Concurrent Air Flow Research Articles

Mechanism of accelerated concurrent flame spread over glass fiber reinforced unsaturated polyester resin composites with ATH/MH retardants under external radiation

This paper reports an experimental investigation of concurrent flame spread over composites, for the first time, with combined flame retardants and external radiation factors. Glass fiber reinforced unsaturated polyester resins without flame retardants (GFUPR) as well as those containing aluminum hydroxide (ATH) and magnesium hydroxide (MH), which were utilized widely in modern high-speed train, were systematically explored. Infrared measurement was employed to track the displacement of pyrolysis front. Because of the dilution of H2O generated during the decomposition of ATH and MH, the flame temperature (Tf) of GFUPR-ATH/MH is thought to be lower than that of GFUPR. Nonetheless, the most noteworthy finding is that the flame spread rate, flame preheat length and flame height for GFUPR-ATH/MH could be larger than that of GFUPR if concurrent airflow velocity exceeds 0.5 m/s under high external radiation. To interpret this unexpected while practically important phenomena, theoretical analysis based on the heat/mass transfer theory is established to explore the general mechanism. It is concluded that in the transition from natural-convection to forced-convection, the different in the flame convection in burning zone between the sample with high Tf (i.e. GFUPR) and the sample with low Tf (i.e. GFUPR-ATH/MH), will decrease rapidly. It is primarily because the sample with low Tf is earlier to enter in the region where forced-convection is controlled as the airflow velocity increases. The critical parameter (Fr2Re)-1 = 1 could be used to characterize this transition. As a result, in forced-convection region, the role of thermal conductivity of the fuel-gas mixture (kmix) may emerge, that the sample with high kmix but low Tf (i.e. GFUPR-ATH/MH) may impart more heat to burning zone than the sample with low kmix but high Tf (i.e. GFUPR), generating more combustible gases in the burning zone hence larger flame heat feedback to preheat zone. Moreover, this effect will be reinforced by the larger flame preheat length of GFUPR-ATH/MH, due to the temperature dependency of molecular diffusivity. This mechanism analysis is well corroborated by the experimental results. This new finding may facilitate understanding of the effect of flame retardants on the heat/mass transfer mechanism in flame spread under concurrent airflow and external radiation.

Experimental study on behaviors of flame spread over aviation kerosene under forced airflow

In realistic industrial scenarios, the leakage of aviation kerosene (RP-5) under forced airflow easily leads to fire spread, which seriously threatens the safety of human life and causes enormous economic losses. Therefore, it is necessary to study the characteristic parameters of flame spread over RP-5 aviation kerosene under forced airflow, such as flame tilt angle (θ), flame height (H), and flame spread rate (V). In this paper, the RP-5 flame spread experiments were carried out by varying the speed (u = 0–6 m/s) and direction (concurrent, opposed, and perpendicular airflows) of the forced airflow. The results show that the flame tilt angle increases as the airflow speed increases and finally tends to be stable, while the flame height decreases monotonically with airflow speed. The special behaviors of flame bifurcation and fire spread rate induced by the critical airflow speed are observed. The phenomenon of "flame bifurcation" will occur due to the influence of differential pressure resistance under high concurrent airflow conditions (u > 1 m/s). When the airflow is relatively small (u ≤ 1 m/s), the mean flame spread rate varies slightly with increasing airflow speed. With further increasing the airflow speed (u > 1 m/s), the mean flame spread rate increases with an increase in the concurrent airflow speed while decreasing as the opposed airflow speed increases. By contrast, the mean flame spread rate remains essentially unchanged under all perpendicular airflows.

