Thermal plumes of kitchen appliances: Idle mode

In the kitchen environment, pollutant fumes of the cooking process are released into the ambient air by the convection plumes. The practical problem is to compute the requested extract air flow rate to maintain good indoor air quality in an energy efficient manner. In the most accurate design method, the design of a kitchen ventilation system is based on the flow rate of the thermal plume. In this method, the amount of heat carried in a convective plume over a cooking appliance at a certain height is calculated. The heat load is then assumed to be a point heat source and the velocity and temperature profiles are approximated to be Gaussian distributed. In commercial kitchens, the location of the extraction point is at a height of 0.9–1.4 m above the heat source where the convection flow is not yet fully developed. This paper demonstrates that the generic plume equation, derived in the region of complete flow similarity, is not accurate in this intermediate zone. However, it gives a reasonable accuracy for practical applications when an individually adjusted empirical factor of the virtual origin is applied. The power intensity of the heat gain has a much more significant effect on the plume characteristic than the previous studies indicate. The plumes are narrower and the spreading angle is smaller with higher heat gains.     

大型厨房通风设计中应注意的问题

针对目前宾馆、饭店等大型厨房通风设计存在的问题 ,阐述了通风系统、气流组织形式与风量、热量平衡计算、风管内气流速度等的确定原则和方法 ,以创造优良的厨房环境和高效节能的通风系统。     

旧厨房空调换气系统改进及测试分析

酒店旧厨房空调换气系统的设计方法存在问题，而导致换气次数高、热能消耗过大。根据不同换气次数条件下污染物浓度分布特点和酒店厨房自身的运作特点，对送风方式、送风位置和排风系统配置做了改进。以组合风幕送风方式将室外新风直接送到炉灶周围和厨师呼吸区污染物浓度超标部位，高效率地满足煤气燃烧需氧量要求、快速稀释超标部位污染物浓度；利用风幕的空气动力控制污染物溢出，减少残留率；采用主、副送排风系统，在煤气用量高峰段和非高峰段分开使用。改进后测试结果表明：换气次数30次／h时厨师呼吸区CO、CO2浓度不超标，残留率减少16％，炉子燃烧状况良好，系统节能显著，运行效果稳定。     

公共厨房的通风设计

分析了目前公共厨房操作间通风设计方式普遍存在的问题，提出了现代公共厨房采用局部送排风加全面排风的解决方法，并简单阐述了公共厨房设计的一般原则以及通风系统的采用形式，包括送风，排风系统设计，排烟罩的选择。排烟罩最小风量的计算等。     

Gas cooking, kitchen ventilation, and exposure to combustion products

We evaluated a questionnaire-based system for classifying homes into groups with distinctly different chances of accumulating combustion products from cooking appliances. The system was based on questions about type of cooking appliance, type and use of ventilation provisions, and kitchen size. Real-time measurements were made of CO, CO(2), temperature, and water vapor, and passive sampling was performed of nitrogen oxides, over a week-long period in 74 kitchens. During the measurements, inhabitants kept a diary to record appliance use time and use of ventilation provisions. The questionnaire-based and diary-based home classifications for the 'Chance of Accumulation of Combustion Products' (CACP) turned out to agree fairly well. For CO(2) as well as for CO a significant difference between the 'high' and 'low' CACP groups was found for the mean accumulation in the kitchen during cooking of the combustion generated concentrations. These facts are considered to be important experimental evidence of the CACP stratification being valid for our study population. In the homes studied, NO(2) as well as CO concentrations were found to be lower compared with previous studies in The Netherlands. Practical Implications Previous studies on indoor combustion product dispersal conducted in the early- to mid-1980s in the Netherlands showed much higher NO(2) and CO concentrations than the present study. Apparently, the removal of combustion products formed during cooking is more efficient in the (mostly newer) homes that we studied than in the homes studied in the early- to mid-1980s. More detailed knowledge of kitchen situations is needed to improve the CACP model. Future studies can achieve this by using questionnaires on the kitchen situation, diaries and real-time measurements of the combustion products under consideration.     

