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High-pressure liquid injection for reciprocating compressors to improve efficiency and operating range.

Number: 1239

Author(s) : SCHMITT J., LANGEBACH R.

Summary

Isentropic or above-isentropic compression in a vapor compression cycle can result in compressor discharge temperatures exceeding the condensing temperature, depending on the refrigerant’s thermophysical properties, initial state, and operating conditions. This discharge superheat is unfavorable in terms of both second law efficiency and practical application limits. Heat rejection during compression can shift the process towards the ideal Carnot cycle, thereby improving cycle efficiency and operating limits due to reduced outlet temperatures. However, due to a comparably high compression frequency and small heat transfer area, the heat rejection through the working chamber walls is often insufficient to achieve substantial temperature reduction. For compressors that can tolerate significant amounts of liquid in their working chamber, particularly screw and scroll compressors, effective temperature reduction can be achieved by direct oil or refrigerant injection. For reciprocating compressors, similar approaches are only applicable to a very limited extent due to the risk of liquid slugging. This study presents a method for high-pressure liquid refrigerant injection for reciprocating compressors, which employs a high-pressure pump and a controllable injection valve in the working chamber. The atomization of the injected refrigerant allows for rapid evaporation, preventing liquid slugging and achieving significant temperature reduction in the working chamber. By controlling the injection rate through variable injection valve timing, the temperature profile during compression can be adjusted. The coupled compression-injection is assessed using an energetic chamber model, and the influence of injection quantity and injection rate on efficiency and discharge temperature is assessed. Technical implications regarding compressor operating limits and injection pressure are outlined. In summary, this study introduces a novel approach for enhancing reciprocating compressor efficiency by employing high-pressure liquid refrigerant injection. The theoretical evaluation of this coupled compression-injection system highlights its potential to achieve significant discharge superheat reduction and, in particular cases, improve efficiency.

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  • Original title: High-pressure liquid injection for reciprocating compressors to improve efficiency and operating range.
  • Record ID : 30033590
  • Languages: English
  • Subject: Technology
  • Source: 2024 Purdue Conferences. 27th International Compressor Engineering Conference at Purdue.
  • Publication date: 2024/07/18

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