Internal Airflow Research Articles

Wind tunnel and CFD analysis of wind-induced natural ventilation in sheds roof building: impact of alignment and distance between sheds

Sheds roof is a natural ventilation strategy that presents roof openings working as air collectors or extractors. A detailed review of the literature indicates a lack of research analyzing the impact of different sheds roof shapes and roof configurations on natural ventilation potential. This paper aim is to evaluate the impact of changes in distance and alignment between windcatcher and leeward sheds roof. The methodology was Computational Fluid Dynamic (CFD) simulation. Tests were performed in an atmospheric boundary layer wind tunnel on a 1:15 scale model to evaluate the accuracy of CFD simulation in different design configurations of sheds roof. The analysis showed that CFD simulations are generally in good agreement with the wind tunnel tests. The difference between the most of the monitored points in the two tools used had errors below 10%. Besides this, the results show that changes in alignment of the sheds and increasing the distance between them decrease and increase the internal airflow to the leeward and windward sheds roof, respectively. In the first case it is due to the reduction in the sheds openings area. In the second these changes turn the sheds more effective in the air capture.

Measurement of cross-ventilation rate in urban multi-zone dwellings

Cross ventilation can effectively improve air quality with larger ventilation rate than single-sided natural ventilation. The measurement of ventilation rate is critical for research on indoor environmental maintenance and air quality control. This investigation compared four methods of obtaining the cross ventilation rate in a residence, including direct measurement by the tracer-gas-decay method, and indirect measurement with ultrasonic anemometers, from the wind speed at a reference position, and from the differential pressure between two sides of the residence. Furthermore, measured wind speed in the direction normal to the opening was used to analyze the unsteady and non-unidirectional flow characteristics, and the airflow consistency σ was found to be in the range of 50%–98%. The results show that when σ > 90%, the internal airflow was close to unidirectional flow, and the ventilation rates in all rooms were similar. As the ratio σ decreased, the error between the measured and calculated ventilation rate at the openings increased. When σ < 70% with severe non-unidirectional flow, the presumed ventilation volume based on the measured wind speed at one opening had a large deviation from the measured ventilation rate at the other. We then calculated the volume of air intake and outflow at the same opening. On the basis of volume conservation, the exchange ventilation rates between internal rooms were obtained by the tracer-gas-decay method combined with ultrasonic anemometers to measure the wind speed at the openings of the multi-zone dwellings. Therefore, single tracer-gas-decay method with ultrasonic anemometer at the openings can measure the cross ventilation rate and obtained the ventilation rate between internal rooms of the multi-zone residence.

Effect of swirl at intake manifold on engine performance using ethanol fuel blend

ABSTRACTEthanol fuel is widely used as an alternative fuel in spark ignition engines. The use of ethanol reduces dependence on fuel from the fraction of hydrocarbons. As such, adding swirl generators to the intake manifold aims to make the internal airflow more turbulent. The influence of swirl on the performance, emissions, and combustion in a constant speed Spark Ignition (SI) engine was studied experimentally. Also, the effects of the addition of ethanol in the fuel on engine performance and emissions under development of the intake manifold with a swirl generator were determined. Thus, the study analyses the effects of adding a swirl generator to the intake manifold on engine performance, fuel consumption, and emissions produced. Influence of the swirl generator on the airflow and swirl pattern testing is done on the three types of swirl generators, which are the concave, flat bottom, and symmetrical with different angle positions. Engine experiment was performed at 2,000, 2,500, 3,000, 3,500, 4,000, 4,500, and 5,000 rpm engine speed at WOT using a concave swirl type generator. Response Surface method (RSM) was used to find the optimum intake manifold design according to response (flow and swirl) and independent variables (a type of swirl generators and angle positions). The concave swirl type generator at 6.53 angle position is considered to be optimum for this particular engine. The highest engine torque and BSFC were with a swirl generator intake manifold. The HC and CO emissions increased with intake manifold with a swirl generator. The CO2 emission reduced with swirl generator intake manifold by 2%, 3%, and 5% with gasoline E10 and E20 compared to the standard intake manifold.

