Radio Frequency Heating Research Articles

Effect of radio frequency roasting on the lipid profile of peanut oil and the mechanism of lipids transformation: Revealed by untargeted lipidomics approach

Radio frequency (RF) heating has been proved an alternative roasting method for peanuts, which could effectively degrade aflatoxins and possesses the advantages of greater heating efficiency and penetration depth. This study aimed to investigate the influences of RF roasting on the lipid profile of peanut oil under 150 °C target temperature with varied peanut moisture contents (8.29 % and 20 %) and holding times (0, 7.5, and 15 min), using ultra-performance liquid chromatography-quadrupole time-of-flight tandem mass spectrometry (UPLC-QTOF-MS/MS)-based lipidomics. In total, 2587 lipid species from 35 subclasses were identified. After roasting, the contents of sterol lipid (ST) and subclasses of glycerophospholipids (GPs) and glycoglycerolipids increased significantly, while fatty acid (FA), Oxidized (Ox-) FA, cholesterol (CE), and all subclasses of glycerolipids (GLs) decreased, and 1084 differential lipids were screened. The highest ST and lowest CE contents in peanut oil were achieved by medium roasting (7.5 min). The raise in moisture content of peanut simply affected a few GPs subclasses adversely. Compared with hot air (HA) roasting, RF decelerated lipid oxidation, showing higher levels of diacylglycerol, triacylglycerol and FA, with no additional negative impact and only 69 exclusive differential lipids. During RF roasting, hydrolysis and oxidation of fatty acyl chains into secondary oxides were the central behaviors of lipids transformation. This study could provide insights into the lipid changes and transformation mechanism of peanut oil by RF roasting processing.

Simulating energetic ions and enhanced fusion rates from ion-cyclotron resonance heating with a full-wave/Fokker–Planck model

Reproducing fast-ion enhanced fusion rates from ion-cyclotron resonance heating (ICRH) in tokamaks requires the self-consistent coupling of a full-wave solver and a Fokker–Planck solver, which evolves multiple simultaneously resonant ion species. We introduce a new self-consistent model that iterates the TORIC full-wave solver with the CQL3D Fokker–Planck solver using the integrated plasma simulator (IPS). This model evolves the bounce-averaged ion distribution functions in both parallel and perpendicular velocity-space with a quasilinear radio frequency (RF) diffusion operator valid in the ion finite Larmor radius (FLR) limit and the RF electric fields with the resultant non-Maxwellian FLR dielectric tensor. This produces non-Maxwellian ICRH simulations that are fully self-consistent, fast, and interoperable with integrated modeling frameworks, such as TRANSP/GACODE/IPS-FASTRAN. We demonstrate our model's capabilities by validating it against experimental data in Alcator C-Mod. We then perform the first RF heating simulations of SPARC using self-consistent non-Maxwellian ion distributions to investigate the potential to enhance fusion rates using ion cyclotron resonance heating generated fast ions.

Developing a combined rotating and air-circulating system for improving radio frequency heating uniformity and controlling Aspergillus in almond kernels

It is important to improve radio frequency (RF) heating uniformity for developing effective pathogen control protocols before storage of almonds. The purpose of this study was to design a combined rotating and air-circulating system (CRACS) in the RF cavity for improving sample temperature uniformity during pasteurization, drying, and cooling of almond kernels. The results showed that the optimal rotating speed of 15 r/min and loading volume ratio of 60% of CRACS were determined to achieve the required RF pasteurization level. The pasteurization protocol was developed based on the above selected parameters of CRACS, RF heating/drying, and forced air cooling. Compared to the five-layer container (five single layers stacked vertically) used for RF pasteurization of almond kernels, the RF heating uniformity in almond kernels using CRACS was clearly improved, resulting in moisture content reduction of only 0.70% wet basis (w.b.). The pasteurization validation curve of almond kernels in CRACS was closer to the predicted survival one based on the cumulative thermal lethal time model, suggesting that CRACS was suitable for the effective RF pasteurization of almond kernels. The moisture content and color values of almond kernels after RF pasteurization were beneficial for maintaining their long-term storage and stable quality. This CRACS in the RF system may provide a practical and effective technology for pasteurizing almond kernels.

