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A comparison of ultrasonic cavitation intensity in liquids
A comparison of ultrasonic cavitation intensity in liquids B. NI EMCZEWSKI
Cavitation intensity in 37 organic liquids is compared with cavitation intensity in water under the same conditions. Temperature ranges are established over which cavitation intensities in these liquids are at their highest.
h = nc/2f
Introduction As is generally known,’ ,2 various liquids can cavitate with different intensities, the intensity depending on temperature (Fig. 1). Moreover, the cavitation intensity while in the process of heating differs from that in the process of cooling (Fig. 2). Also the height of the column of the irradiated liquid influences the intensity of cavitation3’4 _ cavitation is substantially more intense when the height is equal to half the wavelength of the ultrasonic radiation (Fig. 3). This large number of parameters affecting the intensity of cavitation in liquids is probably the reason for the lack of comparative information in the literature concerning cavitation in various liquids. A common opinion is that only water can cavitate intensely and that organic liquids cavitate with an intensity many times lower. However, as yet there is no comparative information on a large number of liquids irradiated under the same conditions. This is the problem to which the present paper is addressed.
where h is the height of the column of liquid which at the given temperature corresponds to a half-wavelength or its multiple, f ultrasonic frequency, n the integer equal to the number of half-wavelengths, and c the sound velocity (varying with temperature). The heights of the column of liquid calculated from this formula, in order to tune the acoustic conditions, were adjusted experimentally by pouring in or out small amounts of the liquid to obtain maximum cavitation. Under such conditions it has been stated that the cavitation intensity in all examined liquids except water and methylene chloride is higher during heating and lower during cooling. The maximum cavitation intensity in water in the column at a height of half a wavelength has been taken as 100. Results
Experimental
procedure
To compare cavitation intensity in 38 liquids and to establish temperatures at which cavitation is most intense, a cavitation intensity meter Model 200 manufactured by Branson Instruments Incorporated (USA) was used. operating on the principle of measuring so called ‘white cavitation noise’.’ The source of the ultrasound, and at the same time the measuring vessel, was a small ultrasonic cleaning tank from the same manufacturer (frequency 46 kHz, power 60 W, dimensions of base 125 x 125 mm, capacity 1 1). In the cleaner there were installed: the cavitation meter probe, a temperature probe, mixer and a vessel for surface cooling or heating of the liquid (removed during measurement). To obtain comparable results of cavitation intensity measurements the amount of each liquid poured into the cleaning tank was chosen so that the height of the column of liquid was equal to half the ultrasonic wavelength or its multiples at the temperature at which cavitation reached its maximum. Therefore diagrams of sound velocity against temperature have been used, plotted according to the data collected by W. Schaaffs6 as well as the following formula: The author is at the Ultrasonics Laboratory, Tele and Radio Research Institute , Ratuszowa 11,03-450, Warsaw, Poland. Paper received 9 April 1979. Revised 8 October 1979.
004; -624X/80/0301 ULTRASONICS.
MAY 1980
Maximum cavitation intensities (mci) were noted as compared with water cavitation, as well as the temperatures at
1
I
I
-20
-10
1 0
I
I
I
I
IO
20
30
40
Temperature [“C] Fig. 1 Cavitation intensities of six halogen solvents (height of liquid column under transducer is 3h); a - methylene chloride; b - tetrachloroethylene; c - trichloroethylene, d - 1 ,l ,l - trichloroethane, e - Freon 11482, f - Freon 113
07-04 $02.00 0
1980 IPC Business Press 107
To check the results at a different frequency of ultrasound some of the above experiments were repeated with a 22 kHz cleaner (power 60 W, dimensions of the base 1 10 x ! 10 mm, capacity 1 1). It has been stated that the relation between cavitation intensities in different liquids at the half-wavelength height is, at the frequency of 22 kHz, identical to that at 46 kHz. This has been illustrated in Table 3. The slight differences in mci values are thought to be due to measurement errors. It should be emphasized that the absolute values of cavitation intensity at 22 and 46 kHz are different, but after setting the water cavitation intensity in each case to 100, the other liquids have the same relative values at the two frequencies.
