Constructal thermodynamic optimization for a novel Kalina-organic Rankine combined cycle to utilize waste heat

Kalina cycle and organic Rankine cycle have different optimal heat source temperatures. To realize cascade utilization of low-temperature waste heat, a model of novel Kalina-organic Rankine combined cycle is established by using a dual-pressure Kalina cycle as top cycle and a dual-pressure organic Rankine cycle as bottom cycle, and constructal thermodynamic optimization is carried out by uniting constructal theory and finite-time thermodynamics. With the total turbine volume and total heat exchanger area being fixed, the optimal tube external diameters of the evaporators in the dual-pressure Kalina cycle and dual-pressure organic Rankine cycle are obtained by maximizing the net power output of the Kalina-organic Rankine combined cycle system. The results prove that the net power outputs of the Kalina-organic Rankine combined cycle system after four progressive optimizations are increased by 2.62%, 5.41%, 15.05% and 16.17%, respectively, compared to the initial one. In the quartic constructal thermodynamic optimization, the optimal tube external diameters of the high- and low-temperature evaporators in the DPKC are 0.024 m and 0.023 m, respectively, and the those in the DPORC are 0.020 m and 0.024 m, respectively. The results obtained will improve the performance of the KORCC and promote the efficient utilization of waste heat. (C) 2021 The Authors. Published by Elsevier Ltd.

Automated summary

Establishing a model of novel Kalina-organic Rankine combined cycle and conducting constructal thermodynamic optimization can improve the net power output of the system and promote the efficient utilization of waste heat.