Effects of air supply operation on the distribution and spatial differences of airflow field in conditioned room: A CFD Study

In air-blast freezer, there are differences in food freezing process at different locations due to the non-uniform airflow distribution in freezing chamber. In this paper, a decoupling method was used to simulate freezing process of food products at different locations. Firstly, the internal airflow distribution model of the freezing chamber was established to simulate the airflow field in freezing chamber under different velocities of air supply. The mainstream air flow rate around each food product was then calculated as the ambient air velocity at which the food freezes. Then, a validated lumped parameter model was used to simulate the freezing process of individual food product, and the effects of freezing conditions on freezing process at different locations were studied. The results showed that there were large differences in the freezing conditions of foods at different locations in freezing chamber, which were mainly reflected by the difference in ambient air velocity. Compared to air velocity, air temperature was distributed rather uniformly in freezing chamber. With the increase of supply air velocity of air coolers, the ambient air velocity around food products in freezing chamber increased almost linearly.

Experimental and numerical investigation of using pulsating heat pipes instead of fins in air-cooled heat exchangers

The goal of this study is the experimental and numerical investigation of using pulsating heat pipes (PHPs) as substitutes for fins in a typical air-cooled heat exchanger. Due to the small temperature difference between the cooling air and internal airflow in the case study, it was necessary that appropriate PHPs with the capability to work in small temperature difference conditions be investigated and an appropriate working fluid be selected. After reviewing various studies, R134a was selected as the best working fluid from the heat transfer standpoint. Afterward, a testing device was designed and fabricated. Additionally, in order to predict the behaviors of the main tubes with pulsating heat pipes and also finned tubes, the computational fluid dynamics was used and pulsating heat pipes and fins were simulated and compared. Different tests were performed with various air flow rates and temperatures. The results indicated that using pulsating heat pipes as fins have a significant effect on improving the heat transfer. In free convection (without external flow over the tubes), using the heat pipes resulted in a better performance in comparison to fins and in the best case, the overall heat transfer coefficient was improved by 310%. This improvement was approximately 263% for the forced convection condition.

Numerical simulation study of novel air-cooled condenser with lateral air supply

Uneven distribution of internal temperature and air flow field are considered to be the essential defects of the Λ-frame air-cooled condenser (ΛACC) in a power plant. Lateral air supplement to a noble, truncated cone-shaped air-cooled condenser (TCACC) is investigated by mean of numerical simulation to solve these problems fundamentally and improve the performance of the air-cooled condenser (ACC) obviously. A Circular ring, installing at the bottom of the heat transfer surface, the structure of which is optimized. According to compare a series of ACCs in different fan inlet air conditions, the TCACC with a lateral air supply (TCACCL) is obtained for heat transfer and safety. The numerical results indicate that the lateral air supplement is an effective way to improve the thermo-flow performance of TCACC.

Parametric analysis of the wind-driven ventilation potential of buildings with rectangular layout

A method to evaluate the wind-driven ventilation potential of buildings is proposed and some schematic examples are given. Two indicators of such potential are put forward: the first concerning the pressure difference between spots (openings) on the facades and the second concerning the ratio between this pressure difference and a simplified measure of the pressure loss by the internal air flow. These indicators allow one to compare shapes and orientations and can help finding the most appropriate ones during a preliminary stage of the design of a naturally ventilated building. To present the proposal, a two-dimensional computational fluid dynamics parametric model of a schematic building is set, the parameters of which are the aspect ratio of the building's rectangular plan and the wind relative direction. The computational fluid dynamics simulations are supported by literature benchmarks and by qualitative experiments in a wind tunnel. Using this model, the pressure field is computed for 66 cases and their ventilation potentials are evaluated; some graphic outputs are then proposed for a preliminary understanding of the pressure field and of the resulting indicators. The optimal morphology given by such analyses is finally compared to that of some naturally ventilated existing buildings, including Iranian badgir towers. Practical application: This paper provides graphs to predict a building's potential for natural ventilation thereby enabling a designer to determine the wind-driven ventilation in a building and evaluate the structure, optimise its orientation, its aspect ratio and opening positions. These can be used, for example, in the evaluation of naturally ventilated multi-storey rectangular plan buildings (that might employ hyper-ventilation or night cooling) or to evaluate possible passive ventilation strategies for existing buildings. With the support of these graphs, which can be used as computationally inexpensive and fast decision tools, it is possible to simulate configurations, considering the parameters that most influence natural ventilation.

