• Title, Summary, Keyword: Microwave heating

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Design and Fabrication of a Dual Cylindrical Microwave and Ohmic Combination Heater for Processing of Particulate Foods

  • Lee, Seung Hyun;Choi, Won;Park, Sung Hee;Jun, Soojin
    • Journal of Biosystems Engineering
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    • v.40 no.3
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    • pp.250-260
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    • 2015
  • Purpose: Dual cylindrical microwave chambers equipped with an ohmic heating tube were designed and fabricated to maximize the electric field strength for expeditious heat treatment of particulate foods. Methods: The efficacy of the combination heater was investigated by simulating the electric field distribution by using COMSOL Multiphysics software. Results: All components of the designed microwave heating unit were suitable for transmitting maximal microwave power to the load. The simulated electric field distribution implied that single-mode microwave heating would be sufficient for the steady generation of a highly localized heating zone in the cavity. During impedance matching, the calculated reflection coefficient ($S_{11}$) was small, possibly implying minimal power loss and wave reflection in the designed microwave heating chamber. Conclusions: This study demonstrates the possibility of concentrating the microwave power at the centerline for a single-frequency microwave, for thermal treatment of multiphase foods without attenuating the microwave power.

Microwave heating of carbon-based solid materials

  • Kim, Teawon;Lee, Jaegeun;Lee, Kun-Hong
    • Carbon letters
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    • v.15 no.1
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    • pp.15-24
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    • 2014
  • As a part of the electromagnetic spectrum, microwaves heat materials fast and efficiently via direct energy transfer, while conventional heating methods rely on conduction and convection. To date, the use of microwave heating in the research of carbon-based materials has been mainly limited to liquid solutions. However, more rapid and efficient heating is possible in electron-rich solid materials, because the target materials absorb the energy of microwaves effectively and exclusively. Carbon-based solid materials are suitable for microwave-heating due to the delocalized pi electrons from sp2-hybridized carbon networks. In this perspective review, research on the microwave heating of carbon-based solid materials is extensively investigated. This review includes basic theories of microwave heating, and applications in carbon nanotubes, graphite and other carbon-based materials. Finally, priority issues are discussed for the advanced use of microwave heating, which have been poorly understood so far: heating mechanism, temperature control, and penetration depth.

Oxidative Stability of Fatty Acids and Tocopherols in the Fats and Oils during Microwave Heating (Microwave 오븐 가열에 의한 유지의 지방산과 토코페롤의 안정성)

  • 주광지;김은미
    • Journal of the Korean Society of Food Science and Nutrition
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    • v.24 no.2
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    • pp.234-241
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    • 1995
  • Effect of microwave heating on the oxidative stability of the soybean oil, sesame oil, butter and margarine were investigated by mearsuring fatty acids amout and tocopherol losses. The index for chemical properteis, free fatty acid, peroxide value, anisidine value, carbonyl value, conjugated diene and triene levels were also mearsured in the oil samples for 5, 10, 15 and 20 min of heating in a microwave oven. No significant difference was observed on the fatty acids composition in the fats and oils before and after microwave heating. During microwave treatment, the oxidative degradation of the tocopherols in the samples became greater with increasing heating time. The amount of tocopherols in the soild fats, butter and margarine, dropped drastically after 5 min of heating and reduced to 95% of their original levels after 20min heating ${\gamma}$-tocopherol in butter showed the most unstable states and completely destroyed during microwave treatment for 20min. On the other hand, 80% of tocopherols in the liquid oils were still remained after 5min of heating except $\delta$-tocopherol in sesame oil.

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Microwave Effect on Curing of Waterborne Polyurethane

  • Lee, Hoi-Kwan;Fang, Chris. Y.;Pantano, Carlo. G.;Kang, Won-Ho
    • Bulletin of the Korean Chemical Society
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    • v.32 no.3
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    • pp.961-963
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    • 2011
  • Spin-coated waterborne polyurethane to protect glass surface from environmental attacks was cured by using microwave heating. The effect of microwave heating on the reaction kinetics, chemical durability, and transmittance of polyurethane was investigated. In comparison to the conventional heating the results show that the microwave heating substantially accelerates the curing process of waterborne polyurethane and the total time for the completion of the reaction is only 1/7 of that in the conventional process. The microwave cured sample showed an excellent caustic resistance compared to conventional cured one. It means that microwave heating produces dense structure during curing process. The dense structure does not affect to the transmittance in the visible region.

Synthesis of NaY Zeolites by Microwave and Conventional Heating (마이크로파 및 기존 가열 방법에 의한 제올라이트 NaY의 합성)

  • Choi, Ko-Yeol;Conner, W. Curtis
    • Applied Chemistry for Engineering
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    • v.18 no.4
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    • pp.344-349
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    • 2007
  • NaY zeolites synthesized by microwave heating were compared with those obtained by conventional heating. When the same temperature increasing rates were adopted in both heating methods, the microwave heating shortened the induction period and enhanced the rate of crystallization of NaY zeolites compared with the conventional heating. Irrespective of microwave radiation, the fast temperature increasing rate also shortened the induction time and enhanced the crystallization of NaY zeolites. The crystal sizes of NaY zeolites were large under the fast temperature raise of the reaction mixture and became larger by microwave radiation. At the same time, the fast temperature increasing rate has reduced the energy consumption due to the fast completion of reaction during the synthesis of NaY zeolite. The energy consumption in the conventional ethylene glycol bath was lower than that in the microwave oven with the same temperature increasing rate in this study, which means that the energy efficiency is not always high in microwave heating. If the temperature increasing rate is carefully controlled, however, NaY zeolite can be produced with high energy efficiency in the microwave oven.