Inactivation of Salmonella Typhimurium and Listeria monocytogenes in dairy systems: Effect of fat and food matrix structure under radio frequency heating

The effect of two food intrinsic factors (fat content, matrix structure) on the radio frequency (RF) inactivation of Salmonella Typhimurium and Listeria monocytogenes was investigated in dairy model systems: i.e., liquids with 0.08% and 5.9% fat and gels with 0.08% and 5.9% fat. In the liquid, higher fat content resulted in higher inactivation for both microorganisms. In gels, inactivation rate was higher with the lower fat content, while opposite behaviour occurred for L. monocytogenes above 70 °C. A gel matrix resulted in higher inactivation of S. Typhimurium, while complex temperature-dependent behaviour was present for L. monocytogenes. Sublethal injury was most significant for L. monocytogenes at 5.9% fat content and high temperatures. Overall, fat content and matrix structure impacted the microbial inactivation during RF heating and should be taken into account when designing novel RF heating food decontamination strategies. Industrial relevanceRadio frequency (RF) heating as a food processing technology has seen increased industrial application in recent years. The technology allows a more homogeneous heating of food products and also enables the treatment of low-moisture foods. The increased knowledge on the influence of fat content and food structure on RF thermal inactivation will lead to the development of improved and more efficient treatments.

Improving the energy efficiency of industrial radio frequency heat treatment by optimizing electrode sizes and reversal cycles

Radio Frequency (RF) heating technology exhibits potential advantages in the heat treatment of bulky products. The influence of electrode size on the RF heating performance by the electric field distribution, electromagnetic loss density, and temperature distribution was evaluated. An electrode reversal device was developed, facilitating the cyclic reversal of the positive and negative electrodes and the effect of electrode reversal was also investigated. Simulation results showed an optimal heating uniformity when the ratio of electrode to product width is 1.4. At that time, the influence of stray electric field between the positive electrode and the cavity on the electromagnetic energy was minimal. The variation in loss angle tangent caused by temperature change was the primary reason for the fluctuation of the electromagnetic-thermal energy conversion efficiency within the same radio-frequency field. The electrode reversal dramatically improved the heating uniformity in the direction of electromagnetic energy decay. The temperature uniformity index (TUI) can be reduced by 32.79 % to 75.41 % with the shorter reversal cycle, but the service life of the device was also curtailed due to more mechanical motions. Considering the stability of the equipment and the heating performance, the optimum reversal cycle was chosen to be 420 s. In this case, the maximum TUI didn’t exceed 0.017, demonstrating better heating uniformity as compared with the commonly used for improving heating uniformity. In conclusion, a suitable electrode width and reversal cycle can effectively avoid the thermal offset effect of larger agricultural products during RF heating, thus improving the heating performance.

Effect of surgical modification of deep brain stimulation lead trajectories on radiofrequency heating during MRI at 3T: from phantom experiments to clinical implementation.

Radiofrequency (RF) tissue heating around deep brain stimulation (DBS) leads is a well-known safety risk during MRI, resulting in strict imaging guidelines and limited allowable protocols. The implanted lead's trajectory and orientation with respect to the MRI electric fields contribute to variations in the magnitude of RF heating across patients. Currently, there are no surgical requirements for implanting the extracranial portion of the DBS lead, resulting in substantial variations in clinical lead trajectories and consequently RF heating. Recent studies have shown that incorporating concentric loops in the extracranial lead trajectory can reduce RF heating. However, optimal positioning of the loops and the quantitative benefit of trajectory modification in terms of added safety margins during MRI remain unknown. In this study, the authors systematically evaluated the characteristics of DBS lead trajectories that minimize RF heating during 3T MRI to develop the best surgical practices for safe access to postoperative MRI, and they present the first surgical implementation of these modified trajectories. The authors performed experiments to assess the maximum temperature increase of 244 distinct lead trajectories. They investigated the effect of the position, number, and size of the concentric loops on the skull. Experiments were performed in an anthropomorphic phantom implanted with a commercial DBS system, and RF exposure was generated by applying a high specific absorption rate sequence (B1+rms = 2.7 µT). The authors conducted test-retest experiments to assess the reliability of measurements. Additionally, they evaluated the effect of imaging landmarks and perturbations to the DBS device configuration on the efficacy of low-heating trajectories. Finally, two neurosurgeons implanted the recommended modified trajectories in patients, and the authors characterized their RF heating in comparison with unmodified trajectories. The maximum temperature increase ranged from 0.09°C to 7.34°C. The authors found that increasing the number of loops and positioning them closer to the surgical burr hole, particularly for the contralateral lead, substantially reduced RF heating. These trajectory modifications were easily incorporated during the surgical procedure and resulted in a threefold reduction in RF heating. Surgically modifying the extracranial portion of the DBS lead trajectory can substantially reduce RF heating during 3T MRI. The authors' results indicate that simple adjustments to the lead's configuration, such as small, concentric loops near the burr hole, can be readily adopted during DBS lead implantation to improve patient safety during MRI.

