Rainfall interception by buildings for urban hydrology modeling

One of the results of elimate change is an increased amount of precipitation and a rise in rainfall intensity. This can lead to an overlaad on the sewer system or to the ground water level if no sewer system is present, and even to flooding. During rain events part of the rainwater can be intercepted by building surfaces (rainfall interception) . This amount of water is temporarily stared on these surfaces and eventually evaporates into the atmosphere. Since this intercepted water does nat reach the ground, it also does nat contribute to the laad on the sewer system. Especially porous materials on building roots but also in facades can intercept large quantities of water. Rainfall interception by buildings therefore becomes more and more important in hydrological modeling, particularly in urban areas. In this research rainfall interception by building facades is studied. In order to do this measurements as well as simulations are performed. Full-scale measurements are executed on a test facade at Eindhoven University of Technology, the Netherlands. The moisture response (mass change) to wind-driven rain of tour material samples is registered. Furthermore micro-meteorological data are gathered. The ditterenee in rainfall interception by two porous building materials is demonstrated. For the brick with high porosity the rainfall interception yields 100%, while the low porous brick accommodates for a minimum of 76.6% during the measurement period. Due to local saturation at the exterior boundary runaft occurred for the latter type of brick. Besides the tuli-scale experiments an extensive set of Iabaratory measurements is performed. Various moisture-related material properties are determined for the two porous building materials. For the numerical part of this study the finite element code HAMFEM is used. Toga in insight into the moisture response of porous building materials to wind-driven rain, one-dimensional heat and moisture transfer simulations are performed using differential balance equations for mass and energy. The micro-meteorological data gathered at the test facade are used as atmospheric boundary conditions and the results of the Iabaratory experiments are used to specity the material properties. The simulation results give the mass change of the materials in time and this is compared to the mass change obtained trom the tuli-scale measurements to verify the correct implementation of the model and the capability to reproduce the measurement results. lt is shown that for the brick with high porosity the model accurately prediets the rainfall interception during one rain event. Rainfall interception foranother rain event is described less precisely however. For the other type of brick the model fails to predict runoff because in the simulations the exterior boundary does nat reach the capillary moisture content, while in reality local saturation does occur because the wind-driven rain intensity on the facade exceeds the absorption rate of the brick. The largest deviations between experimental and numerical results are found in the evaporation process, where the model overestimates the mass decrease due to evaporation. This is to a large extent due to the uncertainty of the heat and moisture transfer coefficients. As a next step meteorological data of several elimate groups according to the Köppen elimate classification are used to specify the boundary conditions. With this the influence of different climates on rainfall interception is studied. lt is shown that for four of the six elimate groups used for the analysis no runoff occurred for the brick with high porosity for the period considered . This means that this type of brick accommodates for 100% rainfall interception in these climates. For the remaining two elimate groups the brick with high porosity yields a minimum RI of only 1.9% and 6% in periods of severe rain, increasing to 100% for moderate rain events. Comparison of the rainfall interception by the two bricks results in a rainfall interception of at least 40% by the brick with low porosity based on the rainfall interception by the other type of brick. lt is demonstrated however that the model nat always succeeds in accurately predicting the runoff. Therefore no hard conclusions can be drawn on the performance regarding rainfall interception by the two porous building