Air Flow Configuration Research Articles

Effect of flow configuration on the performance of spiral-wound heat exchanger

The effects of flow configuration on the heat transfer performance of a spiral wound heat exchanger were experimentally investigated. The spiral-wound heat exchanger was made from stainless steel tubes of 6 mm outside diameter and consisted of 4 helical coils centrally connected in series, with a longitudinal and transverse pitch of 12 mm. Three air flow configurations were tested, namely axial, radial, and mixed axial-radial flows. The overall heat transfer coefficient was determined from the experimental data and the shell-side convection heat transfer coefficient was calculated from the tube-side convection heat transfer coefficient and the total thermal resistance. The measurements were conducted for tube-side Reynolds number in the range of 9000–10,000 (for water flow inside the tubes) and shell-side Reynolds number in the range of 500–6000 (for air flow outside the tubes based on maximum velocity). The results showed that the mixed axial-radial flow configuration has the highest heat transfer coefficient and pressure drop followed by the axial and radial flow configurations. Correlations of Nusselt number, Colburn-j factor, and friction factor were developed for the different flow configurations and a comparison with the Nusselt number correlations for heat transfer over bank of tubes was presented. The correlations are in good agreement with experimental data and has correlation coefficient in the range of 78–98%.

Experimental and Analytical Characterization of Firebrand Ignition of Home Insulation Materials

Wildland firebrands are known to ignite materials in attic spaces of homes. To clarify the effects of choices in attic insulation materials for homes located at the wildland urban interface, this study seeks to characterize the effects of firebrand characteristics on the ignition propensity of several common insulation materials: polyurethane foam, expanded polystyrene (EPS), extruded polystyrene (XPS), flame retarded and non-flame retarded denim, and flame retarded and non-flame retarded loosefill cellulose. An experimental system was developed to explore the effects of firebrand heating, air flow, and firebrand configuration on ignition. For an equal initial mass of wooden material, two firebrand configurations were generated: a single whole firebrand and multiple (five) fragmented firebrands. Relative to whole firebrands, the fragmented firebrands were found to more reliably ignite the insulation materials. Thermoplastic insulation material would only ignite in a temporary flash flame, but did not support sustained burning. Following the flash flame, the firebrands would melt through the synthetic polymer material (XPS and EPS) and cease smoldering. Cellulosic insulation materials would ignite in a sustained fire provided that there was adequate air flow. A simple heat and mass transfer model was developed to describe the ignition process due to firebrand deposition. Traditional lab-scale experiments, thermogravimetric analysis and cone calorimetry, were performed to parameterize the model. Results followed experimentally observed firebrand temperature patterns. There was an average error of approximately 8.5% between firebrand temperature model predictions and experimental measurements. Also, consistent with the experimental results, the model predicted that increasing air flow increased ember temperature and reduced the time to ignition for cases in which ignition occurs.

Air Flow Configurations and Dehumidifying Performance of Four-divided Adsorbent Desiccant Rotor

Air Flow Configurations and Dehumidifying Performance of Four-divided Adsorbent Desiccant Rotor

Applicability of a 3D Laser Scanner for Characterizing the Spray Distribution Pattern of an Air-Assisted Sprayer

Three-dimensional (3D) laser technology has been tested for assessing the performance of air-assisted spraying. A static test using an air-assisted sprayer equipped with two axial fans (front and back) with opposing directions of rotation was developed. The sprayer was adjusted to spread water in a static mode, at a pressure of 10 bars, with four air volumetric flow rates. Measurements were performed using a Leica HDS6000 3D laser scanner. In addition, the flow and velocity of air generated by the air-assisted sprayer were measured using a hot-wire anemometer and a 3D sonic anemometer with the objective of estimating the influence of air flow on the spatial distribution of spray droplets. To carry out the analysis, all of the droplets detected by the laser were considered to be of the same size. The distribution of products was asymmetric when the machine only worked with the back fan, with 41% of the product distributed on the left side versus 59% on the right side, as referenced to the direction of the machine’s advance. This asymmetry was corrected when the machine functioned with the two fans activated. These spray data were concordant with the measured air flow generated by the machine in the different working conditions. For the different regulation settings of the machine, taking the vertical of the machine as 0°, the angular region comprised between 40° and 60° was the one that received the highest quantity of product. The increase of the air flow produced a greater distance of the product. For the highest air flow configuration, 99% of the product detected by the laser was detected within a distance of 16 m from the axis of the machine.

