•Solar radiation, airflow, and ambient heat are collaboratively integrated for desalination.•The salt rejection is avoided through separated construction and brine circulation.•Structural engineering ...of evaporator and device is applied for enhanced airflow utilization.•Balanced water supply and ventilation are achieved with optimized spacer fabric.
Solar steam generation (SSG) is a sustainable way to drive seawater desalination and wastewater purification with green environmental energies including solar radiation, ambient heat, and airflow. Airflow is ubiquitous in outdoor environments, however, the utilization of airflow for accelerated evaporation through structure engineering remains unclear. Herein, environmental energies are efficiently utilized in an integrated way with the rational design of 3D spacer fabric. Carbon fiber bundles with broadband photothermal conversion ability and Tencel yarns with superior hydrophilicity are fabricated into the 3D spacer fabric. The stereoscopic airflow channel, wide evaporation surface area, and separated layers are constructed to optimize airflow pathways. Heat loss is reduced through the accelerated evaporation cooling effect. Extra ambient heat is harvested for cold evaporation by efficient airflow utilization. The evaporation rate of 3D spacer fabric reaches 5.15 kg·m−2·h−1 under a convective airflow of 3.5 m·s−1, which is twice the rate of traditional plain fabrics. The outstanding salt resistance is realized due to the separate design of photothermal and water supply layers as well as the continuous water circulation. The structural engineering of condenser devices is also investigated for enhanced airflow utilization. Overall, this work presents an effective and comprehensive multi-energy harvesting strategy to achieve rapid and durable SSG for practical clean water production.
Air movement dries surfaces by increasing evaporation and convection, which may prevent mould growth. Cladosporium sp. is used as the test organism (dominant fungi in the envelope of rural houses in ...hot summer and warm winter areas), and the effect of fans on inhibiting mould growth on building materials is investigated. Surface mould growth on materials was simulated and compared after rain leakage and surface condensation, and spore germination was studied in high humidity, with or without airflow. The results are as follows: (1) Airflow has an evident inhibitory effect on mould growth on wet building materials. This observation was linked to the availability of moisture content in the building materials. (2) Airflow can slow the appearance of visual mould on the material surface. Mould did not appear on the gypsum surface due to the airflow, and mould growth on a wood surface was delayed for about two days. (3) Periodically, spore eluates were examined by electron microscopy to determine the stage of spore germination, and it was found that airflow delayed mould spore germination for about 2–3 days.
The aeroelastic flutter characteristics of a functionally graded carbon nanotube reinforced composite (FG-CNTRC) truncated conical shell under simultaneous actions of a hydrostatic pressure and yawed ...supersonic airflow are scrutinized. The nonlinearity in geometry of the conical shell is considered in Green–Lagrange sense and the model is derived according to the Novozhilov nonlinear shell theory. The aerodynamic pressure is modeled based on the quasi-steady Krumhaar’s modified supersonic piston theory by considering the effect of the panel curvature and flow yaw angle. Parametric studies are conducted to investigate the effects of boundary conditions, semi-vertex angle, distribution and volume fraction of CNT, Mach number and airflow yaw angle on the stability boundaries and flutter characteristics. The results show that the semi-vertex angle and CNT distribution may alter the stability boundaries. It is also found that the aeroelastic flutter responses of the structure can be significantly improved through a functionally graded distribution of CNT in a polymer matrix. Moreover, the aeroelastic characteristics of the FG-CNTRC truncated conical shell are found to be very sensitive to geometrical parameters and the airflow yaw angle. The results of this study shed a light into developing and using ultra-high-strength and low-weight composites reinforced with CNT for aerospace applications.
This paper focuses on the micro-environment around a human body, and especially on its interaction with the surrounding environment. Research on the free convection flow generated by a human body ...(including the convective boundary layer around the body and the thermal plume above the body), its interaction with external invading flows and the resulting heat- and mass transfer, all of which are important for thermal comfort and inhaled air quality, is discussed. The benefit arising from control of the airflow interaction in the micro-environment, in terms of thermal comfort and inhaled air quality, is demonstrated by several methods that are applicable in practice.
•Human body micro-environment, convective flow, heat- and mass exchange are discussed.•The airflow interaction in the vicinity of the human body is complex and important.•Control of airflow interactions can improve thermal comfort and inhaled air quality.
An aerated hopper with pulsated aeration was designed to study the effect of square‐wave pulsated airflow on the discharge characteristics of cohesive and non‐cohesive powders. Experiments were ...carried out with pulsation frequencies between 0 (continuous) and 50 Hz. Two flow patterns were observed at different aeration rates and pulsation frequencies: intermittent and smooth. For non‐cohesive powders, pulsated aeration has a worsening effect on discharge flow. For cohesive powders, results revealed that pulsated aeration can reduce the minimum aeration necessary to allow continuous discharge. And the maximum discharge rate that can be attained applying pulsated aeration is higher than that of continuous aeration and it is significantly more uniform. The aggregates size of the powder was estimated and used to understand the stabilizing mechanism of pulsated aeration on the aggregative discharge. The model value of the minimum aeration rate and the discharge rate were obtained and compared with the experimental values.
•The Miller cycle and variable valve timing are used in a DI hydrogen engine.•The effects of variable valve timing on the airflow exchange process are analyzed.•The engine can reach 42.22% maximum ...brake thermal efficiency.•Positive effects of exhaust valve timing on a DI hydrogen engine cannot be ignored.
