Search results for " refrigeration"
showing 10 items of 23 documents
Fragmenting gadolinium: Mononuclear polyoxometalate-based magnetic coolers for ultra-low temperatures
2012
The polyoxometalate clusters with formula [Gd(W 5O 18) 2] 9- and [Gd(P 5W 30O 110)] 12- each carry a single magnetic ion of gadolinium, which is the most widespread element among magnetic refrigerant materials. In an adiabatic demagnetization, the lowest attainable temperature is limited by the presence of magnetic interactions that bring about magnetic order below a critical temperature. We demonstrate that this limitation can be overcome by chemically engineering the molecules in such a way to effectively screen all magnetic interactions, suggesting their use as ultra-low-temperature coolers. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Advanced refrigerating plants based on transcritical cycles working with carbon dioxide for commercial refrigeration
2012
Supermarkets and hypermarkets require a huge amount of energy to maintain chilled and frozen food in product display cases and cold storage rooms and thermal comfort in the whole building. Systems exploited require very large refrigerant charges for operation and suffer significant leakages. The challenge for advanced systems, based on equipment which reduce TEWI, suggests the proposal of carbon dioxide: a natural working fluid. This paper deals with a feasibility study of a refrigerating system for a big hypermarket in Sicily based on a three-stage transcritical cycle working with carbon dioxide which is compared with an alternative system composed of two cycles operating as a binary refri…
SETUP OF VIRTUAL EXPERIMENTS AND CRITICAL ANALYSIS OF CONVENTIONAL THERMOECONOMIC DIAGNOSIS OF MULTIPLE FAULTS IN AIR-CONDENSED ROOFTOP SYSTEMS
2012
The diagnosis of soft faults in vapor compression cooling systems is a crucial activity, since malfunctions may provoke heavy degradation in plant performance and increase the power consumption for space cooling. Among the various Faults Detection and Diagnosis techniques developed over the last two decades, thermoeconomic diagnosis has been playing only a marginal role due to the difficulties encountered when applying the conventional thermoeconomic approaches to vapor compression refrigeration plants. In this paper a critical analysis on capabilities and limits of thermoeconomic diagnosis of refrigeration systems is proposed. The reference plant assumed for this study is a 116 kWc air-con…
Field-induced slow magnetic relaxation and magnetocaloric effects in an oxalato-bridged gadolinium(iii)-based 2D MOF
2021
The coexistence of field-induced slow magnetic relaxation and moderately large magnetocaloric efficiency in the supra-Kelvin temperature region occurs in the 2D compound [GdIII2(ox)3(H2O)6]n·4nH2O (1), a feature that can be exploited in the proof-of-concept design of a new class of slow-relaxing magnetic materials for cryogenic magnetic refrigeration.
CO2LD: An innovation educational project for High Degree Professional Training in Refrigeration
2013
EN] Refrigeration is one of the technology sectors that has sufered the most changes in the last twenty years, because of the negative impact of the fuids used in the refrigeration cycles, i.e., refrigerants, due to their impact on the ozone layer and their contribution to global warming. As a result of their negative efects, the European Union has established several directives to restrict the use of refrigerant fuids, and the sector therefore needs to adapt to the new regulations. This process of adaptation of the refrigeration sector to the new regulations must be carried out by all the agents involved, including those engaged in the training and education of the future refrigeration tec…
PERFORMANCE EVALUATION OF CASCADE REFRIGERATION SYSTEMS USING DIFFERENT REFRIGERANTS
2012
Due to the negative effects of synthetic refrigerants on the environment, natural refrigerants have obtained again interest as alternative refrigerants for different applications because of their zero ODP and negligible GWP. This paper presents a thermodynamic analysis of different two-stage cascade refrigeration systems using as refrigerant carbon dioxide (R744) in low-temperature circuit, and, respectively, ammonia (R717), propane (R290), butane (R600), R404A, R410A and R134a in high-temperature circuit. The operating parameters considered in this study include condensing and evaporating temperatures in high-temperature circuit, temperature difference in the cascade heat exchanger, and e…
Critical analysis of conventional thermoeconomic approaches to the diagnosis of multiple faults in air conditioning units: Capabilities, drawbacks an…
2013
Abstract Faults diagnosis in air conditioning systems is a crucial activity, since malfunctions may induce heavy degradation of performance. Among the available techniques, thermoeconomic diagnosis has played a marginal role due to the difficulties encountered when applying the methodology to refrigeration plants. In this paper a critical analysis on capabilities and limits of thermoeconomic diagnosis is proposed. The reference plant is a 120 kWc air-cooled air conditioning system; a simulator is used to evaluate thermodynamic data under normal and faulty conditions, setting up “virtual experiments” to simulate each fault. Five malfunctions are imposed, either individually or simultaneously…
Electronic structure of the austenitic and martensitic state of magnetocaloric Ni-Mn-In Heusler alloy films
2013
Changes of the electronic and magnetic structure near the martensitic phase transition of Ni-Mn-In Heusler alloys doped with Co are investigated by experiment and theory. The nonstoichiometric Ni${}_{48}$Co${}_{5}$Mn${}_{35}$In${}_{12}$ epitaxial film undergoes a transition from a weakly magnetic martensitic phase below ${T}_{m}=350$ K to a ferromagnetic austenitic phase above ${T}_{m}$. Element-specific magnetic moments and the unoccupied density of states function is investigated using x-ray magnetic circular dichroism. We find an antiparallel alignment of Mn and Ni/Co magnetic moments in both phases. The electronic structure is calculated using the SPR-KKR Green's function approach consi…
Refrigeration bound of heat-producing cylinders by superfluid helium
2019
In this paper we go ahead in our studies on refrigeration of nanosystems by superfluid helium, as an appealing subject for future applications to computers or astronautical precision nanodevices. We first recall the effective thermal conductivity in laminar counterflow superfluid helium through arrays of mutually parallel cylinders and we discuss the conditions for the appearance of quantum turbulence around the heat-producing cylinders. We then consider the cooling of an array of heat-producing cylindrical nanosystems by means of superfluid-helium counterflow. We discuss the upper bound on heat removal set by avoidance of quantum turbulence and avoidance of phase transition to normal He I,…
Potential applications using LNG cold energy in Sicily
2008
According to previsions, natural gas could be the main energy source worldwide, inducing relevant geopolitical changes. Most likely, such problems will be solved with the development of a gas transportation mode alternative to traditional pipelines: liquefied natural gas (LNG). The global LNG trade has increased rapidly during recent years. A significant amount of energy is consumed to produce low-temperature LNG, which has plenty of cryogenic exergy/ energy. Therefore, the effective utilization of the cryogenic energy associated with LNG vaporization is very important. Sicily, with more than five million inhabitants, is the second biggest region of Italy and in this region will be realized…