Quasi-three-dimensional numerical simulation of a solid oxide fuel cell short stack: Effects of flow configurations including air-flow alternation

The effects of flow configuration in solid oxide fuel cell (SOFC) stacks are investigated using a quasi-three-dimensional numerical model. Flow configurations with alternated air flows in parallel and perpendicular to the fuel flows are considered in addition to the conventional co-, counter-, and cross-flow configurations. The stacks have eight cells with unity aspect ratio and an active area of 4900 mm2 and are compared at fuel utilization of 0.193, 0.386, 0.579, and 0.772. The numerical model is capable of analyzing both the streamwise and spanwise directions of the cells. Although the counter-flow stack achieves the highest voltage efficiency among the stacks with the conventional flow configurations, it has the highest dispersion of the current density distribution on the cells. Air-flow alternation is effective to achieve uniform and high cell temperature and hence low dispersion of the current density. Alternate air flows parallel to the fuel flows achieve the highest voltage efficiency of 0.797 at a fuel utilization of 0.772, while alternate air flows perpendicular to the fuel flows reduce the risk of local fuel depletion as compared with the cross-flow stacks. Appropriate selection of the air-flow configuration within stacks allows operation at higher efficiency without fuel depletion.

An extensive comparison of modified zero-equation, standard k-ε, and LES models in predicting urban airflow

Accurate CFD simulations of urban airflow are of significant importance for a large variety of environmental studies and associated building energy consumption. As a relatively fast and reliable turbulence model compared to Standard k-ε turbulence model (SKE) and Large Eddy Simulation (LES), the improved Zero-equation (ZEQ) turbulence model has gained attention to simulate outdoor airflow and contaminant dispersion. This study evaluates the performance of four commonly used ZEQ turbulence models applied to flow around urban environments and analyze their sensitivity and uncertainty for different airflow configurations. These configurations entail airflow around (1) an isolated building, (2) regular blocks, and (3) building complexes. The results show that average computational time for these three turbulence modeling approaches (ZEQ: SKE: LES) scaled approximately to a 1:5:30 ratio, which demonstrated the computational competitiveness of ZEQ as a fast turbulence model for prediction of airflow in urban areas. The comparisons between simulation results and experimental data show that previously developed ZEQ models are slightly faster than the SKE turbulence model and have a slightly inferior performance compared to LES. In summary, the performance of the specified ZEQ turbulence model indicates that this turbulence model is a good fit for outdoor airflow studies.

Two dimensional numerical analysis of aerodynamic characteristics for rotating cylinder on concentrated air flow

Over the years, many studies have demonstrated the feasibility of the Magnus effect on spinning cylinder to improve lift production, which can be much higher than the traditional airfoil shape. With this characteristic, spinning cylinder might be used as a lifting device for short take-off distance aircraft or unmanned aerial vehicle (UAV). Nonetheless, there is still a gap in research to explain the use of spinning cylinder as a good lifting device. Computational method is used for this study to analyse the Magnus effect, in which two-dimensional finite element numerical analysis method is applied using ANSYS FLUENT software to examine the coefficients of lift and drag, and to investigate the flow field around the rotating cylinder surface body. Cylinder size of 30mm is chosen and several configurations in steady and concentrated air flows have been evaluated. All in all, it can be concluded that, with the right configuration of the concentrated air flow setup, the rotating cylinder can be used as a lifting device for very short take-off since it can produce very high coefficient of lift (2.5 times higher) compared with steady air flow configuration.

Exergetic and enviroeconomic analysis of semitransparent PVT array based on optimum air flow configuration and its comparative study

This paper carries out the exergetic and enviroeconomic analysis of semi-transparent photovoltaic thermal (PVT) array (size 10.08m×2.16m). Its exergetic and enviroeconomic performance has been compared with glass to tedlar i.e. opaque PVT array termed as case-A which has two integrated columns each having 18 PVT modules in series are connected in parallel and solar cell tile (SCT) based PVT array termed as case-B which has two integrated columns of 18 modules each having 36 PVT tiles (each solar cell having area 0.12m×0.12m) in the module is connected in series. The semi-transparent photovoltaic thermal (PVT) array considered as case-C which also has two integrated columns each having 18 semi-transparent PVT modules in series are connected in parallel. The size of all above array (10.08m×2.16m) is considered same. Four different climatic conditions of India (Delhi, Bangalore, Jodhpur and Srinagar) have been considered and the performances of the all above three cases have been compared on the basis of annual overall thermal energy and exergy gain. The comparative analysis shows that case-C has 28.8% and 12.1% lower cell temperature which yields 9.9% and 3.1% higher electrical efficiency than case-A and B respectively. Also the average outlet air temperature for case-C is higher by 40.6% and 19.1% than case-A and B respectively. The CO2 mitigation and enviroeconomic parameter for Bangalore in terms of overall thermal energy gain for case-C is 104.80tCO2/annum and 1519.56$/annum respectively, while in terms overall exergy gain is 48.76tCO2/annum and 707.09$/annum respectively. The CO2 mitigation potential of case-C is higher by 5.0% and 7.3% than case-B in terms of overall thermal energy and exergy gain respectively which indicates that case-C is a better performer than the other two cases.

