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Transient Conditions (transient + condition)
Selected AbstractsMatrix Representation of Polymer Chain Size Distributions, 3 , Case Studies for Linear Polymerization Mechanisms at Transient ConditionsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 4-5 2008Heloísa L. Sanches Abstract The mass balance equations used to describe different polymerization systems are represented and analyzed with the help of a general matrix framework previously developed. Some of its properties were presented in previous works and are illustrated here in three examples. The first example regards the dynamics of a copolymerization reactor. It is shown that terminal and penultimate models may predict qualitatively different responses in batch reactions. The second example also regards the dynamics of copolymerization reactions. It is shown how manipulation of initial conditions and monomer feed rates can be used to keep copolymer composition constant throughout the batch. The third example concerns the existence of oscillating chain size distributions when there are multiple monomer insertion steps. [source] Differences between young adults and elderly in thermal comfort, productivity, and thermal physiology in response to a moderate temperature drift and a steady-state conditionINDOOR AIR, Issue 4 2010L. Schellen Abstract, Results from naturally ventilated buildings show that allowing the indoor temperature to drift does not necessarily result in thermal discomfort and may allow for a reduction in energy use. However, for stationary conditions, several studies indicate that the thermal neutral temperature and optimum thermal condition differ between young adults and elderly. There is a lack of studies that describe the effect of aging on thermal comfort and productivity during a moderate temperature drift. In this study, the effect of a moderate temperature drift on physiological responses, thermal comfort, and productivity of eight young adults (age 22,25 year) and eight older subjects (age 67,73 year) was investigated. They were exposed to two different conditions: S1-a control condition; constant temperature of 21.5°C; duration: 8 h; and S2-a transient condition; temperature range: 17,25°C, duration: 8 h, temperature drift: first 4 h: +2 K/h, last 4 h: ,2 K/h. The results indicate that thermal sensation of the elderly was, in general, 0.5 scale units lower in comparison with their younger counterparts. Furthermore, the elderly showed more distal vasoconstriction during both conditions. Nevertheless, TS of the elderly was related to air temperature only, while TS of the younger adults also was related to skin temperature. During the constant temperature session, the elderly preferred a higher temperature in comparison with the young adults. Practical Implications ,Because the stock of fossil fuels is limited, energy savings play an important role. Thermal comfort is one of the most important performance indicators to successfully apply measures to reduce the energy need in buildings. Allowing drifts in indoor temperature is one of the options to reduce the energy demand. This study contributes to the knowledge concerning the effects of a moderate temperature drift and the age of the inhabitants on their thermal comfort. [source] A case of benign acute childhood myositis associated with influenza A (H1N1) virus infectionCLINICAL MICROBIOLOGY AND INFECTION, Issue 2 2010M. Koliou Clin Microbiol Infect 2010; 16: 193,195 Abstract Benign acute childhood myositis (BACM) is a rare transient condition usually occurring at the early convalescent phase of a viral upper respiratory tract illness, normally influenza A, and, more frequently, influenza B infection. It is characterized by acute-onset difficulty in walking as a result of severe bilateral calf pain and by elevated muscle enzymes including creatinine kinase. It is self-limiting because there is rapid full recovery usually within 1 week. We describe the first case of BACM in association with the new pandemic influenza A (H1N1) virus infection in an 11-year-old boy from Cyprus. The child had the typical clinical and laboratory characteristics of this clinical syndrome. Prompt diagnosis of this clinical entity is essential to prevent unnecessary investigations and therapeutic interventions and to reassure the patient and parents of the excellent prognosis. [source] Meltwater discharge through the subglacial bed and its land-forming consequences from numerical experiments in the Polish lowland during the last glaciationEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2009Jan A. Piotrowski Abstract Numerical experiments suggest that the last glaciation severely affected the upper lithosphere groundwater system in NW Poland: primarily its flow pattern, velocities and fluxes. We have simulated subglacial groundwater flow in two and three spatial dimensions using finite difference codes for steady-state and transient conditions. The results show how profoundly the ice sheet modifies groundwater pressure heads beneath and some distance beyond the ice margin. All model runs show water discharge at the ice forefield driven by ice-sheet-thickness-modulated, down-ice-decreasing hydraulic heads. In relation to non-glacial times, the transient 3D model shows significant changes in the groundwater flow directions in a regionally extensive aquifer ca. 90 m below the