Effect of transverse triangular wedges on the behavior of the ash deposition and heat transfer of an inline tube bundle

Abstract

The experiment was carried out on an inline 6 rows – 3 columns tube bundle. Free air velocity and coal fly ash feed rate were kept constant at 2.1 ms−1 and 3.65×10−4kgs−1, respectively. The wedges have isosceles triangle cross section and have the same height. The investigation is carried out for four ratios of base to height or aspect ratio: 0.275, 0.550, 0.758 and 1. The wedges are installed transversely across the bundle cross section and parallel to the tubes at the tube bundle inlet, between the second row and the third row, between the fourth row and the fifth row, or at the tube bundle outlet. It is found that flow patterns of the single-phase air flow (SPF) over the tube bundle and the deposition patterns around the tube are related. The deposition coverage angles at the tube upstream start from the points having zero wall flow shear stress and where the flow is toward the surface and having zero wall flow shear stress and where the flow is outward from the surface for the first-row tube and the rest, respectively. For both cases, the ash continues to deposit on the surface to the point having maximum wall shear stress. The average rate of the increase in the shear stress over the coverage angle is an important parameter for predicting the deposition. The deposition decreases as the average rate over the upstream tube surface decreases. It decreases significantly at the adjacent tubes upstream and downstream of the wedges. Based on the deposition and the heat transfer, the optimum wedge position is in the vicinity of the middle length of the tube bundle. In addition, the deposition and the heat transfer decreases and increases with the wedge aspect ratio. In terms of the enhancement of the heat transfer for the same air pumping power, a wedge with an aspect ratio of 0.550 or 0.758 should be installed at the tube bundle inlet.