Exhaust Gas Heat Recovery for an ORC: A Case Study

This work aims at developing a heat exchanger (HEX) sizing approach considering the need to maximize the heat recovery within the limitations of pressure drop and space. The application consists in the recovery of the energy contained in exhaust gases coming from an internal combustion engine (ICE). Two heat exchanger geometries are selected as case studies. The design approach involves the application of design of experiments (DOE) techniques and computational fluid dynamics (CFD) simulations. DOE techniques are used to observe the influence of some selected parameters (factors) in the design of the heat exchangers, and CFD simulations are carried out to determine the performance of the heat exchanger. The information obtained is used to determine local Nusselt number correlations that are used for the design of the heat exchangers

The Cross-Cultural Adaptation of International Medical Graduates to General Practice in New Zealand

This study demonstrates that occupational success is an important factor in the adaptation of highly skilled migrants to host societies, as seen through the experiences of the international medical graduates (IMGs) who came to New Zealand and became general practitioners (GPs). New Zealand is reliant on IMGs to support and deliver quality health care to its population: IMGs constitute over 40% of the current medical workforce. The central contributions of this thesis are to three distinct discourses on the experiences of migrants. The first contribution is an investigation and critical analysis of the experiences of IMGs who came to practise medicine in New Zealand. During the course of analysing the primary data, and relating it to existing literature, it was observed there was a lack of a model that captured the essence of the specific acculturation of highly skilled migrants such as IMGs. Therefore, the second contribution is the development of a concise integrated framework - the Integrated Framework for Acculturative Research (IFAR), for the study of highly skilled migrants’ acculturation to new environments. The experiences of the IMGs who came to New Zealand have been used to develop and discuss the application of the IFAR to cross-cultural adaptation research. There is an historical component to these narratives as the IMGs in this research spanned nearly five decades of acculturation into New Zealand society. The third contribution is in the domain of qualitative research, where email interviews (e-interviews) have been used to gather data within the context of ethnography. While there has been significant literature, theories and models developed about cross-cultural and intercultural adaptation of migrants into host nations, there are gaps in the understanding of the experiences of highly skilled migrants, who are different from other types of migrants, given their predispositions and higher levels of human capital such as education and work experience. There is an emerging literature on this subject, to which this study adds. The IMGs in this study used their human capital to become medical practitioners in New Zealand, achieving their main motivation for migrating in the first place. The reasons the IMGs stated for migration are consistent with existing literature on ‘push’ and ‘pull’ factors; however for all of them, the primary reason was to pursue their medical careers in New Zealand. After arrival, most of them had to do additional training before they were allowed to practise independently. The medical training ranged from those required to achieve the registration of the Medical Council of New Zealand (MCNZ), to those needed to achieve the Fellowship of the Royal New Zealand College of General Practitioners (RNZCGP). The participants noted several challenges during their training period, including a lack of clear information on what was required; having to prove their ability despite many years of experience as medical practitioners; dealing with poor teachers for some; having to travel long distances to attend training seminars; and for a few, dealing with financial constraints. However, they all overcame such challenges and became successful independent GPs. Their age, pre-migration human capital, and post-migration motivation were essential in initiating their desired occupations in New Zealand. These three success factors are supported by emerging literature on highly skilled migrants. The early participants initially worked in hospital settings before choosing general practice. Some left because they experienced issues in the hospital environment such as tensions with local colleagues, and the need to work long unfriendly hours. All participants noted that the reasons for choosing general practice included their desire to work more closely with communities and to experience a greater variety of medicine. Additionally, many reported that the flexibility of working in general practice gave them a better work/life balance that allowed them to do other things within the community and outside of their general practice. Female participants noted that general practice was more conducive when raising a family, compared to hospital-based specialties. These are the strengths of general practice that are well documented in literature. While the participants did not note any major ongoing challenges, some reported being frustrated with the poor links between primary and secondary health care that impacted on the timely care of their patients. With an increase in chronic conditions and mental health issues, coupled with an ageing population, many participants reported that they needed more time and frequent consultations to treat certain patients. Given New Zealand’s co-payment system, participants reported having to consider the appropriate levels of care for patients with chronic conditions so as not to financially overburden them. For participants working in rural and economically deprived areas, there were other social factors that affected their medical practice, such as the high levels of family violence, sexual health issues, teenage pregnancies and substance abuse. These issues are supported by current literature regarding health and society in New Zealand. Despite the challenges they faced, all the IMGs planned on continuing to work in general practice in New Zealand for the foreseeable future. Migrants’ pledge of continuing in their chosen occupations in host nations can be a very good indicator of acculturation and integration. The MCNZ reported that nearly two-thirds of all IMGs left New Zealand two years post-registration. However, retention rates improved significantly once IMGs obtained their vocational registration. Occupational continuity sheds light on immigrants’ level of acculturation because it establishes that they are comfortable living among the hosts, and working in their chosen professions. This study demonstrates that occupational success is a key prerequisite to continuity and long-term integration into host societies. As highly skilled migrants, they could have gone to almost any country but they chose New Zealand. They remain here, having forged their medical careers and a lifestyle of their choosing. They now consider New Zealand their home, at least until they enter a different stage of their lives

