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New tendencies in the thermodynamics of compact heat exchangers.

Author(s) : KHEIRI A., FEIDT M., COSTEA M., et al.

Summary

Studies on charge reduction really started since the 1987 Montreal Protocol that released the concern regarding the ozone's destruction effect by widely used refrigerants. More studies were induced by 1997 Kyoto's agreement which pointed out those fluids negative greenhouse effect. In a simple refrigerant system (compressor + condenser + valve + evaporator) without liquid receiver, it has been noted that refrigerant charge is located in the heat exchangers (evaporator and condenser) with a total rate great than 65% (Poggi et al. 2008). In more sophisticated systems, one can consider that the heat exchangers contain half of the total refrigerant charge. The refrigerant charge is directly related to the whole internal volume of the parts of the refrigerant device. The average density of single or two-phase flow in each part links refrigerant mass and volume, and it is also a critical parameter to take into account in charge reduction effort. Volume reduction of heat exchanger (HEX) for a given heat rate usually leads to more friction losses with consequently less COP especially when decreasing hydraulic diameters. Design parameter optimizations of HEX are classically conducted without charge reduction constraint. It can be affected when such constraint is introduced instead of that regarding exchange area. Furthermore, performances of evaporator and condenser are affected by their refrigerant charge. Hence, there is a need of actual optimization efforts to reach the goal of reducing charge without decreasing COP. The authors propose here to overview first the physical background that allows HEX optimization and secondly the successive steps to achieve a nearly complete optimal design of an HEX for refrigeration purpose with low charge objective. Use of entropy or exergy analysis is particularly considered.

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Details

  • Original title: New tendencies in the thermodynamics of compact heat exchangers.
  • Record ID : 2009-1471
  • Languages: English
  • Source: RCR 2009. 1st IIR Workshop on Refrigerant Charge Reduction in Refrigerating Systems.
  • Publication date: 2009/04/06

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