Thermodynamic properties of lithium bromide-based working solutions for absorption heat pump

Abstract

New working fluids for air-cooled absorption heat pump have been developed. To improve the performance of air-cooled absorption heat pump, lithium bromide+lithium iodide+1,3-propanediol+water (LiBr/LiI mole ratio=4 and (LiBr+ LiI)/$HO(CH_2)_3OH$ mass ratio=4) and lithium bromide+lithium iodide+lithium chloride+lithium nitrate+water (mole ratio=5:1:1:x) systems were selected. Through the measurement of solubility and vapor pressure, Duhring charts of working fluids candidates were constructed. From the Duhring charts, the mixing mole ratio of lithium bromide+lithium iodide+lithium chloride+lithium nitrate+water system was determined as 5:1:1:0.5. On the Duhring charts, the lithium bromide+lithium iodide+1,3-propanediol+water and lithium bromide+lithium iodide+lithium chloride+lithium nitrate+water systems could be operated with appropriate operation range. For more detailed cycle analysis, heat capacities, densities and viscosities of the two selected systems were measured and then the enthalpy-concentration charts were constructed. Through the cycle analysis, the absorption cycle using the lithium bromide+lithium iodide+1,3-propanediol+water (LiBr/LiI mole ratio=4 and (LiBr+LiI)/$HO(CH_2)_3OH$ mass ratio=4) system and lithium bromide+lithium iodide+lithium chloride+lithium nitrate+water (mole ratio=5:1:1:0.5) system was found to have high theoretical COP, low crystallization temperature, and high cooling capacity at the given condition. ($T_e=5℃$, $T_a=T_c=50℃$).