Airflow Uniformity Research Articles

Large Scale Pressurized Water Reactor Passive Containment Cooling System Wind Tunnel Test

The objective of the current work is to shed light on studying the air flow features of the air path which is part of the passive containment cooling system (PCS) in a pressurized water reactor design. A wind tunnel test using a 1:100 scaled model is established to study the characteristic called “wind-neutrality” of the air flow in the air path, which indicates that the environmental wind should not be beneficial or detrimental to the air flow for containment cooling. Test results show that the pressure distribution in the air path is uniform, and wind speeds, wind angles, and surroundings have little effect on air flow uniformity. These investigations show that it is possible to understand air flows in the air path of PCS with a scale wind tunnel test.

Airflow uniformity optimization for modular data center based on the constructal T-shaped underfloor air ducts

Maldistribution of underfloor airflow rate causes the nonuniform cooling power distribution of server racks in large-scale data center. In this regard, the constructal theory improves the uniformity and efficiency of airflow distribution by optimizing the geometric design of fluid distribution network. Thus, the design of a T-shaped underfloor air duct network based on the constructal theory was proposed for airflow uniformity optimization, and the concept of modular data center based on the constructal duct system was introduced in this study. The optimal air structure for the supply terminal was analyzed among 8 configurations by using CFD simulations. And then the optimal terminal was employed in an expanded modular data center with four rack modules and the constructal air ducts system. Finally, the rectifiers and ceiling vents were deployed in the model for improving the airflow uniformity in further. By designing the constructal T-shaped underfloor air duct network with the optimal structure and associated models, the airflow uniformity in the modular data center with 4 modules was improved, and the standard deviations of overall inlet and outlet air temperature of each rack were only 0.98 and 0.56.

Plant factories

Plant factories

A novel curtain design to enhance the aerodynamic performance of Invelox: A steady-RANS numerical simulation

Invelox is a patented structure designed to capture the incident wind from every direction, guide the collected wind to the ground level and increase its velocity. Previous numerical studies have revealed that a considerable portion of the collected wind escapes the structure from the opposite side of the wind entering Invelox. In the present study, three possible curtain designs are proposed to reduce or fully-eliminate this escaping air. The improved capability of Invelox to augment the wind velocity using these curtain systems is evaluated via numerical simulations. The results show that the best configuration can fully eliminate the escaping air and it will not disturb the air flow uniformity inside the Venturi section. On average, the best design can lead to a 25% increase in the average wind velocity inside the Venturi for the wind velocities of 3–12 m/s. The results also show that although it has been claimed that Invelox accepts wind from all directions, it can only be efficient at the incident wind directions of −90 to 90°. Increasing the turbulent intensity of the upcoming wind from 0 to 20%, however, has no considerable effects on the Invelox speed ratio.

Bin coring: a simple practice for improving aeration performance and saving energy: Presentation

The coring operation consists of removing the center portion of the grain mass, or core of the silosilo, to improve airflow distribution. Additional benefit of this practice is the elimination of a significant portion of the fine material, which is a source of fungal inoculum and feed for insects. The effect of coring on airflow distribution through a grain mass has been previously addressed, but the effect on energy savings was not fully quantified. Thus, the goals of this reseach were: 1) to quantify the airflow increase due to the coring operation of a silosilo full of wheat; and 2) to quantify the reduction on fan runtime and energy consumtion due to improvement in airflow distribution and airflow increase after coring. The effect of coring on airflow was quantified using the AireAr software, and the effect on aeration efficiency was studied through simulation using a specialized software (PHAST-FDM). For levels of coring (0%, 3%, 5% and 8% of total grain mass) and four levels of nonuniformity of airflow (center side difference) (30, 20, 10 and 0) were considered. Results indicated that the coring operation reduced the total time to achieve cooling, number of fan run hours, and fan power consumption. The main effect of the coring operation was the increase in specific airflow (up to 45% increase). Energy savings increased with coring, obtaining savings of 11%, 28% and 30% for 3%, 5% and 8% of coring, respectively. It was concluded that coring the silosilo by unloading from 3 to 8% of the stored grain mass is a recommendable practice, because it increases the specific airflow rate and airflow uniformity, reduces fan run hours and generates energy (and cost) savings.