Experimental study on the influence of liquid and air boundary conditions on a planar air-blasted liquid sheet, Part II: prefilming zone length

In this work, experiments were performed on a prefilming atomizer. For this purpose, an injector used for liquid sheet pulverization was adapted to highlight the influence of the prefilming zone. Breakup length, oscillation frequency and drop size were studied for various prefilming zone lengths and airflow configurations (convergent or divergent and different air thicknesses). Various influences were observed depending on the air configuration, with an improvement of the atomization process for convergent configuration when an optimum prefilming zone length is chosen. At the same time, visualizations of liquid dynamics and liquid thickness measurements on the prefilming zone have enabled the classification of liquid evolution in three regimes: “smooth”, “waves” and “accumulation”. The use of primary atomization parameters enables a cartography gathering all of the experimental conditions studied during this work to be proposed. Finally, a comparison of these results with previous correlations highlights the necessity to take into account the geometrical aspect of injection systems to predict the atomization characteristics.

Design, fabrication and performance evaluation of solar dryer for banana

An indirect, active-type, environmentally friendly, low-cost solar dryer was designed to dry various agricultural products. The dryer was built by locally available, biologically degradable, low-cost materials. The dryer consists of solar flat plate air heater with three layers of insulation, drying chamber and a fan with a regulator to induce required air flow in the system. Banana is the chosen crop for the experimentation since it is high in production and also has substantial loss in India. Also, dried bananas are having good nutritive value which makes it as essential diet. The experiments were conducted to dry banana slices and to study its drying characteristics like rate of drying and quality of dried banana in terms of taste, colour and shape. The dryer has the following features: two different air flow configurations (air flow between glass cover and absorber plate called as the top flow and air flow between absorber plate and the bottom insulation of solar collector called as the bottom flow), forced flow with variable flow rates from 0–3 m/s and two different mounting schemes (conventional trays and wooden skewers). In the top and bottom flow experiments, the bottom flow provided about 2.5 °C higher chamber temperatures than the top flow for the same solar energy input. The efficiency of top flow configuration was found to be 27.5 %, whereas the efficiency of bottom flow configuration was found to be higher at 38.21 %. The results also agree well with the theoretical calculations performed as 60 W of energy can be saved for the same energy input. The drying rate was found to increase when wooden skewers were used instead of conventional trays. At the end of the day, the total difference in moisture content is found to be 3.1 % which is considerable knowing that the rate of drying drastically decreases with time. Banana dried at 1 m/s air flow rate was of the best quality in terms of colour, taste and shape when compared to drying at 0.5 and 2 m/s air flow rate while the weather condition and ambient conditions were almost the same for all the cases with negligible difference.

Numerical Investigation of Different Airflow Schemes in a Real Operating Theatre

A study on performances of different ventilation schemes provided by vertical and horizontal uni-directional air flow was carried out in a standard orthopaedic operating theatre (OT). Starting from our previous studies of a real OT under operating use conditions, in this research different air flow configurations, considering some air curtain solutions on the ceiling and at the sliding door always assumed to be open as a basic boundary condition, were investigated by numerical simulations. Indoor air quality (IAQ) indexes and thermal comfort parameters, deduced from simulation results were calculated and discussed referring to the best performance and efficacy between the air flow schemes to contrast the incorrect use conditions of the OT. Referring to the studied schemes, the reciprocal comparison emphasizes that a successful outcome in preventing surgical site infection can depend as much on resolving human factors (i.e. operational use conditions, door opening/closing), as on overcoming physical and technical obstacles.

Numerical Simulation and Investigation of Transonic & Symmetrical Airfoil for Helicopter Main Rotor Blade Application

Helicopter rotor aerodynamics is prognosticated to be one of the most perplexing and enigmatic affliction encountered by both researchers and aviators throughout the ages. The bewilderment of the flow field around the main rotor blade ceaselessly remains unrequited in tangible flight environments. Appalling calamities repeatedly befall owing to these unforeseen and equivocal instances. In order to extricate these impediments, one must go back to the brass tacks and apprehend the cause. However, it is every so often exceedingly disconcerting to obtain experimental data due to intricacy, perplexity and substantial price tag. Subsequently, computational simulation is progressively becoming more of a preferred choice in recent times. Bearing this in mind, this study intended to simulate and visualize the air flow configuration of the main rotor blade using symmetrical and transonic airfoils to demarcate their physiognomies and behavior. Results have revealed that the transonic airfoil has a higher lift coefficient (Cl) than the symmetrical airfoil. Contrariwise, if used in an actual rotorcraft, the transonic airfoil can cause stern apprehension in terms of stability and control.

