Heat transfer improvement by an Al2O3-water nanofluid coolant in printed-circuit heat exchangers of supercritical CO2 Brayton cycle

The supercritical CO2 (SCO2) Brayton cycle is a technology proposed for the next generation power cycles, since it can attain high cycle efficiency. To this end, high cooling demands should be applied in these cycles. A modern technique to enhance heat transfer is the use of a mixture of nanoparticles with conventional base fluids in heat exchangers' channels. An analytical study of the thermal and hydraulic characteristics of a printed-circuit heat exchanger, employed as a precooler for SCO2 Brayton cycles by using an Al2O3-water nanofluid, is presented here. The precooler has a key role in overall performance and, thus, the optimal working fluid is of major importance. A segmental analysis pertaining to the heat exchanger takes place to evaluate the influence of nanofluid usage on the heat transfer coefficient, the exchanger's length and its pressure drop. The maximum nanoparticle volume fraction of 5%, which was used in this investigation, resulted in an improvement of 10% for the heat transfer coefficient as compared with the pure water working fluid. This improvement led to a 0.9% reduction of the total heat exchanger length, while a decrease of the pressure drop up to 14% was accomplished. These analytical calculations are anticipated to be very valuable given the growing progress in the field of nanofluids.