Effects of water mal-distribution on thermostatic-expansion-valve stability and its controlled two-circuit evaporator performance

• Water flow was regulated with Circuit 2 water percentage (F2) from 36.9% to 9.1%.
• Effect of F2 variation on TEV stability and evaporator performance was studied.
• TEV was stable with F2 from 36.9% to 27.0%, and evaporator capacity dropped by 3.4%.
• TEV oscillated with F2 from 27.0% to 9.1%, and evaporator capacity dropped by 14.1%.
• Capacity drop was mainly due to Circuit 2 with smaller heat transfer coefficient.

Effects of water mal-distribution on thermostatic-expansion-valve (TEV) stability and its controlled two-circuit evaporator performance were investigated experimentally and numerically. 7 sets of water mal-distribution were obtained with Circuit 2 water percentage (F2) from 36.9% to 9.1%. Results showed that the TEV control-loop was stable with F2 from 36.9% to 27.0%, and the overall evaporator capacity decreased by 3.4%. However, hunting occurred with F2 from 27.0% to 9.1% due to the evaporator outlet superheat smaller than the TEV minimal stable signal (MSS), hence system parameters such as evaporator pressures and temperatures oscillated over time. Hunting introduced a sharp decrease in the refrigerant flowrate to the evaporator, thus the overall evaporator capacity decreased by 14.1%. With water mal-distribution rate increased, the decrease in overall evaporator capacity was mainly attributed to Circuit 2 with smaller overall heat transfer coefficient.