ice,bed interface and up to 40 km in front of the glacier. Comparison with empirical data suggests that, depending on the model run, only between 5 and 24% of the meltwater formed at the ice sole drained through the bed as groundwater. This is consistent with field observations documenting abundant occurrence of tunnel valleys, indicating that the remaining portion of basal meltwater was evacuated through a channelized subglacial drainage system. Groundwater flow simulation suggests that in areas of very low hydraulic conductivity and adverse subglacial slopes water ponding at the ice sole was likely. In these areas the relief shows distinct palaeo-ice lobes, indicating fast ice flow, possibly triggered by the undrained water at the ice,bed interface. Owing to the abundance of low-permeability strata in the bed, the simulated groundwater flow depth is less than ca. 200 m. Copyright © 2009 John Wiley & Sons, Ltd. [source] Performance of a full-scale biotrickling filter treating H2S at a gas contact time of 1.6 to 2.2 secondsENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 2 2003David Gabriel Emission of objectionable odors is a major problem for wastewater treatment and other processing facilities. Biological treatment is a promising alternative to conventional control methods, such as chemical scrubbing, but historically, biotreatment has always required significantly larger reactor volumes than chemical scrubbers. In this paper, we present several aspects of the operation and performance of a chemical scrubber, retrofitted to operate as a biotrickling filter treating 16,000 m3 h,1 of foul air with the original gas contact time of 1.6 to 2.2 seconds. In continuous operation for more than a year, the biotrickling filter has shown stable performance and robust behavior for H2S treatment, with pollutant removal performance comparable to using a chemical scrubber. Reclaimed water was used as a nutrient source for the process, and to maintain the pH in the biotrickling filter between 1.5 and 2.2. At a gas contact time of 1.6 seconds, H2S removal was in excess of 95% for sustained inlet H2S concentrations as high as 30 ppmv. This corresponds to volumetric elimination rates of 95 to 105 g H2S m,3 h,1. Efficiencies of about 90% were observed under transient conditions at 2.2 seconds gas contact time for inlet concentration peaks up to 60 ppmv. The biotrickling filter also removed significant amounts of reduced sulfur compounds, ammonia, and volatile organic compounds present in traces in the air, which is important in practical applications. Selected experiments, such as intermittent trickling operation and a one-month operation period at neutral pH, are also presented. Results indicate that the intermittent trickling operation does not have a significant effect on H2S removal. However, when operated at neutral pH, biotrickling filter performance clearly decreased, probably due to an excessive chlorine supply to the reactor through the make-up water. The study demonstrates that biotrickling filters can replace chemical scrubbers as a safer, more economical technique for odor control. [source] Unit commitment at frequency security conditionEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 2 2001X. Lei In island grids and weakly interconnected power systems, the loss of a large proportion of generation will cause the system frequency to fall dramatically. In order to ensure a stable operation with the lowest impact to the system, the disturbed power balance must be equalized within a short specified time by activating the second-reserve of on-line units or by load shedding or both. Unit commitment procedures shall consider these factors to ensure a reliable power supply while minimizing the fuel costs. This paper presents a unit commitment procedure taking the frequency security condition of systems into account. The procedure commits and optimizes units, calculates necessary second-reserve capability, and allocates them among the available on-line units. Parallel to the minimization of daily fuel costs, a specified frequency minimum following the loss of generation is employed as a criterion for maintaining system security. A case study on typical island systems with a large number of different units is demonstrated using the proposed procedure. Results from the study validated robust performance of the proposed procedure that minimizes fuel costs while maintaining frequency security condition. This paper considers only the frequency security condition to be handled. However, it can also be extended with other criteria such transmission capability during transient conditions of interconnected systems. [source] Improvement of interactions among facts controlsEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 5 2000X. Lei Interaction among the FACTS (flexible AC transmission systems) devices in a multi-machine system can adversely influence the damping properties of individual FACTS devices. In some critical cases, it may even amplify power swings or increase voltage deviations. This paper presents a global tuning method for the FACTS controllers in a multi-machine system. Based on a non-linear optimization algorithm implemented in a simulation program, the parameter settings of the FACTS controllers involved can be simultaneously optimized at transient conditions in coping with the non-linear nature of the power system. By minimizing