UWE Bristol Engineering showcase 2015

Introduction
The detection of Volatile Organic
Compounds (VOCs) has, for several
decades, been a huge area in sensor
research. Exposure to these
compounds can lead to various health
issues and are widely found across
various work places, making them
important to detect. It is known that
many VOCs are found in the exhaled
breath, urine, faeces and skin
emanations of human beings; and that
there is evidence to suggest that the
presence of specific volatiles in these
are related to cancer.
The system to be created is essentially
a mimicry of the mammalian olfactory
system, using a sensor to mimic the
nose, and an analysis of results along
with pattern recognition to mimic the
brain.
The reaction that occurs upon the
surface of a heated metal oxide when
it comes into contact with a volatile
causes the conductivity of the MO to
change. This phenomenon can be
measured, and used to detect VOCsin
the air.
Cataluminescence is the emission of
light during the catalytic oxidation of
organic compounds, in this case the
metal oxide sensor serves as a catalyst.
Thom Clark
BEng (Hons) Aerospace Engineering (Design)
The Fabrication of a Gas Sensing Device
Combining Measurements of Cataluminescence
and Conductivity change
Initial Design
The old chamber is shown above, as
can be seen, it consists of a bolted on
lid, no means of securing other than
fixings that were added after it was
made and the inside is full of sharp
corners, not desirable for any flow.
After a few stages of configuration, the
design consisted of a cylindrical inside,
screw on lid, linear air inlet-outlet, and
built in bolt holes for fixing. The sensor
sits on the end of the bolt, which is
screwed into the chamber, opposite
this is the inlet for the gas
chromatography column.
Computational Fluid Dynamics
A small amount of basic fluid
dynamic analysis was undertaken
to determine the optimum
arrangement for the chamber.
It was found to be an arrangement
that encouraged circulatory flow,
when the sensor bolt was
horizontal, which was incorporated
in the manufactured design.
Other Equipment
To measure the light emission from
the CTL, a photomultiplier tube was
required, a PMT is a device that
detects photons, and amplifies
them using the photoelectric effect
to emit a current.
The module sourced as part of this
project was the Hamamatsu H7828
photon counting unit, which was
connected to a pulse counter to
record its emissions.
Pulse Count Reading (kHz)
100
90
80
70
60
50
40
30
20
10
0
The Atmospheric Chamber
The second chamber was designed to
detect trace amounts of VOCs in the
atmosphere, it differed from the other
one with the sensory bolt screwed in
through the lid, positioning it opposite
the photocathode of the PMT once
the chamber was screwed onto it.
Equipment Testing
The experimental equipment was
tested using an old, basic sensor
chamber, adapted to fit the PMT.
Pulse Response of Nitrotoluene Vapour
against Time
0 20 40 60 80 100 120
Time from sample injection (s)
This graph shows the difference in
pulse response after the injection of
three different concentrations. Of
course the highest concentration
showed the best response.
Saturated
Diluted
Air
Project Supervisor
Professor Norman Ratcliffe
Project summary
This project involved the design of two sensor
chambers to detect the presence of Volatile Organic
Compounds, using a combination of the
measurements of the conductivity change of metal
oxides and the emission of cataluminescence (CTL).
The starting point for design was an old gas sensor
chamber designed for use in the applied sciences lab
2G5; hence certain criteria were to be fulfilled in the
new design, based upon the experiences of the old
chamber’s use.
Project Objectives
The main objectives for this project were:
• To design two sensory chambers that combine the
detection capabilities of CTL and conductivity
change; one for medical diagnostics, connected to
a gas chromatograph and one for detecting VOCs
in the atmosphere
• To source the required apparatus, such as a
photomultiplier tube module
• To improve upon the previous chamber’s design,
making it easier to use in experimentation
• Perform aerodynamic analysis upon the flow
inside the chamber, identifying undesirable flow
effects and attempting to reduce them
Project Conclusion
Both chambers were designed with what is thought
are optimum designs, based on findings from various
bits of investigation throughout the project and the
results from CFD. However, it was planned from the
start of the project that the chambers would be
manufactured and then tested to validate their
design. Due to unfortunate circumstances neither of
the chambers were manufactured in time, meaning
that the experimental analysis and comparison with
the old chamber could not occur. Despite this, the
design met the desired criteria and was improved in
several ways.