Reduced Air Flow Rate Research Articles

Energy-saving cooling strategies in tunnel-ventilated dairy buildings: Computational fluid dynamics (CFD) simulations and validation

Ventilation is a key strategy for addressing heat stress in dairy cattle. In this study, we developed computational fluid dynamics (CFD) models for a 252-head free stall tunnel-ventilated dairy building equipped with ridge openings and circulation fans. A detailed cow model was developed for a standard 625 kg Holstein cattle. Both tube and floor cooling were developed as supplemental cooling strategies using a ground source heat pump while the ventilation fans continued to operate at a reduced air speed (30 to 65 % reduction). The average air velocity within the stalls for the control (1.4 ± 0.32 m s-1) was significantly higher than the average velocity achieved with floor cooling (1.02±0.41 m s-1) and tube cooling (0.69±0.21 m s-1) (p = 0.043). Despite lower air velocities, CFD simulations showed that the average temperature at cow resting height for tube cooling (27.9 ± 0.21 °C) was significantly lower than that for the control (28.6 ± 0.36 °C) and floor cooling (28.3 ± 0.14 °C) (p = 0.021). For 252 cows, the total electricity consumption for the control was 40,590 kWh during summer, while for floor cooling, it varied between 30,683 and 36,181 kWh, and for tube cooling, it ranged from 15,879 to 21,378 kWh. Ventilation-related greenhouse gas (GHG) emissions from the tunnel-ventilated barn were 0.12 t of CO2 eq. per cow. Future studies could investigate the impact of reduced airflow rates on air quality inside the buildings.

Study on the performance of heat and mass transfer of moisture-conducting fibers for evaporative cooling

Moisture-conductive fibers exhibit potential to serve as evaporative medium in evaporative cooling systems. Their heat and mass transfer performance significantly influences the energy efficiency of evaporative cooling systems. This study evaluated the heat and mass transfer characteristics of moisture-conducting fibers through numerical simulation based on experimental validation. The experimental systems and numerical model with moisture-conducting fibers were developed. The microstructural parameters (porosity and permeability) of fibers were determined according to experimental data and theoretical analysis. The accuracy of parameters and model was verified by experiment. The differences in heat and mass transfer performance of various types of fibers and the effects of ambient air parameters (temperature, relative humidity and flow rate) on the heat and moisture transfer characteristics of fibers were investigated through simulation. The results indicated that the Coolmax fiber had superior heat and mass transfer performance compared to Coolpass, cellulose/PET and polyester fibers. The evaporative cooling efficiency between air and fibers was facilitated by increasing air temperature, decreasing air relative humidity and reducing air flow rate under other conditions unchanged. The results are beneficial to the optimization of the evaporative cooling medium and provide theoretical guidance for the selection of fibers for evaporative cooling.

A novel approach for modeling and simulation of vibrating fluidized bed dryers: Industrial scale case study

Vibrating fluidized bed dryers offer numerous advantages in comparison to conventional fluidized bed dryers, while complex phenomena that occur during this process pose a challenge in modeling and simulation of the process. Thus, a novel, Aspen Plus-based approach was developed and validated with data on industrial drying of aluminium-trihydrate particles. Novelty of the proposed approach consists of custom flowsheet configuration, taking into account both fluidization and drying effects, combined with modified mathematical models for vibrating fluidized bed processes. For validation purposes, solids moisture content profile along the dryer, as well as particle size distributions at dryer outlets were considered, in order to validate drying and fluidization specifications, respectively, and both are in good agreement with experimental data. Obtained simulation model was further used for determination of possible routes for process optimization, where energy consumption reduction of 28% can be achieved by reducing air flow rate in second drying section.

