| In this thesis, a refrigeration scroll compressor as expander for power generation applications with Rankine cycle is analyzed through a comprehensive mathematical model. The methodology adopted has three phases. In the first phase, a scroll compressor is selected from a refrigeration manufacturer catalog namely Copeland ZF06K4E. Based on catalog data and thermodynamic model the specific parameters of the compressor such as built-in volume ratio and leakage coefficient are determined through mathematical regression as 7.3 and 1.36x10 -6, respectively. In the second phase, the parameters and the efficiency of the Rankine cycle are determined, which use the selected scroll machine in reverse, namely as expander, without any geometrical modifications and keeping the range of temperatures and pressures constant as the same as that characterizing the compressor operation. An expander model is used to predict the efficiency of the prime mover and of the Rankine cycle for the working fluids such as R404a, Toulene, R123, R141b, R134a and NH3. The highest efficiency is obtained with R404a as 18% by applying supercritical conditions for the working fluid and it is observed that the expander does not operate optimally when converted from a compressor without any modifications. In the third phase, the geometry of the expander is modified with respect to rolling angle in order to obtain the appropriate built-in volume ratio which assures better efficiency of the Rankine heat engine. R404a clearly gave the best results for the modified geometry and the energy efficiency is increased to 25% from 19% while the exergy efficiency is increased to 61% from 50%. The results showed that it is possible to improve the efficiency of the cycle by adjusting the scroll geometry for the fluids used. |