Effects of Temporal Discretization on Turbulence Statistics and Spectra in Numerically Simulated Convective Boundary Layers

Six state-of-the-art large-eddy simulation codes were compared in Fedorovich et al. (Preprints, 16th American Meteorological Society Symposium on Boundary Layers and Turbulence, 2004b) for three airflow configurations in order to better understand the effect of wind shear on entrainment dynamics in the convective boundary layer CBL). One such code was the University of Oklahoma large-eddy simulation (LES) code, which at the time employed a second-order leapfrog time-advancement scheme with the Asselin filter. In subsequent years, the code has been updated to use a third-order Runge–Kutta (RK3) time-advancement scheme. This study investigates what effect the upgrade from the leapfrog scheme to RK3 scheme has on turbulence statistics in the CBL differently affected by mean wind shear, also in relation to predictions by other LES codes that participated in the considered comparison exercise. In addition, the effect of changing the Courant number within the RK3 scheme is investigated by invoking the turbulence spectral analysis. Results indicate that low-order flow statistics obtained with the RK3 scheme generally match their counterparts from simulations with the leapfrog scheme rather closely. CBL growth rates due to entrainment in the shear-free case were also similar using both timestepping schemes. It was found, however, that care should be given to the choice of the Courant number value when running LES with the RK3 scheme in the sheared CBL setting. The advantages of the largest possible (based on the stability criterion) Courant number were negated by degrading the energy distribution across the turbulence spectrum. While mean profiles and low-order turbulence statistics were largely unaffected, the entrainment rate was over-predicted compared to that reported in the original code-comparison study.

A design of air flow configuration for cooling lithium ion battery in hybrid electric vehicles

Lithium ion batteries are commonly employed in hybrid electric vehicles and achieving high energy density in the battery has been among the most critical issues in the automotive industry. Since thermal management is very important in the automotive batteries with layout limitation, a design strategy for effective cooling should be carefully opted. Particularly, a forced air cooling has been considered as a practical option in the automotive industry. In this article, a specific design of air-cooled battery system is theoretically investigated and numerically modelled to satisfy the required thermal specifications. Since a typical battery system in hybrid electric vehicles consists of the stacked multiple battery cells, cooling performance is determined mainly by the uniform distribution of air flow in the coolant passage which dissipates heat generated from the battery cells. It is demonstrated that the required cooling performance can be achieved by employing the tapered manifold and pressure relief ventilation even without changing the layout/design of the existing battery system. Furthermore, a theoretical analysis is performed as a design guideline to enhance the cooling performance.

A Detailed Heat and Fluid Flow Analysis of an Internal Permanent Magnet Synchronous Machine by Means of Computational Fluid Dynamics

This paper presents a comprehensive computational fluid dynamics (CFD) model of a radial flux permanent magnet synchronous machine with interior magnets. In the CFD model, the water jacket cooling and a simplified model of the topology of the distributed stator winding are considered. The heat sources of the CFD model are determined from a finite-element analysis of the machine. The numerically determined temperature distributions of the machine are compared with measurement results from sensors located both in the stator and rotor. The particular focus of this paper is the analysis of the temperatures and the heat flow in the air gap and from the stator winding heads and the rotor to the inner air. Different operating conditions and two particular rotor designs with different inner air flow configurations are investigated. The potential of improving the thermal utilization of a rotor design with fan blades attached to the mounting plates of the rotor is shown.