materia Is in other climates. One of the results of elimate change is an increased amount of precipitation and a rise in rainfall intensity. This can lead to an overlaad on the sewer system or to the ground water level if no sewer system is present, and even to flooding. During rain events part of the rainwater can be intercepted by building surfaces (rainfall interception) . This amount of water is temporarily stared on these surfaces and eventually evaporates into the atmosphere. Since this intercepted water does nat reach the ground, it also does nat contribute to the laad on the sewer system. Especially porous materials on building roots but also in facades can intercept large quantities of water. Rainfall interception by buildings therefore becomes more and more important in hydrological modeling, particularly in urban areas. In this research rainfall interception by building facades is studied. In order to do this measurements as well as simulations are performed. Full-scale measurements are executed on a test facade at Eindhoven University of Technology, the Netherlands. The moisture response (mass change) to wind-driven rain of tour material samples is registered. Furthermore micro-meteorological data are gathered. The ditterenee in rainfall interception by two porous building materials is demonstrated. For the brick with high porosity the rainfall interception yields 100%, while the low porous brick accommodates for a minimum of 76.6% during the measurement period. Due to local saturation at the exterior boundary runaft occurred for the latter type of brick. Besides the tuli-scale experiments an extensive set of Iabaratory measurements is performed. Various moisture-related material properties are determined for the two porous building materials. For the numerical part of this study the finite element code HAMFEM is used. Toga in insight into the moisture response of porous building materials to wind-driven rain, one-dimensional heat and moisture transfer simulations are performed using differential balance equations for mass and energy. The micro-meteorological data gathered at the test facade are used as atmospheric boundary conditions and the results of the Iabaratory experiments are used to specity the material properties. The simulation results give the mass change of the materials in time and this is compared to the mass change obtained trom the tuli-scale measurements to verify the correct implementation of the model and the capability to reproduce the measurement results. lt is shown that for the brick with high porosity the model accurately prediets the rainfall interception during one rain event. Rainfall interception foranother rain event is described less precisely however. For the other type of brick the model fails to predict runoff because in the simulations the exterior boundary does nat reach the capillary moisture content, while in reality local saturation does occur because the wind-driven rain intensity on the facade exceeds the absorption rate of the brick. The largest deviations between experimental and numerical results are found in the evaporation process, where the model overestimates the mass decrease due to evaporation. This is to a large extent due to the uncertainty of the heat and moisture transfer coefficients. As a next step meteorological data of several elimate groups according to the Köppen elimate classification are used to specify the boundary conditions. With this the influence of different climates on rainfall interception is studied. lt is shown that for four of the six elimate groups used for the analysis no runoff occurred for the brick with high porosity for the period considered . This means that this type of brick accommodates for 100% rainfall interception in these climates. For the remaining two elimate groups the brick with high porosity yields a minimum RI of only 1.9% and 6% in periods of severe rain, increasing to 100% for moderate rain events. Comparison of the rainfall interception by the two bricks results in a rainfall interception of at least 40% by the brick with low porosity based on the rainfall interception by the other type of brick. lt is demonstrated however that the model nat always succeeds in accurately predicting the runoff. Therefore no hard conclusions can be drawn on the performance regarding rainfall interception by the two porous building materia Is in other climates

