Performance improvements of supermarket R744 systems by pivoting compressor arrangements

The adoption of the EU F-Gas regulation 517/2014 and the development of the Multi Ejector concept have led CO2 to take center stage as one of the preferred solutions in several applications, at the expense of synthetic refrigerants. Despite the expected significant energy saving in warm climates using the Multi Ejector, the increase in investment costs and level of complexity would hinder its spread. In this work a numerical and experimental campaign have been performed to explore the implementation of “pivoting” compressors, i.e. a technique that enables the medium temperature (MT) and parallel (IT) compressors in a booster system to be interchangeable according to cooling loads, ambient conditions and ejector capacity. The novel configuration presented in this work helps to downsize the installed compressor capacity in ejector-supported systems while maintaining all the benefits due to the ejector. The basic version of the solution is based on: i) MT and low temperature (LT) compressors, ii) high pressure controlled through a Multi Ejector both during summer and winter conditions. The tests performed in the laboratory proved how the “pivoting” solution is beneficial to attain a higher degree of flexibility with more compact systems while maintaining the efficiency and justifying economically the ejector implementation. An additional solution called LT “pivoting”, i.e. connecting LT compressors either to MT or IT compressors, proved to be particularly useful for energy saving.Performance improvements of supermarket R744 systems by pivoting compressor arrangementsacceptedVersio

Ejector for the world: simplified ejector-supported CO2 refrigeration systems for all climates

The novel configuration presented in this work simplifies the layout of ejector-supported booster systems while maintaining all the benefits of an ejector implementation. The basic version of the solution is based on: i) MT and LT compressor suction groups, ii) flooded MT evaporation with increased evaporation temperature, and iii) ejector utilization throughout the year. The ejector is actively operated as a high-pressure-control device at elevated ambient temperatures ('summer mode'). With lower ambient temperatures the ejector is operated passively, and the high-pressure control is performed by individual metering devices upstream of the different evaporators ('winter mode'). The feasibility tests performed in the laboratory proved that energy-wise this novel system configuration outperforms traditional and parallel compression supported booster systems under any condition. The pressure lift measured with active ejector is sufficient for liquid refrigerant distribution to the evaporators, while the pressure drop recorded in passive mode is negligible for practical applications.Ejector for the world: simplified ejector-supported CO2 refrigeration systems for all climatesacceptedVersio

Assessment of chicken breast shelf life based on bench-top and portable near-infrared spectroscopy tools coupled with chemometrics

Abstract Objectives Near-infrared (NIR) spectroscopy is a rapid technique able to assess meat quality even if its capability to determine the shelf life of chicken fresh cuts is still debated, especially for portable devices. The aim of the study was to compare bench-top and portable NIR instruments in discriminating between four chicken breast refrigeration times (RT), coupled with multivariate classifier models. Materials and Methods Ninety-six samples were analysed by both NIR tools at 2, 6, 10 and 14 days post mortem. NIR data were subsequently submitted to partial least squares discriminant analysis (PLS-DA) and canonical discriminant analysis (CDA). The latter was preceded by double feature selection based on Boruta and Stepwise procedures. Results PLS-DA sorted moderate separation of RT theses, while shelf life assessment was more accurate on application of Stepwise-CDA. Bench-top tool had better performance than portable one, probably because it captured more informative spectral data as shown by the variable importance in projection (VIP) and restricted pool of Stepwise-CDA predictive scores (SPS). Conclusions NIR tools coupled with a multivariate model provide deep insight into the physicochemical processes occurring during storage. Spectroscopy showed reliable effectiveness to recognise a 7-day shelf life threshold of breasts, suitable for routine at-line application for screening of meat quality

Metal-Free Antibacterial Additives Based on Graphene Materials and Salicylic Acid: From the Bench to Fabric Applications

