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In the present study, the dielectric heating option was investigated for various dry materials: USY zeolite, ZSM-5 zeolite, and α- & γ-alumina. These materials are characterized by low effective dielectric loss factors; therefore they are often considered as not accessible for direct dielectric heating. Applying technically relevant volumes up to 20 L, dielectric heating could be demonstrated for all these materials when employing radio waves (RW) whereas heating with microwaves (MW) was difficult or even impossible. Dielectric heating experiments were also simulated with the CST electromagnetic simulation software. It could be shown that for all tested materials RW heating is more suitable than MW heating with regard to heating rates, temperature rise (both at equal power input) and homogeneity of the temperature pattern. The comparison of experimental data and simulation shows an excellent agreement. Thus, dielectric heating utilizing frequencies in the MHz range (radio-frequencies, RF) was demonstrated to be well applicable, even for materials with low loss factors, up to technically relevant temperatures and scales. This study also includes the evaluation of the energy efficiency for RW heating on the basis of the heating and power input data. Reasons for lower efficiencies, even under optimal fitting conditions applying an electronic matching network, are discussed and interpreted using literature and own experimental results, namely temperature-programmed desorption (TPD). [ABSTRACT FROM AUTHOR]

For mitigation of the impact on flood-damaged cultural heritage buildings and sites, solely conservation-compatible and noninvasive strategies can be applied. All procedures have to take into account not only the specific situation after flooding but also the material properties and the characteristics of the artwork related to the building. After a heavy flooding event damaging the monastery Marienthal in Germany demonstration studies were proceeded to evaluate heritage-adequate treatment strategies for the drying of a decorated chapel. To respect and preserve the original gypsum stucco interior drying in certain temperature limits had to be respected. Particularly, direct volumetric heating methods were employed working with electromagnetic waves in the frequency ranges of either microwaves or radio waves. The studies comprised heating tests on site and experiments on a heritage-representative masonry specimen. It could be shown that the removal of water could be significantly enhanced by both techniques. Radio wave heating was demonstrated to allow a more homogeneous and better controlled treatment in comparison to microwave application, which is especially relevant in case of sensitive materials such as gypsum. With respecting that limits the techniques can be applied in combination with efficient removal of moisture from the ambient air by ventilation in order to reduce the drying time thus limiting subsequent damage of the heritage building. [ABSTRACT FROM AUTHOR]

By means of radio-wave technology it is possible to allow the uniform, rapid and accurate, temperature-controlled heating of fresh concrete. This results in the significantly accelerated release of hydration heat. The heat release from this second source can be easily compensated by the temperature-controlled reduction of RF energy input. The consequences are accelerated hydration and higher early-age compressive strength. Early-age concrete, heat-treated by radio waves, have a denser microstructure with a higher gel-pore content and more C-S-H phases than untreated concrete. When cured at the maximum temperature of 80 °C, secondary ettringite can be formed in concrete, whereas this is not the case for the treatment temperatures of 40 °C and 60 °C. At the age of 28 d, heat-treated concretes exhibit a looser microstructure than does untreated concrete. Larger portlandite crystals and secondary ettringite are its characteristic features as a consequence of the much faster reaction rates in the early-age concrete. This results in lower values of the compressive strength of the heat-treated concrete. [ABSTRACT FROM AUTHOR]

Thermal pest control requires long treatment times due to the low thermal conductivity of wood and may lead to the formation of cracks. Here, the thermal treatment with radio waves as well as microwaves has been studied. The direct dielectric heating has the advantage of a good homogeneity. The obtained temperature profiles for radio waves were more homogeneous compared to microwaves. Detailed studies showed that elimination of pests was not related to the application of the electromagnetic field itself, but due to the temperature increase. [ABSTRACT FROM AUTHOR]