Production Technology and Damping Properties of Aerated Polymer Coatings

The process of obtaining aerated (filled with air bubbles) polymer coatings has been developed and investigated by the method of flame spraying with an assessment of their ability to damp vibrations. A technology for the controlled formation of aerated polymer coatings has been developed while using the capabilities of the ОИМ (OIM) 050 polymer thermal atomizer design which consists in providing a concurrent air flow between the flame torch and the jet of powder material. The experiments have been carried out with such thermoplastic polymers as polyethylene terephthalate, high pressure polyethylene, ultra high molecular weight polyethylene, polyamide. It has been found that the aeration coefficient grows almost in direct proportion with an increase in the amount of air in the concurrent flow for all investigated polymer coatings. It is noted that the aeration process is influenced by the rheological properties of liquid polymers, or rather, the value of the polymer melt flow rate. The limiting values of air in the concurrent flow have been determined, which make it possible not to reduce the adhesion of polymer coatings to steel substrates by less than 6 MPa and not to decrease their hardness by more than 25–30 %. Studies of the damping properties of samples with polymer coatings have been carried out on a stand, the kinematic diagram of which is based on loading the free end of a cantilever sample, abrupt removal of the load and registration of free damped oscillations by an induction-type contactless sensor connected to a computer. It is shown that the use of aeration when forming noise-absorbing coatings on steel samples can increase their logarithmic damping decrement by 18–26 %.

Confined combustion of polymeric solid materials in microgravity

Microgravity experiments are performed to study the effects of confinement on the burning behavior of polymeric solid materials. Flat, 100 × 22 × 1 mm PMMA samples are burned in concurrent air flow in a small flow duct aboard the International Space Station. Three different burning scenarios are examined, double-sided, single-sided, and parallel samples. In the first two scenarios, single samples are burned on both sides and on one side, respectively. Flat baffles are placed parallel to the sample to confine the available space for combustion. The distance between the baffle and the sample (H) is varied in different tests. In each test, imposed flow is reduced in steps and steady flame spread is achieved at each flow speed until the flame quenches. The results show that at the same confined condition, steady state flame length and spread rate are proportional to flow speed over the range tested. When confinement increases (or H decreases), the flame spread rate and flame length increase first and then decrease. In addition, the quenching flow speed decreases and then increases with decreasing H. These results suggest that the confinement can increase or decrease solid fuel flammability depending on conditions. In the third burning scenario, two PMMA samples are placed parallel to each other separated by a distance H. Twin flames are observed and combustion is confined between the two samples. Among the three tested burning scenarios, twin flames have the largest flame length and burning rate at the same confinement level (H). This is because the thermal interaction between the twin flames enhances the heat feedback to the solid fuel and reduces the relative heat loss to the surrounding flow duct. Comparing single- and double-sided flames with the same baffle-sample distance, the spread rate of a single-sided flame is slightly less than half of that of a double-sided flame. This is due to the halved pyrolysis area exposed to the flame and heat loss on the back side of the sample. Optimal transport of oxygen to the flames also plays a role.

Effect of sample thickness on concurrent steady spread behavior of floor- and ceiling flames

This paper presents an experimental investigation of the sample thickness effect on the concurrent flame steady spread behavior. Two configurations, ceiling flame and floor flame, as the fundamental diffusion combustion problems and representative scenarios of horizontal flame spread, are concerned herein. PMMA samples with thickness (δ) of 2, 3, 4, 5, 7, 9 mm were employed including both thermally-thin and thermally-thick conditions. A wind tunnel was used to provide the uniform concurrent airflow ranging from 0.3 m/s to 1.2 m/s in 0.3 m/s intervals. Flame characteristics and basic parameters to quantify the flame steady spread process have been studied, including flame spread rate (FSR), equivalent pyrolysis length as well as heat flux feedback in both pyrolysis and preheating zones. Results show that FSR decreases with sample thickness, being more sensitive to sample thickness for ceiling flame configuration than that for floor flame configuration. Equivalent pyrolysis length increases with sample thickness and ceiling flame's equivalent pyrolysis length is larger than floor flame's. Convection feedback is dominant under concurrent airflow regardless of the flame configuration, airflow velocity or sample thickness. In pyrolysis zone, the total heat flux to fuel surface of ceiling flame configuration is larger than that of floor flame configuration for thin samples due to buoyancy, but it decreases rapidly as sample thickness increases. In preheating zone, the heat flux decreases in power law for ceiling flame configuration while a piece-wise fitting is found for floor flame configuration, which is interpreted based on their inherent flame characteristic difference hence the thermal boundary layer conditions between these two configurations. To analyze the sample thickness effect on concurrent flame spread, a characteristic solid temperature (T*) is proposed by theoretical analysis, as an essential parameter to be used in the concurrent flame spread model to represent the coupling effect of heat input in gas phase and in-depth heat loss into the solid phase (or namely thermal inertia controlled by a characteristic thermal penetration depth). The calculated non-dimensional characteristic solid temperature (θ) shows to be less sensitive to flame configuration and concurrent airflow velocity for relatively thicker samples because the thermal penetration depth will tend to approach a limit. A general trend of its variation with sample thickness (δ) can be employed to predict the heat loss into solid phase and its predictive capability is verified by the experimental results. This work advances the fundamental understanding of the sample thickness effect on concurrent flame spread mechanism.

