Improvement of radio frequency (RF) heating-assisted alkaline pretreatment on four categories of lignocellulosic biomass

Abstract Radio frequency (RF) sterilization of low-moisture, high-oil, high-protein, and viscous sauces for instant food (LHHVS) demonstrates many advantages, but uneven heating is a main problem that must be addressed. Main factors that affect heating uniformity are generally considered dielectric properties, shape and size of the sample and its position relative to the electrode plate, in addition the structure and voltage of RF electrode. A method based on texture characteristics of the solid–gel–liquid mixing system of LHHVS for adjustment and control of energy distribution in the RF field is proposed in this study to improve the heating uniformity. First, energy conversion principles and control equations of RF heating were analyzed on the basis of dielectric theory. Second, the influence of RF electromagnetic field-medium polyetherimide (PEI) on the RF heating of peanut butter (RHPB) was investigated on the basis of the numerical model of RHPB that was verified through experiments. Finally, the influence mechanism and its regulation and control effect were analyzed and discussed. The following conclusions can be drawn from this study: the increase of electrode gaps exerts minimal effect although it reduces the unevenness of the energy distribution. However, RF heating protocols must use the smallest possible electrode gap to heat agrifoods and increase the heating rate significantly. The energy distribution on the part of the sample close to PEI varies with the change of geometry and size of PEI when its placement is bias or symmetric. The area of energy enhancement continues to expand where the sample is in contact with PEI as PEI gradually increases. The area where the temperature increases under the influence of PEI will expand along the direction of the sample radius when the thickness of PEI remains unchanged and the radius gradually enlarges; otherwise, it will expand along the direction of the sample thickness. The influence of PEI on the energy distribution of RHPB demonstrates local characteristics. PEI significantly influences the energy distribution and heating mode of RHPB, which is easy to adjust and control, but does not reduce the processing speed and does not increases energy consumption. Hence, PEI is an effective means to interfere with energy distribution of RHPB. Uniform energy distribution can be obtained by selecting the appropriate PEI shape and size. Results of this study can help determine the experimental protocol for RHPB with the optimal uniform distribution and promote the fast commercial application of this technology.

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Volumetric fusion of graphite-doped nylon 12 powder with radio frequency radiation

Rapid Prototyping Journal ◽

10.1108/rpj-09-2020-0218 ◽

2021 ◽

Vol ahead-of-print (ahead-of-print) ◽

Author(s):

Jared Allison ◽

John Pearce ◽

Joseph Beaman ◽

Carolyn Seepersad

Keyword(s):

Radio Frequency ◽

Rf Heating ◽

Thermoplastic Polymers ◽

Content Type ◽

Plate Electrode ◽

Radio Frequency Radiation ◽

Powder Bed ◽

Nylon 12 ◽

Electrode Chamber ◽

Frequency Radiation

Purpose Additive manufacturing (AM) of thermoplastic polymers for powder bed fusion processes typically requires each layer to be fused before the next can be deposited. The purpose of this paper is to present a volumetric AM method in the form of deeply penetrating radio frequency (RF) radiation to improve the speed of the process and the mechanical properties of the polymer parts. Design/methodology/approach The focus of this study was to demonstrate the volumetric fusion of composite mixtures containing polyamide (nylon) 12 and graphite powders using RF radiation as the sole energy source to establish the feasibility of a volumetric AM process for thermoplastic polymers. Impedance spectroscopy was used to measure the dielectric properties of the mixtures as a function of increasing graphite content and identify the percolation limit. The mixtures were then tested in a parallel plate electrode chamber connected to an RF generator to measure the heating effectiveness of different graphite concentrations. During the experiments, the surface temperature of the doped mixtures was monitored. Findings Nylon 12 mixtures containing between 10% and 60% graphite by weight were created, and the loss tangent reached a maximum of 35%. Selective RF heating was shown through the formation of fused composite parts within the powder beds. Originality/value The feasibility of a novel volumetric AM process for thermoplastic polymers was demonstrated in this study, in which RF radiation was used to achieve fusion in graphite-doped nylon powders.

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Inactivation of Salmonella enterica serovar Typhimurium and Staphylococcus aureus in rice by radio-frequency heating

Journal of Food Protection ◽

10.4315/jfp-21-275 ◽

2021 ◽

Author(s):

Ki-Ok Jeong ◽

Sang-Soon Kim ◽

Sang-Hyun Park ◽

Dong-Hyun Kang

Keyword(s):

Staphylococcus Aureus ◽

Radio Frequency ◽

Heating Rate ◽

Foodborne Pathogens ◽

Color Change ◽

Oryza Sativa L ◽

Rf Heating ◽

Pathogen Inactivation ◽

Treatment Conditions ◽

And Staphylococcus Aureus

The objectives of this study were to determine the effect of the milling degree (MD) of Oryza sativa L. (Korean rice) on the heating rate, pathogen inactivation (Salmonella Typhimurium and Staphylococcus aureus), and color change resulting from radio-frequency (RF) heating. Rice samples inoculated with pathogens were placed in a polypropylene jar and subjected to RF heating for 0-75 s. The heating rate of rice with a 2% MD was the highest during RF heating, followed by those with a 0, 8, and 10% MD, and the reduction of pathogens showed the same trend. The reduction of the levels of pathogens in rice with a MD 0 and 2% was significantly higher than that observed for rice with a MD of 8 and 10% under the same treatment conditions. For example, log reductions of S. Typhimurium in rice by 55 s RF heating were 3.64, 5.19, 2.18, and 1.80 for milling degree of 0, 2, 8, and 10%, respectively. At the same treatment conditions, log reduction of S. aureus were 2.77, 5.08, 1.15, and 0.90 for milling degree of 0, 2, 8, and 10%, respectively. The color of rice measured according to L*, a*, and b* was not significantly altered after RF heating, regardless of the MD. Therefore, the MD of rice should be considered before RF heating is applied to inactivate foodborne pathogens.

