The supercritical carbon dioxide (SCO2) Brayton cycle has a wide application prospect in field of waste-heat utilization of the marine gas turbine due to its characteristics of high efficiency, compact, safety and good economy. As the key equipment of the system, the precooler adopted a compact, efficient Printed Circuit Heat Exchanger (PCHE) with good pressure performance, whose heat transfer performance directly affects the thermal cycling efficiency of the system. However, under the influence of the marine environment and drastic changes in thermal physical properties, the SCO2 flowing in the PCHE is extremely complex and its heat transfer mechanisms are still insufficient to understand. Therefore, the convective heat transfer characteristics of SCO2 in PCHE under static and ocean conditions were studied in this paper. Firstly, a numerical model is established to explore the flow and heat transfer behavior of SCO2, and the validity of the model is verified according to the existing experimental results. Then, the unconventional heat transfer phenomenon of SCO2 flowing in the PCHE channel with airfoil fin is discussed under static condition, when the ranges of the temperature and mass flow at the cold side inlet are 278.15-298.15K and 2.15-52.02g/s, respectively, and the range of mass flow at the hot side is 0.34 to 2.54g/s. Finally, the effects of ocean oscillation on heat transfer performance and frictional pressure drop of SCO2 were investigated under different mass flow rate (0.34, 2.54g/s) of hot side, placement position (7-13m), rolling period (5-10s) and rolling amplitude (15°-25°). It can be found that under static&nbsp;condition, the secondary flow generated by the buoyancy effect obviously increases turbulent dissipation on the upper surface of the channel under the low mass flow at hot side, resulting in significant heat transfer difference between the upper and lower walls. However, buoyancy effect has little effect on heat transfer performance at high mass flow rate of hot side. Meanwhile, under ocean condition, the instantaneous heat transfer coefficient and pressure drop fluctuates periodically. The oscillation amplitude of instantaneous pressure drop and heat transfer coefficient increase with the decreasing of rolling period and the increasing of layout position and rolling range. The time-average frictional pressure drop on the cold side always increases, but the increment is small, with maximum increment of 4.2%. The rolling motion has drag reduction effect on the hot side, and the time-average pressure drop at the hot side can be reduced by 20.3% at the high mass flow rate. The time-average heat transfer performance of rolling motion tends to be strengthened, and the strengthening effect is more significant at low mass flow rate. Compared with the static state, the time-average heat transfer coefficient can be increased by up to 4.0%. The research results have important guiding significance for the design of Marine waste heat recovery system.KEYWORDS: Brayton cycle, Supercritical CO2, Ocean oscillation, Printed Circuit Heat Exchanger, Convection heat transfer.

Study on Convective Heat Transfer Characteristics of Supercritical CO2 in Printed Circuit Heat Exchanger Under Ocean Condition

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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