Experimental study of flame spread over thermally-thin inclined fuel surface and controlling heat transfer mechanism under concurrent wind

The fuel inclination and wind velocity play a significant role on the forward flame spread behavior. It deserves further study since the heat transfer mechanism and flame spread characteristics coupled these two factors are not clear yet. In this paper, a thermally thin slab of PMMA that could be inclined from a horizontal (0°) to a vertical (90°) angle is used to investigate flame spread behavior under the condition of the concurrent ambient airflow. A wind tunnel is utilized to provide a uniform concurrent airflow, ranging from 0 (quiescent) to 3 m/s with an interval of 0.5 m/s. Essential flame characteristic parameters are collected to quantify the flame spread process, including flame spread rate (FSR), burning rate, heat release rate as well as heat flux feedback both in the pyrolysis and preheating zones. A mechanism, including the competition between the acceleration of buoyancy brought by inclination and the cooling effect of ambient airflow for relatively high wind velocity, is developed. The relationship between flame length and pyrolysis length is investigated. Moreover, the evolution of both heat release rate per unit width and standoff distance as a function of pyrolysis length are analyzed. A dimensionless heat release rate for upward flame at different wind velocities is used to scale the dimensionless flame length with a power-law exponent of 0.77 and −1.92. In addition, the dimensionless heat flux in preheated zone decay with distance as a function of power law. A predictive formulation of FSR coupled with inclination angle and wind velocity is proposed. This study facilitates the understanding of the interaction of fuel inclination angle and horizontal ambient airflow from aspect of heat and mass transfer.

Analytical model for estimating the production and composition of gas resulted through gasification

For the modelling of gasification processes, several models have been developed over the years. It is remarked that gasification calculation models of very high complexity entail some complications. Therefore, simpler mathematical representations of gasification characteristics and process behavior are required as a first step in addressing such systems. The preliminary calculation simplicity is needed form two perspectives: First – the pre-sizing of gasification installations, and second – the estimation of experimental or functional results. For this kind of topics, an adequate simplified model should be defined. Further, to validate the results it will be necessary to use complex calculation models. The model proposed in this paper addresses gasification with distributive air in the air distribution current, considering general concurrent flow of air fuel. Previous successful investigations, conducted by the present research team, are taken into account within model definition stages. Thus, the work presented here provides useful advances in the field of mathematical modeling of gasification processes. The originality of the model consists in its easy computational accessibility, which allows the approach of technological optimizations, such as the variation of excess air and fuel composition.

