Search

Due to the UE Regulation n. 517/2014 refrigerants with a GWP higher than 150 are not allowed from January 1, 2015 in new domestic refrigerators. Thus, a replacement for HFC134a is needed. In this paper attention is devoted to the evaluation of the environmental impact in terms of greenhouse effect of the substitution of HFC134a with low GWP, HFO refrigerant fluids. The greenhouse effect is accounted for by the experimental evaluation of the TEWI index (Total Equivalent Warming Impact) that takes into account both direct and indirect contributions to global warming. The refrigerant fluids that have been tested as a drop-in are: pure HFO1234yf, the mixture HFO1234yf/HFC134a (90/10 % in weight), pure HFO1234ze, the mixture HFO1234ze/HFC134a (90/10 % in weight). In particular, with the mixture HFC134a/HFO1234yf (10/90 % in weight) there is a reduction of the TEWI of -295% respect to HFC134a.

Refrigeration by an active magnetic regenerative system (AMR) is potentially more attractive, as compared to conventional techniques. Indeed, devices based upon an AMR cycle are more efficient, compact, environment-friendly and can operate over a broad range of temperatures. In this paper, attention is focused to the near room-temperature range. On the other hand, however, the AMR cycle poses a variety of complex problems, in terms of fluid dynamics, heat transfer and magnetic field. In order to identify the optimal operational parameters, the design and optimization of a magnetic refrigeration system can be supported by modelling. In this paper, a dimensionless approach was adopted to simulate an AMR cycle following a Brayton regenerative cycle. In the simulation, the temperature range that has been explored is 260 – 280 K and 275 – 295 K. The heat transfermediums are, respectively, water–glycol mixture (50% by weight) and pure water. The Gd0.8Dy0.2 alloy and pure Gd have been chosen as constituent material for the regenerator of the AMR cycle. With this model, the influence of the different parameters on cycle efficiency has been analysed. In particular, the study has been focused on the influence of the secondary fluid properties,magnetic material particle diameter, fluid blow time, secondary fluidmass flow rate, regenerator geometry and effect of axial thermal conduction. The model enables to find optimal dimensionless numbers in order to maximize the cycle performances. The results can be extended to widely different situations and therefore can be easily employed for the design and the optimization of new experimental prototypes.

Nowadays about 20% of the worldwide energy consumption is attributable to refrigeration that is almost entirely based on vapor compression refrigeration. The elastocaloric refrigeration is being considered in the recent years as one of the most promising alternatives to vapour compression cooling technology. It is based on the latent heat associated with the transformation process of the martensitic phase, found in Shape Memory Alloys (SMA) when they are subjected to uniaxial stress cycles of loading and unloading. SMAs are characterized by the mechanical property of being able to return to the initial form once the uniaxial stress has been removed. Currently the prototypes of elastocaloric cooler developed in the world are less than ten units and they are not close to the industrialization and commercialization, yet. This contribution presents the design processes and the steps of development of the first Italian elastocaloric device: SSUSTAIN-EL. This research involves part of a bigger Italian project, called SUSSTAINEBLE, that involves three research institutes: University of Naples Federico II, University of Genoa and the National Research Council. The aim of research group is the developing of a demonstrative prototype of a continuously elastocaloric cooler, which can represent a fundamental step as "proof of concept".

The aim of this paper is to research the parameters that optimize the thermal performances of a horizontal single-duct Earth to Air Heat eXchanger (EAHX). In this analysis, the EAHX is intended to be installed in the city of Naples (Italy). The study is conducted by varying the most crucial parameters influencing the heat exchange between the air flowing in the duct and the ground. The effect of the geometrical characteristics of the duct (pipe length, diameter, burial depth), and the thermal and flow parameter of humid air (inlet temperature and velocity) has been studied in order to optimize the operation of this geothermal system. The results reveal that the thermal performance increases with length until the saturation distance is reached. Moreover, if the pipe is designed with smaller diameters and slower air flows, if other conditions remain equal, the outlet temperatures come closer to the ground temperature. The combination that optimizes the performance of the system, carried out by forcing the EAHX with the design conditions for cooling and heating, is: D = 0.1 m s−1; v = 1.5 m s−1; L = 50 m. This solution could also be extended to horizontal multi-tube EAHX systems.