1~~~
IO
30
20
40
50
60
‘I1l_ 70
-YJ _~
80
90
100
110
Thus, it can be supposed that the mci value for half-wavelength heights (h/2) is a characteristic value for a given liquid and does not depend on frequency. Unfortunately we have not managed to determine explicitly whether it is similar for heights of liquid other than h/2.
Temperature PC] Fig, 2 Cavitation of tetrachloroethylene as a function of temperature in the Branson cleaner USD 1216/TW (40 kHr, 400 W, 36 I). The cavitation intensity was measured with a Branson cavitation intensity meter
which cavitation reached its maximum intensity and (for liquid column heights equal to the wavelength) the tempcrature ranges over which the cavitation intensity ranged from 70% to 100% of the maximum value. The results obtained are given in Table 1. For ten liquids measurements were made over the range of a column height of up to 5 or 6 half-wavelengths, the results being illustrated in Figs 4 and 5. As can be seen from Figs 4 and 5. cavitation intensity decreases with increasing height of the liquid column (which agrees with other experiments), the decrease being different for each liquid. Because the decrease in water cavitation intensity is relatively the smallest, the difference between cavitation intensities in water and the other liquids becomes bigger as the height of the irradiated liquids increases, and the mutual relation of cavitation intensities in particular liquids changes.
Discussion
When comparing the highest possible cavitation intensities of particular liquids (that is, cavitation intensities in heights of X/2), it can be stated that there are many organic liquids that are able to cavitate with a substantial intensity, even reaching above 70% of the maximum water cavitation intensity. This is important both in ultrasonic cleaning and in sonochemistry because it challenges the prevailing opinion concerning the possibilities of carrying out chemical reactions under the influence of cavitation. As has become evident it is possible to induce in some organic liquids cavitation of intensity almost equal to that achieved in water, provided the liquid is irradiated in a layer of thickness h/2 at the temperature at which cavitation in the particular liquid is most intense. I loo
Starting from five half-wavelengths there is a certain relation established between cavitation intensities in particular liquids, the difference in cavitation intensities of water and most organic liquids being substantial (Table 2). The abovementioned opinion concerning this problem is based on this fact.
I-
r
I ‘_
&
20
L!5 $ 15 m E -- IO s ; E 5 0
OLI
‘.
-- - ---------~I
‘.
1.
. .
---_
t 0
5
--.
I
I
I
I
IO
I5
20
25
I 30
I 35
II-I 40 45
50
55
60
Height of water column [mm] I
Dependence of cavitation intensity on the height of the Fig. 3 water column under the transducer (Bransonic B-l 2 cleaner, 46 kHz, 60 W, capacity 1 I). The cavitation intensity was measured as the quantity of iodine liberated from a 1 I aqueous solution of KI and CC14 in 20 min
108
2
3
4
5
Height of llquld column under transducer [X/Z] Maximum cavitation Intensities (at 46 kHz) of four liquids Fig. 4 as a function of height of the liquid column under the transducer: a ~- water; b ~ toluene; c - benzene; d ~ ethanol
ULTRASONICS.
MAY 1980
Table
1.