Effects of throughput and operating parameters on cleaning performance in air-and-screen cleaning unit: A computational and experimental study

The influences of throughput and operating parameters on internal airflow and cleaning performance for the air-and-screen cleaning unit were investigated. The throughput experiment showed that, the airflow velocities above the vibrating screen decreased by 1.3–15.5% for every 1.0 kg s−1 increase of throughput and which below the vibrating screen decreased by 2.7–8.1%. As a result, the cleaning performance has declined. Then, the airflow velocity measurement and cleaning performance tests were taken under 4.0 kg s−1 throughput with single factor experiment in which fan speed, airflow deflector angle and sieve opening were as factors. And, the Computed Fluid Dynamic (CFD) numerical simulations were carried out to analyze the movement trend of internal airflow as an auxiliary analysis method. The following viewpoints were obtained, the fan speed has a large effect on cleaning performance by affecting the overall airflow velocities in the cleaning unit. And, the airflow velocities above the vibrating screen increased from 0.2 m s−1 to 0.4 m s−1 for every 150 r min−1 increase of fan speed, which below the vibrating screen increased from 0.4 m s−1 to 1.1 m s−1; The highest airflow velocities area above the vibrating screen moved forward to the central position in the longitudinal direction as the airflow deflector angle increased; With the reduction for each 4 mm of chaffer opening, the airflow velocities above the vibrating screen increased by 0.2–0.4 m s−1. At last, making mathematical relations between each operating parameter and the cleaning performance, and proposing the method of adjusting the single operating parameter under rated condition according to the throughput. They provide a basis for real-time automatic adjustment of the operating parameters in the air-and-screen cleaning unit.

Wind tunnel investigations of sidewall opening effects on indoor airflows of a cross-ventilated dairy building

Well-understanding indoor air movement with respect to openings in naturally-ventilated buildings is essential to provide healthy and comfortable indoor climate for livestock. This study investigated the effects of the sidewall opening configurations on internal airflow fields and air velocity characteristics within the animal occupied zone (AOZ). Eight cases with varied opening ratios and locations were tested under 8 m•s-1 free wind speed and wind direction perpendicular to the sidewalls. The ‘up-jet’ airflow pattern was observed when the opening ratio was no greater than 62.71% and the openings located beneath the eaves. Air went across the AOZ without circulating with the surrounding air when no sidewalls were installed below the AOZ height. Both air speed and turbulent kinetic energy increased when the opening was bigger with Pearson's correlation coefficients of 0.8 and 0.9 respectively, but the relationship between the opening size and the turbulence intensity was more complex. Uniform air speed distributions were observed in the AOZ with high sidewalls on bottom. By contrast, the air speed heterogeneity in the AOZ was found when sidewall heights were below the AOZ height. We conclude that care should be taken when using these kinds of opening configurations during extreme cold windy weather conditions.

Study on airflow field in a new type of the main nozzle of an air-jet loom

The main nozzle is a key component in the weft insertion system and the internal airflow characteristic affects the efficiency of an air-jet loom and fabric quality. In order to improvement the weft insertion rate, a kind of new main nozzle is designed by adding a polygon slots inside the needle. In this paper, the transonic/supersonic airflows is numerical simulation with FLUENT software. The distribution of the airflow pressure and axis velocity of the main nozzle are obtained by changing the air tank pressures and geometry of the main nozzle. The numerical results indicated that the velocity along the axis direction is obvious increased by fabricated a pentagon slot inside the needle.

