Numerical investigation of oil injection in a Roots blower operated as expander

Nicola Casari,Ahmed Kovacevic,Ettore Fadiga,Michele Pinelli,Davide Ziviani,Sham Rane,Alessio Suman

doi:10.1088/1757-899x/604/1/012075

Abstract

The adoption of positive displacement machines as expanders in Organic Rankine Cycles (ORCs) is increasingly common, especially in the low to medium power range. At the same time, these devices often serve as compressor in Vapor-Compression Refrigeration Systems. In both cases, the application of Computation Fluid Dynamics (CFD) to optimize such machines has become an integrated tool in the design process. As a consequence, several challenges associated with the numerical simulation have to be taken into account. For example, the modeling of the gap represents a challenge for the stability of the numerical analysis. The dynamic of the process, combined with deformations of the clearances and of the working chamber has to be considered with extra care.To raise the efficiency of the machine, oil is typically injected. Its numerical modeling imply an extra challenge in the simulation of the actual operation of the machine. The present work is mainly focused on the multi-phase nature of the flow, with a particular analysis of the lubricant oil injected. In this work, a two-lobe Roots blower operated as expander has been simulated with the open-source software OpenFOAM-v1812, using the SCORG-V5.2.2. This analysis highlights the areas that are affected the most by the oil presence in order to highlight the sealing effect it provides

Highlights

Organic Rankine Cycles (ORCs) have been increasingly employed in order to tackle the raise in the demand of energy combined with a cleaner way of its production
The adoption of positive displacement machines as expanders in Organic Rankine Cycles (ORCs) is increasingly common, especially in the low to medium power range. These devices often serve as compressor in Vapor-Compression Refrigeration Systems
The dynamic of the process, combined with deformations of the clearances and of the working chamber has to be considered with extra care

Summary

Introduction

ORCs have been increasingly employed in order to tackle the raise in the demand of energy combined with a cleaner way of its production. Such cycles are typically employed for waste heat recovery [1], recovering a share of energy that is typically not exploited. Published under licence by IOP Publishing Ltd efficiency is often the most detrimental of the entire cycle [2]. This remark is more correct as the size of the plant decreases. For plants having an output power smaller than 100 kWe (micro-ORCs), the feeding pump and the expander are the devices that are more studied

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Results

Conclusion