Remediation efficiency of vapour extraction of sandy soils contaminated with cyclohexane: influence of air flow rate, water and natural organic matter content

Abstract This work reports the analysis of the efficiency and time of soil remediation using vapour extraction as well as provides comparison of results using both, prepared and real soils. The main objectives were: (i) to analyse the efficiency and time of remediation according to the water and natural organic matter content of the soil; and (ii) to assess if a previous study, performed using prepared soils, could help to preview the process viability in real conditions. For sandy soils with negligible clay content, artificially contaminated with cyclohexane before vapour extraction, it was concluded that (i) the increase of soil water content and mainly of natural organic matter content influenced negatively the remediation process, making it less efficient, more time consuming, and consequently more expensive; and (ii) a previous study using prepared soils of similar characteristics has proven helpful for previewing the process viability in real conditions.

Comparison of contaminant removal effectiveness and air change efficiency as indicator of air diffusion quality.

The ventilation efficiency concept is an attempt to quantify a parameter that can easily distinguish the different options for air diffusion in the building spaces. Thirteen strategies of air diffusion were measured in a test chamber through the application of the tracer gas method, with the objective to validate the calculation by Computational fluid dynamics (CFD). Were compared the Air Change Efficiency (ACE) and the Contaminant Removal Effectiveness (CRE), the two indicators most internationally accepted. The main results from this work shows that the values of the numerical simulations are in good agreement with experimental measurements and also, that the solutions to be adopted for maximizing the ventilation efficiency should be the schemes that operate with low speeds of supply air and small differences between supply air temperature and the room temperature.

Study on indoor thermal environment and air quality of office rooms controlled by personal displacement ventilation using CFD

Three-dimensional computational simulations are performed to examine indoor environment and micro-environment around human bodies in an office in terms of thermal environment and air quality. In this study, personal displacement ventilation (PDV), including two cases with all seats taken and two middle seats taken, is compared with overall displacement ventilation (ODV) of all seats taken under the condition that supply temperature is 24℃ and air change rate is 60 l/s per workstation. When using PDV, temperature stratification, the characteristic of displacement ventilation, is obviously observed at the position of occupant’s head and clearer in the case with all seats taken. Verticalertical ertical temperature temperature temperature temperature temperature differences below height of the head areare under under under 2℃ in two cases in two cases in two cases in two cases in two cases in two cases in two cases in two cases with all seats taken，and the temperature with PDV is higher than that with ODV. Verticalertical ertical temperature temperature temperature temperature temperature temperature difference is under 3 under 3under 3 under 3℃ in the case in the case in the case in the case in the case in the case in the case with two middle seats taken. CO2 concentration is lower th is lower th is lower this lower this lower than 2 g/man 2 g/m an 2 g/man 2 g/man 2 g/man 2 g/m 3 in the breath zone. in the breath zone. in the breath zone. in the breath zone. in the breath zone. in the breath zone. in the breath zone. in the breath zone. in the breath zone. The results indicate that PDV can be used in the room with big change of occupants’ number to satisfy the need of thermal comfort and air quality. When not all seats are taken, designers should increase supply air requirement or reduce its temperature for thermal comfort. INDEX TERMS

Effects of aluminum-copper alloy filtration on photon spectra, air kerma rate and image contrast

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Influence of specimen size, tray inclination and air flow rate on the emission of gases from biomass combustion

Experiments of biomass combustion were performed to determine whether specimen size, tray inclination, or combustion air flow rate was the factor that most affects the emission of carbon dioxide, carbon monoxide, and methane. The chosen biomass was Eucalyptus citriodora, a very abundant species in Brazil, utilized in many industrial applications, including combustion for energy generation. Analyses by gas chromatograph and specific online instruments were used to determine the concentrations of the main emitted gases, and the following figures were found for the emission factors: 1400 ± 101 g kg-1 of CO2, 50 ± 13 g kg-1 of CO, and 3.2 ± 0.5 g kg-1 of CH4, which agree with values published in the literature for biomass from the Amazon rainforest. Statistical analysis of the experiments determined that specimen size most significantly affected the emission of gases, especially CO2 and CO. •Statistical analysis to determine effects on emission factors.•CO2, CO, CH4 emission factors determined for combustion of Eucalyptus.•Laboratory results agreed with data for Amazonian biomass combustion in field tests.•Combustion behavior under flaming and smoldering was analyzed. © 2013 Elsevier Ltd.

