Development of a thermoelectric sensor for ultrasonic intensity measurement

ultrasonic intensity measurement M. Romdhane, C. Gourdon and G. Casamatta Ecole Nationale Supkrieured’lnghieursde G6nie ChimiquedeToulouse, Chemin de la loge, 31078 Toulouse Cedex, France Received

25 January

1994; revised 19 September

URA 192 CNRS,

1994

The design of ultrasonic reactors lies partly upon the description of the ultrasonic intensity space and time distribution. Among other techniques, the thermoelectric probe seems to be one of the most appropriate tools to measure the intensity available. It consists of a thermocouple embedded in an absorbing material (silicone). The modelling of the heat transfer allows the establishment of the relationship between the temperature signal response of the probe and the ultrasound intensity. It is shown that either the initial rate of temperature rise or the difference between the steady-state probe temperature and the medium temperature can be used. In addition, the measurements show the importance of the height and nature of the liquid sonicated on the ultrasonic intensity distribution. Keywords: thermoelectric transfer

probes; ultrasonic reactors; ultrasound intensity; heat

Ultrasonic cavitation is at the origin of the ultrasonic enhancement of the kinetics of chemical reactions and the yield improvement of the extraction process in solid-liquid systems’. The intensity of the cavitation is obviously linked to the local ultrasonic power, which affects the cavitation regimes (stable or unstable). Consequently, measurement of the ultrasonic intensity is required in order to design ultrasonic reactors. A great variety of methods for the measurement of ultrasonic power and cavitation have been listed in the literature’. For example, chemical dosimetry 3+4:the authors link the ultrasonic power to the activation of a chemical reaction like the oxydation of IL to I;. This method demonstrates the importance of the height of the solution sonicated; aluminium foil method: it was used by Sirotyuk5, Kukoz6, Poddubnyi’ and Pugin4. This method relies upon the observation of the foil erosion activity and the topology of the activation zone; elastic sphere radiometry: the displacement of solid spheres (stainless steel ball bearings) suspended freely in a plane progressive sound field is measured. This displacement is related to the ultrasonic intensitys”; calorimetric method: all the energy entering into the calorimeter is expected to be transformed into heat. The advantage of such a method lies in the possibility of its being used beyond or below the threshold of cavitation; specific probes: hydrophones can directly measure the sound pressure”, or sensitive probes, embedded in an ultrasound absorbing material, have been used in the past. 0041~624)3/95/$09.50$4 1995 - Elsevier Science B.V. All rights reserved SSD!OO41-624X(94)00019-0

In this latter case, the initial rate of change of temperature (dT/dt), (“C s- ‘) has been correlated to the ultrasonic intensity I (W cm-‘) (see References 11 and 12) by the following relationship

(1

pPCP dT P

dto

where p (gcme3) is the absorbing material density, C, (Jg-’ degg’C) the heat capacity per unit mass at constant pressure, and p (cm-‘) is the absorption coefficient of the embedding medium. On the other hand, Moritar3, Weberi4 and Martin” linked the equilibrium temperature T,,(C) to the ultrasonic intensity. A technique based on a thermocouple embedded in an absorbing material is attractive, because it allows a local measurement of the ultrasonic intensity and the experiments are simple and not time consuming. Besides, knowing I, it is also possible to derive the acoustic absorption coefficient p of various materials, if p and C, are known from elsewhere. In the present work, a thermocouple embedded in silicone has been used in order to measure the ultrasonic intensity distribution in various tanks16,’‘: in particular, in an ultrasonic cleaner in which reactors may be placed.

Equipment

The equipment considered consists of: l

an ultrasonic cleaner from Ultrasons-Annemasse (maximum acoustic power: P,,, = 160W; frequency: f = 26 x lo3 Hz; length = 32 cm; breadth = 23 cm;

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1995 Vol 33 No 2

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sensor

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intensity

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M. Romdhane

et al.

absorption of ultrasound as it is transmitted in the medium, while during the cooling step (t > t,), the decrease of the temperature in the absorbing material is caused by stopping the ultrasound emission.