The favorable physicochemical characteristics of hydrogen make it an excellent alternative fuel for IC engines. Compared with hydrogen port injection, hydrogen direct injection provides multiple degrees of freedom for injection strategies and mixture formation, which can effectively suppress abnormal combustion and enhance engine performance. Variable valve timing (VVT) and the Miller cycle, as advanced and effective means of improving engine performance, are less investigated based on a direct-injection (DI) hydrogen engine. Hence, to optimize the performance of a DI hydrogen engine, strategies of the Miller cycle and VVT are introduced. In this work, a 1.5 L direct-injection engine with a VVT system was employed to evaluate the effects of the Miller cycle, intake valve closing (IVC) timing, and exhaust valve opening (EVO) timing on the airflow exchange process, in-cylinder charge characteristics, heat release process, dynamics and emission characteristics. The engine speed was stabilized at 1400 rpm and the strategies of lean combustion and late injection were used. The main results are as follows. As the IVC timing is delayed, the ratio of pumping mean effective pressure to indicated mean effective pressure (PMEP/IMEP) first decreases and then slightly increases, and the engine tends to achieve a high level of brake thermal efficiency (BTE) when PMEP/IMEP is lower. The optimization of intake and exhaust VVT can shorten combustion duration and reduce cyclic variation by increasing volumetric efficiency and improving mixture distribution at ignition timing. Furthermore, the engine reaches 42.22% BTE and a high level of brake mean effective pressure by the cooperative control of IVC and EVO timing. NOx emissions can be controlled below 100 ppm by employing the synergistic effect of the Miller cycle and VVT. It is worth mentioning that exhaust VVT as a way to compensate for the performance of the DI hydrogen engine with the Miller cycle should not be ignored.
This paper presents an experimental study of basic cross-ventilation flow characteristics that are essential inputs for accurate natural ventilation modelling and design. The study focuses on a ...generic single-zone building model tested in a wind tunnel under isothermal flow conditions (wind-driven ventilation). An advanced experimental method based on particle image velocimetry (PIV) was developed to investigate the air velocity field in buildings with cross-ventilation. It was found that airflow patterns in rooms with cross-ventilation are complex and cannot be predicted by simplified macroscopic models such as the orifice equation. Inlet-to-outlet ratio and relative location of openings on a building façade are important parameters to be considered, in addition to the wall porosity. This study provides new insights that enable improved design and control of operable façade elements to enhance space cooling using natural ventilation.
Collapse has consistently posed a critical bottleneck in the laser penetration welding of thick plates. This study proposed a novel method involving the application of bottom airflow to suppress ...collapse. The suppression mechanism was elucidated through high-speed imaging and numerical simulations, and effects of airflow on the microstructure and properties of welded joints were clarified. Firstly, during the welding process, the keyhole underwent periodic changes in a "penetration-closure-penetration" cycle. With the application of bottom airflow, the cycle duration was reduced from 5 ms to 0.4 ms. The more frequent opening of the keyhole facilitated the timely release of pressure and heat from within the molten pool, thereby avoiding the downward movement even the loss of melts. Secondly, the application of bottom airflow provided an upward force of approximately 7.7 mN at the backside of the molten pool, compensating for insufficient surface tension and helping to further suppress the downward collapse of the molten pool. Finally, the bottom airflow introduced beneficial disturbances in flow and cooling, refining the bainite and enhancing the strain degree in ferrite. The changes contributed to strengthen the tensile properties of the welds. This study validated the effectiveness of bottom airflow in suppressing collapse during laser penetration welding, offering a significant solution to this technical bottleneck and presenting a new approach for large-scale equipment manufacturing.
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•The collapse defects were suppressed by applying the following bottom airflow.•Interactions between the bottom airflow, keyhole and molten metal were analyzed.•Suppression mechanism was clarified based on the cyclic behavior of molten pool.•Side effects of bottom airflow on microstructure and performance were elucidated.
Particulate matter (PM) is one of the most severe air pollutants and poses a threat to human health. Air filters with high filtration efficiency applied to the source of PM are an effective way to ...reduce pollution. However, many of the present filtration materials usually fail because of their high pressure drop under high‐velocity airflow and poor thermal stability at high temperatures. Herein, a highly porous Si3N4 nanofiber sponge (Si3N4 NFS) assembled by aligned and well‐interconnected Si3N4 nanofibers is designed and fabricated via chemical vapor deposition (CVD). The resulting ultralight Si3N4 NFS (2.69 mg cm−3) processes temperature‐invariant reversible strechability (10% strain) and compressibility (50% strain), which enables its mechanical robustness under high‐velocity airflow. The highly porous and aligned microstructure result in a Si3N4 NFS with high filtration efficiency for PM2.5 (99.97%) and simultaneous low pressure drop (340 Pa, only <0.33% of atmospheric pressure) even under a high gas flow velocity (8.72 m s−1) at a high temperature (1000 °C). Furthermore, the Si3N4 NFS air filter exhibits good long‐term service ability and recyclability. Such Si3N4 NFS with aligned microstructures for highly efficient gas filters provides new perspectives for the design and preparation of high‐performance filtration materials.
An ultralight α‐Si3N4 sponge assembled by highly aligned nanofibers is constructed via a chemical vapor deposition (CVD) process. It demonstrates high compressibility and stretchability over a large temperature range, with a low pressure drop and over 99.97% efficiency for particulate matter (PM) filtration even at a high temperature and high flow rate. In addition, it can be reused and put into practice.
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