Air Velocity Distribution Research Articles

EVALUATION OF THE INDOOR AIR VELOCITY OF A SIDEWALL INLET AND ROOF EXHAUST VENTILATED BROILER SHED USING COMPUTATIONAL FLUID DYNAMICS

Fast-growing broiler chickens, bred for meat, find it difficult to adapt to warm conditions during hot weather periods in an enclosed environment. They tend to change their behavioural and physiological mechanisms to survive. This study was carried out to evaluate the air velocity distributions within a sidewall inlet and roof exhaust ventilated broiler shed using computational fluid dynamics (CFD). The simulation was conducted using three turbulence models (standard, realizable, and SST ) to determine the best predictive model for the hot weather ventilation of the broiler shed under consideration. The results predicted by the turbulence models were validated with the field experimental results. It was discovered that the standard turbulence model predicted air velocity distributions, close to that of the air velocity distributions obtained during the experimental study except at the centre of the broiler shed where the CFD predicted higher air velocity. This shows that CFD could be adopted by Agricultural Engineers to create appropriate environments for animals before the structures are physically erected.

Design and experimental validation of a new condenser of an automotive air conditioning unit to address non-uniform air velocity distributions

• The front anti-collision beam in a car leads to air maldistribution. • A six-path condenser is an optimization of the traditional four-path condenser. • The new condenser shows better capacity with the anti-collision beam. • The cooling performance of automobile air conditioning system is improved. To improve the efficiency of automobile air conditioning and reduce the impact of non-uniform air velocity distributions caused by the front anti-collision beam on automobiles, we designed a new six-process condenser and tested it under different working conditions. A baffle was positioned to simulate the anti-collision beam during the experiment. We analyzed the condenser by itself and the system level performance of this newly designed condenser under three working conditions compared to a traditional four-process condenser. Condenser heat exchange capacity, condenser inlet pressure, system refrigerant flow rate, refrigerant flow resistance, thermal imaging of condenser outlet air, overall system cooling capacity, and coefficient of performance were compared. The coefficient of performance of the system with this new condenser improved by 8.5%, 7.8%, and 10.3% for the three tested working conditions.

Numerical simulation of the nocturnal cooling effect of urban trees considering the leaf area density distribution

The design of urban areas and building that utilizes the microclimatic effects of trees is a promising approach for reducing the severe heat stress caused by urban heat islands and global warming. Although trees can reduce heat stress through solar shading during the daytime, their influence on the air temperature under and around them during the nighttime, which is important for nighttime thermal comfort, has not yet been fully elucidated. In this study, we investigated the nocturnal cooling effect of trees in a physical urban space by the coupled numerical simulation of longwave radiative transfer and computational fluid dynamics. To represent the spatial structure of an actual urban space, airborne LiDAR-derived three-dimensional data of leaf area density distribution and building shape were used. The species-specific convective heat transfer coefficient was also considered. An analysis of the calculated sensible heat flux shows that both leaf area density and sky view factor are important factors in the production of cool air. According to the calculated distributions of air temperature and velocity, even under the condition of a certain degree of incident flow, the cooled air can flow down to the space under the crown, accumulate, and then diverge when the wind speed is sufficiently low in the crown owing to the crown drag. Buildings contribute to both the accumulation and dissipation of cool air. The findings of the present study suggest that cool spots can be produced during nighttime by trees planted near streets by devising a suitable arrangement and morphology of trees and buildings.

Study on the transmission route of virus aerosol particles and control technology of air conditioning in the enclosed space.

