Research On Thermodynamic Characteristics And Experimental Verification Of ORC Scroll Expander

The Organic Rankine Cycle(ORC)system,as a key technology for the conversion and utilisation of low-grade thermal energy,is mostly used in low-temperature waste heat power generation technology to achieve the efficient utilisation of resources,while the scroll expander,as the core component of the ORC system,can use the work gas to do work to drive the orbiting scroll to do the rotation of flat motion to achieve the conversion of thermal energy into mechanical energy.The eccentric main shaft is connected to the generator by an external belt drive,which drives the generator to generate electricity and convert mechanical energy into electrical energy.In this paper,a scroll expander in an ORC low temperature waste heat power generation system is used as the object of study,the geometric and thermodynamic model of which are established,and its working process is investigated taking into account the actual operating conditions and the variation of the thermal and physical parameters of the working fluid.Finally,the test is verified by means of a built test platform for an organic Rankine cycle low temperature waste heat power generation system.The main research elements are as follows:(1)Firstly,the geometric theory of the scroll profile based on circular involute and the plane curve meshing theory are briefly introduced,the double arc correction adopted for the scroll head part of the research prototype is described,the parametric equations of the profile of the research scroll expander are given,and based on the geometric parameters of the test prototype,the geometric model of the scroll tooth of the expander is constructed after the tooth head correction,and the working chamber of the expander is divided,the change law of the complete working chamber volume and volume change rate of the expander are calculated using MATLAB software and the expansion ratio is briefly described.(2)Based on the geometric model of the scroll teeth of the expander after the head correction,the actual operating conditions of the scroll expander and the thermal property parameters of the working fluid R245 fa are considered,and its thermodynamic model is established based on the first law of thermodynamics,the law of conservation of energy and mass and the actual gas equation of state of the working fluid,the heat transfer area of each working chamber,the length of the leakage line and the leakage mass flow of the working fluid are quantitatively analyzed;the output characteristics,volumetric efficiency and isentropic efficiency of the scroll expander are elaborated,and the expressions for the output power of the scroll expander are derived from the force analysis of the dynamic scroll,and the expressions for the volumetric efficiency and isentropic efficiency of the scroll expander are given.(3)The thermodynamic model is solved by Euler’s method.And the thermal parameters of the work gas R245 fa are called up by PEFPROP software to obtain the pressure,temperature and mass of the work gas in the working chamber of the scroll expander with respect to the spindle angle in the case of integrated leakage and heat transfer.The law of pressure,temperature and mass variation with spindle angle in the adiabatic expansion process are compared and analyzed separately.As the internal leakage between the working chambers of the scroll expander is inevitable and seriously affects its output characteristics,the leakage volume of the working chambers of the scroll expander is simulated and analyzed;then the leakage mass flow is simulated by changing three working conditions inlet pressure,inlet temperature and rotational speed,in order to quantitatively analysis the influence of different working conditions on the leakage characteristics of the scroll expander.(4)The test platform of the Organic Rankine Cycle low-temperature waste heat and power generation system was set up to measure the voltage,current and volumetric of the scroll expander,and then calculate the volumetric efficiency and mechanical efficiency of the scroll expander;the measured output power values of the scroll expander at different inlet pressures and temperatures were compared with the theoretical values to verify the accuracy of the established thermodynamic model;the effect on the output power of the scroll expander and the net output power of the system was investigated by varying the heat and cold source temperatures of the ORC system under different external operating conditions.