Trigger transceiver and timing control system for ADITYA-U tokamak

The trigger transceiver and timing control system described in this study is developed to generate multiple triggers with varying delays to synchronize various subsystems with plasma discharges in the ADITYA Upgrade (ADITYA-U) tokamak (Ghosh et al., 2016) [1]. The Toroidal Field Power Supply (TFPS) is a fundamental component for each plasma discharge in the ADITYA-U, which generates a master trigger pulse for the particular discharge. The rise time of Toroidal Field Power Supply is 2 s and the loop voltage which is required to initiate the plasma discharge begins at 2.4 s after the master trigger. So the loop voltage is time-stamped at t = 0 and the master trigger from TFPS is time-stamped at t = −2.4 s and considered as a pre-trigger. Apart from this master trigger at t = −2.4 s, two more pre-trigger pulses, one at ∼ −40 ms and another at ∼ −4 ms, prior to the initiation of loop voltage trigger are generated by the power supply. These pre-trigger pulses generated by TFPS constitute the backbone of the entire discharge timing sequence, and they operate/control/initiate numerous ADITYA-U subsystems such as the gas puffing system, data acquisition system, radio frequency pre-ionization and heating system, plasma position control, and so on. So a suitable trigger generator system was needed to be developed in which three pre-trigger pulses (time stamped @ −2.4 s, −40 ms, and −4 ms prior to the loop voltage trigger) arriving from the TFPS may be selected and altered based on the experimental needs. To cater these requirements in ADITYA-U, a trigger transceiver and timing control system has been developed. The system has been successfully operated over ∼6000 discharges of ADITYA-U and functioned satisfactorily in all discharges in daily experiments with no failures. This study will discuss the detailed design elements and implementation of the Trigger Transceiver and Timing Control System for ADITYA-U plasma operations.

Advances in Food Processing Through Radio Frequency Technology: Applications in Pest Control, Microbial and Enzymatic Inactivation

AbstractFoodborne illnesses occur due to contamination by pathogenic microorganisms. Therefore, decontaminating food is vital before marketing and circulation. Radio frequency (RF) heating stands out in several branches of industry, mainly food processing, as an alternative method to conventional pasteurization which takes long process times and overheating. RF heating functions without relying on heat conduction. It generates internal heat by inducing the rotation of polar molecules and the motion of ions. The advantages of dielectric heating with greater wave penetration include rapid, uniform and volumetric heating, presenting high energy efficiency. Furthermore, it is an effective, validated method for eliminating pathogens in agricultural products and is free from chemical residues. Although many reviews have discussed this technology, few reviews have covered the research trends in this field in the recent years, during which the number of studies discussing RF treatment of foods have increased. Therefore, this review focuses on the RF applications in the food industry for pest control, microbial and enzymatic inactivation of solid, liquid, and powdered foods in the last five years. Besides covering the fundamental aspects of RF technology, we also examine its benefits and drawbacks, address the challenges it presents, and explore future prospects Graphical Abstract

Hot air–assisted radio frequency drying of corn kernels: the effect on structure and functionality properties of corn starch