Lessons learnt from on-farm mechanical drying of almonds in 2017

In order to collect almonds earlier from the field to minimise weather damage, and manage rain affected almonds, several almond growers in Australia used three different types of dehydration facilities for drying bulk almonds. These systems were fitted with temperature and relative humidity sensors placed in with the almonds at fixed locations. From knowing the moisture status of the air in the bulk almonds and that of ambient conditions, aeration fans were selectively run to condition the almonds to a desired kernel moisture content. Firstly, early season over dried almonds were re-humidified in a shed with a vented floor. The shed was also used to finish dry later season higher moisture almonds. Secondly, stockpiles of almonds with a central aeration vent running along the length of the stockpile and aeration fans at each end were used to finish dry almonds. Tests showed using fans at both ends dried the almonds quicker than using only one fan at one end. Aeration of an uncovered 50 m long stockpile (no tarp) was measured to be uniform and effective along its length. Thirdly, the performance of four modified 12 m open top shipping containers with a false perforated floor was monitored for the drying of end of season rain affected second shake almonds using heated air. It was found that by aerating the very wet almonds for 24 h with heated air and then letting them sit for several days a 6% kernel moisture content could be achieved. The monitoring provided the operators with an insight into the progressive drying of the almonds and provided data for dehydration management decisions. The placing of sensors in the container dehydrators highlighted the need to improve the uniformity of air flow into the almonds. The work showed that the dehydration facilities can be used to reduce the time almonds need to remain in the orchard and thus reduce losses from weather and other sources of damage.

Analysis of transformed fifth order polynomial curve for the contraction of wind tunnel by using OpenFOAM

Contraction is the vital part in wind tunnel hence the designing of contraction is having greater interest among the researchers. Bell and Mehta proposed a fifth order polynomial for the design of the contraction and was widely accepted among the wind tunnel designers. Daniel Brassard proposed a transformed fifth order to provide better results for the fifth order polynomial design by making the radius at the inlet of contraction higher than the radius at the outlet. In this paper the analysis of the transformed fifth order polynomial is investigated by using the open source CFD tool OpenFOAM. Analysis was basically taken considering the uniformity of air flow, wall shear stress distribution and turbulence intensity at contraction outlet and the mid vertical plane at the test section. From the analysis it is found that the transformed model is better compared to the untransformed one in terms of uniformity and turbulence intensity.

Air cooling low concentrated photovoltaic/thermal (LCPV/T) solar collector to approach uniform temperature distribution on the PV plate

In this study, to prevent local excessive temperature on a photovoltaic module, uniformity of air flow as cooling fluid in a low concentrated photovoltaic/thermal (LCPV/T) collector has considered. To obtain a uniform distribution of airflow taking into account the overall operating conditions, eight different geometries of diffuser were investigated theoretically by using computational fluid dynamics (CFD). Simulations were conducted on the most appropriate sketch with acceptable uniform air flow distribution on the PV module. The experimental results showed that the new designed diffuser significantly developed an even distribution of air velocity throughout the collector. Comparing the results with the previously published results showed that the new diffuser concave side walls and three inner deflectors improved the electrical efficiency of the PV/T collector by 20%. Also the effects of air flow rates (three levels) and concentrated solar illumination on the performance of a PV/System was experimentally measured. Using a concentrator improves electrical, thermal and overall efficiency by 36%, 42.2% and 40.5% respectively. By increasing air flow rate from 0.008 to 0.016 (kg/s); the electrical, thermal and overall efficiency were improved by 13.5, 22.75 and 22.41% respectively.

Computational fluid dynamics (CFD) based analysis of the aerodynamic and thermodynamic performances of package designs during cooling of stacked pomegranates

The demand for pomegranate fruit is increasing due to the extensive knowledge acquired on the health benefits of pomegranate and the increased public awareness about functional food. Following this, there has been an increased interest in research to improve storability. A computational fluid dynamics (CFD) model was developed, validated and used to analyse the cooling characteristics of two different package designs used for the postharvest handling of pomegranate fruit. The model incorporated the geometries of the fruits, packaging box, tray and plastic liner. A thin layer of plastic material with conservative interface heat flux was used to model the liners. The accuracy of the model to predict the airflow and temperature distributions were validated against experimental data. The model predicted the airflow through the stacks and cooling rates within experimental error. The stack design markedly affected the airflow profile, rate and uniformity of cooling. The cooling rate of the two package designs differed by 30% and the plastic lining increased the average 7/8th cooling times significantly. The profile of the high and low temperature regions depended considerably on the packaging box design.

