Application of Novel Thermal Technology in Foods Processing

Advanced and novel thermal technologies, such as ohmic heating and dielectric heating (e [...]

Combined Effect of Temperature and Oil and Salt Contents on the Variation of Dielectric Properties of a Tomato-Based Homogenate

Tomato-based processed foods are a key component of modern diets, usually combined with salt and olive oil in different ratios. For the design of radiofrequency (RF) and microwave (MW) heating processes of tomato-based products, it is of importance to know how the content of both ingredients will affect their dielectric properties. Three concentrations of olive oil and salt were studied in a tomato homogenate in triplicate. The dielectric properties were measured from 10 to 3000 MHz and from 10 to 90 °C. Interaction effects were studied using a general linear model. At RF frequencies, the dielectric constant decreased with increasing temperature in samples without added salt, but this tendency was reversed in samples with added salt. The addition of salt and oil increased the frequency at which this reversion occurred. At MW frequencies, the dielectric constant decreased with increasing temperature, salt, and oil content. The loss factor increased with increasing salt content and temperature, except in samples without added salt at 2450 MHz. Penetration depth decreased with increasing frequency and loss factor. Salt and oil contents have a significant effect on the dielectric properties of tomato homogenates and must be considered for the design of dielectric heating processes.

A 3D LTCC-Based Ceramic Microfluidic System with RF Dielectric Heating of Liquids

The design, fabrication and functional evaluation of the radio-frequency dielectric heating of liquids in an LTCC-based ceramic microfluidic system are described and discussed. The device, which relies on the dielectric heating of liquids, was fabricated using a low temperature co-fired ceramic (LTCC) technology. A multilayered ceramic structure with integrated electrodes, buried channels and cavities in micro and millimetre scales was fabricated. The structure with the dimensions of 35 mm × 22 mm × 2.4 mm includes a buried cavity with a diameter of 17.3 mm and a volume of 0.3 mL. The top and bottom faces of the cavity consist of silver/palladium electrodes protected with 100 μm thick layers of LTCC. The power, used to heat a polar liquid (water) in the cavity with the volume of 0.3 mL, ranges from 5 to 40 W. This novel application of RF dielectric heating could enable the miniaturization of microfluidic systems in many applications. The working principle of such a device and its efficiency are demonstrated using water as the heated medium.

Radio-frequency exposure of the yellow fever mosquito (A. aegypti) from 2 to 240 GHz

Fifth generation networks (5G) will be associated with a partial shift to higher carrier frequencies, including wavelengths of insects. This may lead to higher absorption of radio frequency (RF) electromagnetic fields (EMF) by insects and could cause dielectric heating. The yellow fever mosquito (Aedes aegypti), a vector for diseases such as yellow and dengue fever, favors warm climates. Being exposed to higher frequency RF EMFs causing possible dielectric heating, could have an influence on behavior, physiology and morphology, and could be a possible factor for introduction of the species in regions where the yellow fever mosquito normally does not appear. In this study, the influence of far field RF exposure on A. aegypti was examined between 2 and 240 GHz. Using Finite Difference Time Domain (FDTD) simulations, the distribution of the electric field in and around the insect and the absorbed RF power were found for six different mosquito models (three male, three female). The 3D models were created from micro-CT scans of real mosquitoes. The dielectric properties used in the simulation were measured from a mixture of homogenized A. aegypti. For a given incident RF power, the absorption increases with increasing frequency between 2 and 90 GHz with a maximum between 90 and 240 GHz. The absorption was maximal in the region where the wavelength matches the size of the mosquito. For a same incident field strength, the power absorption by the mosquito is 16 times higher at 60 GHz than at 6 GHz. The higher absorption of RF power by future technologies can result in dielectric heating and potentially influence the biology of this mosquito.

Synthesis of 2-Substitued Indoles via Pd-Catalysed Cyclization in an Aqueous Micellar Medium

The synthesis of 2-substituted indoles starting from the corresponding unprotected 2-alkynylanilines was made possible in 3% TPGS-750-M water using Pd(OAc)2 alone as the catalyst. The reaction was sensitive to the heating mode respect to the nature of the starting material as, in many cases, convectional heating was better than microwave dielectric heating. The MW (microwave) delivery mode had also an influence in the formation of by-products and, consequently, product yields. A tandem Sonogashira-cyclisation reaction was also accomplished using Pd(OAc)2/Xphos in the nanomicellar water environment.

