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Moisture Transport (moisture + transport)
Selected AbstractsWärme- und Feuchtetransport in VakuumisolationspaneelenBAUPHYSIK, Issue 6 2008Andreas Beck Prof. Dr. Wegen ihrer extrem niedrigen Wärmeleitfähigkeit und der damit verbundenen Möglichkeiten, mit geringen Bauteildicken hochwertig zu dämmen, haben Vakuumisolationspaneele (VIP) innerhalb kurzer Zeit Verbreitung im Bauwesen gefunden , insbesondere in Situationen, in denen andere Dämmstoffe aus Platzgründen nicht in Frage kommen. Da noch keine Langzeiterfahrungen über die Alterung der Paneele vorhanden sind, muss beim Bemessungswert der Wärmeleitfähigkeit im Moment allerdings noch mit hohen Sicherheitszuschlägen gerechnet werden, vor allem wegen des über die Nutzungsdauer stattfindenden Gaseintrags. Besonders von Interesse ist hierbei das Verhalten von aus der Umgebung eindiffundierendem Wasserdampf. Während die Auswirkungen von trockenen Gasen genau bezifferbar sind, überlagern sich beim Stoff- und Wärmetransport durch Wasser verschiedene Vorgänge, die die Wärmeleitung im VIP deutlich erhöhen, aber messtechnisch nur schwer erfassbar sind. Daher wurde ein theoretisches Modell entwickelt, das den Wärmestrom auf Grundlage der kinetischen Gastheorie für Molekularströmung und Oberflächendiffusion beschreibt und darüber hinaus Rückschlüsse auf die Diffusionseigenschaften des Kernmaterials zulässt. Heat and Moisture Transport in Vacuum Insulation Panels. Due to their extremely low thermal conductivity, vacuum insulation panels (VIP) allow for high standard thermal insulation with slim building components. Within few years, this led to widespread use especially in building situations where space is limited. As there are no long-term experiences concerning the thermal characteristics of VIPs, however, their rated values of thermal conductivity are notably higher than the actual measured values at present, which primarily represents effects of degradation caused by gases infiltrating the panel. Most significant is the influence of water vapour diffusing into the VIP. Whereas the effects of dry gases are well known and can be exactly quantified, water vapour causes different processes of heat and matter transfer which increase thermal conduction within the VIP considerably, but which cannot be separated accurately by means of measuring. Thus a theoretical model was developed which describes heat flux basing on the kinetic theory of gases for molecular diffusion and surface diffusion. It moreover provides information about the diffusion characteristics of the core material. [source] Feuchtetransport in Bauteilen aus wasserundurchlässigem Beton: Grundlagen und PraxisbetrachtungenBETON- UND STAHLBETONBAU, Issue 6 2007Udo Wiens Dr.-Ing. Bei WU-Konstruktionen übernimmt der Beton neben seiner tragenden auch eine abdichtende Funktion. Eine flächenförmige Hautabdichtung entfällt. Die Eigenschaft der Wasserundurchlässigkeit kann hierbei als zusätzliche Gebrauchstauglichkeitseigenschaft gesehen werden. Eine sehr häufig auftretende Fragestellung ist, ob trotz im Erdreich vorhandener Bodenfeuchte oder anstehendem Wasser sowie der im Beton enthaltenen Baufeuchte trockene Innenräume erreichbar sind. Zur Beantwortung der Fragen wurden Untersuchungen mit einem bauphysikalischen Rechenprogramm durchgeführt. Wichtige Eingangsgrößen für das Rechenprogramm wurden an Laborversuchen kalibriert. Ein Vergleich von Baufeuchte zu abführbarer Feuchte durch Lüften und zu nutzungsbedingter Feuchte wird vorgenommen. Moisture Transport in Components made of Water-Tight Concrete Basics and Practical Considerations In water-tight constructions, the concrete takes charge of a sealing function beside a load bearing function. A skin-sealing on the surface is not necessary. The property of water-tightness can be seen herewith as additional serviceability-property. A very often occurring question is, whether despite the in soil appearing ground-humidity or the upcoming water and the in concrete existing building moisture, dry interior rooms are achievable. To give answer to the questions, examinations by the help of a building physical calculation programme were carried out. Essential input parameters were calibrated in laboratory tests. A comparison of the inherent material moisture to the removable humidity by ventilation and to the humidity caused by using is given. [source] A basic study on humidity recovery by using micro-porous media (Effects of thermal condition of fluids and geometrical condition of apparatus on transport performance)HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 8 2006Shixue Wang Abstract Using an experimental apparatus to examine the performance of heat and mass transfer between constant-temperature water and dry air through a porous plate having extremely small pores, the effects of the thermal conditions in the fluids and the geometric condition of the apparatus on moisture transport were measured. The effects of water temperature, thickness of the porous plate, and channel height of the flowing air on moisture transport are noticeable. However, the effect of air temperature in the channel inlet on moisture transport is slight. In addition, in order to evaluate the degree of air humidity absorption, a parameter called the moisture absorption rate was introduced. The moisture absorption rate was shown to decrease with increasing air velocity and varies only slightly for a plate thickness of 1 mm and decreases for a plate thickness of 3.5 mm with increasing water temperature. