1,720,979 research outputs found
Design of a chemical reactor under microwave irradiation in resonance conditions
Full text linkReaction processes often show to be improved by microwave application, but the enhancing effect is not always due solely to the temperature increasing in the medium, which is produced by the radiation exposure. Thus, to study the evolution of such kind of processes needs a strict control of the irradiation conditions and the use of a proper reaction apparatus in which the interaction between radiation and irradiated materials can be precisely defined. The present work is made necessary by the need of operating with controlled and reproducible experimental conditions, and the aim was to design a multi-tube reactor, to work in resonance conditions, inside which the tubes with the fluid to be processed are positioned. In fact, working in resonance conditions allows the irradiated fluid to be exposed to constant microwave power, and the field intensity and power absorption can be accurately calculated and mapped. The cavity was designed by the authors using a proper commercial software for 3D electromagnetic simulation, then the reactor operation was tested by another commercial multiphysic simulation software. The results here presented show the proper geometrical characteristics of the cavity and of the internal tubes to work at 2.45 GHz of frequency while the irradiation power can be varied depending on the needs of the process. The reactor can work with different homogeneous systems, both chemical and biological (enzyme reactions). The future development will be the construction and the real operation of the designed apparatus in order to confirm the simulation results
Heat transfer modeling in bone tumour hyperthermia induced by hydroxyapatite magnetic thermo-seeds
Full text linkBackground: Hyperthermia is an adjuvant oncologic thermal therapy. In the case of deep-seated bone cancers, the interstitial hyperthermia treatment can be performed using thermo-seeds, implanted biomaterial components that are able to convert external electromagnetic power into thermal one. Several magnetic biomaterials have been synthesized for thermal treatments of cancer. However, less attention has been paid to the modeling description of the therapy, especially when the bio-heat transfer process is coupled to the electromagnetic heating. Objective: In this work, a comparison between the available analytical and numerical models is presented. Methods: A non-linear multiphysics model is used to study and describe the performance of cylindrical magnetic hydroxyapatite thermo-seeds to treat residual cancer cells of bone tumours. Results: The thermal dynamics and treatment outcome are carefully evaluated. Under the exposure of a magnetic field of 30 mT, working at 300 kHz, it was found that magnetic hydroxyapatite implants with a size of 10 mm × 10 mm could increase the temperature above 42 °C for 60 min. Conclusion: The proposed model overcomes the limitations of the available theoretical frameworks, and the results reveal the relevancy of the implant geometry to the effectiveness of the hyperthermia treatment
Heat transfer modeling in soil microwave heating
No full textThe agricultural neediness of cost-effective, environmental friendly and chemical-free methods for farmlands disinfection led to the development of microwave-based solutions, an efficient way of directly conveying energy to the target. Harmful agents such as weeds pests, fungi and bacteria can be suppressed heating the contaminated soil up to pasteurization or sterilization temperatures by irradiating electromagnetic energy by an antenna. The treatment can be carefully devised and designed optimizing the temperature distribution and calibrating the exposure time depending on the soil characteristics, and on the environmental and boundary conditions. In this work a computational model to solve the non-linear multi-physic dielectric heating phenomenon is presented, so taking into account the temperature dependence of the dielectric and thermal soil properties, in order to demonstrate the possibility of properly tuning the microwave application depending on the external heat transfer conditions. It was found that, in the specific conditions here analyzed, an increase of the external convection heat transfer coefficient up to 50 W∙m-2∙K-1, despite being a possible critic condition for the surface, brings to the possibility of treating a soil layer of higher thickness, up to 20 cm. On the other hand, doubling the microwave power from 12 to 24 kW∙m-2 generally reduces the treatment time to less than half, with overall energy savings
Permittivity measurements of mixtures as a function of their composition for microwave heating improving
