Theoretical and Experimental Comparison of Box Solar Cookers with and without Internal Reflector

AbstractBox solar cookers are commonly built with internal sheet metal painted black as an absorber. In order to increase the performance, a design which incorporates internal reflection is proposed in this paper. The aim of this paper is to report comparisons made between box solar cookers with and without internal reflector. Theoretical modelling of the two types of cookers has been made by considering the radiation, convection and conduction heat transfer employing the thermal network method. The theoretical analysis made was based on steady state heat transfer analysis of the cookers. Experimental comparisons were also made on two cookers having the same aperture area and made from the same type of materials except the internal absorber. The tests were made as per the American Society of Agricultural Engineers (ASAE) procedure.The result of the theoretical analysis predicts that the performance will be higher in the cooker with internal reflector than the same cooker without reflector. The steady state analysis shows that for the cooker with reflection the temperature of the bottom absorber plate is higher than the cooker without reflector. Similarly, results of dry test and water boiling test show better performance by the cooker with reflector. The standard stagnation temperature and the cooking power were higher in the cooker with reflector as compared to the cooker without reflector. In conclusion, the performance of box solar cookers can be enhanced by making appropriate angle side walls of the absorber and providing internal reflection

Ways of seeing : a study of opsis in Herodotus' Histories

The thesis provides an in-depth study of ὄψις (opsis) (‘seeing’ or ‘sight’) in Herodotus’ Histories. It explores both the use of opsis by Herodotus as a key source for his ἱστορίη (enquiry) and the rich and complex layers of stories involving opsis in the narrative of the text. A close analysis of autopsy statements (direct and indirect) in Herodotus’ metanarrative demonstrates that these are far more numerous than scholars have hitherto realised and that he was developing a new language of autopsy to signify the use of opsis as an investigative tool. When compared with other methods of enquiry such as ἀκοὴ (hearsay) and γνώμη (opinion / judgement / reasoning), opsis clearly emerges as the most reliable of – and a check on the other – sources of evidence. Herodotus’ narrative allows him to communicate a more nuanced portrayal of opsis. While some characters successfully use opsis to learn about the world or manage to manipulate it for their own ends, many misinterpret visual evidence or are deceived by what they see. Yet stories about opsis also closely parallel some of the key themes of the Histories: the rise and fall of great powers, the risks inherent in breaching boundaries and the dangers of ἔρως (desire). Herodotus uses the narrative together with the metanarrative to educate his audience on how to conduct an investigation based on opsis and shows that a certain skill and intelligence (σύνεσις) is required to succeed. This in turn forms a core part of the strongly didactic nature of the text. In his use of opsis, Herodotus was at least in part responding to contemporary debates on the value of empirical evidence for enquiry, as seen in the work of the Hippocratics and the Presocratic philosophers. However, Herodotus’ innovation was to apply investigative methods based on opsis to historical material and an enquiry into past events

The Abortion Act (1967): a Biography

In this paper, we set out what it means to offer a ‘biography’ of a law, illustrating the discussion through the example of the Abortion Act (1967), an important statute that has regulated a highly controversial field of practice for five decades. Biography is taken as a useful shorthand for an approach which requires simultaneous attention to continuity and change in the historical study of a law’s life. It takes seriously the insight that written norms are rooted in the past, enshrining a certain set of historically contingent values and practices, yet that – as linguistic structures that can impact on the world only through acts of interpretation – they are simultaneously constantly evolving. It acknowledges the complex, ongoing co-constitution of law and the contexts within which it operates, recognising that understanding how law works requires historical, empirical study. Finally, it suggests that consideration of a law can offer a unique window through which to explore these broader contexts