Continuous tubular microwave heating of homogeneous foods: evaluation of heating uniformity

Raaholt, Birgitta; Isaksson, Sven; Hamberg, Lars; Fhager, Andreas; Hamnerius, Yngve

doi:10.1080/08327823.2016.1157318

Cited by 15 publications

(9 citation statements)

References 4 publications

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“…problems when dealing with materials that have a low flashing point or in high temperature conditions [16,17]. For studies on microwave heating uniformity improvement, the common methods could be categorized into two aspects [18]: (1) To improve the uniformity of the electromagnetic field in the microwave cavity, such as optimization of microwave power feeding situations [19][20][21][22], introducing of mode stirrers [23,24], application of conductive matter [25,26] and optimization of heating chamber structure [27,28]; (2) to improve the uniformity of microwave energy absorption, such as introducing of a rotating turntable or conveyor belt [29,30], optimization of the shapes and sizes of processing materials [26,31,32]. For studies on the electric discharge phenomena, related research has focused on microwave discharges in sintering of powdered metals.…”

Section: Geometrymentioning

confidence: 99%

Impact of Filled Materials on the Heating Uniformity and Safety of Microwave Heating Solid Stack Materials

et al. 2018

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Microwave heating of solid stack materials is common but bothered by problems of uneven heating and electric discharge phenomena. In this paper, a method introducing fluid materials with different relative permittivity is proposed to improve the heating uniformity and safety of solid stack materials. Simulations have been computed based on the finite element method (FEM) and validated by experiments. Simulation results show that the introducing of fluid materials with proper relative permittivity does improve the heating uniformity and safety. Fluid materials with the larger real part of relative permittivity could obviously lower the maximum modulus value of the electric field for about 23 times, and will lower the coefficient of variation (COV) in general, although in small ranges that it has fluctuated. Fluid materials with the larger imaginary part of relative permittivity, in a range from 0 to 0.3, can make a more efficient heating and it could lower the maximum modulus value of the electric field by 34 to 55% on the whole studied range. However, the larger imaginary part of relative permittivity will cause worse heating uniformity as the COV rises by 246.9% in the same process. The computed results are discussed and methods to reach uniform and safe heating through introducing fluid materials with proper relative permittivity are proposed.

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Section: Geometrymentioning

confidence: 99%

Impact of Filled Materials on the Heating Uniformity and Safety of Microwave Heating Solid Stack Materials

et al. 2018

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“…With the advent of flow-through single-mode cavities, the heating rate improved and different designs were studied (Binner et al, 2013;Kumar et al, 2008;Sabliov, Boldor, Coronel, & Sanders, 2008;Salvi, Boldor, Aita, & Sabliov, 2011;Steed et al, 2008). Compact cylindrical cavities with coiled tubes were also tested (Matsuzawa, Togashi, & Hasebe, 2011;Tuta & Palazoglu, 2017;Vrba, Jansen, & Tamnjong, 2009), as well as tubular systems with multiple microwave ports (Raaholt, Isaksson, Hamberg, Fhager, & Hamnerius, 2016;Stratakos, Delgado-Pando, Linton, Patterson, & Koidis, 2016).…”

Section: Introductionmentioning

confidence: 99%

Model food for microwave‐assisted pasteurization of fruit juices and nectars at 915 and 2,450 MHz

Sobreiro

Sato

Gut

2018

J Food Process Engineering

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A model food based on aqueous solutions of sucrose and sodium chloride is proposed for studying the microwave‐assisted pasteurization of fruit juices and nectars. Relative electrical permittivity, dielectric loss factor, and electrical conductivity of solutions with sucrose up to 40.0 g/100 mL and sodium chloride up to 1.6 g/100 mL were experimentally determined and successfully correlated with concentrations and temperature (from 10 to 90 °C). By adjusting the concentrations of the solutes, it was possible to satisfactorily match the dielectric behavior of 12 examples of products. Thermophysical and flow properties of the model food (density, specific heat, thermal conductivity, and viscosity) could be estimated from literature data, which is useful for process simulation. Practical applications Continuous flow microwave heating is an emerging technology with a potential to be used in the thermal processing of liquid foods. Model foods are important to study heating patterns, test prototypes, test process control, or tuning strategies, to be used as sterilization solutions, or carrier of chemical, biological, or enzymatic markers. The model food proposed here can match dielectric properties of fruit juices or nectars.

