2009
DOI: 10.1007/s11431-008-0286-3
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The precise condition of thermal runaway in microwave heating on chemical reaction

Abstract: The precise condition of thermal runaway in microwave heating on chemical reaction with a feedback control system is quantitatively studied. First, the precise condition of thermal runaway in engineering application is derived based on the principle of the feedback control system. Then, the temperature rising rates for 4 different kinds of reaction systems placed in the waveguide and irradiated by microwave with different input powers are simulated. Finally, the relationship, which is inattentive so far, betwe… Show more

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Cited by 16 publications
(9 citation statements)
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“…The microwave heat generation term per unit volume can be written as Where, f = frequency, = dielectric constant, = food factor loss, = Average electric field intensity. The surface of product being heated by microwave energy has typically convection phenomenon-either natural or forced convection, Where, T = load surface temperature, z = normal to surface, h = convective heat transfer coefficient, m w = evaporation rate, = latent heat vaporization, = Stefan boltzman constant, = radiative surface emissivity of load, = radiant heat flow rate per unit surface area, =surface absorptivity A Fick's second law of diffusion was taken into consideration for evaluation of moisture transport in food material during the analysis of falling rate period, which is given by [9,10] Where, M = free moisture content, kg water/kg dry matter; t= time, sec; x =diffusion path or length, cm; and D = moisture diffusivity, cm 2 s -1 A considerable variation in diffusivity with the method of slopes technique is used for the estimation of effective moisture diffusivity of thin infinite onion slab at varying moisture content under different drying conditions. For a thin infinite slab being dried from only one side, the following assumptions were made:…”
Section: Mathematical Modeling Of Heat and Mass Transfer By Microwmentioning
confidence: 99%
“…The microwave heat generation term per unit volume can be written as Where, f = frequency, = dielectric constant, = food factor loss, = Average electric field intensity. The surface of product being heated by microwave energy has typically convection phenomenon-either natural or forced convection, Where, T = load surface temperature, z = normal to surface, h = convective heat transfer coefficient, m w = evaporation rate, = latent heat vaporization, = Stefan boltzman constant, = radiative surface emissivity of load, = radiant heat flow rate per unit surface area, =surface absorptivity A Fick's second law of diffusion was taken into consideration for evaluation of moisture transport in food material during the analysis of falling rate period, which is given by [9,10] Where, M = free moisture content, kg water/kg dry matter; t= time, sec; x =diffusion path or length, cm; and D = moisture diffusivity, cm 2 s -1 A considerable variation in diffusivity with the method of slopes technique is used for the estimation of effective moisture diffusivity of thin infinite onion slab at varying moisture content under different drying conditions. For a thin infinite slab being dried from only one side, the following assumptions were made:…”
Section: Mathematical Modeling Of Heat and Mass Transfer By Microwmentioning
confidence: 99%
“…Numerical results implied that the adopted arrangement of the substrate is not desirable for continuous growth of large diamond crystals. Huang, et al, [53] studied the precise condition of thermal runaway in microwave heating on chemical reaction with a feedback control system. They derived the condition of thermal runaway according to the principle of the feedback control system, simulated the temperature rising rates for 4 different kinds of reaction systems placed in the waveguide and irradiated by microwave with different input powers, and discussed the www.intechopen.com relationship between the thermal runaway and the sensor's response time.…”
Section: Application Backgroundsmentioning
confidence: 99%
“…Since the great experiments were carried out by Dr. Percy Spencer in 1946, microwave heating has been used widely in food industry, medicine, chemical engineering and so on [1][2] [3][4] [5], for processing many materials ranging from foodstuffs [1][6] [7][8] to tobaccos [9][10] [11], from wood [12][13] [14] to ceramics [15] [16][17] [18], and from biological objects [19][20] to chemical reactions [21][22] [23]. Typical applications include heating and thawing of foods, drying of wood and tobaccos, sintering of ceramics, killing of cancer cells and accelerating of chemical reactions.…”
Section: Introductionmentioning
confidence: 99%
“…Microwave field distribution is influenced by material permittivity, which directly relates to temperature. The usual way to obtain temperature is by optical fiber thermometer, infrared thermometer, or infrared camera [7]. Those methods are suitable for detecting surface or point temperature.…”
Section: Introductionmentioning
confidence: 99%