Drying of a Low Porosity Product (Carrot) as Affected by Power Ultrasound (original) (raw)
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Drying Technology, 2011
Power ultrasound is considered to be a novel and promising technology with which to improve heat and mass transfer phenomena in drying processes. The aim of this work was to contribute to the knowledge of ultrasound application to air drying by addressing the influence of mass load density on the ultrasonically assisted air drying of carrot. Drying kinetics of carrot cubes were carried out (in triplicate) with or without power ultrasound application (75 W, 21.7 kHz) at 40 C, 1 m/s, and several mass load densities: 48, 60, 72, 84, 96, 108, and 120 kg/m 3 . The experimental results showed a significant (p < 0.05) influence of both factors, mass load density and power ultrasound application, on drying kinetics. As expected, the increase of mass load density did not affect the effective moisture diffusivity (D e , m 2 /s) but produced a reduction of the mass transfer coefficient (k, kg water/m 2 /s). This was explained by considering perturbations in the air flow through the drying chamber thus creating preferential pathways and, as a consequence, increasing external mass transfer resistance. On the other hand, it was found that the power ultrasound application increased the mass transfer coefficient and the effective moisture diffusivity regardless of the mass load density used. However, the influence of power ultrasound was not significant at the highest mass load densities tested (108 and 120 kg/m 3 ), which may be explained from the high ratio (acoustic energy/sample mass) found under those experimental conditions. Therefore, the application of ultrasound was considered as a useful technology with which to improve the convective drying, although its effects may be reduced at high mass load densities.
Convective Drying of Foodstuffs Under the Action of High Power Ultrasound
Proceedings of the 2013 International Congress on Ultrasonics, 2013
This work aims to show the most recent advances on the use of power ultrasound to improve the convective drying of foodstuffs. Drying tests have been performed using air-borne ultrasonic radiators working at 22 kHz and power capacities up to 150 W. The ultrasound efficiency for the improvement of the drying rate has been assessed considering the influence of different process variables.
Intensification of Low-Temperature Drying by Using Ultrasound
Drying Technology, 2012
The main aim of this work was to test the feasibility of power ultrasound to intensify low-temperature drying processes. For this purpose, the convective drying kinetics of carrot, eggplant, and apple cubes (side 10 mm) were carried out at atmospheric pressure, 2 m/s, À14 C, and 7% relative humidity with (acoustic power 19.5 kW/m 3 ) and without ultrasound application. Under the same experimental conditions, kinetics studies of ethanol removal from a solid matrix were also performed. Diffusion models were used to describe drying curves and identify kinetic parameters in order to evaluate and quantify the process intensification attained by ultrasound application.
Drying Technology, 2011
The aim of the present work was to ascertain the effect of ultrasonic waves on convective drying performance. In the tested range of process and operating conditions, it was proved that compared to a traditional convective process, ultrasounds enhanced the drying rate of cylindrical carrot samples. The obtained results suggested that ultrasound waves actually affected the external resistance to heat and mass transfer, thus improving the drying process mainly during the constant rate period. The heat transfer coefficient was estimated as a function of both air velocity and food diameter, thus allowing a quantitative comparison between traditional and acoustic-assisted convective drying.
Convective drying of lemon peel assisted by power ultrasound: influence of ultrasonic power applied
Proceedings of the Interntional Congress on Ultrasonics, 2007
The effects associated to the introduction of acoustic energy into a medium may influence food drying processes due to the reduction of mass transfer resistance. In particular, power ultrasound may be useful for drying heat sensitive materials since it permits drying to be increased without significantly heating the material. The main aim of this work was to determine the influence of power ultrasound on lemon peel drying, by evaluating the effect of the ultrasonic power applied. Lemon peel, a by-product of lemon processing, is a source of valuable heat sensitive products.
