1,721,059 research outputs found
Performance analysis of a nitrogen-based Brayton cryocooler prototype
Full text linkWhen very low temperatures are needed for industrial applications, reverse Brayton cryocoolers can be adopted. This paper reports the results of an energy analysis in which the performance of a Brayton cryocooler prototype was studied. The prototype is innovative in both the cycle configuration and the pressure and temperature levels. Moreover, nitrogen, an eco-friendly gas that is safe for people, was used as the working fluid.
Simultaneous measurements of the pressure and temperature at the inlet and outlet of the main thermodynamic cycle components, nitrogen flow rate, and power consumption were taken during the experimental tests. The prototype was tested at design operating conditions (maximum and minimum pressure of 18.5 and 8 bar respectively, and minimum temperature of −120 °C), obtaining a cooling effect of 15.6 kW, a temperature reduction rate at the turbine outlet of 8 °C min−1, and a coefficient of performance of 0.29, which rises to 1.34 when including the waste heat (about 55 kW) that can be recovered at low temperatures (<100 °C). Also, a sensitivity analysis was carried out by testing the prototype at different maximum pressure and minimum temperature levels. The higher the maximum pressure, the higher the prototype performance is, and a minimum temperature of about −140 °C was reached. Our findings demonstrated that the tested prototype shows great promise for several industrial applications where low temperatures are required
Unsupervised detection of vineyards by 3D point-cloud UAV photogrammetry for precision agriculture
Full text linkAn effective management of precision viticulture processes relies on robust crop monitoring procedures and, in the near future, to autonomous machine for automatic site-specific crop managing. In this context, the exact detection of vineyards from 3D point-cloud maps, generated from unmanned aerial vehicles (UAV) multispectral imagery, will play a crucial role, e.g. both for achieve enhanced remotely sensed data and to manage path and operation of unmanned vehicles.
In this paper, an innovative unsupervised algorithm for vineyard detection and vine-rows features evaluation, based on 3D point-cloud maps processing, is presented. The main results are the automatic detection of the vineyards and the local evaluation of vine rows orientation and of inter-rows spacing.
The overall point-cloud processing algorithm can be divided into three mains steps: (1) precise local terrain surface and height evaluation of each point of the cloud, (2) point-cloud scouting and scoring procedure on the basis of a new vineyard likelihood measure, and, finally, (3) detection of vineyard areas and local features evaluation.
The algorithm was found to be efficient and robust: reliable results were obtained even in the presence of dense inter-row grassing, many missing plants and steep terrain slopes. Performances of the algorithm were evaluated on vineyard maps at different phenological phase and growth stages. The effectiveness of the developed algorithm does not rely on the presence of rectilinear vine rows, being also able to detect vineyards with curvilinear vine row layouts
Cost-effective visual odometry system for vehicle motion control in agricultural environments
Full text linkIn precision agriculture, innovative cost-effective technologies and new improved solutions, aimed at making operations and processes more reliable, robust and economically viable, are still needed. In this context, robotics and automation play a crucial role, with particular reference to unmanned vehicles for crop monitoring and site-specific operations. However, unstructured and irregular working environments, such as agricultural scenarios, require specific solutions regarding positioning and motion control of autonomous vehicles. In this paper, a reliable and cost-effective monocular visual odometry system, properly calibrated for the localisation and navigation of tracked vehicles on agricultural terrains, is presented. The main contribution of this work is the design and implementation of an enhanced image processing algorithm, based on the cross-correlation approach. It was specifically developed to use a simplified hardware and a low complexity mechanical system, without compromising performance. By providing sub-pixel results, the presented algorithm allows to exploit low-resolution images, thus obtaining high accuracy in motion estimation with short computing time. The results, in terms of odometry accuracy and processing time, achieved during the in-field experimentation campaign on several terrains proved the effectiveness of the proposed method and its fitness for automatic control solutions in precision agriculture applications
The influence of food composition and tag orientation on UHF RF IDentification
Full text linkUltra-high frequency (UHF) radio frequency (RF) labelling is considered to be one of the most promisingtechniques for automatic identification through all food supply chain phases. However, the efficacy of RFIDentification(RFID)systemshasprovencriticalforsomefoodproducts.Inthispapertheroleofthecompositionandthetemperatureofthefoodproductandofthemutuallabel-reader orientation on identification performances is investigated. For this purpose, basic food constituents,prepared as solutions (salts, sugars, organic acids and ethanol) at different concentrations and temperatures,wereconsideredandthentheidentificationresultswerecomparedtothoseobtainedfromwholefoodproducts.The results show how the reading performances of UHF RFID systems are influenced by the consideredparameters. The reading ranges for the identification of critical food products by UHF RFID systems can beestimatedandthenimprovedbyconsideringthecompositionofthefoodproductdirectlyfromthedesignphase
