•Application of ultrasound in combined convective-microwave drying.•Airborn ultrasound as assist in drying of green pepper.•Analysis of drying effectiveness and the quality of drying ...products.•Mathematical modelling of convective-ultrasound drying of green pepper.•Improvement of drying effectiveness by heating, vibration and synergistic effects.
The effectiveness of hybrid drying based on convective drying with application of ultrasound and microwave enhancement is the main subject of the studies. The drying kinetics, energy consumption as well as the quality aspect of green pepper is analysed. It was shown that hybrid drying methods shorten significantly the drying time, reduce the energy consumption and affect positively the quality factors. Each of the analysed aspects depend on combination of the convective-ultrasound-microwave drying programs. Besides, based on the drying model elaborated earlier by one of the authors, the effects of ultrasound on convective drying assessed by such phenomena as “heating effect”, “vibration effect” and “synergistic effect” are presented.
In this paper the kinetics of osmotic dehydration of carrot and the influence of this pretreatment on the post-drying processes and the quality of obtained products are analysed. Osmotic dehydration ...was carried out in the aqueous fructose solution in two different ways: with and without ultrasound assistance. In the first part of the research, the kinetics of osmotic dehydration was analysed on the basis of osmotic dewatering rate, water loss and solid gain. Next, the effective time of dehydration was determined and in the second part of research samples were initially dehydrated for 30 min and dried. Five different procedures of drying were established on the grounds of convective method enhanced with microwave and infrared radiation. The influence of osmotic dehydration on the drying kinetics and final product quality was analysed. It was found that it did not influence the drying kinetics significantly but positively affected the final product quality. Negligible influence on the drying kinetics was attributed to solid uptake, which may block the pores, hindering heat and mass transfer. It was also concluded that the application of microwave and/or infrared radiation during convective drying significantly influenced the kinetics of the final stage of drying. A proper combination of aforementioned techniques of hybrid drying allows reducing the drying time. Differences between the particular dehydration methods and drying schedules were discussed.
This article is a contribution to modeling and analysis of the cohesion strength of saturated porous bodies during drying processes. The dependence of the drying-induced state of stress, the overall ...(reduced) stress, and the admissible stress on moisture content is discussed. The strength criterion is proposed stating that possible cracking of the material during drying takes place in regions where the reduced stress exceeds the critical admissible value for the given moisture content. Numerical calculations of the drying-induced stresses were carried out for a convectively dried kaolin cylinder, and the regions of possible material cracking within the cylinder were determined. This theoretical prediction of the possible cracking place in the material is consistent with the experimental data previously presented by the authors.
The aim of this article is to present the effect of external action of air-borne ultrasound (US) upon biological wet materials subjected to drying. The study allows to determine the drying ...effectiveness of such products like fruits and vegetables by convective drying with ultrasound enhancement. The vibration and heating effects induced by power ultrasound are considered. The mathematical model of drying is developed and validated experimentally using the data obtained from the experimental tests carried out on the hybrid dryer equipped with ultrasonic generator. The obtained results prove that the vibration effect induced by ultrasound has a great impact on the acceleration of mass transfer without significant elevation of product temperature, and thus on the drying efficiency with respect to energy utilization and the quality of dried products like fruits and vegetables.
•Application of ultrasound in combined convective-ultrasound drying.•Airborn ultrasound as assist in drying.•Analysis of drying effectiveness and deformation of drying products.•Mathematical modeling of convective-ultrasound drying.•Improvement of drying effectiveness by heating, vibration and synergistic effects.
A theory of propagation of stress waves in diluted and densified suspensions is developed to make the theoretical basis for analysis of ultrasonic waves through these media. The formulae for the ...phase velocity and the attenuation coefficient are determined as the function of wave frequency and the suspension structure parameter, which is the volume or mass fraction of the solid phase. These formulae can be use, after suitable calibration, for determination of the solid volume fraction in diluted suspensions, and the solid mass fraction or the water content in densified suspensions, that is, parameters that characterize the structure of a suspension. These structure parameters can be determined by measuring the transition time of ultrasonic wave through a given distance of suspension. The phase velocity dispersion curves and the attenuation coefficients determined theoretically and experimentally are plotted as a function of the volume fraction of the solid phase for dilute suspension, or the solid mass fraction for densified suspension.
