Experimental and Numerical Study of Supercritical CO₂ Cooler: A DESOLINATION Contribution Awarded at the 6th European sCO₂ Conference

Experimental and Numerical Study of Supercritical CO₂ Cooler: A DESOLINATION Contribution Awarded at the 6th European sCO₂ Conference

by | May 14, 2025 | Article, Publications

As part of the Horizon 2020 DESOLINATION project, a new study titled “Experimental and numerical study of supercritical CO₂ cooler” was presented at the 6th European Conference on Supercritical CO₂ (sCO₂) for Energy Systems, held from 9–11 April 2025 in Delft, Netherlands.

The research, led by LUT University in collaboration with TEMISTH, received the Best Paper Award at the conference in recognition of its scientific quality and relevance.

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Investigating PCHE Performance in Supercritical CO₂ Power Cycles

The study focuses on the thermo-hydraulic performance of a printed circuit heat exchanger (PCHE) operating with supercritical carbon dioxide (sCO₂) — a working fluid at the core of DESOLINATION’s innovative power block. PCHEs are a compact and high-efficiency solution suitable for the extreme conditions of sCO₂-based energy systems, such as those integrated into concentrated solar power (CSP) and desalination technologies.

Using a combination of experimental testing and computational fluid dynamics (CFD), the team evaluated the heat transfer and pressure drop characteristics of sCO₂ flowing through PCHE microchannels. The study targeted the pseudo-critical region, where CO₂ exhibits rapid property variations that enhance heat transfer but complicate predictive modelling.

Supporting DESOLINATION’s Objectives

This work directly contributes to DESOLINATION’s goal of developing an efficient, solar-powered desalination system by improving the performance prediction and design of key components in the sCO₂ power cycle. In particular, it provides validated tools and insights essential for integrating high-efficiency heat exchangers into the project’s future demonstration plant.

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Authors: Giuseppe Petruccelli, Teemu Turunen-Saaresti, Damien Serret, Aki Grönman, Aurélien Conrozier, and Amir Momeni Dolatabadi.

DOI: 10.17185/duepublico/83320

Key Results
  • Experimental data were gathered under a wide range of operating conditions at LUT University’s transcritical CO₂ test facility, providing a valuable benchmark for validation of numerical models.
  • The CFD simulations, incorporating real-gas behaviour and the SST k-ω turbulence model, showed good agreement with the measured pressure drops and outlet temperatures.
  • A new friction factor correlation was derived from the experimental results. It accounts for surface roughness and achieved a prediction accuracy within ±10% of the measured values — an important advancement over existing correlations.
  • The study also revealed that commonly used heat transfer correlations tend to underestimate performance in high-Reynolds number, sCO₂ microchannel flows, underlining the need for more tailored predictive models.
Conference Recognition

The 6th European sCO₂ Conference brought together over 100 experts from academia and industry to discuss the latest innovations in sCO₂ technology. In addition to the technical sessions, DESOLINATION was also highlighted during the Friday morning keynote by Dr. Gioele Di Marcoberardino (UNIBS), which presented the project’s overall goals and progress to date.

🏆 The paper received the Best Paper Award at the conference, recognising the quality and relevance of the research to the international sCO₂ research and engineering community. This recognition highlights DESOLINATION’s contribution to advancing component-level understanding crucial for the development of integrated solar-powered desalination systems.

🔬 The DESOLINATION consortium congratulates the authors — Giuseppe Petruccelli, Teemu Turunen-Saaresti, Damien Serret, Aki Grönman, Aurélien Conrozier, and Amir Momeni Dolatabadi — on this well-deserved recognition, and for their valuable contribution to the future of sustainable energy and water systems.

Simultaneous design optimization of binary co2-mixture-based power cycles for concentrated solar power applications

Simultaneous design optimization of binary co2-mixture-based power cycles for concentrated solar power applications

by | Sep 11, 2024 | Publications, Results - CO2 Mixtures in thermodynamic cycles

In the push toward cleaner and more efficient energy, concentrated solar power (CSP) systems have emerged as a promising contender. But their potential has been limited by the need for innovative, cost-effective solutions to convert solar heat into electricity.

We’re thrilled to announce a groundbreaking publication by Teesside University, one of our partners, presented at the ASME (The American Society of Mechanical Engineers) Turbo Expo 2024 (Turbomachinery Technical Conference and Exposition).

This work unveils an innovative approach to optimizing power cycles for CSP systems, driving advancements in efficiency and sustainability.

A recent study introduces an innovative approach to improving power cycles for concentrated solar power (CSP) systems, a key technology in the renewable energy landscape. This research focuses on optimizing the performance of systems that use CO₂-based mixtures as working fluids, offering significant advancements in efficiency, cost-effectiveness, and adaptability to various operating conditions.

