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Two approaches for enhanced evaporation of water at subatmospheric pressure.

Number: AD-HM-1094

Author(s) : VOLMER R., ALARIO N., WEISE J., et al.

Summary

Evaporation of the refrigerant water in adsorption heat pumps and chillers takes place at sub-atmospheric pressures of about 0.8-2.5 kPa in a pure water environment. These low pressure conditions involve special boiling characteristics, different from boiling at elevated pressures, which entails specific requirements for evaporator design. Investigations, e.g. by McGillis et al. [1], confirmed that in pool boiling mode the efficient nucleate boiling regime can usually only be reached by providing relatively high driving temperature differences (wall superheats) which is not a reasonable option in most adsorption module concepts. Most commercially available sorption modules work either with a partially flooded evaporator or a falling film concept, using for instance a tube coil or tube-fin heat exchanger type. However, the first solution mostly suffers from small heat transfer coefficients while the second one requires an additional refrigerant pump which consumes auxiliary energy and complicates the module design.

Details

  • Original title: Two approaches for enhanced evaporation of water at subatmospheric pressure.
  • Record ID : 30022895
  • Languages: English
  • Source: International sorption heat pump conference, ISHPC 2017, Tokyo august 7-10.
  • Publication date: 2017/08/07

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