High temperature heat exchangers for power plants: Performance of advanced metallic recuperators D. Aquaro a, * , M. Pieve b a Dipartimento di Ingegneria Meccanica, Nucleare e della Produzione, Via Diotisalvi, 2, 56100 Pisa, Italy b Dipartimento di Energetica ‘‘Lorenzo Poggi’’, Via Diotisalvi, 2, 56100 Pisa, Italy Received 2 February 2005; accepted 14 July 2006 Available online 4 October 2006 Abstract An overview is given of recent high temperature heat exchangers technology developments, both in the thermal-fluid dynamic inno- vative solutions and in the materials. Gas turbine recuperative cycles, microturbine systems, indirectly fired cycles and high temperature gas cooled nuclear reactors are the investigated fields where this kind of heat exchangers is used. Some common technological features join all of them, namely: new surface geometry design and burdensome material requirements. The most important difficulties arising from the specific conditions of each heat exchange system are pointed out, together with their possible solutions. A comparison among them is presented and some suggestions are proposed about expanding the boundaries of the individual research fields, to get a wider understanding of common critical issues. Finally, the paper focuses on the main current challenges to be faced in the near future in order to get a competitive development of such systems. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Heat exchanger; High temperature; Recuperators 1. Introduction High temperature heat exchangers (arbitrarily meaning temperatures above 650 °C) are required in many industrial systems for process reasons or aiming to attain high effi- ciency. Latter one is the case of power plants. Among these, the most promising in terms of development chances are: – recuperative gas turbine and combined cycles, – externally fired cycles, – recuperative microturbine systems, – high temperature gas cooled nuclear reactors. Each one of these systems has to comply with specific requirements, related to its function. In recuperative gas turbine cycles the feasibility of high temperature heat exchangers should be analysed more dee- ply because of the possibility to get very high thermal effi- ciency, which up today can approach 40% in simple cycles (just without any recuperation) and 62% in combined ones [1–3]. In the application of recuperative heat exchangers in such cycles a high volumetric flow ratio between the streams, due to the high pressure ratio, generally between 12 and 30, 1 is combined with an identical massive flow on both sides of the exchanger. In the following the conse- quences of such different volumetric stream flows will be shown. 1359-4311/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.applthermaleng.2006.07.030 * Corresponding author. Tel.: +39 050 836 631; fax: +39 050 8366 65. E-mail addresses: aquaro@ing.unipi.it (D. Aquaro), m.pieve@ing. unipi.it (M. Pieve). 1 In this range the recuperation is effectively viable, even if when the pressure ratio increases the net temperature difference between the compressor air discharge and the turbine exhaust becomes smaller, so the recuperator is progressively less useful, if considered as single component. www.elsevier.com/locate/apthermeng Applied Thermal Engineering 27 (2007) 389–400