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Reversible heat pump - Organic Rankine cycle systems with zeotropic fluid mixtures for enhanced performance – Experimental and simulative results from a pilot plant.

Number: 2413

Author(s) : WEITZER M., MODEREGGER M., METZNER L., KOLB S., KARL J.

Summary

Carnot batteries are an emerging thermo-mechanical energy storage technology that enables large scale energy storage with storage durations from several hours up to a few weeks. Especially Carnot batteries based on reversible heat pump - Organic Rankine Cycle systems are promising as they enable the integration of low-temperature heat sources, allow for a reversible utilization of components and operate in temperature ranges where simple hot water storages provide a low-cost thermal energy storage. The main challenge of reversible heat pump - Organic Rankine Cycle (HP-ORC) systems is to increase the roundtrip efficiency to a competitive level while keeping the system complexity low to avoid high investment costs. In order to overcome these challenges, this work investigates the use of zeotropic fluid mixtures for such systems. Zeotropic fluid mixtures are characterized by a mixture-dependent temperature glide during phase change. This temperature glide reduces exergy losses in the heat exchangers due to a better temperature match between working fluid and heat transfer fluid.
The present work summarizes the outcomes of extensive simulations with zeotropic fluid mixtures in reversible HP-ORC systems. After screening and selecting suitable fluid mixtures according to environmental and thermo-physical properties, a simulative parameter study discloses the performance improvements of various mixtures for selected boundary conditions. Moreover, first experimental results with fluid mixtures in a reversible HP-ORC pilot plant (15 kWel / 9 kWel) are presented and evaluated in terms of cycle efficiencies. For this purpose, the refrigerants R1336mzz(Z) and R1336mzz(E) were investigated experimentally as pure liquids and as mixtures in 10 wt.-% increments. The simulative and experimental results underline that suitable zeotropic fluid mixtures significantly enhance the efficiency for both, heat pump and Organic Rankine Cycle. Notably, the optimal mixture composition is different for heat pump mode and ORC mode and depends on the operating conditions.

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  • Original title: Reversible heat pump - Organic Rankine cycle systems with zeotropic fluid mixtures for enhanced performance – Experimental and simulative results from a pilot plant.
  • Record ID : 30033138
  • Languages: English
  • Subject: Technology
  • Source: 2024 Purdue Conferences. 20th International Refrigeration and Air-Conditioning Conference at Purdue.
  • Publication date: 2024/07/17

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