The Experts below are selected from a list of 3642 Experts worldwide ranked by ideXlab platform
Luisa F Cabeza - One of the best experts on this subject based on the ideXlab platform.
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control strategies for defrost and evaporator fans operation in walk in Freezers
International Journal of Refrigeration-revue Internationale Du Froid, 2018Co-Authors: Jose Miguel Maldonado, Alvaro De Gracia, Gabriel Zsembinszki, Pere Moreno, Xavie Albets, Miguel A Gonzalez, Luisa F CabezaAbstract:Heat removal is the most extended method for food preservation in food manufacturing industry by lowering food temperatures to stop microorganisms growing, which might spoil the product and could cause toxicity. Therefore, walk-in Freezers are used for that purpose consuming a relevant part of the energy on service sector. The compression refrigeration system of the walk-in Freezers can be blocked by the frost accumulated on the evaporator. For that reason a defrost process, which requires an important part of the energy consumption, has to be launched from time to time. In this paper, the schedule which manages the defrost process is investigated to limit its activation only when it is necessary. Moreover, different fan operation strategies were tested regarding the energy efficiency of the whole refrigeration system. This study has provided a system control strategy both for defrost and fans operation, depending on the frost built up on the evaporator. The control improves the energy performance of the whole refrigeration system.
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active phase change material package for thermal protection of ice cream containers
International Journal of Refrigeration-revue Internationale Du Froid, 2013Co-Authors: Alvaro De Gracia, Luisa F CabezaAbstract:Abstract Temperature sensitive products transportation and storage are global issues because of the new lifestyle of the people. Here, the enhancement of the ice cream storage conditions when it is placed outside the freezer is studied. In commercial applications like in restaurants, the period that the ice cream stays outside the freezer is much higher than for example in households, and therefore the quality of the ice cream decreases. The aim of this paper is to design and to test a phase change material (PCM) package for commercial ice cream containers. A mathematical model was validated with experimental data and following a parametrical study of the design process was done. The experimental results demonstrated that the use of the PCM package is beneficial for ice cream quality when it is placed out of the freezer.
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Improving thermal performance of Freezers using phase change materials
International Journal of Refrigeration, 2012Co-Authors: Eduard Oró, Mohammed Mehdi Farid, Laia Miro, Luisa F CabezaAbstract:Food transport and storage at low temperatures is a matter worldwide due to changes of the dietary habits and the increasing of the population. The issue of improving food storage applies at different applications such as commercial Freezers or refrigerated trucks. The aim of this work is to improve the thermal performance of commercial Freezers using phase change materials (PCMs) under door openings and electrical power failure. A commercial PCM was selected (Climsel-18) with a melting temperature of -18 °C, which is contained in 10mmthick stainless steel panels placed at different locations in the freezer. During 3 h of electrical power failure, the use of PCM maintained the freezer temperature 4-6°C lower and that of the frozen products remains at acceptable levels for much longer time. With frequent door openings the benefit of the PCM is evident when the temperature of the cabinet is near the melting temperature of the PCM
Simon J. G. Lewis - One of the best experts on this subject based on the ideXlab platform.
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Alterations in white matter network topology contribute to freezing of gait in Parkinson’s disease
Journal of Neurology, 2018Co-Authors: Julie M. Hall, James M. Shine, Kaylena A. Ehgoetz Martens, Moran Gilat, Kathryn M. Broadhouse, Jennifer Y. Y. Szeto, Courtney C. Walton, Ahmed A. Moustafa, Simon J. G. LewisAbstract:Freezing of gait (FOG) is a common symptom in advanced Parkinson’s disease (PD). Despite current advances, the neural mechanisms underpinning this disturbance remain poorly understood. To this end, we investigated the structural organisation of the white matter connectome in PD Freezers and PD non-Freezers. We hypothesized that Freezers would show an altered network architecture, which could hinder the effective information processing that characterizes the disorder. Twenty-six Freezers and twenty-four well-matched non-Freezers were included in this study. Using diffusion tensor imaging, we investigated the modularity and integration of the regional connectome by calculating the module degree z score and the participation coefficient, respectively. Compared to non-Freezers, Freezers demonstrated lower participation coefficients in the right caudate, thalamus, and hippocampus, as well as within superior frontal and parietal cortical regions. Importantly, several of these nodes were found within the brain’s ‘rich club’. Furthermore, group differences in module degree z scores within cortical frontal and sensory processing areas were found. Together, our results suggest that changes in the structural network topology contribute to the manifestation of FOG in PD, specifically due to a lack of structural integration between key information processing hubs of the brain.