Caloric refrigeration is an emerging class of cooling technologies based on caloric effects detected in ferro-caloric solid-state materials. Depending of the nature of the driving field, it is possible distinguishing four main caloric refrigerations magnetocaloric, electrocaloric, elastocaloric and barocaloric. Therefore, caloric refrigeration is based on solid-state materials, unlike vapor compression, nowadays still the most diffused cooling technique, whom employs fluids as refrigerants. Solid-state materials do not provide a direct contribution in global warming, since they do not disperse in the atmosphere, but only an indirect impact is registered when they are employed as refrigerants in cooling systems. On the other side, a vapor compression plant is characterized by both direct and indirect contributions to global warming. The main parameter to evaluate global warming impact and carbon-dioxide emissions coming out from a cooler is the Total Environmental Warming Impact (TEWI) index, which accounts both the direct and indirect contributions produced. In this paper a numerical Delta TEWI analysis is presented, comparing the environmental impact of a caloric refrigerator, operating with different caloric materials, with the one of a vapor compression cooler working with HFC134a.

Electrocaloric and magnetic refrigeration are two emerging, solid-state based technology, which could constitute a real chance to overcome vapor compression refrigeration limits. To underline the differences and the affinities concerning such solid-state techniques, in this paper electrocaloric and magnetic refrigeration are compared through some performance parameters. For this purpose, it has been introduced a two-dimensional model, capable to reproduce, in room temperature range, the behaviors of both AMR and AER parallel plates regenerator. AMR and AER are the acronyms of Active Magnetic/Electrocaloric Regenerative cycle, respectively, which are inverse Brayton based thermodynamical cycles. In the model have been tested as refrigerant the most promising magnetic and electrocaloric materials, like Gd, Gd5(SixGe1-x)4, LaFe11.384 Mn0.356Si1.26H1.52, LaFe11.05Co0.94Si1.10, as magnetocaloric, P(VDF-TrFE-CFE)/BSTs, 0.93PMN-0.07PT, PLZTs, as electrocaloric ones. Among them, the PLZT thin film class confers the best results, higher than every magnetocaloric material tested, conferring to electrocaloric refrigeration the real role of the environmental friendly technology of the future.

The thermal performances of a refrigerator incorporating a phase change material By: Maiorino, Angelo; Del Duca, Manuel Gesu; Mota-Babiloni, Adrian; et al. INTERNATIONAL JOURNAL OF REFRIGERATION-REVUE INTERNATIONALE DU FROID Volume: 100 Pages: 255-264 Published: APR 2019 SIRE Full Text from Publisher In this paper, a Phase Change Material (PCM) has been incorporated within the cabinet of a refrigerator, attached to the bare tube evaporator placed below the racks, with the aim of analysing the variation of temperatures and compressor operation, among others. The effect of different control settings (hysteresis) on the performance of such a system, equipped with tap water as PCM, is investigated. Furthermore, the impact of the variation of the ambient temperature and the product mass is highlighted. Two novel parameters are introduced: the first one to estimate the utilisation of the PCM during the cyclic operations of the refrigerator, and the second one is used to evaluate the fluctuation of the product temperature within the cabinet. Experimental results show that the introduction of the PCM has led to a noticeable reduction of the temperature gradient within the cabinet and the fluctuations of product temperature ensuring better conservation conditions, and to extend the OFF time of the compressor. The tests also show that with PCM, hysteresis has lower impact on the fluctuation of the product temperature, ON-time ratio and energy consumption of the refrigerator than without it. On the contrary, the product temperature distribution is more affected by the hysteresis with PCM than without, leading to a better uniformity with higher hysteresis.

