Experimental Study of the Bistable Phenomenon in Cross Flow Over Inline Tube Bundle With P/D = 1.4

Helical tube bundles are usually used for intermediate heat exchangers (IHXs) of High Temperature Gas-cooled Reactors (HTGRs) due to its compactness and low thermal stresses. To clarify the influences of smaller tube pitches, experiments of cross flow over tube bundle with pitch to diameter ratio (P/D) of 1.4 were carried out in a wind tunnel. The time-averaged pressure, pressure fluctuations, and velocity distributions were measured in the fully developed region of the tube bundle. The flow pattern in tube bundles will vary with the Reynolds number. The flow field tends to show an oblique flow phenomenon when Re = 10285, 18000, 44571 and 52500. The turbulent wakes over left four tube layers tend to flow left while the turbulent wakes over right four tube layers tends to flow right. When Re = 36000, the oblique flow phenomenon of the flow field diminished. When Re = 25285, two obvious quasi-stable flow patterns were observed according to the measured surface pressure and the velocity distributions measured by Particle Image Velocimetry (PIV).