A general framework for part-load optimization of air-cooled ORCs with screw expanders

Konstantinos Braimakis, Moritz Westermeier, Christopher Schifflechner, Michel Beaughon, Aldo Serafino, Antonios Charalampidis and Sotirios Karellas

Energy, 2025, vol. 332, issue C

Abstract: The present work focuses on part-load optimization of air-cooled, recuperative Organic Rankine Cycle systems equipped with screw expanders driven by medium temperature (180 °C) waste heat. A series of technical operational constraints along with the off-design performance of heat exchangers and expander, pump and air-cooled condenser (ACC) for different heat source/heat sink temperatures and flow rates are considered. Two operating strategies are examined based on constant (CSH) and variable (VSH) superheating. At part-load, the cooling fluid mass flow rate and expander speed are optimized to maximize overall efficiency. The optimized part-load efficiency is far more sensitive to the cooling fluid temperature than the heat source temperature and flow rate, thanks to pressure ratio optimization achieved by varying the expander speed. The VSH operating strategy offers meaningful performance improvement over the CSH for heat source and sink temperatures exceeding the nominal. Minimum part-load overall efficiency corresponds to highest heat source and heat sink temperature and is equal to roughly 65–70 % of the nominal. The efficiency improvement thanks to expander speed optimization is significant especially at lower heat source flow rates and higher heat sink temperatures. Part-load optimization enables consistent performance across wide range of boundary conditions.

Keywords: ORC; Part-load; Optimization; Operating strategy; Off-design; Screw expander (search for similar items in EconPapers)
Date: 2025
References: Add references at CitEc
Citations:

Downloads: (external link)
http://www.sciencedirect.com/science/article/pii/S0360544225027033
Full text for ScienceDirect subscribers only

Related works:
This item may be available elsewhere in EconPapers: Search for items with the same title.

Export reference: BibTeX RIS (EndNote, ProCite, RefMan) HTML/Text

Persistent link: https://EconPapers.repec.org/RePEc:eee:energy:v:332:y:2025:i:c:s0360544225027033

DOI: 10.1016/j.energy.2025.137061

Access Statistics for this article

Energy is currently edited by Henrik Lund and Mark J. Kaiser

More articles in Energy from Elsevier
Bibliographic data for series maintained by Catherine Liu ().