Numercial modeling for enhanced heat transfer efficiency of spiral coils with supercritical fluid flow under different operating conditions

Abstract

This research investigates the thermohydraulic performance and exergy destruction associated with the flow of supercritical carbon dioxide (sCO₂) within spirally coiled mini tubes. The study examines the impact of different cross-sectional geometries. The primary objective of the study is to examine the impact of critical parameters, including shape, hydraulic diameter, inlet temperature, mass flux, and operating pressure, on important variables such as friction factor, heat transfer coefficient, and exergy efficiency. The computational simulation employs the RNG k−ε model. The Coupled algorithm was utilized for the determination of velocity and pressure fields, utilizing second-order discretization for domain partitioning and first-order discretization for other terms. The carbon dioxide (CO₂) was conceptualized as a compressible gas with complex thermophysical attributes that are contingent upon variations in temperature and pressure. The thermophysical properties of carbon dioxide are evaluated within a defined range of operating conditions (298. 15 K < T < 455 K and 8 MPa < p < 10 MPa). The observed trends in HTC (heat transfer coefficient) demonstrate a correlation with specific heat, showing a peak at lower temperatures under increased operating pressures. Elevated operational pressure results in a reduction of the maximum HTC. The augmentation of mass flux results in an increase in heat transfer coefficient, thereby indicating an improvement in system efficiency. An augmentation in hydraulic diameter yields diminished heat transfer coefficients, mitigated pressure loss, and heightened exergy destruction.