Yeni nesil bir soğutucu akışkanla çalışan buhar sıkıştırmalı soğutma çevriminde genleştirici olarak ejektör kullanımının sayısal ve deneysel olarak incelenmesi

The subject of this thesis is related to ejector expansion refrigeration cycle (EERC). EERC is the modification of the conventional vapor-compression refrigeration cycle (VCRC) with the use of the ejector instead of the expansion valve of the classical cycle and implementation of a liquid-vapor separator to increase cycle performance. The main objective of the thesis is to investigate the performance of the EERC numerically and experimentally. Main working fluids of this thesis are R134a and R1234yf. It is experimentally and numerically shown in the literature that performance of R1234yf is lower than R134a in the conventional cycle. Hence, R1234yf which is an appropriate refrigerant alternative according to F-gas Regulation needs performance improvement in the classical cycle. Firstly, zero-dimensional (0D) comprehensive thermodynamic models are established for constant area and constant pressure mixing ejector theories. Moreover, one-dimensional (1D) model of the motive nozzle is constructed to obtain the pressure and velocity distributions throughout the nozzle. Hence, semi-1D model of the EERC is established after combining 0D thermodynamic models and 1D model of the motive nozzle. Solution algorithm of the mathematical models are built in MATLAB® and properties of the refrigerants are obtained using REFPROP. EERC/VCRC test rig is established to conduct the experimental performance evaluations and to experimentally validate the numerical results obtained from the semi-1D model. Maximum differences between the performance improvement percentages of the semi-1D model and the thermodynamic model are calculated as 14 percent and 20 percent for R134a and R1234yf, respectively. Therefore, it is shown that semi-1D modelling approach is required for more realistic performance evaluations. Results of the experiments declare that sensitivity of the ejector design according to operating conditions and liquid-vapor separator efficiency is critical for the cycle performance. The comparison between the experimental data and numerical results obtained from the semi-1D model of the EERC yields a good agreement in terms of the cycle coefficient of performance (COP), secondary fluid mass flow rate, and entrainment ratio.