No full textMicrowave heating is a more efficient alternative to conventional heating in the chemical reactions field due to its positive effects on conversion and reaction kinetics. Dielectric properties of substances and mixtures are important for the optimization of microwave heating processes; notwithstanding this, specific databases are poor and far from being complete, and in the scientific literature only a few data regarding these properties can be found. Dielectric properties are represented by permittivity, which is a complex measure of a substance behaviour in the presence of an electromagnetic field and depends on the field frequency, as well as on the temperature and composition of the chemical system under study. In this work, some real and imaginary parts of permittivity measurements were carried out using a specially designed measurement system. The apparatus was tested in the estimation of permittivity values in water-ethanol mixtures, varying their composition. The results were compared to literature data and fitted with available literature models to verify their trend as a function of composition. The permittivity real part values increase with reducing the molar fraction of ethanol, whereas the imaginary part decreases, according to the values of water and ethanol permittivity reported in the literature. The regressions carried out to describe the permittivity dependence on composition prove that the measured values can be well described by the models taken into account
Thermal properties of semolina doughs with different relative amount of ingredients
Full text linkThe impact of the relative amount of ingredients, wheat variety, and kneading time on the thermal properties of semolina doughs were investigated by means of thermogravimetric analysis (TGA). The doughs were prepared by mixing water, semolina, yeast, and salt in different proportions. The gelatinized flour fraction plays an important role in the thermal properties' definition, while the water amount influences the development of the dough network and, consequently, the starch gelatinization phenomena. Furthermore, the amount of yeast and salt influences the dough network force and, consequently, the thermal properties. The TGA technique was applied in order to evidence the mass loss as a function of the increasing temperature, considering that this behavior depends on the dough network force and extension. In such a way, it was possible to find some information on the relationship between the dough characteristics and the thermogravimetric analysis outputs. The study is devoted to acquiring deeper knowledge about the thermophysical characteristics of doughs in the breadmaking industrial processes, where the controllability and the energy performances need to be improved. A deeper knowledge of the dough properties, in terms of measurable parameters, could help to decrease the amounts of off-specification products, resulting in a much more energy-efficient and sustainable processing
Microwave heating improvement: permittivity characterization of water–ethanol and water–NaCl binary mixtures
Full text linkMicrowave heating offers a lot of advantages compared to conventional heating methods in the chemical reactions field due to its positive effects on reaction time and selectivity. Dielectric properties, and in particular permittivity, of substances and mixtures, are important for the optimization of microwave heating processes; notwithstanding this, specific databases are poor and far from being complete, and in the scientific literature very little data regarding these properties can be found. In this work, impedance measurements were carried out using a specially designed system to get the real and imaginary parts of the dielectric constant. The apparatus was tested in the estimation of permittivity of water–ethanol and water–NaCl mixtures, varying their composition to obtain a wide range of permittivity values. The results were compared to literature data and fitted with available literature models to verify the correspondence between them, finding that permittivity dependence on mixture composition can be effectively described by the models
Effect of the relative amount of ingredients on the thermal properties of semolina doughs
No full textThe thermal properties of doughs with a different relative amount of ingredients were investigated using Thermogravimetric Analysis (TGA). The doughs were prepared to mix water, semolina, yeast, and salt in different proportions. The gelatinized flour fraction plays an important role in the thermal properties’ definition, while the water amount influences the development of the dough network and consequently the starch gelatinization phenomena. The amount of yeast and salt influences the dough network force and consequently, the thermal properties. In such a way, it was possible to find some information on the relationship between the dough characteristics and the thermogravimetric analysis outputs. The study is devoted to acquiring deeper knowledge about the thermophysical characteristics of doughs in the breadmaking industrial processes, and about their changes during the different process steps, when the relative amount of ingredients changes. This could help to improve the controllability of the breadmaking plants and their energetic performances, and in particular the efficiency of “pani carasau” manufacturing, a typical toasted and high-quality Sardinian bread. Currently, in industrial productions, large amounts of it are lost because off-specification and it is not possible to prevent this, since the bread characteristics can be verified after baking, which is high energy consuming. Consequently, a deeper knowledge of the dough properties could help to decrease the amounts of off-specification products, resulting in a much more energy efficient and sustainable process