The patient’s breathing and air conditioning system in the enclosed space are the main factors that cause indoor cross-infection. However, the research on the influence and the control mechanism of different air conditioning systems on the transmission path of virus aerosol particles exhaled by patients is still limited. To evaluate the effects of different air conditioning systems on the spread of human exhaled pollutants, computational fluid dynamics (CFD) was used to study the movement and diffusion of exhaled air from two rows of 12 sitting adults in a hospital's closed transfusion room. In this paper, three different air conditioning systems are considered: Ceil-supply and Down-return (Ceil-to-Down), Up-supply and Down-return (Up-to-Down), Down-supply and Up-return (Down-to-Up). The distribution of exhaled air velocity, temperature, and virus particle concentration were studied, and it is found that the horizontal diffusion distance of exhaled pollutants is about 0.75 –1.1 m. When up to down systems are used, the air conditioning system shall be closed in time in case of respiratory infectious diseases, so as to avoid cross-infection in the enclosed space. A relatively clean air area with a height of about 1.1 m will be formed, which can inhibit the transmission of the virus to a certain extent when using the down-to-up system. But for those who are exposed to the enclosed space for a long time, the down-to-up system is not the most suitable air conditioning system.

NUMERICAL SIMULATION OF AIR VELOCITY AND TEMPERATURE DISTRIBUTION INSIDE A TWO DIMENSIONAL OFFICE ROOM

A two dimensional turbulence (SST, k-) model is used to predict the distribution of air velocity and temperature in a 2-D office room, containing one person and office furniture for two ventilation conditions. This study use a commercial CFD code FLUENT (version 6.3) for solving the Navier Stocks, energy and turbulence equations using finite volume techniques. The results were presented as velocity vectors with quantitative velocity and temperature distribution. The result can be divided into two parts, First part compared with published result and gives good theoretical agreement, the second part was taken at boundary conditions (Vin, Tin and Twall) according to the Iraqi environmental condition depend on the Iraqi cods of cooling 2012.

CFD Modeling of An Even-Span Greenhouse Dryer Under Natural and Forced Convection Modes

In this study an even-span greenhouse dryer was designed and simulated under two different drying modes, natural and forced convection modes. The CFD simulation was carried out taking into consideration the weather conditions at the mean day of January (winter season) in Marrakech, Morocco. CFD was employed to predict the air velocity, temperature and relative humidity distribution inside the greenhouse dryer. Under forced convection mode the air temperature and relative humidity were uniformly distributed inside the dryer. The highest air temperature and lowest air relative humidity was recorded at the mean hour of the simulation day, under forced convection mode. They were 37 °C and 12%, respectively. These results reveal that under forced convection mode the greenhouse exhibited significant thermal performances.

Effects of meteorological conditions on the air quality in deep open - pit mines in Vietnam

Air quality in open - pit mines is the big concern relating to the occupational safety and healthy, as well as the surrounding environment. In the past years, management of the air quality in open - pit mines is challenge due to the limit of science and technology in the assessment of the effects of meteorological conditions and toxics in open - pit mines. Therefore, this study assessed the effects of meteorological conditions on the air quality in deep open - pit mines. The air velocity distribution and the dispersal mechanism of the air quality were evaluated at the Coc Sau open - pit coal mine (Vietnam) based on the measured and simulated datasets. Two fixed stations were set up in the ground to monitor the wind direction, wind speed and the temperature to evaluate the stable of the actual ozone layer based on the Pasquill ozone layer. The datasets were also used to analysis and 3D simulate to understand the air pollution mechanism in the Coc Sau open - pit coal mine. On the other hand, the change of the temperature in vertical was measured to determine the to determine the existence of a temperature inversion layer. It is considered as the main reason for the air quality reduction and the natural air circulation in deep open - pit mines. The findings indicated the existence of the temperature inversion layer and they are useful for proposing the artificial ventilation in deep open - pit mine, aiming to improve the air quality in open - pit mines. The 3D simulations also revealed that the high dust and gas concentrations in open - pit mines are due to the stable of the ozone layer.