Experimental Research on Optimizing Inlet Airflow of Wet Cooling Towers under Crosswind Conditions

A new approach of installing air deflectors around tower inlet circumferentially was proposed to optimize the inlet airflow and reduce the adverse effect of crosswinds on the thermal performance of natural draft wet cooling towers (NDWCT). And inlet airflow uniformity coefficient was defined to analyze the uniformity of circumferential inlet airflow quantitatively. Then the effect of air deflectors on the NDWCT performance was investigated experimentally. By contrast between inlet air flow rate and cooling efficiency, it has been found that crosswinds not only decrease the inlet air flow rate, but also reduce the uniformity of inlet airflow, which reduce NDWCT performance jointly. After installing air deflectors, the inlet air flow rate and uniformity coefficient increase, the uniformity of heat and mass transfer increases correspondingly, which improve the cooling performance. In addition, analysis on Lewis factor demonstrates that the inlet airflow optimization has more enhancement of heat transfer than mass transfer, but leads to more water evaporation loss.

A Computational Fluid Dynamics Model of Biological Heat and Gas Generation in a Dairy Holding Area

Abstract.The design and operation of ventilation systems for animal housing is a crucial component in maintaining a suitable environment for both animals and workers by removing heat, moisture, and gas species. However, important design and operational criteria, such as profiles of velocity and extent of mixing within animal housing, can be difficult to study experimentally. Thus, a computational fluid dynamics (CFD) model of a commercial dairy holding area, including the generation of transport of heat and gas species within the domain, was developed. The animal-occupied zone (AOZ) was modeled using porous media. The model was evaluated with experimental data of velocity and gas concentration. Results indicated that the airflow uniformity and air speed could be increased within the holding area by modifying the configuration of the side curtain openings and using concrete walls to guide airflow; a 20% increase in average velocity within the AOZ was achieved. Results of the CFD model have shown it to be an effective tool for gaining insight into the complex mixing patterns within holding areas to improve the design of animal housing. Keywords: Animal-occupied zone, Computational fluid dynamics, Greenhouse gas emissions, Holding area.

CFD analysis of a novel modular manifold with multi-stage channels for uniform air distribution in a fuel cell stack

Multiple fuel cells are generally connected in series or in parallel to supply a sufficient power output. Uniform distribution of hydrogen and air supplied to each individual fuel cell is a critical challenge, because the performance of a stack is limited by the single cell which receives the minimum amount of reactants. Various manifolds have been investigated in order to improve the flow distribution uniformity between individual fuel cells in a stack. However, a satisfactory uniformity is hard to obtain, and the existed manifolds are difficult to scale up. Therefore, a tree-type modular manifold is designed and optimized in the present study. Two different channel dimensions are compared regard to air flow distribution uniformity and overall pressure loss. The effects of channel length and air flow rate on the uniformity and pressure drop are studied by CFD simulation. The results show that an air flow uniformity around 0.99, which is the highest value reported in the literature, can be achieved in a wide range of air flow rate for a single fuel cell. The scale-up method by integrating several modular manifolds with a customized manifold to distribute air for larger fuel cell stacks is also explained.

Experimental and numerical study on air flow uniformity in the isobaric windbox of a 600 MW supercritical CFB boiler

Airflow velocity profile of the primary air in the isobaric windbox of the first 600MW supercritical CFB boiler worldwide under cold state and various boiler loads was experimentally measured and numerically simulated to investigate uniformity of the primary air. Experimental measurements were conducted in the furnace under different boiler loads (100%, 85% and 70% BMCR for the right windbox; 100% BMCR for the left windbox) by a hot wire anemometer. Meanwhile, the effect of key structural parameters (including the pressure-stabilization section height W1, inlet area ratio AR, inclined angle θ and windbox depth) on the airflow uniformity of the isobaric windbox were analyzed based on two-dimension simulations of a series of isobaric windboxes with 43 different configurations, using the CFD software package FLUENT. The measured results showed that while the airflow velocity was basically uniform along the width direction of the windbox, it exhibited an obvious non-uniform profile along the depth direction. The airflow velocity was relatively higher in the front wall and obvious lower in the back wall. As the boiler loads increased, the airflow uniformity became worse because of intensified flow turbulence. Moreover, due to the jet flow at the entrance of the isobaric windbox, the airflow velocity in the initial a few simplified tubes was always lower than that of other parts regardless of the windbox depth. In addition, the airflow profile of the isobaric windbox within 12m was significantly different from those beyond 15m. The structural parameters of the isobaric windbox had obvious influence on the airflow uniformity, and this influence decreased with the increase of windbox dimension. The backflow phenomenon resulting from the interaction between W1 and AR was observed in some simulation cases. Finally, the optimal windbox structural parameters for primary air uniformity were determined by an optimization study of the isobaric windbox structural parameters.

