Vibration tests of single heat exchanger tubes in air and static water

The vibrational characteristics of a 7 span straight tube and a 26 span U-tube have been investigated for the effects of fluid medium (air/water), tube-grid clearance, tube-grid contact force, vibration transmission and scale. Measured frequency response and mode shapes compared favourably with theoretical values, vibration with pin-pin tube support being most readily excited. The frequency reduction on immersion in water corresponded to an added mass equivalent to the liquid displaced mass. Dynamic magnifiers varied in the range 12-135 with mean values of 30-40 in water and 45-60 in air. Principal vibration modes and damping values were reproducible in a half-scale model of a U-tube. (author)