Abstract
The non-uniformity of the secondary flow distribution in the twisted oval tube has impeded its further improvement of the heat transfer performance. A novel twisted tube (NTT) improves the distribution of the secondary flow and enlarges the effect of the secondary flow on the main flow, intensifying the radial mixing and equalizing the temperature distribution of the fluid, which strengthens the convective heat delivery in the near wall region and the core zone comprehensively. Heat transfer characteristics and entransy evaluation of water and engine oil in the NTT are investigated in the low Reynolds number (Re) region. The heat delivery performance of the NTT improves with the reduction of the distance ratio (DR) and the twist pitch ratio (PR), and also raises with the increase of Re. The friction factor of the NTT increases with the reduction of DR and PR, and decreases with the rise of Re. Compared with the twisted oval tube, the NTT could elevate the Nusselt number and enlarge the friction factor by 1.49-1.56 times and 1.32-1.41 times, respectively. Compared with the plain tube, the NTT could improve the Nusselt number and increase the friction factor by 2.42-2.76 times and 1.48-1.56 times, respectively. The equivalent thermal resistance of the NTT decreases with the reduction of DR and PR and reduces with the increase of Re. The Case 4 with the minimum DR and the smallest PR shows the supreme heat transfer performance and the lowest equivalent thermal resistance. The NTT could reduce the entransy dissipation remarkably, compared with the plain tube, the NTT could decrease the equivalent thermal resistance by up to 58% for water under the condition of constant wall temperature and could reduce the equivalent thermal resistance by as much as 53% for engine oil under the condition of given heat flux on the tube wall.
NSTL
Elsevier