Choice

of the absorbing

Different

absorbing

l l l l

7

A/D converter

Thermoco”ple

_I-

siliconel: RHODORSIL silicone2: RHODORSIL silicone3: RHODORSIL Uhu glue.

The measurement materials

Absorbing

I

Figure

1

Experimental

material

Uhu glue Silicone1 Silicone2 Silicone3

I

Rack

Ultrasonic emitters

RTV 132A and B; 3B (37211X); 3B (37203P);

A high ultrasound absorption coefficient p(, which guarantees a good sensitivity of the probe. Using the same position for the different absorbing materials in the ultrasonic cleaner, Table 1 shows that the different silicone materials lead to better results.

Table 1 absorbing

Rack gearing

have been investigated:

In order to compare the respective performances, the materials have to be geometrically identical (length L (cm), diameter D (cm), and depth C (cm)) (Figure 3). The main criteria in choosing an absorbing material are as follows. 1

V

materials

material

of

A\T and

(dT/dt),

of

AT = Teq ~ To (“C)

(dTld0,

3.0 11.0 10.1 10.6

1.0 6.3 4.9 5.1

different

1

(“C/s)

device

Temperature

depth = 20 cm; two

emitters

on

the bottom)

(“C)

(see

Figure I); l

a thermoelectric probe composed of a nickel chrome thermocouple (SPECITEC) protected by stainless steel (diameter = 0.05 cm; length = 50 cm). The thermocouple itself has an intrinsic response time of 25 x 10m3 s, which allows the acquisition of temperature every 0.1 s.

The thermocouple is mounted on a rack gearing, which allows accurate horizontal and vertical displacement (Figure 1). A second rack gearing permits a precise positioning of a reactor inside the ultrasonic cleaner

t

Time(s)

s

Figure

2

Response

of the thermoelectric

probe

(Figure I).

The increase of the temperature signal delivered by the sensor is real-time recorded and processed. The data acquisition system consists of an A/D converter and a PC computer. Appropriate software had been developed for the on-line temperature signal processing. In addition, a wattmeter has been used for measuring the power consumption (P,,,,(W)). The response of the thermoelectric probe is characterized by two important parameters (Figure 2): l l

the the T,, T,,

initial rate of change of temperature (dT/dt),; difference between the equilibrium temperature and the temperature of the medium T,(AT= - T,).

During the heating step (0 < r(s) < r,), the temperature increase of the absorbing material is linked to the

140

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1995

Vol 33 No 2

Thermocouple

Absorbing

=_

material

w

4 D

Figure

3

Thermoelectric

probe

-

Thermoelectric

sensor for ultrasonic

Table 2 The influence of the medium on the evolution weight and the size of the absorbing material

of the

Hexane

Ethanol

Distilled water

6.28 1.5 2.6

0.25 _ _

0 0 0

(silicone2) Am/m AD/D AL/L

1.81 1.12 2

0.01

0 0 0

(silicone3) Am/m ADfD AL/L

1.98 0.87 1.6

0.01

0 0 0

(silicone1 Am/m ADID AL/L

)

Am/m represents the relative increase of mass of the absorbing material (dimensionless) AD/D represents the relative increase of diameter of the absorbing material (dimensionless) AL/L represents the relative increase of length of the absorbing material (dimensionless)

2

3

4 5

A compromise had to be found concerning the different dimensions D, L and C (Figure 3). The size of the absorbing material has to be, on one hand, not too large - provided that it can allow a local measurement -and on the other hand not too small - in order to allow good and easy positioning of the thermocouple. In particular, the depth C reveals itself as a key parameter and will be discussed in a future publication. Many preliminary tests have been performed in order to satisfy the former qualitative assertions. Finally, silicone 3, with the following dimensions D = 0.4cm, L= 0.5 cm and C = 0.3 cm, has been selected. Sensitivity

of the thermoelectric

measurement:

M. Romdhane

0 -=ctime

< 30 s: the increase of temperature is the result of sonication during 30 s; 30 s < time < 60 s: the decrease of temperature is due to the ultrasound switching off.

l

It is clearly exhibited that the responses of the probe are identical (Figure 5). Consequently, the temperature Temperature