Hot air (HA) drying caused quality damage of grains with long treatment time. Radio frequency (RF) heating as an emerging technology was applied to improve drying quality of cereals effectively. The effects of HA-RF drying (50 °C, 70 °C, 90 °C) of corn kernels on the morphology, structure, and physicochemical properties of starch were investigated and compared with HA drying. The surface of treated starch became rough, along with fragments and pores. Drying treatments increased the amylose content from 10.59 % to 23.88 % and the residual protein content of starch from 0.58 % to 1.23 %, and reduced the crystallinity from 31.95 % to 17.15 % and short–range order structures of starch from 0.918 to 0.868. The change of structures in turn resulted in the increase of pasting viscosity, gelatinization temperature, storage modulus and loss modulus. Furthermore, the HA-RF dried starch displayed stronger thermal stability, higher gelatinization degree and better gelation properties than the HA-treated starch at the same temperature. The data proved that the synergistic effects of HA and RF were more effective in modulating the starch structure and improving the functional characteristics of corn starch. This paper would like to provide potential reference for better application of HA-RF technologies to corn.

Developing a spouted bed for combined radio frequency-hot air treatments to improve the heating uniformity in high-moisture carrot cubes

Uneven and thermal runaway heating is the biggest obstacle to industrial applications of radio frequency (RF) technology, while the existing research mainly focuses on the RF heating uniformity of low-moisture foods with fewer reports about the useful solutions to avoid heterogeneous heating of high-moisture foods. Thus, the combined RF-hot air treatment in a newly designed spouted bed (RFHASB) was developed in this study to improve the RF heating uniformity of fresh carrot cubes selected as the high-moisture model sample. This RFHASB was used to evaluate effects of four processing parameters (cone angle, nozzle diameter, inlet air speed and electrode gap) on the RF heating rate and uniformity of carrot cubes with comparison of those between the RFHASB and the hot air treatment alone in the spouted bed (HASB). The results showed that the RFHASB effectively alleviated the non-uniform heating in the treated high-moisture carrot cubes through mixing and stirring particles. Both heating rate and uniformity index in RFHASB increased with decreasing cone angles and electrode gaps but decreased when nozzle diameters and inlet air speeds were reduced. The RFHASB had better heating performances than the HASB. These findings may provide the theoretical basis for the effective drying of high-moisture fresh fruits and vegetables in RFHASB.

High-frequency fluctuation and EHO-like mode in the H-mode pedestal on the EAST tokamak

In the pedestal region of the Experimental Advanced Superconducting Tokamak (EAST) during high confinement mode plasma operations with radio-frequency heating, two distinct fluctuations are observed: high-frequency fluctuations (HFFs) and edge harmonic oscillation-like (EHO-like) modes. The HFFs are characterized by intermittent fluctuations with a broadband frequency range of 1−3 MHz and a poloidal wave number ( kθ ) greater than 0.9 cm−1 . On the other hand, the EHO-like mode exhibits characteristics similar to magnetohydrodynamics (MHD)-like modes with n = 1−5 and lower poloidal wave numbers ( kθ⩽0.12 cm−1 ). During the pedestal establishing phase following the L–H transition, a significant concurrent presence of HFF and EHO-like modes in high-density pedestal regions has been noted. In this phase, the EHO-like mode not only modulates the amplitude of the HFF but also engages in nonlinear interactions. The occurrence of EHO-like mode and HFF is associated with particle transport toward the divertor, though it is notably less than that caused by edge coherent modes. During the inter-edge localized mode (ELM) period, a significant decrease in the Dα baseline is observed whenever the low frequency fluctuation (LFF) weakens and the HFF grows, prior to each large ELM. One possible explanation is that the rapid increase of E×B shear stabilizes the LFF and destabilizes the HFF, which lowers the pedestal transport and enables the further growth of the pedestal until the onset of the ELM.

