In fact all three dimensional objects require three numbers to describe them.
Considering this, it is difficult to see how we can arrive at a single number which
uniquely describes the matchbox’s particle size. Obviously the situation is even
more complex for irregularly shaped particles.
In particle size analysis, most people want to have a single measurement to
describe their spray, for example, they wish to say that their spray is made up of
droplets with a 50
m
m diameter. What is required is a unique number that
describes the droplet. If we say we have a sphere with a 50
m
m diameter, this
describes it exactly.
One way to get a single unique number to describe an irregular shaped droplet is
to compare some feature of the actual droplet to an imaginary spherical droplet.
This technique is known as
equivalent spheres
.
Some typical methods of doing this are:
.
Equivalent surface area – calculation of the diameter of a theoretical sphere
that has the same surface area as the original droplet.
.
Equivalent maximum length – calculation of the diameter of a theoretical
sphere that has the same maximum dimension as the original droplet.
.
Equivalent minimum length – calculation of the diameter of a theoretical
sphere that has the same minimum dimension as the original droplet.
Many other methods are also available.
The Spraytec uses the volume of the droplet to measure its size. In the example
above, the matchbox has a volume of 50 x 25 x 10mm = 12500mm
3
. If the
Spraytec was able to measure this size of “particle” it would take this volume and
calculate the diameter of an imaginary sphere that is equivalent in volume – in
this case it is a sphere of about 30mm diameter.
Obviously, a different answer is obtained if the surface area or maximum
dimension of the matchbox is used to calculate an equivalent sphere. All of these
answers are correct but each is measuring a different aspect of the matchbox. We
can therefore only seriously compare measurements that have been made using
the same technique, or measurements of spherical particles.
C H A P T E R 2
S
p
r
a
y
t
e
c
P a g e 2 . 8
M
A
N
0
3
6
8
Summary of Contents for Spraytec
Page 1: ...Spraytec User Manual Spraytec User Manual M A N 0 3 6 8 I s s u e 1 0 N o v 2 0 0 5...
Page 7: ...Part 1 Operator s guide Part 1 Operator s guide...
Page 8: ......
Page 9: ...Introduction to this manual Introduction to this manual C H A P T E R 1...
Page 10: ......
Page 16: ...C H A P T E R 1 S p r a y t e c Page 1 6 M A N 0 3 6 8...
Page 17: ...What is the Spraytec What is the Spraytec C H A P T E R 2...
Page 18: ......
Page 31: ...The Spraytec hardware The Spraytec hardware C H A P T E R 3...
Page 32: ......
Page 42: ...C H A P T E R 3 S p r a y t e c Page 3 10 M A N 0 3 6 8...
Page 43: ...The Spraytec software The Spraytec software C H A P T E R 4...
Page 44: ......
Page 63: ...Measurement tutorial Measurement tutorial C H A P T E R 5...
Page 64: ......
Page 99: ...Interpreting the results Interpreting the results C H A P T E R 6...
Page 100: ......
Page 125: ...Using measurement files Using measurement files C H A P T E R 7...
Page 126: ......
Page 133: ...Basic maintenance Basic maintenance C H A P T E R 8...
Page 134: ......
Page 139: ...Part 2 Supervisor s guide Part 2 Supervisor s guide...
Page 140: ......
Page 141: ...Security Security C H A P T E R 9...
Page 142: ......
Page 151: ...Advanced features Advanced features C H A P T E R 1 0...
Page 152: ......
Page 170: ...C H A P T E R 1 0 S p r a y t e c Page 10 18 M A N 0 3 6 8...
Page 171: ...SOP management SOP management C H A P T E R 1 1...
Page 172: ......
Page 175: ...Part 3 Appendices Part 3 Appendices...
Page 176: ......
Page 177: ...Health and Safety Health and Safety A P P E N D I X A...
Page 178: ......
Page 184: ...A P P E N D I X A S p r a y t e c Page A 6 M A N 0 3 6 8...
Page 185: ...Specification Specification A P P E N D I X B...
Page 186: ......
Page 191: ...Site requirements f r o m M A N 0 3 6 8 I s s u e 1 0 Site requirements A P P E N D I X C...
Page 200: ...A P P E N D I X D S p r a y t e c Page D 3 M A N 0 3 6 8...
Page 201: ...Installation Installation A P P E N D I X E...
Page 202: ......
Page 206: ...A P P E N D I X E S p r a y t e c Page E 4 M A N 0 3 6 8...
Page 207: ...Regulatory statements Regulatory statements A P P E N D I X F...
Page 208: ......
Page 213: ...Index Index...
Page 214: ......
Page 221: ......