Numerical Study Of Piston Expander Based On Water Spray Heat Transfer

Improving the utilization ratio of renewable energy and building a green and low-carbon energy system are important measures for my country’s energy transformation.However,the intermittency and volatility of renewable energy restrict its development.Compressed air energy storage(CAES)can absorb and release energy in a timely manner,which has become a hot research topic.As a key component of compressed air energy storage,the performance of the expander is crucial to the system performance.The spray heat exchange can greatly improve the heat exchange efficiency of the expander,make the working process of the expander tend to be an isothermal process,and then improve the energy utilization efficiency.However,the coupling mechanism between the spray heat transfer and the performance of the expander is not clear at present,and it is difficult to obtain the variation law of the parameters in the expander cylinder by traditional analysis methods.Therefore,based on the CFD dynamic grid technology,this paper studies the internal characteristics of the piston expander,and then studies the expansion process of water spray heat transfer.The specific research contents of this paper are as follows:(1)First,using the p-V diagram,the advantages of isothermal expansion work over adiabatic expansion work are shown from the perspective of energy,indicating that the output work of isothermal expansion is greater than that of adiabatic expansion.From this,a piston expander based on water spray heat exchange is drawn.(2)Secondly,the unsteady simulation of the double-inlet and double-exhaust piston expander is carried out by using the CDF dynamic mesh technology.The simulation shows that the temperature in the expander cylinder first rises rapidly and then continues to drop;when the expansion process begins,the internal pressure of the expander is still relatively large,and the residual pressure energy can be used for secondary use;the expansion process has eddy currents,resulting in pressure loss.The simulation study obtained the relationship curves of intake air temperature,intake pressure,output power and efficiency of the expander.An experimental platform for a piston expander was built,and the results of the two were compared under multiple operating conditions,and the error was less than 5.5%,which verifies the correctness of the simulation.(3)Then,a water spray system was established using the DPM model with Fluent software.The compressed air-water mist coupling simulation shows that spraying water mist into the cylinder increases the temperature of the compressed air expansion and work process.Comparing the p-V diagrams of the water spray heat transfer expansion and adiabatic expansion,it is concluded that the water spray heat transfer model generates more power during the expansion process and consumes less power during the compression process.The output work based on the water spray heat transfer model is greater than that of the adiabatic model.(4)Finally,the relationship between the spray pressure,spray temperature,water mist particle diameter and the output performance of the piston expander is obtained through the orthogonal test.The SPSS range analysis method is used to calculate and show that: the influence degree on the system output power from large to small is spray pressure,spray temperature,water mist particle diameter;the influence degree on system efficiency from large to small is spray temperature,spray pressure,water Fog particle diameter.The optimal spray parameter combination was determined as spray temperature: 373 K,spray pressure: 0.8MPa,and water mist particle diameter: 10μm.