Zur wirtschaftlichen Herstellung von industriell gefertigten Betonbauteilen werden geringe Taktzeiten angestrebt, um die Formen und Schalungen möglichst schnell wiederverwenden zu können. Dafür ist es notwendig, dass der Beton eine hohe Frühfestigkeit entwickelt, um die nötige Ausschalfestigkeit zu erreichen. Um den Hydratationsprozess schneller ablaufen zu lassen, kann einerseits ein Beton mit hohem Zementanteil oder mit einer hohen Zementfestigkeitsklasse verwendet werden, andererseits kann der Frischbeton erwärmt werden. Gegenstand dieses Artikels ist, ein Verfahren zur Wärmebehandlung von Frischbeton vorzustellen, welches eine energieeffiziente, temperaturgesteuerte Erwärmung möglich macht. Durch das elektromagnetische Feld bei der Radiowellen‐Technologie wird der Frischbeton dielektrisch erwärmt, was eine homogene Temperaturerhöhung bewirkt. Durch die Kopplung von Temperaturmessung und Energieeintrag können vorher definierte Temperaturkennlinien und Maximaltemperaturen eingehalten werden, eine genaue Temperatursteuerung wird gewährleistet. Ziel der Untersuchungen zur Wärmebehandlung von Frischbeton mit der Radiowellen‐Technologie ist, Aussagen über Temperatursteuerung, Homogenität und energetischen Wirkungsgrad zu treffen. Weiterhin werden die Auswirkungen der dielektrischen Erwärmung auf die Früh‐ und Endfestigkeit geklärt und es wird die Strukturentwicklung im Beton beschrieben. Die Struktur des wärmebehandelten Betons wird mit verschiedenen Methoden bestimmt, um ein möglichst detailliertes Bild zu bekommen. Zur Charakterisierung der Gefügemorphologie des Betons werden Messungen zur Porengrößenverteilung mit der Quecksilberporosimetrie sowie mikroskopische Untersuchungen mit dem Rasterelektronenmikroskop (ESEM) herangezogen. Radio wave technology used for heat treatment of fresh concrete The economical production of industrially‐produced concrete elements aims for low cycle times in order to be able to reuse the forms and form‐works as soon as possible. Therefore it is necessary that the concrete develops a high early strength to reach the needed demoulding strength. To accelerate the hydration process it is possible to heat the fresh concrete. The subject of this article is to present a new procedure for heat treatment of fresh concrete which enables an energy‐efficient, temperature‐controlled heating. Due to the electromagnetic field of the radio wave technology the fresh concrete can be heated by means of dielectric heating in order to enable homogenous temperature increases. Due to the combination of temperature measurement and energy input it is possible to keep certain temperature characteristics and maximum temperatures that had been defined before; an exact temperature control is guaranteed. The aim of the research about the effects of dielectric heating on early and final strength, as well as the structural development in the concrete, are described. In order to get the broadest possible image the structure of the heat‐treated concrete is examined with different methods. [ABSTRACT FROM AUTHOR]

Applying a new experimental design with a capillary glass reactor and plate electrodes outside of the reactor allowed the initiation of discharges in aqueous electrolytes under the influence of a radio-frequency (RF) electromagnetic field. This study focused on the mechanism leading to the initiation of such discharges in the restriction of a glass tube. The light emission correlated with discharges was analysed with optical emission spectroscopy. Electrons with energies between 20 and 45 eV were responsible for the dissociation of water molecules into (excited) OH, H and O radicals. Current-voltage characteristics were measured before and under discharge conditions. Modelling of the experimental setup and simulation of electrical field strength distribution support the hypothesis of the origin of discharges in general and experimental findings such as ring-shaped discharges and a minimum solution conductivity of about 1 S m-1 required for discharge initiation with RF voltages of 2 kV. [ABSTRACT FROM AUTHOR]

A new type of water dissociation at ambient pressure initiated by the irradiation of aqueous electrolytes using an electromagnetic field with a frequency of 13.56MHz is described in this study. A special reactor design allows the use of ex situ electrodes to form in situ electrical discharges in water vapour bubbles. The observed formation of molecular hydrogen (H2) and oxygen (O2) combined with the emission of light ('burning water' phenomenon) originates from a non-thermal plasma in water vapour bubbles. The influences of type of electrolyte, its concentration, pH value and external RF voltage on the gas formation rate as well as on the gas composition are presented. [ABSTRACT FROM AUTHOR]

The application of distributed fiber optic strain and temperature measurement can be utilized to address a multitude of measurement tasks across a diverse range of fields, particularly in the context of structural health monitoring in the domains of building construction, civil engineering, and special foundation engineering. However, a comprehensive understanding of the influences on the measurement method and the sensors is essential to prevent misinterpretations or measurement deviations. In this context, this study investigated the effects of moisture exposure, including various salt solutions and a high pH value, on a distributed strain measurement using Rayleigh backscattering. Three fiber optic sensors with different coating materials and one uncoated fiber were exposed to five different solutions for 24 h. The study revealed significant discrepancies (∼38%) in deformation between the three coating types depending on the surrounding solution. Furthermore, in contrast to the prevailing literature, which predominantly describes swelling effects, a negative deformation (∼-47 με) was observed in a magnesium chloride solution. The findings of this study indicate that corresponding effects can impact the precision of measurement, potentially leading to misinterpretations. Conversely, these effects could be used to conduct large-scale monitoring of chemical components using distributed fiber optic sensing.