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(8): 568,581, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20133 [source] Seasonal and inter-annual variability of the moisture sources for Alpine precipitation during 1995,2002INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 7 2010Harald Sodemann Abstract This study presents a first quantitative climatology of the moisture sources for precipitation in the European Alps, covering a 7-year period from January 1995 to August 2002. Using a Lagrangian moisture source diagnostic and data from the ERA-40: European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis, the contribution of the following moisture sources to annual mean precipitation has been diagnosed: North Atlantic ocean 39.6%, Mediterranean 23.3%, North Sea and Baltic Sea 16.6%, and European land surface 20.8%. However, strong seasonal variability of the influence of various moisture sources is evident. Most notably, moisture transport to the Alps changes from an oceanic mode characterised by dominantly North Atlantic moisture sources during winter to a continental mode during summer with a marked contribution from Central European land areas. The method identifies inter-annual variability with respect to the location of the moisture sources in the North Atlantic, and the importance of precipitation recycling during summer. Despite the smoothed Alpine orography in the ERA-40 model, the Alps act as an effective barrier for meridional moisture transport, leading to distinct mean moisture source locations at their northern and southern slopes. The Northern Alps are predominantly influenced by the North Atlantic ocean and Central European land sources with a clear seasonality and limited monthly variability. In contrast, the Southern Alps receive a large fraction of precipitation from the Mediterranean with considerable month-to-month variability. Possible implications of these differences for precipitation extremes and stable isotopes in precipitation are discussed. Copyright © 2009 Royal Meteorological Society [source] Inter-decadal variation of the summer precipitation in East China and its association with decreasing Asian summer monsoon.INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 9 2008Part I: Observed evidences Abstract In recent two decades, North and Northeast China have suffered from severe and persistent droughts while the Yangtze River basin and South China have undergone much more significant heavy rainfall/floods events. This long-term change in the summer precipitation and associated large-scale monsoon circulation features have been examined by using the new dataset of 740 surface stations for recent 54 years (1951,2004) and about 123-yr (1880,2002) records of precipitation in East China. The following new findings have been highlighted: (1) One dominating mode of the inter-decadal variability of the summer precipitation in China is the near-80-yr oscillation. Other modes of 12-yr and 30,40-yr oscillations also play an important role in affecting regional inter-decadal variability. (2) In recent 54 years, the spatial pattern of the inter-decadal variability of summer precipitation in China is mainly structured with two meridional modes: the dipole pattern and the positive-negative-positive ("+ , + " pattern). In this period, a regime transition of meridional precipitation mode from "+ , + " pattern to dipole pattern has been completed. In the process of southward movement of much precipitation zone, two abrupt climate changing points that occurred in 1978 and 1992, respectively, were identified. (3) Accompanying the afore-described precipitation changes, the East Asian summer monsoon have experienced significant weakening, with northward moisture transport and convergence by the East Asian summer monsoon greatly weakened, thus leading to much deficient moisture supply for precipitation in North China. (4) The significant weakening of the component of the tropical upper-level easterly jet (TEJ) has made a dominating contribution to the weakening of the Asian summer monsoon system. The cooling in the high troposphere at mid- and high latitudes and the possible warming at low latitude in the Asian region is likely to be responsible for the inter-decadal weakening of the TEJ. Copyright © 2007 Royal Meteorological Society [source] Ten-year climatology of summer monsoon over South China and its surroundings simulated from a regional climate modelINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2006Yiming Liu Abstract In a previous study by the authors, a regional climate model (hereafter the RCM) developed to study the summer monsoon over South China (SC) and the South China Sea (SCS) has been tested and found to be able to simulate to a large extent the precipitation over this region for the months of May and June. To examine the interannual variability of the summer monsoon here, it is necessary to establish a model climatology to serve as a comparison and to reduce or even remove any systematic model biases. This paper presents the analyses of such a 10-year climatology (1991,2000). The model was initialized on 1 April and integrated up to the