Experimental investigation of two-phase flow characteristics of LiBr/H2O solution through orifice plates in vacuum environment

• Flow characteristics of two-phase LiBr/H2O through orifice plates are studied.
• Flash evaporation causes reduction of the mass flow rate of the two-phase flow.
• Mass fraction of gas in the two-phase flow is proportional to the superheat.
• The flows are choked when the mass fraction of gas is larger than 0.70%.
• A regression model for the flow coefficient of the two-phase flow is obtained.

A new type of multi-stage elementary unit for generating and condensing processes in absorption heat pumps was introduced. One stage of the elementary unit was built, in which the LiBr/H2O solution was concentrated by flash evaporation when flowing through an orifice plate to the generating space. Experiments were carried out to study the flow characteristics of LiBr/H2O solution through an orifice plate in generating processes. The experimental results showed that the reduction of the mass flow rate of the two-phase flow reached a maximum of 24.5%. The mass fraction of gas of the two-phase flow was proportional to its superheat. When the mass transfer pressure difference was higher than 7 kPa or the mass fraction of gas was larger than 0.70%, the flow was choked, and the flow coefficient was reduced as the mass fraction of gas increased, reaching a minimum value of 0.64. A regression model for the flow coefficient of the two-phase LiBr/H2O solution was obtained.