On the prediction of uniformity of air flow out from manifold distribution

AbstractComputational fluid dynamics (CFD) was used to simulate a closed‐end multiple outlet pipe to examine the effect of different exit port geometry and size of perforation on performance of manifold distribution. To obtain an optimum design, the amount of fluid discharging from any opening in a pipe is greatly concern in engineering applications because uniform flow distribution has significant influence on the performance of manifold distribution. In this investigation, the vertical manifold system was used to study the hydrodynamics of air flow and simulate with computational fluid dynamics (CFD). Firstly, three different exit port geometry (circular, rectangular and square) are chosen to investigate the effect of exit port on mass flow rate uniformity effusing from distribution manifold. The best performance, which most closely approximating uniform outflow was achieved by the rectangle exit ports. Secondly, three different perforation size (3, 4 and 5 mm) of circular exit port were selected to reach to the finding of uniformity. Results show the 5 mm diameter orifices exit port achieve the uniform outflow of all. The ratio of the total opening area for all cases to the cross‐sectional area of the cylindrical pipe is identical for these two cases. Thirdly, the effect of perforation diameter with variable pipe ratio for equal number of orifices was investigated. The analysis for investigating the changes in the discharge angle of the stream between the orifices of multi‐perforated pipes perform for all cases. Standard k–ϵ turbulence model was considered for the numerical simulation, the finding results of numerical simulation were evaluated by the laboratory experiments.

Effect of raised floor height on different arrangement of under-floor air distribution performance in data center

In the more and more expanding and complicated data center, requirements on air conditioning system and the air distribution arrangement are getting higher and higher. One of the resolutions is improving the airflow uniformity and cooling the local over-hot area by raising the floor in the data center. With a typical mode of four rows of cabinets in the data center as a sample. This paper uses Computational fluid dynamic (CFD) to investigate the influence of the six raised floor heights (0.2m, 0.4m, 0.6m, 0.8m, 1m and 1.2m) on the airflow distribution of three types of under-floor air distribution (the open aisle, the cold aisle containment and the hot aisle containment). Optimization is done on performance indexes, including supply/return heat index (SHI/RHI), return cooling index (RCI) and return temperature index (RTI), with which the condition of subcooling / overheating of all cabinets and the characteristics of the airflow organization in the data center are reflected and the thermal environment in the data center is revealed. Normally, the cooling effect and the uniformity of the airflow can be improved by raising the floor height. However, this won’t work well when the floor height reaches a certain level. Therefore, based on the comparative analysis on the 18 different cases in this investigation, the recommended range of raised floor height in data centers of different construction can be obtained and verified in the experimental tests. The experimental results turn out to be in accordance with the simulation results, which proves the range recommended in this investigation is valuable.

Fluidization of Geldart D type particles in a shallow vibrated gas-fluidized bed

The fluidization behavior of a binary mixture of Geldart D type particles in a shallow vibrated gas-fluidized bed (VFB) was systematically studied by using a high-speed dynamic camera. This study drew a comparison between the fluidization of a VFB and a conventional gas-fluidized bed (CFB). The results show that the characteristic air velocities in a VFB, such as the minimum fluidization velocity, the minimum bubbling velocity and the minimum slugging velocity, have considerable reductions in comparison with that in a CFB. It is indicated that the vibration significantly changes the gas-solid two-phase flow structure and improves the dispersion uniformity of air flow in the bed. The air pressure waves, as the main transmission mode of vibration energy, can improve the air-solid contact efficiency and organize the excess fluidizing air to form periodic slugs. In a VFB of Geldart D type particles, there are four distinct fluidization regimes: static bed, bubbling fluidization, slugging fluidization and turbulent fluidization. The results show that a good performance of density segregation in a VFB of Geldart D type particles happens in the stage of gentle slugging.