Effect of BaTiO3 as a filling material with adjustable dielectric properties on improving the radio frequency heating uniformity in red jujubes

The non-uniformity of radio frequency (RF) heating is a major obstacle to develop successful large-scale disinfestation processes for agricultural products with large particles. To effectively improve the RF heating uniformity in red jujubes, the chemical material of BaTiO3 (BT) with different volume percentages was added into food-grade silicone (FGS) to form FGS/BT composite particles with various dielectric properties. The various FGS/BT composite particles were filled inside the rectangular container of red jujubes and used to evaluate the effect of matching degree of their dielectric constants on the RF heating uniformity. The results showed that the dielectric constant of the composite increased from 3.41 ± 0.14 to 8.31 ± 0.15 as the BT volume percentage increased from 0% to 20% at 25 °C and 27.12 MHz. Compared with FGS, the filled FGS/BT composite with a BT volume percentage of 20% not only improved the heat conduction but also optimized the temperature distributions among red jujube particles, which reduced the heating uniformity index in the top, middle, and bottom layers by 40%, 32%, and 27%, respectively. As the electrode gap increased from 160 mm to 180 mm, the heating rate and uniformity index in FGS/BT filled samples decreased significantly (p < 0.05). There was no significant (p > 0.05) difference in color and textural properties between the treated and control samples. This study provided the effective filling materials with matched dielectric constant in the RF treatment of red jujubes and a feasible method to further improve the RF heating uniformity in large-size agricultural products.

Developing effective radio frequency drying processes for tiger nuts: Dynamic analysis of moisture state, dielectric properties and quality

Radio frequency (RF) heating technology is widely applied to dry agricultural products due to the advantages of fast and volumetric heating, but it lacks systematic and in-depth studies on combination drying methods. This study aimed to investigate the drying mechanism of tiger nuts with hot-air drying (HD), radio frequency drying (RFD), radio frequency assisted hot-air drying (RFHD), and radio frequency-vacuum drying (RFVD), in terms of analyzing dynamic changes of dehydration kinetics, moisture migration, and dielectric properties during the drying processes, as well as quality attributes of dried tiger nuts. The results indicated that the RF drying time (including RFD, RFHD and RFVD) was significantly reduced by 38.60–54.39%, compared with HD. Although RF drying had a positive effect on physical qualities, it caused clear changes to the microstructure. Among all drying methods, the free water content (A23) in the tiger nuts decreased as drying processed, while the immobilized water content (A22) increased first and then decreased. The A23 exhibited strong positive correlations with dielectric constant (ε′) and loss factor (ε″). Correspondingly, ε′ and ε″ gradually decreased due to a reduction in the A23 value. The results may comprehensively understand the RF drying mechanism of tiger nuts to provide high-quality products and optimize the drying process.

Radio frequency food processing. Current status and perspectives – a review

The present review provides a critical overview of the current status and prospects for the development and application of radio frequency food processing. The mechanism of action of radio frequency treatment, the dielectric properties of foods, the mechanisms for inactivating microorganisms and endogenous enzyme systems, the sensory and physicochemical changes occurring in radio frequency treated foods, as well as the application of radio frequency treatment in the food industry are discussed. Radio frequency processing technology has been found to have some advantages over conventional heat exchange systems in terms of time savings, higher profitability and better efficiency. In the available literature, the conducting of additional studies regarding the package violation and its permeability and integrity during radio frequency processing were discussed. Radio frequency heating has been shown to effectively eliminate pathogens and preserve better, physicochemical and sensory properties of food products compared to conventional heating due to shorter processing time. It is concluded that radio frequency energy heating is suitable for processing packaged foods that remain safe and stable during storage. For these reasons, it is concluded that radio frequency food processing has a very bright future.

Treatment with synchronized radiofrequency and facial muscle stimulation: Histologic analysis of human skin for changes in collagen and elastin fibers.

