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In the recent years, great interest has been devoted to the unique properties of nanofluids. The dispersion process and the nanoparticle suspension stability have been found to be critical points in the development of these new fluids. For this reason, an experimental study on the stability of water-based dispersions containing different nanoparticles, i.e. single wall carbon nanohorns (SWCNHs), titanium dioxide (TiO 2 ) and copper oxide (CuO), has been developed in this study. The aim of this study is to provide stable nanofluids for selecting suitable fluids with enhanced thermal characteristics. Different dispersion techniques were considered in this study, including sonication, ball milling and high-pressure homogenization. Both the dispersion process and the use of some dispersants were investigated as a function of the nanoparticle concentration. The high-pressure homogenization was found to be the best method, and the addition of n -dodecyl sulphate and polyethylene glycol as dispersants, respectively in SWCNHs-water and TiO 2 -water nanofluids, improved the nanofluid stability.

In the European Union, 40% of the overall final energy consumption is attributable to the buildings sector. A reason for such data may be found considering that the great majority of the building stock is more than 40 years old. According to the European Commission, an interesting potential lies in the refurbishment of the building sector, and heat pump technology has been recognized as one of the most cost-effective solutions to tackle the environmental issue of this sector. Regarding heat pump technology, ground-source heat pumps (GSHPs) have been proven to be the most efficient solution on equal boundary conditions. Despite this, in most EU states’ markets, GSHPs hold only a small market share with respect to air-source heat pumps. In this paper, the state of art and possible future developments of GSHP technology have been reviewed together with a focus on the potential of such technology, most of all on the refurbishment of existing buildings, and on the obstacles to its spread. The state of art of borehole heat exchangers has been studied, focusing on the parameters characterizing the outside pipe and the pipe itself, i.e., pipe and grout materials. Moreover, an overview on the last developments involving refrigerants and secondary fluids is given. Finally, the design and control strategies of GSHPs have been reviewed.

It is now widely confirmed by scientific evidence that greenhouse gas emissions must be reduced to counteract the effects of global warming. The production of heat for industrial purposes is responsible for 36.8% of world energy-related emissions due to the widespread use of fossil fuels. Heat pumps are a key technology in the transition towards more sustainable industrial processes. In this paper, a systematic review of the literature produced in the last 5 years in international journals regarding the integration of heat pumps in industrial processes is presented. Firstly, papers presenting innovative configurations for high temperature heat pumps (HTHP), i.e., heat pumps delivering temperatures in the range between 100 °C and 200 °C, suitable for many industrial processes but still under development, are reviewed. Then, papers reporting innovative solutions for the integration of heat pumps in specific industrial processes and sectors (e.g., distillation, drying, desalination, etc.) are analyzed. Finally, the literature about alternative low-GWP refrigerants for industrial heat pumps, both pure compounds and mixtures, is described. It is concluded that many progresses have been realized in the last 5 years (2020–2024) regarding the identification of innovative heat pumps for industrial applications, but further research is certainly required.

This work analyzes the dynamic viscosity, surface tension and wetting behavior of phase change material nano–emulsions (PCMEs) formulated at dispersed phase concentrations of 2, 4 and 10 wt.%. Paraffin–in–water samples were produced using a solvent–assisted route, starting from RT21HC technical grade paraffin with a nominal melting point at ~293–294 K. In order to evaluate the possible effect of paraffinic nucleating agents on those three properties, a nano–emulsion with 3.6% of RT21HC and 0.4% of RT55 (a paraffin wax with melting temperature at ~328 K) was also investigated. Dynamic viscosity strongly rose with increasing dispersed phase concentration, showing a maximum increase of 151% for the sample containing 10 wt.% of paraffin at 278 K. For that same nano–emulsion, a melting temperature of ~292.4 K and a recrystallization temperature of ~283.7 K (which agree with previous calorimetric results of that emulsion) were determined from rheological temperature sweeps. Nano–emulsions exhibited surface tensions considerably lower than those of water. Nevertheless, at some concentrations and temperatures, PCME values are slightly higher than surface tensions obtained for the corresponding water+SDS mixtures used to produce the nano–emulsions. This may be attributed to the fact that a portion of the surfactant is taking part of the interface between dispersed and continuous phase. Finally, although RT21HC–emulsions exhibited contact angles considerably inferior than those of distilled water, PCME sessile droplets did not rapidly spread as it happened for water+SDS with similar surfactant contents or for bulk–RT21HC.