Comparison
of ultrasonic
cavitation
intensity
in various liquids
Maximum tation
cavi-
intensity
Temperature
Temperature
at which cavi-
which cavitation
reached from 70% to 100%
Boiling
for a X/2 liquid
tation
intensity
point
column
[“Cl
[%I
mum
100
100
35
20 -
50
146
74
37
24 -
53
3 Toluene
“20 C6’-‘5C2’-‘3 C6’-‘5C’-h
111
71
29
IO-40
4 Tetralin
(AoH
207
70
55
30-
C6HlOO
155
70
36
0 - 45 30 - 80
1 Water 2 Styrene
5 Cyclohexanone
[“Cl
maxi-
of the maximum
Chemical formula
Liquid
(46 kHz)
reaches
(column
C,HaON
128
65
50
C6H4
(CH312
137
64
26
C2H4
(OH),
197
61
93
75 -
120
141
59
49
38 -
70 23
glycol
9 Cyclopentanol IO
CaHaOH C2 HCI,
Trichloroethylene
11 Glycerine 12
C3H5
n-Amy1
acetate
(OH)3
CH3COOC5H,,
8 - 48
87
58
20
0 -
290
57
85
75 -
149
57
18
2 -
32 63
13 Tetrachloroethylene
G?CI4
121
56
42
33 -
14 n-Butyl
CHaCOOC4Ha
126
56
21
-2-27
acetate
105
15
Pyrrole
55
40
25 -
75
Methanol
C4HsN CHaOH
130
16
65
52
19
4 -
23
17
Chloroform
CHC13
61
50
-3
-II-
18
n-Amy1 alcohol
137
47
23
-32
-
46
19
Ethanol
CsHllOH C2H50H
78
46
21
20
Eth.yl acetate
CH3 COOC2 H5
77
45
9
21
Acetone
56
44
22
n-Butyl
(CH,),CO C4HaOH
23
Benzene
24
n-Propyl
25
1,1, 1 -Trichloroethane
26
Methylene
27
Methyl
28
Naphtha
29
Isopropyl
alcohol alcohol chloride
acetate alcohol
15
15-27 -5-50
-36
16 -
-20
118
43
32
IO-45
C6H6
80
43
19
IO-32
C3H70H
97
42
27
c2 H3Cl3
74
41
18
CH,CI,
40
38
CHaCOOCH3 -
57
38
242
38
35
(CHa12CHOH
82
38
16
0 - 30
8 - 44 -7
-
20
-40
-60
-
-25
-32
-40
-
-10
24 -
50
30
Formic
HCOOH
101
37
30
25 - 42
31
Tri-n-butylamine
(C4Ha)aN
214
37
31
15-38
32
Carbon
cc14
77
35
8
0 - 22
33
Cyclohexanol
C6hlOH
160
23
37
35 - 40
34
Propionic
C,H,COOH
141
22
32
35
Triethylamine
(CaHs)aN
89
21
1
36
Freon
113
CzClaF3
48
15
37
Freon
11462
C2Br2F4
47
6
8
38
Acetic
acid
CH,COOH
118
6
48
acid (85%) tetrachloride acid
The 37 organic liquids listed in Table 1 seem to constitute a number sufficient to state that although there is no explicit relation between the chemical structure of the liquid and its ability to undergo intense cavitation, some characteristic features of this structure may in many cases affect the cavitation intensity. It can easily be seen that liquids of cyclic structure are able to cavitate most intensely (as far as maximum cavitation in a h/2 layer is considered), for example, styrene, toluene, tetralin, morpholine, and xylene, but there are exceptions from that rule (cyclohexanol, benzene). The most weakly cavitating liquids are freons, carboxylic acids and aliphatic amines. For acetic acid esters with monohydric alcohols there can be noticed the following regularity: the longer the carbon chain of the alcohol the more intense the cavitation. But alcohols themselves do not exhibit this regularity: methanol cavitates most intensely and in second place is n-amyl alcohol. Naphtha, to which AS. Bebtschuk’
ULTRASONICS.
MAY
1980
-20
value
105
7 Xylene Ethylene
intensity
height X) [“Cl
6 Morpholine 8
range over
12-45 -12
-
14
-30
-
-5
-5
-18
20 - 60
attributed the ability to cavitate more intensely than other organic liquids, in comparable conditions exhibited a cavitation intensity below average. The problem of the temperatures at which maximum cavitation intensities have been observed should also be discussed briefly. It has been noted that the same liquid exhibits different temperatures of maximum cavitation intensities depending on the height of the column of liquid. Differences for multiples of X/2 are generally of a few degrees Celsius, yet a layer of height X/2 sometimes cavitates more intensely at temperatures greatly different from the temperatures of maximum cavitation for other heights. The data in Table 1 concerning the temperature ranges over which cavitation at the level of 70 - 100% of the maximum value has been observed apply only to the conditions of the present experiment and cannot be transferred to other heights of the column of liquid or other parameters of ultrasonic transducers.
109
Table
3.
Maximum
with ultrasound (water
cavitation
at frequencies
intensities
(h/2)
of liquids
of 46 and 22 kHz
= 100) Mci ~__-____
Liquid
46
____-__-~100
Water
2
4
3
6
5
kHz
---
kHz
22
100
Toluene
71
70
Trichloroethylene
58
58
Tetrachloroethvlene
56
57
Benzene
43
44
1, 1, 1 -Trichloroethane
41
41
Haght of liquid column under transducer [A/2] Fig. 5 Maximum cavitation intensities (at 46 kHz) of halogen solvents as a function of height of the liquid column under the transducer: a - methylene chloride; b - tetrachloroethylene; c - trichloroethy. lene; d - 1 ,l ,l -trichloroethane; e - Freon 11462; f - Freon 113
Table
2.
