Cavitation erosion in waters having different surface tensions

Wear and cavitation erosion are the common damages in engine bearing shells. In the case of cavitation damage, the generation and immediate collapse of small gas bubbles cause high pressure pulses and the bearing surface is being locally damaged. Cavitation damage is observed in heavy duty diesel engine due to highly dynamic loading, oscillation of pins, turbulence of oil flow and other factors. Wear damage induces adjustment in the bearing geometry and affects the oil film pressure and the durability of bearing shell. In this paper, wear and cavitation damages in connecting rod big end bearing have been studied. In order to compute the bearing lubrication characteristic such as minimum oil film thickness and maximum oil film pressure, Elasto-Hydrodynamic method that incorporates mass conserving algorithm has been utilized. Wear and cavitation damages in two different designs of connecting rod structure in a heavy duty diesel engine have been assessed and the results have been presented. Furthermore, the effect of connecting rod structure on wear damage has been investigated.

Influence of plasma nitriding and PAPVD Cr 1 − x N x coating on the cavitation erosion resistance of an AISI 1045 steel

Cavitation erosion is discussed through the measurements of the cavitation bubble collapse pressures and the observations of the erosion processes of various materials. The magnitude of impact pressures (impact loads) produced by the collapse of bubbles fluctuates over a wide range, but the number of bubble collapse impacts necessary to form erosion pits impulsively is remarkably small. Cavitation damage is found to be dominated by fatigue fracture due to the repetition of small impact loads as well as a small number of large impact loads. However, there is a threshold value at which impact load begins to contribute to the fatigue fracture of the surface. Comparing the distributions of impact loads with the hypothetical S-N curves of fatigue, Miner's law is followed for the incubation period and the erosion rate regardless of the testing apparatus, cavitation conditions and materials. The erosion resistances of the msterials are also discussed.

Abstract. The reactive uptake of carbonyl-containing volatile organic compounds (cVOCs) by aqueous atmospheric aerosols is a likely source of particulate organic material. The aqueous-phase secondary organic products of some cVOCs are surface-active. Therefore, cVOC uptake can lead to organic film formation at the gas-aerosol interface and changes in aerosol surface tension. We examined the chemical reactions of two abundant cVOCs, formaldehyde and acetaldehyde, in water and aqueous ammonium sulfate (AS) solutions mimicking tropospheric aerosols. Secondary organic products were identified using Aerosol Chemical Ionization Mass Spectrometry (Aerosol-CIMS), and changes in surface tension were monitored using pendant drop tensiometry. Hemiacetal oligomers and aldol condensation products were identified using Aerosol-CIMS. Acetaldehyde depresses surface tension to 65(±2) dyn cm−1 in pure water (a 10% surface tension reduction from that of pure water) and 62(±1) dyn cm−1 in AS solutions (a 20.6% reduction from that of a 3.1 M AS solution). Surface tension depression by formaldehyde in pure water is negligible; in AS solutions, a 9% reduction in surface tension is observed. Mixtures of these species were also studied in combination with methylglyoxal in order to evaluate the influence of cross-reactions on surface tension depression and product formation in these systems. We find that surface tension depression in the solutions containing mixed cVOCs exceeds that predicted by an additive model based on the single-species isotherms.

1. The surface tension of 161 films of DPL have been measured on a Langmuir trough using a Wilhelmy balance under conditions controlled to simulate the state of the alveolar lining in vivo.2. The parameters controlled were temperature (maintained at 37 degrees C), humidity (100% at 37 degrees C), surfactant concentrations (encompassing the best available estimates), area changes (consistent with normal respiration), frequency adaptation to continuous cycling and composition and pH of the aqueous hypophase.3. Simultaneously maintaining all of these parameters within the best estimates of physiological limits, the relationships between surface tension and surface area showed appreciable differences from previous studies, our results showing higher minimum values of surface tension, appreciably less change in surface tension with compression and far less hysteresis between surface tension and surface area.4. The higher minimum values are consistent with original estimates of alveolar surface tension made by von Neergaard, namely 35-41 dyne cm(-1).5. Although appreciably smaller than hitherto reported, the change in surface tension with change in area is still adequate to impart alveolar stability.6. The reversibility between surface tension and surface area under physiological conditions is discussed in connection with compliance hysteresis which is considered to be more dependent upon geometric irreversibility of the alveolar surface than upon any intrinsic property of the surfactant.