Natural ventilation and indoor air quality in educational buildings: experimental assessment and improvement strategies

Indoor environmental conditions in classrooms, in particular temperature and indoor air quality, influence students’ health, attitude and performance. In recent years, several studies regarding indoor environmental quality of classrooms were published and natural ventilation proved to have great potential, particularly in southern European climate. This research aimed to evaluate indoor environmental conditions in eight schools and to assess their improvement potential by simple natural ventilation strategies. Temperature, relative humidity and carbon dioxide concentration were measured in 32 classrooms. Ventilation performance of the classrooms was characterized using two techniques, first by fan pressurization measurements of the envelope airtightness and later by tracer gas measurements of the air change rate assuming different envelope conditions. A total of 110 tracer gas measurements were made and the results validated ventilation protocols that were tested afterward. The results of the ventilation protocol implementation were encouraging and, overall, a decrease on the CO2 concentration was observed without modifying the comfort conditions. Nevertheless, additional measurements must be performed for winter conditions.

Untersuchungen zum thermisch induzierten Luftwechselpotential von Kippfenstern

Die sogenannte natürliche Lüftung - Lüftung infolge Temperatur- und Windeinfluss - über geöffnete Fenster und Türen ist im Wohnbereich noch immer die häufigste Form des Lüftens. Die Wirkung des Lüftens wird einerseits von den baulichen Gegebenheiten, z.B. der Fenstergröße, Öffnungsfläche und Laibungstiefe sowie andererseits durch den Nutzer, der z.B. eine Gardine oder Rollos anbringt, beeinflusst. Über den genauen Einfluss von verschiedenen Faktoren auf den Luftwechsel existieren zur Zeit noch keine gesicherten Erkenntnisse. Die Kenntnis des Luftwechsels ist jedoch für die Planung und Ausführung von Gebäuden in Hinblick auf das energiesparende Bauen sowie unter bauphysikalischen und hygienischen Aspekten wichtig. Der Einsatz von Dreh-Kippfenstern sowie das Lüften über die Kippstellung ist in Deutschland üblich, so dass die Bestimmung des Luftwechsels über Kippfenster von großem Interesse ist. Ziel dieser Arbeit ist es, den thermisch induzierten Luftwechsel über ein Kippfenster unter Berücksichtigung verschiedener Randbedingungen zu beschreiben. Hierbei werden Variationen der Kippweite, Laibungs- und Heizungsanordnung berücksichtigt. Die Arbeit gliedert sich in drei Teile: im ersten Teil werden messtechnische Untersuchungen durchgeführt, im zweiten Teil exemplarisch einige messtechnisch untersuchten Varianten mit CFD simuliert und im dritten Teil ein verbesserter Modellansatz zur Beschreibung des Luftwechsels aus den Messwerten abgeleitet. Die messtechnischen Untersuchungen bei einer Kippweite von 10 cm zeigen, dass bei dem Vorhandensein einer raumseitigen Laibung oder einem unterhalb des Fensters angeordneten Heizkörpers mit einer Reduktion des Volumenstroms von rund 20 Prozent gegenüber einem Fenster ohne Laibung bzw. ohne Heizkörper gerechnet werden muss. Die Kombination von raumseitiger Laibung und Heizung vermindert das Luftwechselpotential um ca. 40 Prozent. Simuliert wird die Variante ohne Laibung und ohne Heizung für die Kippweiten 6 cm und 10 cm. Die Ergebnisse der mit CFD simulierten Tracergas-Messung weisen für beide Kippweiten im Mittel rund 13 Prozent höhere Zuluftvolumenströme im Vergleich zu den Messwerten auf. Die eigenen Messdaten bilden die Grundlage für die Anpassung eines Rechenmodells. Werden vor Ort die lichte Fensterhöhe und -breite, die Kippweite, die Rahmen- und Laibungstiefe sowie die Abstände der Laibung zum Flügelrahmen gemessen, kann die Öffnungsfläche in Abhängigkeit von der Einbausituation bestimmt werden. Der Einfluss der Heizung - bei einer Anordnung unterhalb des Fensters - wird über den entsprechenden Cd-Wert berücksichtigt.