An integrated heat-transfer-fluid-dynamics-mass-transfer model for evaluating solar-dryer designs

This work aims to facilitate the design-improvement process of solar dryers by a computational model that accounts for the interrelationships between the conditions of the drying product (temperature and moisture content), the airflow inside the dryer (temperature, humidity, and velocity), and the surrounding conditions (temperature, humidity, and solar radiation). The model considers not only how the dryer and surrounding affect the drying of the product but also how the conditions of the product itself affect the conditions of the airflow inside the dryer and, by extension, its performance as well. To account for such intricate interrelationships, the model leverages and integrates three physical domains: fluid dynamics, heat transfer, and mass transfer. The model automatically simulates the natural convection inside the dryer and eliminates the need for obtaining the experimental values of the temperature, humidity, and velocity of the internal airflow for calculating the moisture level of the product. It can be used to quantify the effects of mixed-mode solar dryer designs on their drying performance. Simulated results were validated against experimental data and found to be reasonably accurate. Moreover, the model offers insights into how the complex airflow inside the dryer can affect the drying of the product. Practical applications Experiments that are required to understand, compare, and improve the drying performance of different solar dryer designs can be impractical because of long operation time of solar drying and variability of weather conditions, making a typical design process time-consuming. This work aims to facilitate the design-improvement process. The model can quantify the effects of mixed-mode solar dryer designs on their drying performance. The model can also offer useful insights for solar-dryer designers. For instance, results from a case study show that the velocity and humidity of the internal airflow could have stronger influence than that of the temperature on the drying, suggesting that a solar dryer design that aims only to maximize airflow temperature may not lead to optimal drying, and that airflow temperature should not be used as the sole benchmark for solar dryer design.

Digital Tools for the Morphological Design of the Naturally Ventilated Buildings

Naturally ventilated buildings have great potential in terms of comfort and energy saving. However their design is difficult, as the effectiveness of the ventilation is affected by many parameters. Through a parametric CFD (Computational Fluid Dynamics) simulations, graphical tools are generated to evaluate, adopting a comparative approach, the ventilation performance of a morphological family of buildings and to choose the shape of the building, its orientation and the position of the openings. In particular we focus on the interaction between the shape of the building and the wind, that produces a pressure distribution over the building’s envelope, activating an internal airflow through the openings. The pressure difference between any two points lying on the envelope is considered as the force driving of the natural ventilation that depends mainly on the aspect ratio of the building (r) and of its orientation (α). Changing r and α in a specific range, we represent some different configurations. Then we reduce the problem from 3D to 2D, studying the airflow around the vertical and the horizontal cross-section of the building. By knowing the pressure values, we create some plots useful for the positioning of the openings and we calculate an indicator, measuring the global performance of ventilation of the building. By plotting the indicator of the ventilation potential, it is possible to compare the performance of a morphological building family. The graphics can be used by designers without any particular skills in aerodynamics.

Simulation analysis on inner flow field and optimization design of air knife

This paper conducted a parametric modeling for air knife structure in a printing factory, used HYPERMESH software to divide the meshes of air model and combined with actual conditions to define various boundary conditions in the inner flow field of air knife. Meanwhile, this paper adopted fluid dynamics software Fluent to conduct numerical simulation for the internal airflow of air knife, obtained the distribution regulation of flow field, conducted a parametric modeling for air knife structure under many internal structural proposals through ANSYS design module based on the simulation computational result, conducted optimization design for the position of guide plates, the number of outlets and the size of return air tank in the detailed structure in the air knife in order to determine specific dimension parameters and optimal proposals. Based on the computational results of simulation, this paper found that the original air knife structure had a non-uniform flow field and low velocity at the inlet and outlets. With the increase of length of air knife, the velocity of the middle outlet reduced to zero and did not have obvious effects any more. Guide plates in the air knife had a great influence on the inner flow field of air knife. Through optimization design, the inner flow field of air knife became uniform when there was only one guide plate. When the guide plate was close to the front end of the air knife, the inner flow field of air knife was relatively uniform and velocity at the inlet and outlets was relatively high. This paper conducted a model design for air knives with different structural types and determined proposal 4 as the optimal design through repeated analysis. The design method in this paper could provide guidance for studying and designing air knife structures in the aspect of technological approach and theory.