Diffusive isotope fractionation of organic compounds in aqueous solution was investigated by means of liquid-liquid and liquid-gas partitioning experiments under kinetic control. The two-film model was used to describe phase-transfer kinetics. It assumes the diffusion of solutes across a stagnant water boundary layer as the rate-controlling step. For all investigated solutes (benzene-D 0 and -D 6 , toluene-D 0 , -D 5 , and -D 8 , cyclohexane-D 0 and -D 12 ), there was no significant observable fractionation effect between nondeuterated and perdeuterated isotopologues, resulting in a ratio of diffusion coefficients D light : D heavy =1.00±0.01. In addition, isotope fractionation due to equilibrium partitioning of solutes between water and n-octane or gas phase was measured. The deuterated compounds are more hydrophilic than their light isotopologues in all cases, giving rise to fractionation coefficients αH part =K octane/water,H : K octane/water,D =1.085 to 1.15. Thus, thermodynamic fractionation effects are much larger than diffusion fractionation effects. Methodical and environmental implications of these findings are discussed., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The influence of electrical heating on microbiological processes in soil has been studied to evaluate the potential for enhancing biodegradation of pollutants by controlling the temperature. A frequency of 50 Hz (power line frequency) was applied for resistive heating. Dielectric heating was realized using a frequency of 13.56 MHz (radio frequency). Both techniques were compared with conventional heating in a water bath. For experiments in laboratory and full scale, a model soil and a contaminated original soil were used. It was shown that under conditions capable for heating soil to 35 degrees C or even 60 degrees C, soil respiration as a measure for microbial activity was not hindered by electrical heating when temperature and moisture content were comparable with conventional heating. The variations of soil respiration were reversible upon temperature changes. Under certain conditions, periodical fluctuations of microbiological activity were observed. Several possible explanations including chronobiology are discussed without being able to provide an unambiguous interpretation for this effect.

Thermodesorption studies with soil samples from a former filling station for light crude oil contaminated with mineral oil hydrocarbons (mainly benzene, toluene, ethylbenzene, xylenes, naphthalene, alkylnaphthalenes, and C(10) to C(14) alkanes) have revealed an ambivalent influence of water on desorption rates. Particularly, the influences of soil moisture content, humidity of the purge gas, temperature, and content of soil organic matter (SOM) were studied. At low temperature, purge gas humidity strongly affected the mobility of hydrocarbons in the soil organic matter (SOM) leading to an enhanced release of contaminants at higher moisture contents. Heating resulted in a decrease of thermodesorption when connected with desiccation of soil, in spite of the strong temperature impact on the vapor pressure of contaminants. At high water content of the SOM, the transfer of the pollutant molecules into the gas phase was found to be markedly hindered by the formation of water films or pore-filling by bulk water, both acting as diffusion barriers.

Selective dielectric heating using the influence of a coupling medium such as water can lead to the formation of combined temperature-mass transport pulses moving through a packed bed. Depending on the dielectric and sorption properties of the material, these so-called thermo-chromatographic pulses (TCP) can cause large temperature differences between the starting temperature and the peak temperature in the pulse. The impregnation of porous substances with various salts was shown to be a simple method for improving material properties leading to the formation of stable TCP. This procedure was proven to only slightly reduce the specific surface area and the sorption capacity towards organic compounds of the investigated sorbents. Consequently, a wide spectrum of silica gels, zeolites and porous alumina can be applied as matrices for TCP-based processes in chemical engineering and environmental technology.

The occurrence and extent of selective dielectric heating with microwaves (MW) and radio waves (RW) was studied with a variety of model systems using temperature-programmed desorption (TPD). Over a wide pressure and temperature range, selectivity effects were neither found for polar adsorbates (compared to non-polar compounds) nor expressed by an overheating of metal clusters supported on a nearly MW- and RW-transparent support. In contrast, significant temperature gradients between particles consisting of materials with various dielectric losses could be established under certain conditions. The utilization of adsorbates significantly modifying the dielectric properties of a material was investigated as a further approach to initiate selective dielectric heating. Applying water as a coupling medium, a combined heat and mass transport, which we call a thermo-chromatographic pulse, can be created in a packed-bed column consisting of various zeolites. In this case, selective heating of bed zones by more than 100 K was observed. The suitability of a material for the creation of thermo-chromatographic pulses depends on its dielectric properties as well as on its sorption properties with respect to water or other coupling media. The study provided further insight into not only the potential but also the limitations of selective dielectric heating of solid materials relevant to chemical engineering, environmental technology and sorption processing.