Experimental and Numerical Study of Supersonic Non-ideal Flows for Organic Rankine Cycle Applications

Abstract

The organic Rankine cycle is low grade heat recovery technology, for sources as diverse as geothermal, industrial and vehicle waste heat. The working fluids used within these systems often display significant real-gas effects, especially in proximity of the thermodynamic critical point. 3D Computational Fluid Dynamics (CFD) is commonly used for performance prediction and flow field analysis within expanders, but experimental validation with real gases is scarce within the literature. This paper therefore presents a dense-gas blowdown facility constructed at Imperial College London, for experimentally validating numerical simulations of these fluids. The system-level design process for the blowdown rig is described, including the sizing and specification of major components. Tests with refrigerant R1233zd(E) are run for multiple inlet pressures, against a nitrogen baseline case. CFD simulations are performed, with the refrigerant modeled by Ideal Gas, Peng-Robinson, and Helmholtz Energy Equations of State. It is shown that increases in fluid model fidelity lead to reduced deviation between simulation and experiment. Maximum and mean discrepancies of 9.59% and 8.12% in nozzle pressure ratio with the Helmholtz Energy EoS are reported. This work demonstrates an over-prediction of pressure ratio and power output within commercial CFD packages, for turbomachines operating in non-ideal fluid environments. This suggests a need for further development and experimental validation of CFD simulations for highly non-ideal flows. The data contained within this paper is therefore of vital importance for the future validation and development of CFD methods for dense-gas turbomachinery

Shock losses and Pitot tube measurements in non-ideal supersonic and subsonic flows of Organic Vapors

“…Amongst these so-called nozzlefitted facilities is the Test Rig for Organic VApors (TROVA) (Spinelli et al, 2013) at the Laboratory of Compressible Fluid-dynamics for Renewable Energy Applications (CREA Lab) of Politecnico di Milano, where all the experimental campaigns concerning the present work were carried out. Other plants of this kind are the ORCHID (Head et al, 2016) at TU Delft, the CLOWT (Reinker et al, 2017) at Muenster University of Applied Sciences and the dense-gas blowdown facility at Imperial College London (Robertson et al, 2020). Several turbine-fitted facilities mainly devoted to performance measurement of the different components and of the overall thermodynamic cycle also exist, such as the LUT micro-ORC test rig at Lappeenranta -Lahti University of Technology (Turunen-Saaresti et al, 2017).…”

Shock loss measurements in non-ideal supersonic flows of organic vapors

“… 2017 ) at Muenster University of Applied Sciences and the dense gas blowdown facility at Imperial College London (Robertson et al. 2020 ).…”

“…Among these, so-called nozzlefitted facilities is the Test Rig for Organic VApors (TROVA) (Spinelli et al 2013) at the Laboratory of Compressible fluid dynamics for Renewable Energy Applications (CREA Lab) of Politecnico di Milano, where all the experimental campaigns concerning the present work were carried out. Other plants of this kind are the ORCHID (Head et al 2016) at TU Delft, the CLOWT (Reinker et al 2017) at Muenster University of Applied Sciences and the dense gas blowdown facility at Imperial College London (Robertson et al 2020).…”

Experimental characterization of nozzle flow expansions of siloxane MM for ORC turbines applications

“…Given this, the design of such machines is particularly critical, also considering that turbine efficiency impacts the economic competitiveness of the ORC technology. Current computational tools are based on advanced CFD codes ( [7,8,9,10,11]) embedding state-of-the-art thermodynamic models ( [12,13]), but experimental data are only recently becoming available in literature for comparison and verification ( [14,4,5,15]). This is mainly due to the peculiar features of organic fluid flows, as the high temperature, the vicinity to the saturation curve and to the thermal stability limits, which challenge the success of ad-hoc experimental campaigns.…”