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A Study of Gas Generating Technique Using a High Frequency High DC Switching of High Ripple Voltage

S. Ketkaew and A. Jangwanitlert Department of , Faculty of Engineering, King Mongkut’s Institute of Technology Ladkrabang, Bangkok, Thailand 10520 Phone : 662-3264550 E-mail : [email protected], [email protected]

Abstract - This paper presents a study of ozone gas changing to be ozone gas. However, the endurable limit generating technique using high frequency high voltage DC of voltage effects to the break down of air, causing the switching power supply. The high frequency high voltage is generated ozone to vanish during heat from breaking based on a flyback converter. The converter is designed to down. Thus, to generate ozone gas, power and frequency operate at 40 kHz switching frequency through a high have to be controlled. The energy consume for generating frequency flyback , a rectifier and filter circuits. ozone gas is defined from the chemical energy that is The circuit is capable of generating up to 10 kVdc voltage between 493.2 kJ/mol – 682.8 kJ/mol [1]. This energy with a high ripple voltage output at 144 VP-P. By adapting the highly nonuniform to the tube can be transformed to other unit. The necessary energy design of the ozone generator, one-hour operating yields the areas are from 5.58 kWn/m3 – 7.73 kWn/m3. Since there maximum ozone generating capacity of 215.3 mgO3/hr. is approximately 21% oxygen in the air , the necessary energy for generating ozone gas is between 1.172 Keyword : ozone generator, high ripple voltage kWh/m3 and 1.62 kWh/m3 that is enough for occurring ozone gas in the gap. I. INTRODUCTION

Nowadays, ozone gas is brought to use many ways in II. THE PRINCIPLE OF GENERATING OZONE GAS every day life. In practice, ozone gas has both good and bad points – up to what to use for every day life. This is Ozone gas is the gas occurred from 3 atoms of the result to find a method and control the ozone gas oxygen’s gathing. Oxygen bond can be burst if the quantity in order to obtain a good result for the society as outside energy is fed to oxygen gas : O2(g). The oxygen much as possible. The way is to construct the ozone gas gas can be burst to be oxygen’s free atoms (O). Then, generator with high voltage DC switching power supply. they are again gathered to O2 becoming to ozone gas O3. The occurred ozone is from the oxygen’s molecules The energy of ozone gas is less than oxygen gas O2. In dispersion. Oxygen was brought through the producing case of increasing energy to ozone gas O3, only a little steps of a dc high voltage, which is from a high frequency energy can cause O3 to disintegrate. Thus, the system high voltage switching power supply by using IC should not have too much heat inside the gap. For #TL494. This IC will generate the pulse-width example, the heat from breakdown to generate ozone, the modulation (PWM) to use for controlling the flyback chemical energy interval is between 493.2 kJ/mol and converter, which has a Power MOSFET as a switching 682.8 kJ/mol [1,2]. The unit can transform from mole to device. Power MOSFET is the voltage controlled device volume. Ideal gas has dotted model and has no strength to and need very low input current. Furthermore, there is a act each other. 1 mol of ideal gas is written in the high speed switching nano seconds of the unit of very relationship called gas equation, where n is amount of low timing that can provide a high frequency switching. mole. Therefore, gas law is This is the good point to apply with high frequency job. In this case, the high frequency will be applied for a high PV = nRT (1) frequency transformer to get a high voltage square wave about 10,000 . Then, high voltage is supplied to the Real gas is found that gas molecules have the size electrode plate. The energy from electric field is the and strength among molecules called Van der Walls. This factor that effects to the efficiency of producing ozone is a kind of gas’ quality. The approximate real gas gas directly. The type of electrode tubes has to be equation is presented by Van der Walls in (2) supported for providing the corona effect to burst oxygen’s molecules. This takes place a kind of ozone gas  a  p + (v − b ) = RT (2)  2  from the equation, O2 + O = O3. Under high voltage  v  condition, air can be broken down. In addition, The deteriorated air can make the molecule’s structure where V is the gas volume: m3,

1-4244-0844-X/07/$20.00 ©2007 IEEE. 1407 P is atmosphire pressure, d = r2-r1. This is a little value that can make the n is amount of moles, breakdown easily. Decreasing radius of r1 makes the R is gas constant, increasing distance ,d, cause more electric field stress at P = 101.58 x 103 Pascal :Pa, conductor’s surface. Until the break over is occurred, that T = temperature :K, causes the corona effect. Finding out the suitable value of 3 r is between 0 and r that makes the highest withstand R = 8314.3 Pa ∗ m . 1 2 kmol ∗ K voltage without corona effect. The equation for co-core cylinder electrode tube is Define P = 101.5 kPa, T = 300K , so V = 24.55 m3/kmol 1 mol = 0.02455 m3   r2 (6)   = e 3  r1  Thus, 493.2 kJ/mol is 20089.61 kJ/m opt and 682.8 kJ/mol is 27812.63 kJ/m3 where 1J = 2.78 x 10-4 Wh. III. THE DESIGNING OF ELECTRODE TUBE