Physics Procedia, 2010
Power ultrasound application on convective drying of foodstuffs may be considered an emergent technology. This work deals with the influence of power ultrasound on drying of natural materials addressing the kinetic as well as the product's microstructure. Convective drying kinetics of orange peel slabs (thickness 5.95 ± 0.41 mm) were carried out at 40 °C and 1 m/s with (US) and without (AIR) power ultrasound application. A diffusion model considering external resistance to mass transfer was considered to describe drying kinetics. Fresh, US and AIR dried samples were analyzed using Cryo-SEM. Results showed that drying kinetics of orange peel were significantly improved by the application of power ultrasound. From modeling, it was observed a significant (p<0.05) increase in both mass transfer coefficient and effective moisture diffusivity. The effects on mass transfer properties were confirmed from microestructural observations. In the cuticle surface, the pores were obstructed by wax components scattering, which evidence the ultrasonic effects on the interfaces. The cells of the flavedo were compressed and large intercellular air spaces were generated in the albedo facilitating water transfer through it.
Textural properties of vegetables: a key parameter on ultrasonic assisted convective drying
The application of power ultrasound could constitute a way to improve traditional convective drying systems. There still exists a lack of knowledge on this technology in order to address industrial applications. The aim of this work was to identify the influence of the textural properties of different vegetable products on the ultrasonic assisted convective drying. For that purpose, experimental drying kinetics (40 ºC and 1 m/s) of different vegetable products (orange and lemon peel, carrot, potato and eggplant) were carried out applying different ultrasonic powers (0, 6, 12, 18, 25, 30 and 37 kW/m3). In every product, a similar diffusion model was used to identify an average effective diffusivity for the different ultrasonic powers. Product’s textural properties were assessed by Textural Profile Analysis (TPA). Linear relationships were established between the identified effective diffusivity and the applied ultrasonic power for the different products. The positive slopes of the li...
Influence of high-intensity ultrasound on drying kinetics in fixed beds of high porosity
2014
Hot air drying is an energy intensive process and can affect bioactive components. A common method of food drying is in a fixed bed. The application of high-intensity ultrasound could constitute a way of improving traditional convective drying systems. Therefore, the main aim of this work was to assess the influence of high-intensity ultrasound on transfer phenomena during the convective drying in a high-void bed of non-porous materials, like thyme leaves. For this purpose, drying kinetics of thyme leaves were carried out at 1, 2 and 3 m s À1 air velocity at different air temperatures (40, 50, 60, 70, and 80 ± 1.2°C), and different levels of acoustic power density (0, 6.2, 12.3, 18.5 kW m À3 ). To address the effect of US on the drying kinetics, a mathematical model was developed considering time varying boundary conditions for heat and mass transfer between the air and the product. Due to the physical characteristic of the material, the influence of the ultrasound power density applied on the internal resistance to the mass transfer was significantly lower than its influence of the external resistance; therefore process intensification is mainly linked to external resistance. Nevertheless, the influence of the application of ultrasound on transport phenomena was only observed at air temperatures and air velocities below 70°C and 3 m s À1 respectively.
Ultrasonic drying of foodstuff in a fluidized bed: Parametric study
Ultrasonics, 2006
The application of high power ultrasound for dehydration of porous materials may be very effective in processes in which heatsensitive materials such as foodstuffs have to be treated. In fact, high-intensity ultrasonic vibrations are capable of increasing heat and mass transfer processes in materials. The application of ultrasonic energy can be made alone or in combination with other kind of energy such as hot-air. In this case, ultrasound helps in reducing temperature or treatment time. The aim of this work is to study the effect of air flow rate, ultrasonic power and mass loading on hot-air drying assisted by a new power ultrasonic system. The drying chamber is an aluminium vibrating cylinder, which is able to create a high intensity ultrasonic field in the gas medium. To that purpose the chamber is driven at its centre by a power ultrasonic vibrator at 21.8 kHz. Drying kinetics of carrot cubes and lemon peel cylinders were carried out at 40°C for different air velocities, with and without ultrasound. The results show that the effect of ultrasound on drying rate is affected by air flow rate, ultrasonic power and mass loading. In fact, at high air velocities the acoustic field inside the chamber is disturbed and the effect of ultrasound on drying kinetics diminishes.