An experimental study on operation characteristics of the organic Rankine cycle system under the single-and multiple-variables regulation

This work aims to investigate the operation characteristics of an organic Rankine cycle (ORC) system under the variable mass flow rate of the working fluid ((m) over bar (wf)), such as the flow excursion in the field of direct vapor generation (DVG) systems. Besides, the mass flow rate of cooling source ((m) over bar (cs)) was verified as an effective manipulated variable to respond the variation of (m) over bar (wf), which was an easily available freedom in the ORC system. The operation characteristic was tested respectively for (m) over bar (wf) and (m) over bar (cs), where the change form of the single variable was rectangular-wave steps with different amplitudes. To verify the effectiveness of regulating mcs, the operation characteristics under the changes of multiple variables including the (m) over bar (wf) and (m) over bar (cs) were tested. The results indicate that the (m) over bar (wf) dominates the variation of operation parameters of the ORC apparently, especially the evaporation pressure. Specifically, the evaporation pressure increases about 26.10 kPa as the (m) over bar (wf) increases about 0.01 kg/s. The mcs also affects the operation parameters, which shows the opposite trend in evaporation pressure and condensing pressure compared with the increase of (m) over bar (wf). The results show that when the (m) over bar (wf) increases, the increase of pressure can be reduced and the thermal efficiency can be improved by regulating the (m) over bar (cs) in the same direction simultaneously. The increase of the theoretical thermal efficiency of the system is about 11.21% when only the (m) over bar (wf) is inclined 0.01 kg/s, while it is 18.00% when the (m) over bar (cs) is inclined 0.12 kg/s at the same time. The experimental findings enable to give a reference on designing control strategies for the DVG ORC systems.