Abstract
An organic Rankine cycle (ORC) system with R123 working fluid has been utilised for generating electricity from low-temperature geothermal resources. The degree of superheated vapour warrants attention to be studied further. This is because the degree of superheated vapour is the last point to absorb heat energy from geothermal heat sources and influence the amount of expansion power produced by the expander. Therefore, achieving high ORC system efficiency requires a parameter of superheated vapour degree. This paper presents an experimental study on a binary cycle, applying R123 as the working fluid, to investigate the effect of variation in superheated vapour degree on the ORC efficiency. Geothermal heat sources were simulated with conduction oil as an external heat source to provide input heat to the ORC system. The temperature high inlet (TH in) evaporator was designed to remain at 120 °C during the experiment, while mass flow rate was adjusted to make superheated vapour variations, namely set at 278, 280, 282, 284, and 286 K. Furthermore, the effect was observed on heat transfer inlet, pinch, heat transfer coefficient, expander work output, isentropic efficiency, expander shaft power, power generation, thermal efficiency, and ORC efficiency. The experimental results showed that the mass flow rate nearly remained unchanged at different degrees of superheated vapour. The ranges of heat transfer inlet, pinch temperature, and heat transfer coefficient were 25.34–27.89 kJ/kg, 9.35–4.08 °C, 200.62–232.54 W/m2·K, respectively. In conclusion, ORC system efficiency can be triggered by various parameters, including the temperature on the exit side of the evaporator. The superheated vapour of R123 working fluid to higher temperatures has caused a decrease in ORC system efficiency due to the decrease in heat transfer inlets, although theoretically, the work total increased. Further investigation has found that the magnitude of the mass flow rate affects the behaviour of the components of the ORC system.
Highlights
Geothermal energy is a renewable and clean resource that can be utilized by humans around the world who are located in geologically profitable places
2013 [21] presented a complete off-design model of an organic Rankine cycle (ORC) for a low enthalpy heat source geothermal power plant, which consists of a performance diagram of each main component system, such as pump speed, turbine capacity, and air flow rate in the condenser
The utilization of heat energy sources from geothermal was simulated by building ORC systems with an applied binary cycle in laboratory scale to investigate the effect of superheated vapour changes on system performance
Summary
Geothermal energy is a renewable and clean resource that can be utilized by humans around the world who are located in geologically profitable places. 2013 [21] presented a complete off-design model of an ORC for a low enthalpy heat source geothermal power plant, which consists of a performance diagram of each main component system, such as pump speed, turbine capacity, and air flow rate in the condenser They revealed an influenced varying temperature of heat source between 130 and 180 ◦ C and differences in environment temperature at 0 to 30 ◦ C. The authors claimed that the same molecules were accounted for in a multi-objective optimization, reflecting both the total investment cost and net power output They concluded that the strength of this methodology is the possibility of selecting working fluid while optimizing ORC systems using single or multiple thermo-economic performance indicators. This paper provides a direction to compare binary cycle equipment in an ORC system with theoretical analysis, and supports the future ORC for industry 4.0
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