Untersuchung der Sensitivität von Heizungs- / Lüftungsanlagen in Niedrigenergiehäusern

Bei Meßprojekten in denen Gebäude mit installierter Lüftungsanlage untersucht wurden, stellte man immer wieder ein breite Streuung der Meßwerte, als auch eine oftmals deutliche Abweichung vom vorher ermittelten Heizwärmebedarf der Gebäude fest. Es wird vermutet, daß diese Unterschiede systemspezifische Ursachen haben, ein Nachweis kann aufgrund der geringen Anzahl vorhandener Meßpunkte jedoch nicht geführt werden. Um die Sensitivität verschiedener Randbedingungen auf den Energieverbrauch zu ermitteln, wird im vorliegenden Forschungsprojekt ein Simulationsmodell erstellt. Das thermische Verhalten und die Durchströmung des Gebäudes werden durch ein gekoppeltes Modell abgebildet. Unterschiedliche Lüftungsanlagensysteme werden miteinander verglichen. Auf Basis vorhandener Meßdaten wird ein klimaabhängiges Modell zur Fensterlüftung entwickelt, welches in die Modellbildung der Gebäudedurchströmung mit einfließt. Feuchtegeregelte Abluftanlagen sind in der Lage den mittleren Luftwechsel auf ein hygienisch sinnvollen Wert zu begrenzen. Sie erweisen sich im Hinblick auf die Sensitivität verschiedener Randbedingungen als robuste Systeme. Trotz Einsatz von Lüftungsanlagen kann je nach Betriebszustand insbesondere bei Abluftanlagen keine ausreichende Luftqualität sichergestellt werden. Zukünftige Systeme dürfen das "Lüftungssystem" Fenster nicht vernachlässigen, sondern müssen es in das Gesamtkonzept mit einbeziehen.

Particulate matter mass concentration (PM10) under different ventilation methods in classrooms

Recently, studies have shown that the classroom environment is very important for students' health and performance. Thus, the evaluation of indoor air quality (IAQ) in a classroom is necessary to ensure students' well-being. In this paper the emphasis is on airborne concentration of particulate matter (PM) in adult education rooms. The mass concentration of PM10 particulates was measured in two classrooms under different ventilation methods in the University of Reading, UK, during the winter period of 2008. In another study the measurement of the concentration of particles was accompanied with measurements of CO2 concentration in these classrooms but this study is the subject of another publication. The ambient PM10, temperature, relative humidity, wind speed and direction, and rainfall events were monitored as well. In general, this study showed that outdoor particle concentrations and outdoor meteorological parameters were identified as significant factors influencing indoor particle concentration levels. Ventilation methods showed significant effects on air change rate and on indoor/outdoor (I/O) concentration ratios. Higher levels of indoor particulates were seen during occupancy periods. I/O ratios were significantly higher when classrooms were occupied than when they were unoccupied, indicating the effect of both people presence and outdoor particle concentration levels. The concentrations of PM10 indoors and outdoors did not meet the requirements of WHO standards for PM10 annual average.

Post occupancy evaluation of a building employing windcatchers for summer ventilation

A combined windcatcher and light pipe (SunCatcher) was installed in the seminar room at the University of Reading, UK. Monitoring of indoor environment in real weather conditions was conducted to evaluate the application of windcatchers for natural ventilation. In addition, a subjective occupancy survey was undertaken. External weather conditions and internal indoor air quality indicators were recorded. The “tracer-gas decay” method using SF6 was used to establish air change rate for various conditions. The results indicated that the ventilation rate achieved through the windcatcher depends on the difference between internal and external air temperatures, and on wind speed and direction, in agreement with other published work in the area. The indoor air quality parameters were found to be within acceptable levels when the windcatcher was in operation. The measured air change rate was between 1.5ac/h and 6.8ac/h. Occupants’ questionnaires showed 75 per cent satisfaction with the internal conditions and welcomed the installation of the systems in UK buildings.

Passive urban ventilation by combined buoyancy-driven slope flow and wall flow: Parametric CFD studies on idealized city models

This paper reports the results of a parametric CFD study on idealized city models to investigate the potential of slope flow in ventilating a city located in a mountainous region when the background synoptic wind is absent. Examples of such a city include Tokyo in Japan, Los Angeles and Phoenix in the US, and Hong Kong. Two types of buoyancy-driven flow are considered, i.e., slope flow from the mountain slope (katabatic wind at night and anabatic wind in the daytime), and wall flow due to heated/cooled urban surfaces. The combined buoyancy-driven flow system can serve the purpose of dispersing the accumulated urban air pollutants when the background wind is weak or absent. The microscopic picture of ventilation performance within the urban structures was evaluated in terms of air change rate (ACH) and age of air. The simulation results reveal that the slope flow plays an important role in ventilating the urban area, especially in calm conditions. Katabatic flow at night is conducive to mitigating the nocturnal urban heat island. In the present parametric study, the mountain slope angle and mountain height are assumed to be constant, and the changing variables are heating/cooling intensity and building height. For a typical mountain of 500 m inclined at an angle of 20° to the horizontal level, the interactive structure is very much dependent on the ratio of heating/cooling intensity as well as building height. When the building is lower than 60 m, the slope wind dominates. When the building is as high as 100 m, the contribution from the urban wall flow cannot be ignored. It is found that katabatic wind can be very beneficial to the thermal environment as well as air quality at the pedestrian level. The air change rate for the pedestrian volume can be as high as 300 ACH.

