**Preface to "Organic Rankine Cycle for Energy Recovery System"**

The rising trend in the global energy demand poses new challenges to humankind. The energy and mechanical engineering sectors are called to develop new and more environmentally friendly solutions to harvest residual energy from primary production processes. The Organic Rankine Cycle (ORC) is an emerging energy system for power production and waste heat recovery. In the near future, this technology can play an increasing role within the energy generation sectors and can help achieve the carbon footprint reduction targets of many industrial processes. In particular, there are still many un-used hot streams available for recovery in various stationary power generators for civil and tertiary applications and in several highly intensive industries. Additional applications can come from the transportation sector, where waste engine heat in heavy vehicles and ships can be used to achieve fuel savings. Moreover, low-enthalpy flows from renewable sources can be exploited in thermodynamic cycles based on the Rankine architecture. The ORC is already a well-proven option in large-size plants, but not all technological aspects are currently solved/optimized; the state of the art still requires cost-effective improvements in order to enlarge the market opportunities. Meanwhile, the ORC is still developing in small-scale and/or micro-generation applications, where efficient and low-cost ORC components are not ready for the market yet and problems must be solved. This Special Issue focuses on selected research and application cases of ORC-based waste heat recovery solutions. Topics included in this publication cover the following aspects: performance modeling and optimization of ORC systems based on pure and zeotropic mixture working fluids (Andreasen et al.); applications of waste heat recovery via ORC to gas turbines and reciprocating engines (Carcasci et al., Branchini et al., Valencia et al.); optimal sizing and operation of the ORC under combined heat and power and district heating application (Branchini et al.); the potential of ORC on board ships and related issues (Baldasso et al.); life cycle analysis for biomass application (Stoppato et al.); ORC integration with supercritical CO2 cycle (Espinel Blanco et al.); and components for small ORC, including proper design and related internal fluid issues (Casari et al., Fadiga et al.). The current state of the art is considered and some cutting-edge ORC technology research activities are examined in this book.

> **Andrea De Pascale** *Special Issue Editor*

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