Impact of water and flour components in dough investigated through low-field nuclear magnetic resonance
No full textBound and free water within dough strongly affect its rheological behavior and processability, as well as its gluten network. Depending on its total content and on the characteristics of flour constituents, water can be both bound to components and free in the dough. The equilibrium between bound and free water directly impacts the elasticity and extensibility of dough and therefore controls the texture of final products. In this study, Nuclear Magnetic Resonance (NMR) was used to assess the relaxation behavior with the focus on water. The proton spin-spin relaxation measurements were carried out at 20 MHz with a Bruker Minispec mq20 NMR spectrometer (Bruker, Rheinstetten, Germany). The transverse relaxation time in a spin locking field (T1ρ) was determined at 25°C following the Carr–Purcell–Meiboom–Gill (CPMG) sequence. The data were analyzed by the continuous distribution model. The dough was prepared with commercial semolina, which was mixed with water in a Brabender Mixer 350 (Brabender® GmbH, Duisburg, Germany) to reach three different levels of water content (30, 50, and 70%, based on semolina weight) and to study the water distribution as a function of the water total content. The dough characterization was carried out also comparing the T1ρ distribution of semolina dough with that of starch-water and gluten-water mixtures and also of pure starch and gluten to assess the role of each flour component. Additionally, the semolina dough sample was compared with a sample prepared with pastry flour, with a lower content of proteins, to investigate the different behavior as a function of the gluten amount. It was found that the dough presents three relaxation processes: one, very fast, is related to crystalline starch, while the other two are characteristic of two water populations, water in intragranular and in extragranular regions of starch, respectively. The comparison with pastry flour showed that the dough prepared with the latter one was less homogenous than the semolina one, with a clear distinction between free and bound water, while the semolina dough seemed to contain several water populations differently bounded, that were responsible for a broader peak at medium water content (around 50%)
A Chemometric Approach to Assess the Rheological Properties of Durum Wheat Dough by Indirect FTIR Measurements
Full text linkRheological measurements and FTIR spectroscopy were used to characterize different doughs, obtained by commercial and monovarietal durum wheat flours (Cappelli and Karalis). Rheological frequency sweep tests were carried out, and the Weak Gel model, whose parameters may be related to gluten network extension and strength, was applied. IR analysis mainly focused on the Amide III band, revealing significant variations in the gluten network. Compared to the other varieties, Karalis semolina showed a higher amount of α-helices and a lower amount of β-sheets and random structures. Spectroscopic and rheological data were then correlated using Partial Least Squares regression (PLS) coupled with the Variable Importance in Projection (VIP) technique. The combined use of the techniques provided useful insights into the interplay among protein structures, gluten network features, and rheological properties. In detail, β-sheets and α-helices protein conformations were shown to significantly affect the gluten network's mechanical strength
Thermogravimetric analysis of different semolina doughs: Effect of mixing time and gluten content
Full text linkThe thermal properties of different kinds of dough were investigated after different kneading times by means of Thermogravimetric Analysis (TGA). Two varieties of durum wheat semolina were used in this study: Alemanno and Cappelli. The doughs were prepared using a mixograph. The gelatinized flour fraction plays an important role on the thermal properties’ definition, while the mixing time influences the dough network building and consequently the starch gelatinization phenomena. Also, the amount of free water in the dough could be influenced by the mixing time. Thus, the TGA technique was applied in order to evidence the mass loss as a function of the increasing temperature and, from this, the free water content, the residual weight (related to the protein kind and content), and the weight loss rate, i.e. the peaks of the first derivative of the thermogravimetric curve (DTG), which appear at different temperatures and present different heights and positions, depending on the dough network force and extension. In such a way, it was possible to find some correlations between the dough characteristics, like the semolina composition (e.g. the gluten content and quality) and the mixing time, and the thermogravimetric analysis outputs. The results showed that the ratio between free and bond water is strongly dependent on both the mixing time and the semolina variety, and a clear evidence of the protein content in the dough is found because of the position and the size of the peaks in the DTG curve, in combination with the residual mass at fixed temperatures
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