The assessment of aggressiveness of cavitation phenomena through direct measurement of impact forces produced by bubble collapse is studied. This was done by recording impact forces from a commercially available Polyvinylidene Fluoride (PVDF) film sensor which is exposed to cavitation generated by ultrasonic transducer equipment. The ideal number of runs which will better represent the cavitation phenomena was first identified. Results showed good repeatability of every run and that a minimum of 3 experimental trials with time duration of 15 ms are enough to get a consistent data. The preparation of the PVDF films was optimized by selecting among four PVDF films that were setup differently, namely, a PVDF film as obtained from the supplier, a PVDF film topped with one layer of tape as an added protection, PVDF film with two layers of protective tape, and lastly a PVDF film which is folded into half. The PVDF film with one layer of tape is found to be the most suitable film for aggressiveness tests in terms of sensitivity and durability from cavitation damage. This film was then subjected to three different vibration amplitudes and it showed that increasing the oscillation amplitude leads to stronger impacts. Although most impacts were seen to occur at each horn vibration period, there were prominent high impact forces observed to arise after some cycles of horn vibration. This suggests that bubbles coagulate to form large cavity and then collapse more violently at a frequency lower than the frequency of ultrasonic horn vibration. Moreover, these strong impacts occur at a frequency that decreases as the vibration amplitude is increased. The obtained impact force signal was then compared to a previously obtained pitting test data which utilized the same experimental setup as used in this study. A remarkably high difference in the order of magnitude was seen between the cumulative peak rate and pit rate indicating that not all impacts cause pits on the surface of the material. Additionally, if it is assumed that a pit is formed from a single impact force during the incubation period, then a load of 319 N is necessary to create a 0.9 m diameter pit on aluminum alloy.
Anotace v angličtině
The assessment of aggressiveness of cavitation phenomena through direct measurement of impact forces produced by bubble collapse is studied. This was done by recording impact forces from a commercially available Polyvinylidene Fluoride (PVDF) film sensor which is exposed to cavitation generated by ultrasonic transducer equipment. The ideal number of runs which will better represent the cavitation phenomena was first identified. Results showed good repeatability of every run and that a minimum of 3 experimental trials with time duration of 15 ms are enough to get a consistent data. The preparation of the PVDF films was optimized by selecting among four PVDF films that were setup differently, namely, a PVDF film as obtained from the supplier, a PVDF film topped with one layer of tape as an added protection, PVDF film with two layers of protective tape, and lastly a PVDF film which is folded into half. The PVDF film with one layer of tape is found to be the most suitable film for aggressiveness tests in terms of sensitivity and durability from cavitation damage. This film was then subjected to three different vibration amplitudes and it showed that increasing the oscillation amplitude leads to stronger impacts. Although most impacts were seen to occur at each horn vibration period, there were prominent high impact forces observed to arise after some cycles of horn vibration. This suggests that bubbles coagulate to form large cavity and then collapse more violently at a frequency lower than the frequency of ultrasonic horn vibration. Moreover, these strong impacts occur at a frequency that decreases as the vibration amplitude is increased. The obtained impact force signal was then compared to a previously obtained pitting test data which utilized the same experimental setup as used in this study. A remarkably high difference in the order of magnitude was seen between the cumulative peak rate and pit rate indicating that not all impacts cause pits on the surface of the material. Additionally, if it is assumed that a pit is formed from a single impact force during the incubation period, then a load of 319 N is necessary to create a 0.9 m diameter pit on aluminum alloy.
Klíčová slova
Cavitation, ultrasonic cavitation, PVDF Sensor
Klíčová slova v angličtině
Cavitation, ultrasonic cavitation, PVDF Sensor
Rozsah průvodní práce
75
Jazyk
AN
Anotace
The assessment of aggressiveness of cavitation phenomena through direct measurement of impact forces produced by bubble collapse is studied. This was done by recording impact forces from a commercially available Polyvinylidene Fluoride (PVDF) film sensor which is exposed to cavitation generated by ultrasonic transducer equipment. The ideal number of runs which will better represent the cavitation phenomena was first identified. Results showed good repeatability of every run and that a minimum of 3 experimental trials with time duration of 15 ms are enough to get a consistent data. The preparation of the PVDF films was optimized by selecting among four PVDF films that were setup differently, namely, a PVDF film as obtained from the supplier, a PVDF film topped with one layer of tape as an added protection, PVDF film with two layers of protective tape, and lastly a PVDF film which is folded into half. The PVDF film with one layer of tape is found to be the most suitable film for aggressiveness tests in terms of sensitivity and durability from cavitation damage. This film was then subjected to three different vibration amplitudes and it showed that increasing the oscillation amplitude leads to stronger impacts. Although most impacts were seen to occur at each horn vibration period, there were prominent high impact forces observed to arise after some cycles of horn vibration. This suggests that bubbles coagulate to form large cavity and then collapse more violently at a frequency lower than the frequency of ultrasonic horn vibration. Moreover, these strong impacts occur at a frequency that decreases as the vibration amplitude is increased. The obtained impact force signal was then compared to a previously obtained pitting test data which utilized the same experimental setup as used in this study. A remarkably high difference in the order of magnitude was seen between the cumulative peak rate and pit rate indicating that not all impacts cause pits on the surface of the material. Additionally, if it is assumed that a pit is formed from a single impact force during the incubation period, then a load of 319 N is necessary to create a 0.9 m diameter pit on aluminum alloy.
