(75a) Design, Construction and Operation of a Heat Exchanger Test Bed Unique for Leaks Detection and Modeling

Design, Construction and Operation of a Heat
Exchanger Test Bed Unique for Leaks Detection and Modeling

Dan Fernandes^a, Daniel Chen^a,
Tae Hoon Kim^b

a-: Department of Chemical Engineering, Lamar
University

b-: Department of Industrial Engineering, Lamar University

Key Words-: Heat Exchanger, modelling,
corrosion, detection, abnormal situation management

The
Texas Commission on Environmental Quality has laid certain guidelines for the
control of highly reactive organic volatile compounds (HRVOCs) from the cooling
tower heat exchanger system (Rule 115.760) under the Texas Administrative code,
Chapter 115 rules in title 30 for compounds. HRVOCs are defined as
ethylene, propylene, 1,3-butadiene. HRVOCs are emitted from
flares, process vents, cooling towers, and fugitives [1]. Heat exchangers are
one of the major sources of fugitive emissions into the cooling water supply.
This is largely due to the tube wall perforation /pits development caused by erosion-corrosion
on the tube side of the heat exchanger where normally a higher pressure fluid
flows. The shapes of the pinholes are irregular or gully in nature. [2] The
pits can in single or in groups of several pits close to each other. Coolant
and its velocity play an important role in the failure and performance of a
heat exchanger. [3]

A unique test bed for the purposes of modelling and leak detection
was designed, constructed and operated at Lamar University’s Abnormal Situation
Management Lab. The
shell side fluid is water and the tube side fluid is air or water at a higher
pressure than the shell side fluid. The shell is made up of a see-through PVC
6” diameter pipe which is 5’7” long in length. There are four tubes inside the
shell made of copper material. One of the tubes has no holes and it is the
standard tube for the measurement of air/ water flow. Here modelling of leaks
takes place from the tube side fluid which is at higher pressure to the shell
side fluid at lower pressure. The other three tubes have holes of 0.0403 inch,
0.0625 inch and 0.0730 inch respectively. There are around 10-12 holes per tube
which are close to each other so as to mimic a real-life pitting of the tubes.
Fig.1 shows the tube with 0.0625-inch hole size.

  
Fig.1: 0.0625-inch hole size mimicking
a pit type of corrosion in heat exchanger tube

This test bed is very useful for modelling leaks of
different geometries from individual tubes of a heat exchanger which is
susceptible to erosion-corrosion. Here tubes of different corrosion geometry
(pitting, Stress corrosion cracking) can be studied along with bubble dynamics
of the fluid escaping the tubes using high speed camera. The fluid in the tube
can be either liquid or gas. Furthermore, novel techniques of detecting leaks
in heat exchanger can be studied, we are studying whether leaks can be detected
by means of acoustical signature. An imaging sensor such as a digital camera,
Fig. 2, will also be used for gas bubble measurements. Computation Fluid Dynamics
modelling of leaks in heat exchangers of this test bed will be explored.

Fig.2.
Bubble dynamics of leaks from tube side to shell side using high speed camera @
5000 fps

References:

1)     
http://texreg.sos.state.tx.us/public/readtac$ext.TacPage (Texas Administrative Code, Division 2, Cooling water heat
exchange systems, Rule 115.764, Monitoring and Testing Requirements)

2)     
B.
Kuznicka “Erosion-Corrosion of heat exchanger tubes” Engineering Failure Analysis,
Vol.16,2009,pg 2382-2387

3)     
Khalil
Ranjbar” Effect of flow induced corrosion and erosion on failure of a tubular
heat exchanger”, Materials and Design, Vol.31,2010, pg.613-619