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Water Evaporation (water + evaporation)

Distribution by Scientific Domains

Engineering	50%

Selected Abstracts

Influence of moisture content on measurement accuracy of porous media thermal conductivity

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 8 2009
Mingzhi Yu
Abstract The thermal conductivity measurement accuracy of sand was experimentally studied with a hot disk thermal constant analyzer and water morphologies, distribution, and evolution at the pore scale were observed with a charge coupled device (CCD) combined with a microscope. It was found that thermal conductivities of samples with low moisture content (<25%) could not be accurately measured. For samples with low moisture content, the analysis showed that the water in the region adjacent to the analyzer sensor mainly existed as isolated liquid bridges between/among sand particles and would evaporate and diffuse to relatively far regions because of being heated by the sensor during measurement. Water evaporation and diffusion caused the sample constitution in the region adjacent to the sensor to vary throughout the whole measurement process, and accordingly induced low accuracy of the obtained thermal conductivities. Due to high water connectivity in pores, the rate of water evaporation and diffusion in porous media of high moisture content was relatively slow when compared with that of low moisture content. Meanwhile, water in the relatively far regions flowed back to the region adjacent to the sensor by capillary force. Therefore, samples consisting of the region adjacent to the sensor maintained the constant and thermal conductivities of porous media with relatively high moisture content and could be measured with high accuracy. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20272 [source]

The Prospects of Carrying and Releasing Drugs Via Biodegradable Magnesium Foam,

ADVANCED ENGINEERING MATERIALS, Issue 8 2010
Eli Aghion
Abstract Powder metallurgy technology was used to produce magnesium foams in order to evaluate their ability to perform as a solid biodegradable platform for drug delivery. The amount and delivery time of the released drug (gentamicin) was controlled by the level of space-holding particles (spacer) that was mixed with the magnesium powder prior to the sintering process. Metallurgical examination of the magnesium foams was carried out using optical and scanning electron microscopy (SEM) and X-ray diffraction analysis. Microtomography CT analysis was used to evaluate the structural characteristics of the magnesium foams and their internal interconnected porosity configuration. The corrosion behavior of the magnesium foams was evaluated by immersion test in a simulated physiological environment (PBS solution). The absorption of gentamicin was obtained by immersing magnesium foams in concentrated gentamicin solutions within a vacuum chamber, followed by water evaporation. The detection of gentamicin in PBS solution was carried out using a Fluorescence Polarimetry analyzer. The results show that the release profile of gentamicin from magnesium foam with 10 and 25% spacer in PBS solution was in accord with common dissolution kinetics of an active ingredient from polymeric drug delivery systems. [source]

Influence of moisture content on measurement accuracy of porous media thermal conductivity

A parametric study of multi-phase and multi-species transport in the cathode of PEM fuel cells

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 8 2008
Nada Zamel
Abstract In this study, a mathematical model is developed for the cathode of PEM fuel cells, including multi-phase and multi-species transport and electrochemical reaction under the isothermal and steady-state conditions. The conservation equations for mass, momentum, species and charge are solved using the commercial software COMSOL Multiphysics. The catalyst layer is modeled as a finite domain and assumed to be composed of a uniform distribution of supported catalyst, liquid water, electrolyte and void space. The Stefan,Maxwell equation is used to model the multi-species diffusion in the gas diffusion and catalyst layers. Owing to the low relative species' velocity, Darcy's law is used to describe the transport of gas and liquid phases in the gas diffusion and catalyst layers. A serpentine flow field is considered to distribute the oxidant over the active cathode electrode surface, with pressure loss in the flow direction along the channel. The dependency of the capillary pressure on the saturation is modeled using the Leverette function and the Brooks and Corey relation. A parametric study is carried out to investigate the effects of pressure drop in the flow channel, permeability, inlet relative humidity and shoulder/channel width ratio on the performance of the cell and the transport of liquid water. An inlet relative humidity of 90 and 80% leads to the highest performance in the cathode. Owing to liquid water evaporation, the relative humidity in the catalyst layer reaches 100% with an inlet relative humidity of 90 and 80%, resulting in a high electrolyte conductivity. The electrolyte conductivity plays a significant role in determining the overall performance up to a point. Further, the catalyst layer is found to be important in controlling the water concentration in the cell. The cross-flow phenomenon is shown to enhance the removal of liquid water from the cell. Moreover, a shoulder/channel width ratio of 1:2 is found to be an optimal ratio. A decrease in the shoulder/channel ratio results in an increase in performance and an increase in cross flow. Finally, the Leverette function leads to lower liquid water saturations in the backing and catalyst layers than the Brooks and Corey relation. The overall trend, however, is similar for both functions. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Air temperature effect on spray evaporation in sprinkler irrigation,