Evaluación del espesor de una película de agua descendente vertical con visualización y técnicas de reconocimiento de imágenes

The present work is focused on the experimental study of a vertical downward annular flow to determine the thickness and stability of a falling film water flow. For this purpose, it was designed and implemented an experimental set up to generate the annular two-phase flow pattern, provided with an injection head with a special geometry to induce a liquid film inside a cylinder. Due to the small dimensions, the film was visualized using a pulsated laser to illuminate the region and the pictures were taken with a high-speed camera. This technique allowed the determination of the falling film thickness by means of an algorithm to recognize image contours. In some of the studied cases, a concurrent air flow was injected in the center of the cylinder in order to evaluate its influence on the interfacial hydrodynamics of the liquid film. Average film thickness were obtained for different Reynolds numbers in different axial observation points, and it was observed that the liquid film annular area and the shape of the header to inject the water, are important factors for the surface characteristic and thickness of the film, and its stability as well. The experimental results show that the standard deviation increases in proportion to the average film thickness, especially in the turbulent regime.

Combustion of round hydrogen microjet in a concurrent flow

Experimental data on the diffusion combustion of round hydrogen microjet in concurrent coaxial flows are presented. The effects on combustion of the concurrent flow of air and that of air premixed with nanopowder of TiO2 are of interest. The hydrogen microjet is emanated from a round micronozzle which is surrounded by a coaxial slit to produce the concurrent flow. Combustion events found in the present conditions are similar to those observed in the previous studies on diffusion combustion of hydrogen microjets at subsonic and supersonic velocities. In a subsonic range, the so-called “bottleneck-flame region” is generated close to the nozzle exit, while in high-speed conditions the flame separates from the nozzle. At increasing velocity of both the hydrogen microjet and the concurrent flow, the “bottleneck-flame region” is still found and the combustion becomes more intense. The “bottleneck-flame region” is suppressed at the microjet velocity approaching transonic values.

Flame Spread Over Ultra-thin Solids: Effect of Area Density and Concurrent-Opposed Spread Reversal Phenomenon

There are no existing experimental studies of flame spread rate trends for ultra-thin solid samples. Previous theory has predicted that for concurrent flame in kinetic regime, the flame spread rate decreases as the sample thickness decreases and there is a critical thickness below which burning is not possible. To test this hypothesis, a series of microgravity experiments of concurrent-flow flame spread over samples of ultra-low area densities are conducted using NASA Glenn Research Center’s Zero Gravity Research Facility (the 5.18 s drop tower). The tested samples are cellulose-based materials of various area densities, ranging from 0.2 mg/cm2 to 13 mg/cm2, as low as one order of magnitude less than those ever tested before. Each sample is 30 cm long by 5 cm wide and is burned in a low-speed concurrent air flow (5 to 30 cm/s). The results show that the concurrent flame spread rate is proportional to the flow velocity relative to the flame and is inversely proportional to the sample area density. A theoretical formulation, provided in this work, suggests that the flame length has a linear relationship with the relative flow speed and has no direct dependency on the sample area density. The experimental data supports this conclusion. From the images recorded in the experiments, a unique flame base tubular structure directed upstream away from the burnout zone is observed for thin samples. This structure is suspected to be due to flame stretching and localized blowoff caused by the oxidative pyrolysis Stefan flows at the sample burnout. This can be an indication that the chemical time becomes comparable to the flow time of the Stefan flow and the tested samples are approaching the kinetically-limited thickness. For the thinnest tested sample (0.2 mg/cm2), flames with concurrent and opposed dual natures are observed when the air flow rate is low (< 20 cm/s). At the lowest tested flow rate (5 cm/s), the flame spread rate exceeds the air flow rate and the flame transits to an opposed flame in the concurrent flow. The dual nature and flame transition are presented and discussed. This study provides detailed examination through high-resolution images of the transition between the concurrent to opposed flame spread modes.