Effect of mountain breeze in ventilating the city under calm and neutral atmospheric environment: Interaction of airflow structures and ventilation efficiency

Many modern cities locate in the mountainous areas, like Hong Kong, Phoenix City and Los Angles. It is confirmed in the literature that the mountain wind system developed by differential heating or cooling can be very beneficial in ventilating the city nearby and alleviating the UHI effect. However, the direct interaction of mountain wind with the natural-convection circulation due to heated urban surfaces has not been studied, to our best knowledge. This kind of unique interaction of two kinds of airflow structures under calm and neutral atmospheric environment is investigated in this paper by CFD approach. A physical model comprising a simple mountain and three long building blocks (forming two street canyons) is firstly developed. Different airflow structures are identified within the conditions of different mountain-building height ratios (R=Hm/Hb) by varying building height but fixing mountain height. It is found that the higher ventilation rate in the street canyons is expected in the cases of smaller mountain-building ratios, indicating the stronger natural convection due to increasing heated building surfaces. However, there is the highest air change rate (ACH) in the lowest-building-height case and most of the air is advective into the street canyon through the top open area, highlighting the important role played by the mountain wind. In terms of the ventilation efficiency, it is shown that the smallest R case enjoys the best air change efficiency followed by the highest R case, while the worst ventilative street canyons occur at the middle R case. In the end, a gap across the streets is introduced in the modeling. The existence of the gap can greatly channel the mountain wind and distribute the air into streets nearby. Thus the ACH can be doubled and air quality can be significantly improved.

A comparative study of the main mechanisms controlling indoor air pollution in residential flats

The relative contribution of the main mechanisms that control indoor air quality in residential flats was examined. Indoor and outdoor concentration measurements of different type pollutants (black carbon, SO2, O3, NO, NO2,) were monitored in three naturally ventilated residential flats in Athens, Greece. At each apartment, experiments were conducted during the cold as well as during the warm period of the year. The controlling parameters of transport and deposition mechanisms were calculated from the experimental data. Deposition rates of the same pollutant differ according to the site (different construction characteristics) and to the measuring period for the same site (variations in relative humidity and differences in furnishing). Differences in the black carbon deposition rates were attributed to different black carbon size distributions. The highest deposition rates were observed for O3 in the residential flats with the older construction and the highest humidity levels. The calculated parameters as well as the measured outdoor concentrations were used as input data of a one-compartment indoor air quality model, and the indoor concentrations, the production, and loss rates of the different pollutants were calculated. The model calculated concentrations are in good agreement with the measured values. Model simulations revealed that the mechanism that mainly affected the change rate of indoor black carbon concentrations was the transport from the outdoor environment, while the removal due to deposition was insignificant. During model simulations, it was also established that that the change rate of SO2 concentrations was governed by the interaction between the transport and the deposition mechanisms while NOX concentrations were mainly controlled through photochemical reactions and the transport from outdoors.

Resilience to temperature and pH changes in a future climate change scenario in six strains of the polar diatom Fragilariopsis cylindrus

The effects of ocean acidification and increased temperature on physiology of six strains of the polar diatom Fragilariopsis cylindrus from Greenland were investigated. Experiments were performed under manipulated pH levels (8.0, 7.7, 7.4, and 7.1) and different temperatures (1, 5, and 8 °C) to simulate changes from present to plausible future levels. Each of the 12 scenarios was run for 7 days, and a significant interaction between temperature and pH on growth was detected. By combining increased temperature and acidification, the two factors counterbalanced each other, and therefore no effect on the growth rates was found. However, the growth rates increased with elevated temperatures by 20-50% depending on the strain. In addition, a general negative effect of increasing acidification on growth was observed. At pH 7.7 and 7.4, the growth response varied considerably among strains. However, a more uniform response was detected at pH 7.1 with most of the strains exhibiting reduced growth rates by 20-37% compared to pH 8.0. It should be emphasized that a significant interaction between temperature and pH was found, meaning that the combination of the two parameters affected growth differently than when considering one at a time. Based on these results, we anticipate that the polar diatom F. cylindrus will be unaffected by changes in temperature and pH within the range expected by the end of the century. In each simulated scenario, the variation in growth rates among the strains was larger than the variation observed due to the whole range of changes in either pH or temperature. Climate change may therefore not affect the species as such, but may lead to changes in the population structure of the species, with the strains exhibiting high phenotypic plasticity, in terms of temperature and pH tolerance towards future conditions, dominating the population.