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A mathematical model based on heat and mass transfer processes in the porous wick of electronic cigarettes was established to describe the atomization of e-liquids according to max liquid temperature, vaporization rate and thermal efficiency in a single puff. Dominant capillary-evaporation effects were defined in the model to account for the effects of electrical power, e-liquid composition and porosity of the wick material on atomization and energy transmission processes. Liquid temperature, vaporization rate, and thermal efficiency were predicted using the mathematical model in 64 groups, varying with electrical power, e-liquid composition and wick porosity. Experimental studies were carried out using a scaled-model test bench to validate the model’s prediction. A higher PG/VG ratio in the e-liquid promoted energy transfer for vaporization, and the e-liquid temperature was comparatively reduced at a relatively high power, which was helpful to avoid atomizer overheating. Compared with the other factors, wick porosity affected the thermal efficiency more significantly. The vaporization rate increased with a higher wick porosity in a certain range. The modelling results suggested that a greater wick porosity and a higher PG ratio in e-liquids helped to improve the overall thermal efficiency.

Personalized ventilation (PV) has significant potential in improving inhaled air quality, accommodating individual thermal preferences, and reducing energy consumption. However, the performance of PV system is greatly dependent on the structure of the supply air terminal device (ATD) and the resulting airflow patterns. In this study, we introduce a novel PV system equipped with a coaxial double air outlet, designed to achieve a specific velocity profile by modulating the flow rates from both internal and external outlets. The performance of this PV system is investigated using CFD (Computational Fluid Dynamics) simulations in a typical office room with mixing ventilation (MV). To accurately reflect the airflow distributions around occupants, a life-size computational thermal manikin (CTM) is employed. This paper studies the influence of different flow ratios (e.g., 0-1) of the ATD on the inhaled air quality and local thermal comfort of occupant. The results demonstrate that optimizing the velocity profile to a “top-hat” distribution can improve ventilation effectiveness by about 10% compared to a uniform velocity distribution. This study provides valuable references for designing PV systems in different application scenarios.

Human talks, coughs, and sneezes are the primary routes for airborne diseases such as COVID-19. The understanding of the propagation characteristics of these respiratory events is essential to estimate the infection risk of indoor airborne transmission. Turbulent vortex ring structures have been found in the human exhaled flow by using schlieren imaging technique and Direct Numerical Simulation (DNS). In this context, the traditional circular free air jets formula could not accurately predict the transmission distance of the turbulent flows and carried droplets. This paper systematically reviews the correspondences between jet morphologies and stroke ratios. Based on theories of traditional jets and vortex motion, theoretical analysis is conducted to compare the propagation characteristics of exhaled flow with steady jet, starting-interrupted jet, puff and vortex ring morphologies. Calculation results confirm that the vortex ring exhibits lower energy loss, enhanced resistance to disturbances, and longer transmission distances compared to traditional jets, which introduces new characteristics in terms of short-range transmission caused by exhaled flows. Future study could incorporate numerical simulation methods to further investigate the internal structural evolution of exhaled flow to deepen the understanding of the mechanisms of indoor airborne transmission.

Urban overheating caused by urban heat island (UHI) effect has a negative impact on energy consumption, human health and urban air quality. This interaction between the approaching and the buoyancy-driven flows significantly alters the flow patterns around the building, consequently impacting the ventilation and dispersion of pollutants in urban areas. This paper utilized large eddy simulations to investigate the effects of buoyancy flow on the flow field around an isolated cubic building with heated surfaces. Wind tunnel experiments were also conducted to validate the simulation results. Under low wind speed conditions, the study utilized Richardson numbers ( Ri) to quantify the relative contribution of forced convection and buoyancy flow. The Ri ranged from 0 to 4.00, indicating a transition in the flow field from being predominantly influenced by forced convection to being predominantly influenced by mixed convection. The windward, leeward, and all walls of the building were heated individually and compared with an isothermal building. The velocity, temperature and turbulent kinetic energy field were analysed. Significant changes in the flow field characteristics were observed under low Reynolds numbers and high surface temperatures. The thermal effects on the flow patterns led to variations in the length of the reattachment and recirculation zone.

Coughing is one of the major routes for the transmission of respiratory diseases in indoor environments. Previous studies have shown that coughing can form vortex ring structures. However, the conditions under which cough-generated vortex rings form, as well as the influence of boundary condition on the formation and flow characteristics of these vortex rings, remain inadequately understood. This study investigates the effects of three velocity profiles (real-cough, sinusoidal, and pulsation) and five outlet shapes (real-mouth, circular, square, rectangular, and elliptical) on the flow dynamics of cough jets. The results show that the penetration distance of cough-generated vortex rings ranges from 0.56 to 0.68m in 0.5s. Separated (or deviated) vortex rings show a power-law distribution in the cough jets: s ~ t 2/3 (or s ~ t 1/2 ) during the initial stage and s ~ t 1/3 (or s ~ t 1/5 ) during the interrupted stage. Due to the differences between the power-law and existing studies, short-distance infection risk assessment models require further revision. Furthermore, the real-mouth, circular, and square have a relatively minor effect on the formation of saturated vortex ring compared to velocity profiles. The formation conditions for saturated vortex rings can be determined by a dimensionless energy αlim= 0.2±0.06.