a non-explicit target function in which swing characteristics between areas are included, interactions among the FACTS controls at transient conditions in the multi-machine system are minimized. Two multi-machine power systems equipped individually with a TCSC (thyristor-controlled series compensator) and a SVC (static Var compensator) are applied to demonstrate the efficiency of the proposed tuning procedure. The results obtained from simulations validate the improvement in damping of overall power oscillations. The simulations also show that the optimized FACTS controllers are robust in providing adequate damping for a range of conditions on the system. [source] A transmission line modelling (TLM) method for steady-state convection,diffusionINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 9 2007Alan Kennedy Abstract This paper describes how the lossy transmission line modelling (TLM) method for diffusion can be extended to solve the convection,diffusion equation. The method is based on the correspondence between the convection,diffusion equation and the equation for the voltage on a lossy transmission line with properties varying exponentially over space. It is unconditionally stable and converges rapidly to highly accurate steady-state solutions for a wide range of Peclet numbers from low to high. The method solves the non-conservative form of the convection,diffusion equation but it is shown how it can be modified to solve the conservative form. Under transient conditions the TLM scheme exhibits significant numerical diffusion and numerical convection leading to poor accuracy, but both these errors go to zero as a solution approaches steady state. Copyright © 2007 John Wiley & Sons, Ltd. [source] Adaptive transfer function-based control of nonlinear process.INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 10 2007Case study: Control of temperature in industrial methane tank Abstract The state model-based transfer function models are applied for adaptation of linear controller and disturbance compensator in a feedback/feed-forward control system of nonlinear process. An advantage of the presented adaptation method is the avoidance of artificial disturbances or iterative identification procedures for on-line estimation of process dynamic parameters. The adaptation is based on linearization of the process model at each sampling time about the current state point, independent of the process being at steady-state or transient conditions. The linear time-varying dynamics model is updated on-line using measured values of process variables and reduced to the first-order plus time delay transfer function models in order to directly apply well-developed controller tuning rules. Computational aspects of the adaptation method are discussed and computation algorithms are presented. The adaptive feedback/feed-forward control system was applied for controlling temperature in industrial methane tank, dynamic parameters of which vary in a wide range due to variations of methane-tank process load and external conditions. The heat balance-based process state model is developed and validated using observation data of real plant. Computer simulation of the proposed control system performance under extreme operating conditions demonstrates fast adaptation of controller parameters, robust behaviour and significant improvement in the controllers' performance compared to that of fixed-gain controllers. Copyright © 2007 John Wiley & Sons, Ltd. [source] Optimal operation of CVT-based powertrainsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 11 2001Rolf Pfiffner Abstract Continuously Variable Transmissions (CVTs) are considered by many as a promising contribution to the improvement of the fuel economy of passenger cars. This paper discusses the fuel-optimal operation of a CVT-equipped powertrain in stationary and in transient conditions. The well-known optimal solution in the stationary case will be given only a short review discussing the importance of a correct CVT efficiency model. For transient vehicle operation so far only heuristic control strategies are known. This work aims to fill this gap. After detailed modelling of the complete powertrain and the introduction of a meaningful cost function, the resulting nonlinear optimal control problem is solved. The optimization is carried out for two different engines: a conventional SI engine and a downsized supercharged (DSC) SI engine. Each can be considered as a typical representative of the corresponding engine class. In both cases the optimal solutions are shown to be superior to standard CVT control algorithms, yielding larger gains in fuel economy for DSC engines. The optimal feedforward controls are then approximated by suboptimal feedback controllers that realize almost the same benefits in fuel economy at a substantially reduced computational effort. Finally, it is shown how the well-known ,single track modified' control approach can be changed such that it produces the same results as the suboptimal controller. Copyright © 2001 John Wiley & Sons, Ltd. [source] The removal of iron and cobalt from aqueous solutions by ion exchange with Na-Y zeolite: batch, semi-batch and continuous operationJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2002Jong Sung Kim Abstract The removal of single component and binary mixtures of divalent cobalt and iron from water by ion exchange with