Comparison
of maximum
ten liquids for a liquid column
cavitation
height of 5h/2
intensities
of
(for 46 kHz)
Liquid .._ --_
Mci for 5hl2
Water
90
-~
Methylene
chloride
33
Tetrachloroethylene
27
Trichloroethylene
22
Toluene
17
1, 1,1-Trichloroethane
13
Benzene
10
Ethanol
6
while it is well known that ultrasonic cleaning in aqueous solutions can be performed with good effect at temperatures around 50 - 60°C. In the opinion of the author this can be explained as follows. The agents involved in ultrasonic cleaning are not only cavitation, but also liquid streaming due to radiation pressure of the ultrasound, and chemical activity from substances dissolved in the water such as acids, alkalis or detergents. The intensity of both these last agents increases with temperature, and this is why the total activity of all three agents may produce a stronger cleaning effect at 60°C than at 35°C. A similar explanation can be applied to the Freons, which according to the above results support only slight cavitation. Their cleaning power with ultrasound is caused by especially high radiation pressures; this depends inversely on the sound propagation velocity, which in Freons is very 10w.~ References I
Freon
11462
2
Freon
113
2
Nevertheless they give an indication about the temperature range over which most intense cavitation for a given liquid can be expected. A short comment also needs to be made on the fact that the maximum cavitation intensity of water occurs at 35”C,
110
2
3 4 5 6
7
Bebtschuk, A.S. /lk~rsr. Zh. 1 (1957) 91 Niemczewski, B., Proc XXII open bernmar on acouhtics (in Polish). KA PAN, Wroclaw-Swierad6w Zdrdj, vol. II (1975) 536 Shih-Ping Liu, J. ~icousr. Sot. A~rr. 38 ( 1965) 8 17 Niemczewski, B., Proc XV Intern Conf on A
21
ULTRASONICS.
MAY
1980
Cavitation intensity in 37 organic liquids is compared with cavitation intensity in water under the same conditions. Temperature ranges are established over which cavitation intensities in these liquids are at their highest.
h = nc/2f
Introduction As is generally known,’ ,2 various liquids can cavitate with different intensities, the intensity depending on temperature (Fig. 1). Moreover, the cavitation intensity while in the process of heating differs from that in the process of cooling (Fig. 2). Also the height of the column of the irradiated liquid influences the intensity of cavitation3’4 _ cavitation is substantially more intense when the height is equal to half the wavelength of the ultrasonic radiation (Fig. 3). This large number of parameters affecting the intensity of cavitation in liquids is probably the reason for the lack of comparative information in the literature concerning cavitation in various liquids. A common opinion is that only water can cavitate intensely and that organic liquids cavitate with an intensity many times lower. However, as yet there is no comparative information on a large number of liquids irradiated under the same conditions. This is the problem to which the present paper is addressed.
where h is the height of the column of liquid which at the given temperature corresponds to a half-wavelength or its multiple, f ultrasonic frequency, n the integer equal to the number of half-wavelengths, and c the sound velocity (varying with temperature). The heights of the column of liquid calculated from this formula, in order to tune the acoustic conditions, were adjusted experimentally by pouring in or out small amounts of the liquid to obtain maximum cavitation. Under such conditions it has been stated that the cavitation intensity in all examined liquids except water and methylene chloride is higher during heating and lower during cooling. The maximum cavitation intensity in water in the column at a height of half a wavelength has been taken as 100. Results
Experimental
procedure
To compare cavitation intensity in 38 liquids and to establish temperatures at which cavitation is most intense, a cavitation intensity meter Model 200 manufactured by Branson Instruments Incorporated (USA) was used. operating on the principle of measuring so called ‘white cavitation noise’.’ The source of the ultrasound, and at the same time the measuring vessel, was a small ultrasonic cleaning tank from the same manufacturer (frequency 46 kHz, power 60 W, dimensions of base 125 x 125 mm, capacity 1 1). In the cleaner there were installed: the cavitation meter probe, a temperature probe, mixer and a vessel for surface cooling or heating of the liquid (removed during measurement). To obtain comparable results of cavitation intensity measurements the amount of each liquid poured into the cleaning tank was chosen so that the height of the column of liquid was equal to half the ultrasonic wavelength or its multiples at the temperature at which cavitation reached its maximum. Therefore diagrams of sound velocity against temperature have been used, plotted according to the data collected by W. Schaaffs6 as well as the following formula: The author is at the Ultrasonics Laboratory, Tele and Radio Research Institute , Ratuszowa 11,03-450, Warsaw, Poland. Paper received 9 April 1979. Revised 8 October 1979.