(“C) Maximum of ulrrasound emllted

*of_

Time 0

1000

zoo0

3000

4000

Figure 4 Influence of the frequency response of the thermoelectric probe

5000 (automatic

WOOs)

6000 mode)

on the

Temperature PC

Time I WOOS)

probe

An accurate probe has to detect any disturbance arising from a modification in the ultrasound power transmittance in the reactor. The probe has been placed at a given

et al.

distance from the transmitting surface of the ultrasonic probe, which is connected to an UNDATIM generator. This apparatus has the potential to operate under an ‘automatic mode’ which allows one to search for the optimal frequency, and so ensure a maximum power transmitted to the reactor. The response of the thermoelectric probe is shown in Figure 4, during the search for the optimal frequency. Indeed, a variation of 12°C temperature has been recorded in relation to a variation of 200 Hz. Moreover, it can detect the whole cycle of the search of the optimal frequency. It can be noticed that the temperature maximum is obtained for the optimal frequency, corresponding to the maximum ultrasound power transmitted. In addition, the influence of the initial temperature T, of the medium has been studied. Provided that, after a series of experiments, the variation of T, does not exceed 2 “C, some measurements of ultrasound power have been performed at different initial temperatures (20 “C < T, < 23 “C). The responses of the probe for two initial temperatures 20.4 “C and 22.6 “C are reported in Figure 5. l

Therefore, for the further investigations, only silicones have been tested. The properties of materials should not change during the immersion in the sonicated medium. The increases of mass Am (g) and of the dimensions of the probe (diameter AD (cm) and length AL (cm)) are measured after a given exposure time of the material in various solvents. The results are plotted in Tub/e2. Presumably, there is an absorption effect of the organic solvent by the silicone, which modifies the shape of the probe. Consequently, it is easy to conclude that distilled water is recommended as a reference medium for our experiments (Table 2). The surface of the material must not change. This means that the material has to be resistant to the mechanical action of ultrasound, particularly to the erosion due to cavitation. Silicone was sonicated for one hour in the ultrasonic cleaner filled with water, and then, the state of the surface was checked with a microscope. It seems that silicone is unchanged after 1 hour of ultrasound exposure. It must be easy to handle. There must be good reproducibility.

intensity

Figure 5 Influence of the initial rate of temperature of the medium, 7, on the response of thermoelectric probe

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Th~rrn~e~e~tri~ sensor for ultrasonic

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of the medium does not appear as a main parameter. In further experiments, the temperature will be fixed at around 21 “C.

Using Equation (6) we obtain

interpretation

When t --, 0, the initial rate of temperature will be written as follows

of the probe

response

Heat transfer modelling has been undertaken in order to interpret the probe response shapes. seating

step (Figure 2)

(7)

(8)

The general equation of heat transfer in the transient regime can be formally expressed as follows:

when t -+ infinity (in the stationary Equation (6) gives

E-S=A-G

T-To=TEY-To=g=K2

(1)

E: thermal energy flux entering the absorbing material s: thermal energy flux leaving the absorbing material = wi + W2+ w3 A: thermal energy rate accumulated in the absorbing material G: thermal energy flow generated in the absorbing material w*: heat ioss by radiation heat loss by conduction along the thermocouple wire W2: heat loss by convection through the surrounding w3: liquid phase = hA(T- T,) where h (J s- ’ cm-’ deg-‘C) is the heat transfer coefficient and A (cm’) is the area of the absorbing material

Using equations (8) and (9), Equation (6) will be written as

the radiation and conduction fluxes are neglected in comparison with the convection fluxes; h, p, C, and ~1are independent of the temperature; the temperature measured by the thermocouple is constant in different points of the absorbing material; T, (“C), temperature of the medium remains constant.

l l l

According to these assumptions, it is possible to derive that E=O S = w, = hA(T- T,) A = pi”, (dT/dt) where li (cm3) is the volume of the absorbing material G = /.0 Equation (1) can be rewritten

(10)

T-T,=K,jI-exp(-$t)j

Then, the ultrasonic intensity is reached either by using the initial rate of temperature (dT/dt),, where Equation (8) becomes

(11) or, by using the equilibrium temperature (9) becomes

It is assumed that: o

regime, T+ Teq),

I=

Z(T,- To)

