DEVELOPMENT OF MEASUREMENT EQUIPMENT
OF OZONE HALF LIFE
Seiji Baba*, Saburoh Satoh and Chobei Yamabe
Department of Electrical and Electronic Engineering,
School of Science and Engineering, Saga University,
1,Honjo-machi,Saga-shi 840-8502,Japan
Abstract In the present research, a new measurement method and the mechanism of Ozone decay
half life τ (h) is proposed Ozone is generated by such electric discharge as silent or surface discharge and
has a strong oxidization power and is widely used for air or water purification. But to determine the dosage of ozone, it is necessary to know the ozone decay time [half life τ (h)] in air or water. Ozone decay is
found to change in a natural logarithmic way. Through measurement the time duration τ (h) and the
concentration x (g/m3) at t ,ozone decay half life τ is calculated.
KEYWORD: Ozone purification, Ozone decay, Half life of Ozone, Ozone concentration.
1. INTRODUCTION
When the contaminated room and/or water are purified by diffusing ozone gas, quantitative analysis is necessary to know how they are contaminated. For this purpose, in general, the concentration
substance is measured. However, when there are many kinds of contamination substance at the same
time, it is very difficult to determine the overall contamination extent in the room or water. On the
other hand ozone reacts on various kinds of contamination substances like organic or inorganic compounds at the same time. If this ozone reaction is measured overall by quantitative way like COD
(Chemical oxygen demand) or BOD(Biological oxygen demand),a practical, simple and overall measurement method is established.
In our present research, we develop the ozone decay half life measurement equipment and propose ozone decay half life τ (h) as quantitative scale of the contamination of a room or water.
The principal advantages of this method are as follows:
The ozone half life τ (h) is calculated by one time ozone concentration measurement value.
Gaseous and liquid phase contamination is determined.
The contamination extent is evaluated instantaneously.
In this paper, the theoretical formula which closely models experimental results, and determines
the ozone half life τ and constitution of measurement equipment are presented.
2. CALCULATION
In case ozone gas is distributed in the room of volume V(m3)(Figure1),the ozone concentration in
the room x(g/m3) is determined by the following differential equation.
dx = (Z/V)dt-(γx)dt
(1)
Here, x : ozone concentration(g/m3)
Z : ozone distribution quantity(g/h)
Z (g/h)
V : volume of room(m3)
γ : ozone decay ratio
t : distributing time(h)
V(m3)
By solving equation (1),
x = (Z/V)(τ /0.693)[1-exp(-0.693t/τ )]
(2)
Here, τ :ozone decay half life (h).
By equation (2), the ozone decay half life τ (h) is calculated as
Fig.1 Room ozone distribution
follows.
*Electronic address : [email protected]
When t = t0, x = x0
x0 = (Z/V) (τ /0.693) [1 - exp(-0.693t0/τ )]
Here, (Z/0.693V)=C,
then,
x0 = (Cτ )-(Cτ )exp(-0.693t0/τ )
1- (x0/Cτ ) = exp(-0.693t0/τ )
When K = x0/C, T = 0.693t0, τ x = 1/τ ,
then,
1- Kτ x = exp(-Tτ x)
ln(1-Kτ x) = Tτ x
Here, ln(1-Kτ x) = -Kτ x+(K2τ x2)/2-(K3τ x3)/3…
When Tτ x = ln(1-Kτ x) = Kτ x+(K2τ x2)/2,
then,
-Kτ x + (K2τ x2)/2 = -Tτ x
(3)
Fig.2 τ -x0 characteristics
By solving equation (3),
2
τ = X /2 (X-0.693t0)
(4)
Here, X = x0/[(Z/V) (1/0.693)]
By equation (4) the relationship between x0 and τ is shown in the following graph (Figure 2).
When X = 0.693t0, or x0/[(Z/V) (1/0.693)] = 0.693t0, the behavior is shown below in Figure 2.
From τ -x0 characteristics, those values Z (g/h) and V (m3) should be chosen the proper values
by which the calculated τ (h) is considered physically effective. The quadrant (1) is available and
shows the practically effective range.
3. EXPERIMENTAL APPARATUS AND METHOD
To examine equation (1) and equation (4), the following experiments were performed.
The experimental apparatus, shown in Fig.3, consists of an ozone generator, reaction chamber, stir fan,
ozone concentration monitor and analogue recorder.
For the control of ozone decay half life τ, several kinds of organic substances like a banana, a
cigarette stub and raw fish which have a strong smell.
Ozonizer
x0(g/m3)
Stir fan
τ = X/2 (X-0.693t0)
X = x0/[(Z/V) (1/0.693)
O3
Reaction
Chamber.
Ozone monitor
Analogue
0
t0(h)
recorder
Fig.3 Experimental apparatus
Fig 4. Ozone concentration measurement
The ozone generator in Fig.3 is an ultraviolet ray type and ozone generation is 0.3 – 0.7 mg/h.
