Performance Optimizations of the Transcritical CO₂ Two-Stage Compression Refrigeration System and Influences of the Auxiliary Gas Cooler

• Main Authors: Yuyao Sun, Jinfeng Wang, Jing Xie
• Format: Article
• Language: English
• Published: MDPI AG 2021-09-01
• Series: Energies
• Subjects: energy analysis; exergy analysis; coefficient of performance; exergy efficiency; auxiliary gas cooler; intermediate pressure
• Online Access: https://www.mdpi.com/1996-1073/14/17/5578

To optimize the performance of the transcritical CO₂ two-stage compression refrigeration system, the energy analysis and the exergy analysis are conducted. It is found that higher COP, lower compression power, and less exergy destruction can be achieved when the auxiliary gas cooler is applied. Moreover, the discharge temperature of the compound compressor (HPS) can be reduced by decreasing the temperature at the outlet of the auxiliary gas cooler (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>T</mi><mrow><mi>a</mi><mi>g</mi><mi>c</mi><mo>,</mo><mi>o</mi><mi>u</mi><mi>t</mi></mrow></msub><mo stretchy="false">)</mo></mrow></semantics></math></inline-formula>. When the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>T</mi><mrow><mi>a</mi><mi>g</mi><mi>c</mi><mo>,</mo><mi>o</mi><mi>u</mi><mi>t</mi></mrow></msub></mrow></semantics></math></inline-formula> is reduced from 30 to 12 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>°</mo><mi mathvariant="normal">C</mi></mrow></semantics></math></inline-formula>, the discharge temperature of the compound compressor (HPS) can be decreased by 13.83 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>°</mo><mi mathvariant="normal">C</mi></mrow></semantics></math></inline-formula>. Furthermore, the COP and the exergy efficiency can be raised by enhancing the intermediate pressure. Based on these results, the optimizations of system design and system operation are put forward. The application of the auxiliary gas cooler can improve the performance of the transcritical CO₂ two-stage compression refrigeration system. Operators can decrease the discharge temperature of the compound compressor (HPS) by reducing the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>T</mi><mrow><mi>a</mi><mi>g</mi><mi>c</mi><mo>,</mo><mi>o</mi><mi>u</mi><mi>t</mi></mrow></msub></mrow></semantics></math></inline-formula>, and increase the COP and the exergy efficiency by enhancing the intermediate pressure.