Teq, Equation

(12)

From Equations (11) and (12) it is stated that the ultrasonic intensity I is directly proportional to the initial rate of temperature and to the difference between the equilibrium and initial temperature. We will study now the heat transfer in the absorbing material during the cooling step. Experimental Validation

study

of the heat transfer modet

Using Equations (8) and (9), we can note that the ratio of the initial rate of change of temperature (dT/dt),, identified by a least squares method over the difference between the equilibrium and initial temperature, is a constant value for a given experiment (Equation (13)) First validation.

dT = -hAT+

@AT, f /dV)

( dt, > (T,, - I’d

The solution of Equation (3) is (41

The boundary conditions are: at t = 0: T= T,, Equation (4) becomes (5) substituting Equation (5) in Equation (4)

T-

142

To=(g){1 -exp[

-($)“I)

Ultrasonics 1995 Vol 33 No 2

(6)

K, =-=K2

hA PCJ

(13)

According to this relationship, it would be interesting to check experimentally whether this ratio remains constant. (dT/dt), and (T,, - T,) have been measured in different locations inside the ultrasonic cleaner. In Figure 6 it is shown that there is a linear relationship between these two terms. This result seems to validate the relationship proposed in Equation (13). Moreover, the slope that gives the value of the ratio of Equation 13 has been derived from the experimental results plotted in Figure 6 and is equal to 0.5 s-l with a linear regression coefficient of 0.93. A, V and p being known, and C, estimated, it is then possible to derive h under ultrasonic conditions.

sensor for ultrasonic

Thermoelectric

intensity

measurement:

M. Romdhane

et al.

from the experimental values, and it is shown in Figure 7 that the theoretical curve fits the experimental one perfectly.

validation. The exponential growth (Equation (10)) derived from the heat transfer modelling is in good agreement with the exponential shape of the experimental temperature profile. Indeed, K, and K, are identified Second

Results and discussion (dTldt)0 I (“C/s)

Influence of the height and the nature of the liquid on the power consumption. Before measuring the distribution

70

1 60

of local ultrasound intensity, we intend to examine the influence of the height and nature of the liquid on the power consumption P,,,, (Watts). Figure 8 clearly shows the influence of both parameters, especially in the case of water. For example, for two heights of water (2cm and 3 cm), P,,,, is equal to 200 and 260 W respectively. In the same figure, we can also note that P,,,, is very sensitive to the nature of the liquid. Indeed, the following result is obtained

n

50 40 30 20 10 T

0

-T eq

0

20

40

60

80

100

0

(“C)

> PAwater) The characteristic acoustic impedance of the medium seems to be at the origin of this result. In Table 3, it is to the shown that P,,,, is inversely proportional characteristic acoustic impedance of the medium, in accordance with some earlier works2*18. Finally, it is important to remember that, in chemical processes assisted by ultrasound, the performance of one solvent in comparison with another is not only linked to its physicochemical and selectivity properties, but also to the actual ultrasound power transmitted.

120

Figure 6 initial rate of temperature (dT/dt), versus the difference between the equilibrium temperature and the temperature of the medium (AT= T,, - Te)

a Temperature

(“C)

P,,,,(hexane)

> P&acetone)

Ultrasonic

stationary

Influence

waves

of the water level

In this case, the influence of the distance H between the air/water interface and the ultrasonic emitter is investigated. Figure 9a shows the ultrasound intensity profiles measured along the central axis of the ultrasonic cleaner with H = 13 cm. The intensity profiles of resonating stationary waves have been observed at different levels,

b Temperature

> P&kerosene)

(“C)

140_

[-X 100 _

80_ 60_ 40_ 20 0

100:

I * 1 8 I c I 2 4 6 8

I ’ I I I aI 3 I I I 10 12 14 15 18 20

Time (s)

0

3

Characteristic

Temperatyre (‘C) ; ;!ysml, ) Z = p*C (kg masse’)

acoustic

impedance

of different

,

,

,

,

4

6

8

10

Heighr of the hquld above the UlIrasoniC enutters (cm)

Figure 8 Influence of the height and the nature of the liquid on the power consumption (ultrasonic cleaner; frequency = 26 kHz; temperature = 25 -C)

