Salma Salah successfully passes PhD Viva at City, University of London

As SCARABEUS heads towards the last months of the project, and research outcomes are being disseminated amongst different stakeholders, the younger researchers in the project are also achieving their scientific objectives.

This last week saw Salma Salah, a young researcher at City, University of London, successfully pass her PhD Viva. Within WP3, Salma has worked very hard on the development of the SCARABEUS turbine, in collaboration with Baker-Hughes and interacting with University of Seville to ensure seamless integration with the work carried out in WP5. Let’s have Salma presenting this with her own words:

I have been working during the last four years on a PhD research project entitled “the design and analysis of supercritical carbon dioxide axial turbines”. This research is a part of the SACARABEUS project which aims to demonstrate the application of CO2 blends for Concentrated Solar Power (CSP) plants to enable cycle efficiencies greater than 50%, and hence enhance competitiveness of CSP technologies in the energy market. Considering that the turbine efficiency significantly affects the overall plant performance, the overall aim of my research is to develop design and optimisation tools for a 100 MWe scale sCO2 multi-stage axial turbine design for concentrated solar power cycles.

Turbine design is a multi-stage process that starts with preliminary aerodynamic design and optimisation using a combination of one-dimensional mean-line design suitable loss models. These models are used to quantify the energy losses that the working fluid experiences during the expansion in the blade rows, and hence they can predict overall turbine performance. To develop a turbine design operating with CO2 blends that stands from a practical design, other considerations should be considered, such as mechanical and rotor-dynamic considerations, to ensure a turbine design withstands the applied stresses and can operate safely under the different operation conditions. Therefore, the scope of this research focused on exploring the existing design methodologies to produce a mean line design for a multi-stage axial turbine operating with CO2 blends and to investigate the validity of the loss models for non-conventional working fluids (such as CO2 and organic fluids). Within this research I worked on developing a mean-line design tool that can optimise the aerodynamic turbine performance alongside complying with rotordynamic and mechanical design criteria.

Additionally, multiple design loss models have been integrated for turbines operating with these non-conventional working fluids. Using the developed tool, the loss models have been computed for air, sCO2 and ORC turbines.

Ultimately, a 14-stage CO2/SO2 flow path has been designed for a 100 MW CSP plant and the financial feasibility of the turbine flow path has been investigated to ensure that the design stands from an economic point.”

The SCARABEUS team would like to congratulate Salma Salah on this major step in her scientific career, and also the supervisors Prof. Abdulnaser Sayma (City, University of London) and Dr. Martin White (University of Sussex) and the entire team at City, University of London. Best of luck for your future professional development Salma!

A copy of Dr. Salah’s thesis can be downloaded from the repository at City, University of London:


Paper on ACC design presented by University of Seville at the 5th European Conference on Supercritical Carbon Dioxide Energy Systems, Prague (Czech Republic)


Schematic of ACC used as reference for SCARABEUS


The researchers at University of Seville have presented their work on the design and operation of air-cooled condensers for integration into Concentrated Solar Power plants using the SCARABEUS technology. This work has been carried out in the context of Work Package 5 (Techno-economic, Social and Environmental Assessments) but also in close collaboration with Work Package 4 (Air Cooled Condenser and Heat Exchanger Development).

Condensation of the working fluid at high ambient temperature is a differential feature of the SCARABEUS CONCEPT, setting it apart from standard supercritical Carbon Dioxide cycles where the working fluid cannot be condensed due to the unfeasibility of cooling CO2 down below the critical temperature. The design of condensers for operation at high pressure (~80 bar) and low temperature is therefore a innovation of the project. Also, the definition of operating strategies in order to reduce the negative impact of auxiliary (fan) power consumption on net cycle efficiency is critical in order to effectively attain the thermodynamic superiority of the SCARABEUS concept.


Flow chart of the Air Cooled Condenser design code

The paper can be downloaded free of charge from the conference website (link). Check the abstract below:

The SCARABEUS project investigates the use of CO2–based mixtures as working fluid in power cycles for nextgeneration Concentrated Solar Power plants. These fluids exhibit a critical temperature higher than pure CO2, enabling dry condensation of the working fluid even at the high ambient temperatures typical of sites with a high solar radiation. As a consequence, the SCARABEUS power cycle achieves higher thermal efficiency than standard sCO2 cycles, whose performance deteriorates significantly with ambient temperature. In any case, the actual feasibility of this concept is still to be confirmed by a complete techno-economic assessment. To that purpose, it is critical to accurately estimate the power consumption of the Heat Rejection Unit (HRU), which is one of the most important parasitic loads of the system.

Bearing all this in mind, this manuscript presents the design of a horizontal, direct air-cooled condenser (ACC). The bundle geometry proposed is comprised of seven tubes in three passes, with a staggered arrangement. The complete thermal model, developed in MatLab, has been already disclosed by the SCARABEUS consortium in a previous paper, and validated both experimentally in a dedicated test rig and against results obtained by the commercial software Xace®. The novelty in the present manuscript lies in the integration of this thermal model of the tubes with a complete design and integration tool of the whole heat rejection sub-system, including the design of a rotoronly axial fan and supporting frame. The impact of several design parameters (i.e., air temperature rise, acceptable hot pressure drops, tube length) is studied, taking into account auxiliary power consumption, footprint and cycle efficiency as main figures of merit. Two candidate mixtures are taken into account, identified in previous works by the same authors (85%CO2-15%C6F6 and 80%CO2-20%SO2), and a pure sCO2 case is also considered for the sake of comparison. The results show that, for a given gross cycle output, using pure sCO2 yields the smallest ACC with the lowest fan power consumption. Moreover, tube length and air face velocity are found to be the key-parameters driving the design process of an ACC, for which increasing tube length is always beneficial as far as the ACC design is concerned. Finally, various considerations regarding the role played by the optimum design of the ACC within the global optimisation of the power plant are made. It is found that the rationale employed for the design of the ACC may be in conflict with that used from an overall plant optimisation standpoint. It is hence concluded that the definition of the optimal design space of an Air-cooled Heat Exchanger (ACHE) must be included in the global optimisation of the power plant.

Paper on SARABEUS rig design and operation presented by Technical University of Vienna and Kelvion Thermal solution at the 5th European Conference on Supercritical Carbon Dioxide Energy Systems, Prague (Czech Republic)


Front view of the SCARABEUS test rig at TU Wien



The researchers at the Technical University of Vienna (Austria) and Kelvion Thermal Solutions (France) have presented their work on the design of and operation of the SCARABEUS test rig at the Austrian academic institution. This work has been carried out in the context of Work Package 4 (Air Cooled Condenser and Heat Exchanger Development) and Work Package 6 (Test Rig and Experimental Validation) of SCARABEUS and is a cornerstone of the project, given the uniqueness of the rig constructed to validate the operation of heat exchangers on Carbon Dioxide mixtures.

Schematic of the SCARABEUS test rig at TU Wien


The paper can be downloaded free of charge from the conference website (link). Check the abstract below:

At TU Wien, a test facility working with supercritical carbon dioxide (sCO2) was commissioned in 2018. Since then, it has been used for various research tasks. This paper gives an overview about the three configurations of the facility with a focus on design, operation, and results. The authors present the design of components in the three configurations of the test facility: proof of concept of the simple cycle in supercritical and transcritical operation mode, heat transfer measurements, and future work. Special emphasis is given to challenges during engineering and operation. Our most relevant lessons learned are: that a commercial CO2 pump is not sufficient for cycle experiments, how to design a measurement section for heat transfer measurements, and that during experimental research, measurement-concepts and data reduction must be prioritized at all times.