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Radio frequency heating of metallic and semiconducting single-walled carbon nanotubes

Nanoscale ◽

10.1039/c9nr01600g ◽

2019 ◽

Vol 11 (19) ◽

pp. 9617-9625 ◽

Cited By ~ 9

Author(s):

Muhammad Anas ◽

Yang Zhao ◽

Mohammad A. Saed ◽

Kirk J. Ziegler ◽

Micah J. Green

Keyword(s):

Carbon Nanotubes ◽

Radio Frequency ◽

Single Walled Carbon Nanotubes ◽

Rf Heating ◽

Radio Frequency Heating ◽

Single Walled Carbon ◽

Walled Carbon Nanotubes ◽

Frequency Heating

Here we report the effect of metallic (m-) and semiconducting (s-) properties of single-walled carbon nanotubes (SWCNTs) on the response of SWCNT films to radio frequency (RF) heating.

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Design, Implementation, Evaluation and Application of a 32-Channel Radio Frequency Signal Generator for Thermal Magnetic Resonance Based Anti-Cancer Treatment

Cancers ◽

10.3390/cancers12071720 ◽

2020 ◽

Vol 12 (7) ◽

pp. 1720

Author(s):

Haopeng Han ◽

Thomas Wilhelm Eigentler ◽

Shuailin Wang ◽

Egor Kretov ◽

Lukas Winter ◽

...

Keyword(s):

Magnetic Resonance ◽

Radio Frequency ◽

Cancer Treatment ◽

Antenna Arrays ◽

Power Level ◽

Signal Generator ◽

Rf Heating ◽

Anti Cancer ◽

Rf Antenna ◽

Rf Channels

Thermal Magnetic Resonance (ThermalMR) leverages radio frequency (RF)-induced heating to examine the role of temperature in biological systems and disease. To advance RF heating with multi-channel RF antenna arrays and overcome the shortcomings of current RF signal sources, this work reports on a 32-channel modular signal generator (SGPLL). The SGPLL was designed around phase-locked loop (PLL) chips and a field-programmable gate array chip. To examine the system properties, switching/settling times, accuracy of RF power level and phase shifting were characterized. Electric field manipulation was successfully demonstrated in deionized water. RF heating was conducted in a phantom setup using self-grounded bow-tie RF antennae driven by the SGPLL. Commercial signal generators limited to a lower number of RF channels were used for comparison. RF heating was evaluated with numerical temperature simulations and experimentally validated with MR thermometry. Numerical temperature simulations and heating experiments controlled by the SGPLL revealed the same RF interference patterns. Upon RF heating similar temperature changes across the phantom were observed for the SGPLL and for the commercial devices. To conclude, this work presents the first 32-channel modular signal source for RF heating. The large number of coherent RF channels, wide frequency range and accurate phase shift provided by the SGPLL form a technological basis for ThermalMR controlled hyperthermia anti-cancer treatment.

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Critical review of radio-frequency (RF) heating applications in food processing

Food Quality and Safety ◽

10.1093/fqsafe/fyz002 ◽

2019 ◽

Vol 3 (2) ◽

pp. 81-91 ◽

Cited By ~ 5

Author(s):

Ammar Altemimi ◽

Salah Naji Aziz ◽

Asaad R S Al-HiIphy ◽

Naoufal Lakhssassi ◽

Dennis G Watson ◽

...

Keyword(s):

Radio Frequency ◽

Critical Review ◽

Food Processing ◽

Rf Heating

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Analysis of the Heat Transfer of Ginkgo Biloba Seeds during Radio-Frequency Heating

International Journal of Food Engineering ◽

10.1515/ijfe-2019-0014 ◽

2019 ◽

Vol 16 (1-2) ◽

Author(s):

Chunfang Song ◽

Yao Chen ◽

Jingke Wu ◽

Zhenfeng Li ◽

Haiying Chen ◽

...

Keyword(s):

Heat Transfer ◽

Radio Frequency ◽

Electric Fields ◽

Ginkgo Biloba ◽

Simulation Method ◽

High Water ◽

High Water Content ◽

Rf Heating ◽

Distribution Law ◽

Simulated Temperature

AbstractFresh ginkgo biloba (GB) seeds are seasonal and susceptible to microbial spoilage, especially the growth of mold owing to GB seeds’ high-water content, which greatly limits their shelf life. As an efficient and special heating method, radio-frequency (RF) heating can be used to dehydrate ginkgo to preserve its nutritional value and reduce postharvest losses. However, the non-uniformity of RF heating restricts the development in industrialized application. In this study, the RF drying of GB seeds was performed to investigate the effect of RF heating on temperature. The distribution law of the entire temperature field was also observed. Using numerical simulation method, the coupling model of electromagnetic and heat transfer was established. The model was validated by the 6-min heating profile of GB seeds in a 12 kw and 27.12 MHz RF system. The model was also qualitatively validated by comparing the simulated temperature profiles on the three planes in the GB seeds with the corresponding thermal images. Quantitative validation was performed by comparing the simulated temperature of GB seeds on the three planes with experimental temperature acquired at places using thermocouples. Furthermore, the model can be effectively used to identify the distribution of electric fields in different positions and to achieve satisfactory heating uniformity.

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