A manikin-based assessment of loose-fitting powered air-purifying respirator performance at variable flow rates and work rates

Loose-fitting powered air-purifying respirators (PAPRs) are used in healthcare settings, although barriers to routine, everyday usage remain, including usability concerns and potential interference with work activities. Loose-fitting PAPRs are approved by the National Institute for Occupational Safety and Health (NIOSH) and must meet minimum performance requirements, including a minimum airflow requirement of 170 L/min. One course of action to address usability concerns is to allow for the use of PAPRs designed with reduced airflow rates. The primary objective of this study was to assess the effect of PAPR flow rate and user work rate on PAPR performance, using a manikin-based assessment method. PAPR performance was quantified using the “Manikin Fit Factor” (mFF), a ratio of the challenge aerosol concentration to the in-facepiece concentration. Flow rates from 50–215 L/min and low, moderate, and high work rates were tested. Two models of NIOSH Approved loose-fitting facepiece PAPRs were tested, both having an Occupational Safety and Health Administration Assigned Protection Factor (APF) or expected level of protection, of 25. A two-way analysis of variance with an effect size model was run for each PAPR model to analyze the effects of work rate and flow rate on PAPR performance. Flow rate and work rate were found to be significant variables impacting PAPR performance. At low and moderate work rates and flow rates below the NIOSH minimum of 170 L/min, mFF was greater than or equal to 250, which is 10 times the OSHA APF of 25 for loose-fitting facepiece PAPRs. At high work rates and flow rates below 170 L/min, mFF was not greater than or equal to 250. These results suggest that some loose-fitting facepiece PAPRs designed with a flow rate lower than the current NIOSH requirement of 170 L/min may provide respirator users with expected protection at low and moderate work rates. However, when used at high work rates, some loose-fitting facepiece PAPRs designed with lower flow rates may not provide the expected level of protection.

Melting Characteristics of Hybrid Nano Enhanced Phase Change Material in a Finned Circular Tube

In this study, the melting characteristics of hybrid nano-enhanced phase change material in a finned circular tube were studied by using the Finite volume method. This setup of circular tubes with a phase change material is used as cooling systems in automotive industries, air-conditioning, refrigerators, and other applications of cooling systems. There is a need for enhancing the specific heat capacity of this system to ensure that the system works even at high temperatures. As the current problem includes many design parameters and boundary constraints, the finite volume method has been performed to obtain a detailed report and data to examine the deformation of the hybrid nanoparticles and heat transfer rate on the corresponding surface. The current paper reviews and focuses mainly on the high-temperature PCM. And the suitable PCM has been selected based on its limitations and properties. To ensure the increased specific heat capacity, a salt-based phase change material, i.e., a mixture of NaNO3-KNO3 (60:40 ratio) binary salt. This PCM could hold a temperature up to 334◦C before melting to change its phase. In addition to spherical-shaped nanoparticles of silica (SiO2) in this binary salt, it tends to have a significant potential for enhancing the thermal storage characteristics of the NaNO3-KNO3 binary salt. On an extended surface, Finns are used on the peripheral of the circular tube to increase the surface area, which leads to an increase in frictional resistance resulting in a reduced airflow rate in the vicinity of the finned surface. From case studies, it has been found that the optimum fork-shaped fin array with two branches gives higher heat dissipation than the optimum rectangular fin. In the majority of the cases, the optimum fork-shaped fin array gives a 59.9% higher heat transfer rate compared to the rectangular fin array. Thus, the melting characteristics of the hybrid of NaNO3- KNO3 with nanoparticles of silica are studied when placed in a circular tube containing fork-shaped fins.

Simultaneous Reduction of Thermal Stratification and Ammonia Concentrations in Poultry House During Brooding and in Cool Weather