Experimental investigation of the velocity field and airflow pattern generated by cooling ceiling beams

In the modern office environment there are numerous heat generating equipment, heat loads from solar radiation and heat produced by people. The loads will often exceed the load the ventilation system can cope with. To meet this demand on extra cooling capacity the commercial market provides cooling ceiling panels and chilled beams. A chilled beam is a source of natural convection, creating a flow, vulnerable to disturbances, of cold air into the occupied zone. Experiments have been conducted in a mock up of an office room; qualitative information has been obtained by visualisation. Instantaneous velocity profiles of the airflow generated by the chilled beam has been registered. In addition, the temperature field below the chilled beam has been measured with a whole field measuring technique. The results show that the airflow from the chilled beam has behaviour similar to a two-dimensional plume but exhibits strong oscillation both sideways and along the chilled beam. These oscillations (intermittence) might cause a sensation of draught but in order to clarify this further investigations are required. Furthermore, airflow generated by heat sources in the room may reverse the flow generated by the chilled beam.     

A simple model to study the influence of fluctuating airflow on the effective air exchange rate when using natural ventilation

Fluctuating airflow may strongly influence the real air exchange rate when using natural ventilation, resulting in a larger “effective” air exchange rate than the “mean” air exchange rate calculated by conventional methods (i.e., the network method). To study the effective air exchange rate during natural ventilation under conditions of actual use, this study proposes a simple model that accounts for fluctuating airflow. The model assumes that the airflow near a building opening fluctuates regularly and velocity is assumed to have either a square or sine wave pattern. Our analysis shows that the effective air exchange rate is larger when accounting for fluctuating airflow. This suggests that the mean air exchange rate should not be calculated without consideration of real airflow fluctuations.     

细水雾控制高层住宅烟道火灾的有效性及参数优化

为了有效控制高层住宅厨房烟道火灾,构建细水雾控制厨房食用油火和带分支烟道的高层住宅厨房烟道油垢火的FDS数值模型,分析高层住宅厨房烟道细水雾灭火系统有效性的影响因素及最佳设计参数。结果表明,如果未能即时扑灭高层住宅底层厨房食用油火,在强烈的烟囱效应作用下,高温火焰和烟气会引燃烟道内油垢,造成火势的迅速蔓延。本文所建的30 m高厨房烟道火模型中,最佳细水雾灭火系统运行模式为关闭厨房抽油烟机,即时开启厨房灶台上方和主烟道内分段设置的细水雾喷头,雾流量分别为0.6,10 L/min,细水雾最佳参数为喷射流速10 m/s、喷射角度60°、水雾粒径500 μm。     

Development of new and validation of existing convection correlations for rooms with displacement ventilation systems

Building airflow, thermal, and contaminant simulation programs need accurate models for the surface convective boundary conditions. This is, especially, the case for displacement ventilation (DV) systems, where convective buoyancy forces at room surfaces significantly affect the airflow pattern and temperature and contaminant distributions. Nevertheless, for DV, as a relatively new ventilation system, the convective correlations are adopted from more traditional mixing ventilation correlations, or non-existent. In this study, the existing recommended correlations are validated in a full-scale experimental facility representing an office space. In addition, new correlations are developed for floor surfaces because the current literature does not provide necessary correlations, even though, the floor surface is responsible for >50% of the total convective heat transfer at the envelope. The convective correlations are typically functions of a surface-air temperature difference, airflow parameters, and characteristic room dimensions. Validation results show that the floor convection correlations expressed as a function of volume flow rate are much stronger than the correlations expressed as a function of a temperature difference between the surface and local air. Consequently, the new convection correlation for floor surfaces is a function of the number of hourly room air changes (ACH). This correlation also takes into account buoyant effects from local floor heat patches. Experimental data show that the existing correlation can be successfully applied to vertical and ceiling surfaces in spaces with DV diffuser(s). Overall, the new and the existing convection correlations are tabulated for use in building simulation programs, such as annual energy analyses or computational fluid dynamics.     