In the European Union (EU), buildings are responsible for about 40% of the total final energy consumption, and 36% of the European global CO2 emissions. The European Commission released directives to push for the enhancement of the buildings energy performance and identified, beside the retrofit of the current building stock, Heating, Ventilation, and Air Conditioning (HVAC) systems as the other main way to increase renewable energy sharing and overall building energy efficiency. For this purpose, Ground Source Heat Pumps (GSHPs) represent one of the most interesting technologies to provide energy for heating, cooling, and domestic water production in residential applications, ensuring a significant reduction (e.g., up to 44% compared with air-source heat pumps) of energy consumption and the corresponding emissions. At present, GSHPs mainly employ the refrigerant R410A as the working fluid, which has a Global Warming Potential (GWP) of 2087. However, following the EU Regulation No. 517/2014 on fluorinated greenhouse gases, this high GWP refrigerant will have to be substituted for residential applications in the next years. Thus, to increase the sustainability of GSHPs, it is necessary to identify short time alternative fluids with lower GWP, before finding medium-long term solutions characterized by very low GWP. This is one of the tasks of the UE project \"Most Easy, Efficient, and Low-Cost Geothermal Systems for Retrofitting Civil and Historical Buildings\" (acronym GEO4CIVHIC). Here, a thorough thermodynamic analysis, based on both energy and exergy analysis, will be presented to perform a comparison between different fluids as substitutes for R410A, considered as the benchmark for GSHP applications. These fluids have been selected considering their lower flammability with respect to hydrocarbons (mainly R290), that is one of the main concerns for the companies. A parametric analysis has been performed, for a reversible GSHP cycle, at various heat source and sink conditions, with the aim to identify the fluid giving the best energetic performance and to evaluate the distribution of the irreversibilities along the cycle. Considering all these factors, R454B turned out to be the most suitable fluid to use in a ground source heat pump, working at given conditions. Special attention has been paid to the compression phase and the heat transfer in evaporator and condenser.

The European building sector is responsible for approximately 40% of total energy consumption and for 36% of greenhouse gas emissions. Identifying technological solutions capable of reducing energy consumption and greenhouse gas emissions is one of the main objectives of the European Commission. Ground source heat pumps (GSHPs) are of particular interest for this purpose, promising a considerable reduction in greenhouse gas emissions of HVAC systems. This paper reports the results of the energetic analysis carried out within the EU research project GEO4CIVHIC about the performance of geothermal heat pumps working with low-GWP refrigerants as alternatives for R134a and R410A. The work has been carried out through computer simulations based on base and regenerative reverse cycles. Several heat sink and heat source temperature conditions have been considered in order to evaluate the GSHPs’ performance in the whole range of real conditions that can be found in Europe. Particular attention has been paid to the evaluation of compression isentropic efficiency and its influence on the overall cycle performance when dealing with steady-state heat pump simulations. To do so, five different scenarios of isentropic efficiency calculation have been studied and discussed.

Nanofluids are obtained by dispersing nanoparticles and dispersant, when present, in a base fluid. Their properties, in particular their stability, however, are strictly related to several other parameters, knowledge of which is important to reproduce the nanofluids and correctly interpret their behavior. Due to this complexity, the results appear to be frequently unreliable, contradictory, not comparable and/or not repeatable, in particular for the scarcity of information on their preparation. Thus, it is essential to define what is the minimum amount of information necessary to fully describe the nanofluid, so as to ensure the possibility of reproduction of both their formulation and the measurements of their properties. In this paper, a literature analysis is performed to highlight what are the most important parameters necessary to describe the configuration of each nanofluid and their influence on the nanofluid’s properties. A case study is discussed, analyzing the information reported and the results obtained for the thermophysical properties of nanofluids formed by water and TiO2 nanoparticles. The aim is to highlight the differences in the amount of information given by the different authors and exemplify how results can be contradictory. A final discussion gives some suggestions on the minimum amount of information that should be given on a nanofluid to have the possibility to compare results obtained for similar nanofluids and to reproduce the same nanofluid in other laboratories.