A. Electrode tube designing for generating ozone gas Therefore, the necessary energy should be between The designing 2 layers co-core cylinder electrode tube 3 3 5.58 kWh/m - 7.73 kWh/m . Because there is 21% of is based on the principle of designing ozone gas quantity. 3 oxygen in the air, the needed energy of 1.172 kWh/m – The ozone gas well occur in the nonuniform electric field. 3 1.62 kWh/m is sufficient to the occurring ozone in the Thus, the designing electrode tube of 2-layer insulators is gap. chosen because permittivity is different. It is appropriate with nonuniform electric field that cause the A. Co–core cylinder : ozone tube’s structure electric field stress in each layer. Therefore, the design of Electric field flux is on the radius line and the surface 2-layer co-core cylinder is composed of : of cylinder. Potential surface is based on Maxwell’s → → - PVC, the first insulator, is chosen because it has equation Q = D ⋅ dA for co – core cylinder of 1 radius ∫s so a little effect to generating ozone, where permittivity length: r r ≤ r ≤ r ()1 2 (ε 1) = 5, 4.2 cm diameter and 25 cm length - Air is the second insulator with permittivity (ε ) = 1 The electric field is given by [2] 2 - Cathode frilled aluminum (for rubbing pots) in

fillament coil inside of the pvc’s electric insulator is used. Q 1 Er = ⋅ (3) The reason is aluminum has a high conductivity. 2πεl r - Anode is a cylinder stainless steel because stainless steel does not effect to generate ozone gas, where a Voltage (V) across between both cylinders is given by: diameter is 4.68 cm and length is 25 cm.

r2 Q r dr V = E dr = ln 2 The electrode design is shown in Figs. 1 and 2. ∫ r r 2πεl r1 r 1 B. The calculation of electrode tube Q r V = ln 2 From Fig. 1 shows the calculating of electrode tube at 2πεl r 1 = 25 cm , r = 1.9cm , r = 2.1 cm , r = 2.34 l 1 2 3 cm ,ε = 5 of PVC, and ε = 1 of air V ( r1 < r < r2 ) (4) 1 2 Er = r2 r ln The energy interval per volume is between 5.58 r1 kWh/m3 and 7.73 kWh/m3 because there is 21 % of 3 The maximum electric field stress is occurred on the oxygen so the energy is 1.172 – 1.620 kWh/m . inside of cylinder’s surface given by: 2 Air volume = π (rr − r2 ) l V (5) 2 3 E = E = = π (2.34 − 2.1) × 25 = 4.52 cm MAX r1 r r ln 2 1 r At the energy per volume of 1.172 kWh / m3 , 1

B. The suitable dimension for ozone tube. W = 1.172 ×103 × 4.52 ×10 −6 In high voltage electrical engineering, the suitable = 0.00529 Wh dimension is the design of smallest dimension in order to resist the highest voltage. For example, determination of At the energy per volume of 1.62 kWh / m3 outer radius electrode,r2 is close to inner radius electrode 3 −6 r1. The distance between outer and inner electrode tube is W = 1.62 ×10 × 4.52 ×10 = 0.00732 Wh

1408 C = 2πε l

 r2  ln    r1 

= 2π ×8.854 ×10 −12 × 0.025  2.1 ln  1.9 

= 13.9 pF

Fig. 1. Structure of electrode tube. IV. TEST OF HIGH FREQUENCY HIGH VOLTAGE DC SWITCHING POWER SUPPLY OF HIGH RIPPLE VOLTAGE

The high frequency high voltage DC switching power supply of high ripple voltage is controlled by IC #TL494 [3] as shown in Fig. 3. Switching devices, Power MOSFET #IRFP350, are used in the Flyback converter controlled by the PWM strategy from IC #TL494. The switching frequency is 50 kHz. The energy from inverter can transfer through a flyback transformer #TLF 14511 to produce high frequency high voltage of high ripple

voltage supplying the ozone tube [2] as shown in Fig. 4. Fig. 2. Electrode tube with PVC and air insulator

1 From W = ()vol εE 2 dv 2 ∫

2W Emin = ε.vol

= 2× 0.00529 = 16.26 kV / cm 8.854×10−12 × 4.52

2× 0.00732 Fig.3. High frequency high voltage DC switching power supply of Emax = = 19.13 kV / cm high ripple voltage. −12 8.854×10 × 4.52

The permittivity of (PVC) = 5 and (Air) = 1 ε1 ε 2

  r   r  E ⋅ r ⋅ε ε ln 3  + ε ln 2  2 2  1   2    r2   r1  V =   ε1 ×ε 2

  2.34   2.1 16,260× 2.1×15ln  +1ln   2.1  1.9  Vmin =   5×1

= 4.38 kV

  2.34   2.1 19,130× 2.1×15ln  +1ln    2.1  1.9  Vmax = 5×1

= 5.15 kV Fig. 4. Output voltage at 10 kVdc and high ripple voltage at 144 VP-P of flyback transformer.