Figure 7 (a) Theoretical profile in comparison with the experimental profile (AT= 24.6’C); (b) theoretical profile in comparison with the experimental profile (AT = 97.3 “C)

Table

, 2

liquids

Water

Kerosene

Acetone

Hexane

25 1000 1500

34 1295 825

20 1192 792

25 1111 670

15.00 x 105

10.68 x 10s

9.44 X 105

I

7.44 x 10s

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Thermoelectric

sensor for ultrasonic intensity measurement:

a AT((“CJ 120

u/2

)

h/2

)

(dT/dt)O(“C/s)

h/2

, 60

80 _

- 40 ----c - 30

AT=Teq-To(‘C) (dT/dtJO(Ws)

60.

M. Romdhane

et al.

level of intensity has been recorded when the reactor is placed at a maximum (h, = 14 cm). Indeed, we think the main reason for this result depends on the whole distance h, (h3 = h, + hi). h, represents the distance separating the bottom of the ultrasonic cleaner and the air/water interface in the reactor, so that: h,=14cm,

h,=lOcm-h3=24cm=(2n+1)A/4

(n=8)

h, = 12.5 cm, h, = 10 cm + h, = 22.5 cm = d/2 20

.

0

.

.

.

,e...r

.. .

L.

(n = 8)

To

15 10 5 Distance probe I bottom of the ultrasonic cleaner (cm)

b Teq-To (“C) 100

__; Reactor3

: Reactor1 (flat bottom)

Reactor2 (COnVc?X

t3OltOmJ

(concave

tJOttOtIIJ

0 0

2

4

6

8

10

12

14

16

18

20

Figure

10

Different

reactors used in this study

Distance probe I bottom of the ultrasonic cleaner (cm)

Figure 9 Ultrasound intensity profile measured in an ultrasonic cleaner (frequency = 26 kHz) at various water levels: (a) 13 cm; (b) 16 cm. All profiles measured along the central axis of the cleaner

at a distance of A/2; with the wavelength in water (L) at f = 26 kHz being nearly equal to 5.6 cm. In the same figure, it is shown that the initial rate of change of temperature and the equilibrium temperature techniques lead to similar results. Compared with Figure 9b, in which H = 16cm, the positions of the maxima and minima remain constant. However, the intensity is more important, with the smaller value of H. This result can be explained by the fact that the value of H = 13 cm is close to (2n + 1)%/4 (see Reference 19), which is not the case with H = 16 cm. It is expected, that the intensity of the resonating waves decreases with distance from the bottom of the cleaner, where the emitters are placed. This means that there is a loss of intensity during the propagation. This phenomenon has been detected in the case of H = 16 cm, but reversed with H = 13 cm.

I

r-

(diffck?komsJ

Thermoelectrical probe

Ultrasonic cleaner

Emitters

Figure 11 f= 26kHz)

Experimental

device of protocol

1 (ultrasonic

cleaner:

Teq-To (“C) 120 ~

100 _

Reactor

flask in an ultrasonic

cleaner

The objective of the present work is to measure the intensity profiles in different glass reactors, with various shaped bottoms (Figure IO). Protocol

1 (Figure

Ultrasonics

60 _

11)

The reactor has been fixed on the central axis of the ultrasonic cleaner. The water levels in the reactor and ultrasonic cleaner are, respectively, 10 cm and 17 cm. The two distances, separating the radiating surface from the bottom of the reactor, have been chosen as 12.5 cm and 14 cm. These distances correspond respectively to the location of a minimum and a maximum of the ultrasonic intensity (Figures 9a and 96). With the first reactor, Figure 12 shows that a higher

144

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40

20

I 2

0

I 4

Distance probe/reactor-bottom

Figure

12

intensity

1 6

I 8

I 10

(cm)

profiles measured in a flat reactor fixed in the

central axis of an ultrasonic cleaner (f= 26 kHz). separating the radiating surface from the bottom 0 h, = 12.5cm; n h, = 14cm

Two distances of the reactor:

Thermoelectric

sensor for ultrasonic

intensity

measurement:

et al.

