A comprehensive study on the heat transfer characteristics of windward bend lattice frame structure
Xiaohui Bai a,b, Cunliang Liu a,b,*, Changxian Zhang c, Xianlong Meng a,b, Jinbo Li a,b, Xianlong Zhang a,b
a. School of Power and Energy, Northwestern Polytechnical University, Xi'an, 710072, China
b. Shaanxi Key Laboratory of Thermal Sciences in Aero-engine System, Xi'an, 710072, China
c. Aero Engine Academy of China, Beijing, 101304, China
Abstract: The windward bend lattice frame structure (WB structure) is characterized by a high heat transfer coefficient and low friction factor. The WB structure can be applied for thermal protection system, protecting outer walls of afterburner and nozzles from being damaged by the heating load of hot gas, for air cooling system of the power battery module, dissipating the heat generated during its charging and discharging. In this paper, the heat transfer characteristics of the windward bend lattice frame structure have been comprehensively studied. A systematic 3D numerical simulation has been conducted to investigate the effects of the structural parameters of the WB structure, including the pitches in both flow direction and transverse direction, the diameter and the inclination angle of windward bend ligament, on its flow resistance and heat transfer enhancement, which has been evaluated by comparing its Nusselt number under an equal pumping power. Furthermore, the contribution of an important parameter, i.e., the ratio of the interstitial heat transfer rate to the end-wall heat transfer rate (RQ), to the overall heat transfer rate has been fully discussed. As a result, the case of 6 units in the longitudinal direction and 2.5 units in the transverse direction, i.e. (nx=6, nz=2.5) exhibits the best performance in the light of the value of the Nusselt number. Moreover, the structure with a ratio of RQ ranges in 4.5~5.0 achieves a better heat transfer performance. Finally, two color contour graphs showing an optimal range of Nusselt number coordinated by unit numbers (nx, nz) for pumping powers of 2500 and 3000 have been presented. The graphs correctly reflect the variation of Nusselt numbers of structures with different nx and nz, and the conclusions remain consistent with the discussion in sections 4.2 and 4.3, instructing the reasonable selection of structural parameters of a thermal protection system embedded with WB structure.
Keywords: Windward bend structure; Heat transfer characteristics; Flow resistance; Thermal protection; Nusselt number