In this paper are reported the results of an experimental comparative analysis between R134a and HFO1234ze, when they are employed as refrigerants in a domestic refrigerator. Under sub-tropical conditions, it have been measured the energy consumptions in accordance with the UNI-EN-ISO15502. For each experiment it have been estimated both the TEWI and the Life Cycle Climate Performance indexes to assess the environmental impact due to HFO1234ze when used in place of R134a.

Electrocaloric is a novel emerging not-in-kind cooling technology based on solid-state materials exhibiting the electrocaloric effect, i.e., the property of changing their temperature because of an adiabatic change in the intensity of the electric field applied. This technology has only attracted the interests of the scientific community in the last two decades, even though it has the main feature of being based on eco-friendly materials that, because of their solid-state nature, do not provide a direct contribution in global warming. Even if some steps have already been taken, the research fields connected to electrocaloric cooling are still open: The identification of the most appropriated thermodynamic cycle, electrocaloric refrigerants, as well as the development of efficient cooling systems. To this purpose, this review paper provides a snapshot of the electrocaloric world and compares the progress made by the inherent scientific community in all the connected fields: the thermodynamic cycles, materials, experimental devices, numerical models, energy performances and prospective cooling applications.

Magnetic refrigeration is an ecofriendly solid state technology employing magnetocaloric materials in an Active Magnetic Regenerating refrigerant cycle (AMR), a Brayton-based thermodynamical cycle. Magnetic refrigeration is based on magnetocaloric effect (MCE), a physical phenomenon that couples an external magnetic field with the magnetic moments of magnetocaloric materials. In the case of ferromagnetic materials, MCE is a warming as the magnetic moments of the atom are aligned by the application of a magnetic field, and the corresponding cooling upon removal of the magnetic field. Gadolinium is the benchmark material for magnetic refrigeration in room temperature range, thanks to its marked magnetocaloric effect which is maximum at 294 K. In this paper the results of numerical investigations on magnetocaloric materials are presented: the energetic performances of different magnetocaloric materials have been investigated through a two-dimensional model of an AMR regenerator. The model has been previously experimentally validated with a Rotary Permanent Magnet Magnetic Refrigerator. Exploring the behavior of the regenerator under variable working condition, a performance map has been obtained for gadolinium. The results, collected in terms of temperature span, coefficient of performance and mechanical power associated to circulation pump, lead to formulize viewpoints on employing magnetocaloric materials under optimized AMR working conditions

Magnetic Refrigeration (MR) is a novel refrigeration technique based on eco-friendly solid materials as refrigerants, whom react to the application of magnetic fields, with warming and cooling by magnetocaloric effect. The thermodynamical cycle which best suits the magnetic refrigeration is Active Magnetic Regenerator cycle (AMR). Regenerator is the core of a magnetic refrigerator, since that it plays a dual-role: it operates both as refrigerant and regenerator in an AMR cycle. An AMR cycle consists of two adiabatic stages and two isofield stage. In this paper an investigation is conducted about the magnetocaloric refrigerator design through two-dimensional multiphysics numerical models of two different magnetocaloric regenerators: (1) a packed bed and (2) a parallel plates magnetic regenerators made of gadolinium, operating at room temperature under a 1.5T magnetic field induction. Both models employ water as secondary fluid. The tests were performed with variable fluid flow rate at fixed AMR cycle frequency. The results obtained are presented in terms of temperature span, cooling power, coefficient of performance and mechanical power of the circulation pump, and they indicate under which operating conditions packed bed configuration is to be preferred to parallel plates and vice versa.