Experimental study and numerical simulation of the interior flow in a telecommunications cabinet

The sector of information and communication technologies, especially telecommunications, has grown in a relentless way, leading to an increase in the number of necessary infrastructure to ensure the geographical coverage of the service, having the outdoor telecommunications cabinets (OTC) been an increasingly preferred choice of this type of infrastructure. These cabinets need cooling systems to maintain interior temperatures between desired values, but an effective cooling depends directly on the air flow inside. This paper includes the experimental results of the internal flow and heat transfer in a model a of real OTC, in order to characterize its thermal behavior. The internal air flow is visualized through experimental methods and compared with numerical predictions. The flow occurs mainly in turbulent regime, possessing greater magnitude on the back area of the OTC, where also exist some recirculation zones that can difficult an effective cooling. The results allow to conclude that forced ventilation is an effective method of OTC cooling, combined with low energy consumption.

Effect of natural ventilation mode on thermal comfort and ventilation performance: Full-scale measurement

Natural ventilation can provide building occupants with thermal comfort and a healthy indoor environment. Among all the design related parameters that affect ventilation performance, ventilation mode (i.e. single-sided and cross ventilation) is perhaps the main one. The current study uses full-scale in-situ measurements to investigate the effect of ventilation mode on thermal comfort and ventilation performance of a high-rise case study unit. Two modes of natural ventilation, single-sided and cross ventilation, are investigated. Air velocity, temperature and relative humidity were measured for both ventilation modes on two consecutive days in summer. Indoor thermal conditions were evaluated using the extended Predicted Mean Vote (PMV) and Standard Effective Temperature (SET*) comfort models. In addition, the relationship between reference wind speed and internal airflow, airflow distribution, and the effect of wind direction on internal airflow were investigated for both single-sided and cross ventilation. Finally, the implications of the research outcomes on natural ventilation design are discussed. Indoor thermal conditions were found to be within the comfort zone for more than 70% of the time under cross ventilation operation while single-sided ventilation provided adequate thermal conditions for only 1% of the time. Results from this study highlight a significantly better performance of cross ventilation over single-sided ventilation.

The effect of conical dimple spacing on flow structure and heat transfer characteristics of internal flow using CFD

In the present study, heat transfer and flow characteristics simulations over the surface of conical dimple were investigated. Single dimple row with inline arrangement was formed on the internal surface of the 3-D rectangular wind tunnel model. The air flow was perpendicular to the centre line of every dimple and the printed diameter of dimples on the surface was D=26.4mm. The depth of dimple on the surface of wind tunnel was H/D=2. The space between dimple-to-dimple was varied for S/D=1.125, 1.25,1.5, and 2. The Reynold number based on the hydraulic diameter of internal air flow was 20,000 depending on the wind tunnel hydraulic diameter. The numerical computation was applied with a Shear Stress Transport (SST) k-ω turbulence model. The average Nusselt number for the S/D=1.125 case is the highest. When the spacing becomes increase, the value of average Nusselt number tends to decrease.

Numerical simulation of moisture-heat coupling in belt dryer and structure optimization

In order to improve internal air flow field of belt dryer and increase moisture standard deviation of drying material in dryer, we used FLUENT software to study influences of material thickness, air velocity, air temperature and air relative humidity on material moisture content and uniformity in dryer on the basis of computational fluid mechanics and heat and mass transfer theory. Viscous dissipation was added to the energy equation. Porous medium model and evaporation model were used to improve result accuracy. A comparison between the moisture content of material inside the dryer was made when no deflector, a common deflector and a wing deflector are applied. Results show that air velocity in each measuring point is consistent with the numerical simulation. Material thickness had the largest influence on moisture content uniformity among four factors, followed by drying air velocity. The result of variance of material moisture content indicates that the thicker material thickness was, the better moisture content uniformity would be. When test conditions were shown as follows: 80mm thickness; 343K inlet air temperature; 1.5m/s air velocity; 0.24 air initial humidity, moisture standard deviation of material was optimal. The wing deflector reduced material moisture content as a whole and moisture content uniformity was improved.

