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Purpose – The main aim of the present study is to explore field of Six Sigma and discover the limitation of the present research work. The study also tries to find emerging aspects, trends and future directions and explore unfocused areas of Six Sigma. The present study involves an analysis of 179 research articles published from 1995 to 2011 in 52 selected reputable journals. Design/methodology/approach – The methodology of critical assessment involves selection and classification of 179 research articles on Six Sigma. The selected articles are classified by: time distribution of articles, research methodology, research stream, authorship patterns, sector-wise focus of articles, integration with other manufacturing philosophies, implementation status and performance measurement of the models or framework. Then, the suggestions for the future scope of research possibilities and development are identified. Findings – The study provides a taxonomical and integrated review of articles. Further, this study provides perspectives on conceptualization and various critical parameters for research. Through this literature review, many issues are addressed which have not previously been adequately covered. The findings include: increase in empirical nature of research articles, need for spreading research in the field of Six Sigma implementation, need for more interregional research collaborations, need for integration of Six Sigma philosophy with other philosophies and lack of implementation, i.e. testing and validation of the proposed models or frameworks by researchers. Practical implications – The present study has explored an unfocused area of Six Sigma which will help future researchers to concentrate on the grey areas of Six Sigma. The study will help professionals to get a comprehensive database of Six Sigma articles and their use in practical situation. The results obtained from the study are expected to help researchers, academics and professionals to focus on the growth, pertinence and research developments to implement Six Sigma principles. Originality/value – This paper will be of great help for those carrying out research in Six Sigma field including academics and practitioners in terms of Six Sigma growth describing the trends, sources and findings. The unique feature of this research is the large sample size and a time span of 16 years (1995-2011). The unique feature of this research is the large sample size and a time span of 16 years (1995-2011).

Phase change material (PCM) based latent heat thermal storage (LHTS) systems offer a challenging option to be employed as an effective energy storage and retrieval device if the energy source is intermittent and time dependent. However, the performance of LHTS systems is limited by the poor thermal conductivity of PCMs employed. The addition of high conductivity particles is proposed as one of the promising performance enhancement techniques for LHTS. In our study, an attempt is made to investigate the performance enhancement of a shell and tube storage unit applicable to solar water heaters due to the addition of high conductivity particles (copper) through exergy analysis. The enthalpy based two dimensional-transient equations are solved numerically for discharging process using FLUENT—a commercial computational fluid dynamics code. The numerical results show good agreement with experimental results available in the literature. The thermal behavior and performance of particle dispersed PCM unit in terms of exergy efficiency and total exergy recovered are compared with that of pure PCM unit. It is observed that the discharging time is reduced by around 28% by adding particles of volume fraction 0.1 and by around 85% with 0.6 volume fraction. However, the decrease in discharging time is not much appreciable beyond the particle volume fraction of 0.4. Similarly, the exergy efficiency and total exergy recovered are increased by 12% and 15%, respectively, with 0.1 volume fraction and by 50% and 60%, respectively, with 0.4 volume fraction. Different Reynolds numbers (i.e., Re=200–10 000) are considered in the numerical trials to investigate the influence of mass flow rate of heat transfer fluid (HTF) on the performance of the system. The results reveal that the role of HTF mass flow rate in increasing the overall thermal performance of LHTS unit is insignificant.

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