An intracooling system for a novel two-stage sliding-vane air compressor

Stefano Murgia,Ida Costanzo,Giulio Contaldi,Gianluca Valenti,Daniele Colletta

doi:10.1088/1757-899x/232/1/012054

Abstract

Lube-oil injection is used in positive-displacement compressors and, among them, in sliding-vane machines to guarantee the correct lubrication of the moving parts and as sealing to prevent air leakage. Furthermore, lube-oil injection allows to exploit lubricant also as thermal ballast with a great thermal capacity to minimize the temperature increase during the compression. This study presents the design of a two-stage sliding-vane rotary compressor in which the air cooling is operated by high-pressure cold oil injection into a connection duct between the two stages. The heat exchange between the atomized oil jet and the air results in a decrease of the air temperature before the second stage, improving the overall system efficiency. This cooling system is named here intracooling, as opposed to intercooling. The oil injection is realized via pressure-swirl nozzles, both within the compressors and inside the intracooling duct. The design of the two-stage sliding-vane compressor is accomplished by way of a lumped parameter model. The model predicts an input power reduction as large as 10% for intercooled and intracooled two-stage compressors, the latter being slightly better, with respect to a conventional single-stage compressor for compressed air applications. An experimental campaign is conducted on a first prototype that comprises the low-pressure compressor and the intracooling duct, indicating that a significant temperature reduction is achieved in the duct.

Highlights

Intercooling is an established practice in compression technology for reducing discharge temperature and power requirement [1,2]
This study presents the design of a two-stage sliding-vane rotary compressor in which the air cooling is operated by high-pressure cold oil injection into a connection duct between the two stages
An experimental campaign is conducted on a first prototype that comprises the low-pressure compressor and the intracooling duct, indicating that a significant temperature reduction is achieved in the duct

Summary

Introduction

Intercooling is an established practice in compression technology for reducing discharge temperature and power requirement [1,2]. As known, intercooling is the cooling of the compressed gas between two compression stages by way of a heat exchanger employing typically water or air as coolant. Thermal power is transferred from the gas to the liquid, but not to the environment. When applied to an oil-flooded compressor, such as a sliding-vane air compressor considered here, the lubricant itself can be used as sprayed liquid. In this case, intracooling with respect to intercooling allows for fewer pieces of equipment, as shown by Figure 1, and it allows for oil to be available at the highest pressure, a condition that may be exploited for a better injection.

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