Prerequisites for a dry powder inhaler for children with cystic fibrosis

Correct inhalation technique is essential for effective use of dry powder inhalers (DPIs), as their effectiveness largely depends on the patient’s inhalation manoeuvre. Children are an especially challenging target population for DPI development due to the large variability in understanding and inspiratory capacities. We previously performed a study in which we determined the prerequisites for a paediatric DPI in a mostly healthy paediatric population, for which we used an empty test inhaler with variable internal airflow resistance and mouthpiece. In the current study we investigated what specifications are required for a DPI for children with cystic fibrosis (CF), for which we expanded on our previous findings. We recorded flow profiles of 35 children with CF (aged 4.7–14.7 years) at three airflow resistances (0.031–0.045 kPa0.5.min.L-1) from which various inspiratory parameters were computed. Obstructions in the mouth during inhalation were recorded with a sinuscope. All children were able to perform a correct inhalation manoeuvre, although video analysis showed that children did not place the inhaler correctly in the mouth in 17% of the cases. No effect was found of medium to high airflow resistance on total inhaled volume, which implies that the whole resistance range tested is suitable for children with CF aged 4–14 years. No effect could be established of either mouthpiece design or airflow resistance on the occurrence of obstructions in the mouth cavity. This study confirms our previous conclusion that the development of DPIs specifically for children is highly desired. Such a paediatric DPI should function well at 0.5 L inhaled volume and a peak inspiratory flow rate of 20 to 30 L/min, depending on the internal airflow resistance. This resistance can be increased up to 0.045 kPa0.5.min.L-1 (medium-high) to reduce oropharyngeal deposition. A higher resistance may be less favourable due to its compromising effect on PIF and thereby on the energy available for powder dispersion.

The simulated air flow pattern around a moving animal transport vehicle as the basis for a prospective biosecurity risk assessment.

Research that investigates bioaerosol emissions from animal transport vehicles (ATVs) and their importance in the spread of harmful airborne agents while the ATVs travel on roads is limited. To investigate the dynamical behaviour of theoretically released particles from a moving ATV, the open-source computational fluid dynamics (CFD) software OpenFOAM was used to calculate the external and internal air flow fields with passive and forced ventilated openings of a common ATV moving at a speed of 80 km/h. In addition to a computed flow rate of approximately 40,000 m3/h crossing the interior of the ATV, the visualization of the trajectories has demonstrated distinct patterns of the spatial distribution of potentially released bioaerosols in the vicinity of the ATV. Although the front openings show the highest air flow to the outside, the recirculations of air masses between the interior of the ATV and the atmosphere also occur, which complicate the emission and the dispersion characterizations. To specify the future emission rates of ATVs, a database of bioaerosol concentrations within the ATV is necessary in conjunction with high-performance computing resources to simulate the potential dispersion of bioaerosols in the environment.

Drying of Almonds I: Single Particle

Drying is an essential unit operation required in food processing industries, particularly in the dry fruits industry. Drying of almonds exhibit many characteristic features such as non-spherical shape, swelling/ shrinkage as a function of moisture content, uneven drying because of their peculiar shape and proximity to other almond kernels and so on. In this study, we have investigated the drying of almonds through experiments and computational modelling. In this regard, Mettler Toledo Halogen moisture analyzer unit was used to conduct experiments for a single almond kernel. In this widely used equipment, internal air flow patterns and therefore heat and mass transfer depend on natural circulation of air. A detailed three-dimensional computational fluid dynamics (CFD) model was used to simulate the air flow pattern, heat and mass transfer in the drying unit. Carefully designed experiments with a single almond kernel were carried out at different temperatures to estimate key parameters of interest (drying kinetics and effective diffusivity). The CFD model was also used to quantify non-uniform heat and mass transfer and therefore non-uniform drying of a single almond kernel. The presented approach, models and results might be useful to improve the performance of drying units in industrial systems. The results and models presented here will also provide a basis for further work on multiple almond kernels and on tray dryer unit.