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Ultrasonic velocity measurements on some liquids under thermal cycle: Ultrasonic velocity hysteresis
Food Research International 39 (2006) 1076–1083 www.elsevier.com/locate/foodres
Ultrasonic velocity measurements on some liquids under thermal cycle: Ultrasonic velocity hysteresis Ali Bulent Koc b
a,* ,
Mustafa Vatandas
b
a Department of Agricultural Machinery, Faculty of Agriculture, Harran University, Sanliurfa, Turkey Department of Agricultural Machinery, Faculty of Agriculture, Ankara University, 06110 Dıskapı-Ankara, Turkey
Received 26 May 2006; accepted 6 September 2006
Abstract This study was performed to determine the existence of hysteresis during ultrasonic velocity measurements on methanol, ethanol, distilled water, processed water and glycerol under thermal cycle (5–50 C). The ultrasonic velocity of the liquids were measured with 1.0 MHz transducers using a through transmission ultrasonic system. Statistical analyses results showed that there were ultrasonic velocity hystereses on the liquid samples under thermal cycle. The study of liquids undergoing thermal cycle is useful for determining the temperature effects on ultrasonic velocity and will help developing precise control applications in food industry by reducing the uncertainties in ultrasonic velocity measurements. 2006 Elsevier Ltd. All rights reserved. Keywords: Ultrasonic velocity; Hysteresis; Water; Methanol; Ethanol; Glycerol
1. Introduction Thermal processing is one of the most important food processing technologies, which involves heating and cooling treatments of food to destroy any harmful bacteria or organisms and to develop textures, flavor and color. Lack of heating or cooling would result in inappropriate pasteurization, sterilization, cooking, freezing, texture, flavor or color. Therefore, it is important to know the measurement uncertainties to develop a precise measurement system for heat treatment operations in food quality control. During heating and cooling operations, especially where there is a phase change, the measurement system would act differently. The system’s reaction to a certain temperature during heating would be different at the same temperature during cooling. This kind of behavior would indicate a hys* Corresponding author. Present address: Department of Agricultural Machinery, Faculty of Agriculture, Ankara University, 06110 DıskapıAnkara, Turkey. Tel.: +90 536 2328791; fax: +90 312 3183888. E-mail address: [email protected] (A.B. Koc).
0963-9969/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2006.09.004
teresis in the system. The word hysteresis is of the Greek origin and means ‘shortcoming’. In other words, it is a delay in the system’s reaction when the forces acting on a system are changed. Hysteresis indicates that the response of a system under external influence is not only dependent on the magnitude of the influence, but also on the history of the system. Due to this phenomenon, nonlinearities occur in system behavior. In physics and engineering, hysteresis is the difference between the conditions to start and stop an action. Common sources of hysteresis in physical systems are usually mechanical or electrical. In mechanical systems, hysteresis is a measure of deformation energy. The deformation energy can not be stored but turns into heat. Because of this energy conversion, usually a hysteresis loss is mentioned in some systems. Hysteresis loops occur when the system is exposed to a cycle (i.e. cooling action following a heating action). In measurement systems, errors or uncertainties due to hysteresis are usually calculated as (Dunn, 2005): y up y down eH ¼ ð1Þ FSO
A.B. Koc, M. Vatandas / Food Research International 39 (2006) 1076–1083
where eH yup ydown FSO
hysteresis error, output value that occurs when performing an upscale, output value that occurs when performing a downscale, full-scale output.
In the literature, it is reported that a nonlinear thermal hysteresis was observed due to thermal cycling while ultrasound energy propagated through lithium niobate with ferroelectric crystalline structure (Breazeale, Ostrovskii, & McPherson, 2004). The physical mechanism which had an impact on this situation is called ‘acoustic memory’. It was observed that these physical mechanisms, even though they were not explained well, depended on the frequency and temperature. Experiment results indicated that there was a nonlinear difference in the ultrasonic attenuation values between increasing and decreasing temperatures due to the acoustic memory effects. Typical thermal hysteresis characteristics were observed in the ultrasonic velocity values measured during the cascade heating and cooling cycle of palm oil in oil–water emulsion (Hodate et al., 1997). Technological developments allowed the manufacturing of general and special purpose ultrasonic transducers. These transducers increased the use of low intensity nondestructive ultrasonic test techniques in food industry. Low intensity ultrasound has less than 1 W/cm2 power levels (McClements, 1997; Villamiel, Van Hamersveld, & De Jong, 1999). Low intensity ultrasonic applications do not cause alteration in the physical or chemical properties of materials, do not change the temperature and could be used for monitoring purposes only. Once the ultrasound is removed, the material takes its original shape and no change occurs in the structure. The frequency range of low intensity ultrasound is between 100 kHz and 20 MHz. Ultrasonic velocity and attenuation coefficient are the most commonly measured parameters in low intensity ultrasound applications. During the last decade, several ultrasonic test techniques for different materials are presented in the literature. Some of these applications include determining fish composition (Ghaedian, Coupland, Decker, & McClements, 1998) chicken composition (Chanamai & McClements, 1999), dried fermented sausage composition (Benedito, Carcel, Glemenete, & Mulet, 2001), and fatty tissue and musclefatty tissue compositions (Miles & Fursey, 1977). To determine the water, oil and other solids in oil waste Benedito, Mulet, Clemente, and Garcia-Perez (2004) measured the ultrasonic velocity in water, oil and oil waste separately between 6 C and 50 C. Saggin and Coupland (2001) employed an ultrasonic non-contact air-coupled transducer to measure the thickness of some food products using ultrasonic velocity. Another study for determining the physical properties of cheddar cheese using air-coupled transducers was conducted by Cho, Irudayaraj, and Bhardwaj (2001).
