Abstract
A prototype device based on a modified domestic microwave oven for liquid food products pasteurization is presented. This novel design has a coiling glass pipe adapted inside a microwave cavity to allow liquid continuous flow, in which several temperature optical sensors based on Fiber Bragg Grating were installed to measure, by means of contact, the circulating liquid temperature in the pipe, while the oven is on, to obtain the profile temperature as a function of time at different pipe points. The temperatures at liquid input and output were also measured with thermocouples. This device was tested to establish how well it may perform using different standardized liquids with well-known physicochemical and dielectric properties, such as water, water with dissolved sugars, water with dissolved salts, and water with dissolved sugars and salts. It could be observed that the maximum temperature reached was 90 °C for distilled water, 80 °C for water with dissolved salts, 60 °C for water with dissolved sugars and 80 °C for water with dissolved sugars and salts, showing that these data were in agreement with previous results in the literature. This type of device would be potentially useful to establish the device’s efficiency in terms of retention time, energy consumption, and volume of processed liquid, thus, broadening the use of this microwave heating technology with several types of liquid substances.
Highlights
Microwaves offer several advantages in thermal food processes when compared to conventional heating methods, due to the volumetric heating resulting in processing time reduction, enhancing quality parameters such as the nutritional value and organoleptic properties of processed products [1,2]
This paper presents two sections: materials and methods in which modifications on the microwave and glass pipe design, temperature monitoring, and validation system are described, followed by a results section in which the device assembly and experimental measurement on the modified microwave oven are presented
This was provided by a liquid container (A), from which the liquid was pumped through a control flow system (B) to change the flow and holdback of liquid going round into the coiling glass, in which FBG sensors (D) are located, inside a modified microwave oven (C)
Summary
Microwaves offer several advantages in thermal food processes when compared to conventional heating methods, due to the volumetric heating resulting in processing time reduction, enhancing quality parameters such as the nutritional value and organoleptic properties of processed products [1,2]. Microwave heating is supported by the ability of any dielectric material to absorb electromagnetic energy and convert a portion of it into thermal energy [3,4,5]. The relative electrical permittivity represents the material ability to polarize and store electric energy in response to an applied electric field, while the dielectric loss factor is associated to energy dissipation as heat [3,4,5]. The more common uses of modified microwave ovens are drying processes [8,9], extraction processes [7,10], pyrolysis processes, [11,12] pasteurization processes, [13,14,15] and others
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