synthetic Y zeolite has been studied in batch, semi-batch and continuous modes of operation; the initial metal solution concentration did not exceed 2,mmol,dm,3. Binary Co/Na and Fe/Na ion exchange equilibrium isotherms (294,K) are presented wherein exchange site heterogeneity is evident in the case of the iron treatment. Under conditions of stoichiometric ion exchange, removal efficiencies for both cobalt and iron decrease with increasing metal concentration (0.2,2,mmol,dm,3) and the values were similar for both metals. Removal of cobalt under transient conditions was found to be temperature dependent. In the fixed bed operation, break-through behavior was sensitive to changes in both flow rate and inlet concentration. The break-through profiles for both metals under competitive and non-competitive conditions are presented; iron removal is lower in the presence of cobalt and vice versa. An in situ regeneration of the fully loaded zeolite by back exchange with sodium is considered and the exchange capacity of the regenerated zeolite is reported. The feasibility of employing cycles of heavy metal uptake/zeolite regeneration is addressed. © 2002 Society of Chemical Industry [source] CONCENTRATION BOUNDARY CONDITIONS IN THE THEORETICAL ANALYSIS OF CONVECTIVE DRYING PROCESSJOURNAL OF FOOD PROCESS ENGINEERING, Issue 5 2007AHMET KAYA ABSTRACT In the theoretical analysis of convective drying process, two boundary conditions are common for concentration: constant concentration and convection. In this study, these two boundary conditions were comparatively examined by comparing theoretical results obtained with regard to experimental ones. Pumpkin (Cucurbita pepo) was considered as the product to be dried while air was the drying medium. The drying characteristics of pumpkin were determined for various values of drying air parameters, including temperature, velocity and relative humidity. Sorption isotherms of the dried pumpkin were also determined for different temperatures and water activities. The values of the effective moisture diffusivity, Deff, and the convective mass transfer coefficient, hm, were predicted, and these values were found to agree fairly well with those available in the existing literature. PRACTICAL APPLICATIONS Convective drying as well as other drying techniques are used in order to preserve and store agricultural products for longer periods by removing some of their moisture content. Drying is a complicated process involving simultaneous heat and mass transfer under transient conditions. Understanding the heat and mass transfer in the product will help to improve drying process parameters and hence the quality. [source] A structured model for the simulation of bioreactors under transient conditionsAICHE JOURNAL, Issue 11 2009Jérôme Morchain Abstract Modeling the transient behavior of continuous culture is of primary importance for the scale-up of biological processes. Spatial heterogeneities increase with the reactor size and micro-organisms have to cope with a fluctuating environment along their trajectories within the bioreactor. In this article, a structured model for bioreactions expressed in terms of biological extensive variables is proposed. A biological variable is introduced to calculate the growth rate of the population. The value is updated on the basis of the difference between the composition in the liquid and biotic phase. The structured model is able to predict the transient behavior of different continuous cultures subject to various drastic perturbations. This performance is obtained with a minimum increase in the standard unstructured model complexity (one additional time constant). In the final part, the consequences of decoupling the growth rate from the substrate uptake rate are discussed. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Experimental investigation of transient and thermal effects on lubricated non-conformal contactsLUBRICATION SCIENCE, Issue 4 2007R. Bassani Abstract In this work, thermal and transient effects on non-conformal lubricated contacts are investigated through experimental analyses. Experiments between a ball and a plane surface of a disc are described. Friction coefficients and film thicknesses are measured (the film thickness only for the glass-on-steel contact). A paraffin base mineral oil is used as a lubricant. First experiments are carried out under steady-state conditions. To include effects due to different thermal properties of contacting materials, a steel-on-steel and a glass-on-steel contact with different slide-to-roll ratios are tested. If the contacting materials have different thermal properties, as in the case of a glass-on-steel contact, thermal effects like the temperature,viscosity wedge action could clearly be shown. It is found that the friction coefficients are influenced by the slide-to-roll ratio and the thermal properties of the contacting materials. Under transient conditions, the entraining velocity is varied with a sinusoidal law. Squeeze effects explain ,loops' of friction and film thickness found also in previous works. The formation of friction loops is related to the measured film thickness differences. However, also under non-steady-state conditions, thermal effects, like the temperature,viscosity wedge action, influence the friction coefficients. Copyright © 2007 John Wiley & Sons, Ltd. [source] Development of an improved method for investigating the frictional properties of lubricants under transient EHD conditionsLUBRICATION SCIENCE, Issue 4 2002B.