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Waste Heat Recovery through Organic Rankine Cycle
Supported by the ICER, International Centre for Energy Research in collaboration with TUM, Germany

Researchers (visit the PEOPLE webpage for more infos)

  • Asst. Prof. Alessandro Romagnoli, PI

  • Asst. Prof. Christoph Wieland, PI, TUM, Germany

  • Mr. Manuel Jimenez Arreola, PhD student

  • Mr. Roberto Pili, PhD student, TUM, Germany


Description of the project

The project aims at investigating waste heat recovery from industrial and mobile applications, as well as increasing the efficiency of these processes by means of ORC systems.

It is typical for waste heat sources to have a high variability of thermal power during operation. In these dynamic conditions, optimal design and robust control are of primary importance. In the case of ORC the transients are dominated by the heat exchangers, in particular the evaporator which is the link between the heat source and the rest of the components. The project investigates the evaporator design in particular as a means to achieve a system with higher efficiency potential and robust to the variability of the source.



The project makes use of detailed dynamic models of the ORC components, in particular the heat exchangers in the software DYMOLA, as well as validation with experimental results from an in-house test rig.

Activities include:

  • Modelling, simulation and experimental validation of ORC systems under dynamic conditions

  • Dynamic characterization of ORC components under transient conditions

  • Direct evaporation feasibility in highly dynamic condition

  • Simultaneous component and control design for system robustness to transients.



  • Response time maps for evaporator geometry and material selection based on desired thermal damping of the source and protection from chemical decomposition of the fluid.

  • Comparison of response time between different geometries of direct evaporation such as fin-and tube and louvered-fin-and plate heat exchangers.

  • Methodology based on engine driving cycle to find the values of frequencies and amplitudes of fluctuations for which robust control is most critical when using direct evaporation.

  • Comparison of response time and thermal damping between direct and indirect evaporation options.

  • Potential of weight and volume reduction of evaporator of 90% and 70% respectively when using direct evaporation instead of indirect.



  • Increase system output by increasing evaporation temperature an decreasing off-design conditions

  • Feasibility of direct evaporation to reduce size of system for mobile applications

  • Design “tailored” dynamic behaviour of ORC to achieve the best control strategy. 

ORC images.png

Dynamic model of ORC evaporator

Problem being investigated


Maps of response time for Fin and tube direct evaporator

Comparison of thermal damping (Amplitude Ratio AR) for direct and indirect evaporation options as function of frequency and amplitude of source fluctuations

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