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Alterations in white matter network topology contribute to freezing of gait in Parkinson's disease
'Springer Science and Business Media LLC', 2018Co-Authors: Hall, Julie M, Jennifer Y. Y. Szeto, Shine, James M, Martens, Kaylena A Ehgoetz, Gila Mora, Oadhouse, Kathry M, Walton, Courtney C, Moustafa, Ahmed A, Simon J. G. LewisAbstract:Freezing of gait (FOG) is a common symptom in advanced Parkinson's disease (PD). Despite current advances, the neural mechanisms underpinning this disturbance remain poorly understood. To this end, we investigated the structural organisation of the white matter connectome in PD Freezers and PD non-Freezers. We hypothesized that Freezers would show an altered network architecture, which could hinder the effective information processing that characterizes the disorder. Twenty-six Freezers and twenty-four well-matched non-Freezers were included in this study. Using diffusion tensor imaging, we investigated the modularity and integration of the regional connectome by calculating the module degree z score and the participation coefficient, respectively. Compared to non-Freezers, Freezers demonstrated lower participation coefficients in the right caudate, thalamus, and hippocampus, as well as within superior frontal and parietal cortical regions. Importantly, several of these nodes were found within the brain's 'rich club'. Furthermore, group differences in module degree z scores within cortical frontal and sensory processing areas were found. Together, our results suggest that changes in the structural network topology contribute to the manifestation of FOG in PD, specifically due to a lack of structural integration between key information processing hubs of the brain.status: publishe
Vittal Prabhu - One of the best experts on this subject based on the ideXlab platform.
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mathematical modeling and simulation of cryogenic tunnel Freezers
Journal of Food Engineering, 2007Co-Authors: Nazrul I Shaikh, Vittal PrabhuAbstract:Modern food industries employ either mechanical or cryogenic methods for freezing products. A wealth of literature is available on design, implementation and optimization of mechanical freezing systems in the food industry. Cryogenic freezing is a relatively new technology for the food industry and there is a need for developing mathematical models to characterize this technology. Our focus here is to develop analytical and numerical models for describing the dynamics of the cryogenic freezing tunnel system. Two models for sizing and rating of the tunnel freezer have been developed. A composite model combining the freezer and the food freezing dynamics using a two step finite difference methods has been proposed for sizing the tunnel freezer. The error in prediction the temperature profile of the food material and the tunnel freezer is reduced to less than 5%, consequently reducing cryogen consumption by up to 30%. The proposed model can be useful for minimizing the operating costs of tunnel Freezers by deriving suitable control strategies and provide insights for improvements in their design. A dynamic tank model has been developed for rating the tunnel freezer. The tank model guarantees stability of the system, is accurate, and can be readily extended to complex designs and applications where there are multiple zones with nozzles and fans.
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model predictive controller for cryogenic tunnel Freezers
Journal of Food Engineering, 2007Co-Authors: Nazrul I Shaikh, Vittal PrabhuAbstract:Abstract Cryogenic freezing is an upcoming food processing technology that is gaining popularity because of the lower setup costs and improved food quality when compared to mechanical freezing. However, high operating costs are its major deterrent: the cost of cryogenic freezing is almost eight times that of its mechanical counterpart, and this is mainly attributed to the cost of the cryogen that is used. When the variability in the input heat load and/or the product characteristics is high, the economics become highly unfavorable due to either over or under freezing, which in turn imply either excess use of cryogen or reduced throughput. There is therefore a need for a good control mechanism that will minimize the losses due to over or under freezing while maintaining the required throughput. Current industrial Freezers use programmable logic controllers (PLCs), which have conservative set-points and consequently significant operational costs. This paper proposes and tests the design of a model predictive control (MPC) algorithm with a zero absolute error (ZAE) minimizer that addresses these issues simultaneously. The controller combines features of feedback–feedforward control to adjust cryogen consumption and throughput rate of the tunnel Freezers to minimize the deviation of the end temperature of the food product from the desired set point temperature at the outlet. The stability, accuracy and robustness of the proposed method are tested on a simulation model. The controller guarantees stability, and for an input variance of 10%, the average deviation of the temperature from the set point was found to be less that 0.25%.
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vision system for model based control of cryogenic tunnel Freezers
Computers in Industry, 2005Co-Authors: Nazrul I Shaikh, Vittal PrabhuAbstract:This paper presents a novel solution, using a vision-sensor, to a challenging control problem in cryogenic food freezing industry. This industrial application is characterized by significant variation in input food products because cryogenics-freezing technology with its inherent process flexibility is typically used in low volume/high mix applications. Current industrial controllers use PLCs for regulating the belt speed of the tunnel, which leads to conservative set-points and consequently significant operational cost and frequent over-freezing. Servo control of the process is difficult because of the complicated non-linear dynamics of cryogenic freezing caused by phase-change, and thermal dynamics between the frozen products and the tunnel. The solution presented in this paper uses a vision-sensor to estimate the shape, size, and heat load of food products that will enter the freezing tunnel. An analysis of the sensor location and its impact on disturbance feed-forward control is also presented. Efficacies of these developments are verified in an industrial case study using a commodity webcam for capturing and processing two-dimensional streaming images, and integrating the processed information with an industrial control system using model-predictive control architecture. The proposed solution is especially attractive for the food industry because of the low-cost and non-contact features of webcam, operational cost savings through reduced consumption of cryogen, and improved quality through reduction in variation of temperature of the frozen products.