Airflow Fluctuation from Linear Diffusers in an Office Building: The Thermal Comfort Analysis

In buildings, the HVAC systems are responsible for a major part of the energy consumption. Incorrect design or selection of the system and improper installation, operation, and maintenance of the systems’ elements may result in increased energy consumption. It is worth remembering that the main aim of the appropriate system is to maintain the high quality of the indoor environment. Appropriate selection of the HVAC solution ensures both thermal and quality parameters of the air, independently of the internal and external heat loads. The microclimate of a room is affected not only by air temperature, humidity, and purity, but also by air velocity in the occupied zone. The proper air velocity distribution prevents discomfort, particularly at workstations. Based on the measurements in the office building, an analysis of velocity profiles of air supplying two different types of linear diffusers was carried out. The analysis was made based on the results of measurements performed with thermoanemometers in the actual facility. During the study, temperature of the supply air was lower that the air in the room. Analysis was focused on the airflow fluctuation and its impact on the users’ comfort. This is an obvious topic but extremely rarely mentioned in publications related to air diffusers. The results show the importance of air fluctuation and its influence on the users’ comfort. During the measurements, the instantaneous air velocity for one of the analyzed types of the diffuser was up to 0.34 m/s, while the average value from the period of 240 s for the same measuring point was relatively low: it was 0.19 m/s. Only including the airflow variability over time allowed for choosing the type of diffuser, which ensures the comfort of users. The measurements carried out for two linear diffusers showed differences in the operation of these diffusers. The velocity in the occupied zone was much higher for one type (0.36 m/s, 3.00 m from diffusers) than for another one (0.22 m/s, 5.00 m from diffusers). The improper selection of the diffuser’s type and its location may increase the risk of the draft in the occupied zone.

A new wall function for indoor airflow with buoyancy effect

Convective heat transfer on interior surfaces of the building envelope is important for predicting building energy consumption. The buoyancy effect is a key factor in convective heat transfer. Reynolds-averaged Navier-Stokes (RANS) models combined with the standard wall function are often used to simulate the convective heat transfer coefficient of an interior wall. However, since the buoyancy effect is not considered in the standard wall function, the convective heat transfer is often underestimated, which in turn will affect the prediction of indoor air velocity and temperature distributions. Several researchers have modified the standard wall function by adjusting the wall Prandtl number, but this ad hoc adjustment has not always been effective and has no physical basis. This investigation developed a new wall function that accounts for the influence of buoyancy on heat transfer by adding a buoyancy source term to the Navier-Stokes equation for the near-wall region. The source term varies with the ratio of buoyancy and inertia forces and is linear to the logarithm of the Richardson number. Five typical indoor flows were then simulated with the new wall function to test its performance. The results show that the predicted profiles of air velocity and air temperature and the local Nu number were significantly better than those predicted with the standard wall function. The study concluded that the new wall function can correctly predict convective heat transfer on an interior wall.

Fish-ridge wind turbine aerodynamics characteristics in Oscillating Water Column (OWC) system

This paper analyzes the fish-ridge type wind turbine performance and characteristics of energy extraction applied in a low wave Oscillating Water Column (OWC) system. This article contributes to providing a better understanding of the application of OWC and VAWT in a low wave environment. The aerodynamic characteristics of the three-blade fish-ridge turbine in an OWC chamber have been successfully investigated. CFD simulation with Reynolds-Averaged-Stokes (RANS) equations was used to obtain airspeed and air pressure contours under compressed and decompressed conditions in the turbine blades. Experiments on laboratory scale test rig also obtained data. The blade torque and turbine power coefficient at different AoA were validated through the experimental test to obtain numerical equations for the relationship between airspeeds, torque, tip speed ratio, and turbine power. The turbine design was 0.2 m long and 0.1 m wide and with an overlap ratio of 15%. The maximum tested airspeed was 20m/s. We found that the fish-ridge turbine has a homogeneous air velocity distribution and pressure due to the 15% overlap area. The maximum efficiency of the fish-ridge turbine under compressed conditions was 30% at TSR 0.9, while under decompressed conditions, the maximum efficiency reached 28% at TSR 0.6.