HighlightsPen-scale system eliminated thermal stratification while full-scale system reduced thermal stratificationPen-scale system was moderately effective in trapping ammonia and reduced pen ammonia concentrations modestlyAmmonia trapping performance was mainly affected by dust build-upDust build-up was partly mitigated by a shakerCitric acid coated burlap placed upstream of livestock barn exhaust fans may reduce ammonia and dust emissionsAbstract. High ammonia (NH3) concentrations during poultry brooding can reduce bird performance and welfare. Thermal stratification during brooding can increase energy use and reduce bird welfare. A proof-of-concept heat recovery and NH3 control (HRAC) system consisting of a low-cost NH3 filter consisting of citric acid treated burlap placed upstream of a fan was evaluated for its ability to reduce barn NH3 concentration and thermal stratification. In the lab, 5% citric acid on burlap trapped 13 times more NH3 per unit mass of sorbent than activated carbon reported in the literature. Pen-scale and barn-scale HRAC prototypes using 15% citric acid on burlap eliminated and greatly reduced thermal stratification, respectively. The pen-scale HRAC had significant NH3 removal efficiencies ranging from the 17% to 42% in seven of nine events and compared, to the Control pens (no HRAC), significantly reduced floor [NH3] in two of nine events by 26% and 42%. The pen-scale HRAC also reduced footpad dermatitis at 15 d. Performance of the full-scale HRAC was highly variable. Clogging of the filter with particulate matter reduced airflow rates that was partially mitigated using a shaker. A vertical HRAC with a shaker might improve performance. There is need to investigate the effectiveness of 5% citric acid. The citric acid-treated burlap screen placed upstream of barn exhaust fans could reduce dust and NH3 emissions. Keywords: Breakthrough curve, Burlap, Citric acid, Emissions, Energy use, Footpad dermatitis.

Sensitivity analysis of SARS-CoV-2 aerosol exposure.

As vaccination campaigns are in progress in most countries, hopes to win back more normality are rising. However, the exact path from a pandemic to an endemic virus remains uncertain. While in the pre-vaccination phase many critical indoor situations were avoided by strict control measures, for the transition phase a certain mitigation of the effect of indoor situations seems advisable. To better understand the mechanisms of indoor airborne transmissions, we present a new time-discrete model to calculate the level of exposure towards infectious SARS-CoV-2 aerosol and carry out a sensitivity analysis for the level of SARS-CoV-2 aerosol exposure in indoor settings. Time limitations and the use of any kind of masks were found to be strong mitigation measures, while how far the effort for a strict use of professional face pieces instead of simple masks can be justified by the additional reduction of the exposure dose remains unclear. Very good ventilation of indoor spaces is mandatory. The definition of sufficient ventilation in regard to airborne SARS-CoV-2 transmission follows other rules than the standards in ventilation design. This means that especially smaller rooms most likely require a significantly greater fresh air supply than usual. Further research on 50% group models in schools is suggested. The benefits of a model in which the students come to school every day, but for a limited time, should be investigated. In terms of window ventilation, it has been found that many short opening periods are not only thermally beneficial, they also reduce the exposure dose. The fresh air supply is driven by the temperature gradient and wind speed. However, the sensitivity towards these parameters is not very high and in times of low wind and temperature gradients, there are no arguments against keep windows open in order to make up for the reduced air flow rate. Long total opening periods and large window surfaces will strongly reduce the exposure. Additionally, the results underline the expectable fact that exposure doses will increase when hygiene and control measures are reduced. It seems advisable to investigate what this means for the infection rate and the fatality of infections in populations with partial immunity. Very basic considerations suggest that the value of aerosol reduction measures may be reduced with very infectious variants such as delta.

Process intensification in binary adsorption of VOC-water vapor on zeolite in a countercurrent fluidized bed adsorber

In this study, fast ideal adsorbed solution theory was coupled with a two-phase bubbling bed approach to describe the adsorption of volatile organic compounds (VOCs) on zeolite in the presence of water vapor in a multistage fluidized bed adsorber. The binary adsorption of VOC-water vapor was predicted using their single component adsorption isotherms. The model was verified by experimental data obtained at a wide range of operating conditions before being used for studying the process intensification. Validation tests revealed that the model could accurately predict the experimental removal efficiencies (R2 = 0.94), as well as VOC concentration profiles inside the bed (R2 = 0.98). The intensification simulations showed that increasing the adsorbent feed rate is effective when there is a need for more adsorption sites (e.g. at high inlet concentrations), and is quite ineffective when the adsorption process is limited by low solid-gas contact time (e.g. high air flow rates). Increasing the adsorbent feed rate can also diminish the interference of water vapor in adsorption of VOC (even at RH as high as 75%). Reducing air flow rate at constant VOC load is always effective specially when there are enough adsorption sites available (e.g. high adsorbent feed rate, and low VOC loads and RHs). Similarly, increasing the number of stages can effectively improve the fluidized bed performance at high adsorbent feed rates and low VOC inlet concentrations and RHs. Using 3 adsorbers of 2 stages instead of 1 adsorber of 6 stages can improve the removal efficiency up to 34.5% in the range of operating conditions simulated. While having the same high weir height along the bed yields better performance than having the same low weir height, an optimized arrangement of weir heights in a descending order from the top to the bottom of the bed would maximize the removal efficiency.