-O. Åhrström Abstract In the design and evaluation of mechanical system performance it is important to know the frictional qualities of the lubricant. Without correct numerical treatment of the lubricant during simulations of large systems, e.g., drive trains in trucks and buses, the results will, to a large extent, be inaccurate. However, obtaining detailed information places demands on the test equipment as the events are both transient and highly loaded. Under quasi-static conditions, forces are measured with force transducers, but in elasto-hydrodynamically lubricated conjunctions, where pressures are so high that the surrounding surfaces deform elastically, this cannot be done without permanently damaging the equipment. The conceptual design of the test equipment must therefore incorporate the measuring process in transient conditions (loading-unloading times of 200,500 ,s) being performed in real time, and allow extreme pressures of up to 3 GPa without component destruction. One way to obtain accurate friction data successfully is to apply a concentrated force pulse to a non-instrumented surface and to measure the response from that pulse elsewhere. The development of a measurement technique, the Lulea ball and bar apparatus, which utilises wave propagation theory, is presented in this paper. An oblique impact on a robust end plate on a rod was used to generate both non-dispersive compression waves and dispersive flexural waves. The normal force created by the axial wave was measured using strain gauges, while the transverse force was derived from the fast Fourier transforms of two lateral acceleration histories, using dynamic beam theory. The relation between the normal and tangential force histories showed the frictional properties at the impact as a function of time. A variety of lubricants was also studied at Hertzian pressures of up to 2.5 GPa, and the development of the method and results are presented. Experiments indicate that different lubricants exhibit different frictional properties and that the resolution in the test equipment is sufficient to indicate this. [source] Matrix Representation of Polymer Chain Size Distributions, 2,MACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2007Fundamental Analysis of Linear Polymerization Mechanisms at Transient Conditions Abstract Analysis of the mass balance equations that describe a reaction system may be useful to provide information about its dynamics, such as the restricted set of compositions that can be achieved from a given set of initial compositions and the effect of feeding reactants to the reaction environment along the reaction course. Since these results may be important for the formulation of reaction policies, this work presents the properties of a matrix polymerization model previously developed and extended to describe transient conditions. This model is based on the definitions of two matrices: the consumption matrix (A,,,Kt), which contains information about chemical transformations among the many active polymer species in the system, and the propagation matrix Kp, which contains information about chain growth. It is shown that the set of mass balance equations that describes the dynamics of active chemical species in polymerization reactions has a stable and unique solution, which is bounded if feed rates are also bounded. It is also shown that the set of compositions that may be reached through manipulation of the feed rates is restricted and may not include all possible chemical compositions. Finally, it is shown that the obtained molecular weight distributions are special multiple time convolutions of the initiation rates. [source] The effect of transient conditions on an equilibrium permafrost-climate modelPERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2007Dan Riseborough Abstract Equilibrium permafrost models assume a stationary temperature and snow-cover climate. With a variable or changing climate, short-term energy imbalances between the active layer and permafrost result in transient departures from the equilibrium condition. This study examines the effects of such variability on an equilibrium permafrost-climate model, the temperature at the top of permafrost (TTOP) model. Comparisons between numerical results and temperatures predicted by the TTOP-model suggest that stationary inter-annual variability introduces an error in the top-of-permafrost temperature obtained with the equilibrium model that is higher where permafrost temperature is close to 0°C, although multi-year averaging reduces the error to 0.1°C or less. In the presence of a warming trend, the equilibrium model prediction tracked the changing top-of-permafrost temperature until permafrost temperatures reached 0°C, after which the equilibrium model produced significant errors. Errors up to 1°C were due to the temperature gradient through the developing talik, and depended on the warming rate, and the thickness of the talik. For all warming rates, the error was largest when the permafrost table was about 4,m below the surface, with the error declining as the permafrost table fell. Copyright © 2007 John Wiley & Sons, Ltd. [source] Kinetics of heavy metal vaporization from coal in a fluidized bed by an inverse modelASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2010Jing