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Although there have been studies on gravitational settling of non-spherical particles, only few studies have incorporated the diffusion of non-spherical particles into particle deposition. Non-spherical particles occupy a large proportion of particles in indoor environments, and their deposition is a key factor that influences the level of indoor particulate matter pollution. In this study, we modified drag coefficient and diffusion coefficient based on settling experiment and Langevin equation to fulfill a semi-analytical modeling of particle deposition on indoor surfaces. The modified diffusion coefficient and deposition velocity agree well with the experimental results for fibers. With the modified diffusion coefficient, we further modeled the deposition of non-spherical particles on indoor surfaces under typical air friction velocity conditions. The results showed that the deposition velocity between spherical and non-spherical particle deviated by 10–25% with the same aerodynamic diameter for diffusion-controlled region, while the application of aerodynamic diameter would lead to 10% to over 100% deviation with 10 μm particle for particle depositing on side walls. However, the deposition of non-spherical particle can be estimated rightly through spherical particle with the same aerodynamic diameter when gravitational settling dominates the deposition process. The modification of the diffusion coefficient and deposition velocity of non-spherical particles is expected to help in understanding the effect of particle shape on its deposition and may be further applied to indoor particle pollution modeling. Copyright © 2022 American Association for Aerosol Research

The effects of different human walking patterns on contaminant dispersion in residential kitchens were investigated through computational fluid dynamics simulation with the dynamic mesh method. A tracer gas experiment was performed to verify the feasibility and accuracy of the simulation method. Flow characteristics induced by human walking were minutely described, and the transient capture efficiency of the range hood was adopted to assess the impact of human walking quantitatively. Human walking parallel to a counter, human walking parallel to a counter manned by another human, and human walking toward a counter were studied. Results showed that the mutual effect of the wake and thermal plume caused contaminant dispersion and decreased the performance of the range hood as the human subject walked beside the counter. Even a standing person operated ahead the counter, the wake would affect the thermal plume in a certain extent. The decrement of capture efficiency approached 0.5 in the most unfavorable situation. Moreover, the coaction of the positive/negative pressure zone and impinging air jet drew the thermal plume to the human body. The fluctuation of capture efficiency in this condition was moderate relative to that for the human walking pattern beside the counter. This research could provide a comprehensive overview of different human walking patterns and their impact on residential kitchens and thereby facilitate the maintenance of kitchen air quality.

Central flues are now commonly adopted in high-rise residential buildings in China for cooking oil fumes (COF) exhaust. Range hoods of all floors are connected to the central shaft, where oil fumes were gathered and exhausted through the outlet at the building roof. As households may cook and use their range hood at random periods, there is great uncertainty of the amount of COF being exhausted. In addition, users can often adjust the exhaust rate of the range hood according to their needs. As a result, thousands of possible operating conditions consisting of distinct combinations of on/off conditions and fan speed occur randomly in the central COF exhaust system, causing the exhaust performance to vary considerably from condition to condition. This work developed a mathematical model for characterizing the operation of the central COF exhaust system in a high-rise residential building as well as its iterative solving method. Full-scale tests coupled with CFD simulation referring to a real 30-floor building were conducted to validate the proposed model. The results show that the model agreed well with the CFD and experimental data under various system operating conditions. Moreover, the Monte-Carlo method was introduced to simulate the random operating characteristics of the system, and a hundred thousand cases corresponding to distinct system operating conditions were sampled and statistically analyzed.

Terrorist attacks through building ventilation systems are becoming an increasing concern. In case pollutants are intentionally released in a building with mechanical ventilation systems, it is critical to localize the source and characterize its releasing curve. Previous inverse modeling studies have adopted the adjoint probability method to identify the source location and used the Tikhonov regularization method to determine the source releasing profile, but the selection of the prediction model and determination of the regularization parameter remain challenging. These limitations can affect the identification accuracy and prolong the computational time required. To address the difficulties in solving the inverse problems, this work proposed a Markov-chain-oriented inverse approach to identify the temporal release rate and location of a pollutant source in buildings with ventilation systems and validated it in an experimental chamber. In the modified Markov chain, the source term was discrete by each time step, and the pollutant distribution was directly calculated with no iterations. The forward Markov chain was reversed to characterize the intermittently releasing profile by introducing the Tikhonov regularization method, while the regularized parameter was determined by an automatic iterative discrepancy method. The source location was further estimated by adopting the Bayes inference. With chamber experiments, the effectiveness of the proposed inverse model was validated, and the impact of the sensor performance, quantity and placement, as well as pollutant releasing curves on the identification accuracy of the source intensity was explicitly discussed. Results showed that the inverse model can identify the intermittent releasing rate efficiently and promptly, and the identification error for pollutant releasing curves with complex waveforms is about 20%.