Evaluating the effect of air flow rate on hybrid and conventional membrane bioreactors: Implications on performance, microbial activity and membrane fouling

This study addressed the impact of air flow rate on the performance, membrane fouling behaviour and microbial community of a sequencing batch conventional membrane bioreactor (SB-MBR) and a sequencing batch hybrid membrane bioreactor (SB-HMBR) with carrier media for biofilm growth. Two different scenarios were evaluated: high (6.4 L min−1) and low (1.6 L min−1) air flow rates, associated with high (4.5 mg L−1) and low (1.5 mg L−1) dissolved oxygen (DO) concentrations and specific aeration demand per membrane area (SADm) of 0.426 and 0.106 m3 m−2 h−1, respectively. Both reactors were subjected to alternating non-aerated and aerated conditions for organic matter (as chemical oxygen demand - COD), nitrogen and phosphate removal from a municipal wastewater. From the bacterial community analysis, the key players in nutrient removal processes were assessed. The results showed that COD removal efficiencies were above 95% in both MBRs, regardless of the aeration intensity, while complete ammonium removal was observed at the higher DO. However, nitrifying activity was adversely affected under low DO levels. High nitrification levels were re-established faster in the hybrid MBR, thanks to the presence of biofilm, where nitrifying activity was favoured and the bacterial community profile did not exhibit substantial changes upon DO reduction. A higher denitrification potential was found for the carrier-based MBR, resulting in lower effluent nitrate concentrations. Regarding phosphorus removal, a slight improvement was observed in the SB-HMBR at reduced DO, while in the SB-MBR it remained practically constant. Moreover, the specific phosphate uptake rate exhibited a significant increase, especially in the hybrid MBR, reaching 44.6 mgP gVSS−1 h−1. At lower aeration rate, however, worse filterability and higher membrane fouling rates were observed, especially in the conventional MBR. Overall, the results demonstrated that the hybrid MBR better withstood the reduced air flow rate and DO as compared to the conventional counterpart.

Experimental and Computational Investigations of the Thermal Environment in a Small Operational Data Center for Potential Energy Efficiency Improvements

Abstract The share of equipment and power use in smaller data centers (DCs) is comparable with that of more massive counterparts. However, they grabbed less attention in the literature despite being less energy-efficient. This study highlights the challenges of setting up a computational fluid dynamics (CFD) model of a 180-m2 small-size high-performance computing (HPC) DC and the validation procedure leading to a reasonably accurate model for the investigation of the thermal environment and potential energy efficiency improvements. Leaky floors, uneven placement of computing equipment and perforated tiles preventing separation of hot and cold air, low-temperature operation, and excessive cooling capacity and fan power were identified sources of energy inefficiency in the DC. Computational fluid dynamics model predictions were gradually improved by using experimental measurements for various boundary conditions (BCs) and detailed geometrical representation of large leakage openings. Eventually, the model led to predictions with an error of less than 1 °C at the rack inlet and less than 5 °C at the rack outlet. The ultimate objective was to use the validated CFD model to test various energy efficiency measures in the form of operational or design changes in line with the best practices. Impact of leakage between the raised floor and the room, reduced airflow rate, cold-aisle and hot-aisle separation, workload consolidation, and higher temperature operation were among the phenomena tested by using the validated CFD model. The estimated power usage effectiveness (PUE) value reduced from 1.95 to 1.40 with the proposed energy efficiency measures.

The effect of metal salts on aerosol performance of spray dried carrier-free formulations of levofloxacin.