[Image: see text] The custom functionalization of a graphene surface allows access to engineered nanomaterials with improved colloidal stability and tailored specific properties, which are available to be employed in a wide range of applications ranging from materials to life science. The high surface area and their intrinsic physical and biological properties make reduced graphene oxide and graphene oxide unique materials for the custom functionalization with bioactive molecules by exploiting different surface chemistries. In this work, preparation (on the gram scale) of reduced graphene oxide and graphene oxide derivatives functionalized with the well-known antibacterial agent salicylic acid is reported. The salicylic acid functionalities offered a stable colloidal dispersion and, in addition, homogeneous absorption on a sample of textile manufacture (i.e., cotton fabrics), as shown by a Raman spectroscopy study, thus providing nanoengineered materials with significant antibacterial activity toward different strains of microorganisms. Surprisingly, graphene surface functionalization also ensured resistance to detergent washing treatments as verified on a model system using the quartz crystal microbalance technique. Therefore, our findings paved the way for the development of antibacterial additives for cotton fabrics in the absence of metal components, thus limiting undesirable side effects

Experimental analysis of an advanced R744 refrigeration system

This work explores the implementation of the pivoting technology and CTES in a R744 refrigeration system. The study allows to highlight the benefits of having a pivoting arrangement, such as a reduction in number of compressors installed and investment cost, an increment of the flexibility of the rack. Furthermore, a thermal design of the CTES and a numerical simulation of a two-phase thermosyphon loop has been done

Experimental analysis of advanced R744 refrigeration system

Carbon dioxide is one of the oldest refrigerants, as it was used widely at the end of the nineteenth century. However, around 1931 it started its decline when synthetic refrigerants came into the market showing a higher efficiency and a cheaper implementation in the refrigeration systems, in terms of equipment. Nonetheless, carbon dioxide as a refrigerant is gaining more and more space over the last years due to its thermodynamic properties, the capability to be an optimal refrigerant for many applications and its usage reduces the emissions of greenhouse gases (GHG). Its wide implementation is confirmed by the fact that the energy demand of supermarkets can be fully satisfied by subcritical or transcritical cycles, depending on whether the climate is cold or hot respectively. In this thesis, the background of the description of refrigeration cycles using R744, both with ejector and not, are introduced at the beginning of the first chapter. The chapter continues with the description of Cold Thermal Energy Storages, i.e. CTES, which are currently investigated as an optimal solution that grants an enhancement in terms of energy saving. This technology allows energy production and storage when the electricity prices are at their lowest (when charged during the night), in order to provide further cooling capacity when the electricity prices are at their highest (during the day, when people come back from work) and to smooth the usage peak which normally happens over the afternoon. This Master Thesis project is focused on two different tasks. The first part of the Master Thesis is dealing with the investigation on the pivoting technology which is capable to reduce the number of compressors installed in the rack by using at the suction port of some compressors two valves that switch according to their position and the need. The second part is dealing with the design of a CTES located on the top of a supermarket’s display cabinet. The first task was planned to start from a numerical simulation to simulate the performance of a simplified refrigeration system using the polynomial equations for each compressor, ending with an experimental campaign that has been carried out at the SuperSmart-Rack at NTNU, Trondheim. The investigation of the pivoting technology has been done considering two different high-pressure (HP) control devices, as high-pressure valve and high pressure lift multi–ejector block, and many different temperatures at the outlet of the gas cooler to reproduce different ambient conditions. As it has been seen during the experimental campaign the most critical situation to predict accurately is when the HP multi-ejector is in operation because of the performance of the block itself. This allowed also to highlight the need to improve the ejector, since it is an expensive technology and can be used only over a certain period of the year, depending on the geographical area. From the obtained results, the pivoting enhances the flexibility of the rack lowering the number of compressors installed by one, and when the multi-ejector block is used to control the high pressure the number can be reduced further by another compressor. However, the implementation of the ejector without pivoting technology would be unsatisfactory as the number of compressors needed would raise. Because of the ejector, a lot of capacity is shifted to the parallel side. A common practice will be to include a new compressor to cover the load, that it will be used for few operating conditions. Moreover, no degradation has been seen when pivoting are working, leading to the same power consumption and COP. The second task of this Master Thesis is the modeling of a phase change thermal storage, that uses R744 as refrigerant, and water as the phase change material. The task required the design and the numerical simulation of the phase change process that occurs inside the CTES during the discharging stage. As reported widely in literature, the key factor of a two-phase thermosyphon loop is the investigation of the pressure losses over all the circuits. The cabinet available at the NTNU/SINTEF laboratories in Trondheim was used as a reference for the installation of the CTES on the top of the cabinet itself, considering the evaporator installed with its own geometric and construction features. The CTES has been modeled to match the duty of this evaporator, as well as the liquid and vapor line that linked the inlet-outlet of the evaporator with outlet-inlet of the CTES. It was concluded that, because of the low heat transfer in the CTES, stable and effective use of the thermosyphon principle can be used for a higher temperature application, for instance, the conservation of vegetables. It has been proven that a very small temperature difference between CTES and the evaporator leads to a huge heat transfer area. The cold storage was designed like a tank with circular finned over smooth tubes and is used to condensate the vapor coming from the evaporator. A liquid head of approximately 1.8 meters is used to overcome all the pressure losses in the system. The design was followed by numerical simulation of the implemented system.

