Anwar Sadath, K T
(2014)
Dynamics of Cross Flow Heat Exchanger Tubes with Multiple Loose Supports.
Masters thesis, Indian Institute of Technology Hyderabad.
Abstract
Dynamics of cross
ow heat exchanger tubes with two loose supports has been studied. The analytical
model of a cantilever beam that include the time delayed displacement term along with two
restrained spring forces has been used to model the
flexible tube. The model consists of one loose
support placed at the free end of the beam and the other at the mid-span of the beam. The critical
flow has been obtained after solving a free vibration model of the system. The beam equation is
discretized to five second order delay differential equations using Galerkin approximation, and solved
numerically. It has been found that, for
ow velocity less than the critical
ow velocity the system
shows a positive damping leading to a stable response. Beyond the critical velocity, the system
becomes unstable, but a further increase in the velocity leads to the formation a negative damping
which stabilize the system at an amplified oscillatory state. For a sufficiently high
ow velocity the
tube impacts on the loose supports and generates more complex and chaotic vibrations. The loose
supports have been modelled as a cubic spring and a tri-linear spring. The effect of spring constants
and free-gap of the loose support on the dynamics of the tube has been studied.
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