Abstract. The object of the study are substances that are used as a working fluid in systems operating on the basis of an organic Rankine cycle. The purpose of research is to find substances with the best thermodynamic, thermal and environmental properties. Research conducted on the basis of the analysis of thermodynamic and thermal properties of substances from the base "REFPROP" and with the help of numerical simulation of combined-cycle plant utilization triple cycle, where the lower cycle is an organic Rankine cycle. Base "REFPROP" describes and allows to calculate the thermodynamic and thermophysical parameters of most of the main substances used in production processes. On the basis of scientific publications on the use of working fluids in an organic Rankine cycle analysis were selected ozone-friendly lowboiling substances: ammonia, butane, pentane and Freon: R134a, R152a, R236fa and R245fa. For these substances have been identified and tabulated molecular weight, temperature of the triple point, boiling point, at atmospheric pressure, the parameters of the critical point, the value of the derivative of the temperature on the entropy of the saturated vapor line and the potential ozone depletion and global warming. It was also identified and tabulated thermodynamic and thermophysical parameters of the steam and liquid substances in a state of saturation at a temperature of 15 qC. This temperature is adopted as the minimum temperature of heat removal in the Rankine cycle when working on the water. Studies have shown that the best thermodynamic, thermal and environmental properties of the considered substances are pentane, butane and R245fa. For a more thorough analysis based on a gas turbine plant NK-36ST it has developed a mathematical model of combined cycle gas turbine (CCGT) triple cycle, where the lower cycle is an organic Rankine cycle, and is used as the air cooler condenser. Air condenser allows stating material at a temperature below 0 qC. Calculation of the parameters of all substances in the model are based on a base "REFPROP". Numerical investigations on this model showed that the highest net efficiency will be at work on pentane. Butane and R245fa have the same net efficiency, for 0.8% lower than pentane. Ammonia has a net efficiency of 2.5% is lower than pentane. CCP net efficiency strongly depends on the condensation temperature of the substance, as for pentane at lower temperature of condensation at 10 °C it is increased by 1%.a Corresponding
Abstract. Relevance of the work is due to the need to create a mathematical model of thermal processes in the air condenser section (AC). The purpose of the work is to the development and testing a mathematical model applied to the section AC condensation of low-boiling substances used as working materials in the organic Rankine cycle. A mathematical model was developed, and allows complex investigations that involve a change in the type of working material and geometric and operational parameters section AC. For the calculation of thermal parameters using a database of properties of substances «REFPROP». On the basis of the mathematical model in Excel spreadsheet package developed a program for calculating the parameters and performance measures of AC. The numerical model studies have shown that the characteristics and performance indicators AC highly dependent on the type of substance. When changing external air temperature from -40 to 40 °С heat flux in the AC falls to 175 ÷ 185 W/m 2 . The model allows to determine the number of sections and investments in the condenser of the known heat flow. Heat flow must be selected based on outdoor temperature taking into account the climatic conditions of the AC.
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