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Booster ejector enhanced vapor compression cycle performance for industrial refrigerating facilities.

Number: 2572

Author(s) : BUYADGIE O., DRAKHNIA O., BUYADGIE D.

Summary

Challenges associated with the mandatory lubrication of the refrigerant gas compressors have led to the development of the oil-less dynamic centrifugal compressors, which among undoubtful operation advantages have a major drawback - limits of the compression lift at single stage design for desirable condensation temperatures range, especially at most unfavorable ambient conditions. The application of two or more compression stages leads to a disproportional increase in material cost and unacceptable hydraulic losses. But even two-stage oil-less
compressors will operate at refrigeration mode with 1.15-1.4 times lower to nominal COP if ambient temperature will apparently raise above 30°C (87°F). Such conditions increase the cost of water-or air-cooled condensation by an increased cooling media flow rates or mass-dimensional characteristics of the condensation heat release subsystems.
Internal cooling cycle potential as well as external (waste or renewable) energy sources can be utilized to support compressor operation at higher compression ratios and ambient temperature conditions compared to the designed ones. The internal cycle potential ensures an improvement of the oil-less compressor cooling system's COP without any additional energy input. It only requires equipping the system with simple and inexpensive booster ejector devices. For this scenario, reduction of the compressor power consumption at the same cooling capacity production rate is achieved by two means. The first one refers to a ballast vapor or at least its main fraction to produce additional compression work in the booster ejector or recirculate it via the second stage of a compressor, bypassing the first stage. The other mean is an additional subcooling of the main liquid flow by evaporation of another portion of the working fluid at the intermediate temperature. The evaporated vapor flows to the second suction stage of the
compressor or is added to ballast vapor to perform a compression of the main vapor flow from the evaporator. The integral COP of the Booster Ejector Enhanced Compressor Refrigerating system (BEECR) using the oil-less compressor increases by 10-20% and highly depends on operating conditions of the refrigerating system. With an external low-grade heat driven booster ejector subsystem, the overall COP of BEECR increases by additional 5-15% depending on the heat grade, working fluids properties and schematic solution applied. The article provides an analysis of various vapor-compression refrigerating systems (VCRS) performance
enhancement approaches, characteristics of simulated ejectors, technical and economic feasibility of the most effective options for the conditions of Danfoss Turbocor oil-less compressor-based industrial chillers operating at evaporation temperature of -6.5°C (20°F), condensation temperature of 30°C (87°F) to 51°C (124°F), and variable cooling capacity of 192.7 to 220.3 kW (54.8-62.6RT), operating on R134a and R513a refrigerants. The presented study describes how COP of BEECR depends on operating parameters of the system and selected refrigerant's thermophysical properties. The study showed that support of the main compressor by enhancing with booster ejector devices on both newly built or retrofitted VCRSs allows decreasing power consumption by a minimum of 15%, which leads to saving of about 2.5% of overall consumed electricity by chillers, improves reliability and durability of the compressor and, as a result, lowers the impact on environment.

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  • Original title: Booster ejector enhanced vapor compression cycle performance for industrial refrigerating facilities.
  • Record ID : 30030776
  • Languages: English
  • Subject: Technology
  • Source: 2022 Purdue Conferences. 19th International Refrigeration and Air-Conditioning Conference at Purdue.
  • Publication date: 2022

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