Experimental Investigation of

Fluid Elastic Instability in Cross

Flow Shell and Tube Heat

Exchanger Bundles

Research Supervisor : DR. Shahab Khushnood

Research Scholar : Muhammad Awais

12-MS-FT-TSE-03

Problem Statement

Cross flow shell and tube heat exchangers are frequently used in

petrochemical industries, such as in oil refineries, fertilizer plants and in

different chemical industries.

When the fluid passes over the tube bundle array, fluid elastic instability

mechanism occurs, which produces flow induced vibrations (FIVs) in the

tube bundle with large amplitude beyond a critical velocity of fluid flow.

Due to this problem fretting wear and necking (at baffle holes) type

failures occur in the tube bundle. So, this mechanism of flow induced

vibrations in heat exchangers leads to equipment breakdown and hence

expansive repair and process shutdown.

Aims and Objectives The objective of this research is the experimental investigation of fluid elastic instability

in cross flow shell and tube heat exchanger tube bundle during partial admission of

liquid water in cross flow.

Comparison of results for two different tube bundle arrays :

1- Triangular.

2- Square.

Relation between the parameters on which this mechanism of flow induced vibrations

depends and which of these parameters are more influenced during fluid elastic instability

mechanism. Some of these parameters are:

Mass-damping parameter.

Tube frequency of vibration.

Strouhal number.

Critical velocity of fluid.

Damping ratio.

Introduction

Fluid elastic instability is the most catastrophic flow-induced vibration mechanism in

cylinder arrays subjected to cross-flow (Paidoussis 1980).

During fluid flow across the flexible tube array, due to the fluid forces the tubes displaced

from the initial position.

The damping force of the tubes that tries to restore the tubes back to their equilibrium

position opposes this change in fluid force.

Thus, a competition results between the energy input by the fluid force and the energy

expended in damping.

When the energy expended in damping is more than the energy input by the fluid, the

vibrations die down.

However, if the fluid forces dominate, sufficient energy is imparted to the tube to sustain the

vibrations and an unstable situation is reached where the tube vibrates with large amplitude.

In shell-and-tube heat exchangers, this limit is known as fluid-elastic instability and

leads to tube damage like fretting wear.

Fluid Elastic Instability Mechanism

Experimental Setup

TEST SECTIONBASIC SCHEMATIC OF EQUIPMENT SETUP

Expected Results:

The result expected in this research is to minimize

the flow induced vibrations (FIV) in tube bundle

during non-uniform cross flow of fluid around the

tubes.

Utilization of Research Results

By utilization of results of this experimental investigation

we can easily point out those parameters which are more

influenced during fluid elastic instability mechanism.

Through the results of this research it is easily visualized

that which mode of vibration occurs during each critical

velocity of non uniform fluid flow around the tubes.

Project Work Schedule

PROPOSED WORKING SCHEDULE (2013-2014)

ACTIVITY APRIL 2013 MAY 2013 JUN. 2013 JUL. 2013 AUG. 2013SEP.

2013

OCT.

2013

NOV.

2013

DEC.

2013

JAN.

2014

Literature

Collection

Literature Study

Experimentation

Results

Formulation

Report Writing &

Submission

References

Paidoussis, M.P., P rice, S. J., 1988, “The Mechanisms Underlying Flow Induced Instabilities

of Cylinder Arrays in Cross Flows”. Journal of Fluid Mechanics, vol.187, pp.45- 59 .

Mitra, D.R., 2005, “Fluid Elastic Instability in Tube Arrays Subjected To Air-Water and Steam-

Water Cross-Flow”, Ph.D Thesis, University of California, Los Angles.

Parrondo, J.L., Santolaria, C., Weaver, D.S., 1995, “ Fluid Elastic Instability in a Tube Array

Subjected to Partial Admission Water Cross Flow”. Journal of Fluid and Structures, Vol. 11,

pp.149-181.

Olinto, C.R., Endres, L.A.M., Moller, S.V., 2007, “Experimental Study of the Characteristics

of the Flow in the First Rows of Tube Banks”, Transactions, SMIRT 19, Toronto.

Any questions…..?