Concurrent Flame Spread and Blow-Off Over Horizontal Thin Electrical Wires

Electrical wires with the flammable polymer insulation and the metal core are responsible for many fire accidents in buildings, nuclear power plants, aircraft, and spacecraft. For the first time, this work studies the horizontal flame spread and blow off under the concurrent airflows over the thin copper-core wires. Four wires of about 1-mm diameter with different insulation thicknesses and core diameters are tested in a horizontal wind tunnel. Results show that as the concurrent airflow velocity increases, the flame spread rate first quickly increases to a maximum value, and then slightly decreases until blow-off at about 2 m/s. Heat transfer analysis shows that the preheating from flame and core have different dependences on the airflow. The flame spread is slower for a larger copper core diameter because the heat-sink effect of the core is highlighted by increasing the thermal inertia. We found a critical Froude number of 3.6 which helps determine the critical concurrent airflow velocity when the fastest flame spread is achieved. This study not only provides valuable information about the worst scenario of wire fires but also advances the fundamental understanding of the concurrent flame spread mechanism over thin fuels.

Combustion and flame spreading characteristics of diesel fuel with forced air flows

Research on combustion and flame spreading behaviors in a system with forced air flow is crucial for actual fire protection design and scientific meanings. Flame spread tests over sub-flash diesel fuel are conducted by using a self-developed cross flow system, in both opposed and concurrent configurations. Some key parameters to characterize the flame spread performance, namely, flame tilt, flame spread rate, temperature distribution and scale characteristic of subsurface flow are achieved and analyzed. The variations of flame tilt angle in opposed and concurrent flame spreads follow well with Thomas’s classical model, and the tangent value of the flame tilt angle is correlated with the wind Froude number with the power value of 0.8. The flame spread rate decreases monotonically with an increase in the opposed air flow velocity. By contrast, the flame spread rate decreases initially and increases afterwards as the concurrent air flow velocity increases, with the critical air velocity of 1.725 m/s. Furthermore, the step temperature rise remains stable in the range of 27 °C to 30 °C for opposed air flows, but it is not pronounced for concurrent air flows. The subsurface flow length increases with opposed air flow velocity, while it becomes irregular under concurrent air flows. The primary contribution of heat transfer to flame spread is liquid-phase thermal convection for opposed or low-speed concurrent air flow conditions, whereas it is flame radiation and gas conduction for high-speed concurrent air flow conditions. The finding of current study is favorable for the fire hazard assessment of spilling hydrocarbon fuel in air flow environments.

Measuring Spray Droplet Size from Agricultural Nozzles Using Laser Diffraction

When making an application of any crop protection material such as an herbicide or pesticide, the applicator uses a variety of skills and information to make an application so that the material reaches the target site (i.e., plant). Information critical in this process is the droplet size that a particular spray nozzle, spray pressure, and spray solution combination generates, as droplet size greatly influences product efficacy and how the spray moves through the environment. Researchers and product manufacturers commonly use laser diffraction equipment to measure the spray droplet size in laboratory wind tunnels. The work presented here describes methods used in making spray droplet size measurements with laser diffraction equipment for both ground and aerial application scenarios that can be used to ensure inter- and intra-laboratory precision while minimizing sampling bias associated with laser diffraction systems. Maintaining critical measurement distances and concurrent airflow throughout the testing process is key to this precision. Real time data quality analysis is also critical to preventing excess variation in the data or extraneous inclusion of erroneous data. Some limitations of this method include atypical spray nozzles, spray solutions or application conditions that result in spray streams that do not fully atomize within the measurement distances discussed. Successful adaption of this method can provide a highly efficient method for evaluation of the performance of agrochemical spray application nozzles under a variety of operational settings. Also discussed are potential experimental design considerations that can be included to enhance functionality of the data collected.

Measuring Spray Droplet Size from Agricultural Nozzles Using Laser Diffraction.