end of June for the ten years. The initial atmospheric conditions and lateral boundary data used in this study are from the European Centre for Medium-range Weather Forecasts ,40-year' reanalyses. The RCM can reproduce well the main features of the monsoon circulation and vertical structure of the atmosphere. The RCM can simulate the intensification and northwestward displacement of the south Asian upper anticyclones from May to June, as well as the low-level moisture transport from the Bay of Bengal to SC. In the simulation, the average SCS summer monsoon onset occurs in the fourth pentad of May, which is consistent with the results from previous observational research. In addition, the RCM can reproduce the main characteristics of the onset such as the change of the low-level zonal flow from easterly to westerly as well as the rapid increase in daily precipitation. The SC and SCS precipitation anomalies have the correct sign in almost all the years. The shortcomings of the model simulation include an under-prediction of the strength of the subtropical high over the Northwest Pacific and the moisture transport from the Bay of Bengal to the Indochina Peninsula (IC) and SCS. A cold bias in surface air temperature is also observed, with the 10-year mean biases of the simulated surface air temperature over SC, SCS and IC in May and June being about ,2.1 °C, ,2.4 °C and ,1.4 °C respectively. The 10-year mean biases of the simulated daily precipitation rate over SC, SCS and IC are about 2.0, ,3.8 and 3.5 mm d,1 respectively. Copyright © 2005 Royal Meteorological Society. [source] Interannual variability of lower-tropospheric moisture transport during the Australian monsoonINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2002Christopher R. Godfred-Spenning Abstract The interannual variability of the horizontal lower-tropospheric moisture transport associated with the Australian summer monsoon has been analysed for the 1958,99 period. The 41-season climatology of moisture flux integrated between the surface and 450 hPa showed moderate levels of westerly transport in the month before Australian monsoon onset, associated with cross-equatorial flow in the Sulawesi Sea and west of Borneo. In the month after onset the westerly moisture transport strengthened dramatically in a zonal belt stretching from the Timor Sea to the Western Equatorial Pacific, constrained between the latitudes 5 and 15 °S, and associated with a poleward shift in the Intertropical Convergence Zone and deepening of the monsoon trough. Vertical cross-sections showed this transport extending from the surface to the 500 hPa level. In the second and third months after onset the horizontal flow pattern remained similar, although flux magnitudes progressively decreased, and the influence of trade winds became more pronounced over northern Australia. Nine El Niño and six La Niña seasons were identified from the data set, and composite plots of the affected years revealed distinct, and in some cases surprising, alterations to the large-scale moisture transport in the tropical Australian,Indonesian region. During an El Niño it was shown that the month prior to onset, in which the moisture flux was weaker than average, yielded to a dramatically stronger than average flux during the following month, with a zone of westerly flux anomalies stretching across the north Australian coast and Arafura Sea. The period of enhanced moisture flux during an El Niño is relatively short-lived, with drier easterly anomalies asserting themselves during the following 2 months, suggesting a shorter than usual monsoon period in north Australia. In the La Niña composite, the initial month after onset shows a tendency to weaker horizontal moisture transport over the Northern Territory and Western Australia. The subsequent 2 months show positive anomalies in flux magnitude over these areas; the overall effect is to prolong the monsoon. Comparison of these results with past research has led us to suggest that the tendency for stronger (weaker) circulations to arise in the initial month of El Niño (La Niña) events is a result of mesoscale changes in soil moisture anomalies on land and offshore sea surface temperature (SST) anomalies, brought about by the large-scale alterations to SST and circulation patterns during the El Niño,Southern Oscillation. The soil moisture and SST anomalies initially act to enhance (suppress) the conditions necessary for deep convection in the El Niño (La Niña) cases via changes in land,sea thermal contrast and cloud cover. Copyright © 2002 Royal Meteorological Society. [source] Ocean-atmosphere-land feedbacks in an idealized monsoonTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 576 2001C. Chou Abstract An intermediate-complexity atmospheric model coupled with a simple land-surface model and a mixed-layer ocean model is used to investigate the processes involved in an idealized monsoon occurring on a single rectangular continent. Idealized divergences of ocean heat transports are specified as an annual average ,Q-flux'. In this simple coupled configuration, the mechanisms that affect land-ocean contrast and, in turn, the seasonal movement of the continental convergence zones are examined. These include soil-moisture feedbacks: cooling of tropical oceans by ocean transpoit; ventilation, defined as the import into