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As a renewable energy source and potential substitute for fossil fuels, biodiesel plays an increasingly important role in both energy security and environmental protection. Accurate thermal conductivity data of biodiesels and their mixture with diesel are critical to engine design to achieve high combustion efficiency. This study measured the thermal conductivity of binary mixtures of heptane and biodiesel components, specifically methyl myristate, methyl laurate, and methyl caprate, over a temperature range of 298.15–328.15 K, using the two-wire 3ω method. Based on the experimental data, the effect of mass fraction, temperature, and carbon chain length of the fatty acid ester on the thermal conductivity was analyzed. The second-order Scheffé polynomial model, Flippov equation, Jamieson equation, and Chen equation were used to correlate the experimental data and compare to find a better one. The Flippov equation shows the lowest absolute average relative deviation of 0.80% for the binary mixtures of heptane with methyl myristate, methyl laurate, and methyl caprate.

In order to build Beijing into a world-class harmonious and livable capital city, its energy and environmental issues deserve special attention. Considering London’s experience and achievements in tackling smog crisis, New York’s world-class city positioning and influence, and Tokyo’s geographical and cultural characteristics, these three world-class megacities are taken as examples in this study for investigating and analyzing the establishment and optimization of an urban energy system which is clean, efficient, safe, and sustainable. The urban planning strategies, planning experience, and related energy policy of these three megacities for building low-carbon cities are reviewed and their enlightenment to Beijing is discussed. The study of international cases has a certain reference effect on the energy structure adjustment and urban planning practices related to Beijing’s construction of a low-carbon city.

Metallic nanowires (NWs) and their different compounds display incredible prospects for their use in various applications including media storage, sensor and solar cell devices along with the biological drug delivery systems. In this research work, the metallic NWs like nickel nanowires (Ni-NWs) are synthesized successfully by employing electrodeposition process. Anodic aluminum oxide (AAO) templates are employed as a platform with copper metal coating which acts as an active cathode. The synthesized Ni-NWs are examined through various characterization techniques including X-ray diffraction (XRD), scanning electron microscope (SEM) and vibrating sample magnetometer (VSM) to study the crystal structure, surface morphology and magnetic properties, respectively. The XRD analysis shows the development of various diffraction planes like Ni (111), Ni (200), Ni (220) which confirms the formation of polycrystalline nickel NWs. The SEM analysis reveals that the range of diameter and length of nickel NWs are found to be ∼160 to 200 and ∼4 to 11 micron respectively showing high aspect ratio (ranged from ∼200 to 300). The ferromagnetic behavior of Ni-NWs is confirmed by the hysteresis loop carried out for parallel and perpendicular configurations having Hc = 100 and 206 Oe, respectively. The obtained results suggest that the synthesized Ni- NWs may be used for high-density media storage devices.

Ionic liquids (ILs) are promising electrolytes or solvents for numerous applications owing to their unique properties. However, it is a challenge to design the ideal IL with the required properties. Variational autoencoders (VAEs) trained by significantly large datasets have shown good performance in drug discovery. However, low generation efficiency and small sparse datasets prevent their application on IL. In this work, we propose a high generation efficiency molecular design model for IL, which realizes multi-objective optimization on a small dataset. The model combines VAE, multilayer perceptron, and particle swarm optimization for property prediction and molecule optimization. The thermal conductivity and heat capacity of the ILs are chosen as a case to verify the advantages of our model. The results shows that by setting molecular validity judgments to optimization target, 98% output of our method are valid molecules. Besides, the heat capacity and thermal conductivity are improved by 39% and 15%, respectively. Our model improves the applicability to small sparse datasets and the generation efficiency of VAE-like generation model. By multi-objective design ILs for given properties, our model can provide guidance for the design and application of ILs.

Rural energy is related to the domestic energy supply, consumption, and improvement of living standards of more than one-third of the population in China. In the “14th Five-Year Plan,” it has been clearly pointed out that it is necessary to strengthen the clean utilization of coal and implement the construction of rural clean energy projects. At present, the energy consumption structure of rural areas in China is transiting from traditional solid energy to commercial energy and clean energy. Based on this background, this paper reviews the transition trend, influencing factors, and regional differences of China’s rural household energy consumption structure from the 1990s. Taking into account China’s goal of carbon peaking by 2030 and carbon neutrality by 2060, carbon dioxide and pollutant emissions generated in the process of energy consumption and the energy-saving potential of rural households are analyzed and discussed. Moreover, the evolution of rural energy policies in China is presented and related proposals are also made. This review aims to provide reference for relevant researchers and policy makers.

The supercritical CO2 (SC-CO2) thermodynamic cycle has been a promising and revolutionary technology. Related research has put higher demands on CO2 physical property calculations in terms of computational accuracy and speed. In this study, the deviations between the experimental data and predicted data calculated by several models of CO2 physical property calculation were obtained. According to the comparison results, the Span–Wagner equation of state, the Vesovic model, and the free-volume viscosity model are selected to construct a set of high-precision CO2 property calculation models. For the time-consuming problem of commonly used models, new models were developed by using the polynomial fitting and interpolation method, which improved the speed of the physical property calculation by five orders of magnitude while ensuring high accuracy. On this basis, a physical property calculation program for the SC-CO2 thermodynamic cycle could be developed, which can meet the demands of engineering applications in accuracy and calculation speed.

