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Given the growing demand for cooling, and taking into account the impact of global warming associated with cooling technologies the global climate commitment to reduce the impact of fluorinated gases and the regulations controlling their use in the European Union has increased . This thesis investigates new refrigerants that have been recently proposed to meet the demands of the heat pumps in the refrigeration industry, which must satisfy the legislative requirements of the F-gas Regulation and facilitate meeting the goals of Montreal and Kyoto Agreement.The fluids R32, R1234ze, R1234yF, R452b and R454b have been theoretically analyzed in comparison with the commonly used fluorinated refrigerant in heat pump: R410A. To compare these refrigerants, an excel sheet has been used to calculate the COP for the different cases studied using the REFPROP computer program to know the thermodynamic data of each fluid. The cases studied are the three different heat pump applications : radiators, radiant floor and fan coil and it has been studied for an evaporator temperature range of -15 to 12 ºC, i.e. the COP has been calculated for eighteen different situations. For all of them, the same conclusion has been concluded: all these five proposed fluids have a higher COP than the fluid to be replaced, R410A. It based on this COP for all the cases studied, the best fluids are R454b and R1234Ze(E). Choosing the fluid R454b as the best alternative because its latent heat and vapour density are higher that R1234ze(E) and therefore the flow and size of the pump is smaller, which generally translates into economic savings.However, this refrigerant shows flammability characteristics. For this reason, this paper is checked the fluid risk by a risk assessment. For this assessment two scenarios are analyzed by numerical model, Plume Model: outside and inside of 20 m2 scenario using a 50 kW heat pump. Concluding on the one hand, that in outside conditions a leak would not enter ignition due to the concentration obtained is less than the minimum necessary. In addition from 200 meters of distance the concentration of this fluid would be zero.And that in the hypothetical case that a jet fire takes place is observed that from 10 meters of the leak there is no more radiation.On the other hand, for the room scenario the calculated concentration would be 550 g/m3. This concentration is higher than the acute toxicity exposure limit (435 g/m3) so it is not safe for a human being to work in the situations described.

Pressure relief valves are mechanical devices used in the industry to protect systems against excessive pressure, thus preventing accidents from occurring. Nowadays, a multitude of flows can pass through these pressure relief valves, such as the biphasic ones, in which this master's thesis is going to be framed. These are used in industries such as the oil and chemical industries. The problem comes when trying to characterize them since there is not enough experimental data in the literature to be able to develop a good model, in addition to the fact that if the valves are over-sized or under-sized, it could lead to more economic costs and possible safety problems.In this context, the present Master's thesis aims to find a calculation model that allows the adjustment of some experimental data to predict their behaviour. To achieve this goal, the different methods that can be used for pressure relief valves with two-phase flows will be studied and an analysis of the results will be carried out to find the model that best predicts the behaviour and adjusts to the experimental data provided.In this thesis, we have taken as reference the experimental data provided by the University of La Sapienza, Rome, in which the mass flow rate of a steam/water mixture passing through a valve of 0.01 m diameter has been measured for different initial pressures and qualities of the inlet vapour of the mixture. Therefore, it was decided to try to fit some experimental data to some of the existing models (HEM, HNE-DS, API, ISO) to describe the behaviour of these fluids.The results obtained have shown the differences that exist between the two homogeneous models (HEM, HNE-DS) as well as the similarity of each of them with the other two described (API, ISO). The conclusion has been reached that the model that best fits the behaviour of the data is the homogeneous non-equilibrium model since it is in this model that a greater similarity is found between the experimental mass flow rate provided and the theoretical mass flow rate calculated. This hypothesis has been corroborated thanks to a comparison made to the HEM and HNE-DS models in which it has been concluded that at high pressures the homogeneous equilibrium model is the one that best fits the data but the model has wide spread results, but at the end, for all the experimental data the homogenous non-equilibrium model is the one that in the end best fits the them.

The transportation of hazardous materials via pipelines is often considered a safer alternative to other transportation modalities such as railway, road and ship. However, pipelines often cross industrial and highly populated areas, so that their failure can pose a significant risk to the surrounding environment and the exposed population: the possible release of flammable and/or toxic materials in such areas can generate catastrophic events with very severe consequences. A number of accidents have actually occurred in the past years, and even when no deaths or injured are reported, significant damages to the surrounding environment often occur. This suggests that, given the extremely wide extension of the network worldwide, and the very high amounts of transported materials, a careful analysis is still required. In addition, the construction of pipelines also involves the contribution of expertise from a range of technical areas. As a consequence, the occurrence of accidents and the impact of their consequences, depend on the combination of a large number of parameters. In the present paper, an analysis of data relative to pipelines transporting hazardous materials has been carried out, and the influence of specific issues connected with their type and operation, has been assessed.

Electric vehicle industry has been rapidly developing internationally due to the renewed interest in low- or zero-emission vehicles. So far, Lithium-Ion batteries, is the technology that best fits the needs of electric vehicles, due to their large specific energy density and specific power, making these cells ideally suited for high rate-of-discharge applications such as during acceleration. In spite of this, there are safety concerns using Lithium-ion cells because of the use of high energy materials. Heat is a major battery killer and Lithium secondary cells need careful temperature control. Operating at high temperatures brings on a set of different problems which may result in the destruction of the cell: unless heat is removed faster than it is generated, a thermal runaway may occur. Tests with an air cooling system were carried out using an experimental loop specially designed: the tests were performed on a module consisting of four pouch cells, manufactured by EiG, connected in series. The module was discharged with a current of 80 A (4C discharge) and cooled with air at velocity ranging from 0 to 7 m/s. It was found that it is possible to completely discharge the batteries using air velocities higher than (or equal to) 4 m/s. Increasing the air velocity the temperature difference between the centre of the cell and the electrodes decreases. In spite of this, it was not possible to reach a uniform temperature distribution within a cell, and within the pack, using air as cooling fluid.

The continuously increasing power involved in many applications, coupled with the very small size of a number of component devices, is pushing the technical community to look for more efficient heat transfer systems, to remove the heat generated and keep the system under controlled operating conditions. In particular, significant interest has been devoted to the use of the so-called nanofluids, obtained by suspending nano-sized particles in conventional heat transfer liquids. According to some literature, these suspensions present enhanced heat transfer capabilities, without the inconveniencies of particles settlement and clogging of the channels encountered using larger particles. However, other results show that the actual improvement in the heat transfer efficiency may depend on the adopted working conditions and on the reference parameters (fluid velocity, Reynolds number, pressure drop, etc.) assumed to compare the performances of the nanoparticles suspensions with those of the clear thermal fluid. In the present work heat transfer experiments were carried out on a number of nanofluids systems, varying the type and the concentration of the nanoparticles, and the fluid dynamic regime. The investigated suspensions gave rise to heat transfer coefficients different from those of their respective clear thermal fluid, the thermal efficiency being higher or lower, depending on the fluid dynamic parameter used as a base for comparing the systems. Generally speaking, in most cases nanofluids may give an advantage from the heat transfer point of view only when the conditions are unfavorable for the traditional thermal fluids.