Cavitation models with thermodynamic effect for organic fluid cavitating flows in organic Rankine cycle systems: A review

Zhibin Yu,Wenguang Li

doi:10.1016/j.tsep.2021.101079

Abstract

Organic Rankine cycle (ORC) power plants are considered as one of the most promising technologies to generate power from low temperature heat sources such as biomass combustion, industrial waste heat, geothermal heat, and solar thermal energy. A feed pump is a key component of an ORC power plant to circulate the working fluid within the system. Owing to the low boiling temperature of most organic fluids, the feed pumps of ORC power plants are more vulnerable to suffer from cavitation. Cavitation of the organic fluid in the feed pump in an ORC system can degrade the evaporator performance and cause instabilities in the system operation. Properly determining the required net positive suction head or subcooling for the pump is critical for the ORC system design and operation. Thus, this paper presents a systematic review of cavitation models with thermodynamic effect in simulations of cavitating flows. Methods for implementing thermodynamic effect were summarised. The features of the cavitation models were characterised and criticized, and their drawbacks were identified. A number of newly established cavitation models were explained and discussed in detail. Homogeneous mixture cavitation models have advantages such as less computational effort and easier implementation of thermodynamic effect in comparison with fully coupled multiscale models. However, when the thermodynamic effect is considered in the existing cavitation models, the cavitation regimes are not distinguished and applied properly. Nucleation cavitation models for organic fluids in ORC systems should be developed in terms of experimental nuclei profile and non-condensable gas concentration in future.

Highlights

The organic Rankine cycle (ORC) is a Rankine cycle that employs an organic fluid as working medium to generate power from lower tem perature sources such as biomass combustion, industrial waste heat, and geothermal heat [1,2,3,4,5]
A laboratory-scale pumpless ORC system was tested [6,7] and thermo fluidic feed pumps have been tested in laboratory ORC systems [8,9], mechanical feed pumps are still commonly employed in laboratory- or large-scale ORC systems [10,11] due to their simple constructure and easy operation
A systematic review of cavitation models with thermodynamic effect potentially applied to computational fluid dynamics (CFD) simulations of cavitating flows in feed pumps in organic Rankine cycle systems has been presented

Summary

Introduction

The organic Rankine cycle (ORC) is a Rankine cycle that employs an organic fluid as working medium to generate power from lower tem perature sources such as biomass combustion, industrial waste heat, and geothermal heat [1,2,3,4,5]. Since an improper mechanical feed pump can impair the perfor mance of the evaporator, and, in turn, the performance of the expander in an ORC system, a number of studies have been conducted on me chanical feed pumps in ORC systems to clarify pump performance and cavitation behaviour when delivering organic fluids. The pumping work in ORC systems was estimated analytically for 18 different organic fluids [12]; it was identified that the feed pump in ORC systems should develop high head (0.2–40 bar) and low mass flow rate (0.01–10 kg/s) [13]. At the same head and flow rate, the positive displacement pump usually has better effi ciency but higher maintenance costs and more complicated pipe systems in comparison with the rotodynamic pump

Methods

Discussion

Conclusion