Improving Thermal Comfort in Aircraft Cockpit Based on Optimization of Supply Air Grille

Pilot’s thermal comfort and performance are directly affected by air flow field and temperature field in cockpit. A three-dimensional cockpit model of a certain civil aircraft is established, and the distribution of air velocity and temperature is obtained with the method of computational fluid dynamics (CFD). Aiming at the problems of high local air speed and uneven temperature distribution in the cockpit, two new supply air grilles are proposed. The results show that one of the grilles can obviously optimize air flow field and temperature in the cockpit and improve the thermal comfort of the pilots.

Research on Indoor Thermal Environment of Building Corridor Based on Numerical Simulation

As an important connecting structure between modern buildings, because of its closed structure and high frequency of people’s passing, the local “greenhouse effect” formed by solar radiation causes strong discomfort to human body during the summer in northern China. In this paper, a building corridor in Tianjin is modelled by CFD, and the internal environment of the building corridor is simulated by turbulence model, heat transfer model and radiation model. It is found that K - ε model and DO radiation model in the numerical method can be used to simulate the internal thermal environment and solar radiation conditions of the building corridor. According to the distribution of air temperature and velocity in the corridor, a new type of building should be proposed in further study.

Numerical simulation of the effects of canopy properties on airflow and pollutant dispersion in street canyons

The air flow and pollutant concentration fields in a street canyon affected by trees could affect the comfort and health of residents. At present, the description of the non-uniform/discontinuous distribution of leaves is difficult. In this study, the leaf distribution in the canopy was characterized by establishing non-continuous (uniform/random) algorithm based on a numerical simulation method, and the effects of canopy properties including, height, porosity and uniform/random leaf distribution, on the airflow and pollutant concentration fields in urban street canyons were investigated. The position of the tree canopy was found to directly affect the airflow field form and the air velocity distribution in the street canyon at low inflows. The average air velocity in the street canyon could be reduced significantly when the top of the tree canopy is near the top of the street canyon. The air velocity and pollutant concentration in the street canyon would vary only slightly due to the canopy porosity. Due to the increasing canopy porosity, the air velocity would increase, and the pollutant concentration would be reduced. The leaves are non-continuous and uniformly distributed at constant porosity, which does not significantly change the velocity distribution and pollutant concentration in the street canyon.

A novel point source oxygen supply method for sleeping environment improvement at high altitudes

The hypoxic environment at high altitudes causes various sleep disorders. Diffuse oxygen enrichment is an effective way to alleviate sleep disorders and improve the built environment in high altitude areas. In this study, a novel point source local diffuse oxygen supply method was proposed to improve the sleeping oxygen environment. The oxygen supply performance was investigated by the computational fluid dynamics (CFD) method including the oxygen concentration and air velocity distributions. A sleeping experiment was conducted on the plateau to validate the CFD model. The occupied zone including the inhalation zone and the active zone was defined. The results showed that the oxygen concentration showed a rapid rise, then decreased slowly, and finally tended to be stable. The oxygen concentration after stabilization was remarkably influenced by indoor ventilation rate. The sleeping environment’s improvement was examined considering the oxygen enrichment efficiency, uniformity, stability and human comfort demand. The optimal strategies were recommended with a ventilation rate of 1 air change per hour, supplied oxygen concentration of 90%, and jet distance of 0.50 m. The study contributes to improving the oxygen environment and human sleep quality in an effective and energy-saving approach to the sustainable development of buildings in high altitude areas.

Experimental and computational investigation of wall-mounted displacement induction ventilation system

Traditional displacement ventilation (DV) creates high indoor air quality in occupied zone in cooling season due to thermal plume created by heat sources which then effectively purge contaminants out of the breathing zone, but tend to be challenged when high cooling loads are present. In addition, traditional DV, when supplying heated air via its diffusers has low ventilation effectiveness in heating season. This study investigated a novel wall-mounted displacement induction ventilation (DIV) system in comparison to traditional DV system. The investigation used an environmental chamber to mimic a typical classroom and measured the distributions of air velocity, air temperature, and contaminant concentration for validating the subsequent computational fluid dynamics (CFD) model developed across an array of operational modes. Then the CFD model was employed to evaluate the performance of DIV system in terms of ventilation effectiveness, mean age of air and vertical temperature gradient as it relates to thermal comfort. Each DIV unit receives 100% outdoor (or primary) air to its plenum chamber. As the primary air pressurizes the chamber, it exits a series of nozzles, creating a low pressure which then induces room air across the integral hydronic coil. A room is typically supplied with multiple DIV units, which allows for individual control operation during both cooling and heating modes. Results showed that stratified air distribution was achieved in both cooling and heating modes with DIV system, which remedied the current limitation of traditional DV.

