Transient Cavitation Behavior in an Undulating Pipe under Different Water Temperatures

A visualized undulating pipe experimental rig is designed and used to investigate the effect of water temperature variation on multipoint transient cavitation flow induced by valve rapid closure. The specific effects of temperature on the lasting duration, transient pressure, and cavitation evolution at initial flow velocities of 0.75 m/s (Reynolds numbers (Re) = 37373, 46833, 57006, and 67795), 1.135 m/s (Re = 56558, 70874, 86269, and 102596), and 1.71 m/s (Re = 85176, 106749, 129913, and 154447) are studied, respectively. The experimental results show that as the water temperature increases, the vapor pressure gradually increases, which is easier to cause cavitation. Meanwhile, the cavitation lasting duration becomes longer, and the cavitation region extends further. For an initial flow velocity of 0.75 m/s, an increase in the water temperature enlarges the cavitation regions, with a particularly obvious increase in the bend pipe. Compared with the length of the cavitation region of 17.5 cm at 20 °C, the cavitation region length increased by an additional 10.2, 18.2, and 12.3 cm at 30, 40, and 50 °C. For an initial flow velocity of 1.135 m/s, intensive cavitation cavities are formed, and water temperature significantly affects the cavity shape. Specifically, at 20, 30, 40, and 50 °C, the downstream valve cavities successively evolve into two small cavities, a large-volume cavity and a small-volume cavity, an irregular stripe-shaped cavity, and a regular stripe-shaped cavity. For an initial flow velocity of 1.71 m/s, more intensive cavitation leads to a near flow cutoff cavity, and higher water temperature has a more significant effect on the expansion of the cavity, especially the cavity length of an additional 12.3 cm at 50 °C compared with that at 40 °C.