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Resa, Elvira, and Espinosa (2004) conducted ultrasonic velocity measurements on some carbohydrate aqueous solution mixtures of glucose–water, fructose–water, sucrose–water and ethanol–water to monitor the changes during alcoholic fermentation in-line. Gestrelius, Hertz, Nuamu, Person, and Lindstrom (1993) worked on monitoring the microbial activity in milk containers using non-destructive acoustic streaming method. Miles, Shore, and Langley (1990) determined the ultrasonic attenuation coefficient in milk. It was reported that one of the important factors affecting the ultrasonic attenuation was the distribution of fat globules in milk, which is an indication of the degree of homogenization. Ultrasonic technology was also applied to monitor the crystallization and to determine the solid fat content of edible fats on-line by Martini, Bertoli, Herrera, Neeson, and Marangoni (2005a, 2005b) Martini, Herrera, and Marangoni (2005c). The purpose of this research was to measure the ultrasonic velocity on some liquids (distilled water, processed water, ethanol, methanol and glycerol) during heating and cooling applied in bioprocesses and food processes and to determine thermal hysteresis ultrasonically. The result of this research would have two benefits. First, thermal hysteresis must be considered when ultrasound is used in food processes for reliable and precise measurements. Second, measuring thermal hysteresis will be beneficial for developing new technologies for food quality monitoring. 2. Materials and methods 2.1. Materials The liquids used in this research were distilled water (DW), processed water (PW), ethanol (E), methanol (M) and glycerol (G). Among these liquids, distilled water was produced by distillation processes in a laboratory and processed water (Turkuaz, Coca Cola Ic¸ecek A.S., Istanbul, Turkey) was purchased from a local market. Methanol (Birpa Ltd. Sti., Ankara, Turkey), ethanol (Best Kimyasallari, Ankara, Turkey) and glycerol (Emir Kimya, Ankara, Turkey) were purchased from a dealer. Some properties and purity levels of these liquids are shown in Table 1. These liquids were stored in a refrigerator at 4 C until the experiment day. For each experiment, 250 ml liquid were placed in the measurement cell and the experiments were started around 5 C. The specific densities of the liquids were measured by measuring the weight of 100 ml liquid using a balance with 1/100 g sensitivity at the temperature indicated in Table 1. 2.2. Measurement cell The measurement cell was fabricated from Plexiglass material with 6 mm thickness. The dimensions of the cell were 69.3 · 60.6 · 70.4 mm. The transducers were mounted to the measurement cell as shown in Fig. 1. The distance
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A.B. Koc, M. Vatandas / Food Research International 39 (2006) 1076–1083
Table 1 Some properties of experimental liquids
2
Volume weight (g/cm3)
Molar weight (g/mol)
Distilled water Processed water Methanol (CH3OH) (purity > 95%) Ethanol (C2H5OH) (purity > 96%) Glycerol (C3H8O3) (purity > 96%)
1.00 (20.0 C) 1.00 (20.0 C) 0.79 (20.0 C)
18.00 18.00 32.04
0.75 (13.5 C)
46.07
1.26 (20.0 C)
92.10
1
Amplitude (V)..
Material
0
U2
U0
-1
U3
-2
t
U1
-3 0
5
10
15
20
25
30
35
40
Time (10-5 s)
Fig. 2. A typical ultrasonic waveform on oscilloscope screen (t: Time, U0: Original pulse, U1: Amplitude of the transmitted pulse, U2: Amplitude of the reflected pulse of U1, U3: Amplitude of the reflected pulse of U2).
monitored on oscilloscope screen. A typical waveform is shown in Fig. 2. The through transmission mode was used and the ultrasonic velocities were measured using Eq. (2) d ¼vt
Fig. 1. Ultrasonic measurement system (GPIB: general purpose interface bus, T: transmitter, R: receiver, DTC: digital thermocouple).
between the active surfaces of the transducers was 61.8 mm. The upper side of the cubic measurement cell was left open to the atmosphere and the liquids were filled from this side. The measurement cell was placed in a water bath of 30 l. 2.3. Ultrasonic velocity measurement system Ultrasonic velocity was measured using two broadband immersion type ultrasonic transducers (1 MHz, 38 mm crystal diameter, V392 model, Panametrics, Waltham, MA, USA). An ultrasonic pulser/receiver was used to drive the transducers (Panametrics, 500 PR, Waltham, USA). The pulser/receiver can be used in both pulse-echo and through transmission modes. The frequency of the pulses, noise control and gain factors could be adjusted on the pulser/receiver. The transmitted and received signals were monitored on a two-channel digital storage oscilloscope (Tektronix, TDS 3032, Tektronix Inc, Wilsonville, OR, USA). The oscilloscope was connected to a personal computer with general purpose interface bus (GPIB). Experimental data were recorded and analyzed with a program written in G-programming language (Labview 6.1, National Instruments, Mopac Expwy, Austin, TX, USA). To minimize noise error, 512 pulses were averaged and
ð2Þ
Where, d is the distance (m) between the transducers; v is the ultrasonic velocity (m/s); t is time (s). Ultrasonic wave’s time of flight can be measured from the waveforms on the oscilloscope screen. In this study, ultrasonic velocities were calculated from the known distance and measured time of flight automatically with the computer program. Each measurement took about 3 s. The ultrasonic velocity was calculated from the minimum magnitude of U1 and velocity change with temperature was displayed on the computer screen in real time and recorded to a file. Alternatively, the change of ultrasonic velocity with temperature is also calculated from Eq. (3) dv v2 v1 ¼ dT T 2 T 1
ð3Þ
Where, (v2 v1) is the difference between the two ultrasonic velocities measured at temperatures of T1 and T2. 2.4. Experimental The room temperature, relative humidity and atmospheric pressure were measured and recorded before the experiments were started. During heating, water at 75 C was circulated around the measurement cell until the temperature of the liquid in the cell increased to 50 C. During cooling, water at 3 C was circulated around the measurement cell until the temperature of the liquid in the cell dropped to 5 C. The temperature of the liquid in measurement cell was measured with a digital thermometer (0.1 C sensitivity). The measurements were taken 2.5 C intervals. After each measurement, the program was paused until the liquid temperature reached to the next level. Ultrasonic velocity measurements on test liquids during heating and
A.B. Koc, M. Vatandas / Food Research International 39 (2006) 1076–1083