Metal salts are used in formulation of dry powder inhalers (DPIs) for different purposes. Recently the role of these salts in production of small, dense but highly dispersible particles has emerged. In this study the effect of some such salts on dispersibility and respirability of spray dried levofloxacin formulations was evaluated in normal and reduced inhalation air flow or by increasing powder filling in capsules. levofloxacin was co-spray dried with different concentrations of common metal chlorides (NaCl, KCl, CaCl2 and MgCl2) either with or without leucine as dispersibility enhancer. Particle size, moisture, morphology, triboelectrification tendency and fine particle fraction (FPF) of resulting powders were evaluated. In addition, the effect of these salts and leucine on dispersibility of resulting powders in reduced air flow rate and increased capsule filling mass were evaluated. Presence of higher tested concentrations of divalent cations increased water content, and reduced FPF significantly. Addition of leucine reduced water content and electrostatic charge, increased particle size and FPF and improved spray drying yield significantly. Lower concentrations of salts did not affect FPF of leucine containing powders significantly, but presence of 2.5% NaCl or MgCl2 preserved the dispersibility in higher capsule fillings. A 2.5% concentration of NaCl in such formulations preserved dispersibility in lower air flows. Higher amounts of divalent salts increases triboelectrification and moisture absorption, and reduces FPF. Lower concentrations of NaCl could not improve FPF of leucine containing formulations significantly, but preserves dispersibility in low air flows and high capsule fillings. Graphical abstract.

Performance Degradation of Proton Exchange Membrane Fuel Cell Caused by an Accelerated Stress Test

AbstractProton exchange membrane fuel cell (PEMFC) experiences inevitably performance decay due to various mechanisms. Among those, carbon corrosion is extremely detrimental. In this study, an accelerated stress test (AST) is conducted to a single cell to mimic the conditions when carbon corrosion occurs. The cell performance is characterized intermittently, and the experiment results show although electrochemical active area (ECA) decreases continuously from beginning‐of‐life (BOL) due to carbon corrosion at catalyst layer (CL), kinetic degradation is not apparent until AST 3 h. After that, kinetic loss increases progressively, while ohmic loss increases continuously. However, due to decrease of water generation under voltage‐controlled condition, or enhancement of water removal by phase change induced flow (PCI) under current‐controlled condition, the mass transport is slightly improved at later period of AST. To confirm such variation of mass transport loss, cell performance and EIS are measured at reduced air relative humidity (RHc) and reduced air flow rate. Both cell performance and EIS results show that in a degraded fuel cell, reduced air RHc and higher air flow rate are beneficial to cell performance. Hence, more sophisticated water management strategies for PEMFCs is recommended for different periods in their lifetime for a fuel cell stack.

Performance investigation of indoor thermal environment and air handling unit in a hub airport terminal

Airport terminal is a typical large space building with large high interspaces and multitudinous functional zones. The task of heating, ventilation and air conditioning (HVAC) system is to ensure the thermal environment of these zones with different functions. A typical terminal in cold region of China is investigated in present paper, where indoor environment and performance of air conditioning system in summer are emphasized. The results indicate that the indoor temperature and humidity parameters at a height of 1.5 m in each zone of the terminal can be effectively controlled. The indoor temperature at a height of 1.5 varies in the range of 24~27°C, and the temperature difference is 0.5~4.9°C in the vertical direction. The temperature at the top of the terminal is greatly affected by the outdoor temperature where is higher and fluctuates obviously, while the temperature at the height of the occupant area is lower and more stable under the control of the air-conditioning system. The indoor carbon dioxide concentration is also at a reasonable level, all below 900 ppm, indicating that the equivalent outdoor air volume per capita is greater than 35 m3/h. Even in the case of high load caused by flight delays, the thermal environment in the terminal can be basically controlled at a comfortable level. As for the air handling unit, air handling process is tested to investigate the cooling capacity. The results show that the actual water supply of the AHU is relatively higher than the set value, but the air volume is almost equal to the set value which leads to an unsatisfactory energy efficiency. The tested energy efficiency ratio (EER) of AHU is only 5~7, almost approaching to that of the cooling plant. Reducing air flow rate could greatly improve the EER of the current air-conditioning system.