Comparison of Satellite and UAV-Based Multispectral Imagery for Vineyard Variability Assessment
Full text linkIn agriculture, remotely sensed data play a crucial role in providing valuable information on crop and soil status to perform effective management. Several spectral indices have proven to be valuable tools in describing crop spatial and temporal variability. In this paper, a detailed analysis and comparison of vineyard multispectral imagery, provided by decametric resolution satellite and low altitude Unmanned Aerial Vehicle (UAV) platforms, is presented. The effectiveness of Sentinel-2 imagery and of high-resolution UAV aerial images was evaluated by considering the well-known relation between the Normalised Difference Vegetation Index (NDVI) and crop vigour. After being pre-processed, the data from UAV was compared with the satellite imagery by computing three different NDVI indices to properly analyse the unbundled spectral contribution of the different elements in the vineyard environment considering: (i) the whole cropland surface; (ii) only the vine canopies; and (iii) only the inter-row terrain. The results show that the raw s resolution satellite imagery could not be directly used to reliably describe vineyard variability. Indeed, the contribution of inter-row surfaces to the remotely sensed dataset may affect the NDVI computation, leading to biased crop descriptors. On the contrary, vigour maps computed from the UAV imagery, considering only the pixels representing crop canopies, resulted to be more related to the in-field assessment compared to the satellite imagery. The proposed method may be extended to other crop typologies grown in rows or without intensive layout, where crop canopies do not extend to the whole surface or where the presence of weeds is significant
Steam batch thermal processes in unsteady state conditions: Modelling and application to a case study in the food industry
Full text linkMany industrial processes require high amounts of steam. Design and operation of steam plants are particularly complex when the steam supply is required for short periods and with a varying time schedules. To fulfil the discontinuous needs of steam users, avoiding the steam boiler oversizing to the peak value of the steam request, a thermal energy storage (TES) system can be adopted. The proper sizing of TES systems, which, in this application, is constituted by a steam accumulator vessel installed between the steam generator and the consumer, cannot be based on the sole initial and final state conditions of the steam storage, since a performance prediction of the process time-evolution is also required.
In this paper, a model of steam batch processes for industrial thermal treatments, able to describe unsteady operative conditions, is presented. More in detail, a three-stage steam plant, with a sequentially interconnected steam boiler, steam accumulator and processing tank, has been considered. The dynamic model of the charging and discharging processes of the steam accumulator has been applied to a real case study in the food industry: the batch debacterisation process of cocoa beans. Nevertheless, the obtained results can be profitably employed in the design and the performance assessments of a wide set of applications involving the steam processing fluid, such as desalination plants, solar thermal power plants, retorts, steam ovens and others
Reversed Brayton cycle for food freezing at very low temperatures: Energy performance and optimisation
Full text linkFreezing is a valuable method to increase food shelf life and to ensure high quality standards during long-term storage. Additional benefits to frozen food quality can be achieved by freezing at very low temperatures (< −50 °C): small ice crystal formation during fast freezing reduces food cell wall rupture, preventing water and texture loss during thawing. This paper presents the design of an innovative food freezing system operating at very low temperatures, based on a modified reversed Brayton cycle (rB cycle). The plant is composed of two interconnected sub-systems: a primary thermodynamic closed loop, operated by an rB cycle, and a secondary airflow loop which is devoted to food freezing by batch process. Relevant features of the designed rB cycle rely on the adopted environmentally safe working fluid, the optimised thermodynamics working conditions and the innovative cycle layout. A modelling framework for the system was developed to identify and design efficient operative settings for the plant components (turbo-machineries, heat exchangers, etc.) and to assess, via sensitivity analysis, the influence of the main design parameters on the global energy performance. The proposed system configuration, designed to maximise the coefficient of performance (CoP) value of the plant, was determined by means of nonlinear multivariable optimisation. In addition, the energy performance of the system can be increased by recovering waste heat available from the rB cycle
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