Nanofluids Application as Nanolubricants in Heat Pumps Systems

In the last years, various applications have been proposed for nanofluids in the Heating, Ventilation, Air Conditioning and Refrigeration (HVACR) field; their use as primary and secondary fluids, also as lubricants, was kept into account to improve the systems performance. The present work was developed to test the applicability of nanofluids as lubricants in the compressors of the heat pump systems, with the purpose to experimentally detect the possible positive effects of nanolubricants. Several nanolubricants, formed by Polyolester (POE) or mineral oil, as base fluid, and titanium oxide (TiO2) or single wall carbon nano-horns (SWCNH), as nanoparticles, were studied in a dedicated test rig. In contrast with the published literature, no improvement was detected using nanofluids instead of commercial oil. All results will be deeply discussed in the paper

Experimental stability analysis of different water-based nanofluids

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 (TiO2) 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 TiO2-water nanofluids, improved the nanofluid stability

Characterization of nanofluids formed by fumed Al2O3 in water for geothermal applications

The European Project Cheap-GSHPs, recently approved, aims at reducing the total cost of shallow geothermal systems by 20-30%, also improving actual drilling/installation technologies and designs of Ground Source Heat Exchangers (GSHEs), in combination with a holistic engineering approach to optimize the entire systems for building and district heating and cooling applications, across the different underground and climate conditions existing within the EU. In this frame, the efficiency of the system heat pump/GSHE will be an important task and a part of this project will be on the analyses of possible alternative secondary fluids to be used in the geothermal probe. Here, suspensions of fumed Al2O3 in water will be considered as possible efficient secondary fluids. Three different concentrations will be studied, i.e. 10%, 30% and 40%, and the stability, thermal conductivity and dynamic viscosity of these fluids will be characterized, in order to analyse their possible employment as thermal fluids

Correction to "New Measurements of the Apparent Thermal Conductivity of Nanofluids and Investigation of Their Heat Transfer Capabilities"

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Thermodynamic Analysis for the Selection of low GWP Refrigerants in Ground Source Heat Pumps

One of the main objectives of the European Commission in the buildings sector, responsible for approximately 40% of total energy consumption and 36% of greenhouse gas emissions, is to identify technological solutions capable of reducing energy consumption and at the same time greenhouse gas emissions. For this purpose, ground source heat pump system (GSHPs) is a technology of particular interest that promises to considerably reduce greenhouse gas emissions of HVAC systems (up to 44% compared to air source heat pumps). In order to develop and test innovative GSHPs to be used for heating and cooling in the various European climatic zones, EU has funded the GEO4CIVHIC project, which will have a duration of 4 years and will end in 2022. As part of the project, the problem of identifying new generation low environmental impact refrigerants to be used in innovative GSHPs is tackled. In this article, we report the results of an energetic and exergetic analysis of the performance of heat pumps based on simulations carried out both on simple reverse cycles and on more complex cycles. Low pressure alternative fluids have been considered as an alternative to R134a and high pressure fluids as an alternative to R410A. The simulations were conducted at various heat sink and heat source temperature conditions, in order to evaluate the GSHPs performance in the whole range of real conditions that can be found in Europe. Particular attention was paid to the compression phase, with the aim to simulate the compressor performance in a more realistic way than simply assuming constant isentropic efficiency

Energy Costs Division and Plant Modification in a Large Research Complex: the Experience of Padova National Research Council (CNR) Area

The CNR area was built in the 1970s in Padova (Italy): many buildings hosting different Institutes are served by the central heating and cooling system and a common Medium and Low voltage supply. Costs division criteria, mainly based on the number of personnel units and the size of buildings of each Institute, were used in the past; due to current high costs of energy, these criteria have been revised and based on more objective parameters. This paper deals with the methods that have been studied to reduce thermal and cooling energy consumption, based on the operative conditions of buildings and specific characteristics of area HVAC (Heating Ventilation and Air Conditioning) plants. As a result of this optimization, some plant modifications have been evaluated and implemented. The results of new plant configuration and energy consumption are presented and discussed

Analysis of the Parameters Required to Properly Define Nanofluids for Heat Transfer Applications

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