Parametric optimization of organic Rankine cycle for middle-grade waste heat recovery by ant colony algorithm

The investigation was conducted on the matching criterion between working fluids and cycles under variable working conditions for the organic Rankine cycle (ORC). The ant colony algorithm was applied to examine the performance of the basic ORC (BORC) and the ORC with an internal heat exchanger (IHORC) under the different operating conditions (i.e., working fluid and heat source temperature). On the basis of the results calculated, a matching criterion between the working fluids having different critical temperatures and the heat source temperatures was achieved. The results show that the IHORC displays higher exergy efficiency than the BORC. The BORC system has a higher thermal efficiency and output net power when the heat source temperature reaches the upper limit of the region; when a working fluid with high critical temperature is adopted, the condenser runs at negative pressure, reducing the stability and economy of the system. At a given heat source temperature, the working fluid can be selected according to its optimum temperature region.