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Solutions for enhancing the performance of Voorhees-modified R744 cycles.

Number: pap. n. 241

Author(s) : CHESI A., FERRARA G., FERRARI L., et al.

Summary

The use of carbon dioxide as a refrigerant is attracting an ever increasing interest due to its intrinsic environmental friendliness in comparison with synthetic refrigerants. Yet, due to its thermodynamic properties, it features lower performance indexes when compared to its competitors. The Voorhees-modified cycle layout has been proposed as a method to enhance the performance of refrigerating equipment operating with R744. Although being a relatively simple solution, the Voorhees modified reciprocating compressor leads to a set of phenomena which heavily limit its potential in increasing the COP, the most important being the loss of available volume during the suction phase, and the limited admission time. A proper timing of the opening and closing of the admission port, which could possibly be obtained with a dedicated piece of equipment, can minimise the overall detrimental effect of such phenomena. Moreover, the use of a flash-tank as phase separator and of economiser heat exchangers to subcool the liquid entering the evaporator also deeply affect the overall cycle performance, possibly leading to improvements in COP and capacity. This paper aims to develop a lumped parameters numerical model of the compression phases, in order to estimate the potential advantage in terms of efficiency and capacity of using some methods of controlling the injection timing. In particular, the model takes into account the position of the admission port and its opening time, aiming to better understand the effect of such parameters. The possibility of using an economiser heat exchanger, which uses the admission mass flow to subcool the refrigerant entering the evaporator, will also be considered, evaluating the effect of its position in the circuit layout. The increase in performance obtained with such modified layouts is then compared to a reference case, employing a flash-tank as separator, no timing device for the admission port and no economiser heat exchanger.

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Pages: 9 p.

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Details

  • Original title: Solutions for enhancing the performance of Voorhees-modified R744 cycles.
  • Record ID : 30004553
  • Languages: English
  • Source: 10th IIR-Gustav Lorentzen Conference on Natural Working Fluids (GL2012). Proceedings. Delft, The Netherlands, June 25-27, 2012.
  • Publication date: 2012/06/25

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