On a deterministic mathematical model which efficiently predicts the protective effect of a plant extract mixture in cirrhotic rats

In this work, we propose a mathematical model that describes liver evolution and concentrations of alanine aminotransferase and aspartate aminotransferase in a group of rats damaged with carbon tetrachloride. Carbon tetrachloride was employed to induce cirrhosis. A second groups damaged with carbon tetrachloride was exposed simultaneously a plant extract as hepatoprotective agent. The model reproduces the data obtained in the experiment reported in [Rev. Cub. Plant. Med. 22(1), 2017], and predicts that using the plants extract helps to get a better natural recovery after the treatment. Computer simulations show that the extract reduces the damage velocity but does not avoid it entirely. The present paper is the first report in the literature in which a mathematical model reliably predicts the protective effect of a plant extract mixture in rats with cirrhosis disease. The results reported in this manuscript could be used in the future to help in fighting cirrhotic conditions in humans, though more experimental and mathematical work is required in that case

Thermal Simulation of the Fresh Food Compartment in a Domestic Refrigerator

In the field of domestic refrigeration, it is important to look for methods that can be used to simulate, and, thus, improve the thermal behavior of the fresh food compartment. In this sense, this study proposes some methods to model the thermal behavior of this compartment when the shelves’ positions are changed. Temperature measurements at specific locations in this compartment were obtained. Several shelf position combinations were performed to use three 2D interpolation methods in order to simulate the temperature mean and the temperature variance. The methods used were: Lagrange’s interpolation, cubic spline interpolation and bilinear interpolation. Two validation points were chosen to verify the proposed methods. By comparing the experimental results with the computer simulations, it was possible to conclude that the method of Lagrange’s interpolation provided values that were not close to the real measured values. On the other hand, it was observed that the method of bilinear interpolation offered the best results, estimating values which were very close to the actual experimental measurements. These interpolation methods were used to build color thermal graphs that can be used to find some of the most appropriate shelf position combinations in this type of refrigerator. By inspection of these thermal graphs, it can be seen that the lowest average temperature was obtained when one shelf was located at 24.5 cm while the second shelf was located at 29.5 cm measured from the top of the compartment. In the same way, it can be seen that the minimum temperature variance was obtained when only one shelf was inside the compartment and this shelf was located at 29.5 cm

Automated modelling of complex refrigeration cycles through topological structure analysis

We have developed a computational method for analysis of refrigeration cycles. The method is well suited for automated analysis of complex refrigeration systems. The refrigerator is specified through a description of flows representing thermodynamic sates at system locations; components that modify the thermodynamic state of a flow; and controls that specify flow characteristics at selected points in the diagram. A system of equations is then established for the refrigerator, based on mass, energy and momentum balances for each of the system components. Controls specify the values of certain system variables, thereby reducing the number of unknowns. It is found that the system of equations for the refrigerator may contain a number of redundant or duplicate equations, and therefore further equations are necessary for a full characterization. The number of additional equations is related to the number of loops in the cycle, and this is calculated by a matrix-based topological method. The methodology is demonstrated through an analysis of a two-stage refrigeration cycle. © 2009 Elsevier Ltd. All rights reserved

Second Law Analysis of a Mobile Air Conditioning System with Internal Heat Exchanger Using Low GWP Refrigerants

This paper investigates the results of a Second Law analysis applied to a mobile air conditioning system (MACs) integrated with an internal heat exchanger (IHX) by considering R152a, R1234yf and R1234ze as low global warming potential (GWP) refrigerants and establishing R134a as baseline. System simulation is performed considering the maximum value of entropy generated in the IHX. The maximum entropy production occurs at an effectiveness of 66% for both R152a and R134a, whereas for the cases of R1234yf and R1234ze occurs at 55%. Sub-cooling and superheating effects are evaluated for each one of the cases. It is also found that the sub-cooling effect shows the greatest impact on the cycle efficiency. The results also show the influence of isentropic efficiency on relative exergy destruction, resulting that the most affected components are the compressor and the condenser for all of the refrigerants studied herein. It is also found that the most efficient operation of the system resulted to be when using the R1234ze refrigerant

Análisis de redes en twitter para la inserción en comunidades : El caso de un producto agroindustrial

The hashtags and relevant content in Twitter, related to the agroindustrial product mezcal were analysed, and the so-called ‘influencers’ were also identified. For doing this, 57.362 tweets were extracted and stored; three networks were built: users-hashtags, retweets, and mentions, which were studied by using social network analysis (SNA). The application of the SNA allowed revealing certain kind of hidden patterns within the social media complex relationships, which can be useful for designing strategies aimed at positioning actors and spread information. The results allow stating that in order to get inserted in the social network, the following should be considered: the use of combined hashtags, the message content kind, including pictures attached, and mentioning the most influential accounts who are embedded in already formed communities.</p