cooling cycle were replicated twice for each liquid and the averages were used to conduct the statistical analyses. 2.5. Statistical analysis Regression analyses were conducted on the ultrasonic velocities for the same temperature levels measured while heating and cooling and the relationship between the temperature and ultrasonic velocity were evaluated. The significance of the differences between the ultrasonic velocities measured during heating and cooling for the same liquid using Wilcoxon Signed Ranks Method. Mann-Whitney Test Method was used for comparison of the ultrasonic velocities measured under thermal cycle on different liquids (Sumbuloglu & Sumbuloglu, 2002). 3. Results and discussion In this research, ultrasonic velocities were measured for different liquids under thermal cycle to determine the existence of ultrasonic velocity hysteresis. For this purpose, the liquids were exposed to heating from 5 C to 50 C. Following heating the liquids were cooled down to 5 C. At each temperature level, the ultrasonic velocity of a liquid measured during cooling was different than the ultrasonic velocity measured during heating. It was same for all of the liquids. For all the liquids except glycerol, the ultrasonic velocities measured during heating were lower than cooling. The hypothesis of no difference in ultrasonic velocities during heating and cooling cycle for the same liquid was tested. The statistical test results show that ultrasonic velocities measured during heating and cooling are significantly different for the same liquid (p < 0.05). These differences indicate the existence of ultrasonic velocity hysteresis between the ultrasonic velocities measured at the same temperature during heating and cooling. The analyses of the ultrasonic velocity–temperature graph for the test liquids under heating and cooling cycle show that one ultrasonic velocity value was measured at two different temperatures for the same liquid. One ultrasonic velocity value at two different temperatures for the same liquid shows the hysteric behavior of the liquid under heating and cooling cycle. For distilled water and processed water, the ultrasonic velocities
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measured at two subsequent temperatures were significantly different during heating or cooling cycle and these differences were not the same for all temperatures. The varying differences represent the nonlinear relationship between ultrasonic velocity and temperature for distilled and processed waters. However, for ethanol, methanol and glycerol, the change in ultrasonic velocities measured at two subsequent temperatures was consistent because of the linear relationship between temperature and ultrasonic velocity. Statistical analysis results for the comparison of ultrasonic velocity values measured during heating and cooling of different liquids are shown in Table 2. The table shows the ultrasonic velocities of distilled water compared with the other liquids and also the comparison results of methanol and ethanol. These comparisons were conducted to possibly distinguish the type of test liquids with ultrasonic velocity measurements at different cycles. Ultrasonic velocities for different liquids under the same thermal cycle were significant (p < 0.05). When distilled water velocity values were compared with processed water values, the velocities measured during the cooling cycle were significantly different (p < 0.05). When methanol was compared with ethanol, the ultrasonic velocities were significantly different during heating cycle (p < 0.05). These results indicated that ultrasonic velocity measurements under either heating or cooling cycles could be used for qualitative identification of these test liquids. Ultrasonic velocity measurements of distilled water during heating and cooling are shown in Fig. 3a. Velocities measured during heating increased with the increasing temperature, but the rate of increase in velocity decreased as the temperature continued to increase. Similar results were reported by Benedito et al. (2004) and Ghaedian et al. (1998). The increase in ultrasonic velocity with increasing temperature was not linear (Fig. 4a). The rate of increase in ultrasonic velocity measured for distilled water reached a maximum during the heating cycle at the temperature of 22.5 C and during the cooling cycle at the temperature of 27.5 C. Ultrasonic velocity in distilled water increased with temperature up to 20 C positively, but the rate of velocity increase became smaller over 22.5 C. Similarly, the ultrasonic velocity change with temperature was not linear during cooling. Ultrasonic velocity change with
Table 2 Statistical analysis results for comparing the ultrasonic velocities of the liquids under the same cycles Liquid
Distilled water Processed water Ethanol Methanol
Cycle
Heating Cooling Heating Cooling Heating Cooling Heating Cooling
Significance level (p) Processed water
Methanol
Heating
Heating
Cooling
0.081
Ethanol Cooling
0.000 0.020
Heating
Glycerol Cooling
0.000 0.000
0.000
Heating 0.000
0.000 0.000
0.000
Cooling 0.000
0.000 0.000
0.000 0.000 0.000
0.000
0.000 0.370
0.000
1080
A.B. Koc, M. Vatandas / Food Research International 39 (2006) 1076–1083 1560
a
Heating Cooling
b 1560
1540
Heating Cooling
1540
1520 Ultrasonic velocity (m/s)
Ultrasonic velocity (m/s)
1520 1500 1480 1460
1500
1480
1460
1440
1440
1420 1400 5
10
15
20
25
30
35
40
45
1420
50
5
10
15
20
25
Temperature (°C)
c
d
1300
Heating
Cooling
35
40
45
50
1320
Heating
1280
Ultrasonic velocity (m/s)
1250
Ultrasonic velocity (m/s)
30
Temperature (°C)
1200
1150
1100
Cooling
1240
1200
1160
1120
1080
1050
0 5
10
15
20
25
30
35
40
45
10
50
Temperature (°C)
e
30
40
50
1980
Heating
1960
Ultrasonic velocity (m/s)
20
Temperature (°C)
Cooling
1940 1920 1900 1880 1860 1840 5
10
15
20
25
30
35
40
45
50
Temperature (°C)
Fig. 3. Ultrasonic velocity change with temperature during heating and cooling of test liquids under thermal cycle. (a) Distilled water, (b) processed water, (c) methanol, (d) ethanol and (e) glycerol. Average room temperature was 18 C, average relative humidity was 42% and average atmospheric pressure was 985 mbar during the tests. Error bars show the standard error of the ultrasonic velocity estimation.
temperature during heating was reciprocal to the cooling for distilled water. Ultrasonic velocity measurements of processed water during heating and cooling at different temperatures are
shown in Fig. 3b. As with the ultrasonic measurements of distilled water, for the same temperature level, the velocities measured during heating were lower than the velocities measured during cooling. Fig. 4b shows the rate
A.B. Koc, M. Vatandas / Food Research International 39 (2006) 1076–1083
a
14
b
12
dv/dT (heating)
4.5
dv/dT (cooling)
4.0
10
dv/dT (heating) dv/dT (cooling)
3.5
dv/dT (m/ s/°C)..
dv/dT (m/ s/°C)
1081
8
6
4
3.0 2.5 2.0 1.5 1.0
2 0.5 0.0
0 0
10
20
30
40
0
50
10
20
c
d
0
50
dv/dT (Heating) dv/dT (Cooling)
-2.4
dv/dT (m/s/ °C)
-1
dv/dT (m/ s/°C)
40
-2 -2.2
dv/dT (heating) dv/dT (cooling)
-0.5
30
Temperature (°C)
Temperature (°C)
-1.5 -2 -2.5
-2.6 -2.8 -3 -3.2 -3.4
-3
-3.6 -3.5
-3.8
-4
-4 0
10
20
30
40
50
0
10
e
30
40
50
-1.7
dv/dT (heating) dv/dT (cooling)
-1.8 -1.9
dv/dT (m/ s/°C)
20
Temperature (°C)
Sicakhk (°C)
-2 -2.1 -2.2 -2.3 -2.4 -2.5 0
10
20
30
40
50
Temperature (°C)
Fig. 4. The rate of velocity change over temperature change during heating and cooling of (a) distilled water, (b) processed water, (c) methanol, (d) ethanol and (e) glycerol.
of ultrasonic velocity over temperature change with temperature. Ultrasonic velocity change with temperature for processed water during heating was similar to cooling. The largest difference in ultrasonic velocities from the third degree polynomial during heating and cooling was measured at 10 C. The rate of ultrasonic velocity change with temperature during heating and cooling was equal at 22.5 C (Fig. 4b). During the ultrasonic velocity measurements on distilled and processed waters air bubbles formed on transducers’ surfaces and measurement cell walls while heating at above
10 C. The number and the size of the bubbles increased with the increasing temperature. Although some of the air bubbles ascended to the surface of the water with the increasing temperature, most stayed intact with the transducer surfaces. The size of the bubbles reduced during cooling, but never disappeared, even when cooling down to the starting temperature. We think that the reason for bubble formation was due to the dissolved gases in water. Initially, the gas bubbles were too small to be recognized but with heating, the number and the sizes of the bubbles increased. We think that the amount of dissolved gasses in processed water is smaller than in distilled water.