004; -624X/80/0301 ULTRASONICS.
MAY 1980
Maximum cavitation intensities (mci) were noted as compared with water cavitation, as well as the temperatures at
1
I
I
-20
-10
1 0
I
I
I
I
IO
20
30
40
Temperature [“C] Fig. 1 Cavitation intensities of six halogen solvents (height of liquid column under transducer is 3h); a - methylene chloride; b - tetrachloroethylene; c - trichloroethylene, d - 1 ,l ,l - trichloroethane, e - Freon 11482, f - Freon 113
07-04 $02.00 0
1980 IPC Business Press 107
To check the results at a different frequency of ultrasound some of the above experiments were repeated with a 22 kHz cleaner (power 60 W, dimensions of the base 1 10 x ! 10 mm, capacity 1 1). It has been stated that the relation between cavitation intensities in different liquids at the half-wavelength height is, at the frequency of 22 kHz, identical to that at 46 kHz. This has been illustrated in Table 3. The slight differences in mci values are thought to be due to measurement errors. It should be emphasized that the absolute values of cavitation intensity at 22 and 46 kHz are different, but after setting the water cavitation intensity in each case to 100, the other liquids have the same relative values at the two frequencies.
1~~~
IO
30
20
40
50
60
‘I1l_ 70
-YJ _~
80
90
100
110
Thus, it can be supposed that the mci value for half-wavelength heights (h/2) is a characteristic value for a given liquid and does not depend on frequency. Unfortunately we have not managed to determine explicitly whether it is similar for heights of liquid other than h/2.
Temperature PC] Fig, 2 Cavitation of tetrachloroethylene as a function of temperature in the Branson cleaner USD 1216/TW (40 kHr, 400 W, 36 I). The cavitation intensity was measured with a Branson cavitation intensity meter
which cavitation reached its maximum intensity and (for liquid column heights equal to the wavelength) the tempcrature ranges over which the cavitation intensity ranged from 70% to 100% of the maximum value. The results obtained are given in Table 1. For ten liquids measurements were made over the range of a column height of up to 5 or 6 half-wavelengths, the results being illustrated in Figs 4 and 5. As can be seen from Figs 4 and 5. cavitation intensity decreases with increasing height of the liquid column (which agrees with other experiments), the decrease being different for each liquid. Because the decrease in water cavitation intensity is relatively the smallest, the difference between cavitation intensities in water and the other liquids becomes bigger as the height of the irradiated liquids increases, and the mutual relation of cavitation intensities in particular liquids changes.
Discussion
When comparing the highest possible cavitation intensities of particular liquids (that is, cavitation intensities in heights of X/2), it can be stated that there are many organic liquids that are able to cavitate with a substantial intensity, even reaching above 70% of the maximum water cavitation intensity. This is important both in ultrasonic cleaning and in sonochemistry because it challenges the prevailing opinion concerning the possibilities of carrying out chemical reactions under the influence of cavitation. As has become evident it is possible to induce in some organic liquids cavitation of intensity almost equal to that achieved in water, provided the liquid is irradiated in a layer of thickness h/2 at the temperature at which cavitation in the particular liquid is most intense. I loo
Starting from five half-wavelengths there is a certain relation established between cavitation intensities in particular liquids, the difference in cavitation intensities of water and most organic liquids being substantial (Table 2). The abovementioned opinion concerning this problem is based on this fact.
I-
r
I ‘_
&
20
L!5 $ 15 m E -- IO s ; E 5 0
OLI
‘.
-- - ---------~I
‘.