When making an application of any crop protection material such as an herbicide or pesticide, the applicator uses a variety of skills and information to make an application so that the material reaches the target site (i.e., plant). Information critical in this process is the droplet size that a particular spray nozzle, spray pressure, and spray solution combination generates, as droplet size greatly influences product efficacy and how the spray moves through the environment. Researchers and product manufacturers commonly use laser diffraction equipment to measure the spray droplet size in laboratory wind tunnels. The work presented here describes methods used in making spray droplet size measurements with laser diffraction equipment for both ground and aerial application scenarios that can be used to ensure inter- and intra-laboratory precision while minimizing sampling bias associated with laser diffraction systems. Maintaining critical measurement distances and concurrent airflow throughout the testing process is key to this precision. Real time data quality analysis is also critical to preventing excess variation in the data or extraneous inclusion of erroneous data. Some limitations of this method include atypical spray nozzles, spray solutions or application conditions that result in spray streams that do not fully atomize within the measurement distances discussed. Successful adaption of this method can provide a highly efficient method for evaluation of the performance of agrochemical spray application nozzles under a variety of operational settings. Also discussed are potential experimental design considerations that can be included to enhance functionality of the data collected.

Bubbly-to-cap bubbly flow transition in a long-26 m vertical large diameter pipe at low liquid flow rate

The concurrent upward two-phase flow of air and water in a long vertical large diameter pipe with an inner diameter (D) of 200mm and a height (z) of 26m (z/D=130) was investigated experimentally at low superficial liquid velocities from 0.05009 to 0.3121m/s and the superficial gas velocities from 0.01779 to 0.5069m/s. The resultant void fractions range from 0.03579 to 0.4059. According to the observations using a high speed video camera, the flow regimes of bubbly, developing cap bubbly and fully-developed cap bubbly flows prevailed in the flows. The developing cap bubbly flow appeared as a flow regime transition from bubbly to fully-developed cap bubble flow in the vertical large diameter pipe. The developing cap bubbly flow changes gradually and lasts for a long time period and a wide axial region in the flow direction, in contrast to a sudden transition from bubbly to slug flows in a small diameter pipe. The analysis in this study showed that the flow regime transition depends not only on the void fraction but also on the axial distance in the flow and the pipe diameter. The axial flow development brings about the transition to happen in a lower void fraction flow and the increase of pipe diameter causes the transition to happen in a higher void fraction flow. The measured void fraction showed an N-shaped axial changing manner that the void fraction increases monotonously with axial position in the bubbly flow, decreases non-monotonously with axial position in the developing cap bubbly flow, and increases monotonously again with axial position in the fully-developed cap bubbly flow. The temporary void fraction decrease phenomenon in the transition region from bubbly to cap bubbly flow can be attributed to the formation of medium to large cap bubbles and their gradual growth into the maximum size of cap bubble and/or cluster of large cap bubbles in the developing cap bubbly flow. In order to predict the N-shaped axial void fraction changing behaviors in the flow regime transition from bubbly to cap bubbly flow, the existing 12 drift flux correlation sets for large diameter pipes are reviewed and their predictabilities are studied against the present experimental data. Although some drift flux correlation sets, such as those of Clark and Flemmer (1986) and Hibiki and Ishii (2003), can predict the present experimental data with reasonable average relative deviations, no drift flux correlation set for distribution parameter and drift velocity can give a reliable prediction for the observed N-shaped axial void fraction changing behaviors in the region from bubbly to cap bubbly flow in a vertical large diameter pipe.

The influence of gas coflow in a pulse aerosol on evaporation cooling process

Experimental data on the influence of the continuous concurrent air flow on the heat exchange coefficient of a pulse spray and vertical flat heat exchanger are presented. It is shown that continuous air flow not only contributes to cooling but significantly effects the cooling efficiency by including in the heat exchange secondary drops, which originate in the process of bombardment of the cooling film by large drops and their return by the air flow to the surface of dry zones of the heat exchanger.

Prevalence of airflow limitation in outpatients with cardiovascular diseases in Japan.