管道燃气厨房事故通风问题辨析

讨论使用管道燃气的公共厨房实际运行中燃气泄漏的可能性,分析现行国家相关标准规范的有关规定,指出其中的不明确、不协调之处,认为通风良好的管道燃气厨房无需设置事故通风。通过统计分析近年来国内重大燃气爆炸事故案例,参考借鉴美国相关标准,对相关标准的制修订以及以确保防火安全为目的的燃气厨房通风系统设计提出一些意见和建议。     

Indoor air pollution from particulate matter emissions in different households in rural areas of Bangladesh

Indoor air pollution from the combustion of traditional biomass fuels (wood, cow dung, and crop wastes) is a significant public health problem predominantly for poor populations in many developing countries. It is particularly problematic for the women who are normally responsible for food preparation and cooking, and for infants/young children who spend time around their mothers near the cooking area. Airborne particulate matter (PM) samples were collected from cooking and living areas in homes in a rural area of Bangladesh to investigate the impact of fuel use, kitchen configurations, and ventilation on indoor air quality and to apportion the source contributions of the measured trace metals and BC concentrations. Lower PM concentrations were observed when liquefied petroleum gas (LPG) was used for cooking. PM concentrations varied significantly depending on the position of kitchen, fuel use and ventilation rates. From reconstructed mass (RCM) calculations, it was found that the major constituent of the PM was carbonaceous matter. Soil and smoke were identified as components from elemental composition data. It was also found that some kitchen configurations have lower PM concentrations than others even with the use of low-grade biomass fuels. Adoption of these kitchen configurations would be a cost-effective approach in reducing exposures from cooking in these rural areas.     

Simulation of inhalable aerosol particle distribution generated from cooking by Eulerian approach with RNG k–epsilon turbulence model and pollution exposure in a residential kitchen space

Cooking-generated fume contains large amounts of fine particle pollutants with high concentration. To study the influence of the aerosol particle pollutant in kitchen, a typical format of residential kitchen in northern China is selected in this paper. FLUENT software is applied to simulate interior space airflow as well as pollutant mass fraction in breathing-section and cooking-section area in the residential kitchen under different vent cases. Furthermore, occupant’s exposure to inhalable aerosol particle is obtained integrated with human inhale model and pollution exposure calculation model. The results demonstrate that cooking side of respiratory region in pollutant mass fraction can be significantly reduced when opening the door, but mass fraction gradient is larger in the vicinity of the stove. The average pollution exposure in the maximum value is about 90 times than that of the minimum value around the cooking personnel with the most adverse conditions in winter when the doors and windows are all closed. The research output can provide valuable reference for the further study on fine particles concentration level as well as to determine individual intake fraction of particles generated in the process of cooking in the residential kitchen.     

The impact of various hood shapes, and side panel and exhaust duct arrangements, on the performance of typical Chinese style cooking hoods

In Chinese commercial kitchens, a large amount of moisture and heat is produced and must be removed, which can require ventilation rates resulting in huge levels of energy consumption. Excessive airflow rates can increase unnecessary energy consumption and system life-cycle costs. For many middle and small scale commercial kitchens in China, the indoor, thermal environment is far worse than acceptable levels. The use of an efficient kitchen hood is essential to ensure a comfortable working environment and better energy conservation. In this study, many types of hood shapes and side panels were developed to improve the capture efficiency of traditional Chinese style cooking hoods. The arrangement of the exhaust ducts was also investigated. Basic site tests and computational fluid dynamics (CFD) analysis were conducted. The simulated results showed that increasing hood volume did not improve capture performance. However, side panels did improve the capture efficiency, especially at higher positions. In addition, when the exhaust opening was located at the rear of the hood, the hood capture efficiency improvement was enhanced.     

公共建筑厨房通风系统设计

探讨了公共建筑厨房通风系统中通风量的计算、风量平衡方法及控制原则。     

Modeling of cooking-emitted particle dispersion and deposition in a residential flat: A real room application

Maintenance of good indoor air quality for residences could be very challenging. Episodic event such as cooking emits a large amount of ultrafine and supermicron particles. A numerical model is used to simulate a 10-min cooking process in a real room, followed by a few more minutes to allow the decay and removal of particles. Particle dispersion and deposition in the kitchen and the living room are simulated by a new drift-flux model. Strong buoyancy flow is observed and particle concentration is significantly affected by the thermal plume. Results show that for supermicron particles strong non-uniformity of concentration is observed in the kitchen but the non-uniformity is less obvious in the living room. Exposure analysis must take into account the influence of the particle sizes.     