The integration of heat pump technology into sludge drying combines heat pumps with traditional convective drying techniques. The process of moisture and apparent morphology changes during sludge convective drying is succinctly summarized from literatures. The analysis also covers the effects of drying conditions, including temperature and airflow velocity, on the energy consumption of heat pump drying. Leveraging the precise and independent control capabilities of heat pump dryers, various heat pump intermittent drying methods are compared. By adjusting drying conditions at different stages of sludge drying, a balance can be achieved between rapid external moisture diffusion and reduced energy consumption of the heat pump system.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can be transmitted through fecal aerosols in building drainage pipes (BDS) has been demonstrated, so there is an urgent need to understand its specific transmission pathways and mechanisms. This paper reviews the two periods of vertical transmission of aerosols in BDS: airflows caused by pressure fluctuations during toilet flushing and airflows induced by the chimney effect. Subsequently, recent advances in research methods and factors affecting the vertical transmission of aerosols in BDS are discussed. Finally, we conclude the vertical transmission pathway of aerosols in BDS as “bathroom - drainage pipe - failed floor drain – bathroom”. Additionally, more consideration needs to be given to the driving force brought on by the chimney effect when the transient pressure created by toilet flushing dissipates. Further study is imperative to establish a quantitative understanding of the relative importance and duration of aerosol vertical transmission effects during these two periods. Overall, both designers and academics can utilize this review as a reference to mitigate the potential risk of vertical transmission of aerosols in BDS, so that BDS can be appropriately designed to minimize pressure fluctuations and the water seals in floor drains can be regularly checked.

Residential areas are the basic unit related to the living quality of urban residents, and their comfort is one of the key concerns of residents. Greening has always been an important means to improve the living environment of residential communities. In this paper, ENVI-met V4 simulation software is verified and used to discuss the influence of the residential scale and green ratio on the outdoor thermal environment. By comparing the difference in outdoor thermal comfort with or without greening measures in residential blocks of different scales, the effects of vegetation on optimizing the outdoor thermal comfort of different scale residential blocks are investigated. The meteorological parameters selected for this case study analysis include a wind speed of 2.5 m/s at 10 m height and an air temperature range of 28 °C to 35 °C. The results show that the wind speed and air temperature in the residential area are less affected by the residential scale and more affected by the greening rate. There are obvious differences in the improvement in outdoor thermal comfort by vegetation at different times. With the increase in residential area scale, the improvement effect of vegetation on outdoor thermal comfort also increases, which in 5 × 5 blocks residential area is 0.2–0.5 °C, higher than that in 2 × 2 blocks small-scale residential area. A modified index, PET (Physiological Equivalent Temperature) drop per green ratio, is proposed for cost performance. Reasonable and feasible greening suggestions for residential buildings are summarized.

The energy balance of residential blocks in different climate zones is simulated and analysed. The influence of climate characteristics on the residential-scale energy budget is clarified, and the temporal evolution patterns of sensible heat flux, latent heat flux and heat storage flux in the surface energy balance are obtained. From the perspective of residential blocks energy distribution, ENVI-met simulation software is used to explore the laws of climate characteristics on the change of residential scale energy balance during summer and winter in three representative cities of typical climate zones in China.. Though surface energy balance simulations, vertical surfaces are found to be a significant source of net radiation received by settlements for northern regions and horizontal surfaces for southern regions. Most of the net radiation absorbed by the residential blocks during the day is transferred to the atmosphere in the form of sensible heat fluxes.

Electrically heated tobacco products (EHTPs) could release effective aerosol components from tobacco materials at relatively low temperatures without a burning phenomenon. It is essential to grasp the temperature distribution and release mechanism of key components in heated tobacco materials. The existing experimental studies have provided initial insights into the thermodynamic behavior of tobacco materials under various conditions. However, current numerical models are still in their early stages of development, with the majority failing to correlate heat transfer with component release. Based on this, a coupled numerical model of gas flow, heat transfer, and the release of key components in the electrically heated tobacco product is established in this study, which exhibits improvements in revealing the internal heat and mass transfer characteristics in the porous media of tobacco and is capable of evaluating the influence of component contents and product design parameters. The release rates of water, glycerol, and nicotine components are quantitatively described by the first-order Arrhenius formula, and the transport of heat and gas flow is simulated using the Navier-Stokes equation. The accuracy of the model is validated through experiments, including temperature monitoring at multiple measurement points and determination of residual contents in the tobacco substrate after each puff. The simulation results suggest that an appropriate component ratio and tobacco filler mass can enhance both the release amount and release efficiency of key components, and reducing either the diameter or length of the tobacco section can help to improve the heat transfer performance. A slower heating rate matched with longer preheating times enables the complementary release of water and glycerol components, which helps to regulate the uniformity of component content in the aerosol to some extent. This study helps to provide suggestions for the design and optimization of electrically heated tobacco products.