A Mixed Integer Formulation for Energy-efficient Multistage Adsorption Dryer Design

This work presents a mixed integer nonlinear programming (MINLP) formulation for the design of energy-efficient multistage adsorption dryers within constraints on product temperature and moisture content. Apart from optimizing temperatures and flows, the aim is to select the most efficient adsorbent per stage and product to air flow configuration. Superstructure models consisting of commonly used adsorbents such as zeolite, alumina, and silica-gel are developed and optimized for a two-stage, low-temperature, adsorption drying system. Results show that the optimal configuration is a hybrid system with zeolite as the first-stage adsorbent and silica-gel as the second-stage adsorbent in counter-current flow between drying air and product. A specific energy consumption of 2,275 kJ/kg is achieved, which reduces to 1,730 kJ/kg with heat recovery by a heat exchanger. Compared to a conventional two-stage dryer at the same drying temperature, this represents a 59% reduction in energy consumption. The optimal system ensures the exhaust air temperature of the first-stage regenerator is high enough to regenerate the second-stage adsorbent so no utility energy is spent in the second stage. A higher second-stage adsorbent wheel speed favors energy performance as it becomes optimized for energy recovery while the first is optimized for dehumidification. Although this work considers three candidate adsorbents in a two-stage system, the same reasoning can be applied to systems with more stages and adsorbents. The developed superstructure optimization methodology can, by extension, be applied to optimize multistage hybrid drying systems in general for any objective.

Some innovative concepts for car drag reduction: A parametric analysis of aerodynamic forces on a simplified body

The aerodynamic torsor of a vehicle is among the most crucial parameters in new car development. This torsor has been decreased over the years by more than 33%, but beyond that further improvement has become difficult and challenging for car manufacturers. In this context, the present paper focuses on a parametric analysis of the trends in the aerodynamic forces. We report here aerodynamic force measurements carried out on a simplified vehicle model. Tests were performed in wind tunnel S4 of Saint-Cyr l’Ecole for different airflow configurations in order to isolate the parameters that affect the aerodynamic torsor and to confirm others previously suspected. The simplified model has flat and flexible air inlets and several types of air outlet, and includes in its body a real cooling system and a simplified engine block that can move in the longitudinal and lateral directions. The results of this research, which can be applied to any new car design, show configurations in which the overall drag coefficient can be decreased by 2%, the aerodynamic cooling drag coefficient by more than 50% and the lift coefficient by 5%. Finally, new designs for aerodynamic drag reduction, based on the combined effects of the different parameters investigated, are proposed.

Modeling of Air Flow in an Industrial Countercurrent Spray-Drying Tower

This article presents both theoretical and experimental determination of the hydrodynamics of drying air in an industrial countercurrent spray dryer. Air velocity measurements were performed in selected areas of the tower to determine the flow pattern in the dryer and to collect data to validate the computational fluid dynamics (CFD) modeling and verify the results. For no-swirl operation mode, 3D CFD calculations showed high instability of the air flow in the dryer. A bent, pillow-shaped flow above the drying air inlet, which promotes deposition of particles in this area of the wall, was detected. CFD calculations also proved that when drying air was introduced to the tower tangentially; from 20° to 30° in relation to the initial air flow configuration in the spray-drying tower, the air flow was stabilized and air velocity near the wall increased, which might reduce wall deposition of particles. Comparison of experimental and theoretical results showed that the CFD model of countercurrent spray-drying process developed in this study can be used for a reliable estimation of tower performance.

Flame spread over porous sand beds wetted with propenol

AbstractA comprehensive set of experiments was carried out to investigate the spread of flames over porous sand beds wetted with finite quantities of propenol. The aim was to examine the key characteristics of flame propagation over porous beds when a limited supply of liquid fuel to the flame zone was available. Experiments were conducted over beds with depths ranging from 13.3 to 39.9 mm and average particle diameters between 0.5 and 5 mm under quiescent, assisted and opposed airflow configurations. It was found that the flame spread rate for both assisted and opposed airflow configurations dramatically decreased as the air speed was increased although the extent of decay in the flame spread rate was more pronounced in the case of the opposed airflow configuration. The experimental observations were explained by correlating the flame spread rate with the Damköhler number and fuel consumption flux. The practical implications of the findings are briefly discussed in this paper. Copyright © 2010 John Wiley & Sons, Ltd.

Liquid Consumption of Wetted Wall Bioaerosol Sampling Cyclones: Characterization and Control

Advances in microfluidic, lab on chip, and other near-real-time biological identification technologies have driven the desire to concentrate bioaerosols into hydrosol sample volumes on the order of tens of microliters (μL). However, typical wet biological aerosol collector outputs are an order or two of magnitude above this goal. The ultimate success of bioaerosol collectors and biological identifiers requires an effective coupling at the macro-to-micro interface. Liquid collection performance was studied experimentally for a family of dynamically scaled wetted wall bioaerosol sampling cyclones (WWC's). Steady-state liquid collection rates and system response times were measured for a range of environmental conditions (temperatures from 10°C to 50°C and relative humidities from 10% to 90%), liquid input rates, and WWC airflow configurations. A critical liquid input rate parameter was discovered that collapsed all experimental data to self-similar empirical performance correlations. A system algorithm was ...