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Thermal conductivity of NH3-LiNO3.

Author(s) : CUENCA Y., VERNET A., VALLÈS M.

Summary

The increasing price of primary energy and the interest in protecting the environment has favoured the use of absorption chillers driven by waste heat or solar thermal energy. Nowadays, absorption refrigeration systems and heat pumps use H2O-LiBr and NH3-H2O mixtures as working fluids. These working fluids have some drawbacks, such as crystallization and corrosion problems and low pressure operation for the H2O-LiBr mixture, and the need of rectification of the refrigerant vapour at the desorber outlet for the NH3-H2O mixture. Alternative working fluids, such as NH3-LiNO3 have been proposed. Some advantages of this mixture in front of the conventional working mixtures NH3-H2O and H2O-LiBr are: (a) no rectification is need; (b) the absorption cycle can operate at lower driven temperature allowing the use of flat plate solar collectors to obtain the input energy; (c) no crystallization problems at high heat sink temperature allowing air cooling. The knowledge of thermodynamic and transport properties of the working fluid used in absorption refrigeration cycles is necessary if these systems have to be appropriately evaluated and designed. The absorber usually is the largest element of absorption machines due to its low heat and mass transfer coefficients, and this fact determines the final design of the whole system. The main objective of this work is to measure the thermal conductivity of the binary mixture NH3-LiNO3 for the typical compositions (from 30 to 50%) and temperature (from 35 to 50ºC) found in the absorber of a single-stage absorption refrigeration cycle operating with this mixture. A transient hot wire apparatus with a platinum wire coated with a Teflon insulation layer was set for measurements. The reliability and accuracy of the experimental method was confirmed with measurements on pure water, and H2O-LiNO3 with well known thermal conductivity values. The measured values of thermal conductivity were compared with the correlation proposed by Infante Ferreira (1984) showing remarkable differences.

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Pages: 155-164

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Details

  • Original title: Thermal conductivity of NH3-LiNO3.
  • Record ID : 30001188
  • Languages: English
  • Source: Sources/sinks Alternative to the Outside Air for Heat Pump and Air-conditioning Techniques (Alternative Sources - AS), Padua, Italy, April 5-7, 2011. / International Sorption Heat Pump Conference (ISHPC11), Padua, Italy, April 6-8, 2011.
  • Publication date: 2011/04/06

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