A.B. Koc, M. Vatandas / Food Research International 39 (2006) 1076–1083
Distilled water is produced by distillation whereas the processed water is produced by reverse osmosis. It is believed that the differences in the production of distilled and processed water affected the ultrasonic wave propagation. Similar heating and cooling processes were applied to methanol, ethanol and glycerol and ultrasonic velocities were measured. Unlike distilled and processed water, as the temperature increased, the ultrasonic velocities on these three alcohols decreased linearly. Fig. 3c shows the ultrasonic velocity change with temperature for methanol during heating and cooling. Ultrasonic velocity on methanol decreased with increasing temperature and increased with decreasing temperature. The largest difference (73.2 m/s) in ultrasonic velocity during heating and cooling was measured at 7.5 C. The rate of ultrasonic velocity over the temperature change with temperature for methanol is shown in Fig. 4c. The rates of ultrasonic velocity change over temperature change were 2.75 m/s/C during heating and 3.52 m/s/C during cooling. That is, 1 C increase in temperature resulted in 2.75 m/s decrease in the ultrasonic velocity. In a similar way, 1 C decrease in temperature resulted in 3.52 m/s increase in the ultrasonic velocity. Ultrasonic velocity change with temperature for ethanol exposed to heating and cooling is shown in Fig. 3d. The differences in ultrasonic velocities during heating and cooling were less than the differences observed for methanol. The maximum measured difference was 14.7 m/s and observed at 5 C. The rates of ultrasonic velocity change over temperature with temperature for ethanol is shown in Fig. 4d. For 1 C increase in temperature the ultrasonic velocity of ethanol decreased 3.14 m/s and a 1 C decrease in temperature during cooling increased the ultrasonic velocity 3.44 m/s. The graph showing ultrasonic velocity change with temperature for glycerol is different than the graphs for methanol and ethanol (Fig. 3e). Unlike methanol, ethanol, and distilled and processed waters, the ultrasonic velocities of glycerol measured at a certain temperature during heating were greater than the ultrasonic velocities measured during cooling. The reason for the difference is that an inverse relationship exists between the ultrasonic velocity of a material and the material’s density and compressibility, as shown in Eq. (4) (Hykes, Hedrick, & Starchman, 1992). 1 c ¼ pffiffiffiffiffiffiffiffiffiffi bq
ð4Þ
where, c is the ultrasound velocity (m/s), q is the density of the medium (kg/m3) and b is the compressibility of the medium, which is the reciprocal of the elastic modulus (N/m2). Eq. (4) indicates that as density decreases, the speed of sound increases. However, because compressibility is highly affected by density, a small increase in density creates a large decrease in compressibility. Compressibility becomes a more dominant factor than density, so the ultrasound velocity of a substance increases with increasing density (Hykes et al., 1992).
7
DW ME
6
PW ET
GL
5 Hysteresis (%)
1082
4 3 2 1 0 5
10
15
20
25 30 Temperature (°C)
35
40
45
50
Fig. 5. Ultrasonic velocity hysteresis of liquids under test change with temperature during thermal cycle (DW: distilled water, PW: processed water, GL: glycerol, ME: methanol, ET: ethanol).
Compared with the other liquids, glycerol has higher density and its melting temperature is 17.8 C. Glycerol at below melting temperature has a syrup-like gel structure and is a highly hygroscopic substance. Since the upper surface of glycerol was in contact with air, glycerol may have absorbed some moisture from the air. Glycerol also showed phase changes during heating and cooling. Similar to methanol and ethanol, as the temperature was increased, the ultrasonic velocity decreased. For 1 C increase in temperature of glycerol, ultrasonic velocity decreased 3.17 m/s and for 1 C decrease in temperature, the ultrasonic velocity increased 2.4 m/s (Fig. 4e). For all of the liquids tested, ultrasonic velocity hysteresis was calculated using Eq. (1) and the ultrasonic velocity hysteresis change with temperature is shown in Fig. 5. Among these liquids, methanol had the greatest ultrasonic velocity hysteresis. The ultrasonic velocity hysteresis of distilled and processed water showed a nonlinear change with temperature. For methanol, ethanol and glycerol, as the temperature increased, hysteresis was decreased. This indicated that the ultrasonic velocity hysteresis was lower during transition from heating to cooling for all the liquids and as time passed, the hysteresis increased. 4. Conclusions Ultrasonic velocities measured on five liquids at different temperatures during heating and cooling were presented in this paper. Statistical analysis results showed the existence of ultrasonic velocity hysteresis on liquids under thermal cycle. It is well-known that temperature is an important factor in the ultrasonic velocity of a material. There are several studies in the literature using ultrasonic velocity at different temperatures to determine the concentration or composition of materials. This research showed that ultrasonic velocity is not only affected by temperature, but also from the history of the process temperature. For more accurate measurements and sensitive transducer developments, ultrasonic velocity hysteresis due to the thermal cycle should be considered, especially in ultrasonic
A.B. Koc, M. Vatandas / Food Research International 39 (2006) 1076–1083
instrumentation. The differences measured in ultrasonic velocities during heating and cooling can be used as a parameter for the identification of liquids. Some future research possibilities include qualitative and quantitative analysis of food products using ultrasonic velocity measurements. References Benedito, J., Carcel, J. A., Glemenete, G., & Mulet, A. (2001). Quality control of cheese maturation and defects using ultrasonics. Journal of Food Science, 66, 100–104. Benedito, J., Mulet, A., Clemente, G., & Garcia-Perez, J. V. (2004). Use of ultrasound for the composition assessment of olive mill wastewater (alpechin). Food Research International, 37, 595–601. Breazeale, M. A., Ostrovskii, I. V., & McPherson, M. S. (2004). Thermal hysteresis of nonlinear ultrasonic attenuation in lithium niobate. Journal of Applied Physics, 96(5), 2990–2994. Chanamai, R., & McClements, D. J. (1999). Ultrasonic determination of chicken composition. Journal of Agricultural and Food Chemistry, 47, 4686–4692. Cho, B., Irudayaraj, J., & Bhardwaj, M. (2001). Rapid measurement of physical properties of cheddar cheese using non-contact ultrasound technique. Transactions of the ASAE, 44(6), 1759–1762. Dunn, D. F. (2005). Measurement and data analysis for engineering and science. McGraw Hill International Edition, p. 540. Gestrelius, H., Hertz, T. G., Nuamu, M., Person, H. W., & Lindstrom, K. (1993). A non-destructive ultrasound method for microbial quality control of aseptically packaged milk. Lebensmittel-Wissenschaft undTechnologie, 26(4), 334–339. Ghaedian, R., Coupland, J. N., Decker, E. A., & McClements, D. J. (1998). Ultrasonic determination of fish composition. Journal of Food Engineering, 35, 323–335.