Improving natural ventilation in renovated free-stall barns for dairy cows: Optimized building solutions by using a validated computational fluid dynamics model

Natural ventilation is the most used system to create suitable conditions, removing gases, introducing oxygen in livestock buildings. Its efficiency depends on several factors and above all on the number, the dimensions and the position of wall openings and internal layout of livestock buildings. The aim of this research was to develop optimized layout solutions for improving natural ventilation effectiveness in free-stall barns for dairy cows by using a CFD approach. A validated computational fluid dynamics (CFD) model was applied in a case study which is highly representative of building interventions for renovating the layout of free-stall barns for dairy cows located in an area of the Mediterranean basin. Firstly, dairy cow behaviour was analysed by visual examination of time-lapse video-recordings. Then, simulations were carried out by using the validated CFD model and changing the position of internal and external building elements (i.e., internal office and external buildings for milking) in order to find the best condition for the thermal comfort of the animals. The results showed that the best conditions were recorded for a new configuration of the building in terms of air velocity distribution within the resting area, the service alley and the feeding alley for dairy cows, and in the pens for calves. In this new layout, the office areas and the north-west wall openings were located by mirroring them along the transversal axis of the barn. Therefore, the CFD approach proposed in this study could be used during the design phase, as a decision support system aimed at improving the natural ventilation within the barn.

Modeling of Air Distribution in an Office Building Using Microperforated Textile Air Duct

The article is devoted to improving the efficiency and efficiency of ventilation systems through the use of new types of air distribution devices. These include textile air ducts made of polyester. This material allows you to cut micro-holes of a given diameter on the surface of the air duct with a laser. The advantage of micro-perforated air ducts is the possibility of supplying supply air with micro-jets with a small pulse, which eliminates the possibility of drafts in the workplace. The results of experimental and theoretical studies of air distribution using textile air ducts are analyzed. It is concluded that there are no data on the study of the distribution of supply air using textile air ducts with microperforation. The results of comparative numerical modeling of air distribution in an office space with two supply air supply schemes are presented: traditionally, through supply grilles and through a microperforated textile air duct. The fields of temperature and air velocity distribution over the room height are obtained. It is concluded that the use of a microperforated textile air distribution device increases the efficiency of assimilation of heat surpluses in comparison with traditional air supply sources (ventilation grilles).

A critical zone observatory dedicated to suspended sediment transport: The meso‐scale Galabre catchment (southern French Alps)

AbstractThe 20 km2 Galabre catchment belongs to the French network of critical zone observatories (OZCAR; Gaillardet et al., Vadose Zone Journal, 2018, 17(1), 1–24). It is representative of the sedimentary lithology and meteorological forcing found in Mediterranean and mountainous areas. Due to the presence of highly erodible and sloping badlands on various lithologies, the site was instrumented in 2007 to understand the dynamics of suspended sediments (SS) in such areas. Two meteorological stations including measurements of air temperature, wind speed and direction, air moisture, rainfall intensity, raindrop size and velocity distribution were installed both in the upper and lower part of the catchment. At the catchment outlet, a gauging station records the water level, temperature and turbidity (10 min time‐step). Stream water samples are collected automatically to estimate SS concentration‐turbidity relationships, allowing quantification of SS fluxes with known uncertainty. The sediment samples are further characterized by measuring their particle size distributions and by applying a low‐cost sediment fingerprinting approach using spectrocolorimetric tracers. Thus, the contributions of badlands located on different lithologies to total SS flux are quantified at a high temporal resolution, providing the opportunity to better analyse the links between meteorological forcing variability and watershed hydrosedimentary response. The set of measurements was extended to the dissolved phase in 2017. Both stream water electrical conductivity and major ion concentrations are measured each week and every 3 h during storm events. This extension of measurements to the dissolved phase will allow progress in understanding both the origin of the water during the events and the partitioning between particulate and dissolved fluxes of solutes in the critical zone. All data sets are available at https://doi.osug.fr/public/DRAIXBLEONE_GAL/index.html.

