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In the present study, hydrodynamic (HD) cavitation was combined with sodium percarbonate (SP) for the pretreatment of lignocellulosic biomass. For HD cavitation, a circular flow system equipped with a venturi tube was employed. The combined system of HD and SP (HD-SP) was compared to a pretreatment system using ultrasonication and SP (US-SP). The efficacy of each pretreatment method was evaluated by measuring lignin removal, and glucose and xylose formation. Fourier transform infrared spectra indicated that both systems resulted in a similar degree of lignin removal; however, the HD-SP system was more efficient than the US-SP system for glucose and xylose production. Neither system generated the inhibitor furfural, while it was detected in dilute acid (DA)-pretreated biomass. Furthermore, changing the venturi tube throat diameter improved the efficacy of the HD-SP system. The HD-SP system is promising for the industrial pretreatment of lignocellulosic biomass.

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The erosion produced by cavitation is a serious problem in hydraulic machinery. During investigations of the dynamic loading generated by collapsing cavitation on a surface, a dynamic pressure transducer was developed. The piezoelectric polymer PVDF (Polyvinylidene fluoride) was used as the pressure sensitive material. A novel method of dynamic calibration has also been developed. The transducer is loaded through pencil lead by a beam supported at its other end on a knife edge and loaded at the center by weights. As the static load is increased, the pencil lead breaks and the load is released suddenly. The unloading time is faster than for any other conventional calibration method and is of the same order as cavitation loading. Descriptions of the developments of both the calibration method and the transducer are given. The principal advantages of the new method are the short pulse duration and the simplicity of the test procedure. The paper is an extension of the previously reported work by Momma and Lichtarowicz (1994), giving further information on the operating characteristics of the transducer in comparison with the traditional ball-dropping method.

In order to enhance the aggressive intensity of a cavitating jet for practical applications, the effect of the geometry of the nozzle through which the jet is driven on the aggressive intensity was investigated. The nozzle under test was cylindrical and consisted of a plate and a cap with a hole bored through it. The aggressive intensity of the jet was estimated by the erosion suffered by pure aluminum test specimens. The parameters varied were the bore diameter, D, and length, L, the standoff distance, the nozzle throat diameter, d, and the upstream and downstream pressures of the nozzle. The mass loss at the optimum standoff distance, where the mass loss was at a relative maximum, was found for each bore diameter and length, and then the optimum bore diameter and length were obtained. The optimum ratio of d : D : L was shown to be 1 : 8 : 8, and this was the optimum for both d =1 mm and d =2 mm. It was also the optimum ratio for upstream pressures of 15 MPa and 30 MPa, and downstream pressures of 0.1 MPa and 0.42 MPa.

Cavitation impact, which normally produces severe damage in hydraulic machinery, can be used to modify surfaces in the same way as shot peening. Cavitation impact enables the surface of a material to be peened without the use of shot, thus it is called cavitation shotless peening. As there are no solid body collisions occurring in this peening process, the roughness of the peened surface should be less than that produced by shot peening. This characteristic makes it suitable for peening soft metals. In order to demonstrate the improvement of the fatigue strength of aluminum alloy by this process, specimens were subjected to the process, and then tested in a rotating bending fatigue test. Cavitation impacts were produced and controlled by using a submerged high speed water jet with cavitation, i.e., a cavitating jet. It was revealed that the fatigue strength of an aluminum alloy specimen treated by this peening process was 50% stronger than that of a specimen without peening.

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