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Hodate, Y., Ueno, S., Yano, J., Katsuragi, T., Tezuka, Y., Tagawa, T., et al. (1997). Ultrasonic velocity measurement of crystallization rates of palm oil in oil–water emulsions. Colloids and Surfaces, 128, 217–224. Hykes, D. L., Hedrick, W. R., & Starchman, D. E. (1992). Ultrasound physics and instrumentation (2nd ed.). St. Louis, Missouri: Mosby-Year Book, Inc., pp. 5–23. Martini, S., Bertoli, C., Herrera, M. L., Neeson, I., & Marangoni, A. G. (2005a). In-situ monitoring of solid fat content by means of p-NMR and ultrasonics. Journal of the American Oil Chemists Society, 82, 305–312. Martini, S., Bertoli, C., Herrera, M. L., Neeson, I., & Marangoni, A. G. (2005b). Attenuation of ultrasonic waves: influence of microstructure and solid fat content. Journal of the American Oil Chemists Society, 82, 319–328. Martini, S., Herrera, M. L., & Marangoni, A. G. (2005c). New technologies to determine solid fat content on-line. Journal of the American Oil Chemists Society, 82, 313–317. McClements, D. J. (1997). Ultrasonic characterization of foods and drinks: principles, methods, and applications. Critical Reviews in Food Science and Nutrition, 37(1), 1–46. Miles, C. A., & Fursey, G. A. J. (1977). Measurement of the fat content using ultrasonic waves. Food Chemistry, 2, 107–118. Miles, C. A., Shore, D., & Langley, K. R. (1990). Attenuation of ultrasound in milks and creams. Ultrasonics, 28, 394–400. Resa, P., Elvira, L., & Espinosa, F. M. (2004). Concentration control in alcoholic fermentation processes from ultrasonic velocity measurements. Food Research International, 37, 587–594. Saggin, R., & Coupland, J. N. (2001). Non-contact ultrasonic measurements in food materials. Food Research International, 34, 865–870. Sumbuloglu, K., & Sumbuloglu, V. (2002). Biostatistics. Ankara: Hatipoglu Publications, p. 269. Villamiel, M., Van Hamersveld, E. H., & De Jong, P. (1999). Review: Effect of ultrasound processing on the quality of dairy products. Milchwissenschaft, 54(2), 69–73.
Ultrasonic velocity measurements on some liquids under thermal cycle: Ultrasonic velocity hysteresis Ali Bulent Koc b
a,* ,
Mustafa Vatandas
b
a Department of Agricultural Machinery, Faculty of Agriculture, Harran University, Sanliurfa, Turkey Department of Agricultural Machinery, Faculty of Agriculture, Ankara University, 06110 Dıskapı-Ankara, Turkey
Received 26 May 2006; accepted 6 September 2006
Abstract This study was performed to determine the existence of hysteresis during ultrasonic velocity measurements on methanol, ethanol, distilled water, processed water and glycerol under thermal cycle (5–50 C). The ultrasonic velocity of the liquids were measured with 1.0 MHz transducers using a through transmission ultrasonic system. Statistical analyses results showed that there were ultrasonic velocity hystereses on the liquid samples under thermal cycle. The study of liquids undergoing thermal cycle is useful for determining the temperature effects on ultrasonic velocity and will help developing precise control applications in food industry by reducing the uncertainties in ultrasonic velocity measurements. 2006 Elsevier Ltd. All rights reserved. Keywords: Ultrasonic velocity; Hysteresis; Water; Methanol; Ethanol; Glycerol
1. Introduction Thermal processing is one of the most important food processing technologies, which involves heating and cooling treatments of food to destroy any harmful bacteria or organisms and to develop textures, flavor and color. Lack of heating or cooling would result in inappropriate pasteurization, sterilization, cooking, freezing, texture, flavor or color. Therefore, it is important to know the measurement uncertainties to develop a precise measurement system for heat treatment operations in food quality control. During heating and cooling operations, especially where there is a phase change, the measurement system would act differently. The system’s reaction to a certain temperature during heating would be different at the same temperature during cooling. This kind of behavior would indicate a hys* Corresponding author. Present address: Department of Agricultural Machinery, Faculty of Agriculture, Ankara University, 06110 DıskapıAnkara, Turkey. Tel.: +90 536 2328791; fax: +90 312 3183888. E-mail address: [email protected] (A.B. Koc).
0963-9969/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2006.09.004
teresis in the system. The word hysteresis is of the Greek origin and means ‘shortcoming’. In other words, it is a delay in the system’s reaction when the forces acting on a system are changed. Hysteresis indicates that the response of a system under external influence is not only dependent on the magnitude of the influence, but also on the history of the system. Due to this phenomenon, nonlinearities occur in system behavior. In physics and engineering, hysteresis is the difference between the conditions to start and stop an action. Common sources of hysteresis in physical systems are usually mechanical or electrical. In mechanical systems, hysteresis is a measure of deformation energy. The deformation energy can not be stored but turns into heat. Because of this energy conversion, usually a hysteresis loss is mentioned in some systems. Hysteresis loops occur when the system is exposed to a cycle (i.e. cooling action following a heating action). In measurement systems, errors or uncertainties due to hysteresis are usually calculated as (Dunn, 2005): y up y down eH ¼ ð1Þ FSO
A.B. Koc, M. Vatandas / Food Research International 39 (2006) 1076–1083
where eH yup ydown FSO
hysteresis error, output value that occurs when performing an upscale, output value that occurs when performing a downscale, full-scale output.
In the literature, it is reported that a nonlinear thermal hysteresis was observed due to thermal cycling while ultrasound energy propagated through lithium niobate with ferroelectric crystalline structure (Breazeale, Ostrovskii, & McPherson, 2004). The physical mechanism which had an impact on this situation is called ‘acoustic memory’. It was observed that these physical mechanisms, even though they were not explained well, depended on the frequency and temperature. Experiment results indicated that there was a nonlinear difference in the ultrasonic attenuation values between increasing and decreasing temperatures due to the acoustic memory effects. Typical thermal hysteresis characteristics were observed in the ultrasonic velocity values measured during the cascade heating and cooling cycle of palm oil in oil–water emulsion (Hodate et al., 1997). Technological developments allowed the manufacturing of general and special purpose ultrasonic transducers. These transducers increased the use of low intensity nondestructive ultrasonic test techniques in food industry. Low intensity ultrasound has less than 1 W/cm2 power levels (McClements, 1997; Villamiel, Van Hamersveld, & De Jong, 1999). Low intensity ultrasonic applications do not cause alteration in the physical or chemical properties of materials, do not change the temperature and could be used for monitoring purposes only. Once the ultrasound is removed, the material takes its original shape and no change occurs in the structure. The frequency range of low intensity ultrasound is between 100 kHz and 20 MHz. Ultrasonic velocity and attenuation coefficient are the most commonly measured parameters in low intensity ultrasound applications. During the last decade, several ultrasonic test techniques for different materials are presented in the literature. Some of these applications include determining fish composition (Ghaedian, Coupland, Decker, & McClements, 1998) chicken composition (Chanamai & McClements, 1999), dried fermented sausage composition (Benedito, Carcel, Glemenete, & Mulet, 2001), and fatty tissue and musclefatty tissue compositions (Miles & Fursey, 1977). To determine the water, oil and other solids in oil waste Benedito, Mulet, Clemente, and Garcia-Perez (2004) measured the ultrasonic velocity in water, oil and oil waste separately between 6 C and 50 C. Saggin and Coupland (2001) employed an ultrasonic non-contact air-coupled transducer to measure the thickness of some food products using ultrasonic velocity. Another study for determining the physical properties of cheddar cheese using air-coupled transducers was conducted by Cho, Irudayaraj, and Bhardwaj (2001).
