High population density, dense high-rise buildings, and impervious pavements increase the vulnerability of cities, which aggravate the urban climate environment characterized by the urban heat island (UHI) effect. Cities in China provide unique information on the UHI phenomenon because they have experienced rapid urbanization and dramatic economic development, which have had a great influence on the climate in recent decades. This paper provides a review of recent research on the methods and impacts of UHI on building energy consumption, and the practical techniques that can be used to mitigate the adverse effects of UHI in China. The impact of UHI on building energy consumption depends largely on the local microclimate, the urban area features where the building is located, and the type and characteristics of the building. In the urban areas dominated by air conditioning, UHI could result in an approximately 10–16% increase in cooling energy consumption. Besides, the potential negative effects of UHI can be prevented from China in many ways, such as urban greening, cool material, water bodies, urban ventilation, etc. These strategies could have a substantial impact on the overall urban thermal environment if they can be used in the project design stage of urban planning and implemented on a large scale. Therefore, this study is useful to deepen the understanding of the physical mechanisms of UHI and provide practical approaches to fight the UHI for the urban planners, public health officials, and city decision-makers in China.

Nanorefrigerant is a mixture of nanoparticles and pure refrigerant, which can increase heat transfer characteristics in refrigeration and air conditioning equipment. The performance of four different Al₂O₃ nanorefrigerants and their pure fluids (R600a, R134a, R1234yf, and R1233zd(E)) is analyzed in a vapor-compression refrigeration cycle. The enthalpy of a nanorefrigerant in the refrigeration cycle is calculated by using the prediction method based on the density of nanorefrigerant. A numerical model is established for the thermodynamic analysis, and the results show that adding nanoparticles to the pure refrigerant enhances heat transfer in heat exchangers, increases cooling capacity, reduces compressor power consumption, and finally improves the performance of the refrigeration system. The COP improvement of R1233zd(E) + Al₂O₃ nanorefrigerant is the highest, and the COP improvement of R134a + Al₂O₃ and R1234yf + Al₂O₃ are close to each other. When the mass fraction of Al₂O₃ nanoparticles increases to 0.30%, the COP of R1233zd(E) and R600a increases by more than 20%; the maximum exergy efficiency is 38.46% for R1233zd(E) + Al₂O₃, and the minimum exergy efficiency is 27.06% for pure R1234yf. The results provide a basis for the application of nanorefrigerants in the vapor compression refrigeration cycle.

Urban development always has a strong impact on the urban thermal environment, but it is unclear to what extent urbanization factors influence urban heat island intensity (UHII) in mountainous cities, and fewer studies have been conducted on the trends of long-term UHII in mountainous cities. Chongqing, as the only municipality directly under the central government in Southwest China and a typical mountainous city, is chosen as the case study. This study analyzed the interannual and seasonal variations of UHII based on the data from meteorological stations in Chongqing from 1959 to 2018 using the least-squares method and the Mann–Kendall test, and explored the relationship between urbanization factors (urban resident population, gross domestic product (GDP), fixed investments, and gross industrial output value) and UHII. The results show that the increasing rates of temperature in urban areas of Chongqing are significantly higher than those in rural areas affected by urbanization. Using the Mann–Kendall test, it is found that almost all abrupt temperature changes in Chongqing occurred after the rapid urbanization of Chongqing in the 21st century. The annual mean UHII increased from 0.1 °C to 1.5 °C during the study period, with summer making the largest contribution. It is also found that the UHII in Chongqing has increased year by year, especially after the 1980s. The increasing rates of UHII are larger at night and smaller during the day. The increasing trends of nighttime UHII are statistically significant, while those of daytime UHII are not. In addition, UHII and urbanization factors are found to be correlated using the grey relational analysis (GRA). Eventually, a comprehensive UHII index and a comprehensive urbanization index are constructed using principal component analysis (PCA). A tertiary regression model of UHII and urbanization index is established, which reflects that the UHII in Chongqing will continue to grow rapidly with the development of the city.

In recent years, there has been great interest in developing cooling systems with humidity- and temperature-independent control capabilities that can operate efficiently at varying temperatures. This paper proposes a bi-loop double-evaporator ejection–compression cycle, which utilizes low-grade heat and is suitable for the construction industry. The proposed cycle involves the concurrent operation of a vapor compression cycle and an ejector refrigeration cycle that enables it to handle altered pressure levels and operate with varying compression ratios all the way to a common condenser pressure. Conventional computational fluid dynamics (CFD) approaches often model steam as an ideal gas with single-phase flow. In contrast, this research employs the wet steam model to optimize ejector geometry. The wet steam model takes into account non-equilibrium water vapor condensation, thus providing a more precise assessment of spontaneous condensation behavior and its impact on ejector performance. When compared to the conventional dry gas model, the use of the wet steam model dramatically decreases the entrainment ratio error from 16.24% for single-phase steam to 3.92% when compared to experimental data. This study concentrates on four critical attributes of wet steam, including Mach number, droplet nucleation rate, average droplet radius, and liquid mass fraction, to develop a strategy for enhancing ejector performance and efficiency. The study demonstrates that optimal area and primary nozzle diameter ratios for the steam ejector are 5 and 2.4, respectively. Increasing the area ratio mitigates condensation intensity, thereby reducing the liquid mass fraction in the diffuser. Overall, this paper provides valuable insights into improving and optimizing ejector performance, thus highlighting the importance of considering the behavior of spontaneous condensation in ejector design and modeling.

Indirect evaporative cooling (IEC), which utilizes natural cooling sources, is an advanced and promising technology to reduce the energy consumption of cooling systems in a data center (DC). This study presents a model of an IEC air-conditioning unit in a DC using TRNSYS simulation software validated using actual operational data to investigate the adaptability of IEC units in data centers located in regions with varying humidity levels, providing a reference for their application and promotion in DCs. Based on this premise, the authors analyzed the meteorological characteristics of Urumqi (a dry region), Beijing (a region with medium humidity), and Shanghai (a region with high humidity), which are representative cities in different humidity zones. The analysis identified the annual operating hours of the unit’s three operation modes, including fresh-air indirect heat transfer (FAIHT), IEC, and hybrid. Simultaneously, the authors conducted a simulation of the unit’s yearly energy consumption and determined time change curves for annual energy consumption, hourly coefficient of performance (COP) throughout the year, and mechanical cooling in various locations. The results indicate that IEC air-conditioning systems are highly effective in promoting the efficiency of data centers in various humidity regions. Dry locations demonstrate the greatest adaptability, followed by regions with medium humidity and, finally, regions with high humidity. The findings indicate that IEC units provide significant energy efficiency and cost-effectiveness when deployed in typical urban DCs across various humidity zones in China. The average annual power-usage effectiveness (PUE) of each city’s DC utilizing the unit is less than 1.3, and the unit’s annual operational cost savings exceed 30%.

Double- and triple-walled ${\text{TiO}}_2$ /iron oxide nanotubes with well defined interfaces have been produced in nanoporous alumina templates using atomic layer deposition method. The structural properties of each individual layer are found to be dependent on the deposition temperatures. The outer layers of ${\text{TiO}}_2$ are polycrystalline and consist of a phase mixture of anatase and rutile, while the inner ${\text{TiO}}_2$ layers grown at lower temperature are amorphous. The iron oxide layers consist of pure hematite when deposited at $500°\text{C}$ , while a phase mixture of hematite and magnetite was obtained at $400°\text{C}$ . The magnetization measurements reveal that the studied nanotubes exhibit weak ferromagnetic behavior and magnetic anisotropy with an easy axis perpendicular to the tube axis.