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Initial design and experimental results of a novel near-isothermal compressor for heat pump applications.

Number: 1444

Author(s) : KOWALSKI S., RENDALL J., ABUHEIBA A., CHEEKATAMARLA P., GEHL A., MOMEN A., NAWAZ K.

Summary

Efforts to increase the efficiency of residential and commercial air conditioners and heat pumps have demonstrated that the compressor has the highest electrical energy usage of the system. Therefore, the efficiency of this component should be improved to reduce its energy usage. Another challenge with heat pump design is that some compressor types have drawbacks that make modulation difficult. To address these challenges, we developed a near-isothermal liquid compressor at the US Department of Energy’s Oak Ridge National Laboratory. The compressor uses propylene glycol to compress CO2. In the compression chamber the propylene glycol can enter from the bottom to create a liquid piston for compression or through a spray nozzle at the top of the chamber. In the latter case, heat transfer from the gas to be compressed to the liquid droplets is high. This allows near isothermal operation of the compressor, which increases the efficiency by 17% to 30% compared to adiabatic compression. Furthermore, the isothermal liquid compressor enables very efficient and simple part load modulation. Experimental results demonstrating the operation of the liquid compressor using CO2 are presented. Initial data demonstrated a temperature rise of 7 K at pressure ratios of almost 4. For comparison at the same initial pressure, temperature, and pressure ratio, adiabatic compression would result in a temperature rise of approximately 70 K. Data plotted on a pressure-enthalpy diagram demonstrated that the compression started at superheated state and ended in supercritical state. Testing was performed with repeated compressions in the superheated region of the pressure-enthalpy diagram at liquid flow rates of 2 x 10-3 m3/min and 3 x 10-3 m3/min to understand the limitations of the prototype for use with an actual heat pump system. This work demonstrated a novel cycle on a temperature-entropy diagram. Results from this work will be used to develop a second-generation prototype in which more rapid cycling is possible.

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  • Original title: Initial design and experimental results of a novel near-isothermal compressor for heat pump applications.
  • Record ID : 30030365
  • Languages: English
  • Subject: Technology
  • Source: 2022 Purdue Conferences. 26th International Compressor Engineering Conference at Purdue.
  • Publication date: 2022/07/15
  • Document available for consultation in the library of the IIR headquarters only.

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