1,720,966 research outputs found
Effects of geometry and orientation of food products on heating uniformity during radio frequency heating
No full textIn radio frequency (RF) assisted heat treatment of food products, heating behavior depends on the composition and geometry of a product. In this study, the effect of salt added to a food simulant on its dielectric properties and penetration depth (dp) were determined across a temperature range from 5 to 80 °C. Three primitive geometries (cube, cylinder and sphere) of a food simulant having a standardised volume (3.98 × 10−4 m3) heated in a custom-built 50 Ω RF system to investigate the impact of sample geometry and orientation on power absorption and heating uniformity. Experimental results revealed vertical oriented cylinder samples followed by cubes showed better temperature uniformity. The temperature at the core of food simulant samples after 6 min RF heating using 500 W power was 44 ± 7.1 °C, 45.3 ± 0.9 °C and 52.9 ± 3.5 °C in cube, cylinder, and sphere sample, respectively. However, the sphere sample was characterized by having the hottest spot at the bottom section. RF power level also played a significant role in heating uniformity with lower power input resulting not only in a slower heating rate but also in less uniform temperature distribution. This study provided a potential insight on the use of food simulants for evaluating RF heating design and performances
Update on emerging technologies including novel applications: radio frequency
No full textRadio frequency (RF) heating is known as capacitive dielectric heating and has been recognized as an innovative emerging technology for food processing. The lower power generation within the product due to the lower frequency and the larger penetration depth of the RF energy due to the longer wavelength make it suitable for bulk size product processing, especially for the industrial scale. With the increased use of RF processing and literature studies, the objectives of this chapter were: -to introduce a review on the industrial systems (self-oscillator RF generators and 50 Ω RF amplifiers) with various electrode configurations (through field electrodes, fringe field or stray field electrodes and staggered through field electrodes); -to review the literature for RF applications on the disinfestation of agricultural products, pasteurization of food products and food powders, and tempering and thawing applications of frozen food commodities; and -to present a computational background on the mathematical modeling approaches for process innovation, design and optimization. For the given objectives, a detailed analysis of the literature was presented
Computer simulation of radio-frequency heating applied to block-shaped foods: Analysis on the role of geometrical parameters
No full textDuring radio frequency (RF) processing, geometrical factors such as distance between electrodes and projection of top electrode on the samples' exposed surface area (area that electric field passes through the sample) have a certain effect on power absorption, temperature distribution, heating rates and heating uniformity in the samples. Knowing the role played by these factors can be helpful for further studies in optimization of design parameters of an RF heating process. Therefore, to evaluate effect due to distance between electrodes and projection area during RF heating process, samples of same volume but exhibiting different projection areas were used to determine the variability in their power absorption, temperature change and heating rates. RF electrodes in this system were positioned with a fixed gap between samples' top-bottom surfaces and the electrodes and, case by case, at different distance between electrodes. The results indicated that both parameters have strong effect on power absorption, temperature distribution, heating rates and heating uniformity in the samples, which is further amplified when it is combined with the change of dielectric properties with temperature. In the investigated range, wider projection area and shorter distance between electrodes led to faster heating, in terms of average temperature, but less uniform temperature distribution, at least in the early stage of the RF heating process, before the changes in dielectric properties of the heated load started modifying the trend of the loss tangent and penetration depth. The results of this study are expected to be used in planning geometrical configuration and design parameters of RF systems and sample dimensions for further optimization studies. © 2016 The Institution of Chemical Engineers
Computational study for natural convection effects on temperature during batch and continuous industrial scale radio frequency tempering/thawing processes
No full textRadio frequency (RF) processing have been used for tempering and thawing. There have been significant experimental and mathematical model based studies for this process especially in the last two decades. The modeling studies applied the convective boundary condition with effective heat transfer coefficient and constant medium temperature in through field flat plate RF systems. The objective of this study was first to develop a mathematical model for conjugate heat transfer (natural convection) in a staggered through field electrode RF system and to use this model for natural convection effects in industrial scale processes. For this purpose, the developed comprehensive mathematical model was experimentally validated using the data from frozen tuna samples. The air temperature variation was also used for validation. Then, the developed model was used in industrial scale process simulations with the presence of natural convection. The industrially preferred flat plate systems were used in this part to determine the temperature and electric field evolutions. The results demonstrated the significant effect of the natural convection on sample surface temperature distribution and temperature change of air within the cavity. The evolved natural convection resulted in the variation of the heat transfer coefficient along the sample surfaces with significant changes in temperature. Based on these results, it might be concluded that the effect of air temperature change within the cavity during an RF processes should also be controlled and considered for industrial system design and process optimization
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Computational modeling of axial rotation for the evolution of temperature in horizontal toroidal cans under pasteurization conditions
No full textAxial rotation mechanism has been widely used during thermal processing of liquid containing cans. Besides this can geometry modification might be an innovative approach to increase heat transfer rates. Therefore, the objective of this study was to determine temperature distribution and effect of rotation rate in axially rotating toroidal cans. For this purpose, experimental and numerical modeling studies were carried out. In the experimental studies, toroidal cans including distilled water were processed in hot water, and temperature data were used for computational model validation and mesh independency. Then, the second set of simulations were conducted to determine the rotational effects on temperature evolution. Effects of gravitational buoyancy, centrifugal and Coriolis forces were determined, and Coriolis forces increased up to 4 times with increased rotation rates (20–160 rpm). With this aspect, process time for 70 °C increase was reduced by ≈40 and 33.3% at 80 and 160 rpm compared to conventinal cylindrical cans. This study is an introduction to modify can geometry and process parameters to reduce quality losses and decrease energy use. However, industrial practice has still significant challenge for manufacturing and using in the process line
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