continental regions of low moist static-energy air from ocean regions where heat storage opposes summer warming; and the ,interactive Rodwell-Hoskins mechanism', in which Rossby-wave-induced subsidence to the west of monsoon heating interacts with the convection zone. The fixed ocean transports have a substantial impact on the continental convection. If Q-flux is set to zero, subtropical subsidence and ventilation tend to substantially limit the poleward movement of summer monsoon rainfall. When land hydrology feedbacks are active, the drying of subtropical continents disfavours continental convection even in the tropics. When ocean transports are included, tropical oceans are slightly disfavoured as regions for producing convection which, by contrast, favours continental convection. The monsoon circulation then produces moisture transport from the ocean regions that allows substantial progression of convection into the subtropics over the eastern portion of the continent. The western portion of the continent tends to have a dry region of characteristic shape. This east-west asymmetry is partly due to the interactive Rodwell-Hoskins mechanism. The ventilation is of at least equal importance in producing east-west asymmetry and is the single most important process in limiting the poleward extent of the continental convection zone. [source] Trends and abrupt changes of precipitation maxima in the Pearl River basin, ChinaATMOSPHERIC SCIENCE LETTERS, Issue 2 2009Q. Zhang Abstract We applied the Mann-Kendall (MK) test and Bayesian model to systematically explore trends and abrupt changes of the precipitation series in the Pearl River basin. The results showed that no significant trends were detected for annual precipitation and summer or winter precipitation totals. Significant negative trends were identified for the number of rainy days across the Pearl River basin; significant positive trends were observed regarding precipitation intensity (PI). In particular, the precipitation totals and frequencies of extremely high precipitation events are subject to significant positive trends. In addition, the number of extremely low precipitation events was also increasing significantly. Factors affecting the changes in precipitation patterns are the weakening Asian monsoon and consequently increasing moisture transport to Southern China and the Pearl River basin. In summary, the main findings of this study are: (1) increased precipitation variability and high-intensity rainfall was observed though rainy days and low-intensity rainfall have decreased, and (2) the amount of rainfall has changed little but its variability has increased over the time interval divided by change points. These finds indicate potentially increased risk for both agriculture and in locations subject to flooding, both urban and rural, across the Pearl River basin. Copyright © 2009 Royal Meteorological Society [source] Energetisch und bauphysikalisch optimierte Sanierung eines Baudenkmals in GörlitzBAUPHYSIK, Issue 3 2007Christian Conrad Dipl.-Ing. Mit den angewendeten Sanierungsmassnahmen an einem barocken Gebäude in Görlitz (Innendämmung Straßenfassade, WDVS Hoffassade, Solaranlage, Lüftungsanlage mit WRG, Grauwassernutzung und Fußbodenabwasserheizung) wurden unter Einhaltung der Auflagen des Denkmalschutzes die Energieeffizienzklasse A+ erreicht, die Belange des Umweltschutzes berücksichtigt und die Dauerhaftigkeit und Zuverlässigkeit der Konstruktionen gewährleistet. Die erreichten Ergebnisse werden u.a. mit instationären Simulationsrechnungen (Wärme-, Luft- und Feuchtetransport in kapillarporösen Baustoffen) für die einzelnen Bauteile und instationären Simulationsrechnungen anlagentechnischer Komponenten verifiziert. Dabei wird bauphysikalisch der Einfluss der hohen Bauwerksmasse ganzjährig quantifiziert. Die Auswirkungen der eingesetzten Anlagentechnik auf historische Bauteile, wie z. B. die Holzbalkendecken, werden untersucht. Auf der Grundlage der Erfahrungen zur Vermeidung der Kondensat- und Reifbildungen bei hochdämmenden geneigten Verglasungen wurde gemeinsam mit einem ortsansässigen Glaswerk eine neue Wärmeschutzverglasung mit einer außenliegenden Beschichtung entwickelt/kombiniert und eingesetzt. Optimized energy saving rehabilitation of a baroque building monument. With the rehabilitation of the baroque building Handwerk 15 in Görlitz the authors achieved the energy efficiency class A+ under observance of all conditions from preservation of historic buildings and monuments, taking into account the environmental issues as well as durability and safety of the constructions in the house. The rehabilitation includes the internal thermal insulation of the historically valuable façade on the street side, the thermal insulation of the façade on the backyard side, the use of solar energy for hot water and for the support of heating especially in summer for heating the ground floor, a ventilation system with heat exchanger, the use of gray water generated from domestic processes such as laundry and bathing, and an underfloor heating for the ground floor with waste water as medium. The measurement results will be verified with numerical simulations (temperature, air, moisture transport in porous materials) of the separate building constructions and the technical components. The physical influence of the high building mass is quantified. The effects of the HVAC system on the historical building construction like for instance the timber beam floor will be investigated. Based on experiences about avoiding condensate and hoarfrost on inclined insulated glass together with a glass producing firm a new insulate glass with a special coating was developed. [source] Rechnerische Bewertung von Trocknungsverfahren für hochwassergeschädigtes MauerwerkBAUPHYSIK, Issue 2 2006Research Associated Professor John Grunewald Dr.