Spray deposition and distribution on the targets and losses to the ground as affected by application volume rate, airflow rate and target position

Greenhouse crop production in China has in the recent years expanded widely. To minimize compromised pesticide use and adverse environmental impact in these structures, it is essential to optimize the working parameters and settings of sprayers. Experiments using an air assisted greenhouse sprayer and artificial plants with attached fruits were conducted to investigate the effects of volume rate, target location, and airflow rate on spray deposition and distribution uniformity on leaves, fruits and losses to the ground. Three spray volume rates (530, 368 and 220 l ha−1) and three nozzle's outlet volumetric airflow rates (374.4, 289.4 and 234.7 m3 h−1) were evaluated. Ground speeds were set at 0.36 and 0.31 m s−1 for volume rate and airflow rate trials, respectively. Artificial targets (filter-paper collectors) were attached on either sides of leaves, fruits and the ground to collect deposits of a food colourant used as a tracer (Spray solution). Deposition was quantified through UV-VIS spectroscopy at a wavelength of 508 nm. Results indicated that volume rate significantly influenced deposition and distribution uniformity. Reducing the volume rate reduced deposition but improved distribution homogeneity. Quantified absolute deposits on upper leaf surfaces declined by 27.4% (MV) and 43.3% (LV). Normalized deposition displayed under-leaf to upper-leaf deposition ratios of between 16.1% (HV) to 20.0% (LV). Ground deposits were reduced by roughly 37.3% (MV) and 54.7% (LV). Similar to volume rate, airflow rate influenced spray deposition on leaves but followed an opposite trend. Reducing airflow rate improved deposition although the effect attained a threshold at medium airflow rate beyond which further reduction the deposition decreased though the reduction was not statistically significant (P = 0.069). Airflow rate did not significantly affect ground deposits (P = 0.315) it reduced the quantity of spray lost by 7% (MF) and 8.4% (HF).

Impact of demand controlled ventilation on system performance and energy use

Demand-controlled-ventilation (DCV) refers to a ventilation system with controlled air flow rate based on indoor air quality. DCV operates at reduced air flow rates during most of the operation time. Therefore, less energy is required for fan operation, compared to a constant-air-volume (CAV) ventilation system.Typically, DCV has a two-layer control with variable-air-volume (VAV) valves, and a fan speed control to maintain a constant-static-pressure in the duct system based on a pressure set point.However, this nominal design based fan pressure setpoint is higher than required when all VAV-valves are closed to a certain extent. Therefore, advanced pressure-reset (PR) control - resetting the pressure set point - potentially reduces fan energy use even further.This paper assesses the impact of fan control on both fan energy use and ventilation performance in DCV system of a densely occupied office. Results of a simulation model and realistic measurement setup are compared. The PR control, using air flow rate and VAV-valve position measurements as feedback, causes significantly reduction on fan energy use. These reductions compared to conventional DCV and CAV respectively, are approximately 10% and 72% in case of high occupancy and 50% and 93% in case of low occupancy. Largely, DCV with PR control is strongly considered, especially when occupancy is often expected to deviate significantly from the nominal conditions. Moreover, both simulations and measurements show that there is a clear trade-off between air flow rate deficit and fan energy use, when the fan energy use is lower, the air flow rate deficit is higher and vice versa. Furthermore, the results show that VAV-valve accuracy, characteristics and its lower operational limit hamper the ventilation system in achieving the predicted performance as in the simulation.