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Resa, Elvira, and Espinosa (2004) conducted ultrasonic velocity measurements on some carbohydrate aqueous solution mixtures of glucose–water, fructose–water, sucrose–water and ethanol–water to monitor the changes during alcoholic fermentation in-line. Gestrelius, Hertz, Nuamu, Person, and Lindstrom (1993) worked on monitoring the microbial activity in milk containers using non-destructive acoustic streaming method. Miles, Shore, and Langley (1990) determined the ultrasonic attenuation coefficient in milk. It was reported that one of the important factors affecting the ultrasonic attenuation was the distribution of fat globules in milk, which is an indication of the degree of homogenization. Ultrasonic technology was also applied to monitor the crystallization and to determine the solid fat content of edible fats on-line by Martini, Bertoli, Herrera, Neeson, and Marangoni (2005a, 2005b) Martini, Herrera, and Marangoni (2005c). The purpose of this research was to measure the ultrasonic velocity on some liquids (distilled water, processed water, ethanol, methanol and glycerol) during heating and cooling applied in bioprocesses and food processes and to determine thermal hysteresis ultrasonically. The result of this research would have two benefits. First, thermal hysteresis must be considered when ultrasound is used in food processes for reliable and precise measurements. Second, measuring thermal hysteresis will be beneficial for developing new technologies for food quality monitoring. 2. Materials and methods 2.1. Materials The liquids used in this research were distilled water (DW), processed water (PW), ethanol (E), methanol (M) and glycerol (G). Among these liquids, distilled water was produced by distillation processes in a laboratory and processed water (Turkuaz, Coca Cola Ic¸ecek A.S., Istanbul, Turkey) was purchased from a local market. Methanol (Birpa Ltd. Sti., Ankara, Turkey), ethanol (Best Kimyasallari, Ankara, Turkey) and glycerol (Emir Kimya, Ankara, Turkey) were purchased from a dealer. Some properties and purity levels of these liquids are shown in Table 1. These liquids were stored in a refrigerator at 4 C until the experiment day. For each experiment, 250 ml liquid were placed in the measurement cell and the experiments were started around 5 C. The specific densities of the liquids were measured by measuring the weight of 100 ml liquid using a balance with 1/100 g sensitivity at the temperature indicated in Table 1. 2.2. Measurement cell The measurement cell was fabricated from Plexiglass material with 6 mm thickness. The dimensions of the cell were 69.3 · 60.6 · 70.4 mm. The transducers were mounted to the measurement cell as shown in Fig. 1. The distance
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Table 1 Some properties of experimental liquids
2
Volume weight (g/cm3)
Molar weight (g/mol)
Distilled water Processed water Methanol (CH3OH) (purity > 95%) Ethanol (C2H5OH) (purity > 96%) Glycerol (C3H8O3) (purity > 96%)
1.00 (20.0 C) 1.00 (20.0 C) 0.79 (20.0 C)
18.00 18.00 32.04
0.75 (13.5 C)
46.07
1.26 (20.0 C)
92.10
1
Amplitude (V)..
Material
0
U2
U0
-1
U3
-2
t
U1
-3 0
5
10
15
20
25
30
35
40
Time (10-5 s)
Fig. 2. A typical ultrasonic waveform on oscilloscope screen (t: Time, U0: Original pulse, U1: Amplitude of the transmitted pulse, U2: Amplitude of the reflected pulse of U1, U3: Amplitude of the reflected pulse of U2).
monitored on oscilloscope screen. A typical waveform is shown in Fig. 2. The through transmission mode was used and the ultrasonic velocities were measured using Eq. (2) d ¼vt
Fig. 1. Ultrasonic measurement system (GPIB: general purpose interface bus, T: transmitter, R: receiver, DTC: digital thermocouple).
between the active surfaces of the transducers was 61.8 mm. The upper side of the cubic measurement cell was left open to the atmosphere and the liquids were filled from this side. The measurement cell was placed in a water bath of 30 l. 2.3. Ultrasonic velocity measurement system Ultrasonic velocity was measured using two broadband immersion type ultrasonic transducers (1 MHz, 38 mm crystal diameter, V392 model, Panametrics, Waltham, MA, USA). An ultrasonic pulser/receiver was used to drive the transducers (Panametrics, 500 PR, Waltham, USA). The pulser/receiver can be used in both pulse-echo and through transmission modes. The frequency of the pulses, noise control and gain factors could be adjusted on the pulser/receiver. The transmitted and received signals were monitored on a two-channel digital storage oscilloscope (Tektronix, TDS 3032, Tektronix Inc, Wilsonville, OR, USA). The oscilloscope was connected to a personal computer with general purpose interface bus (GPIB). Experimental data were recorded and analyzed with a program written in G-programming language (Labview 6.1, National Instruments, Mopac Expwy, Austin, TX, USA). To minimize noise error, 512 pulses were averaged and
ð2Þ
Where, d is the distance (m) between the transducers; v is the ultrasonic velocity (m/s); t is time (s). Ultrasonic wave’s time of flight can be measured from the waveforms on the oscilloscope screen. In this study, ultrasonic velocities were calculated from the known distance and measured time of flight automatically with the computer program. Each measurement took about 3 s. The ultrasonic velocity was calculated from the minimum magnitude of U1 and velocity change with temperature was displayed on the computer screen in real time and recorded to a file. Alternatively, the change of ultrasonic velocity with temperature is also calculated from Eq. (3) dv v2 v1 ¼ dT T 2 T 1
ð3Þ
Where, (v2 v1) is the difference between the two ultrasonic velocities measured at temperatures of T1 and T2. 2.4. Experimental The room temperature, relative humidity and atmospheric pressure were measured and recorded before the experiments were started. During heating, water at 75 C was circulated around the measurement cell until the temperature of the liquid in the cell increased to 50 C. During cooling, water at 3 C was circulated around the measurement cell until the temperature of the liquid in the cell dropped to 5 C. The temperature of the liquid in measurement cell was measured with a digital thermometer (0.1 C sensitivity). The measurements were taken 2.5 C intervals. After each measurement, the program was paused until the liquid temperature reached to the next level. Ultrasonic velocity measurements on test liquids during heating and
A.B. Koc, M. Vatandas / Food Research International 39 (2006) 1076–1083
cooling cycle were replicated twice for each liquid and the averages were used to conduct the statistical analyses. 2.5. Statistical analysis Regression analyses were conducted on the ultrasonic velocities for the same temperature levels measured while heating and cooling and the relationship between the temperature and ultrasonic velocity were evaluated. The significance of the differences between the ultrasonic velocities measured during heating and cooling for the same liquid using Wilcoxon Signed Ranks Method. Mann-Whitney Test Method was used for comparison of the ultrasonic velocities measured under thermal cycle on different liquids (Sumbuloglu & Sumbuloglu, 2002). 3. Results and discussion In this research, ultrasonic velocities were measured for different liquids under thermal cycle to determine the existence of ultrasonic velocity hysteresis. For this purpose, the liquids were exposed to heating from 5 C to 50 C. Following heating the liquids were cooled down to 5 C. At each temperature level, the ultrasonic velocity of a liquid measured during cooling was different than the ultrasonic velocity measured during heating. It was same for all of the liquids. For all the liquids except glycerol, the ultrasonic velocities measured during heating were lower than cooling. The hypothesis of no difference in ultrasonic velocities during heating and cooling cycle for the same liquid was tested. The statistical test results show that ultrasonic velocities measured during heating and cooling are significantly different for the same liquid (p < 0.05). These differences indicate the existence of ultrasonic velocity hysteresis between the ultrasonic velocities measured at the same temperature during heating and cooling. The analyses of the ultrasonic velocity–temperature graph for the test liquids under heating and cooling cycle show that one ultrasonic velocity value was measured at two different temperatures for the same liquid. One ultrasonic velocity value at two different temperatures for the same liquid shows the hysteric behavior of the liquid under heating and cooling cycle. For distilled water and processed water, the ultrasonic velocities
