Imperial College London


Faculty of EngineeringDepartment of Chemical Engineering

Professor of Clean Energy Technologies



+44 (0)20 7594 1601c.markides Website




404ACE ExtensionSouth Kensington Campus






BibTex format

author = {Chatzopoulou, MA and Lecompte, S and De, Paepe M and Markides, C},
publisher = {Elsevier},
title = {Off-design operation of ORC engines with different heat exchanger architectures in waste heat recovery applications},
url = {},

RIS format (EndNote, RefMan)

AB - Organic Rankine cycle(ORC)engines in waste-heat recovery applications experience variable heat-source conditions (i.e. temperature and mass flow ratevariations). Therefore maximisingthe ORC system performance under off-design conditions is of key importance, for the financial viability and wider adoption of these systems. In this paper,the off-design performance of an ORC engineis investigated, with screw expander andtwoheat exchanger (HEXs)architectures, while recovering heat from an internal combustion engine (ICE).Unlike previous studieswhere the ORC expanderand HEXsperformance is assumed fixed duringoff-design operation, in this work we consider the time-varying characteristics of the system components.Firstly, nominal system sizing results indicate that the screw expander isentropic efficiency exceeds 80%,whilethe plate HEXs (PHEXs) heat transferarea requirements are 50% lower,than the respective ones for double pipe (DPHEX) design. Next, the ORC engine operation is optimised at part-load (PL) ICE conditions.Although, the HEXs heat transfer coefficients decrease by 30% with part-load, the HEX effectiveness increasesby up to 20%, due to higher temperature difference across the working fluids.Findingsalso reveal that the PHEX performance is less sensitive to the off-design operation. Optimum off-design power output maps indicatethattheORC enginePL reduces to 72%, for ICE PL of 60%, while ORCengines with PHEXsgenerate slightlymore power,for the same heat source conditions. Overall, the modelling tool developed predictsthe ORC performance over an operating envelope and allows the selection of optimal designs and sizes of ORC HEXsand expanders.The findings can be used by ORC plant operators to optimise the ORC engine power output, given the varying heat source conditions observed on their site,and by ORC vendors to inform HEX andexpander design decisions.
AU - Chatzopoulou,MA
AU - Lecompte,S
AU - De,Paepe M
AU - Markides,C
PB - Elsevier
SN - 1876-6102
TI - Off-design operation of ORC engines with different heat exchanger architectures in waste heat recovery applications
UR -
ER -