/VI Romdhane

easy to make conclusions on the ~rforman~e of the respective reactors according to the wave propagation, because even if the flat bottomed reactor gives a greater intensity in the first half of the reactor, the opposite has been produced in the second half. (dT/dt& (‘C/S)

‘,-‘b(“c) 100

80

0; 0

I

I

I

I

I

2

4

6

8

10

Distance probe/reactor

bottom

60

20

40

_20

(cm)

20

Figure 13 intensity profiles measured in different reactors ([? flat bottom; w convex bottom) fixed in the central axis of the ultrasonic cleaner (f= 26 kHz). Distance separating the reactor from the bottom of the ultrasonic cleaner h, = 14 cm

_I0

~

c

O6

4

IO

8

14

12

Distance probe f ultrasonic cleaner bottom (cm)

Comparing the results obtained with the different geometries (Figure 13), it appears that the intensity transmitted in the case of a flat bottom is more important than that obtained with a hemispherical bottom. The same resuit has been found by Weber14. This result can be explained by the fact that a part of the waves generated has been reflected from the hemispherical bottom (reactor2). Moreover, it is possible that another part of the waves generated along the central axis of the ultrasonic cleaner has not been transmitted along the central axis of the reactor, but somewhere else in the reactor. Figures 12 and 13 show several peaks. But compared with the intensity profiles in the ultrasonic cleaner, the distance separating two consecutive maxima peaks was often not identical and was larger than A/2, especially when the reactor was placed at h, = 14 cm. The distance h, may be at the origin of these disagreements. Then, experiments have been performed (protocol 2) with h, = 0 in order to explain the previous phenomena. Protocol

2

As in protocol 1, the reactor has been fixed at the central axis of the ultrasonic cleaner, the water level being fixed equal to 13 cm, but h, = 0. For reactorl, three heights h, have been chosen, respectively 6, 7.5 and 10 cm, but only one height (hi = 7.5 cm) for reactor2 and reactor3. For all the experiments, the initial rate of change of tem~rature and the equiIibrium temperature techniques lead to the same intensity profiles. Figure 14 has been chosen as an example to illustrate these results. If we superimpose the intensity profiles in an ultrasonic cleaner with those obtained with a flat bottomed-reactor at different heights (h,), the intensity of stationary waves is observed. Furthermore, the minima and maxima remain at the same positions (Figure 15), but with a lower intensity. This result proves that the part of the waves generated on the central axis of the ultrasonic cleaner has been reflected from the different reactor bottoms. The same result has been found with reactor2 and reactor3. For h, = 7.5 cm, in Figure 16, the intensity profiles measured in the different reactors are compared. It is not

Figure 14 intensity profile measured in a flat bottomed reactor fixed in the central axis of the ultrasonic cleaner (f = 26 kHz; water level N = 13 cm; distance of the reactor from the bottom of the ultrasonic cleaner h, = 6 cm)

01 I

m

*

t

’

0

II

’

’

5

r

18

u

*

‘1

10

I5

Distance probe/ultrasonic cleaner-bottom (cm)

Figure 15 Intensity profile in an ultrasonic cleaner (U) in comparison with those measured in a flat reactor. The reactor is fixed at different distances (a: h, = 6 cm; @: h, = 75cm; 0: h, = 10 cm) from the bottom of the ultrasonic cleaner (f = 26 kHz; water level H = 13 cm)

100

80

60

40

20

0 I

7

’

I

*

I-

I

8 9 IO 11 Distance probe I ultrasonic cleaner bottom (cm)

’

f

12

t

I

13

Figure 76 intensity profiles measured in different reactors (m flat bottom; •J convex bottom; l concave bottom) fixed in the central axis of the ultrasonic cleaner (f = 26 kHz; distance of the reactor from ultrasonic bottom h, = 7.5 cm; water level H = 13 cm)

Ultrasonics 1995 Vol 33 No 2

145

Thermoelectric

sensor

for ultrasonic

intensity

measurement:

