A new method for online measurement of the concentration of working fluids in absorption refrigeration systems

This paper proposes a new method for online measurement of the concentration of working fluids in absorption refrigeration systems: electrical conductivity is measured to determine the concentration of the solution. Compared with the common density-concentration method, electrical conductivity-concentration method has the same accuracy but helps to save cost when applied in absorption systems with ammonia-salt solutions. This novel method is also suitable for systems with traditional working fluids like water-lithium bromide solution. Electrical conductivities of ammonia-lithium nitrate, ammonia-sodium thiocyanate and water-lithium bromide solutions were measured between (293.15 and 333.15) K, using an Industrial Conductivity Meter. The ammonia mass fraction varied from 0.35 to 0.48 for ammonia-lithium nitrate solution and from 0.35 to 0.50 for ammonia-sodium thiocyanate solution. For water-lithium bromide solution, the mass fraction of lithium bromide was within the range of 40%-60%. The experimental data were correlated as a function of temperature and composition using the extended Casteel-Amis equation. In addition, correlations of refrigerant mass concentration as a function of electrical conductivity and temperature of the solution are proposed.