Demand controlled ventilation (DCV) in school and office buildings: Lessons learnt from case studies

Demand controlled ventilation (DCV) refers to a ventilation system with air flow rates that are controlled based on a measurement of an indoor air quality (IAQ) and/or on a thermal comfort parameter. DCV operates at reduced air flow rates during a large amount of the operation time and thus consumes less energy for fan operation and heating/cooling the supply air. The aim of the present research is to assess the IAQ, ventilation efficiency, and the operation and energy efficiency of real operating DCV systems in moderate climates.Measurements are carried out for at least two weeks in autumn and winter 2015-2016. The following parameters were monitored: CO2 concentrations and air temperatures at different positions in the room and at the extract air grill, position of the variable air volume (VAV) boxes, supply and extract air flow rates and the occupancy of the room. Four case studies with large and varying occupancy rate and with different use and ventilation systems are selected. Two classrooms and three landscaped offices were evaluated.The results show that a DCV is interesting in rooms with a large and varying occupancy rate such as lecture rooms and landscaped offices. A good IAQ is measured in all cases studied even at reduced air flow rates. The effect of the reduced air flow on the ventilation efficiency is negligible. The VAV boxes react well to predefined set points for CO2 concentration. During the measurement period, the reduction for fan energy ranges from 25 to 55% and ventilation heat losses 25–32% compared to a constant air volume system (CAV) with a design airflow rate of 29 m3/(h.pers), i.e., IDA3 in EN 13779. However, commissioning of the DCV is necessary to obtain and maintain these performances.

Preliminary measurements on microwave plasma flame for gasification

In this paper, the effects of plasma power and plasma gas flow rate on the geometrical dimensions, the shape of plasma flame and temperature distribution in gasification reactor have been investigated. The effects of plasma power and plasma gas flow rate on the geometrical dimensions, shape of plasma flame and temperature distribution in gasification reactor are presented. The plasma pictures at a variety of plasma power ranging from 300 to 4200 W with the range of plasma gas which is air from 50 to 100 L/min are presented. As expected, an increase in power causes the generation of intensive plasma with enhancement of the plasma flame volume. On the other hand, air flow rate is inversely proportional to the volume of the plasma flame. It is observed that both power and air flow rate has a significant effect on plasma flame shape. The spreading shape of plasma flame is observed at low powers. However, the shape of flame is pointed toward its end with an increase in plasma power. Meanwhile, reducing air flow rate causes a change in shape at lower power levels. The interactive influence of air flow rate and plasma power is confirmation of different plasma flow regimes. The temperature measurements confirm the effects of air flow rate and power on plasma flame regime from 1800 to 6000 W power. Increasing power level causes increment in the reactor temperature. The average temperature in the reactor is increased from 480 °C at 1800 W power to 1018 °C at 6000 W power. The flow rate has a reverse effect on magnitude of the temperature. The average temperature in the reactor is reduced from 480 to 348 °C at 1800 W power and 1018 to 918 °C at 6000 W power when the flow rate is increased from 50 to 100 L/min. However, the temperature distribution is more uniform in higher flow rates. It is also related with the shape of plasma. While the magnitude of temperature and its gradient is high in pointed end plasma, the effects are reversed in spreading shape plasma.

Optimization of air sparging and in-line coagulation for ultrafiltration fouling control

Abstract A major drawback to ultrafiltration membrane operation for drinking water treatment is fouling, which results in lower water production and increased maintenance costs. The impact of different fouling mitigation strategies including, sparging conditions (duration and air flow rate) as well as phased in-line coagulation were investigated at pilot-scale. Unexpectedly, sparging during permeation and backwash resulted in a significantly higher rate of increase in irreversible resistance compared to Sparging only during backwash. Lower irreversible fouling observed without sparging during permeation was attributed to the formation of a protective layer on the membrane in the absence of sparging. Sparging at reduced air flow rates and intermittently, during the permeation cycle did not improve the irreversible resistance rate when compared to sparging only during backwash. The application of phased in-line coagulation to pre-coat membranes was also investigated. Coagulating for only the first half of the permeation cycle (phased coagulation) did not negatively impact membrane performance in terms of irreversible resistance and organics removal. Phased coagulation, which would lead to reduced coagulant and sludge disposal costs, appears to be a promising fouling control strategy.