Background and objectivesCardiovascular disease (CVD) and chronic obstructive pulmonary disease (COPD) commonly coexist and share common risk factors. The prevalence of COPD in outpatients with a smoking history and CVD in Japan is unknown. The aim of this study was to determine the proportion of Japanese patients with a smoking history being treated for CVD who have concurrent airflow limitation compatible with COPD. A secondary objective was to test whether the usage of lung function tests performed in the clinic influenced the diagnosis rate of COPD in the patients identified with airflow limitation.MethodsIn a multicenter observational prospective study conducted at 17 centers across Japan, the prevalence of airflow limitation compatible with COPD (defined as forced expiratory volume (FEV)1/FEV6 <0.73, by handheld spirometry) was investigated in cardiac outpatients ≥40 years old with a smoking history who routinely visited the clinic for their CVD. Each patient completed the COPD Assessment Test prior to spirometry testing.ResultsData were available for 995 patients with a mean age of 66.6±10.0 years, of whom 95.5% were male. The prevalence of airflow limitation compatible with COPD was 27.0% (n=269), and 87.7% of those patients (n=236) did not have a prior diagnosis of COPD. The prevalence of previously diagnosed airflow limitation was higher in sites with higher usage of lung function testing (14.0%, 15.2% respectively) compared against sites where it is performed seldom (11.1%), but was still low.ConclusionThe prevalence of airflow limitation in this study indicates that a quarter of outpatients with CVD have COPD, almost all of whom are undiagnosed. This suggests that it is important to look routinely for COPD in CVD outpatients.

Pressure drop and its reduction of gas–non-Newtonian liquid flow in downflow trickle bed reactor (DTBR)

The influences of concurrent flow of air–Newtonian and non-Newtonian liquid systems on pressure drop and on its reduction in downflow trickle bed reactor are presented in the present work. The pressure drop at different flow regimes in the trickle bed is enunciated by the dynamic interaction model based on the framework of the momentum balance. From the analysis, it is observed that the non-ideality factor of bubble flow regime is higher than that of pulse and trickle flow regimes which may influence efficiency of the reactor. The present work also concludes that the percentage of pressure reduction increases with increasing the surfactant concentration. However there is a limitation of change of concentration, above which no more reduction can be obtained. The present study may be useful for further understanding and modelling of multiphase reactor with non-Newtonian liquid, which has great industrial applications.

Water flow exchange characteristics in coarse granular filter media

Elution of inhibitory metabolites is a key parameter controlling the efficiency of air cleaning bio- and biotrickling filters. To the authors knowledge no studies have yet considered the relationship between specific surface area related elution velocity and physical media characteristics, which constitutes a scientific gap. This study investigates the impact of particle size distribution (considering materials with multiple particle sizes) and irrigation rate on the overall specific surface area related elution velocity distribution in porous granular media. The elution measurements performed in this study are performed at a concurrent airflow of 0.3ms−1, water irrigation rates of 1–21cmh−1 in materials with particle diameters ranging from 2 to 14mm to represent media and operation conditions relevant for low flow biotrickling filter design. Specific surface area related elution velocity distribution was closely related to the filter water content, water irrigation rate, media specific surface area and particle size distribution. A predictive model linking the specific surface area related elution velocity distribution to irrigation rate, specific surface area and particle size distribution was developed and predicted the observed specific surface area related elution velocity distributions with a mean error of 9%.

Measurement and classification methods using the ASAE S572.1 reference nozzles

Abstract An increasing number of spray nozzle and agrochemical manufacturers are incorporating droplet size measurements into both research and development. Each laboratory invariably has their own sampling setup and procedures. This is particularly true about measurement distance from the nozzle and concurrent airflow velocities. Both have been shown to significantly impact results from laser diffraction instruments. These differences can be overcome through the use of standardized reference nozzles and relative spray classification categories. Sets of references nozzles, which defined a set of classification category thresholds, were evaluated for droplet size under three concurrent air flow velocities (0.7, 3.1 and 6.7 m/s). There were significant, though numerically small, differences in the droplet size data between identical reference nozzles. The resulting droplet size data were used to categorize a number of additional spray nozzles at multiple pressure and air flow velocities. This was done to determine if similar classifications were given across the different airspeeds. Generally, droplet size classifications agreed for all airspeeds, with the few that did not, only differing by one category. When reporting droplet size data, it is critical that data generated from a set of reference nozzles also be presented as a means of providing a relative frame of reference.