Anotace v angličtině
The assessment of aggressiveness of cavitation phenomena through direct measurement of impact forces produced by bubble collapse is studied. This was done by recording impact forces from a commercially available Polyvinylidene Fluoride (PVDF) film sensor which is exposed to cavitation generated by ultrasonic transducer equipment. The ideal number of runs which will better represent the cavitation phenomena was first identified. Results showed good repeatability of every run and that a minimum of 3 experimental trials with time duration of 15 ms are enough to get a consistent data. The preparation of the PVDF films was optimized by selecting among four PVDF films that were setup differently, namely, a PVDF film as obtained from the supplier, a PVDF film topped with one layer of tape as an added protection, PVDF film with two layers of protective tape, and lastly a PVDF film which is folded into half. The PVDF film with one layer of tape is found to be the most suitable film for aggressiveness tests in terms of sensitivity and durability from cavitation damage. This film was then subjected to three different vibration amplitudes and it showed that increasing the oscillation amplitude leads to stronger impacts. Although most impacts were seen to occur at each horn vibration period, there were prominent high impact forces observed to arise after some cycles of horn vibration. This suggests that bubbles coagulate to form large cavity and then collapse more violently at a frequency lower than the frequency of ultrasonic horn vibration. Moreover, these strong impacts occur at a frequency that decreases as the vibration amplitude is increased. The obtained impact force signal was then compared to a previously obtained pitting test data which utilized the same experimental setup as used in this study. A remarkably high difference in the order of magnitude was seen between the cumulative peak rate and pit rate indicating that not all impacts cause pits on the surface of the material. Additionally, if it is assumed that a pit is formed from a single impact force during the incubation period, then a load of 319 N is necessary to create a 0.9 m diameter pit on aluminum alloy.
Klíčová slova
Cavitation, ultrasonic cavitation, PVDF Sensor
Klíčová slova v angličtině
Cavitation, ultrasonic cavitation, PVDF Sensor
Zásady pro vypracování
State of art in the investigation of the cavitation aggressiveness.
Definition and preparation of the experimental setup.
Selection of an appropriate method for the bubble generation.
Preparation and testing of PVDF sensors for the measurement of the cavitation aggressiveness.
Realization of cavitation aggressiveness measurements using PVDF sensors.
Analysis of results and their interpretation regarding the pitting tests.
Zásady pro vypracování
State of art in the investigation of the cavitation aggressiveness.
Definition and preparation of the experimental setup.
Selection of an appropriate method for the bubble generation.
Preparation and testing of PVDF sensors for the measurement of the cavitation aggressiveness.
Realization of cavitation aggressiveness measurements using PVDF sensors.
Analysis of results and their interpretation regarding the pitting tests.
Seznam doporučené literatury
\matsymb{lbrack}1\matsymb{rbrack} {KIM, Ki-Han, Georges CHAHINE, Jean-Pierre FRANC a Ayat KARIMI.} Advanced experimental and numerical techniques for cavitation erosion prediction. {Dordrecht: Springer, [2014]. Fluid mechanics and its applications, v. 106.}
\matsymb{lbrack}2\matsymb{rbrack} Acoustic cavitation and bubble dynamics. {New York, NY: Springer Berlin Heidelberg, 2017. ISBN 9783319682365.}
\matsymb{lbrack}3\matsymb{rbrack} {BRENNEN, Christopher E.} Cavitation and bubble dynamics. {New York: Oxford University Press, 1995. ISBN 0195094093.}
\matsymb{lbrack}4\matsymb{rbrack} {FRANC, Jean-Pierre a Jean-Marie MICHEL.} Fundamentals of cavitation. {Boston: Kluwer Academic Publishers, c2004. ISBN 1402022328.}
Seznam doporučené literatury
\matsymb{lbrack}1\matsymb{rbrack} {KIM, Ki-Han, Georges CHAHINE, Jean-Pierre FRANC a Ayat KARIMI.} Advanced experimental and numerical techniques for cavitation erosion prediction. {Dordrecht: Springer, [2014]. Fluid mechanics and its applications, v. 106.}
\matsymb{lbrack}2\matsymb{rbrack} Acoustic cavitation and bubble dynamics. {New York, NY: Springer Berlin Heidelberg, 2017. ISBN 9783319682365.}
\matsymb{lbrack}3\matsymb{rbrack} {BRENNEN, Christopher E.} Cavitation and bubble dynamics. {New York: Oxford University Press, 1995. ISBN 0195094093.}
\matsymb{lbrack}4\matsymb{rbrack} {FRANC, Jean-Pierre a Jean-Marie MICHEL.} Fundamentals of cavitation. {Boston: Kluwer Academic Publishers, c2004. ISBN 1402022328.}
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