Abstract
In this study, experimental research was conducted to investigate the performance of a small-scale Organic Rankine Cycle (ORC) system utilising low grade heat sources to generate electric power at different operating conditions. The experiment setup consisted of typical ORC system components, such as a turboexpander with high speed generator, finned-tube condenser, ORC pump and plate evaporator. R245fa was selected as a working fluid in the experimental system, considering its appropriate thermosphysical properties for the ORC system and low ozone depletion potential (ODP). At constant heat sink (ambient) parameters, extensive experiments were carried out to examine the effects of various important parameters including heat source temperature and working fluid pump speed etc. on system performance. Results showed that at a fixed working fluid speed, the thermal efficiency of the tested ORC system could be improved with an increased heat source temperature. On the other hand, at a constant heat source temperature, the working fluid pump speed could be optimised to maximise system thermal efficiency. Both the heat source temperature and ORC pump speed were found to be important parameters in determining system thermal efficiency and the component operations. The experimental outcomes can instruct future optimal system design and controls.
Highlights
The extensive consumption of fossil fuels worldwide has been contributing increasingly towards global warming, air pollution and the imminent energy crisis
After the test rig was setup, a series of experiments were conducted to evaluate the performance of the Organic Rankine Cycle (ORC) system with turboexpander at different heat source temperatures and running speeds of ORC pump
The thermal oil temperatures were controlled from 138 °C to 156 °C by modulating the CHP system power outputs while the ORC pump speeds were varied from 630 R245fa pump speed (RPM) to 779 RPM by changing the ORC pump motor frequencies
Summary
The extensive consumption of fossil fuels worldwide has been contributing increasingly towards global warming, air pollution and the imminent energy crisis. Since these ORC working fluids are all pure substances and operate under subcritical cycles, the temperature mismatch between the hot and cold side fluids in the high pressure side heat exchanger will increase the irreversible loss and affect system efficiency. For a given heat source temperature of 105 °C, experiments and simulation on an R245fa ORC with scroll expanders of different displacements were carried out with a maximum system thermal efficiency of 3.2% [16]. It is known from the literature that the heat source temperature is an important parameter in determining the appropriate selection of working fluids in an ORC system. This paper introduces a small-scale R245fa ORC system test rig in which a turboexpander and air cooled finned-tube condenser were utilised. The research outcomes can contribute significantly to the ORC fluid selections, system component designs and system controls
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