Organic Rankine cycle(ORC) power systems can convert low-temperature(150 ℃) thermal energy into mechanical energy to generate electricity. To improve the performance of small-scale ORC power systems

an ORC test-rig was built

which has a scroll expander directly connected to the generator. With a 24 kW variable-temperature heat source and the work fluid R245fa

the effects of the variations of load resistance(50～200 Ω) and the heat source temperatures(75～95 ℃) on the performance of the ORC test-rig were explored.The results indicate that

both the output shaft work and the thermal efficiency initially increase and then decrease with rising the load resistance. An optimal load resistance exists to maximize either the output shaft work or thermal efficiency

and this value varies with the heat source temperature. When the heat source temperature is 95 ℃

the output shaft work and thermal efficiency both reach the maximum at 100 Ω load resistance value

which is 722 W and 2.30%. When the heat source temperature is 75 ℃

the output shaft work reaches the maximum at 200 Ω load resistance

which is 532 W

but the thermal efficiency reaches the maximum at 150 Ωload resistance

which is 1.7%. The variation of the resistive load or the heat source temperature can change the scroll expander rotation speed and thus affect system flow rate. Therefore

the simultaneous changes of the resistance load and the heat source temperature have a synergistic effect on the system performance. The results highlight the importance of matching the resistance load and the heat source temperature. The experimental data also provide a direction for optimizing the ORC power systems.