Vol. 2 No. 1 (2024)

Global warming, environmental pollution, and energy scarcity have emerged as significant problems for human society due to the swift advancement of modernization. Some of these problems may be resolved with research and applications of clean energy technologies. Readers can get helpful information about such studies from the nine excellent articles in this issue. In particular, this issue includes four review articles, four commentary articles, and one original research paper.

The airflow organization of the data center directly affects the temperature control performance and the energy efficiency of the cooling equipment. The servers at the bottom of the rack usually suffer from insufficient airflow rate and poor cooling effect. This is because of the limited distance between the bottom servers and the perforated floor, and the small horizontal velocity of the supply air flow. This study aims to improve the uniformity of the cooling airflow in the vertical direction of the rack by the air deflectors, thereby further improving the overall airflow organization in the data center. The size and installation of the deflectors in the data center were optimized according to both the experiment and numerical simulation results. From the results, it is recommended to install the deflector with a width of 100 mm at an angle of 45° under the perforated floor for the rack with the single-side airflow supply. For the rack with the double-side airflow supply, the width of the deflector should be 100 mm and installed at an angle of 30° to the perforated floor to achieve the best airflow distribution. Consequently, the intake airflow rate for the bottom servers significantly increased, and the occurrence of the local hot spots was effectively reduced. The numerical simulation of the airflow organization with and without the deflector was conducted by ANSYS. The results show that, the installation of the deflectors increased the inlet airflow rate for the rack by 16.98% and improved the energy efficiency of the dater center air conditioners by 1.98%.

Oily sludge is a common by-product of the petroleum exploration industry, which is rich in resources and has strong toxicity. It is categorized as hazardous waste in many nations worldwide. Owing to the distinct physical and chemical characteristics of sub/supercritical water, the application of hydrothermal conversion technology, which uses sub/supercritical water as a medium, has been growing in the utilization of resources and the safe disposal of oily sludge. In this article, the research on the oxygen-free hydrothermal transformation of oil sludge, including hydrothermal carbonization, hydrothermal liquefaction, hydrothermal upgrading, and supercritical water gasification, is reviewed. Due to the significant impact of nitrogenous and sulfurous compounds in sludge on hydrothermal conversion products, the hydrogenation conversion, reaction path, and kinetics for these two compounds were discussed. Finally, a summary and comparison of the studies conducted on carriers and catalysts in hydrothermal processes are provided. This review can offer recommendations for future studies, as well as guidance for the hydrothermal catalytic treatment of oily sludge.

As a result of the array of problems arising from the use of fossil fuels, it is necessary to develop and optimize alternative energy technologies. Despite hydrogen being an ideal form of energy, its primary source is still fossil fuels via conventional methods. Therefore, several hydrogen-production resources and techniques have been investigated, providing feasibility for clean and effective hydrogen production. This paper provided a mini-review of hydrogen production technologies, including renewable energy, chemical looping, water electrolysis, photocatalysis, and plasma.

With the maturity of hydrogen storage technologies, hydrogen-electricity coupling energy storage in green electricity and green hydrogen modes is an ideal energy system. The construction of hydrogen-electricity coupling energy storage systems (HECESSs) is one of the important technological pathways for energy supply and deep decarbonization. In a HECESS, hydrogen storage can maintain the energy balance between supply and demand and increase the utilization efficiency of energy. However, its scenario models in power system establishment and the corresponding solution methods still need to be studied in depth. For accelerating the construction of HECESSs, firstly, this paper describes the current applications of hydrogen storage technologies from three aspects: hydrogen production, hydrogen power generation, and hydrogen storage. Secondly, based on the complementary synergistic mechanism of hydrogen energy and electric energy, the structure of the HECESS and its operation mode are described. To study the engineering applications of HECESSs more deeply, the recent progress of HECESS application at the source, grid, and load sides is reviewed. For the application of the models of hydrogen storage at the source/grid/load side, the selection of the solution method will affect the optimal solution of the model and solution efficiency. As solving complex multi-energy coupling models using traditional optimization methods is difficult, the paper therefore explored the advantages of deep reinforcement learning (DRL) algorithms and their applications in HECESSs. Finally, the technical application in the construction of new power systems supported by HECESSs is prospected. The study aims to provide a reference for the research on hydrogen storage in power systems.

Cold plasma has been extensively studied and developed in the field of energy storage and conversion, with a focus on its ability to assist in catalyst synthesis, surface modification, the introduction of heteroatoms, the generation of defects and vacancies, the improvement of catalyst dispersion, and the reduction of particle size. In contrast to conventional calcination and chemical methods, the energy from cold plasma can be transferred directly to the catalyst and carrier during the treatment process, which can improve the interaction between the loaded catalyst and carrier by changing the internal structure and surface morphology of the catalyst. Therefore, these properties make cold plasma quite green, safe, and efficient for catalyst synthesis and modification. In this paper, the characteristics and applications of various cold plasma technologies, as well as the synergistic treatment of cold plasma technology with thermodynamic principles on catalysts, are analyzed. Based on current research progress, this paper provides a summary and outlook on the synthesis and modification of catalysts using cold plasma.

Adsorption-based water management and evaporative cooling personal thermal management (PTM) technologies offer great potential to achieve adaptive temperature regulation, wide applicability, and low energy consumption. However, designing high-performance and durable hygroscopic composites that combine efficient heat dissipation with wear comfort is a challenge. More recently, Xu et al. used two hygroscopic polymers and crosslinking strategies to develop moisture-absorbent fabrics with excellent hygroscopicity, durability, ductility, air permeability, washable resistance, and antibacterial properties. This work paved an intriguing PTM application prospect of an all-polymer hygroscopic composite to achieve energy-efficient moisture sorption and evaporative cooling.

Since the industrial era, the extensive use of fossil energy has led to a continuous increase in greenhouse gas emissions, thereby accelerating global warming. Cooling energy consumption represents a significant portion of total energy usage, accounting for approximately 20% of global energy consumption. Therefore, there is an urgent necessity to develop new cooling technologies that are low-energy consumption, highly efficient, and environmentally friendly to meet the growing demand for cooling.

Freshwater and electricity are foundational to human civilization's advancement. Yet, the duel against their scarcity intensifies as modernization progresses. Solar energy, hailed for its inexhaustibility and environmental friendliness, has emerged as a promising ally in generating both freshwater and electricity. Despite significant interest and strides in solar cogeneration, the challenge of enhancing both freshwater and electricity outputs concurrently has stymied broader application.

The energy balance between the earth (and its atmosphere) absorbing solar radiation and its radiation into space determines the equilibrium temperature of the earth’s surface. The process of the earth and its atmosphere as a whole radiating long-wave electromagnetic waves into space includes the transmission of surface radiation by the atmosphere, absorption, reflection, reverse radiation, and atmospheric radiation to space, etc. When the concentration of greenhouse gases such as CO₂ in the atmosphere changes, the absorption of surface radiation by the atmosphere also changes immediately, thereby changing the equilibrium temperature of the atmosphere and the surface. The relationship between equilibrium temperature and atmospheric CO₂ content, or so-called the earth’s climate sensitivity, is a focus of climate dynamics research.