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Free-Piston Heat Recovery Using Stirling and Organic Rankine Cycles

Title:

Free-Piston Heat Recovery Using Stirling and Organic Rankine Cycles

Sayyad Nazary, Ali ORCID: https://orcid.org/0000-0002-7364-3459 (2026) Free-Piston Heat Recovery Using Stirling and Organic Rankine Cycles. Masters thesis, Concordia University.

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Abstract

All energy consumed in data centers is ultimately rejected as low-temperature heat, representing
a 2016 cost of 152B dollars. Projected 2030 carbon emissions are 8000 million tons. Waste heat recovery
(WHR) allows the recovery of rejected energy, lowering both costs and emissions. The most
interesting WHR thermodynamic cycles are the Organic Rankine Cycle (ORC) and the over-looked
Stirling cycle. Both ubiquitously suffer from limitations resulting from their use of rotary devices.
ORCs traditionally use turbines, only efficient in narrow operating conditions. Stirling engines
link piston motions through a crankshaft-type mechanism, causing near sinusoidal motion and
deviations from the ideal cycle. A free-piston expander coupled to a linear generator (FPE-LG)
can be used with both Stirling and ORC engines to control the piston(s) motion, leading to a
wider operation range (ORC) or a more ideal thermodynamic path (Stirling). In this work, the
ideal velocity profile for alpha-type Stirling engines is formulated, the influence of a realistic FPE-LG
implementation (finite acceleration rate) on cycle efficiency and characteristics are examined. An
FPE-LG Stirling is compared to a sinusoidal and Rhombic-drive Stirling, and FPE-LG ORC. Time resolved, semi-analytical adiabatic Stirling models are solved. The infinite-acceleration FPE-LG
Stirling has better efficiency than Rhombic and Sinusoidal drives. The FPE-LG ORC under performs the Stirling cycles at most temperatures examined, except at very small delta-T . For a finite
acceleration FPE-LG Stirling engine, higher accelerations cause higher efficiencies up to a critical
value, beyond which the improvement is minimal. A new direction for WHR cycles is proposed.

Divisions:Concordia University > Gina Cody School of Engineering and Computer Science > Mechanical, Industrial and Aerospace Engineering
Item Type:Thesis (Masters)
Authors:Sayyad Nazary, Ali
Institution:Concordia University
Degree Name:M.A. Sc.
Program:Mechanical Engineering
Date:10 March 2026
Thesis Supervisor(s):Kiyanda, C.B.
Keywords:Data Center, Organic Rankine Cycle (ORC), Stirling Cycle, Free-Piston Expander (FPE), Waste Heat Recovery (WHR)
ID Code:996996
Deposited By: Ali Sayyad Nazary
Deposited On:29 Jun 2026 14:49
Last Modified:29 Jun 2026 14:49

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