the first time and proposes a heat loss correction equation for sunlight conditions. Additionally, overhead and buried pipelines were compared within the same modeling framework. The results show that selecting insulation materials with low thermal conductivity and increasing the insulation thickness can effectively reduce steam pipeline heat loss. For overhead pipelines, as sunlight radiation intensity increased from 0 W/m² to 800 W/m², actual heat loss decreased from 68.43 W/m² to 58.03 W/m². A sunlight-dependent effective heat transfer coefficient, h_Sunlight (E, T), was fitted to extend surface temperature heat loss calculations under sunlightt conditions, in which determination (R²) is 0.9951 and the average error is 5.57%. Under the same operating conditions, the heat loss of the buried pipelines was 62.59 W/m², which was 8.5% lower than that of the overhead pipelines. The findings provide a theoretical basis for the insulation design, thermal efficiency assessment, and operational optimization under sunlight radiation conditions of steam injection pipelines.

During heavy oil development, the gathering and transportation of low-temperature wellhead-produced fluids are often accompanied by high viscosity, pipe-wall deposition, and high flow resistance, threatening the continuous and stable operation of gathering systems. Existing studies on wellhead heating mainly focus on overall steady-state heating performance, while variable-flow heat transfer and start–stop control in local heating systems remain insufficiently explored. This study aims to evaluate the steady-state heating capacity, transient thermal response, and start–stop control performance of a localized electric heating section under variable-flow conditions. A 3D fluid–solid-coupled heat-transfer model of the heating element, pipe wall, and internal fluid was developed using COMSOL Multiphysics. The steady-state temperature field, transient heating and cooling behavior, and start–stop control characteristics were analyzed under different flow rates. The results show that, at a heating power of 15 kW and a flow rate of 20 m³/d, the maximum outer-wall temperature reached 564 K, and the average outlet fluid temperature reached 308.83 K, indicating effective heating performance. As the flow rate increased from 10 m³/d to 30 m³/d, the maximum pipe-wall temperature and fluid temperature rise both decreased, whereas the average fluid-side heat-transfer coefficient increased from approximately 700 W/(m²·K) to 1800 W/(m²·K), demonstrating enhanced convective heat transfer. Under a dual-threshold control strategy of 463.15–483.15 K, the system maintained the target temperature near 473.15 K under all tested conditions, while the load factor increased from 37.83% to 86.15%. These findings provide theoretical references and engineering support for optimizing power configuration and improving temperature control strategies in local heating systems for wellhead-produced fluids.