1409 A. The testing of breakdown voltage of electrode tube as - Dissolve potassium iodide (KI) 2.5 grams in 100 table I ml. of pure water, stored in dark bottle for 1 night before using, TABLE I - Dissolve sulphuric acid (H2SO4) to be dense at 1N The result of testing of breakdown voltage of electrode tube H SO , 2 4 - Dissolve Na2S2O3 • 5H2O at 25 grams in 1 litre of order Breakdown Voltage kV(avg) water to be dense 0.1 N Na S O , 1 15.37 2 2 3 2 14.79 - Dissolve 1 gram of starch liquid to be 180 ml. 3 15.18 4 15.37 The procedures of chemical method ozone quantity 5 15.26 analysis expressed as: 6 14.78 1. Absorb ozone gas from generating ozone 7 14.89 8 15.29 generator into the pareshape bottle that has potassium 9 15.36 inside with 100 ml. pure water in 1 minute. The solvent 10 15.30 changes color from white to yellow or orange 2. Bring the solvent from step 1 to adjust pH value The average value of breakdown voltage is by adding sulphuric acid at density 1 N H2SO4,3 ml. with 1 ml. starch liquid as an indicator. The solvent will 151.59 VBreakdown(avg) = = 15.16 kV(avg) change color from yellow or orange to blue. 10 3. Bring the acid from step 2 to tritrate using sodium tiosulphate 0.1 N Na2S2O3 density until blue color is Use 10 kV because it is lower than breakdown voltage. paled. Then, record the value of 0.1 N Na2S2O3 to use for calculating ozone quantity From table I, the breakdown voltage can be easily seen in From the relationship 0.1 N Na2S2O3 1 ml =2.4 mgO , Fig. 5. the calculation for using 0.1 N Na2S2O3 in tritrate 1.4 ml. The ozone absorbed into water within 1 minute can get the ozone gas quantity

1.7 x 2.4 x 60 = 122.4 mgO3/hr

C. The relationship between the frequency and ozone gas quantity From the experiment, the controlling circuit has the switching frequency at 40 kHz , Vout = 10 kVdc and ripple voltage at 144 Vp-p as shown in table II

Table II The relationship between the frequency and ozone gas quantity

frequency V I P V in(rms) in(rms) in out Ozone (kHz) (V) (A) (W) PF (kVdc) quantity Fig. 5. The graph of breakdown voltage of electrode tube. mgO3 /hr

40 150 0.72 86.4 0.8 10 215..3

(a) (b) Fig. 7. The chemicals in testing and equipment set which used in the Fig. 6. (a) The equipment for testing of breakdown voltage and (b) The testing. testing of breakdown voltage of electrode. Fig. 7 shows the quantity of ozone gas occurred by B. Ozone gas quantity analysis [2]. using chemicals for testing. The process of preparing chemicals is used in ozone quanlity analysis given by:

1410 Where parameters of Table II are :

- frequency (kHz) is a frequency of flyback converter - Vin(rms) (V) is the input voltage of high voltage DC supply - Iin(rms) (A) is the input current of high voltage DC supply - Pin (W) is the input power of high voltage DC supply - PF is a power factor of input high voltage DC supply - Vout (kVdc) is the output voltage of high voltage DC supply - Ozone gas quantity (mgO3/hr) is ozone gas generated by ozone generator

V. CONCLUSION

From the experiment of ozone gas generator, a high voltage high frequency dc switching power supply with high ripple voltage, it was found that the high output ripple voltage was able to help to generate the plenty of ozone gas. The generating of ozone gas was called as the phenomenon. This caused the changing of oxygen’s molecules in the air to be ozone gas. That could provide the relationship between the energy from chemicals and power energy. Thus, ozone gas generating tube in this design could ionize by supplying the high voltage, not breaking down. From the test, it was found that the ionization was occurred at the electrode while supplying electric voltage of 2 kV. Also, electric voltage of 12 kV was able to be used without breakdown. Ozone gas generating set was designed to use at 10 kV because it was the appropriate voltage to produce the most ozone gas (mgO3/hr) and not too much heat. Ozone gas did not quickly vanish. The quantity of generated ozone can solve other ways such as the environmental problems. In addition, it can use a lot of other usefulness.

REFERENCES

[1] T. Lekpipat, “Ozonizer using high voltage flyback converter,” Master Thesis in Department of Electrical Engineering, Faculty of Engineering, Mahanakorn University of Technology, Thailand , 2002. [2] D. Changtong, “Ozonizer using high frequency high voltage half bridge inverter,” Master Thesis in Department of Electrical Engineering, Faculty of Engineering, Mahanakorn University of Technology, Thailand, 2002. [3] TL 494 Data sheet, Pulse-width- modulation control circuits, Texas Instruments, 2002, pp. 1-10.

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