Development Of An Auto-tuning Area Ratio Ejector

Ejector can be driven by low-temperature heat sources such as solar energy,industry waste heat and automobile exhaust for refrigeration,which gives a new approach for the utilization of low grade heat energy and promotes the energy conservation and emission reduction in China.However,compared with traditional compression refrigeration,the main disadvantage of the ejector refrigeration system is that the system efficiency is not high,and it cannot run stably under variable conditions,which limits the development and application of ejector refrigeration.In this paper,an auto-tuning area ratio ejector is designed to solve the problem.It can maintain a high entrainment ratio under the varying primary flow pressures,which has important theoretical significance for the development and application value of ejector refrigeration system.Firstly,the relation between the optimal area ratio and primary flow pressure was studied.The variation of entrainment and secondary flow mass under different area ratios was studied numerically.The results showed that the entrainment ratio increased firstly and then decreased with the primary flow pressure under different area ratios,but the extreme points of the entrainment ratio were different and the entrainment ratios of different area ratios were different under the same pressure.Based on these extreme points,the relationship between the optimal area ratio and the primary flow pressure was obtained.The relationship between the entrainment ratio and the back pressure under different primary flow pressures was also studied.Compared with the variation curve of the entrainment ratio with the primary flow pressure,it was found the trend of the entrainment ratio with the primary flow pressure was affected by the back pressure.Secondly,this paper proposed and designed an auto-tuning area ratio ejector to achieve optimal ejector performance under varying conditions.The elastic bellows was added into the nozzle part of the ejector.The elastic bellow expanded and contracted with the variation of primary flow pressure,which pushed the spindle to change the blocking area of the nozzle for changing the area ratio of the ejector.Every primary flow pressure corresponded to an optimal area ratio.The shape of the spindle was influenced by both the bellows expansion and contraction and the optimal area ratio,which was not simply cone-shaped but approximately resembled a circular truncated cone with a raised surface.And the entrainment ratio of both auto-tuning area ratio ejector and the fixed area ratio ejector was compared.It was found that the work time of fixed area ratio ejector was only from 26.2%to 81.7%of a sine cycle and the ratio of maximal entrainment ratio of fixed ejector to the entrainment ratio of auto-tuning AR was only from 27.8%to 89.9%.The auto-tuning ejector can always worked at the whole cycle and had a higher entrainment ratio.Finally,the ejector test experimental platform was set up to study the performance of the auto-tuning ejector and prove the feasibility of the proposed auto-tuning ejector.In this paper,the entrainment ratio of the ejector with replaceable nozzles and spindles was measured by the experimental platform.The relationship between the entrainment ratio of the ejector and the primary flow pressure under different area ratios was also tested.The results showed that different primary flow pressures corresponded to the highest entrainment ratio of the optimal area ratio,which were consistent with the simulation results.In addition,the entrainment ratios between the simulation and experiment were compared by 20 different working conditions.The maximum error was 9.3%,and the simulation and experiment was mutually verified.In summary,the auto-tuning area ratio ejector can improve the stable and performance of the ejector effectively under varying conditions.It can be applied into an ejector refrigeration system driven by low-grade heat source and enhance the cooling performance of the system.