A Study on Adsorption of Volatile Organic Compound by Activated Carbon Fiber Coated with Dielectric Heating Element and Desorption by Applying Microwave (유전가열물질을 코팅한 활성탄소섬유의 휘발성 유기화합물 흡착 및 마이크로파 인가에 의한 탈착 연구)

  • Kim, Sang-Guk;Chang, Ye-Rim
    • Journal of Korean Society for Atmospheric Environment
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    • v.25 no.2
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    • pp.122-132
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    • 2009
  • Adsorption of toluene by activated carbon fiber (ACF) coated with dielectric heating element and desorption by applying microwave were investigated. In order to prepare adsorbent so that VOC can be desorbed by microwave heating, fine dielectric heating element with nano size was coated on the surface of the ACF using hybrid binder. Eight adsorbents (ACF-DHE, Activated Carbon Fiber coated with Dielectric Heating Element) were prepared with different amount of dielectric heating element, kinds of hybrid binder, and solvent. In order to investigate adsorption characteristics, BET surface area, pore volume, and average pore size were measured for each adsorbent including ACF. Breakthrough experiments with toluene concentration, flow rate, bed length using fixed bed reactor were performed to investigate adsorbality of adsorbent, and results were compared with that of the ACF. Desorption reactor was constructed with modified microwave oven to investigate heating effect on ACF-DHE by applying microwave power. Each adsorbent saturated with toluene were put into desorption reactor. Composition of desorbed gas generated by applying controlled microwave power to reactor was measured. Up to now, hot air desorption method has been used. Experimental results showed that desorption method with new adsorbent prepared by coating dielectric heating element on ACF can be used for industrial application.

Effect of Microwave Vacuum Heating on Inactivation of Enzymes (마이크로파 진공가열방법이 효소의 불활성화에 미치는 영향)

  • Moon, Eun-Kyung;Han, Ki-Young;Kim, Suk-Shin;Kim, Sang-Young;Noh, Bong-Soo
    • Korean Journal of Food Science and Technology
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    • v.29 no.2
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    • pp.284-291
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    • 1997
  • Microwave vacuum heating method (2450 MHz) was used for a low intensity of heat treatments. High vacuum under the microwave heating could bring low temperature condition. Inactivation of ${\alpha}-amylase,\;{\beta}-amylase$, glucoamylase and peroxidase by microwave vacuum heating were investigated at 60-$80^{\circ}C$. It was compared with conventional heating. The heating condition of microwave vacuum heating was confirmed by the destruction of ascorbic acid. When thermal inactivations of the enzymes by microwave vacuum heating were determined, it was less effective than that of conventional method at the initial stage of heating. It was due to a lag time of microwave heating. However, the heating time for complete inactivation of the enzymes by microwave vacuum heating could be reduced comparing with that of conventional heating. Optimum conditions for inactivation of the enzymes could be obtained by microwave vacuum heating.

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Co-firing of Dielectric and Electrode with Conventional and Microwave Heating in Plasma Display Panel (전형적인 열처리와 마이크로웨이브 열처리에 따른 PDP용 전극과 투명 유전체의 동시 소성)

  • Hwang, Seong-Jin;Veronesi, Paolo;Leonelli, Cristina;Kim, Hyung-Sun
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.463-463
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    • 2008
  • The glass frit has been used in transparent dielectric, barrier rib and electrode of PDP (Plasma display panel). In PDP fabrication, the firing temperature of glass frit is normally 550~$580^{\circ}C$ with conventional heating. However, there are a problem that silver in electrode is diffused throughout the transparent dielectric. For inhibiting the Ag diffusion we considered use of the microwave heating. We investigated firing of glass frit compared between conventional and microwave heating. After firing by two types of heating, the diffusion of silver is determined using a optical microscope and UV-spectrometer. Based on the our results, the microwave heating should be a candidate to heating source for high efficacy in PDP.

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Electrochemical Characterization of Tin Oxide Prepared by Microwave Heating (마이크로파로 합성한 주석산화물의 전기화학적 특성)

  • Kim, Won-Tae;Lee, Eu-Kyung;Cho, Byung-Won;Lee, Joong-Kee;Na, Byung-Ki
    • Korean Chemical Engineering Research
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    • v.46 no.6
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    • pp.1119-1123
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    • 2008
  • Tin oxide was prepared by microwave heating for anode material of lithium ion battery. The samples were heated at 300, 500 and $700^{\circ}C$ for 3h under flowing oxygen after microwave heating. The effect of microwave heating on the electrochemical performance of the manufactured tin oxide and the reversible capacity performance were investigated. Tin oxide heated at $500^{\circ}C$ showed higher capacity than those at $300^{\circ}C$ and $700^{\circ}C$ under microwave heating condition. Comparing microwave and furnace heating, microwave heating condition showed higher capacity. The discharge capacity after microwave heating and $500^{\circ}C$ heating showed 1,500 mAh/g.

Thermal stress and pore pressure development in microwave heated concrete

  • Akbarnezhad, A.;Ong, K.C.G.
    • Computers and Concrete
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    • v.8 no.4
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    • pp.425-443
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    • 2011
  • Most previous studies have generally overlooked the contribution of thermal stresses generated within the concrete mass when subjected to microwave heating and reported on pore-pressure as being the dominant cause of surface spalling. Also, the variation in electromagnetic properties of concrete and its effects on the microwave heating process have not been studied in detail. In this paper, finite element modeling is used to examine the simultaneous development of compressive thermal stresses and pore-pressure arising from the microwave heating of concrete. A modified Lambert's Law formulation is proposed to estimate the microwave power dissipation in the concrete mass. Moreover, the effects of frequency and concrete water content on the concrete heating rate and pattern are investigated. Results show high compressive stresses being generated especially in concrete with a high water content when heated by microwaves of higher frequencies. The results also reveal that the water content of concrete plays a crucial role in the microwave heating process.