Range hood is a common ventilation appliance applied in a kitchen for maintaining healthy environment. This paper numerically studied the effect of air curtain on capture performance of a range hood, which was equipped in a residential kitchen chamber of 3.5 m * 2.7 m * 2.4 m. Two key parameters of air curtain, air-supply velocity and angle were investigated for improving the capture performance with CFD methods. Only when both the air-supply velocity and angle were well defined simultaneously, could the range hood have a good capture performance. When air-supply angle is 4°, air-supply velocity is recommended at 2.0–2.5 m/s. When air-supply velocity is 4.5 m/s, air-supply angle is recommended at 10°–14°. In the above situation, the range hood has better capture performance. The findings showed that the air curtain with reasonable air-supply velocity and angle could effectively improve the capture performance of range hood and protect the cook.

The discharge capacity of the range hood for cooking-related pollution under current exhaust airflow rate (EAR) standard of 300–500 m 3 /h is limited when cooking temperature near the smoke point of edible oil. This study endeavored to determine appropriate EAR for cooking temperature varies from 200 to 300 °C, which comprised smoke points of different edible oils, considering whether the kitchen was ventilated with the adjacent room or not, and the cooking position of the left/right stove. Particles generated from a simplified cooking process of oil heating test, tracer gas experiment, and flow visualization experiment were conducted. CFD simulation with capture efficiency as an evaluation index was performed. Evidence is presented that when the cooking temperature is 200 °C, the pollutant control effect does not change much when the EAR is above 700 m 3/h, while an EAR of 800 m3 /h may be necessary at 300 °C. For open-door and closed-door cooking, a minimal difference exists in demand for a suitable EAR in this local ventilation system . However, the hood continues to exhaust air during post-cooking period, thereby showing that a higher EAR is necessary to control the pollutants in open-door cooking. The primary and secondary cross draft airflows caused by different air supply positions are observed, which play a vital role in selecting suitable left/right cooking position. The location of the left stove is conducive to the elimination of cooking-related pollutants due to primary cross draft, while it is the right stove due to secondary cross draft.

This paper presents the effect of a personalized air curtain on respiratory protection. Influencing factors (opening angle, tilt angle, velocity, and width) and the impact from real respiratory process were considered by conducting experiments and computational fluid dynamics (CFD) simulations. Results showed that the entrainment and diffusion of contaminants occurred around the air curtain with varying parameters. Opening angle of 180° and tilt angle of 0° are recommended due to good protection factor (PF). Without interference, width of 30 mm and low velocity (0.8–0.9 m/s) were most beneficial for PF because of the good protection against contaminants both inside between the air curtain and the face and outside of the curtain. With respiratory interference, PF decreased under the same air curtain parameters due to the disruption of the air curtain jet by inhalation, and the interference became increasingly weak at velocities above 1.5 m/s. PF reached 220 when the parameters were width of 30 mm, velocity of 1.5 m/s under respiratory interference. This study reveals the potential of using personalized air curtains for personal respiratory protection in industrial air-contaminated environments.

This study proposed a novel integrated design combing an air cleaner with the conventional exhaust hood for the improvement of indoor air quality in the residential kitchen. Airflow interaction between the exhaust confluence of the range hood and the strong momentum induced by air cleaner was investigated for this kind of compact configuration. The potential of energy saving by using the air cleaner was discussed. Firstly, numerical simulation was employed to obtain well-organized recirculation purification parameters under different air outlet widths and angles and experiments were conducted to verify the control effect of pollutant concentration in the kitchen space with the good design. Results show that the oblique upward air supply of the air cleaner was found significantly better to clean the kitchen space than horizontal and oblique downward supply. The relative purification effect of the integrated air cleaner is less affected by the exhaust flowrate of the hood. The PM 2.5 concentration reduction rate by the air cleaner at the breathing zone is near 60%, while the TVOC concentration reduction approximately 30%. Secondly, concentration decay rate at post-cooking period with/without the integrated air cleaner was measured and compared. It was found that the concentration decay rate achieved by the integrated air cleaner with 100 m3/h and oblique upward air supply is close to the decay rate of exhaust hood with 200 m3/h. It means that the integrated design proposed in this study is effective in reducing human exposure to cooking-related pollutants and has a significant energy-saving potential.

