Special edition of Applied Thermal Engineering

Applied Thermal Engineering 27 (2007) 2159–2160 www.elsevier.com/locate/apthermeng Editorial Special edition of Applied Thermal Engineering The papers presented in this special edition of Applied Thermal Engineering offer a section of those presented at the Heat Powered Cycles conference held at Larnica, Cyprus in October 2004. The conference was primarily concerned with co- or tri-generation of electrical energy combined with heating and cooling. Eighty papers in all were presented. A number concentrated on a total-energy system approach, and these included contributions covering thermodynamic and thermo-economic studies. Others described and evaluated developments in engine technology, heat powered cooling systems and district heating systems. There were also a substantial number of papers concerned with use of solar energy for both heating and electricity generation and there several sessions dedicated to specialist topics such as heat and mass transfer. The papers presented at the conference were of a high quality and provided a balanced mix of theory and practice. It was difficult, therefore, to select papers for this special issue. However, there was a choice to make and because of the extensive coverage of some subjects in other journals, the editors decided to concentrate this issue primarily on the novel research reported at the conference on combined heat and power systems, sorption cooling and including one of several contributions on microbore tube heat exchange. Distributed energy systems offer an alternative to centralised energy generation for isolated communities in areas remote from power grid networks. In a fully integrated form they offer the possibility of utilising mixed primary energy supplies, both new and renewable sources, such as wind power, geothermal and solar and so contributing to reducing greenhouse emissions. Combined cycles have the potential of high thermal efficiency. The design of such systems must take account, not only of thermo-economics issues, but also environmental impact. For example this might include a local knowledge of wind patterns and solar loading as well as requiring details of building design and energy demand and can predict CO2 production and generated 1359-4311/$ - see front matter Ó 2005 Published by Elsevier Ltd. doi:10.1016/j.applthermaleng.2005.07.018 power shortfall. As these types of system are relatively new they are not had the benefit of many years of development of the centralised generation and distribution networks with which they will inevitable compete in some instances. The design and simulation of distributed systems is problematic because of the lack of firm data relating to the performance (design and off design) and the lifetime costs of the components. The issues of system stability and prioritising component use to reduce overall costs or emissions are also of interest. The next six papers selected illustrate how some of these problems can be addressed. The contributions by Hinojosa et al. and Ameli et al. illustrate the different approaches to overall system modelling describing the necessary features and architecture of the software. The characteristics and useful features of existing software are described with views about future development and desirable characteristics of new software. The performance of a variable speed micro-turbine operating in combined CHP mode is described by Kaikko et al. who address some component description issues of interest in overall system simulation and illustrate the utility of generic type models in the absence of specific component performance data from a manufacturer. Chmieliak et al. address some issues of CHP plant that have relevance to the question of prioritising component use, which was discussed by Hinojosa. The paper by Henning et al. describes a trigeneration CHP based system that could be incorporated into a distributed energy system and discusses some of the issues relating to operating strategies aimed at minimise operating costs. In any tri-generation system the efficient, reliable and low capital cost production of cooling, for both refrigeration and space conditioning is essential if the technology is to be usefully employed in reducing greenhouse gas emissions. Solid-sorption cooling offers great potential in this endeavour. The next three papers offer useful contributions in the continued development of this 2160 Editorial / Applied Thermal Engineering 27 (2007) 2159–2160 important technology. Chang et al. describe a novel compact 4.3 kW experimental machine using aluminium, flat tube heat exchangers with corrugated fins. This type of heat exchanger was used by the authors to form the evaporator, condenser and sorbent bed. With a heat source temperature of 90 °C, a heat sink temperature of 30 °C and chilled water of 14 °C this machine is reported to give a COP of 0.45. This relatively low heat source temperature will enable the use of a solar thermal heat as an energy source to provide air conditioning, but equally the machine could be powered by any suitable source of low-grade waste heat. The paper describes the configuration of the machine, which results in a compact and apparently easy to manufacture way that should provide a low capital cost design. In the next paper, Freni et al. describe their research into more rapid chemisorption cycles through the development of heat exchanger fins coated by a mesoporous silica matrix containing calcium chloride. Their results demonstrate a much greater heating intensity, though this seems to be at the cost of a decrease in COP, when compared with trails using a pelletised form of the adsorbent tested earlier. However, the authors believe that the COP of the system using this novel approach can be improved and they go on to explain why this is. In the paper which follows Núñez et al. provide an interesting comparison between the performance of the SorTech silica gel–water machine, which is under development and two commercially available, although much larger machines. The research described covers a range of operating conditions and considers both heating and cooling modes. The concept of Ôreduced temperatureÕ is developed by the authors to simplify analysis. The power density and COP of the new machine are shown to be lower than those of the reference machines, but very competitive with the current range of experimental devices aiming at the sub-15 kW size range. Any account of heat powered cooling cycle research would be incomplete without mentioning something of the recent work on absorption cycles. Zohar et al.Õs contribution describes their recent theoretical work on the ammonia-water diffusion absorption cycle. Although this technology has been available for many years, it is interesting to note that several groups are now working to improve its performance and the inclusion of this paper, which looks into the effect of sub-cooling of the refrigerant prior to entering the evaporator, is thought timely. The use of renewable hydrocarbons, such as biogas is becoming more common and use addition in the fight to reduce greenhouse gas emissions. Fagenle et al.Õs thermodynamic analysis of a steam injected gas turbine engine provides an insight into a novel application of biogas and their research study aimed at improving the performance of the plant, which reveals both the challenges that face designers and areas for improvement. Research into compact heat exchangers, both in terms of heat transfer and pressure loss was featured strong at the conference. The paper by Targanski et al. on the evaporation of R407C/oil mixtures provides an example of the work being current done by several groups in the area of micro-tube technology. The paper provides some useful experimental data and for this reason was selected for this special edition. It is hoped that the reader will find the following papers both stimulating and enjoyable. A full set of conference papers can be found in the Proceedings of the 3rd international Heat powered Cycles Conference, Larnace, Cyprus October 2004, ISBN 01874418353. Guest Editors Brian Agnew Robert Critoph Ian W. Eames Tassos G. Karayiannis Department of Mechanical, Materials and Manufacturing Engineering, School of Mechanical and Systems Engineering, University of Newcastle Upon Tyne, Newcastle upon Tyne NE1 7RU, United Kingdom Tel.: +44 191 222 6211; fax: +44 191 222 8600 E-mail address: brian.agnew@ncl.ac.uk (B. Agnew)