Yuanzineng kexue jishu (Sep 2023)
Experimental Study on Dynamic Characteristics of SCO2 Cycle Cold-end Printed Circuit Heat Exchanger
Abstract
In the SCO2 Brayton cycle, the cold-end SCO2 working fluid is in a near-critical state, and the physical properties change drastically, which directly affects the efficiency of the whole cycle and the safety of system operation, so it is of great significance to study the dynamic characteristics and flow and heat transfer performance changes of the SCO2 Brayton cycle cold-end heat exchanger under different disturbances for the operation, control and performance of the SCO2 Brayton cycle system. At present, SCO2 circulating cold-end heat exchangers mostly use printed circuit heat exchangers, and the researches on them are mainly based on numerical simulations. There are few experimental studies which mainly focus on the flow and heat transfer performance of cold-end heat exchangers in steady state, and there are less experimental studies on their dynamic characteristics under different disturbances. Therefore, the dynamic characteristics of the 100 kW class SCO2 printed circuit heat exchanger for the cold-end of SCO2 Brayton cycle were experimentally studied. Through this experiment, the dynamic response characteristics of the cold-end heat exchanger under different parameter disturbances such as cooling water mass flow, SCO2 mass flow rate and SCO2 heating power and the influence of different disturbances on heat transfer coefficient, heat exchanger efficiency and working fluid pressure drop of the heat exchanger were obtained. It is found that the time for the SCO2 outlet temperature and pressure to reach steady state again increases with the disturbance amplitude. In the cooling water side mass flow disturbance experiment, the SCO2 outlet temperature and pressure reach steady state after 150-200 s of the disturbance. In the SCO2 mass flow disturbance experiment, the SCO2 outlet temperature and pressure reach steady state again after 100-150 s of disturbance. In the heater power disturbance experiment, the minimum time for the SCO2 outlet temperature and pressure to re-reach the steady state is 200-220 s and the longest is 400-420 s. It’s also found that the disturbance of water mass flow and SCO2 mass flow has the opposite effect on the outlet parameters of SCO2, the change of pressure on the SCO2 side and the change of outlet temperature are positively correlated. The increase of water mass flow and SCO2 mass flow can increase the overall heat transfer coefficient of the heat exchanger, and the increase of SCO2 mass flow has a more obvious effect on the heat transfer coefficient, but it will also cause the increase of working fluid pressure loss. The increase of heating power makes the average temperature of SCO2 side increase which makes the heat transfer coefficient decrease.