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“…Continuous flow microwave heating has a potential to replace conventional heat exchangers in the food industry, given its advantages such as fast volumetric heating, lower tube surface temperature and cleaner work environment without the need of steam and boiler (Ahmed & Ramaswamy, 2007). This emerging technology is on the verge of industrial application with some pilot scale systems available worldwide (Arjmandi et al, 2017;Marszałek, Mitek, & Skąpska, 2015; Raaholt, Isaksson, Hamberg, Fhager, & Hamnerius, 2016;Resurreccion et al, 2013;Stratakos, Delgado-Pando, Linton, Patterson, & Koidis, 2016;Tang, 2015;Tuta & Palazo glu, 2017). However, its adoption requires prior assessments in terms of process design, scaling-up, economic feasibility, and product quality improvements (Awuah, Ramaswamy, & Economides, 2007;Banga, Balsa-Canto, Moles, & Alonso, 2003;Salazar-González, San Martín-González, López-Malo, & Sosa-Morales, 2012).…”

Section: Introductionmentioning

confidence: 99%

“…Earlier studies on continuous flow microwave-assisted pasteurization of liquid foods were based on adapted household microwave ovens (Nikdel, Chen, Parish, MacKellar, & Friedrich, 1993;Tajchakavit & Ramaswamy, 1995). The design of different microwave cavities has been under investigation, such as multimode rectangular (Gentry & Roberts, 2005), single mode cylindrical (Binner et al, 2013;Kumar et al 2008;Salvi, Boldor, Aita, & Sabliov, 2011), multimode cylindrical (Matsuzawa, Togashi, & Hasebe, 2011;Vrba, Jansen, & Tamnjong, 2009;Tuta & Palazo glu, 2017) or tubular systems with various microwave ports (Raaholt et al, 2016;Stratakos et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

“…Earlier studies on continuous flow microwave‐assisted pasteurization of liquid foods were based on adapted household microwave ovens (Nikdel, Chen, Parish, MacKellar, & Friedrich, ; Tajchakavit & Ramaswamy, ). The design of different microwave cavities has been under investigation, such as multimode rectangular (Gentry & Roberts, ), single mode cylindrical (Binner et al, ; Kumar et al ; Salvi, Boldor, Aita, & Sabliov, ), multimode cylindrical (Matsuzawa, Togashi, & Hasebe, ; Vrba, Jansen, & Tamnjong, ; Tuta & Palazoğlu, ) or tubular systems with various microwave ports (Raaholt et al, ; Stratakos et al, ). Studies have also been conducted regarding microbial and enzyme inactivation (Benlloch‐Tinoco, Pina‐Pérez, Martínez‐Navarrete, & Rodrigo, ; Cañumir, Celis, de Bruijn, & Vidal, ; Matsui, Gut, de Oliveira, & Tadini, ; Siguemoto, Gut, Martinez, & Rodrigo, ; Siguemoto, Pereira, & Gut, ; Tajchakavit, Ramaswamy, & Fustier, ; Xu et al, ) as well as preservation of quality and nutritional characteristics (Arjmandi et al, ; Bornhorst, Liu, Tang, Sablani, & Barbosa‐Cánovas, ; Fratianni, Cinquanta, & Panfili, ; Igual, García‐Martínez, Camacho, & Martínez‐Navarrete, ).…”

Section: Introductionmentioning

confidence: 99%

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Evaluation and modeling of a microwave‐assisted unit for continuous flow pasteurization of liquid foods: Residence time distribution, time–temperature history, and integrated lethality

Siguemoto

Pires

Funcia

et al. 2018

J Food Process Engineering

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Focused microwave heaters have potential to replace heat exchangers in continuous flow pasteurization of liquid foods. The objective of this work was to evaluate a pilot scale unit used for microwave assisted pasteurization of low viscosity liquid foods in order to model the heat transfer and residence time distribution (RTD) to, subsequently, predict the average time–temperature history and estimate the level of heat treatment of the process and contributions from each step. RTD data using water showed that it was possible to assume plug‐flow (negligible axial dispersion). Heat transfer experiments using water provided heat transfer coefficients as functions of Reynolds number and microwave power absorption. Mathematical modeling was used to determine the temperature distribution along the product path, and results were validated. Integrated lethality calculated from the time–temperature histories (pasteurization at 70 °C) revealed the contribution of each process step. Results showed that focused microwave heating provided the necessary temperature increase in a very short time, with a lethality contribution of only 0.7% as compared to 59–68% when using only the conventional heat exchanger. The methods described can be useful for the evaluation of other continuous flow pasteurization units processing low viscosity liquid foods. Practical applications The mathematical modeling approach and experimental methods presented herein can be used for the analysis of continuous flow pasteurization systems based on tubular heat exchangers and with low axial dispersion (plug flow), providing temperature and lethality distribution along the product path, showing the contribution from each section on inactivation. Specifically for the equipment used in the experiments, the obtained heat transfer and resident time distribution parameters will be useful to study the processing of low viscosity foods such as fruit juices and nectars on ongoing works from the group.

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Continuous tubular microwave heating of homogeneous foods: evaluation of heating uniformity

Cited by 15 publications

References 4 publications

Impact of Filled Materials on the Heating Uniformity and Safety of Microwave Heating Solid Stack Materials

Impact of Filled Materials on the Heating Uniformity and Safety of Microwave Heating Solid Stack Materials

Model food for microwave‐assisted pasteurization of fruit juices and nectars at 915 and 2,450 MHz

Evaluation and modeling of a microwave‐assisted unit for continuous flow pasteurization of liquid foods: Residence time distribution, time–temperature history, and integrated lethality

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