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measured at two subsequent temperatures were significantly different during heating or cooling cycle and these differences were not the same for all temperatures. The varying differences represent the nonlinear relationship between ultrasonic velocity and temperature for distilled and processed waters. However, for ethanol, methanol and glycerol, the change in ultrasonic velocities measured at two subsequent temperatures was consistent because of the linear relationship between temperature and ultrasonic velocity. Statistical analysis results for the comparison of ultrasonic velocity values measured during heating and cooling of different liquids are shown in Table 2. The table shows the ultrasonic velocities of distilled water compared with the other liquids and also the comparison results of methanol and ethanol. These comparisons were conducted to possibly distinguish the type of test liquids with ultrasonic velocity measurements at different cycles. Ultrasonic velocities for different liquids under the same thermal cycle were significant (p < 0.05). When distilled water velocity values were compared with processed water values, the velocities measured during the cooling cycle were significantly different (p < 0.05). When methanol was compared with ethanol, the ultrasonic velocities were significantly different during heating cycle (p < 0.05). These results indicated that ultrasonic velocity measurements under either heating or cooling cycles could be used for qualitative identification of these test liquids. Ultrasonic velocity measurements of distilled water during heating and cooling are shown in Fig. 3a. Velocities measured during heating increased with the increasing temperature, but the rate of increase in velocity decreased as the temperature continued to increase. Similar results were reported by Benedito et al. (2004) and Ghaedian et al. (1998). The increase in ultrasonic velocity with increasing temperature was not linear (Fig. 4a). The rate of increase in ultrasonic velocity measured for distilled water reached a maximum during the heating cycle at the temperature of 22.5 C and during the cooling cycle at the temperature of 27.5 C. Ultrasonic velocity in distilled water increased with temperature up to 20 C positively, but the rate of velocity increase became smaller over 22.5 C. Similarly, the ultrasonic velocity change with temperature was not linear during cooling. Ultrasonic velocity change with
Table 2 Statistical analysis results for comparing the ultrasonic velocities of the liquids under the same cycles Liquid
Distilled water Processed water Ethanol Methanol
Cycle
Heating Cooling Heating Cooling Heating Cooling Heating Cooling
Significance level (p) Processed water
Methanol
Heating
Heating
Cooling
0.081
Ethanol Cooling
0.000 0.020
Heating
Glycerol Cooling
0.000 0.000
0.000
Heating 0.000
0.000 0.000
0.000
Cooling 0.000
0.000 0.000
0.000 0.000 0.000
0.000
0.000 0.370
0.000
1080
A.B. Koc, M. Vatandas / Food Research International 39 (2006) 1076–1083 1560
a
Heating Cooling
b 1560
1540
Heating Cooling
1540
1520 Ultrasonic velocity (m/s)
Ultrasonic velocity (m/s)
1520 1500 1480 1460
1500
1480
1460
1440
1440
1420 1400 5
10
15
20
25
30
35
40
45
1420
50
5
10
15
20
25
Temperature (°C)
c
d
1300
Heating
Cooling
35
40
45
50
1320
Heating
1280
Ultrasonic velocity (m/s)
1250
Ultrasonic velocity (m/s)
30
Temperature (°C)
1200
1150
1100
Cooling
1240
1200
1160
1120
1080
1050
0 5
10
15
20
25
30
35
40
45
10
50
Temperature (°C)
e
30
40
50
1980
Heating
1960
Ultrasonic velocity (m/s)
20
Temperature (°C)
Cooling
1940 1920 1900 1880 1860 1840 5
10
15
20
25
30
35
40
45
50
Temperature (°C)
Fig. 3. Ultrasonic velocity change with temperature during heating and cooling of test liquids under thermal cycle. (a) Distilled water, (b) processed water, (c) methanol, (d) ethanol and (e) glycerol. Average room temperature was 18 C, average relative humidity was 42% and average atmospheric pressure was 985 mbar during the tests. Error bars show the standard error of the ultrasonic velocity estimation.
temperature during heating was reciprocal to the cooling for distilled water. Ultrasonic velocity measurements of processed water during heating and cooling at different temperatures are
shown in Fig. 3b. As with the ultrasonic measurements of distilled water, for the same temperature level, the velocities measured during heating were lower than the velocities measured during cooling. Fig. 4b shows the rate
A.B. Koc, M. Vatandas / Food Research International 39 (2006) 1076–1083
a
14
b
12
dv/dT (heating)
4.5
dv/dT (cooling)
4.0
10
dv/dT (heating) dv/dT (cooling)
3.5
dv/dT (m/ s/°C)..
dv/dT (m/ s/°C)
1081
8
6
4
3.0 2.5 2.0 1.5 1.0
2 0.5 0.0
0 0
10
20
30
40
0
50
10
20
c
d
0
50
dv/dT (Heating) dv/dT (Cooling)
-2.4
dv/dT (m/s/ °C)
-1
dv/dT (m/ s/°C)
40
-2 -2.2
dv/dT (heating) dv/dT (cooling)
-0.5
30
Temperature (°C)
Temperature (°C)
-1.5 -2 -2.5
-2.6 -2.8 -3 -3.2 -3.4
-3
-3.6 -3.5
-3.8
-4
-4 0
10
20
30
40
50
0
10
e
30
40
50
-1.7
dv/dT (heating) dv/dT (cooling)
-1.8 -1.9
dv/dT (m/ s/°C)
20
Temperature (°C)
Sicakhk (°C)
-2 -2.1 -2.2 -2.3 -2.4 -2.5 0
10
20
30
40
50
Temperature (°C)
Fig. 4. The rate of velocity change over temperature change during heating and cooling of (a) distilled water, (b) processed water, (c) methanol, (d) ethanol and (e) glycerol.
of ultrasonic velocity over temperature change with temperature. Ultrasonic velocity change with temperature for processed water during heating was similar to cooling. The largest difference in ultrasonic velocities from the third degree polynomial during heating and cooling was measured at 10 C. The rate of ultrasonic velocity change with temperature during heating and cooling was equal at 22.5 C (Fig. 4b). During the ultrasonic velocity measurements on distilled and processed waters air bubbles formed on transducers’ surfaces and measurement cell walls while heating at above
10 C. The number and the size of the bubbles increased with the increasing temperature. Although some of the air bubbles ascended to the surface of the water with the increasing temperature, most stayed intact with the transducer surfaces. The size of the bubbles reduced during cooling, but never disappeared, even when cooling down to the starting temperature. We think that the reason for bubble formation was due to the dissolved gases in water. Initially, the gas bubbles were too small to be recognized but with heating, the number and the sizes of the bubbles increased. We think that the amount of dissolved gasses in processed water is smaller than in distilled water.
