Professor S.B. Riffat
Head of the School of the Built Environment
School of the Built Environment, University of Nottingham, University Park, Nottingham, NG7 2RD, United Kingdom

The School of the Built Environment has a worldwide reputation for its innovative research into sustainable technologies including absorption/adsorption heat pumps, ejector refrigeration systems, desiccant technology, hybrid/solar driven CHP systems, solar/thermal systems and ground-source heat pumps. The School has obtained grants from the Engineering, Physical Sciences Research Council (EPSRC), the European Commission and industry to develop several new technologies, which have been licensed to industry .The School has also established new research facilities including the Marmont Centre for Renewable Energy and the David Wilson EcoHouse. This paper reviews some of the School's recently funded research projects and facilities.

Adrian Bejan
J.A. Jones Professor of Mechanical Engineering
Duke University, Durham, NC 27708-0300, USA

This paper presents a broad view of the principle that generates structure and performance improvements in power and refrigeration systems. Such systems owe their thermodynamic imperfection to a multitude of internal and external flows (heat, fluid, electricity) that must overcome resistances. Systems are destined to remain imperfect, because resistances are reflections of.the global constraints that are imposed (e.g., finite size, weight, cost). Resistances compete against each other. They must be optimized together, and balanced against each other. In this way the thermodynamic imperfection (irreversibility) is distributed in a near-optimal way (more uniformly) through the system, such that the global performance level is maximized. Optimal distribution means structure, configuration, form and design.
The generation of structure in the pursuit of optimal global performance subject to global constraints is illustrated by means of several class-wide examples: the optimal distribution of heat exchanger inventory in a power plant, the optimal distribution of intermediate cooling along the thermal insulation structure of a low-temperature refrigerator or liquifier, the optimal intermittent (on & off) operation of defrosting refrigerators and power plants with periodically cleaned heat exchangers, and the optimal cruising speed for powered flight (airplanes, birds, insects). The analogies between flow resistances in engineering, travel times in transportation, and costs in econornic transactions, allow us to extend this principle to the generation of geographic structure in econornics. Examples are the tree-shaped paths that guide the flow of goods and people between areas and points.

GAS TURBINE REACTORS – CHEMICALS, HEAT & POWER

D.A. Reay, David Reay & Associates,
PO Box 25, Whitley Bay, Tyne & Wear NE26 1QT, UK
Email : DAReay@aol.com

Prime movers of all types, ranging from Stirling engines and micro-turbines to Multi-MW reciprocating engines and aero-derivative gas turbines, are becoming increasingly used for providing heat and power – combined heat & power. In a number of instances, where air conditioning and/or refrigeration is a priority, such machines can also provide cooling, either via a heat-driven absorption machine, or indirectly, providing electricity to power vapour compression cycles. Such combinations are routine in large scale applications. An additional characteristic of prime movers, in particular gas turbines, is the opportunity to use them as chemical reactors. Thus the prime mover additionally becomes a chemicals factory.
Two examples of the several opportunities which will be discussed in the paper are intercoolers and turbine blade thermal control. The intercooler on a multi-stage compressor of a gas turbine is a heat exchanger used to cool the working fluid (e.g. air) between compression stages, increasing the efficiency. Intercoolers are heat exchangers, and in more recent times have been selected from a range of compact types. Compact heat exchangers are also used as heat exchanger-reactors (HEX-reactors), where one or more sides may be coated with a catalyst, to allow a reaction to take place there. This suggests that one might examine the feasibility of using the compact intercooler as an endothermic reactor, with the heat removed from the compressed air by this reaction. At the same time, a useful chemical product could result from the reactor side of the intercooler. One may envisage exothermic reactions taking place in reheaters, too. Those familiar with chemically-recuperated and other more exotic gas turbine cycles will recognise the basis for these concepts.
Another challenge to gas turbine manufacturers in their search for improved efficiency centres on turbine blade life at high temperatures. Blade cooling by air, steam etc. is an approach which can overcome the need to use ceramics – but it has its limitations, in terms of heat transfer coefficients. Although improvements are being made, and a scan of recent patents confirms the efforts being made in this direction, a more radical approach to blade thermal control may be needed. The second example is thus the us of a catalyst on or inside the blade, to again carry out a reaction which will cool the external blade surface, without adversely interfering with the blade geometry/performance.
The paper will discuss these and other concepts, identifying technical barriers and opportunities.

CO- AND TRI-GENERATION ENVIRONNEMENTAL IMPACT

F. Meunier
CNAM - IFFI, EA 1408
292, rue Saint-Martin, 75141 Paris cedex 03, France

Abstract :
The conditions for co-and tri-generation to reduce CO₂ emissions are discussed as well the global impact of these techniques if they were extensively used. CO₂ emissions saving will depend on the CO₂ emissions of the electricity from the network. Saving as high as 15% can be foreseen. Moreover, if biofuels are to be used, saving will be much more important.

Résumé :
Les conditions pour que la co-et tri-génération réduisent les émissions de CO₂ ainsi que l'impact planétaire de ces techniques sont discutées. Les économies d'émissions de CO₂ dépendent des émissions de CO₂ associées à la production d'électricité du réseau. Des économies pouvant atteindre 15% sont envisageables. De plus, si des biocarburants sont utilisés, les économies seraient encore beaucoup plus importantes.