Triangular cross-section duct

Analysis The widths of the sides of the triangular cross section of the duct arc ti, /.7, and Ls, and the surface areas corresponding to them are Ai, A, and As, respectively. Since the duct is infinitely long, the fraction of radiation leaving any surface that escapes through the ends of the duct is negligible. Therefore, the infinitely long duct can be considered to be a three-surface enclosure, Af= 3. 

As a second example consider a long duct, triangular in cross section, with its three walls at dilferent temperatures. The walls need not be flat, but they must have no concavities i.e., each wall must see no portion of itself. Under these conditions the view factors are given by ... 

Schenkel [279] has also determined the fully developed friction factors for laminar flow in circular ducts having triangular corrugations with an angle of 60°, as shown in Fig. 5.59, inset c. For this type of duct, the cross section of the fluid flow area Ac and wetted perimeter P can be calculated as follows ... 

The cross-sectional area and perimeter of a flat duct with spanwise triangular corrugation can be found by ... 

Turbulent flow in the jackets with triangular helical ducts is simulated applied CFD software. The fully developed flow field and the distribution of the turbulence kinetic energy are obtained. When turbulent fluid flows in the jackets, the structure of secondary flow in the cross section is steady two vortices. The turbulent kinetic energy near the outer walls is larger than that near the inner wall. The fRe oc on the inner wall is almost symmetric about / = 0 and the variation of/ iocai on the outer walls with y is vastly different from that on the inner wall. In the study range, the mean coefficient of resistance on the outer walls is about 1.41 1.57 times of that on the inner wall. The effects of Re and k on the flow field, the local coefficient of resistance at the boundary walls and the mean coefficient of resistance are analyzed. With the increase o Re, the intensity of secondary flow and the turbulent kinetic energy are all enhanced and the /K iocai on the boundary walls is increased as well. However, the locai near the center of the inner wall decreases with increasing k. The mean coefficient of resistance can increase as Re or k increases. 

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