Skin's exposure to intrinsic and extrinsic factors causes age-related changes, leading to a lower amount of dermal collagen and elastin. This study investigated the effects of a novel facial muscle stimulation technology combined with radiofrequency (RF) heating on dermal collagen and elastin content for the treatment of facial wrinkles and skin laxity. The active group subjects (N = 6) received four 20-min facial treatments with simultaneous RF and facial muscle stimulation, once weekly. The control subject (N = 1) was untreated. Skin biopsies obtained at baseline, 1-month and 3-month follow-up were evaluated histologically to determine collagen and elastin fibers content. A group of independent aestheticians evaluated facial skin appearance and wrinkle severity. Patient safety was followed. In the active group, collagen-occupied area reached 11.91 ± 1.80 × 106 μm2 (+25.32%, p < 0.05) and 12.35 ± 1.44 × 105 μm2 (+30.00%, p < 0.05) at 1-month and 3-month follow-up visits. Elastin-occupied area at 1-month and 3-month follow-up was 1.64 ± 0.14 × 105 μm2 (+67.23%, p < 0.05), and 1.99 ± 0.21 × 105 μm2 (+102.80%, p < 0.05). In the control group, there was no significant difference (p > 0.05) in collagen and elastin fibers. Active group wrinkle scores decreased from 5 (moderate, class II) to 3 (mild, class I). All subjects, except the control, improved in appearance posttreatment. No adverse events or side effects occurred. Decreased dermal collagen and elastin levels contributes to a gradual decline in skin elasticity, leading to facial wrinkles and unfirm skin. Study results showed noticeable improvement in facial appearance and increased dermal collagen and elastin content subsequent to simultaneous, noninvasive RF, and facial muscle stimulation treatments.

Using computed tomogram atrial myocardial thickness maps in high-power short-duration radiofrequency pulmonary vein isolation: UTMOST AF.

High-power short-duration (HPSD) ablation creates wide, shallow lesions using radiofrequency (RF) heating. It is uncertain if adjusting RF energy based on atrial wall thickness provides extra benefits. We studied the safety and effectiveness of tailored HPSD energy based on left atrial (LA) wall thickness (LAWT) for circumferential pulmonary vein isolation (CPVI) in patients with paroxysmal atrial fibrillation (PAF). We enrolled 212 patients (68.4% male, mean age: 59.5 ± 11.0 years) and randomly assigned them to two groups: LAWT-guided CPVI (WT, n = 108) and conventional CPVI (control, n = 104). Both groups used an open irrigated-tip deflectable catheter to apply 50 W for 10 s to the posterior LA, while controls used 60 W for 15 s on other LA regions. RF delivery time in WT was titrated (15 s at LAWT > 2.1 mm, 13 s at 1.4-2.1 mm, and 11 s at <1.4 mm) according to the computed tomogram-myocardial thickness color map. After a mean follow-up of 13.4 ± 7.0 months, the WT and control groups showed no significant difference regarding clinical recurrence rate (13.9% vs. 5.8%, respectively; p = .061) and major complication rate (4.6% vs. 3.8%, respectively; p > .999). The total procedure time, cardioversion rate, and post-procedural AAD prescription rates did not significantly differ between the groups. The LAWT-guided energy titration strategy did not result in improved procedural safety and efficacy compared to the conventional 50-60 W-HPSD CPVI in patients with PAF.

Evaluation of mechanical properties, heating rate and radio frequency explosive puffing (RFEP) quality of purple sweet potato under different moisture contents and moisture equilibrium process

The effects of different initial moisture contents (15–55%) and moisture equilibrium process (MEP) on the mechanical properties of the gas-blocking surface layer of purple sweet potato chips and the radio frequency (RF) heating rate, uniformity, and radio frequency explosion puffing (RFEP) quality were discussed in this article. Low-field nuclear magnetic resonance indicated that hot-air pre-drying reduced the amount of free water and caused the transfer of immovable water to bound water. This process was accompanied by an increase in the thickness and elastic modulus of the gas-blocking surface layer, resulting in a significant increase in the RF heating rate and uniformity. Prolonged RF heating time led to a decrease in anthocyanin content. The results demonstrated that the puffing rate initially increased and then decreased with increasing initial moisture content. The puffed sample with an initial moisture content of 45% exhibited the highest puffing rate, crispiness, and porosity. X-ray micro-tomography results reveal that MEP improved the morphology of puffed products, ensuring even distribution of small pores and reducing the presence of hard edges. In conclusion, considering the heating time and anthocyanin retention rate, the initial moisture content ranges from 35% to 45% after MEP was the best pre-treatment.

