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Pressure drop in condensing superheated zone.

Number: pap. 2551

Author(s) : MEYER M., HRNJAK P.

Summary

Traditionally, condensation is characterized by division into three zones: desuperheating, condensation and subcooling. It was shown that condensation starts even in the presence of superheated vapor, when the wall temperature reaches saturation. Heat transfer effects of that process were described earlier but not pressure drop that was later found to indicate the presence of condensate, the same as shown by heat transfer results. Pressure drop in condensers has traditionally been modeled separately for single-phase and two-phase regions. When plotted as a function of enthalpy, the correlations show a discontinuity between the single-phase and two-phase zones because the models typically assume thermodynamic equilibrium during condensation. This assumption indicates that the first drop or film of condensate would form when the bulk refrigerant enthalpy reached the saturated vapor enthalpy. In reality, condensation starts when the wall temperature reaches the saturation temperature even if the bulk enthalpy is still indicating a superheated state. That makes a fourth zone in the condenser: it begins when the wall temperature reaches the saturation temperature and ends when the bulk enthalpy reaches saturated vapor, and is classified as the condensing superheated zone. In this condensing superheated zone, the interaction between the condensate film and vapor increases the pressure drop compared to vapor alone. This paper presents experimental results for pressure drop in that zone of the condenser for R32, R134a and R1234ze(E). The pressure drop was found to be higher than predicted by single-phase correlations such as Colburn (1933).

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Pages: 8 p.

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Details

  • Original title: Pressure drop in condensing superheated zone.
  • Record ID : 30013198
  • Languages: English
  • Source: 2014 Purdue Conferences. 15th International Refrigeration and Air-Conditioning Conference at Purdue.
  • Publication date: 2014/07/14

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