Abstract:This paper describes investigation of the influence of the protective layer thickness on the calibration sensitivity of PVDF films sensors for the cavitation impacts measurements. The PVDF film sensor is casted into an aluminium block. The drop ball method is used for the measurement of the relation between impact force and the voltage detected on the PVDF film sensor. The calibration constants are measured for three different protective layers thicknesses. Five different ball weights for 400 mm drop height ar… Show more
“…It will be necessary in future work to measure the pressure inside the chamber. One possibility would be to install PVDF film sensors [ 30 ] on one or both side faces of the compression chamber and to complement these measurements with simulations employing high-order schemes [ 31 ] to accurately describe the non-spherical collapse and the pressure field in the gas and liquid media (inside and outside the bubble).…”
A mechanical device inspired by the rapid rotational motion of the pistol shrimp plunger has been developed to experimentally study the contraction/expansion dynamics of a gas bubble inside a confined liquid volume and in the vicinity of solid surfaces. The apparatus consists of a limb with a V-shaped end, which fits into a socket forming a cylindrical compression chamber. Air bubbles of different sizes and in different positions inside the chamber were seeded to study their shape evolution in liquids when subjected to pressure pulses induced by the limb closure. By changing the standoff and curvature parameters, as well as the closing power of the limb it was possible to control the dynamical behavior of the cavity. Four stages describing the dynamic behavior of the bubble were found: 1) A slight expansion-contraction stage accompanied by very weak volumetric oscillations. 2) First compression stage. The formation of gas and liquid micro-jets is observed when the vertical symmetry axis of the bubble is initially located outside of the chamber symmetry axis, on the other hand, when there is a coincidence between these axes, the bubble only contracts exhibiting non-spherical shapes, alternating between oblate and prolate spheroidal structures. 3) An expansion stage where the cavity reaches the walls of the chamber exhibiting irregular shapes on its surface. 4) Second compression stage. This process begins when the limb rebounds and stops sealing the chamber allowing a jet of liquid to enter from the fluid medium outside, inducing a very violent collapse accompanied by the emission of light. The proposed technique represents a novel alternative to study the dynamic evolution of bubbles near and on solid boundaries of various geometries. Other attractive features of the apparatus are its low manufacturing cost, simple design and compact size which makes it easily portable.
“…It will be necessary in future work to measure the pressure inside the chamber. One possibility would be to install PVDF film sensors [ 30 ] on one or both side faces of the compression chamber and to complement these measurements with simulations employing high-order schemes [ 31 ] to accurately describe the non-spherical collapse and the pressure field in the gas and liquid media (inside and outside the bubble).…”
A mechanical device inspired by the rapid rotational motion of the pistol shrimp plunger has been developed to experimentally study the contraction/expansion dynamics of a gas bubble inside a confined liquid volume and in the vicinity of solid surfaces. The apparatus consists of a limb with a V-shaped end, which fits into a socket forming a cylindrical compression chamber. Air bubbles of different sizes and in different positions inside the chamber were seeded to study their shape evolution in liquids when subjected to pressure pulses induced by the limb closure. By changing the standoff and curvature parameters, as well as the closing power of the limb it was possible to control the dynamical behavior of the cavity. Four stages describing the dynamic behavior of the bubble were found: 1) A slight expansion-contraction stage accompanied by very weak volumetric oscillations. 2) First compression stage. The formation of gas and liquid micro-jets is observed when the vertical symmetry axis of the bubble is initially located outside of the chamber symmetry axis, on the other hand, when there is a coincidence between these axes, the bubble only contracts exhibiting non-spherical shapes, alternating between oblate and prolate spheroidal structures. 3) An expansion stage where the cavity reaches the walls of the chamber exhibiting irregular shapes on its surface. 4) Second compression stage. This process begins when the limb rebounds and stops sealing the chamber allowing a jet of liquid to enter from the fluid medium outside, inducing a very violent collapse accompanied by the emission of light. The proposed technique represents a novel alternative to study the dynamic evolution of bubbles near and on solid boundaries of various geometries. Other attractive features of the apparatus are its low manufacturing cost, simple design and compact size which makes it easily portable.
“…2 (a)). The impulse–momentum theorem equation proposed by Hujer and Müller [34] is used to calculate the mean impact force: Fig. 2 PVDF sensor calibration.…”
“…Polyvinylidene fluoride (PVDF) membranes, which are a type of piezoelectric polymer transducer, were used to measure the pulse pressure (or shock pressure) after the USW was generated. The piezoelectric polymer transducers were calibrated by using drop test method (Sahaya Grinspan and Gnanamoorthy, 2010;Hujer and Müller, 2018). The calibration results are shown in Eq.…”
The present work aimed to investigate the effect of underwater shock wave (USW) on palm oil yield. Palm fruits were prepared and treated by applying USW before oil extraction. Strong USWs were generated by discharging high electric voltage into water, and varying the supplied voltage in the range of 2 - 10 kV. Following USW treatment, two methods of palm oil extraction namely screw-press and solvent extraction were used to determine the oil yield. Oil yield extraction and microstructure morphology of palm mesocarp were also investigated. It was found that at 10 kV of the USW treatment, the highest yield of palm oil extraction through screw-press method was 66.35%, while the solvent extraction method yielded 70.38%, which were 3.1 and 6.3% improvement, respectively, as compared to the untreated extraction. Microstructure analysis by scanning electron microscope (SEM) of palm mesocarp showed that the oil cells had significant cracks on the surface following treatment with USW. This confirmed that the application of USW was effective in increasing palm oil yield extraction. With a reliable strength and repetition of the treatment, USW treatment is promising for practical application in the palm oil industry and also other plant oil extraction.
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