Conclusions

5

The present work has focussed on the development of a measurement technique for determining the intensity profiles of ultrasound in different reactors. Silicone3 has revealed itself as the more appropriate absorbing material for a thermoelectric probe of the following dimensions (D = 0.4 cm, L= 0.5 cm and C = 0.3 cm). A heat transfer model has been developed, and the theoretical response of the probe has been shown to be in good agreement with the experimental results. The thermoelectric probe developed allows the measurement of the ultrasound intensity either by means of: the initial rate of change of temperature (dT/dt),; or by the difference between the equilibrium temperature T,, and the temperature of the medium (AT= T,, - 7-J.

l l

M. Romdhane

Furthermore, measurements reported in this paper show the influence of the height and nature of the sonicated liquid on the power consumption, which is strongly linked to the power emitted. Moreover, we have distinguished the influence of the reactor shapes from the reflected ultrasound.

6

I

8 9

10 11

12

13 14

15

16

References I 2

3

4

146

Romdhane, M., Haunold, C., Gourdon, C. and Casamatta, G. R&nrs Pro&s en Gdnie Des Procbdhs C’ompiPyne (1991) 5 233-238 Saksena, T.K. Methods of reliable measurement of ultrasonic power and cavitation in liquids J Acoust Sot India (1980) VIII I January Suslick, KS., Schubert, P.F. and Goodale, J.W. Chemical dosimetry of ultrasonic cavitation Proc IEEE Ultramic .S!,ntp (1981) 612-616 Pugin, B. Qualitative characterization of ultrasound reactors for

Ultrasonics

1995

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17

18 19

et al.

heterogeneous sonochemistry Ultrusonics (1987) 25 49-55 Sirotyuk, M.G. Effect of the temperature and gas content of the liquid on cavitation processes Sov Ph.w Acoust (1966) 12 199 Kukoz. FL Poddubnvi. B.N. and Charenskava. E.G. Aluminium foil for iniestigation ‘of the energy parameters and spatial distribution of an ultrasonic cavitation field Proc Sis/h All-uniorr Acoustics Conf (1969) Moskow-D 17 Poddubnyi, B.N. Improvement of erosion-test methods based on aluminium foil damage and on sample weight loss Sol; Phys Acousi (1976) 22 325-321 Hasegawa, T. Acoustic radiation force on a solid elastic sphere J Acoust Sot Am (1969) 1139-1143 Dunn, F., Averbuch, A.J. and O’Brien, W.D. A primary method for determination of ultrasonic intensity with the elastic sphere radiometer Acustica (1977) 38 58-61 Shombert, D.G., Smith, S.W. and Harris, G.R. Angular response ofminiatureultrasonic hydrophones MedPh~s(1982)9484492 Fry, W.J. and Fry, R.B. Determination of absolute sound levels and acoustic absorption coefficients by thermocouple probes -Theorv J Acoust Sot Am (1954) 26 294310 Fry, W.J. and Fry, R.B. Determination of absolute sound levels and acoustic absorption coefficients by thermocouple probes Experiment J Acous~ Sot Am (1954) 26 311-317 Morita, S. Sonde method of measuring ultrasonic field intensity J Sot ofJapm (1952) 7 214-219 Weber, M.E. and Chon, W.Y. Distribution of Ultrasonic Cavitation Intensities in a Liquid System The Cunudim J Chem Dug (1967) 45 238-240 Martin, C.J. and Law, A.N.R. The use of thermistor probes to measure energy distribution in ultrasound field Ultrasonics (1980) 18 127-133 Romdhane, M., Gourdon, C. and Casamatta, G. Thermosensitive probe based technique of local investigation of ultrasonic reactors Ultrasonics International 93 Conjbrence Proceedings (1993) 139-142 Romdhane, M., Gourdon, C. and Casamatta, G. Development of measuring techniques of ultrasonic power distribution and consumption in an ultrasonic cleaner (1993) European Society of Sonochemistry, 3rd meeting-Figueira da foz, Portugal 28 March-l April (1993) Mikhailov, I.G. and Shutilov, V.A. On the absolute measurement of ultrasonic fields in solids Sor Ph.vs Acousr (1964) IO 77-80 Franklyn, A., Timmerhaus, D. and Fogler, S. Effect of resonance parameter on chemical reaction subjected to ultrasonic wave AlChE (1967) 13 453456