1.
. .
---_
t 0
5
--.
I
I
I
I
IO
I5
20
25
I 30
I 35
II-I 40 45
50
55
60
Height of water column [mm] I
Dependence of cavitation intensity on the height of the Fig. 3 water column under the transducer (Bransonic B-l 2 cleaner, 46 kHz, 60 W, capacity 1 I). The cavitation intensity was measured as the quantity of iodine liberated from a 1 I aqueous solution of KI and CC14 in 20 min
108
2
3
4
5
Height of llquld column under transducer [X/Z] Maximum cavitation Intensities (at 46 kHz) of four liquids Fig. 4 as a function of height of the liquid column under the transducer: a ~- water; b ~ toluene; c - benzene; d ~ ethanol
ULTRASONICS.
MAY 1980
Table
1.
Comparison
of ultrasonic
cavitation
intensity
in various liquids
Maximum tation
cavi-
intensity
Temperature
Temperature
at which cavi-
which cavitation
reached from 70% to 100%
Boiling
for a X/2 liquid
tation
intensity
point
column
[“Cl
[%I
mum
100
100
35
20 -
50
146
74
37
24 -
53
3 Toluene
“20 C6’-‘5C2’-‘3 C6’-‘5C’-h
111
71
29
IO-40
4 Tetralin
(AoH
207
70
55
30-
C6HlOO
155
70
36
0 - 45 30 - 80
1 Water 2 Styrene
5 Cyclohexanone
[“Cl
maxi-
of the maximum
Chemical formula
Liquid
(46 kHz)
reaches
(column
C,HaON
128
65
50
C6H4
(CH312
137
64
26
C2H4
(OH),
197
61
93
75 -
120
141
59
49
38 -
70 23
glycol
9 Cyclopentanol IO
CaHaOH C2 HCI,
Trichloroethylene
11 Glycerine 12
C3H5
n-Amy1
acetate
(OH)3
CH3COOC5H,,
8 - 48
87
58
20
0 -
290
57
85
75 -
149
57
18
2 -
32 63
13 Tetrachloroethylene
G?CI4
121
56
42
33 -
14 n-Butyl
CHaCOOC4Ha
126
56
21
-2-27
acetate
105
15
Pyrrole
55
40
25 -
75
Methanol
C4HsN CHaOH
130
16
65
52
19
4 -
23
17
Chloroform
CHC13
61
50
-3
-II-
18
n-Amy1 alcohol
137
47
23
-32
-
46
19
Ethanol
CsHllOH C2H50H
78
46
21
20
Eth.yl acetate
CH3 COOC2 H5
77
45
9
21
Acetone
56
44
22
n-Butyl
(CH,),CO C4HaOH
23
Benzene
24
n-Propyl
25
1,1, 1 -Trichloroethane
26
Methylene
27
Methyl
28
Naphtha
29
Isopropyl
alcohol alcohol chloride
acetate alcohol
15
15-27 -5-50
-36
16 -
-20
118
43
32
IO-45
C6H6
80
43
19
IO-32
C3H70H
97
42
27
c2 H3Cl3
74
41
18
CH,CI,
40
38
CHaCOOCH3 -
57
38
242
38
35
(CHa12CHOH
82
38
16
0 - 30
8 - 44 -7
-
20
-40
-60
-
-25
-32
-40
-
-10
24 -
50
30
Formic
HCOOH
101
37
30
25 - 42
31
Tri-n-butylamine
(C4Ha)aN
214
37
31
15-38
32
Carbon
cc14
77
35
8
0 - 22
33
Cyclohexanol
C6hlOH
160
23
37
35 - 40
34
Propionic
C,H,COOH
141
22
32
35
Triethylamine
(CaHs)aN
89
21
1
36
Freon
113
CzClaF3
48
15
37
Freon
11462
C2Br2F4
47
6
8
38
Acetic
acid
CH,COOH
118
6
48
acid (85%) tetrachloride acid
The 37 organic liquids listed in Table 1 seem to constitute a number sufficient to state that although there is no explicit relation between the chemical structure of the liquid and its ability to undergo intense cavitation, some characteristic features of this structure may in many cases affect the cavitation intensity. It can easily be seen that liquids of cyclic structure are able to cavitate most intensely (as far as maximum cavitation in a h/2 layer is considered), for example, styrene, toluene, tetralin, morpholine, and xylene, but there are exceptions from that rule (cyclohexanol, benzene). The most weakly cavitating liquids are freons, carboxylic acids and aliphatic amines. For acetic acid esters with monohydric alcohols there can be noticed the following regularity: the longer the carbon chain of the alcohol the more intense the cavitation. But alcohols themselves do not exhibit this regularity: methanol cavitates most intensely and in second place is n-amyl alcohol. Naphtha, to which AS. Bebtschuk’
ULTRASONICS.