Radio frequency heating induced 3D printed white croaker (Argyrosomus argentatus) surimi gelation: Effectiveness and gel quality evaluation

Two-stage water bath (WB) heating is commonly used in surimi gelation as an effective thermal treatment method but produces wasted water. Radio frequency (RF) has the potential substituting the WB heating with its fast, volumetric and adjustable heating characteristics for saving treatment time and water usage. This study examined the effectiveness of RF to substitute one of or both stages of WB heating on surimi prepared with conventional and 3D printed methods. Four treatments including two-stage WB heating, RF heating, and different combinations (RF-WB and WB-RF) with the same target temperature of 85 °C were conducted and the essential quality parameters of surimi products were analyzed. Results showed that RF heating had the highest heating rate of ∼8.6 °C/min with a linear heating curve, among which the 3D printed surimi samples had a slower heating rate than conventionally prepared ones. RF heating resulted in higher water holding capacity (67.24%) comparing to traditional WB method (59.60%). The gel strength of the conventionally prepared surimi samples was not significantly different among four treatments. However, the 3D printed surimi samples treated with WB had lower gel strength than those RF-induced ones. Also, the 3D printed surimi gel had a more compact and uniform gel network structure compared to traditionally prepared ones among all treatments. The proposed non-contact RF treatment method protects the delicate shape of samples from deforming. The results of this study assist the development of more efficient and emission-free surimi processing techniques.

Dielectric properties of in-shell peanuts with radio frequency and microwave heating treatment and RF heating performance

Radio frequency (RF) heating technology has potential advantages for drying or sterilization of in-shell peanuts, with a critical need for understanding the dielectric properties governing energy conversion. In this study, the dielectric properties of peanut shells and kernels were measured over the frequency range of 10 MHz ∼ 3 GHz, spanning temperatures from 20 to 80 °C. Results showed that the dielectric constant of all the samples decreased rapidly with increasing frequency, the loss factor of peanut shells and kernels with lower moisture content exhibited an initial decrease within the RF band followed by a slight increase within the microwave (MW) band, while loss factor of peanut kernels with higher moisture content decreased continuously with increase in frequency. A high temperature will enhance the sample polarization, while an elevated moisture content will provide the more polar molecules and release the more ions, so that both of them have the positive effect on the dielectric properties. It should be noted that the disruption of the coarse fiber structure and clumping phenomenon in the samples might mitigate the temperature effect. The numerical simulation results of RF heating based on the cubic regression model of dielectric properties showed that: since the loss factor was more sensitive to temperature and moisture content than dielectric constant, the loss angle tangent of the samples increased significantly with increasing moisture content, which subsequently hindered the heating rate of the samples. Meanwhile, this simulation results derived the optimal conditions, with the fastest heating rate at 20% moisture content and the most uniform RF heating (UI=0.16331) at 30% moisture content. Consequently, the loading thickness of in-shell peanuts should be controlled within 11 cm when designing a 27.12 MHz RF dryer. This research has a profound meaning to promote the efficiency of RF heat treatment of in-shell peanuts.

Applied Mathematics in the Numerical Modelling of the Electromagnetic Field in Reference to Drying Dielectrics in the RF Field

The processing of dielectric materials in the radio frequency field continues to be a concern in engineering. This procedure involves a rigorous analysis of the electromagnetic field based on specific numerical methods. This paper presents an original method for analysing the process of drying wooden boards in a radio frequency (RF) installation. The electromagnetic field and thermal field are calculated using the finite element method (FEM). The load capacity of the installation is also calculated, since the material being heated in the radio frequency heating installations is placed in a capacitor-type applicator. A specific method is created in order to solve the problem related to mass, a quantity which tends to change during the drying of the dielectric. In addition, special consideration is given to issues regarding the coupling of the electromagnetic field and the thermal field, along with aspects pertaining to mass. These are implemented numerically using a program written in the Fortran language, which takes the distribution of finite elements from the Flux2D program, the dielectric thermal module, intended only for the study of RF heating. The results obtained after running the program are satisfactory and they represent a support for future studies, especially if the movement of the dielectric is taken into account.