Hydrodynamics Performances in Cracking Furnace Tube with Twisted Slice: Experiments and Simulations

Employing air as fluid media, hydrodynamics performances in cracking furnace tube with twisted slice were studied, then the flow field (velocity, pressure drop, and resistance loss) of heat transfer enhancement was simulated based on CFX, at last, the effect of twist ratio on flow field was analyzed. The experimental results showed that boundary layer in the tube became thin compared with circular tube, which leaded to the increase of heat transfer coefficient. So heat transfer was enhanced. Axial velocity distribution in central area of the tube was smoother than that of circular tube, while velocity grad in near wall area was greater. Pressure drop increased in the tube, whereas pressure distribution was even along tube axis, in agreement with that in circular tube. The simulated results showed that tangential velocity increased rapidly while fluid flowed into the twisted slice, and then decreased gradually along tube axis and augmented gradually along tube diameter while fluid flowed out from the twisted slice. In the direction of the tube diameter, there existed a point where axial velocity was equal to the average axial velocity of the whole cross section. The whole pressure drop in the tube and local pressure drop in twisted slice section both rose with the increase of inlet velocity, and were independent of the tube diameter. Average resistance coefficient in the tube had a linear relationship with Reynolds number (Re), which reduced with the increase of Re. Local resistance loss in twisted slice section enhanced with the increase of Re and the decrease of the tube diameter. Twist ratio had an influence on the flow field in the tube, whose optimal numeric area was 2.4~2.6 in the studies.