The function of air curtain range hood in improving human exposure was investigated by conducting experiment and CFD simulation. The intake fraction was estimated to reflect the effect of the air curtain. Factors affecting human exposure, including the exhaust rate, heat source intensity, air supply angle, air supply velocity, and slot width of the air curtain, were incorporated according to an orthogonal design. To comprehend the roles that the air curtain performed, the characteristics of flow and concentration field were captured through visualization experiment and CFD method. Furthermore, the effect of using an air curtain to resist the impact of human walking on human exposure was examined. The exhaust rate, heat source intensity, and air supply angle were significant factors that affect human exposure with a significance level of 0.01. Compared with the traditional range counterpart, air curtain range hood could decrease the intake fraction by factor of 1.5–5. Air curtain could reduce turbulent intensity around the range hood and improve local airflow organization. Meanwhile, air curtain would considerably protect walking humans from exposure to pollutants. The outcome of this study could help us understand the effect of air curtain range hood with a comprehensive perspective.

A rotating disk with spokes was developed recently for its benefits in preventing grease accumulation. Parametric design of disk structure based on the particle capture efficiency and flow resistance has not been widely studied. This work performed experiments and computational fluid dynamic (CFD) simulations to analyze factors influencing the performance of this rotating disk. The experimental and simulation results of the pressure drop and particle capture efficiency were compared to validate the feasibility of CFD simulations and identify the best turbulence model among the three tested. Orthogonal tests performed for parametric analysis showed that spoke width, number of spokes, disk diameter, rotating speed, and air flow rate significantly affect the resistance of the rotating disk, whereas spoke width, spoke thickness, number of spokes, rotating speed, and air flow rate significantly affect particle capture efficiency. Structure improvement of the rotating disk was conducted to balance the particle capture efficiency and flow resistance. Finally, structure-improved disks manufactured by corrosion were evaluated in an experimental system with an artificial cooking oil fume (COF) particle generating apparatus. Experimental results show that the total particle removal efficiency of COF particles can reach up to 62.5% for a rotating disk with optimized structure under rotating speed 1500 rpm and penetrating airflow rate 360 m³/h, while the measured pressure drop is as low as 15.3 Pa. This study can contribute to the efficient design of rotating disk used for purification of COF in residential kitchen or oil-coated particles in industrial environment.

Studies have shown that the ventilation is of great significance in controlling the harmful cooking oil fume (COF) that is generated during cooking process and is mainly composed of thermal oxidation decomposition products produced by the chemical reactions of food and oil at high temperature. In order to fully understand the performance of the ventilation system and to assess the suitable ventilation methods for various spatial organizations of residential kitchens (RKs), this paper reviewed and summarized the presented literatures on the ventilation methods and the assessment index used for ventilation system in residential kitchens via a literature research of publications. The results showed that three assessment index can be used to evaluate the performance of the ventilation system and six ventilation methods have been employed in the three kinds of spatial organizations of RKs. The performance of the ventilation system and the indoor environment varies very large between different ventilation methods and spatial organization of the kitchen. Among the existing ventilation methods, the use of the natural ventilation does not provide a reliable indoor environment and the use of the mechanical ventilation with natural make-up air does not provide a satisfactory indoor environment in RKs. The use of the organized make-up air and high-efficiency range hood are effective methods to improve the performance of the ventilation system in RKs. The new measurements to improve the performance of the ventilation system and the strategies to prevent the COF disperses to the adjacent room in the open kitchen should be further studied to create a good indoor environment in RKs. The results of this study will facilitate to design and choose the suitable ventilation methods in RKs.

This study proposed a control logic for a novel constant-air-volume (CAV) range hood. The Field Oriented Control vector was used to adjust the fan speed by comparing the current exhaust volume to the desired value. Experiments were conducted to test the air volume retention ability of the developed constant-air-volume range hood. Test results show that within a certain range of fan static pressure, the exhaust air volumes of the constant-air-volume range hood can remain constant. To verify the operation performance of such constant-air-volume range hood in a real central exhaust shaft, the performance curves of the fan obtained from the experiments were substituted into the our previously developed ductwork hydraulic model to calculate the distribution of the exhaust air volume under varied fan curves and shaft coincidence factors. Modeling results indicate that in a central exhaust shaft, the CAV range hood can meet user’s varied exhaust demand at low coincidence factor (e.g., 0.2) but its capability to maintain constant exhaust air volume decreases when the coincidence factor of the central shaft is high (0.4 or 0.6). A staged multi-gear control method was also proposed to address the fan noise concern and static pressure limitation. The fan can automatically switch to a lower exhaust gear when it reaches the threshold of the rotating speed.

