Working fluid selection and design of small-scale waste heat recovery systems based on organic Rankine cycles

Demand for the use of energy systems, entailing high efficiency as well as availability to harness renewable energy sources, is a key issue in order to tackling the threat of global warming and saving natural resources. Organic Rankine cycle (ORC) technology has been identified as one of the most promising technologies in recovering low-grade heat sources and in harnessing renewable energy sources that cannot be efficiently utilized by means of more conventional power systems. The ORC is based on the working principle of Rankine process, but an organic working fluid is adopted in the cycle instead of steam. This thesis presents numerical and experimental results of the study on the design of small-scale ORCs. Two main applications were selected for the thesis: waste heat re- covery from small-scale diesel engines concentrating on the utilization of the exhaust gas heat and waste heat recovery in large industrial-scale engine power plants considering the utilization of both the high and low temperature heat sources. The main objective of this work was to identify suitable working fluid candidates and to study the process and turbine design methods that can be applied when power plants based on the use of non-conventional working fluids are considered. The computational work included the use of thermodynamic analysis methods and turbine design methods that were based on the use of highly accurate fluid properties. In addition, the design and loss mechanisms in supersonic ORC turbines were studied by means of computational fluid dynamics. The results indicated that the design of ORC is highly influenced by the selection of the working fluid and cycle operational conditions. The results for the turbine designs in- dicated that the working fluid selection should not be based only on the thermodynamic analysis, but requires also considerations on the turbine design. The turbines tend to be fast rotating, entailing small blade heights at the turbine rotor inlet and highly supersonic flow in the turbine flow passages, especially when power systems with low power outputs are designed. The results indicated that the ORC is a potential solution in utilizing waste heat streams both at high and low temperatures and both in micro and larger scale appli- cations.

The role of nuclear and other conventional power plants in the flexible energy system

This thesis reviews the role of nuclear and conventional power plants in the future energy system. The review is done by utilizing freely accesible publications in addition to generating load duration and ramping curves for Nordic energy system. As the aim of the future energy system is to reduce GHG-emissions and avoid further global warming, the need for flexible power generation increases with the increased share of intermittent renewables. The goal of this thesis is to offer extensive understanding of possibilities and restrictions that nuclear power and conventional power plants have regarding flexible and sustainable generation. As a conclusion, nuclear power is the only technology that is able to provide large scale GHG-free power output variations with good ramping values. Most of the currently operating plants are able to take part in load following as the requirement to do so is already required to be included in the plant design. Load duration and ramping curves produced prove that nuclear power is able to cover most of the annual generation variation and ramping needs in the Nordic energy system. From the conventional power generation methods, only biomass combustion can be considered GHG-free because biomass is considered carbon neutral. CFB combusted biomass has good load follow capabilities in good ramping and turndown ratios. All the other conventional power generation technologies generate GHG-emissions and therefore the use of these technologies should be reduced.

In search of good relationships to music : understanding aspiration and challenge in developing music school teacher practices

This study focuses on teacher practices in publicly funded music schools in Finland. As views on the aims of music education change and broaden, music schools across Europe share the challenge of developing their activities in response. In public and scholarly debate, there have been calls for increased diversity of contents and concepts of teaching. In Finland, the official national curriculum for state-funded music schools builds on the ideal that teaching and learning should create conditions which promote ‘a good relationship to music’. The meaning of this concept has been deliberately left open in order to leave room for dialogue, flexibility, and teacher autonomy. Since what is meant by ‘good’ is not defined in advance, the notion of ‘improving’ practices is also open to discussion. The purpose of the study is to examine these issues from teachers’ point of view by asking what music school teachers aim to accomplish as they develop their practices. Methodologically, the study introduces a suggestion for building empirical research on Alperson’s ‘robust’ praxial approach to music education, a philosophical theory which is strongly committed to practitioner perspectives and musical diversity. A systematic method for analysing music education practices, interpretive practice analysis, is elaborated with support from interpretive research methods originally used in policy analysis. In addition, the research design shows how reflecting conversations (a collaborative approach well-known in Nordic social work) can be fruitfully applied in interpretive research and combined with teacher inquiry. Data have been generated in a collaborative project involving five experienced music school teachers and the researcher. The empirical material includes transcripts from group conversations, data from teacher inquiry conducted within the project, and transcripts from follow-up interviews. The teachers’ aspirations can be understood as strivings to reinforce the connection between musical practices and various forms of human flourishing such that music and flourishing can sustain each other. Examples from their practices show how the word ‘good’ receives its meaning in context. Central among the teachers’ concerns is their hope that students develop a free and sustainable interest in music, often described as inspiration. I propose that ‘good relationships to music’ and ‘inspiration’ can be understood as philosophical mediators which support the transition from an indeterminate ‘interest in music’ towards specific ways in which music can become a (co-)constitutive part of living well in each person’s particular circumstances. Different musical practices emphasise different aspects of what is considered important in music and in human life. Music school teachers consciously balance between a variety of such values. They also make efforts to resist pressure which might threaten the goods they think are most important. Such goods include joy, participation, perseverance, solid musical skills related to specific practices, and a strong sense of vitality. The insights from this study suggest that when teachers are able to create inspiration, they seem to do so by performing complex work which combines musical and educational aims and makes general positive contributions to their students’ lives. Ensuring that teaching and learning in music schools remain as constructive and meaningful as possible for both students and teachers is a demanding task. The study indicates that collaborative, reflective and interdisciplinary work may be helpful as support for development processes on both individual and collective levels of music school teacher practices.