The reaction chamber is made of PVC (Polyvinyl chloride) and the volume is 1(m3).
Experiment 1
Ozone gas is diffused into the chamber and at t0(h) later, the ozone concentration x0(g/m3) is
measured. According to formula (4) the ozone decay half life τ (h) is calculated as,
τ = X2/2 (X-0.693t0), X = x0/[(Z/V) (1/0.693)].
Note : Fig.4
Experiment 2
.
Ozone gas is diffused for a long time until the ozone concentration saturates and after the concentration value saturates, ozone
diffusion is stopped.
x0(g/m3)
Ozone feed stop
x1 (g/m3)
x2 (g/m3)
τ (h)
0
t(h)
Fig.5 Ozone concentration vs time
According to the experimental result (recorded ozone concentration curve), the actual ozone decay
half life τ (h) is measured.
Table 1. Ozone half life control substance
TEST No.
1
2
3
4
Half life control substance in chamber
Nothing (chamber vacant)
Banana
Cigarette stub
Raw fish
4. EXPERIMENTAL RESULTS
Experiment 1
Table 2 shows the results of experiment 1.
Here, ozone concentration x0 (g/m3) at t0 (h) is
measured and the half life τ (h) is calculated by
formula (4).
Experiment 2
Fig.6 shows the results of experiment 2
which ozone concentration is measured continuously by an analogue recorder. From the
curve of ozone concentration, the ozone half
life τ (h) is measured in each test.
TEST 1
Table 2. Calculated τ by experiment 1.
Test No.
1
2
3
4
t0
1/4
(h)
1/4
(h)
1/60
(h)
1/60
(h)
TEST 2
x0
0.31(ppm)
=0.664(mg/m3)
0.30(ppm)
=0.685(mg/m3)
0.26(ppm)
=0.55(mg/m3)
0.15(ppm)
=0.32(mg/m3)
Calculated τ
τ 1=0.99(h)
τ 2=0.79(h)
τ 3=0.48(h)
τ 4=0.30(h)
TEST 3
TEST 4
Fig.6 Ozone concentration transition
5. DISCUSSION
5.1
Fig 7 shows the comparison curves of measured and calculated ozone concentration in the reaction
chamber. The calculated value is the results of calculation using formula (2) and very closely approximates actually measured value. The formula from differential equation (1) is considered acceptable in practical usage in the ozonation scheme.
TEST 1
TEST 3
TEST 2
TEST 4
Fig.7 Comparison transition curves of ozone concentration
5.2
Table 3 shows the comparison of the calculated ozone half life τc (h) to the actually measured half life
τm (h).
Table 3.Comparison of the value τ (h)
Test No
1
2
3
4
τm (h)
1.0
0.8
0.6
0.25
τ-
0.99
0.79
0.48
0.30
Ozonizer
I/O
5.3
Schematic of ozone decay half life measurement
equipment is shown in Fig.8.
5.4
The ozone concentration decrease calculation
formula below is acceptable too, but in this case
we need two times the ozone concentration
measurements. We will add this algorithm in the
measurement equipment.
x = x0exp(-0.693t/τ ),
where x0 is the initial concentration (g/m3) and x
(g/m3) is the concentration at after t(h).
Timer
Reaction
Chamber
RAM
CPU
ROM
Ozone
Monitor
Fig.8.Schematic diagram of the half life measurement equipment.
x0
x = x0exp(-0.693t/τ ),
x
0
t
time t
Fig. 9 Concentration decrease measurement
6. CONCLUSION
When the ozonation scheme of such deodorization, sterilization and purification of air or water is
made, it is necessary to know the ozone decay half life τ (h) of object contaminated room or water for
determination of necessary ozone dosage. ere, we propose a new and simple ozone decay half life τ (h) measurement method which
includes a calculation formula and a schematic diagram of the measurement equipment.
We confirmed experimentally that the linear reaction equation below agrees well with actual
ozone concentration diffusion.
dx = (Z/V)dt - (γ
Also the τ (h) calculation formula for measurement equipment,
τ = X2/2 (X-0.693t0), where X = X0/[(Z/V)] (1/0.693)],
is acceptable.
References
[1] Satoh S, Ihara S, Yamabe C ; Proceeding of the 9 th Annual Conference on Ozone Science and
Technology in Japan.2000-3.p.179-182(in Japanese).
[2] Baba S, Satoh S, Yamabe C ; Proceeding of the 10 th Annual Conference on Ozone Science
and Technology in Japan.2000-10.p.39-42(in Japanese).
[3] Baba S, Satoh S, Nagao H, Yamabe C; Proceeding of Electric Discharge Research Report of IEEJ
2000-9.ED-00-114,p.55-58(in Japanese)