IRRIGATION AND DRAINAGE, Issue 4 2002
Dr Giulio Lorenzini
évaporation aérienne; irrigation par arroseur; équipement expérimental Abstract The temperature effect of the surrounding environment on mean steady aerial water evaporation in sprinkler irrigation is investigated. An experimental set-up was designed and built to work at opportune operating conditions holding all the other variables constant to minimise the experimental error. One hundred and thirty-seven tests were performed for this work, of which 81 were considered valid for a statistical analysis of the data measured. Evaporation ranged from 4.15 to 7.73% as the air temperature varied from 21.0 to 27.0° C. Results show a clear dependence of sprinkler water evaporation on air temperature with a logarithmic relation. Further investigations will examine broader temperature intervals to improve the assessment and will consider the effects due to other parameters affecting the phenomenon. Copyright © 2002 John Wiley & Sons, Ltd. Résumé Les effets de la température de l'environnement sur l'irrigation par arroseur ont été examinés. Un eq,uipement expérimental a été conçu et créé pour fonctionner dans des conditions d'emploi propices, et on a travaillé aussi pour tenir les autres variables le plus possible constantes pour minimiser l'erreur expérimentale. On a réalisé 137 tests et seulement 81 ont été considérés bons pour l'analyse statistique. On a vu que l'évaporation change de 4.15 à 7.73 pour cent avec le changement de température de 21.0 à 27.0° C. Les résultats montrent une claire dépendance logarithmique de l'évaporation avec la température de l'air. On propose dans le futur d'étendre l'intervalle des températures pour confirmer les résultats déjà vus et aussi de tester les influences d'autres variables d'intérêt pour ce phénomène. Copyright © 2002 John Wiley & Sons, Ltd. [source]

DTG thermal analyses and viscosity measurements of three commercial agar impression materials

JOURNAL OF ORAL REHABILITATION, Issue 7 2002
M. Taira
Three commercial agar impression materials, two for clinical uses and one for dental laboratory, were examined for their thermal properties by differential thermogravimetric (DTG) thermal analyses and viscosity measurements. On DTG profiles, an endothermic peak along with weight loss at around 100 °C was observed on all three agar impression materials as a result of water evaporation. Two clinical agar impression materials were more susceptible to this trend than the remaining one dental laboratory agar impression material. The viscosity of three agar impression materials could be expressed in the exponential function of temperature. Viscosity at 46 °C of one dental laboratory agar impression material far exceeded those of two clinical agar impression materials. Monitoring the viscosity could facilitate the detailed analysis of setting process of agar impression materials upon cooling, and might be useful for future development of agar-based dental impression materials. [source]

,18O of water vapour, evapotranspiration and the sites of leaf water evaporation in a soybean canopy

PLANT CELL & ENVIRONMENT, Issue 9 2008
LISA R. WELP
ABSTRACT Stable isotopes in water have the potential to diagnose changes in the earth's hydrological budget in response to climate change and land use change. However, there have been few measurements in the vapour phase. Here, we present high-frequency measurements of oxygen isotopic compositions of water vapour (,v) and evapotranspiration (,ET) above a soybean canopy using the tunable diode laser (TDL) technique for the entire 2006 growing season in Minnesota, USA. We observed a large variability in surface ,v from the daily to the seasonal timescales, largely explained by Rayleigh processes, but also influenced by vertical atmospheric mixing, local evapotranspiration (ET) and dew formation. We used ,ET measurements to calculate the isotopic composition at the sites of evaporative enrichment in leaves (,L,e) and compared that with the commonly used steady-state prediction (,L,s). There was generally a good agreement averaged over the season, but larger differences on individual days. We also found that vertical variability in relative humidity and temperature associated with canopy structure must be addressed in canopy-scale leaf water models. Finally, we explored this data set for direct evidence of the Péclet effect. [source]

Thermographic visualization of cell death in tobacco and Arabidopsis

PLANT CELL & ENVIRONMENT, Issue 1 2001
L. Chaerle
ABSTRACT Pending cell death was visualized by thermographic imaging in bacterio-opsin transgenic tobacco plants. Cell death in these plants was characterized by a complex lesion phenotype. Isolated cell death lesions were preceded by a colocalized thermal effect, as previously observed at sites infected by tobacco mosaic virus (TMV) (Chaerle et al. 1999Nature Biotechnology 17, 813,816). However, in most cases, a coherent front of higher temperature, trailed by cell death, initiated at the leaf base and expanded over the leaf lamina. In contrast to the homogenous thermal front, cell death was first visible close to the veins, and subsequently appeared as discrete spots on the interveinal tissue, as cell death spread along the veins. Regions with visible cell death had a lower temperature because of water evaporation from damaged cells. In analogy with previous observations on the localized tobacco,TMV interaction (Chaerle et al. 1999), the kinetics of thermographic and continuous gas exchange measurements indicated that stomatal closure preceded tissue collapse. Localized spontaneous cell death could also be presymptomatically visualized in the Arabidopsis lsd2 mutant. [source]