Display omitted
•Sonication caused a remarkable improvement in drying kinetics and reduced energy consumption.•Ultrasound efficiency was dependent on drying temperature and ultrasound ...power.•Ultrasound application eventuated to the generation of sustainable and qualified dried seeds.
The objective of the present issue was to inquire the effect of ultrasound assisted convective drying on a thin layer of sunflower seeds. The process was carried out utilizing a hybrid chamber dryer, outfitted with an ultrasound generator with indirect transmission toward the material surface. Drying behavior was analyzed by drying time, effective moisture diffusivity (Deff), energy consumption (EC), water activity (aw), and total color change (ΔE). Independent variables of air temperature and ultrasound power determined the efficiency of sonication during drying. So that, ultrasound contributed to a noticeable increase in Deff up to 44.84%. Thereafter, a reasonable decrease was found in drying time, energy consumption, and total color change up to 40.85%, 32.95%, and 44.56%, respectively when collocating the variables of 35°C, 3.5m/s, and 2.4W/g. The optimum drying condition in the pure convective drying domain was improved from 50.74°C and 2m/s to the condition of 40.64°C, 2m/s, and 3.932W/g after sonication. In this point, significant reductions of 19.89% and 19.32% were observed in drying time and energy consumption. Optimization results confirmed that ultrasound intervention could provide an intensified and energy-efficient drying process, which generates sustainable and qualified dried seeds.
A new approach to fruit drying with the application of ultrasound to enhance convective and combined convective–microwave drying is presented. High-power ultrasound was used in the experimental ...studies, in which the acoustic energy significantly affected the drying of sensitive biological material like raspberries. The raspberries were first subjected to pure convective drying as a reference process and then to hybrid drying as a combination of convective, microwave and ultrasound drying methods. The combined hybrid processes significantly improved the drying kinetics as well as the energy utilization, however, not in each case given the acceptable product quality in comparison with the pure convective drying. The global model of drying was used to compare the theoretical drying kinetics with the experimental one. Moreover, the effectiveness of ultrasound-assisted convective drying was evaluated in terms of drying rate and such ultrasound phenomena as “heating effect”, “vibration effect” and “synergistic effect” were analyzed.
1. Research objectives
Product quality is a very important indicator that enables to assess the effectiveness of the drying process. For biological materials such as vegetables and fruits, that are characterized by instability and a delicate and sensitive internal structure to temperature, quality is a priority because it determines the functional value of these products. The traditional drying techniques, eg. convective drying, affect negatively on the final quality of dried biomaterials. Due to long exposure to a relatively high temperature and a high content of harmful oxygen in the drying agent, there is a change in the internal structure, deterioration of the sensory properties (color, aroma, texture) and changes in chemical composition (loss of bioactive components). One of the recommended modes to minimize these adverse changes is to carry out the drying process in non-stationary conditions. This method is based on the periodical changes in the process parameters such as temperature, humidity or flow rate. As a result, product quality is definitely better, at approximately the same drying time. Alternatively, drying may be carried out by hybrid method, providing the energy by a combination of several mechanisms, such as convection with microwave radiation, or with ultrasounds, which also leads to a significant improvement in quality of dried fruits and vegetables.
The purpose of this article is a deep analysis of the effect of variable hybrid drying conditions, ie. cyclic supply of microwave and ultrasound energy during convective drying on a variety of properties of dried biomaterials. The research assumes that if drying results in changes of the biological material properties, a modification of the process parameters should minimize its negative effects and gain better quality products. The authors believe that a proper and skillful combination of different drying techniques will develop an optimal and effective drying method of thermo-labile materials, which retains their high quality, with reduced time and lower power consumption. Therefore, it is necessary to optimize the convective drying with microwave and ultrasound enhancement, in order to select the best process parameters for the established objective functions.
2. Research project impact
The experimental results will contribute to the development of modern drying technologies of biological materials, characterized by, eg.:•much better and more controlled product quality (low level of processing),•much shorter process time resulting from the intensification of heat and mass processes due to additional sources of energy (microwaves and ultrasounds),•lower energy consumption resulting from the possibility of carrying out the drying process at much lower temperatures of the drying agent.