Multi Ejector and pivoting-supported R744 application with AC for supermarkets

CO2 refrigeration units are gaining market shares thanks to the ability to provide an energy efficient performance for industrial and commercial refrigeration applications in any climate. As with all the applications, the investment and operation costs should be kept as low as possible, to reduce the payback time and promote the introduction of innovative system solutions. In this work the flexibility achieved by implementing the pivoting technology in a supermarket refrigeration application is investigated both at design- and partial load conditions. The air conditioning (AC) load is also considered within a wide range of ambient temperatures. The Multi Ejector block utilized will be analyzed in terms of performance and its effect on the compressor combinations at different operating conditions. The objective is to increase the flexibility of the centralized rack through a proper design and sizing of the compressor pack equipped with the pivoting technology, while maintaining the efficiency and reducing the investment costs. This work shows that a Multi Ejector pivoting-supported system will be beneficial from the flexibility and capital costs point of view, and the benefit will be more consistent if the AC load is part of the integrated system architecture. Furthermore, a thorough investigation has been conducted whenever the ejector capacity is too high compared to the load, proposing two alternative solutions.acceptedVersio

Multi Ejector and pivoting-supported R744 application with AC for supermarkets

CO2 refrigeration units are gaining market shares thanks to the ability to provide an energy efficient performance for industrial and commercial refrigeration applications in any climate. As with all the applications, the investment and operation costs should be kept as low as possible, to reduce the payback time and promote the introduction of innovative system solutions. In this work the flexibility achieved by implementing the pivoting technology in a supermarket refrigeration application is investigated both at design- and partial load conditions. The air conditioning (AC) load is also considered within a wide range of ambient temperatures. The Multi Ejector block utilized will be analyzed in terms of performance and its effect on the compressor combinations at different operating conditions. The objective is to increase the flexibility of the centralized rack through a proper design and sizing of the compressor pack equipped with the pivoting technology, while maintaining the efficiency and reducing the investment costs. This work shows that a Multi Ejector pivoting-supported system will be beneficial from the flexibility and capital costs point of view, and the benefit will be more consistent if the AC load is part of the integrated system architecture. Furthermore, a thorough investigation has been conducted whenever the ejector capacity is too high compared to the load, proposing two alternative solutions

Intraoperative end-tidal concentration of isoflurane in cats undergoing ovariectomy that received tramadol, buprenorphine or a combination of both

The aim of the study was to evaluate the end-tidal concentration of isoflurane required to maintain heart and respiratory rate within \ub1 20% of basal measurement in cats undergoing ovariectomy that received buprenorphine, tramadol or a combination of both

Evaluation of sedation and clinical effects of midazolam with ketamine or dexmedetomidine in pet rabbits.

The effects of two sedation protocols combining midazolam with ketamine (ketamine group) or dexmedetomidine (dexmedetomidine group) were studied in dwarf companion rabbits undergoing abdominal ultrasound scan. The onset of sedation was faster in the ketamine group; a few rabbits in the dexmedetomidine group required additional doses to lose the righting reflex, although sedation time was not different between groups. A semi-quantitative scale was used to score sedation quality, which was higher in rabbits that received dexmedetomidine rather than ketamine. Pulse rate was lower in the dexmedetomidine group (206 vs 240 bpm), although Doppler blood pressure was higher than in the ketamine group (109 vs 89 mm Hg). Respiratory rate decreased in relation to the baseline values with both protocols but arterial haemoglobin saturation with oxygen was maintained similar to the pre-sedation values throughout the entire procedure, regardless of protocol used and without oxygen supplementation. Both protocols allowed performance of ultrasound scanning, although dexmedetomidine may be preferred if a deep sedation level is required