Heating mechanisms in induction welding of thermoplastic composites

The heat generated within thermoplastic carbon composite laminates during induction welding can be attributed to one, or a combination of the three heating mechanisms discussed in the literature: (i) Joule heating of fibers; (ii) Joule and/or dielectric heating of polymer; and (iii) fiber-to-fiber contact resistance heating. The answer to the question, which of the three heating mechanisms is most dominant, remains open. This research aims to provide an answer to this question through finite element simulations using both an in-house developed numerical Whitney-elements based toolbox for induction welding simulations (WelDone), and the commercially available software, ANSYS Maxwell. The simulations are done at two levels; first, using WelDone laminate-level simulations are performed to see in which direction: fiber-, transverse to the fiber-, or thickness direction, most of the heat was generated; and second, ANSYS Maxwell was used to simulate the solid loss on a microscopic, inside fiber and resin, level with and without the presence of resin. In the latter series of simulations, contact between fibers in different layers was explicitly modeled. The numerical simulations revealed that on the laminate-level most heat is generated in the fiber- and thickness directions. The former coincides with Joule heating of fibers, while the latter can be attributed to either Joule heating of polymer and fiber-to-fiber contact resistance heating, or both. The fiber level simulations, however, revealed that both fiber-to-fiber contact and no-fiber-to-fiber contact conditions have a significantly small effect on the solid loss compared to presence of resin. Based on the latter, the heat generation in the thickness direction was attributed to a second heating mechanism; Joule heating of polymer. It must be noted that the dielectric heating of polymer was ignored due to the relatively low operating frequency at which induction welding takes place.

Heat transport in turbulent electro-hydrodynamics

<p>Electro-hydrodynamics (EHD) plays an important role in many industrial applications. Ink-jet printers, microwave drying facilities, and lab-on-a-chip devices utilize dielectric properties of the working fluids and their manipulation without moving parts. Another application is found in heat exchangers, where the dielectrophoretic force is used to increase heat transfer due to thermal buoyancy. In particular, the dielectrophoretic force has great advantages in low- and micro-gravity conditions since the force can be used to mimic a gravitational force field. Hence, convection in a rectangular cavity induced by EHD is a model system comparable to Rayleigh-Benard (RB) convection. However, the electric-driven buoyancy term and dielectric heating make the system more complex. The direction of the triggering dielectrophoretic force depends mainly on the temperature gradient which can be used to manipulate the heat flux or the entire structure of the convective flow. Layer formation, comparable to double-diffusive convection, and convective overshooting are two representative cases which can be established by EHD, too. We will present first results of turbulent convection induced by EHD in the rectangular cavity and the impact of volumetric heating. For this purpose, the Boussinesq approximation, as well as compressible models for EHD, are tested also for applicability in geophysical relevant regimes. This is a crucial point as the limitations by incompressible modeling are not well-understood for EHD. The main focus of the study is the analysis of the heat flux as a function of the thermo-electric feedback and the dielectric heating rate. Convective overshooting and layer formation are examined closely. Results of this study are used to estimate transport properties and time scales. Applications using EHD are the GeoFlow and AtmoFlow experiments. The GeoFlow experiment was conducted several years on the International Space Station and gained deep insight into EHD driven convection in the spherical shell geometry. The AtmoFlow experiment is under construction and is planned for operations on the ISS in 2024. This experiment is designed to study atmospheric like flows in the spherical shell.</p>

Microfluidic Modules Integrated with Microwave Components—Overview of Applications from the Perspective of Different Manufacturing Technologies

The constant increase in the number of microfluidic-microwave devices can be explained by various advantages, such as relatively easy integration of various microwave circuits in the device, which contains microfluidic components. To achieve the aforementioned solutions, four trends of manufacturing appear—manufacturing based on epoxy-glass laminates, polymer materials (mostly common in use are polydimethylsiloxane (PDMS) and polymethyl 2-methylpropenoate (PMMA)), glass/silicon substrates, and Low-Temperature Cofired Ceramics (LTCCs). Additionally, the domains of applications the microwave-microfluidic devices can be divided into three main fields—dielectric heating, microwave-based detection in microfluidic devices, and the reactors for microwave-enhanced chemistry. Such an approach allows heating or delivering the microwave power to the liquid in the microchannels, as well as the detection of its dielectric parameters. This article consists of a literature review of exemplary solutions that are based on the above-mentioned technologies with the possibilities, comparison, and exemplary applications based on each aforementioned technology.