Mathematical Modelling of a Reciprocating Piston Expander

Modern internal combustion (IC) engines reject around two thirds of the energy provided by the fuel as low-grade waste heat. Capturing a portion of this waste heat energy and transforming it into a more useful form of energy could result in a significant reduction in fuel consumption. By using the low-grade heat, an organic Rankine cycle (ORC) can produce mechanical work from a pressurised organic fluid with the use of an expander.
Ideal gas assumptions are shown to produce significant errors in expander performance predictions when using an organic fluid. This paper details the mathematical modelling technique used to accurately model the thermodynamic processes for both ideal and non-ideal fluids within the reciprocating expander. A comparison between the two methods illustrates the extent of the errors when modelling a reciprocating piston expander. Use of the ideal gas assumptions are shown to produce an error of 55% in the prediction of power produced by the expander when operating on refrigerant R134a.

Psychic Distance, its Business Impact and Modes of Coping: A Study of British and Indian Partner SMEs

This paper reports one of the first investigations to analyze inter-partner perceptions of psychic distance between two countries. Its empirical focus is British and Indian SMEs engaged in business with each other. It examines different dimensions of psychic distance, their impact and modes of coping with them. Potential firm-level and individual influences are also taken into account. The paper aims to transcend some of the conceptual and methodological limitations of previous research on the subject and to identify the theoretical and practical implications that arise. A ‘mirror’ approach is applied, accessing both partners’ perceptions. These are assessed through a ‘mixed’ method combining quantitative measurement with qualitative interpretations. Psychic distance dimensions are found to vary in their impact on doing business with the other country, and there is also variation according to the firm’s sector. There is considerable asymmetry in British and Indian partners’ perceptions of psychic distance but the degree of difference between their psychic distance evaluations lacks predictive power. Culturally embedded psychic distance dimensions tend to have less impact and to be easier to cope with than institutionally embedded dimensions. Four categories of coping are identified. The principal theoretical implication of this study is that a contingency perspective needs to be adopted in the field of ‘distance’ research, taking account of factors such as a firm’s sector, and that this will require a more complex analytical framework that hitherto.

Mathematical modelling of quantum yield enhancements of methyl orange photooxidation in aqueous TiO2 suspensions under controlled periodic UV LED illumination

Quantum yields of the photocatalytic degradation of methyl orange under controlled periodic illumination (CPI) have been modelled using existing models. A modified Langmuir-Hinshelwood (L-H) rate equation was used to predict the degradation reaction rates of methyl orange at various duty cycles and a simple photocatalytic model was applied in modelling quantum yield enhancement of the photocatalytic process due to the CPI effect. A good agreement between the modelled and experimental data was observed for quantum yield modelling. The modified L-H model, however, did not accurately predict the photocatalytic decomposition of the dye under periodic illumination.

Extracting statistically dominant modes of a steel truss bridge from vehicle-induced vibrations

This study is intended to investigate the validity of the stability diagram (SD) aided multivariate autoregressive (MAR) analysis for identifying modal parameters of a real truss bridge. The MAR models are adopted to fit the time series of the dynamic accelerations recorded from a number of observation points on the bridge; then the modal parameters are extracted from the MAR model coefficient matrix. The SD is adopted to determine statistically dominant modes. In plotting the SD, a number of stability criteria are further adopted for filtering out those modes with unstable modal parameters. By the present method, the first five modal frequencies and mode shapes are identified with very high precision, while the damping ratios are identified with high precision for the 1st mode but with poorer precision for higher modes. Moreover, the ability of the SD in selecting structural modes without getting involved in any model-order optimization problem is highlighted through a comparison study.

A Cyber-Physical Security Analysis of Synchronous-Islanded Microgrid Operation

Cyber-security research in the field of smart grids is often performed with a focus on either the power and control domain or the Information and Communications Technology (ICT) domain. The characteristics of the power equipment or ICT domain are commonly not collectively considered. This work provides an analysis of the physical effects of cyber-attacks on microgrids – a smart grid construct that allows continued power supply when disconnected from a main grid. Different types of microgrid operations are explained (connected, islanded and synchronous-islanding) and potential cyber-attacks and their physical effects are analyzed. A testbed that is based on physical power and ICT equipment is presented to validate the results in both the physical and ICT domain.

Exploring the micro-politics of place: lifestyle migrants, collective identities and modes of belonging

Taking up Hopkins and Dixon’s (2006) call to attend to the micro-politics of everyday constructions of space and place, which necessarily involves psychological concepts such as identity, belonging and attachment, this paper aims to show how a critical socio-cognitive approach to discourse analysis is an effective means of unpacking the ways in which versions of place are (re)produced and negotiated through discursive practices, and in particular the ways in which ‘legitimate’ collective identities are constructed in relation to place. I focus on the contemporary social phenomenon of lifestyle migration. Within Europe, this typically involves relatively affluent northern Europeans moving to destinations in southern Europe that are strongly linked to tourism. Although lifestyle migrants are generally viewed by their hosts as ‘desirable’ migrants due to their perceived economic and socio-cultural capital, their integration into destination communities is often minimal. The question arises as to how these migrants construct modes of belonging in relation to their adopted home-place and how they relate to the other social groups with whom they share it. Using texts from a variety of sources, including in-depth interviews with British migrants in Portugal, I explore not only how migrants position themselves (and others) discursively in relation to places, but also how they are already positioned by discursive practices in the public sphere. I also examine to what extent the construction of a ‘legitimate’ mode of belonging involves the construction of intergroup cooperation within that place.

Theorising and analysing digital labour: from global value chains to modes of production

This paper considers the following question—where do computers, laptops and mobile phones come from and who produced them? Specific cases of digital labour are examined—the extraction of minerals in African mines under slave-like conditions; ICT manufacturing and assemblage in China (Foxconn); software engineering in India; call centre service work; software engineering at Google within Silicon Valley; and the digital labour of internet prosumers/users. Empirical data and empirical studies concerning these cases are systematically analysed and theoretically interpreted. The theoretical interpretations are grounded in Marxist political economy. The term ‘global value chain’ is criticised in favour of a complex and multidimensional understanding of Marx’s ‘mode of production’ for the purposes of conceptualizing digital labour. This kind of labour is transnational and involves various modes of production, relations of production and organisational forms (in the context of the productive forces). There is a complex global division of digital labour that connects and articulates various forms of productive forces, exploitation, modes of production, and variations within the dominant capitalist mode of production.

Mathematical modelling of supercritical CO2 extraction of volatile oils from aromatic plants

The modelling of the experimental data of the extraction of the volatile oil from six aromatic plants (coriander, fennel, savoury, winter savoury, cotton lavender and thyme) was performed using five mathematical models, based on differential mass balances. In all cases the extraction was internal diffusion controlled and the internal mass transfer coefficienty (k(s)) have been found to change with pressure, temperature and particle size. For fennel, savoury and cotton lavender, the external mass transfer and the equilibrium phase also influenced the second extraction period, since k(s) changed with the tested flow rates. In general, the axial dispersion coefficient could be neglected for the conditions studied, since Peclet numbers were high. On the other hand, the solute-matrix interaction had to be considered in order to ensure a satisfactory description of the experimental data.