Flow structure with mixed turbulent flow of supercritical CO2 heated in helically coiled tube. (5th May 2021)

• Record Type: Journal Article
• Authors: Liu, Xinxin; Xu, Xiaoxiao; Jiao, Youzhou; He, Chao; Liu, Liang; Dang, Chaobin
• Is Part Of: Applied thermal engineering. Volume 189(2021)
• Publication Date: 2021-05-05
• Subjects: Supercritical CO2 -- Helically coiled tube -- Heat transfer -- Buoyancy force -- Centrifugal force; Heat engineering -- Periodicals; Heating -- Equipment and supplies -- Periodicals; Periodicals; 621.40205
• DOI: 10.1016/j.applthermaleng.2021.116684
• Languages: English
• ISSNs: 1359-4311

Abstract

Highlights: Relationship of flow direction, buoyancy force and centrifugal force in HC-tube is theoretical analyzed. Flow structure of SCO2 in horizontal and vertical HC-tube are numerically analyzed. Flow dynamic discrepancies are compared between HC-tube and straight tube. Abstract: The mixed turbulent convection heat-transfer characteristics of supercritical CO2 (S-CO2 ) heated in both vertical and horizontal oriented helically coiled tube (HC-tube) is investigated via experimental and numerical methods. Firstly, the coupled equations of flow direction, buoyancy force and centrifugal force in HC-tube are established. Then, the influence of the three factors on axial and radial heat transfer coefficient (HTC) performance are discussed. In vertical oriented HC-tube, the HTC first increases progressively and then drop swiftly, presenting a peak value at the pseudo-critical point. But, in horizontal oriented HC-tube, due to buoyancy force effects, the HTC oscillates dramatically which indicates the poor heat-transfer stability. Meanwhile, the numerical simulation, corresponding to the experiment condition, is carried out. To capture the flow structures, 6 characteristic lines on each cross-section are selected and the corresponding velocity and the turbulent kinetic energy distributions are comparative analyzed. The results showed that the coupling effects of centrifugal force and buoyancy force mainly affect heat-transfer on the inside of a cross-section. In addition, different from the M-type velocity in straight tube, the salient point of M-type velocity in HC-tube always locate at the outer side of the buffer-layer and the heat-transfer is slightly affected. The local heat-transfer deterioration mainly occurs at inside of a cross section where the velocity is obviously suppressed.