10,278 research outputs found
Airflow and Thermal Behavior within Peaches Packaging Box Using Computational Fluid Dynamics - A Preliminary Study
Post-harvest cold storage of peaches is an essential element to maintain the quality of the fruits without any loss. This work aims to present a CFD model, to predict airflow patterns and temperature profiles in ventilated packaging systems, during the forced-air cooling of Peaches stored in a cold chamber. Transient CFD simulations are performed for the chamber containing four ventilated boxes and the evaluation of the results show that the temperature removal near the vent holes and the hand holes is relatively high when compared to other regions of the packaging box. This preliminary study reveals the airflow behavior develop an uneven temperature distribution within the box. To overcome the flaws, future work is focused on modifying the vent hole design to improve the airflow phenomenon to maintain the temperature homogeneity throughout the box.
Keywords: Peach, Computational fluid dynamics, Airflow, Heat transfer, Packagin
Phase transitions and statistical mechanics for BPS Black Holes in AdS/CFT
Using the general framework developed in hep-th/0607056, we study in detail
the phase space of BPS Black Holes in AdS, for the case where all three
electric charges are equal. Although these solitons are supersymmetric with
zero Hawking temperature, it turns out that these Black Holes have rich phase
structure with sharp phase transitions associated to a corresponding critical
generalized temperature. We are able to rewrite the gravity variables in terms
of dual CFT variables and compare the gravity phase diagram with the free dual
CFT phase diagram. In particular, the elusive supergravity constraint
characteristic of these Black Holes is particulary simple and in fact appears
naturally in the dual CFT in the definition of the BPS Index. Armed with this
constraint, we find perfect match between BH and free CFT charges up to
expected constant factors.Comment: 14 pages, 5 figures, corrected typos and references adde
Testing of a resistive sensor with fabric medium for monitoring frost formation in refrigeration systems
Refrigeration is one of the key elements for food preservation. With global temperatures increasing due to global warming, the efficiency in refrigerated storage systems must be improved. One of the problems that is yet to be solved in these systems is the efficient and accurate removal of the frost formed on the heat exchanger surface. In previous works, a low-cost resistive sensor has been developed to detect frost formation for accurate removal. This paper shows the results of an experimental study carried out to increase the accuracy, by placing different configurations of a fabric medium in between the sensor electrodes.This study is within the activities of project “Pack2Life – High performance packaging”, project IDT in consortium No.33792, call No.03/SI/2017, Ref. POCI-01-0247-FEDER-033792, promoted by COMPETE 2020 and co-funded by FEDER within Portugal 2020.
This work has been supported by the project Centro-01-0145-FEDER000017 - EMaDeS - Energy, Materials and Sustainable Development, co-funded by the Portugal 2020 Program (PT 2020), within the Regional Operational Program of the Center (CENTRO 2020) and the European Union through the European Regional Development Fund (ERDF).
The authors thank the opportunity and financial support to carry on this project to Fundação para a Ciência e Tecnologia (FCT) and R&D Unit "Centre for Mechanical and Aerospace Science and Technologies" (C-MAST), under project UIDB/00151/2020.info:eu-repo/semantics/publishedVersio
ARCHI: pipeline for light curve extraction of CHEOPS background star
High precision time series photometry from space is being used for a number
of scientific cases. In this context, the recently launched CHEOPS (ESA)
mission promises to bring 20 ppm precision over an exposure time of 6 hours,
when targeting nearby bright stars, having in mind the detailed
characterization of exoplanetary systems through transit measurements. However,
the official CHEOPS (ESA) mission pipeline only provides photometry for the
main target (the central star in the field). In order to explore the potential
of CHEOPS photometry for all stars in the field, in this paper we present
archi, an additional open-source pipeline module{\dag}to analyse the background
stars present in the image. As archi uses the official Data Reduction Pipeline
data as input, it is not meant to be used as independent tool to process raw
CHEOPS data but, instead, to be used as an add-on to the official pipeline. We
test archi using CHEOPS simulated images, and show that photometry of
background stars in CHEOPS images is only slightly degraded (by a factor of 2
to 3) with respect to the main target. This opens a potential for the use of
CHEOPS to produce photometric time series of several close-by targets at once,
as well as to use different stars in the image to calibrate systematic errors.