Airflow Resistance through Bulk Sweet Potato Roots

Abstract. Storage of sweet potato roots in bulk is common in tropical and subtropical countries. Hot spots and mold damage may occur during storage, especially if the roots are not ventilated. Airflow resistance data are therefore required to predict the uniformity of airflow and to design optimum ventilation systems. This study presents the resistance to airflow through unwashed and clean sweet potato roots over a superficial velocity range of 0.08 to 1.70 m s -1 . The results were correlated by a physically meaningful modified Ergun model and compared with the modified Shedd‘s model. In the modified Ergun model, the physical properties of the roots, such as porosity, shape factor, and surface roughness, were explicitly incorporated into the model. The modified Ergun model exhibited higher values for coefficient of determination, lower root mean square error, and lower percentage error and therefore provided the best fit when compared with the modified Shedd‘s model. The model can therefore be used to predict resistance to airflow through bulk sweet potato roots realistically. The differences in the pressure drop between sweet potato roots arranged differently to airflow and with or without soil fraction on the surfaces of the roots were further explained by the contribution of particle drag and surface friction. The pressure drop through unwashed and clean sweet potato roots was observed to increase with higher airflow, bed depth, root grade composition, and presence of soil fraction. The results for the effect of soil fraction stress the importance of cleaning sweet potato roots before storage. Airflow was the most significant factor affecting pressure drop of unwashed and clean sweet potato roots compared with root grade composition and presence of soil fraction for all batches studied. The results obtained from this study are comparable to those reported by other researchers, particularly for other agricultural roots.

A CFD study on improving air flow uniformity in indoor plant factory system

Indoor plant factories are one of the alternative ways to meet the demands of food production for the increased urban dwellers. It enables growers to grow food crops consistently and locally with high quality. In an indoor plant factory, a forced convection based ventilation and circulation system is used to control the growing environment and maintain climate uniformity. Lettuce is a common leafy crop grown in indoor plant factories and an improper design could cause the tip burn of lettuces which usually occurs at inner and newly developing leaves with low transpiration rate due to the existence of a stagnant boundary layer under high transpiration demand. A three-dimensional computational fluid dynamics (CFD) model was developed and validated through simulating the growing environment in a single shelf production system. An improved air circulation system was designed and proposed to help providing a dynamic and uniform boundary layer which could help preventing tip burn occurrences in lettuce production. A perforated air tube with three rows of air jets was designed to provide vertical air flow down to the crop canopy surface. Four cases with the perforated air tubes were compared with a control treatment. The results indicated that the case with two perforated air tubes was able to provide an average air velocity of 0.42 m s−1 with a coefficient of variation of 44%, which was recommended as the optimal design of air circulation system among four cases in this study.

Experimental study on the air flow field in the water collecting devices

This paper deals with the experimental analysis on the air flow field inside the different water collecting devices (WCDs). The wind tunnel experiment is first employed in the WCDs research. The resistance to the airflow caused by the WCDs is analyzed. The stability of the air flow field in the experimental model is studied. Coefficient of the ventilation uniformity is proposed to qualitatively reveal the airflow uniformity. Compared with the conventional natural draft wet cooling tower, the cooling performance of the cooling tower with WCDs can be enhanced due to the greater air mass flow rate caused by the Venturi effect of the WCDs. The air flow field in the WCDs with rectangular channel is the most turbulent, and this kind of WCDs is recommended not to be used in practical application. Preliminary study on the numerical simulation is conducted. The CFD models for both the scaled size WCDs and the real size WCDs are developed and validated in comparison to the experimental measurements. Studies in the paper indicate that the numerical analysis on the WCDs is feasible. These conclusions lay an experimental foundation for the numerical research on the air flow field inside the WCDs.

Numerical Investigation on Airflow Distribution of Automotive Radiator

In automobiles due to styling and packaging constraints there are several blockages in the upstream and downstream direction of radiator, which interrupts the uniform airflow distribution. However, airflow distribution on the radiator face plays a key role in improving its effectiveness. The objective of this work is to analyze the impact of airflow distribution and uniformity index with different types of blockages ahead of the radiator using Computational Fluid Dynamics (CFD) tool. Four different geometry blockages are considered for this study and analyzed further to arrive at the better Uniformity index. The different blockage geometries considered are horizontal, vertical, side to side and side to center. It is observed that side to side geometry blockage gives poor velocity distribution compared to others. Also CFD model is validated with experimental result and good agreement has been observed between predicted and measured velocity pattern over the radiator. In addition to this, a statistical study is conducted to analyze the influence of various parameters like fan speed and ram air speed along with types of blockage on the uniformity index. It is observed that, type of blockage have the significant impact on the uniformity index. The interpretations of this work can serve as a design guideline for the thermal system and styling engineers of automotive domain.