Numerical investigation of the unsteady flow characteristics of human body thermal plume

Human thermal plume is quite important to the study of airflow organization in the indoor environment, especially in the micro-environment research such as personalized ventilation, infectious disease transmission through air, etc. In order to investigate the unsteady fluctuation of the thermal plume around human body, a series of transient numerical simulations are conducted in this study. Numerical simulation based on 9.7 million grids and 0.02 s time step is performed to obtain the detail quantitative data of flow field. The obvious fluctuation and separation are captured in the upper flow region of human body based on the high resolution grids. The maximum time-averaged velocity of the thermal plume is found to be 0.25 m/s while the maximum fluctuate velocity is about 0.07 m/s. The further analysis of frequency spectrum shows that the thermal plume around the body is mainly dominated by the low frequency fluctuation which is lower than 1 Hz and the principal frequency is around 0.1 Hz. In order to overcome the drawback of the high computation cost for application of the engineering simulation, a new numerical simulation method combining a modified k–ε turbulence model and coarse grids is presented. This modified k–ε model can reduce the calculation error of Reynolds stress in the flow region of natural convection through redefining the turbulence viscosity coefficient segmentally and avoid a high numerical viscosity appeared due to the central difference scheme. It can reasonably predict the general fluctuation velocity and the frequency distribution during simulation process in coarse grids and show a huge potential to be applied to the engineering application.     

载人航天器舱内通风空调特性和数值模拟

由于载人航天器这一密闭狭小空间及其微重力这一特殊环境,舱内通风空调问题和热舒适环境与地面的HVAC问题不同,微重力效应特别是自然对流大为减弱影响着通风换热效果。本文首先分析了舱内通风空调问题的特殊性,通过无量纲分析和计算微重力的流体力学效应,然后利用FLUENT软件对两种集中通风方式进行数值模拟。模拟结果表明：微重力下几乎不存在“冷风下坠”或者“热羽”现象;集中斜进风在一定的进风角度和Re数下出现分岔解现象;与常重力相同通风条件下,微重力下自然对流的减弱使得舱内温度降低,换热减少,因此满足常重力热舒适要求的通风条件不一定满足微重力下热舒适性的要求。     

饮食业厨房通风设计中应注意的若干问题

本文针对饮食业的厨房排风,讨论了几个在通风系统设计中对风量、压力等影响较大而又常不被注意的问题。以期对厨房通风的设计提供一点参考。     

Convective heat transfer prediction in large rectangular cross-sectional area Earth-to-Air Heat Exchangers

An Earth-to-Air Heat Exchanger (ETAHE) uses the ground's thermal storage capacity to dampen ambient air temperature oscillations by delivering the outdoor air to the indoors through a horizontally buried duct. With their lower airflow resistance, large cross-sectional area ETAHEs have been found to be more energy efficient than the conventional small ones, especially when integrated in hybrid ventilation systems. However, the lack of available methods for determining the heat convection at the duct surfaces has made accurate energy simulation and proper system design overly difficult. In this study, numerical experiments using computational fluid dynamics (CFD) were conducted to investigate the airflow and thermal behavior in the large ducts. A two-layer turbulence model was used to ensure accuracy in resolving the flow information in the near-wall region, which is critical for predicting accurate heat convection. The modeling method was verified by comparing its results with measurements from literature. Parametric studies were conducted to identify the influential design and operation variables for the heat convection. Thirty numerical experimental setups designed with the Latin Hypercube Sampling method were simulated to prepare a database with six design parameters as the simulation inputs and average Nusselt numbers over the duct ceiling, wall, and floor as the outputs. Based on the database an artificial neural network (ANN) model was trained to build a mathematical relation between the design variables and the Nusselt numbers. The developed ANN model showed very accurate prediction when compared with test data.     

商业厨房的安全设计与实践

根据澳门商业厨房的特点,提出商业厨房的安全设计措施。合理地布置厨房内的燃气设施,选用配置熄火保护装置的燃具,建立可靠的联动系统及高效的油烟制控系统,以保证厨房场所的安全。