We also show one clear scientific application where the study of the companion
light curve can be important for the understanding of the contamination on the
main target.Comment: 14 pages, 13 figures, accepted for publication in MNRAS, all code
available at https://github.com/Kamuish/arch
Medium materials for improving frost detection on a resistive sensor
Reducing food waste demands improvements in refrigeration systems. Furthermore, the rise of temperatures worldwide demands more capable and efficient refrigeration equipment. One of the problems that affects refrigeration equipment is the accumulation of frost in the heat exchanger that reduces efficiency, and in extreme cases, blocks the air flow. Usually, defrosting is timed for the worst-case scenario, which results in many unnecessary defrosting operations that compromise the efficiency, and temperature stability in the refrigerated environment. This paper presents a low-cost resistive sensor’s reliability case studies,
using several materials and configurations.This study is within the activities of project “Pack2Life – High performance packaging”, project IDT in
consortium n.o 33792, call n.o 03/SI/2017, Ref. POCI-01-0247-FEDER-033792, promoted by COMPETE 2020
and co-funded by FEDER within Portugal 2020.
This work has was supported by the project Centro-01-0145-FEDER000017 - EMaDeS - Energy, Materials and
Sustainable Development, co-funded by the Portugal 2020 Program (PT 2020), within the Regional Operational
Program of the Center (CENTRO 2020) and the EU through the European Regional Development Fund (ERDF).
The authors thank the opportunity and financial support to carry on this project to Fundação para a Ciência e
Tecnologia (FCT) and R&D Unit “Centre for Mechanical and Aerospace Science and Technologies” (C-MAST),
under project UIDB/00151/2020.
The authors also thank Cláudia Monteiro for her assistance in the production of the ceramic samples.info:eu-repo/semantics/publishedVersio
Active and Intelligent Packaging with Phase Change Materials to Promote the Shelf Life Extension of Food Products
Active packaging aims to extend the shelf life of fruits and vegetables using active agents such as Oxygen, Carbon-di-oxide, ethylene scavengers and moisture absorber. Intelligent packaging provides information about the fruits quality inside the package to the customer and this packaging technology detects the internal changes of fruits and vegetables using sensors and indicators. Further to improve the post-harvest storage PCM such as Rubitherm can be used depending on the package box dimension to remove the field heat from the products and maintain its temperature with low variation during transport and display. Gel packs having less weight with PET and PS can also be an alternate method in the packaging. The application of these technologies may lead to a revolution in post-harvest storage, transportation, and further retail sale. This paper reviews the theoretical principles of food packaging and recent developments in packaging technologies using PCMs.
Keywords: Active packaging, Intelligent packaging, Phase change materials, Shelf life extension, Fruit
Experimental study of a hybrid solar photovoltaic, thermoelectric and thermal module
Nowadays, solar energy, which can be photovoltaic and thermal, is a clean and reliable source of energy for the production of electric and thermal power. However, new ways for improving photovoltaic efficiency are fundamental for an extensive application of this technology. Most of the energy absorbed by the PV panel converts itself into heat, which usually is lost and does not have any energetic value. The performance of a combined photovoltaic (PV), thermoelectric generator (TEG) and water heating panel is tested in practice. The thermoelectric set is applied on the back of the PV panel so that the two devices have approximately the same temperature. On the other face of the thermoelectric set, there is the water heating panel, which consists of an aluminium heat exchanger specially designed for this hybrid module. The exposed surface of the hybrid panel has an area of about 2.72 dm2. Experimental tests were conducted in direct solar exposure during July. The experimental results indicate that the maximum global module efficiency was 91.3% for an irradiance of 1089 W/m2. The power peak production was 29.7 W, at 2 p.m., with an irradiance value of 1230 W/m2.info:eu-repo/semantics/publishedVersio
Rotatory power reversal induced by magnetic-current in bi-isotropic media
Bi-isotropic media constitute a proper scenario for scrutinizing optical
effects stemming from magnetoelectric parameters. Chiral magnetic current is a
macroscopic effect arising from the chiral magnetic effect that enriches the
phenomenology of a classical dielectric medium. This work examines optical
aspects of bi-isotropic media in the presence of magnetic conductivity. The
full isotropic scenario manifests circular birefringence described by a
dispersive rotatory power that changes sign at a given frequency. For a
bi-isotropic medium with antisymmetric magnetic conductivity, an intricate
dispersive rotatory power is attained, supplied with sign reversal as well.
This scenario also indicates a handedness reversion of the medium, an unusual
property in dielectrics, which may work as a signature of bi-isotropic media
supporting chiral magnetic current.Comment: 9 pages, 3 figure
Algorithmic properties of inverse monoids with hyperbolic and tree-like Sch\"utzenberger graphs
We prove that the class of finitely presented inverse monoids whose
Sch\"utzenberger graphs are quasi-isometric to trees has a uniformly solvable
word problem, furthermore, the languages of their Sch\"utzenberger automata are
context-free. On the other hand, we show that there is a finitely presented
inverse monoid with hyperbolic Sch\"utzenberger graphs and an unsolvable word
problem
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