The coordinated development of the Beijing-Tianjin-Hebei region has become China's national strategy with great and far-reaching significance. The construction of Energy Internet is an important measure to strengthen the coordination of green energy development in Beijing-Tianjin-Hebei region and promote the development of renewable energy. In this paper, based on the development status of renewable energy in the Beijing-Tianjin-Hebei region, the problems and challenges existing in the renewable energy development in the Beijing-Tianjin-Hebei region and related considerations for their solution are reviewed and discussed. Energy Internet has also become a booster for the rapid development of clean and renewable energy. The policies on the Energy Internet Construction issued by Beijing, Tianjin, and Hebei during the 13th Five-Year Plan Period (2016–2020) and at the beginning of the 14th Five-Year Plan Period (2021–2025) are summarized. The focuses of all these policy documents are analyzed. The development status of seven Energy Internet demonstration projects in Beijing-Tianjin-Hebei region is reviewed. On this basis, some considerations on Energy Internet construction in the Beijing-Tianjin-Hebei region are analyzed and proposed.

Energy saving and environmental protection have become the core development concept of China construction industry. There are still a large number of old urban buildings in Beijing, whose energy consumption far exceeds the current building energy efficiency standards. The energy-saving renovation of these old buildings has been becoming the focus and difficulty of urban building energy-saving. In this paper, a calculation model based on the TNM Decree is proposed to calculate and analyze the energy consumption of heating and domestic hot water supply in winter before and after the renovation of old urban buildings in Beijing. The calculation results show that the thermal insulation performance of building envelope is a key factor affecting the energy consumption of old urban buildings. After the renovation, the energy-saving rate of the old urban buildings completed between 1978 and 1985 can reach 65.53%. The energy-saving rate of the buildings completed between 1986 and 1995 and that between 1996 and 2005 can reach 55.04% and 32.79%, respectively.

As a powerful tool to solve nonlinear problems, artificial neural network method (ANN) gets a wide range of applications in data regression. However, the overfitting often occurs during the ANN training process, which results in high accuracy of correlating the training data but poor prediction performance. At the same time, the principle of k-Nearest Neighbor method (kNN) makes it impossible to make an accurate prediction exceeding the range of the training data, but it can confine the overfitting of ANN. In this work, combining ANN and kNN, a new machine learning method called ANN-kNN combination method (AKC) for thermophysical property prediction of material is proposed. To evaluate the performance of AKC, we take the thermophysical properties of natural gas as an example. The inputs of AKC are temperature, pressure and the components of natural gas, the outputs are the compressibility factor, speed of sound and viscosity. AKC not only overcomes the overfitting problem but also needs less training data than ANN. The average absolute relative deviation of AKC for prediction are 2.5%, which are better than ANN (5.9%) and kNN (19.2%).

Aiming to investigate the rotation effect on the natural convection and heat transfer of nanofluid, which has an important application in the control of heat transfer, the velocity field and temperature distribution inside the square cylinder with the rotating heat source in the center were numerically studied and presented in detail at different Hartman numbers and aspect ratios using the immersed boundary-lattice Boltzmann method. Then, the average Nusselt number on the surface of the heat source was calculated to compare the heat transfer rate in different cases. The results showed that the rotation would reduce the effect of gravity on the flow and suppress the heat transfer between the rotating heat source and nanofluid, while the external magnetic field would reduce the rotation effect on the flow and suppress or promote the heat transfer depending on the rotational speed and aspect ratio. Moreover, the smaller aspect ratio of the heat source to the square cylinder would enhance the heat transfer rate and make the retarding effect of magnetic field on rotation more apparent. In addition, the dimensionless rotational speed was proposed in this work, by which much computational time could be saved during the calculation of the immersed-boundary lattice Boltzmann method for the problem of rotation.

Bus rides have become a routine choice for the large population to travel in Beijing. By the end of November 2020, 82.84% of all buses in Beijing had switched to electric vehicles. A solution to the problem of charging a huge number of battery electric buses (BEBs) in urban areas, especially in crowded cities with large populations, has to be found. In the present paper, a calculation model based on the levelized cost of electricity (LCOE) is established for comparison and analysis of the BEB charging. The calculation results show that the hybrid charging mode is economically feasible. Moreover, from the perspectives of optimizing operation shifts and responding to emergency situations, hybrid charging mode is applicable to the current electric bus system. The calculation results also show that the use of BEBs as the main ground public transportation in Beijing can substantially reduce CO2 emissions and save huge fuel costs. Its application is a very wise choice. The analogy calculation on Tongzhou District, the sub center of Beijing which is under construction, shows that the use of BEBs in Tongzhou can reduce CO2 emissions by about 34.6% on average compared with fuel buses. The population is the main influencing factor of analogy calculation.

The vibration analysis, based on the Donnell thin shell theory, of single-walled carbon nanotubes (SWCNTs) has been investigated. The wave propagation approach in standard eigenvalue form has been employed in order to derive the characteristic frequency equation describing the natural frequencies of vibration in SWCNTs. The complex exponential functions, with the axial modal numbers that depend on the boundary conditions stated at edges of a carbon nanotube, have been used to compute the axial modal dependence. In our new investigations, the vibration frequency spectra are obtained and calculated for various physical parameters like length-to-diameter ratios for armchair and zigzag SWCNTs for different modes and in-plane rigidity and mass density per unit lateral area for armchair and zigzag SWCNTs on the vibration frequencies. The computer software MATLAB is used in order to compute these frequencies of the SWCNTs. The results obtained from wave propagation method are found to be in satisfactory agreement with that obtained through the previously known numerical molecular dynamics simulations.