They couldn't predict if high-speed fluid would cause the tubes to vibrate and eventually snap.
Heat exchangers are essentially massive tuning forks. The cross-flow velocity of the fluid can match the natural frequency of the tubes. When this happens, acoustic resonance or tube vibration occurs. htri heat exchanger design top
Would you like the (geometry, baffles, nozzles, tube layout) or a vibration calculation detail from this case? They couldn't predict if high-speed fluid would cause