Regulations like the F-gas Regulation (EU) 2024/573 and the Kigali Amendment to the Montreal Protocol, along with efforts to mitigate climate change, drive research into alternatives to fluorinated greenhouse gases for high-temperature heat pumps and power generation. Ideal refrigerants should have low GWP, high efficiency, non-flammability, non-toxicity, material compatibility and cost effectiveness. HCFOs have emerged as promising candidates, both as pure fluids and in mixtures with HCs. These blends show efficiency and potential non-flammability for high-temperature applications, but experimental data on their thermophysical properties remain scarce. This study presents the first experimental measurements on the {n-pentane (R601) + trans-1-chloro-3,3,3-trifluoro-1-propene (R1233zd(E))} binary system. In particular, the compressed liquid density of three mixture compositions have been measured employing a vibrating tube densimeter within the temperature range from 283.15 K to 423.15 K and at pressures ranging from 1 MPa to 12 MPa. A novel technique was applied to ensure a combined uncertainty ( k =2) not greater than 0.0003 mol · mol - 1 in the mixture composition, leading to final combined uncertainty ( k =2) on the liquid density of no more than 0.2%. Finally, a new mixture model based on the Helmholtz-energy-explicit Equation of State has been developed from such experimental data. This model accurately represents the behaviour of the binary mixture, enhancing the available understanding of its thermodynamic properties.

Regulations like the F-gas Regulation (EU) 2024/573 and the Kigali Amendment to the Montreal Protocol, along with efforts to mitigate climate change, drive research into alternatives to fluorinated greenhouse gases for high-temperature heat pumps and power generation. Ideal refrigerants should have low GWP, high efficiency, non-flammability, non-toxicity, material compatibility and cost effectiveness. HCFOs have emerged as promising candidates, both as pure fluids and in mixtures with HCs. These blends show efficiency and potential non-flammability for high-temperature applications, but experimental data on their thermophysical properties remain scarce. This study presents the first experimental measurements on the n-pentane (R601) + trans-1-chloro-3,3,3-trifluoro-1-propene (R1233zd(E)) binary system. In particular, the compressed liquid density of three mixture compositions have been measured employing a vibrating tube densimeter within the temperature range from 283.15 K to 423.15 K and at pressures ranging from 1 MPa to 12 MPa. A novel technique was applied to ensure a combined uncertainty ( k =2) not greater than 0.0003 mol$$\\cdot$$· mol$$^{-1}$$- 1 in the mixture composition, leading to final combined uncertainty ( k =2) on the liquid density of no more than 0.2%. Finally, a new mixture model based on the Helmholtz-energy-explicit Equation of State has been developed from such experimental data. This model accurately represents the behaviour of the binary mixture, enhancing the available understanding of its thermodynamic properties.

The progressive phase-out of high-GWP refrigerants as mandated by the Kigali Amendment to the Montreal Protocol and the EU F-gas Regulation necessitates the exploration of sustainable alternatives within the HVAC&R industry. A recent proposal by the Council and the European Parliament aims to significantly reduce Hydrofluorocarbons (HFCs) consumption by 2050, including specific bans on high-GWP fluorinated gases in heat pumps and small air conditioning units. Heat pumps, pivotal in mitigating climate change, are expected to see a significant rise in residential applications. However, R134a, widely employed in these systems, has a high GWP of 1530, highlighting the need for more eco-friendly substitutes. Hydrofluoroolefins (HFOs) and natural fluids, particularly hydrocarbons (HCs), have emerged as promising fourth-generation refrigerants due to their negligible ozone depletion potential (ODP) and very low global warming potential (GWP). Despite the potential of these new refrigerants, an optimal replacement for R134a in heat pumps has yet to be found. In this regard, this study investigates the potential of the low-GWP HFO/HC mixture R1234yf/R600a (0.85/0.15) as a drop-in replacement for R134a in water-to-water heat pumps. The research conducts a comparative analysis between R134a and the nearly-azeotropic mixture, assessing their performance under identical heating conditions across 20 different combinations of heat sink and heat source temperatures, ranging from 35 °C to 70 °C and from 10 °C to 20 °C respectively. The R1234yf/R600a mixture exhibited a lower pressure ratio and higher mass flow rates compared to R134a. Additionally, the mixture showed favorable performance in terms of power consumption and compressor outlet temperatures, with slightly lower COP compared to the baseline fluid. These findings suggest that with proper optimization, the R1234yf/R600a mixture could be a viable and sustainable alternative to R134a in residential heat pump applications.