The Research On Structure Optimization Of Roots-type Steam Engine

In industrial production,with a large amount of waste,low grade steam is a low pressure,low temperature,unstable airflow.To recovery low steam heat economically and effectively,the research group developed a roots-steam engine to recycle low grade heat to produce power,which specializes in recovering stream with pressure less than 0.8MPa and the temperature lower than 230?.In order to further explore the characteristics of roots power machine and improve adaptability of it to low grade steam,the paper researched three rotor with different structure by theoretical derivation,numerical simulation and experimental analysis.These three structure types are two straight-leaves,three straight-leaves and three twisted-leaves.1.The paper elaborated the principle and composition of the power generation device and established the mathematical model of roots type steam engine.The stability of three structures was analyzed from the meshing coincidence degree.The arc involute treated as the end face of the three rotors.And the derivation of the equation of the end face of the three leaf rotor was finished based on plane meshing theory.Based on the spatial meshing theory,the derivation of the helical surface equation of the twisted blade rotor was carried out.Further more,the theoretical flow rate,leakage model and the discharge flow pulsation of the three kinds of structures are deduced.2.The three-dimensional model of machine parts was established by Solidworks,and the flow field model was formed by boolean operation,which the flow field domain model is introduced into Ansysworkbench for mesh generation.According to the operation principle of generating set,this paper analyzed the rated power and the physical properties of the low grade steam refrigerant,considered the interaction of refrigerant temperature and engine cooling system.And the boundary conditions and initial conditions are set up for the numerical analysis model.3.The moving grid method was used to simulate internal flow of rotor engine.The UDF function is programmed to control the rotor speed,and the meshing motion of the rotor is simulated.The unsteady numerical calculation was used to obtain the pressure and velocity of the rotor at different positions.By comparing the solution results of three kinds of rotors,the running stability of the three twisted-leaves is higher than that of the three straight-leaves,and the running stability of the three straight-leaves is higher than that of the two straight-leaves.And the sensitivity of the three kinds of rotor to the fluctuation of steam source is increased in turn,which the three twisted-leaves rotor is more able to adapt to the fluctuation characteristics of low grade steam.4.A test platform is established for three straight-blade power generation device,which the engine driven by compressed air.By comparing the speed curve of three-leaves engine with the test data of two-leaves engine,the results show that three straight-leaves engine can work more stably than two straight-leaves in wave source power.