CFD and statistical approach to optimize the average air velocity and air volume fraction in an inert-particles spouted-bed reactor (IPSBR) system

Inert-particles spouted bed reactor (IPSBR) is characterized by intense mixing generated by the circular motion of the inert particles. The operating parameters play an important role in the performance of the IPSBR system, and therefore, parameter optimization is critical for the design and scale-up of this gas–liquid contact system. Computational fluid dynamics (CFD) provides detailed modeling of the system hydrodynamics, enabling the determination of the operating conditions that optimize the performance of this contact system. The present work optimizes the main IPSBR operating parameters, which include a feed-gas velocity in the range 0.5–1.5 m/s, orifice diameter in the range 0.001–0.005 m, gas head in the range 0.15–0.35 m, mixing-particle diameter in the range 0.009–0.0225 m, and mixing-particle to reactor volume fraction in the range 2.0–10.0 vol % (which represents 0.01–0.1 kg of mixing particles loading). The effects of these parameters on the average air velocity and average air volume fraction in the upper, middle, and conical regions of the reactor were studied. The specific distance for each region has been measured from the orifice point to be 50 mm for the conical region, 350 mm for the middle region and 550 mm for the upper rejoin. The selected factors were optimized to obtain the minimum air velocity distribution (maximum gas residence time) and the maximum air volume fraction (maximum interfacial area concentration) because these conditions will increase the gas holdup, the gas–liquid contact area, and the mass transfer coefficient among phases. Response surface methodology (RSM) was used to determine the optimum operating conditions. The regression analysis showed an excellent fit of the experimental data to a second-order polynomial model. The interaction between the process variables was evaluated using the obtained three-dimensional surface plots. The analysis revealed that under the optimized parameters of a feed-gas velocity of 1.5 m/s, orifice diameter of 0.001 m, gas head of 0.164 m, mixing-particle diameter of 0.0225 m, and mixing-particle loading of 0.02 kg, the minimum average air velocity and highest air volume fraction were observed throughout the reactor.

Air and H2 feed systems optimization for open-cathode proton exchange membrane fuel cells

In this study, air and H2 feed systems optimization for open-cathode proton exchange membrane fuel cells (PEMFCs) has been evaluated. For air feed system, a spoiler was introduced. The air velocity distribution, polarization curve, single-cell voltage distribution, and temperature distribution of the 11-cell open-cathode fuel cell stack with blowing, blowing-spoiler, and drawing air feed system were assessed. On this basis, the influences of the distance between the fan and stack with different air feed systems were investigated. The results show that the application of the spoiler could solve the problem of low air velocity in the middle of the stack and increase stack performance by 7.3%. And drawing air feed system could enhance the heat dissipation capacity of the stack and the uniformity of temperature distribution, resulting in the 7.9% stack performance increase. Optimization of the distance between the fan and stack enhances the full development of turbulence and the rate of heat transfer. In addition, the effects of four different H2 feed systems and the flow direction between air and hydrogen on the fuel cell performance were also investigated. It is beneficial for open-cathode PEMFC to be operated with the location of the H2 inlet and outlet staggered in two different endplates for better stack performance and single-cell voltage uniformity. Evidence also shows that the higher performance also could be obtained when the flow direction of air and hydrogen is vertical with lower ohmic resistance, charge and mass transfer resistance. The study contributes to the design of the open-cathode fuel cell stack to get better performance and reliability.