Jianlin Yu - One of the best experts on this subject based on the ideXlab platform.
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theoretical investigation on the performance of an ejector enhanced refrigeration cycle using hydrocarbon mixture r290 r600a
Applied Thermal Engineering, 2020Co-Authors: Qi Chen, Yunho Hwang, Jianlin YuAbstract:Abstract This paper proposes an ejector enhanced vapor compression refrigeration cycle (EVRC) using zeotropic hydrocarbon mixture R290/R600a for applications in domestic refrigerator/Freezers. An internal heat exchanger and a phase separator are utilized in EVRC to improve the system performance. An ejector is adopted to further enhance the cycle performance. The energy and exergy analysis of EVRC are performed to evaluate the system operating characteristics and compared with the Lorenz-Meutzer vapor compression refrigeration cycle (LVRC) and the traditional vapor compression refrigeration cycle (TVRC). The results indicate that EVRC can provide the uppermost advantages over both TVRC and LVRC under the operating conditions. Compared with TVRC, the EVRC can significantly improve the coefficient of performance, volumetric refrigeration capacity and exergy efficiency by 13.5%, 19.3%, and 13.4%, respectively. The performance characteristics of the proposed cycle demonstrate its potential advantages for application in domestic refrigerator/Freezers.
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performance evaluation of a modified refrigeration cycle with parallel compression for refrigerator freezer applications
Energy, 2019Co-Authors: Zhongcheng Fang, Jianlin YuAbstract:Abstract This paper proposes a modified refrigeration cycle (MRC) with zeotropic mixture R290/R600a for refrigerator-freezer applications. In the MRC, the use of two parallel compressors enables the two evaporators to be operated at two proper evaporation temperatures, which reduces the irreversibility of evaporator heat transfer processes. Noted that a subcooler is installed between the two loops for improving the system performance. Moreover, the MRC applies a phase separator to ensure more low-boiling point refrigerant to go to the freezer evaporator for increasing the freezer evaporation pressure. Energy and exergy performances of MRC are investigated based on a thermodynamic model. The simulation results indicate that compared with the conventional refrigeration cycle (CRC), the COP and exergy efficiency of MRC obtain the same improvement of 30.4% at a fixed condensation temperature of 35°C. In addition, from the viewpoint of exergy analysis, the high priority in need of improvement for the MRC is ordered as the compressors, condensers, expansion valves, two evaporators, subcooler and internal heat exchanger. Generally, applying the MRC could be an effective and practical method to enhance refrigerator-freezer energy efficiency.
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energy and exergy analysis of zeotropic mixture r290 r600a vapor compression refrigeration cycle with separation condensation
International Journal of Refrigeration-revue Internationale Du Froid, 2015Co-Authors: Jianlin YuAbstract:Abstract This paper proposes a modified vapor-compression refrigeration cycle (MVRC) system operating with the zeotropic mixture R290/R600a for domestic refrigerator-Freezers. In the MVRC system, a phase separator is introduced to enhance the overall system performance. A theoretical energy and exergy analysis on the performance of the MVRC is carried out by using the developed mathematical model, and then compared with that of the traditional vapor-compression refrigeration cycle (TVRC) operating with the refrigerant R600a and the zeotropic mixture R290/R600a, respectively. According to the simulation results of these two cycles, the MVRC can give the most excellent performances in the COP (coefficient of performance), the volumetric refrigeration capacity, the total exergy destruction and the exergetic efficiency under the same given operating conditions. Therefore, the performance characteristics of the MVRC may show its promise in domestic refrigerator-freezer applications.