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Traditionally, CSP systems rely on converting solar heat into electricity through power cycles. This study enhances that process by developing a simultaneous optimization strategy. It considers the design of the power cycle, the selection of chemical additives (dopants), and the specific composition of the CO₂-based working fluids. By analyzing these factors together, the researchers aim to maximize system efficiency while reducing costs.

The study tests these innovations under realistic scenarios, including two operating temperature ranges: 550°C, typical of current CSP systems, and a higher 700°C for advanced designs. It also accounts for ambient temperatures of 30°C, 35°C, and 40°C, reflecting the diverse environments where CSP systems operate.

One of the key breakthroughs is the use of binary mixtures of CO₂ combined with chemical dopants like sulfur dioxide (SO₂) or acetonitrile (C₂H₃N). These additives enhance the thermodynamic properties of the working fluid, allowing the system to perform more effectively under varying conditions. The research team employed advanced modeling techniques to evaluate these mixtures, ensuring precise predictions of their performance.

Optimization in this context focuses on two main objectives: maximizing thermal efficiency (the amount of solar energy converted into electricity) and improving specific work (the energy produced per unit of working fluid). These improvements reduce the size and cost of system components, like power blocks and thermal energy storage (TES), making CSP systems more economically viable.

This innovative approach holds great promise for the future of renewable energy. By addressing technical and financial challenges, the study opens the door for CSP systems to play a larger role in the global transition to cleaner energy. With its flexible methodology, capable of incorporating new materials and designs, this research sets the stage for continued advancements in solar power technology.
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Authors: Balkan Mutlu, Kumar Patchigolla, Dhinesh Thanganadar

DOI: https://doi.org/10.1115/GT2024-124083

Preliminary Characterization of the Desolination Project Demo Plant: Design and Off-Design Operability

Preliminary Characterization of the Desolination Project Demo Plant: Design and Off-Design Operability

by | Sep 5, 2024 | Milestones, Publications, Results - Pilot plant preparation

The DESOLINATION project, a beacon of innovation in renewable energy, has taken a major step forward with the preliminary performance analysis of its demonstration plant.

Recently unveiled at the ASME Turbo Expo 2024, this work brings together the expertise of TEMISth, UNIBS (University of Brescia), and Politecnico di Milano (POLIMI) to explore the potential of a novel power cycle built for sustainability and efficiency.

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What makes this Demo Plant unique?

This demo plant operates a simple recuperative transcritical power cycle, a system that sets new standards in energy conversion. Here’s what makes it stand out:

  • Innovative Working Fluid: Instead of conventional fluids, the plant uses a mixture of CO₂ and SO₂, selected for its unique thermodynamic properties.
  • Adapted to Harsh Conditions: Designed to thrive in environments with high solar radiation and elevated ambient temperatures, this air-cooled system mirrors real-world challenges faced by Concentrated Solar Power (CSP) plants.
Key features of the cycle
  • Powerful yet Compact: At the heart of the system is an axial turbine handling a flow rate of 0.2 m³/s, enabling a power output of 1.8 MWel.
  • Next-Gen Heat Exchangers: Equipped with gyroid-structured recuperators and heat exchangers, these components maximize thermal transfer while minimizing material use.
  • Modeling Precision: Advanced simulations in MATLAB, enhanced by Computational Fluid Dynamics (CFD) results, ensure the system is optimized for both design and off-design conditions.
How efficient is it?

Efficiency is key for renewable energy systems, and the DESOLINATION demo plant doesn’t disappoint. By operating in a sliding pressure mode, the cycle achieves impressive efficiencies of over 30%, even when running at partial load.

Adapting to changing temperatures

One of the standout features of this system is its ability to handle varying ambient conditions:

  • At high ambient temperatures (above 30°C), the cycle functions seamlessly, thanks to fixed-speed condenser fans.
  • At lower temperatures (around 10°C), the air velocity can be adjusted to ensure optimal operation.
Handling the system’s inventory

The study also delves into the plant’s piping system, revealing that the total fluid inventory is heavily influenced by the condenser’s operation. Adjustments in fluid storage of up to 300 kg are required to maintain stability when switching between different temperature conditions.

This research represents a significant milestone in the DESOLINATION project’s mission to develop renewable energy systems that are not only efficient but also adaptable to a variety of real-world conditions. By bridging the gap between innovative design and practical application, the demo plant is a glimpse into the future of clean, sustainable power generation.
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Authors: Ettore Morosini, Marco Astolfi, Michele Doninelli, Paolo Iora, Damien Serret, Jean-Michel Hugo and Giampaolo Manzolini.