MAY
1980
-20
value
105
7 Xylene Ethylene
intensity
height X) [“Cl
6 Morpholine 8
range over
12-45 -12
-
14
-30
-
-5
-5
-18
20 - 60
attributed the ability to cavitate more intensely than other organic liquids, in comparable conditions exhibited a cavitation intensity below average. The problem of the temperatures at which maximum cavitation intensities have been observed should also be discussed briefly. It has been noted that the same liquid exhibits different temperatures of maximum cavitation intensities depending on the height of the column of liquid. Differences for multiples of X/2 are generally of a few degrees Celsius, yet a layer of height X/2 sometimes cavitates more intensely at temperatures greatly different from the temperatures of maximum cavitation for other heights. The data in Table 1 concerning the temperature ranges over which cavitation at the level of 70 - 100% of the maximum value has been observed apply only to the conditions of the present experiment and cannot be transferred to other heights of the column of liquid or other parameters of ultrasonic transducers.
109
Table
3.
Maximum
with ultrasound (water
cavitation
at frequencies
intensities
(h/2)
of liquids
of 46 and 22 kHz
= 100) Mci ~__-____
Liquid
46
____-__-~100
Water
2
4
3
6
5
kHz
---
kHz
22
100
Toluene
71
70
Trichloroethylene
58
58
Tetrachloroethvlene
56
57
Benzene
43
44
1, 1, 1 -Trichloroethane
41
41
Haght of liquid column under transducer [A/2] Fig. 5 Maximum cavitation intensities (at 46 kHz) of halogen solvents as a function of height of the liquid column under the transducer: a - methylene chloride; b - tetrachloroethylene; c - trichloroethy. lene; d - 1 ,l ,l -trichloroethane; e - Freon 11462; f - Freon 113
Table
2.
Comparison
of maximum
ten liquids for a liquid column
cavitation
height of 5h/2
intensities
of
(for 46 kHz)
Liquid .._ --_
Mci for 5hl2
Water
90
-~
Methylene
chloride
33
Tetrachloroethylene
27
Trichloroethylene
22
Toluene
17
1, 1,1-Trichloroethane
13
Benzene
10
Ethanol
6
while it is well known that ultrasonic cleaning in aqueous solutions can be performed with good effect at temperatures around 50 - 60°C. In the opinion of the author this can be explained as follows. The agents involved in ultrasonic cleaning are not only cavitation, but also liquid streaming due to radiation pressure of the ultrasound, and chemical activity from substances dissolved in the water such as acids, alkalis or detergents. The intensity of both these last agents increases with temperature, and this is why the total activity of all three agents may produce a stronger cleaning effect at 60°C than at 35°C. A similar explanation can be applied to the Freons, which according to the above results support only slight cavitation. Their cleaning power with ultrasound is caused by especially high radiation pressures; this depends inversely on the sound propagation velocity, which in Freons is very 10w.~ References I
Freon
11462
2
Freon
113
2
Nevertheless they give an indication about the temperature range over which most intense cavitation for a given liquid can be expected. A short comment also needs to be made on the fact that the maximum cavitation intensity of water occurs at 35”C,
110
2
3 4 5 6
7
Bebtschuk, A.S. /lk~rsr. Zh. 1 (1957) 91 Niemczewski, B., Proc XXII open bernmar on acouhtics (in Polish). KA PAN, Wroclaw-Swierad6w Zdrdj, vol. II (1975) 536 Shih-Ping Liu, J. ~icousr. Sot. A~rr. 38 ( 1965) 8 17 Niemczewski, B., Proc XV Intern Conf on A
21
ULTRASONICS.
MAY
1980