Solid-state refrigeration technologies are considered nowadays emerging alternative to vapor compression refrigeration. In this paper is introduced a two-dimensional model of solid-state refrigerator, which employs materials experiencing a combined electrocaloric-elastocaloric effect and it operates at room temperature. A numerical investigation is performed to explore the energetic performance of the refrigerators. The results reveal that PbTiO 3 as elastocaloric refrigerant confers the best performances in terms of COP; the highest cooling power estimated are proper of combined elastocaloric-electrocaloric effect, with increments around +65% than employing PbTiO 3 in single electrocaloric/elastocaloric refrigeration, on equal operative conditions.

In this paper, a comparative experimental analysis between HFC134a, HFO1234yf and a refrigerant mixture of HFC134a/HFO1234yf (10/90% weight) implemented in a domestic refrigerator is introduced. Adding 10% of HFC134a to HFO1234yf, the mixture becomes non-flammable with GWP still less than 150. The experimental tests have been conducted under sub-tropical conditions in accordance with the UNI-EN-ISO15502 standard. Two kinds of tests have been shown: pull down and 1-day energy consumption. The results show that HFC134a/HFO1234yf (10/90% weight) is the best drop-in refrigerant fluid for HFC134a in the domestic refrigerator used for the experimental tests. The refrigerant mixture has the closest behaviour to that of HFC134a in terms of temperatures and pressures. Furthermore, the cycle working with the optimal charge of the mixture shows an energy saving of 16 and 14% with respect to HFC134a and HFO1234yf, respectively.

The latest international regulations on the reduction of greenhouse gases are strongly redesigning the scenario of use of refrigerants, gradually eliminating the possibility of employing the HFCs. Among all sectors of refrigeration, one of the most affected by these restrictions is the domestic refrigeration. Although for it have been suggested some solutions, such as the construction of household refrigerator operating with the hydrocarbons, there remains the need to find a substitute for HFC134a. In particular, the substitution may involve both existing machines and already in operation, which cannot be loaded with hydrocarbons, and new devices. With the aim of finding a simple implementation solution, in the present work, it is reported an experimental investigation carried out on a domestic refrigerator designed and built to operate with HFC134a and for which a drop-in with HFO1234yf has been realised. The experimentation has been addressed so as to highlight the behaviour of the system as a result of the drop-in, with a particular interest in the energy performance variation. A slight energy saving has been recorded with HFO1234yf, and an improving of the cooling capacity has been noticed.

The interest of the scientific community regarding magnetic refrigeration at room temperature is constantly growing. In recent years, there has been an increase in the experimental work relating to both new prototypes and new magnetocaloric materials. The magnetic refrigerators built to date still have some limitations that make them uncompetitive when compared with conventional vapour compression systems. However, among the different configurations realized, one can recognize that rotary devices, having rotating magnets and static regenerators, are of particular interest because of their good energy performances. In this paper, we report an experimental investigation on the identification of the energy performances of a Rotary Permanent Magnet Magnetic Refrigerator. Employing 1.20 kg of gadolinium and operating at a temperature of heat rejection equal to 296 K, the system was subjected to different operating conditions obtained by varying the thermal load, volumetric flow rate of the regenerating fluid and cycle frequency.

An experimental study is carried out to investigate the characteristics of the evaporation heat transfer for different fluids. Namely, pure refrigerants fluids (R22 and R134a), azeotropic and quasi-azeotropic mixtures (R404A, R410A, R507) and zeotropic mixtures (R407C and R417A). The test section is a smooth, horizontal, stainless steel tube (6 mm ID, 6 m length) uniformly heated by the Joule effect. The flow boiling characteristics of the refrigerant fluids are evaluated in 250 different operating conditions. Thus, a data-base of more than 2000 data points is produced. The experimental tests are carried out varying: (i) the refrigerant mass fluxes within the range 200–1100 kg/m2 s; (ii) the heat fluxes within the range 3.50–47.0 kW/m2; (iii) the evaporating pressures within the range 3.00–12.0 bar. In this study, the effect on measured heat transfer coefficient of vapour quality, mass flux, saturation temperature, imposed heat flux, thermo-physical properties are examined in detail.

A desiccant dehumidification system with air can be driven by low grade (