Thermodynamic modelling and experimental validation of a laboratory scale ORC scroll expander

Abstract

The detailed geometrical and thermodynamic modelling and experimental vali dation of scroll expander is presented in this thesis. Firstly, a fully mathematical model is developed for moving and fixed scrolls inside the scroll expander, benefiting from an arc of spiral shape. Scroll expander contains two scroll structures which are interlaced so that one of the scrolls can move within the boundary of the other scroll. Once the scroll spirals are defined mathematically, the chamber volumes between moving and fixed scrolls are calculated. However, the scroll wall thickness is assumed to be constant throughout the study. Besides, a thermodynamic modelling is conducted in the chambers by means of first law of thermodynamic and ideal gas equations. The working fluid is assumed to be an ideal gas and all of the leakages and heat transfer between chambers or between scroll expander and outside are neglected. The dynamic process of scroll expander comprises of three phases which are charging, expansion and exhaust. Thus, temperature, pressure and volume variation charts for every chamber are given. The motion analysis of moving scroll is covered and torque calculation which results in the rotation speed of scroll expander is given. The mathematical model and simulation process are implemented in Matlab. Then, the simulated model is com pared and validated by a reference model. In the experiment chapter, the test rig is introduced in detail at first and the scroll expander is run with compressed air. Test results are presented with two different supply pressure values and also validated by the simulation results with compressed air. Finally, a simulation study of scroll expander running with HFC-134a is also performed and the results are presented in chapter 5.