Flow characteristics induced by human walking and the effect of human walking on the performance of range hood in residential kitchen were investigated by performing transient CFD simulation with dynamic mesh method. Transient capture efficiency was used to evaluate the effect of human walking on range hood. Tracer gas experiment and visualization experiment were conducted. Results showed that the process of human walking could be divided into five stages, and the interaction between wake and thermal plume was the main reason for the fluctuation of the thermal plume. The capture efficiency had a decrement of 0.5 at the most unfavorable conditions. The factor analysis involved intensity of heat source, exhaust rate, walking speed, and distance between human and counter and showed that the parameters related to human walking were significant contributors to the undulation of capture efficiency. Air curtain range hood was introduced in this study to assess its function to resist the effect of human walking. Compared with increasing the exhaust rate, air curtain could prevent the effect induced by human walking with less increment in air volume, which saved energy that would be wasted on increasing the exhaust rate. This study extended the understanding of human walking and its effect and helped in comprehending the similar condition where pollutant/heat source and human activity existed.

The emission standards of non-methane total hydrocarbon were tightened from 120 mg/m3 to 10 mg/m3 for Chinese industries in 2012. Despite the investment into environmental treatment, many factories have since been struggling to hit the emission reduction target. Emissions from various production processes have the characteristics of low concentration and intermittency, so the conventional ventilation systems relying on high flow rates to collect and exhaust the low-concentration pollutants often result in large scale, high economic and energy consequences, but poor performance. In this study, a novel circulating system was proposed to concentrate pollutants and reduce the exhaust air volume using a rubber refining process as an example. Firstly, a circulating ventilation model based on the mass balance was established to predict the variation of pollutant concentration within the system, and two control strategies (i.e. continuous or intermittent exhaust scheme) were developed to improve the pollutant capture efficiency of the system. Secondly, the emission intensity of pollutants in the rubber refining process was measured and further used as boundary conditions in the subsequent simulation. Thirdly, the CFD simulation was adopted to optimize the circulating air volume, return air jet angle, and exhaust air volume of the circulation system. Results showed that the optimized design of the circulation system with the continuous/intermittent exhaust scheme can achieve a 14.5/32.6 fold increase in the exhaust concentration of VOCs and a 75.8%/53.8% reduction in exhaust air volume.

Using a radial jet at the outer edge of a circular exhaust hood can effectively reduce the velocity attenuation in front of the exhaust hood. The velocity distribution, especially the centerline velocity, is a key parameter in the effective design and use of an exhaust hood. In this paper, based on the derivation of the prediction formula of the suction velocity, the study of the suction velocity of jet-enhanced rectangular exhaust hood that considers the jet enhanced, viscous and geometrical effects is presented via the experimental and numerical methods. To understand the suction velocity distribution, the centerline velocity is investigated by varying the jet velocity, jet angle, jet slot width, exhaust rate and aspect ratio of the hood. It is found that the critical jet velocity condition is a most effective and energy-saving working condition for this kind of hood. Based on the critical jet velocity working condition, reducing the jet angle instead of increasing the exhaust rate is an airflow-rate-saving way to further increase the centerline velocity at a relatively large distance away from the hood opening. Calculation equations for the prediction of the centerline velocity of rectangular jet-enhanced exhaust hood are proposed. The error of the formula is proven to be within 10%, and its application range is proposed. The outcome of this work can help to efficiently design and use this type of energy-saving exhaust hood in residential and industrial local ventilation applications.

Air curtain range hood was developed recently for its beneficial effect on preventing spillage of pollutant and maintenance of good indoor air quality in kitchens. Orthogonal experiments were conducted in this study to investigate factors that affect the function of the air curtain range hood. The contaminant removal efficiency was measured and employed as an assessment index for variance analysis. Single-factor analysis based on the significance level was conducted using computational fluid dynamics method and experiment including tracer gas and visualization experiment. Results showed that exhaust rate was the main factor affecting the performance of air curtain range hood, followed by intensity of heat source, air curtain velocity, interaction between air curtain velocity and slot width, air curtain slot width, and air curtain angle. Compared with conventional range hoods (range hoods without air curtain), contaminant removal efficiency was enhanced with the air curtain range hood. The single-factor analysis defined three jet patterns, namely, “invalid,” “enhanced,” and “destructive” jets. The range of “enhanced jet” was then proposed. Assessment of another air supply parameter, air curtain angle, demonstrated that it had no significant influence on the performance of the air curtain range hood. The results of this study can provide additional details and help in the efficient design of air curtain range hoods for residential kitchens.