The expected results of the drying tests relate to the development of research activities in this field and to link a cooperation between science and industry. The effective transfer of new solutions in the field of chemical engineering and technology between science and industry is a hope of improving the quality of dried products, as well as the rational use of raw biomaterials (to prevent their losses from reaching about 50% of produced foods). The proposed drying method will also have a positive value for consumers and contribute to the reduction in influence of that branch of industry on the environment. In the consideration of the increasing demands of product quality, the need for better control of unit processes and minimization of its energy intensity, this new technique would be extremely competitive with currently used, expensive and environmentally damaging drying methods.
•Application of ultrasound in combined convective–microwave drying•Airborne ultrasound as assist in drying of raspberries (Rubus idaeus L.)•Analysis of drying effectiveness and the quality of drying products•Mathematical modeling of convective–ultrasound drying of raspberries•Improvement of drying effectiveness by heating, vibration and synergistic effects
•The impact of ultrasonic intervention on paddy drying in deep bed was studied.•Dying time, ER, broken kernel, niacin, TPC and energy of grain were analyzed.•Ultrasound application during paddy ...air-drying improved drying kinetics.•Advances were found in grain quality in ultrasound assisted air drying domain.
This study investigates the feasibility of achieving a modified rough rice air-drying with ultrasound intervention (US) set at 21 kHz frequency. The process was carried out using an ultrasound assisted convective dryer and analyzed in terms of drying time, energy consumption (EC), evaporation rate (ER), broken kernel (BK), water activity (aw), vitamin B3 (niacin), and total phenolic content (TPC). The lab-scale dryer was set to transmit energy at power levels of 30, 60, 90, 120, and 150 W in the air temperatures of 35, 40, 45, 50, and 55 °C and velocities of 0.2, 0.5, 0.8, 1.1, and 1.4 m/s for a thickness of 20 cm. The results showed that in-range drying parameters played a major role in response analysis, suggesting that ultrasound efficiency during convective drying heavily depends on the power, air temperature, and velocity levels. Ultrasound assistance significantly increased bed evaporation rate up to 38.93%. Subsequently, it caused a reasonable reduction in total drying time, EC, and BK percentage up to 27.92%, 25.98%, and 34.22%, respectively in the case of 35 °C, v = 0.8 m/s, and P = 90 W. Remarkable advances were attained in the ultrasound assisted drying domain in grain quality via acceptable decrease in niacin and TPC losses within shorter drying time. There was a significant linear trend in BK, niacin, and TPC values across the bed thickness, which all was increased by the ultrasound application. The highest nutrient retention and physical quality preservation belonged to the top layer, which was influenced by the ultrasound radiation by the highest degree.
► General equations of drying kinetics based on thermodynamics are developed. ► We calculate numerically the net energy consumption for a given drying process. ► The drying model considers shrinkage ...of dried fruits and vegetables. ► The propose model can be helpful for construction of energy efficient drying processes.
The aim of this paper is to develop a possibly general model of drying kinetics based on thermodynamics which can be used for different drying methods and shrinkable products such as fruits and vegetables. This model, developed on the thermodynamic basis, has well-defined coefficients and enables numerical computation for both the drying curves and temperatures of dried bodies as a function of time for the total drying process. Such a model should assure satisfactory adherence of the kinetic curves determined numerically to the experimental ones, and thus should provide the basis for numerical calculation of the net energy consumed for drying. Such well-formulated drying kinetics then offers the basis for the construction of energy-efficient drying processes due to their optimization with respect to drying time and energy consumption.
The main aim of this article is to find an optimal method for drying of biological materials. Eight schedules of combined (hybrid) drying processes were carried out experimentally with the use of ...different techniques like convective, microwave, and infrared radiation. The drying time and the quality of dried products were the points of interest. Beetroot (Beta vulgaris) was used as the experimental material. The kinetic curves of drying for the beetroot samples were determined and the dried samples were photographed for visual assessment of the sample quality. Based on the result, attempts were made to suggest suitable drying methods for the application of biological materials in terms of drying time and product quality.
PDF