-Ing. Überschwemmungen sind ein globales Phänomen, was durch die jüngsten Ereignisse in Zentral- und Nordeuropa wieder bestätigt wurde. Die Fluten hinterlassen beträchtliche Schäden an Gebäuden und beeinträchtigen das menschliche Zusammenleben. Sind Schäden an Einrichtungen zu verzeichnen, stehen staatliche Institutionen, Versicherungsunternehmen und Reparaturdienstleister in der Verantwortung, die Eigentümer bei der Instandsetzung zu unterstützen. Eine Voraussetzung zur Kostenminimierung ist dabei eine auf die lokalen Gegebenheiten zugeschnittene Trocknungsstrategie, die sowohl die örtlichen klimatischen Bedingungen als auch die verwendeten Baumaterialien einbezieht. Der Beitrag stellt eine Methode zur Bewertung von Trocknungsmaßnahmen hochwassergeschädigter Gebäude aus Ziegelmauerwerk vor. Die Verwendung von Simulationsrechnungen zur Vorhersage des Erfolges verschiedener Trocknungsverfahren wird anhand von unterschiedlichen historischen Mauerwerksarten gezeigt. Es lassen sich Aussagen über die Feuchteabgabe nach innen, über Anzahl und Dauer des Einsatzes von Luftentfeuchtungsgeräten, über den Verlauf der Trocknung, Gesamtdauer und Kosten der Maßnahmen treffen. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) Optimal drying of of flooded masonry structures. Flooding is a global phenomenon as recently highlighted by the major catastrophic events in Central and Northern Europe. When flooding occurs in an area populated by humans, it can cause substantial damage to property and threaten human life. When properties are damaged by flooding, governmental institutions, insurers and repairers are called upon to provide services to homeowners in order to return the dwellings back to a habitable state. As one prerequisite to minimize costs for rehabilitation, such services should comprise drying measures tailored to local particularities as climatic conditions and building material properties. The paper introduces a new methodology to schedule drying measures and to evaluate their success for brick masonry buildings. The capabilities of computer simulation to predict the costs of alternative drying strategies are demonstrated by means of flooded masonry for different types of brickwork frequently used in historical buildings. The numerical simulation of moisture transport in flooded brickwork masonry allows statements about the moisture release to the indoor air, the recommended duration of usage and number of air dehumidifiers, the current drying state, the total time to return the brickwork back to a dry state and the drying costs as function of time. [source] Atmospheric large-scale dynamics during the 2004/2005 winter drought in portugalINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2007J. Santos Abstract The unusually dry conditions during the 2004/2005 winter in Portugal led to the development of an extreme/severe drought episode throughout the country with major socioeconomic impacts. In fact, at some locations, this winter was the driest in at least the last 60 years. A K-means classification of days into a set of five weather regimes (WRs), relevant for winter precipitation in Portugal, reveals a large prevalence of the two driest weather regimes during the 2004/2005 winter. These two regimes are basically linked to either anticyclonic circulation or easterly winds over Portugal and their prevalence explains the significant precipitation deficit. Winter precipitation variability in Portugal is indeed skillfully represented by linear models where the predictors are the frequencies of occurrence (FO) of these weather regimes. The dominance of the ,dry phases' of the main coupled modes between winter precipitation in Portugal and the large-scale atmospheric circulation also supports the prevalence of the dry regimes and the corresponding lack of precipitation. The predominance of the dry regimes can be explained by a remarkably strong enhancement of the climate-mean North Atlantic ridge, manifested by dynamically coherent anomalies in the geopotential heights, vorticity and temperature fields over the North Atlantic. The persistence of a warm-core asymmetrical eddy over the North Atlantic, with a nearly barotropic equivalent structure, is a manifestation of this large-scale anomaly. The blocking of the westerlies and the consequent northward shift in the axis of maximum moisture transports over the North Atlantic was one of the most striking changes in the large-scale atmospheric flow. Consequently, the main track of the developing baroclinic disturbances was sufficiently distant from Portugal to hamper the development of rain-generating conditions. As these dynamical conditions are common to other reportedly dry winters, they effectively constitute a key factor for the occurrence of a precipitation deficit in Portugal. Copyright © 2006 Royal Meteorological Society [source] | |||||||||||||