Liu Abstract This study addresses the kinetics of heavy metal vaporization during fluidized bed thermal treatment of coal. Both direct and inverse models were developed in transient conditions. The direct model predicts the time course of the metal concentration in the gas from the vaporization rate profile. The inverse model was developed and validated to predict the metal's vaporization rate from its concentration in the outlet gas. A method to derive the kinetic law of heavy metal vaporization during fluidized bed thermal treatment of coal from the global model and the experimental measurements is derived and illustrated. A first-order law was fitted for the mineral matrix and a second-order law was fitted for coal. This method can be applied to any matrix, whether it is mineral matrix or organic matrix. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] A model for the dynamic behavior of a commercial scale slurry bubble column reactor applied for the Fischer,Tropch synthesisASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2010Samira Ghasemi Abstract Fischer-Tropsch synthesis (FTS) is an important chemical process for the production of liquid fuels. In the present study, a dynamic model for a commercial size slurry bubble column reactor (SBCR) operating under heterogeneous flow regime and dealing with the FTS has been developed. In such a model a detailed kinetics expressions for the FTS and water gas shift (WGS) reactions have been considered. A selectivity model combined with SBCR hydrodynamics and the multicomponent VLE scheme have been applied to estimate the distribution of olefins and paraffins in the products. In addition, the effects of catalyst deactivation on reactor performance and product distribution under transient conditions may be predicted from this model. The data calculated from the model have been correlated with the experimental results available in the literature. It seems that the present model could be applied to estimate the main characteristics of the reactor's dynamic behavior. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Experimentelle Bestimmung der hygrischen Sorptionsisotherme und des Feuchtetransportes unter instationären BedingungenBAUPHYSIK, Issue 2 2006Assistent und Laborleiter Rudolf Plagge Dr.-Ing. Mit der vorgestellten Augenblicksprofil-Methode (APM) werden sowohl die relative Luftfeuchte und die Temperatur, als auch der volumetrische Wassergehalt in bestimmten Positionen in einem porösen Material bestimmt. Die Messungen werden kontinuierlich unter instationären Bedingungen durchgeführt. Damit erlaubt die APM eine dynamische und gleichzeitige Messung der hygroskopischen Sorptionsisotherme und der hygrischen Feuchteleitfähigkeit für einzelne Kompartimente innerhalb der Materialprobe. Die Feuchteleitfähigkeit wird aus den sich zeitlich ändernden Potentialgradienten und den dazugehörigen Feuchteverteilungen für die jeweiligen Kompartimente berechnet. Die Anwendung nicht konstanter Randbedingungen in der APM erlaubt die Untersuchung des hygrodynamischen Verhaltes von porösen Materialien. In der vorliegenden Studie werden die zeit- und prozeßabhängige Feuchtespeicherung und der Feuchtetransport bestimmt. Die vorgestellten Adsorptions- und Desorptionsexperimente wurden an dem kapillar- aktiven Wärmedämmstoff Calciumsilikat durchgeführt. Die Ergebnisse geben das Hystereseverhalten und den Einfluß der Dynamik der Prozesse wider. In Positionen mit schnellen Feuchteänderungen wird die Feuchtespeicherfunktion im Vergleich mit Regionen langsamer Feuchteänderung nach oben verschoben. Die Feuchteleitfähigkeit als Funktion der relativen Luftfeuchte zeigt eine bedeutende Hysterese. Hingegen ist die Feuchteleitfähigkeit in Relation zum Wassergehalt nicht hysteretisch. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) Experimental determination of the hygroscopie sorption isotherm and the moisture conductvity under transient conditions. By means of the proposed Instantaneous Profile Method (IPM) the relative humidity or the capillary pressure as well as the volumetric water content at specific locations inside a porous medium can be determined. The measurements are carried out under transient conditions and continuously in time. Thus, the IPM allows dynamic measurements of the hygroscopic sorption isotherm and the hygroscopic moisture conductivity. In addition, the moisture conductivity can be obtained via calculation of the moisture flow distribution from the temporal change of moisture contents in the compartments of the sample. The application of non-constant boundary conditions in the IPM allows investigation of the hygrodynamic behaviour of porous materials. In the presented study, the time and process dependent moisture retention characteristic and moisture conductivity are determined. The adsorption and successive desorption experiments presented here have been performed on the capillary active insulation material Calcium Silicate. The results show a hysteretic behaviour with a pregnant influence of the process dynamics. At locations with a rapid moisture increase, the moisture retention characteristic is shifted up in comparison to regions with slow moisture change. The moisture conductivity as function of relative humidity shows a remarkable hysteresis. However, the moisture conductivity in relation to the water content turned out to be non-hysteretic. [source] | |||||||||||||