DOI: https://doi.org/10.1115/GT2024-127246

Experimental study on coalescer efficiency for liquid-liquid separation

Experimental study on coalescer efficiency for liquid-liquid separation

by | Jul 8, 2024 | Publications, Results - Draw solution

The global community acknowledges water demand and accessibility as major challenges impacting human well-being. Forward Osmosis (FO) desalination coupled with concentrate solar power might represent a promising solution to combine water production with renewable sources. This work assesses the performance of a liquid-liquid separator (coalescer), an important component of the FO process, when using a polymeric thermo-responsive draw agent (PAGB2000). Experimental characterization of the coalescer is carried out for different regeneration temperatures (from 50 to 80 °C), residence time, draw concentration (from 0.30 to 0.60) and metal meshes. The separation efficiency of the coalescer can be as high as 95% for high residence time and regeneration temperatures (> 70 °C). Eventually, an analytical expression of the coalescer efficiency as function of the main operating parameters is proposed both to support desalination plant design and to enable understanding its applicability beyond its original context.

https://doi.org/10.1016/j.desal.2024.117840

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Authors:

Igor Matteo Carraretto, Davide Scapinello, Riccardo Bellini, Riccardo Simonetti, Luca Molinaroli, Luigi Pietro Maria Colombo, Giampaolo Manzolini – Dipartimento di Energia, Politecnico di Milano, Via Lambruschini 4, Milano 20156, Italy

Experimental Isochoric Apparatus for Bubble Points Determination: Application to CO2 Binary Mixtures as Advanced Working Fluids

Experimental Isochoric Apparatus for Bubble Points Determination: Application to CO2 Binary Mixtures as Advanced Working Fluids

by | Jun 21, 2024 | Publications, Results - CO2 Mixtures in thermodynamic cycles

Carbon dioxide binarFIGy mixtures are increasingly considered as working fluids in transcritical power cycles, due to the capability to perform liquid-phase compression even at high environmental temperatures. However, a robust thermodynamic model is essential for optimal and reliable design conditions. It is widely recognized that fine-tuning the equation of state with experimental vapor-liquid equilibrium data of the mixture significantly enhances its reliability.

In this work, a new apparatus dedicated to vapour-liquid equilibrium measurements of mixtures is presented. The proposed method consists of a constant-volume system, where bubble points are identified from the divergence of slope of the isochoric lines between the two-phase and liquid regions, in the temperature-pressure plane. The temperature and pressure limits of the apparatus are 503 K and 25 MPa. Bubble points of CO2 binary mixtures with hexafluorobenzene (C6F6) and n-pentane (C5H12) have been measured and compared with previous literature data for validation purposes. Then, the CO2 mixture with octafluorocyclobutane (c-C4F8) is experimentally studied, addressing a literature gap in bubble point data.

The data are used to calibrate the thermodynamic model, leading to affordable design conditions of the power cycle compared to the non-optimized thermodynamics scenario, in a concentrated solar power tower plant.

 

https://doi.org/10.1016/j.ijft.2024.100742

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Authors:

  • M. Doninelli, G. Di Marcoberardino, C.M Invernizzi and P. Iora – Università degli Studi di Brescia, Dipartimento di Ingegneria Meccanica ed Industriale, via Branze, 38, 25123, Brescia, Italy

Commercial thermo-responsive polyalkylene glycols as draw agents in forward osmosis

Commercial thermo-responsive polyalkylene glycols as draw agents in forward osmosis

by | May 24, 2024 | Publications, Results - Draw solution

Forward osmosis (FO) is a promising technology for efficient water reclamation at low operating costs. It has shown potential in producing fresh water from seawater; however, the regeneration of the diluted draw solution (DS) still holds back further development. Thermo-responsive polymers, especially polyalkylene glycol (PAG) based copolymers with hydrophilic ethylene oxide and hydrophobic propylene oxide units, have shown suitability as DSs in FO using low-temperature waste heat to regenerate the DS. In this study, we explored five commercially available copolymers: Pluronic® PE 6400, Pluronic® L-35, Pluronic® RPE 1740, Unilube® 50 MB-26, and Polycerin® 55GI-2601 as DSs in a laboratory FO setup, with DI water as the feed solution (FS). The water
flux and reverse solute flux varied from 1.5 to 2.0 L⋅m􀀀 2⋅h􀀀 1 and from 0.04 to 0.4 g⋅m􀀀 2⋅h􀀀 1, respectively.

Furthermore, all polymer solutions showed the ability to be recovered and reused using temperatures below 100◦C. Therefore, the tested PAGs turned out to be promising as draw solutions for FO systems that utilize low-grade waste heat. The re-usage in FO was shown for regenerated Pluronic® L-35 through a three-step experiment where its recovery was 91.1 %, 93.1 %, and 91.9 % for each FO cycle, respectively.

Keywords: Forward osmosis, Draw solution, Osmotic pressure, Polyalkylene glycols, Lower critical, solution temperature, Reuse of polymer.

Authors: Irena Petrinic, Natalija Jancic, Ross D. Jansen van Vuuren, and Hermina Buksek.

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