Using a radial active air jet ejected from the slot surrounding a circular exhaust hood opening can increase the air speed generated by the hood as well as achieve a larger capacity to exhaust pollutants. Critical parameters of the Aaberg hood have been identified to ensure the positive effect of the active jet. This paper proposed a novel type of enhanced exhaust hood using the rectangular opening in place of the circular one in Aaberg hood to meet the needs of different shape and size of exhaust hood. To understand the performance of this kind of exhaust hood and to determine the critical velocity of the active air jet, the flow characteristics and the centerline velocity are investigated by changing the exhaust rate, hood size, jet angle, jet velocity and jet slot width via experimental and numerical methods. Results show that the critical jet velocity exists between two working modes of the novel exhaust hood, one is the ineffective mode with the short-circuit jet, and the other is jet-enhanced mode with the developed radial jet. The near-wall circulation along the hood opening perimeter is not attributed to the existence of the jet. The suggested equation which error is proven to be within 12.5% for the critical velocity presented in this paper is simple in structure, and will help to facilitate the choice of the energy-efficient exhaust hood design in residential and industrial buildings to save energy that would be wasted on increasing the exhaust rate.

Chinese residents often use range hoods to exhaust cooking oil fumes (COF) and at the same time open inner/outer doors and windows for natural air supplement. Factors such as the layout of kitchens, the exhaust efficiency of range hoods, and the effect of natural air supplement, directly determine transmission characteristics of COF, which in turn affect the capture efficiency of range hoods and the COF exposure of residents. This study carried out a survey on the ventilation conditions in residential kitchens and conducted measurement of residents’ COF exposure. In an old residential community of Shanghai, we measured the three-dimensional size of kitchens, the areas and positions of doors and windows and the exhaust rate of range hoods of 30 residential kitchens. 7 households were randomly selected to monitor 24-h PM2.5 concentration around stoves in kitchens. Meanwhile, one volunteer from each of the 30 households participated in personal PM2.5 monitoring using wearable sensors. To quantify the occupant exposure during cooking, two indexes including the exposure contribution rate and additional exposure concentration were introduced. The results showed that the ventilation conditions in these kitchens were generally poor and considerably different from each other. Meanwhile, the concentration dynamics of PM2.5 during cooking showed short-term (about 10–20 min) and high-dose (the peak concentration reached 800–1000 μg/m3) characteristics compared with that in other periods.

Fast locating the sources of hazardous pollutants in indoor environments is extremely important for ensuring indoor air quality and indoor environmental safety. Considering the timely and smooth implementation of the subsequent emergency measures, tracking hazardous sources in buildings with ventilation systems has a higher requirement on computation time. It imposes a great challenge on model abstraction and method selection. In this work, a Markov-chain-based inverse approach was established to locate hazardous pollutant sources in case of emergencies. If the complete prior concentration distribution was obtained, the posteriori source location could be directly identified. If the prior concentration distribution was incomplete, the Bayes Theorem that based on the Markov chain simulations was introduced to determine the source location. To validate the applicability of the proposed inverse approach, both the CFD simulation and concentration-measured experiment were conducted. The simulated data from the Markov chain method and CFD model, as well as the measured data from the tests were used as model inputs respectively to identify the source location. The results showed that both inverse approaches were able to correctly locate the source and could significantly reduce the computing cost and time. The impact of measuring errors, measuring points number and placement was extensively discussed. Such sensitivity analysis could be used to determine the upper limit of the sensor errors and the most economical measuring point number for a specific case. The expansion of the Markov-chain-based Bayes method for multiple sources localization was also speculated.

If hazardous gaseous pollutants are deliberately released in public buildings, it is necessary to detect them and warn promptly indoor occupants to evacuate. In this study, we propose a Markov-chain based probabilistic approach to optimize an indoor sensor network against a deliberately released contaminant and demonstrate it for a simple multi-zone building and a real experimental cabin. The probabilistic approach is mathematically an ergodic method, which contains two objective functions: to minimize expected time to detection and to maximize the number of successful detections. The Markov chain method uses the multi-zone model or CFD simulation to calculate the transition probability matrix. If such a matrix is determined, simulating indoor pollutant distributions takes almost no time since the Markov chain model does not require iterations. The Markov chain method combines with the probabilistic approach to design the sensor placements for the detection of pollutants. The first case is a simple building with a recirculating air system using the multi-zone-based Markov chain method as the simulation tool. Utilizing the probabilistic method, we determine the optimal sensor placements with different sensor number. The relationship between the sensor network performance and airflow rates of the ventilation system is revealed. Next we conduct a concentration-measured case in an experimental cabin connected with an all-air system and in this case uses CFD-based Markov chain method as the simulation tool. The impact of sensor properties (including sensitivity, the miss alarm rate, sample interval time and response time) on the sensor network performance is discussed for this case.