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Comparative studies of ejector-expansion vapor compression refrigeration cycles for applications in domestic refrigerator-Freezers
Energy, 2014Co-Authors: Xiao Wang, Jianlin Yu, Mengliu Zhou, Xiaolong LvAbstract:EVRCs (ejector-expansion vapor-compression refrigeration cycles) applied in domestic refrigerator-Freezers have been concerned duo to their potentials of improving cycle performance. However, the previously presented EVRCs with various cycle configurations are still limited to favorable performance improvement. Therefore, further development is required to promote the use of EVRCs. This paper summarizes the existing EVRCs for promising applications in domestic refrigerator-Freezers. Considering the limited capacity of the existing EVRCs to enhance cycle performance, we further present a novel MEVRC (modified EVRC), in which the use of the two-phase ejector to more efficiently recover the expansion work would significantly enhance the overall system performance. A mathematical model is developed to carry out comparative simulation studies between different EVRCs. According to the results of the simulation for the EVRCs using the refrigerant R600a, the MEVRC can reach a highest pressure lift ratio of the ejector and give most excellent performance improvements in the COP (coefficient of performance) and the volumetric refrigeration capacity compared with the other EVRCs. Therefore, the potential use of MEVRC deserves further experimental validation. The present study aims to provide a deep insight into EVRCs and contribute to the development of ejector expansion refrigeration technologies in domestic refrigeration.
Nazrul I Shaikh - One of the best experts on this subject based on the ideXlab platform.
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mathematical modeling and simulation of cryogenic tunnel Freezers
Journal of Food Engineering, 2007Co-Authors: Nazrul I Shaikh, Vittal PrabhuAbstract:Modern food industries employ either mechanical or cryogenic methods for freezing products. A wealth of literature is available on design, implementation and optimization of mechanical freezing systems in the food industry. Cryogenic freezing is a relatively new technology for the food industry and there is a need for developing mathematical models to characterize this technology. Our focus here is to develop analytical and numerical models for describing the dynamics of the cryogenic freezing tunnel system. Two models for sizing and rating of the tunnel freezer have been developed. A composite model combining the freezer and the food freezing dynamics using a two step finite difference methods has been proposed for sizing the tunnel freezer. The error in prediction the temperature profile of the food material and the tunnel freezer is reduced to less than 5%, consequently reducing cryogen consumption by up to 30%. The proposed model can be useful for minimizing the operating costs of tunnel Freezers by deriving suitable control strategies and provide insights for improvements in their design. A dynamic tank model has been developed for rating the tunnel freezer. The tank model guarantees stability of the system, is accurate, and can be readily extended to complex designs and applications where there are multiple zones with nozzles and fans.
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model predictive controller for cryogenic tunnel Freezers
Journal of Food Engineering, 2007Co-Authors: Nazrul I Shaikh, Vittal PrabhuAbstract:Abstract Cryogenic freezing is an upcoming food processing technology that is gaining popularity because of the lower setup costs and improved food quality when compared to mechanical freezing. However, high operating costs are its major deterrent: the cost of cryogenic freezing is almost eight times that of its mechanical counterpart, and this is mainly attributed to the cost of the cryogen that is used. When the variability in the input heat load and/or the product characteristics is high, the economics become highly unfavorable due to either over or under freezing, which in turn imply either excess use of cryogen or reduced throughput. There is therefore a need for a good control mechanism that will minimize the losses due to over or under freezing while maintaining the required throughput. Current industrial Freezers use programmable logic controllers (PLCs), which have conservative set-points and consequently significant operational costs. This paper proposes and tests the design of a model predictive control (MPC) algorithm with a zero absolute error (ZAE) minimizer that addresses these issues simultaneously. The controller combines features of feedback–feedforward control to adjust cryogen consumption and throughput rate of the tunnel Freezers to minimize the deviation of the end temperature of the food product from the desired set point temperature at the outlet. The stability, accuracy and robustness of the proposed method are tested on a simulation model. The controller guarantees stability, and for an input variance of 10%, the average deviation of the temperature from the set point was found to be less that 0.25%.
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vision system for model based control of cryogenic tunnel Freezers
Computers in Industry, 2005Co-Authors: Nazrul I Shaikh, Vittal PrabhuAbstract:This paper presents a novel solution, using a vision-sensor, to a challenging control problem in cryogenic food freezing industry. This industrial application is characterized by significant variation in input food products because cryogenics-freezing technology with its inherent process flexibility is typically used in low volume/high mix applications. Current industrial controllers use PLCs for regulating the belt speed of the tunnel, which leads to conservative set-points and consequently significant operational cost and frequent over-freezing. Servo control of the process is difficult because of the complicated non-linear dynamics of cryogenic freezing caused by phase-change, and thermal dynamics between the frozen products and the tunnel. The solution presented in this paper uses a vision-sensor to estimate the shape, size, and heat load of food products that will enter the freezing tunnel. An analysis of the sensor location and its impact on disturbance feed-forward control is also presented. Efficacies of these developments are verified in an industrial case study using a commodity webcam for capturing and processing two-dimensional streaming images, and integrating the processed information with an industrial control system using model-predictive control architecture. The proposed solution is especially attractive for the food industry because of the low-cost and non-contact features of webcam, operational cost savings through reduced consumption of cryogen, and improved quality through reduction in variation of temperature of the frozen products.