Impact of dust loading on long term portable air cleaner performance

Although there has been many studies conducted on the initial performance of portable air cleaners (PACs), there is little research on the evaluation of their long term performance. This paper quantifies the effects of particle loading on PAC particle removal, airflow rate, power consumption and ozone emissions for a HEPA- and electrostatic precipitator (ESP) - based PAC. Ozone emission rates decreased in a linear fashion for the ESP-based PAC suggesting dust masking on the unit's discharge electrode. Performance in terms of particle clean air delivery rates (CADR), airflow rates and power consumption reduced for both units as dust was loaded up to the filter's half-life. For the HEPA based PAC, particle CADR reductions are due to reduced airflow rates. As a consequence, the particle single pass efficiencies (SPEs) grew indicating dust accumulation on the filter. This phenomenon is not observed on the ESP-based PAC where both particle CADR as well as SPE reduced upon dust loading. This study demonstrates the importance of regular filter maintenance for PAC to ensure optimal performance.

Wheezing and Bronchial Hyper-responsiveness in Early Childhood as Predictors of Newly Diagnosed Asthma in Early Adulthood: A Longitudinal Birth-Cohort Study

Stern DA, Morgan WJ, Halonen M, Wright AL, Martinez FD. Lancet. 2008;372(9643):1058–1064PURPOSE OF THE STUDY. To estimate the contributions of gender and early life factors to newly diagnosed and persistent asthma in young adults.STUDY POPULATION. The study evaluated 849 enrollees of the Tucson Children's Respiratory Study who had adult data at 22 years of age.METHODS. The cohort was derived from all healthy infants born in Tucson, Arizona, between 1980 and 1984. Shortly after birth, the parents completed a questionnaire on demographic data and were instructed to see a collaborating pediatrician at the first sign of lower respiratory illness. Physician-diagnosed asthma or wheezing was assessed at 2, 3, 6, 8, 11, and 16 years of age. At 6 years of age, allergy skin-prick tests were performed for all participants, and cold air bronchial challenge was performed for participants with a history of lower respiratory illness. At 22 years of age, an in-depth evaluation was performed with questionnaires on asthma symptoms, asthma medication use, and smoking history. Allergy skin-prick tests and spirometry were performed for participants still living in the Tucson area.RESULTS. Subjects with adult data at 22 years of age were more likely to have nonsmoking, nonminority parents with higher levels of education than were those without adult data. Of the 849 participants, 255 (30%) had asthma diagnosed at some time in their lives, 181 (22%) had active asthma, and 224 (26%) reported current smoking. Participants with inactive asthma had pre- and postbronchodilator spirometry results comparable to those of participants who never had asthma. Participants with newly diagnosed asthma had lower forced expiratory volume in 1 second/forced vital capacity ratios, which were not bronchodilator responsive. Factors associated with newly diagnosed asthma, chronic asthma, or shortness of breath with wheezing at 22 years of age included female gender, parental asthma, late-onset (>3 years of age) wheeze, persistent wheeze, Alternaria mold sensitivity at 6 years of age, cold air bronchial hyperresponsiveness, and reduced air flow rates at 6 years of age. Seventy percent of participants with current asthma and 63% with newly diagnosed asthma reported episodes of wheeze before 6 years of age. Male gender was a significant indicator of asthma remission by early adulthood. The combination of Alternaria sensitivity and cold air bronchial hyperresponsiveness at age 6 years and persistent wheeze at age 6 years were strong predictors of chronic asthma at age 22 years.CONCLUSIONS. Children with transient early wheezing were at much less risk for chronic asthma that persisted through childhood or reappeared more intensely in early adult life, compared with children with persistent or late-onset wheezing. Women were twice as likely to have new asthma diagnosed between 16 and 22 years of age.REVIEWER COMMENTS. This comprehensive study confirms previous longitudinal studies of the same age group. The lack of bronchodilator response of the forced expiratory volume in 1 second in newly diagnosed asthma is disconcerting but does not necessarily reflect permanent obstruction. Initial oral corticosteroid treatment has been shown to improve pulmonary function and to unmask bronchodilator responsiveness. Limitations of the study include the use of physician-diagnosed asthma in the absence of the demonstration of bronchodilator reversibility, a significant loss of participants over the course of time, with resulting skewed participant demographic characteristics, and selected assessment of responses to cold air. No risk factor alone identifies all of the possible forms of asthma.