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Distilled water is produced by distillation whereas the processed water is produced by reverse osmosis. It is believed that the differences in the production of distilled and processed water affected the ultrasonic wave propagation. Similar heating and cooling processes were applied to methanol, ethanol and glycerol and ultrasonic velocities were measured. Unlike distilled and processed water, as the temperature increased, the ultrasonic velocities on these three alcohols decreased linearly. Fig. 3c shows the ultrasonic velocity change with temperature for methanol during heating and cooling. Ultrasonic velocity on methanol decreased with increasing temperature and increased with decreasing temperature. The largest difference (73.2 m/s) in ultrasonic velocity during heating and cooling was measured at 7.5 C. The rate of ultrasonic velocity over the temperature change with temperature for methanol is shown in Fig. 4c. The rates of ultrasonic velocity change over temperature change were 2.75 m/s/C during heating and 3.52 m/s/C during cooling. That is, 1 C increase in temperature resulted in 2.75 m/s decrease in the ultrasonic velocity. In a similar way, 1 C decrease in temperature resulted in 3.52 m/s increase in the ultrasonic velocity. Ultrasonic velocity change with temperature for ethanol exposed to heating and cooling is shown in Fig. 3d. The differences in ultrasonic velocities during heating and cooling were less than the differences observed for methanol. The maximum measured difference was 14.7 m/s and observed at 5 C. The rates of ultrasonic velocity change over temperature with temperature for ethanol is shown in Fig. 4d. For 1 C increase in temperature the ultrasonic velocity of ethanol decreased 3.14 m/s and a 1 C decrease in temperature during cooling increased the ultrasonic velocity 3.44 m/s. The graph showing ultrasonic velocity change with temperature for glycerol is different than the graphs for methanol and ethanol (Fig. 3e). Unlike methanol, ethanol, and distilled and processed waters, the ultrasonic velocities of glycerol measured at a certain temperature during heating were greater than the ultrasonic velocities measured during cooling. The reason for the difference is that an inverse relationship exists between the ultrasonic velocity of a material and the material’s density and compressibility, as shown in Eq. (4) (Hykes, Hedrick, & Starchman, 1992). 1 c ¼ pffiffiffiffiffiffiffiffiffiffi bq
ð4Þ
where, c is the ultrasound velocity (m/s), q is the density of the medium (kg/m3) and b is the compressibility of the medium, which is the reciprocal of the elastic modulus (N/m2). Eq. (4) indicates that as density decreases, the speed of sound increases. However, because compressibility is highly affected by density, a small increase in density creates a large decrease in compressibility. Compressibility becomes a more dominant factor than density, so the ultrasound velocity of a substance increases with increasing density (Hykes et al., 1992).
7
DW ME
6
PW ET
GL
5 Hysteresis (%)
1082
4 3 2 1 0 5
10
15
20
25 30 Temperature (°C)
35
40
45
50
Fig. 5. Ultrasonic velocity hysteresis of liquids under test change with temperature during thermal cycle (DW: distilled water, PW: processed water, GL: glycerol, ME: methanol, ET: ethanol).
Compared with the other liquids, glycerol has higher density and its melting temperature is 17.8 C. Glycerol at below melting temperature has a syrup-like gel structure and is a highly hygroscopic substance. Since the upper surface of glycerol was in contact with air, glycerol may have absorbed some moisture from the air. Glycerol also showed phase changes during heating and cooling. Similar to methanol and ethanol, as the temperature was increased, the ultrasonic velocity decreased. For 1 C increase in temperature of glycerol, ultrasonic velocity decreased 3.17 m/s and for 1 C decrease in temperature, the ultrasonic velocity increased 2.4 m/s (Fig. 4e). For all of the liquids tested, ultrasonic velocity hysteresis was calculated using Eq. (1) and the ultrasonic velocity hysteresis change with temperature is shown in Fig. 5. Among these liquids, methanol had the greatest ultrasonic velocity hysteresis. The ultrasonic velocity hysteresis of distilled and processed water showed a nonlinear change with temperature. For methanol, ethanol and glycerol, as the temperature increased, hysteresis was decreased. This indicated that the ultrasonic velocity hysteresis was lower during transition from heating to cooling for all the liquids and as time passed, the hysteresis increased. 4. Conclusions Ultrasonic velocities measured on five liquids at different temperatures during heating and cooling were presented in this paper. Statistical analysis results showed the existence of ultrasonic velocity hysteresis on liquids under thermal cycle. It is well-known that temperature is an important factor in the ultrasonic velocity of a material. There are several studies in the literature using ultrasonic velocity at different temperatures to determine the concentration or composition of materials. This research showed that ultrasonic velocity is not only affected by temperature, but also from the history of the process temperature. For more accurate measurements and sensitive transducer developments, ultrasonic velocity hysteresis due to the thermal cycle should be considered, especially in ultrasonic
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instrumentation. The differences measured in ultrasonic velocities during heating and cooling can be used as a parameter for the identification of liquids. Some future research possibilities include qualitative and quantitative analysis of food products using ultrasonic velocity measurements. References Benedito, J., Carcel, J. A., Glemenete, G., & Mulet, A. (2001). Quality control of cheese maturation and defects using ultrasonics. Journal of Food Science, 66, 100–104. Benedito, J., Mulet, A., Clemente, G., & Garcia-Perez, J. V. (2004). Use of ultrasound for the composition assessment of olive mill wastewater (alpechin). Food Research International, 37, 595–601. Breazeale, M. A., Ostrovskii, I. V., & McPherson, M. S. (2004). Thermal hysteresis of nonlinear ultrasonic attenuation in lithium niobate. Journal of Applied Physics, 96(5), 2990–2994. Chanamai, R., & McClements, D. J. (1999). Ultrasonic determination of chicken composition. Journal of Agricultural and Food Chemistry, 47, 4686–4692. Cho, B., Irudayaraj, J., & Bhardwaj, M. (2001). Rapid measurement of physical properties of cheddar cheese using non-contact ultrasound technique. Transactions of the ASAE, 44(6), 1759–1762. Dunn, D. F. (2005). Measurement and data analysis for engineering and science. McGraw Hill International Edition, p. 540. Gestrelius, H., Hertz, T. G., Nuamu, M., Person, H. W., & Lindstrom, K. (1993). A non-destructive ultrasound method for microbial quality control of aseptically packaged milk. Lebensmittel-Wissenschaft undTechnologie, 26(4), 334–339. Ghaedian, R., Coupland, J. N., Decker, E. A., & McClements, D. J. (1998). Ultrasonic determination of fish composition. Journal of Food Engineering, 35, 323–335.
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