Düşük Sıcaklıkta Isı Kaynağı Kullanan Organik Rankine Çevrimi Uygulamaları İçin Hidrofloroolefinlerin Performans Değerlendirmesi
Performance Evaluation of the Hydrofluoroolefins for the Organic Rankine Cycle Applications Utilizing Low Temperature Heat Source

The organic Rankine cycle has the same working principle as the Rankine cycle. The difference is the utilization of organic substances as the working fluid instead of water. The organic Rankine cycle is a popular alternative since water has some limitations as a working fluid. As water hashigh boiling temperatures at high pressures, it requires high-temperature heat sources. Thus, an important amount of low-temperature energy sources, i.e. exhaust heat from industrial processes, hot fluids heated by solar energy, and geothermal hot water, etc., is wasted. The organic Rankine cycle has the potential for power generation from low- and medium-grade heat sources, i.e. waste heat and renewable energy sources, due to the relatively low boiling point of the organic substances. Although commonly used refrigerants are good alternatives for working fluid selection, F-gas regulation puts strict limitations on the global warming potential of the substances. As a result of the restrictions on the working fluids having high global working potential values, new alternatives are tried to be adapted without compensation for the cycle performance. Hydrofluoroolefin group working fluids are among the promising options since they are categorized as environmentally friendly. This study displays a performance assessment on the organic Rankine cycle employing hydrofluoroolefins such as R1234yf, R1234ze(E), and R1234ze(Z).

The commonly used working fluid, R134a is added to the performance assessments to create a comparative base although it has a high global working potential value. Net power output and thermal efficiency are analyzed based on the turbine inlet pressure for each working fluid. There are various working fluid investigations in the literature as the selection of the working fluids is of critical importance to the organic Rankine cycle performance. However, this investigation focuses on the Hydrofluoroolefin group working fluid alternatives only and compares candidates of this group according to their performance for the utilization of a low-temperature heat source of 360 K. Thermodynamic modeling equations based on the conservation of energy and mass are solved in MATLAB® and the thermodynamic properties of the working fluids are obtained from REFPROP version 10.0. There is a specific turbine inlet pressure yielding the maximum net power output for each working fluid. While evaluating within their own operating range, the highest net power output is calculated for R1234yf as 25.17 kW at the turbine inlet pressure of 13.5 bar. When comparing the thermal efficiencies of the working fluids at turbine inlet pressures giving the maximum net power outputs, the highest value is calculated as 5.38% at the turbine inlet pressure of 14 bar for R134a.