THE CO2 TRANSCRITICAL POWER CYCLE FOR LOW GRADE HEAT RECOVERY-DISCUSSION ON TEMPERATURE PROFILES IN SYSTEM HEAT EXCHANGERS

Carbon dioxide transcritical power cycle has many advantages in low-grade heat source recovery compared to conventional systems with other working fluids. This is mainly due to the supercritical CO2's temperature profile can match the heat source temperature profile better than other pure working fluids and its heat transfer performance is better than the fluid mixtures, which enables a better cycle efficiency. Moreover, the specific heat of supercritical CO2 will have sharp variations in the region close to its critical point, which will create a concave shape temperature profile in the heat exchanger that used for recovering heat from low-grade heat sources. This brings more advantage to carbon dioxide transcritical power systems in low-grade heat recovery. This study discusses the advantage of carbon dioxide power system in low-grade heat source recovery by taking this effect into account. A basic carbon dioxide transcritical power system with an Internal Heat Exchanger (IHX)(1) is employed for the analysis and the system performance is also compared with a basic Organic Rankin Cycle (ORC). Software Engineering Equation Solver(2) (EES) and Refprop 7.0(3) are used for the cycle efficiency and working fluid properties calculations.