Definition and classification of interferences in analytical procedures

Based on a survey of various alternatives found in the literature a definition of interference is presented and recommendations are given for the classification of interferences in analytical procedures. It is recommended that the usage of the term interference will be restricted to the effects caused by concomitants in the sample. Several examples are given

Modelling of non-steady-state concentration profiles at ISFET-based coulometric sensor—actuator systems

Acid or base concentrations can be determined very rapidly by performing an acid—base titration with coulometrically generated OH− or H+ ions at a noble metal actuator electrode in close proximity to the pH-sensitive gate of an ion-sensitive field effect transistor (ISFET). The ISFET is used as the indicator electrode to detect the equivalence point in the titration curve. Typical values for the time needed to reach the equivalence point are 0.5–10 s for acid or base concentrations ranging from 0.5 × 10−3 to 20 × 10−3 mol l−1.\ud \ud A model is presented, giving an analytical description of the diffusion phenomena that occur with the sensor—actuator system. The results of this analytical model description, using linearized concentration gradients, are presented together with the results of numerical simulations. Both results are in good agreement with measurements

Modelling of the migration effect occurring at an ISFET-based coulometric sensor-actuator system

The migration effect, in addition to diffusion, occurring at an ion-selective field-effect transistor (ISFET)-based coulometric sensor-actuator system has been studied. A diffusion-migration model is presented, based on the numerical solution of the Nernst-Planck equations of which a digital simulation is realized. Corresponding experiments were carried out and compared with the simulation. The results are in good agreement with the simulation.\ud Typical titration times of this system were found to be 0.5–10 s, corresponding to fully dissociated acid concentrations of 0.5×10−3−6.5×10−3 mol 1−1 with excess of supporting electrolyte. Both the simulation and experimental results show that if the concentration of the supporting electrolyte is 20 times higher than that of the species to be titrated, the deviation caused by migration is less than 5% and within the experimental error when pure diffusion is considered. At relatively low concentrations of supporting electrolyte, the migration effect should be taken into account to determine the concentrations of titrated species

pH sensor properties of electrochemically grown iridium oxide

The open-circuit potential of an electrochemically grown iridium oxide film is measured and shows a pH sensitivity between −60 and −80 mV/pH. This sensitivity is found to depend on the state of oxidation of the iridium oxide film; for a higher state of oxidation (or more of the oxide in the high valence state), the sensitivity is also higher. This high sensitivity can be explained on the basis of the extra proton release as a result of the acidic character of the porous hydrous oxyhydroxide, in combination with the redox behaviour.\ud \ud The response time to a pH step is measured and is found to depend mainly on the thickness of the oxide; it varies from 40 ms to 0.35 s due to the porous nature of the film.\ud \ud Drift measurements show that an iridium oxide film in reduced state is slowly oxidized by dissolved oxygen, whereas a pre-oxidized film in a pH = 4.01 buffer solution in contact with air shows a long-term drift of <0.3 mV/h

Determination of buffer capacity by means of an ISFET-based coulometric sensor-actuator system with a gate-covering porous actuator

In this paper we propose a dynamic way to measure the buffer capacity of an electrolyte by means of an ISFET-based coulometric sensor-actuator system whose gate is covered with a porous actuator. A theoterical model for this measurement is presented. Experiments are carried out in nitric and acetic acid as well as in phosphoric acid solutions. A fairly good agreement has been found between the theoretical calculations and the experimental results

Unstable coronal loops : numerical simulations with predicted observational signatures

We present numerical studies of the nonlinear, resistive magnetohydrodynamic (MHD) evolution of coronal loops. For these simulations we assume that the loops carry no net current, as might be expected if the loop had evolved due to vortex flows. Furthermore the initial equilibrium is taken to be a cylindrical flux tube with line-tied ends. For a given amount of twist in the magnetic field it is well known that once such a loop exceeds a critical length it becomes unstableto ideal MHD instabilities. The early evolution of these instabilities generates large current concentrations. Firstly we show that these current concentrations are consistent with the formation of a current sheet. Magnetic reconnection can only occur in the vicinity of these current concentrations and we therefore couple the resistivity to the local current density. This has the advantage of avoiding resistive diffusion in regions where it should be negligible. We demonstrate the importance of this procedure by comparison with simulations based on a uniform resistivity. From our numerical experiments we are able to estimate some observational signatures for unstable coronal loops. These signatures include: the timescale of the loop brightening; the temperature increase; the energy released and the predicted observable flow speeds. Finally we discuss to what extent these observational signatures are consistent with the properties of transient brightening loops.Comment: 13 pages, 9 figure

Adaptive thermal comfort explained by PMV

Predicted Mean Vote (PMV) is a well known example of a thermal comfort performance indicator. Alternative indicators have gained interest over the last decade. Developments are found in higher resolution indicators, applying, e.g. thermo-physiological models. The adaptive thermal comfort approach (ATC), applying the indoor operative temperature in relation to the outdoor air temperature as the main performance indicator, represents an example of a less complex indicator. A clear advantage of the latter is the relative simple comfort assessment in use and the perceptibility of the indicator. However, the heat balance approach has a larger flexibility and a wider applicability. In this paper the linkage between PMV and ATC is elaborated on by investigating the search space for PMV input parameters in relation to the ATC assessment. The results show that for a moderate maritime outdoor climate as in The Netherlands the PMV-approach is well able to explain the results derived from the ATC approach