Lung surfactant dysfunction in tuberculosis: Effect of mycobacterial tubercular lipids on dipalmitoylphosphatidylcholine surface activity

The one of the common causes of damage of water turbines, marine propellers, pumps or other components of hydraulic machinery, which contribute to their faster failure, is the cavitation erosion. The cause of cavitation erosion is the phenomenon of cavitation which is caused by formation and collapse of bubbles in liquids that are subjected to frequent pressure change. The cavitation erosion tests were performed in cavitation tunnel equipped with system of the barricades. The following flow velocity values were obtained: 2.30 m∙s-1, 2.49 m∙s-1, 2.67 m∙s-1 and 2.83 m∙s-1. The tested materials were two types of the austenitic stainless steels – 1.4301 and 1.4541 after heat treatment. The study compares the impact of mechanical properties, the chemical composition of steel and the flow velocity on cavitation resistance. The test results showed that steel 1.4301 had better cavitation erosion resistance than 1.4541 steel at all set flow rates. The differences in weight loss and roughness (Ra parameter) were about two times higher for 1.4541 steel compared to 1.4301steel. However, the similar mechanisms of surface degradation were observed. The conducted tests showed a significant influence of the fluid flow, chemical composition and mechanical properties on the cavitation erosion resistance.

Surface tension (ST) analysis was performed on solutions used to prime bubble oxygenators in order to determine what changes, if any, took place during preparation and clinical use of the cardiopulmonary bypass (CPB) circuit. Samples were taken as follows: crystalloid solution prior to its addition to the circuit; after 5 and 20 minutes of pre-CPB recirculation; after addition of albumin; and post-CPB. ST values, as measured with a Du Nouy tensiometer dropped from 71 dynes/em to values in the mid 60s, with additional decreases (mid 50s) following the albumin. Post-CPB values of plasma derived from centrifugation of perfusate were in the upper 40 dynes/em range. This preCPB drop in ST raises the question of wash-off of defoamer and its possible effect on gaseous microemboli (GME) removal by arterial screen filters. Removal of GME by filtration is dependent, in part, upon ST phenomenon according to the "bubble point" concept and the equation of capillarity. Another concern is the potential removal of defoamer during pre-CPB filtration with subsequent inadequate oxygenator debubbling.

Cavitation erosion resistance of plastics

Van Iterson's experiments show that cavitation erosion is produced by the collapse of minute air bubbles in water in a state of air supersaturation. This is contrary to the usual conception that cavitation erosion is due to the collapse of vapour bubbles. The author gives results of experiments which indicate that the bubbles which form and collapse at the stage of incipient cavitation in aerated water are air bubbles in a supersaturated state. The experiments also show that vapour bubbles which collapse in de-aerated water are in thermal equilibrium. It is shown that the collapse of bubbles in thermal equilibrium cannot cause erosion because the vapour pressure inside and the hydrostatic pressure surrounding the bubbles are balanced during collapse. The energy producing cavitation erosion is the free surface energy liberated by the collapse of the air bubbles. The final collapse velocity is the velocity of sound in water and the magnitude of the blow produced is of the order of 120 tons per sq. in. or more. The effect of these views on the interpretation of the model tests in cavitation tunnels and on the cavitation number is discussed.

Measurements were made of the surface tension of the aqueous solutions of p-(1,1,3,3-tetramethylbutyl) phenoxypoly(ethylene glycols) having 10 oxyethylene groups in the molecule (Triton X-100, TX100) and cetyltrimethylammonium bromide (CTAB) with Zonyl FSN-100 (FC6EO14, FC1) as well as with Zonyl FSO-100 (FC5EO10, FC2) ternary mixtures. The obtained results were compared to those provided by the Fainerman and Miller equation and to the values of the solution surface tension calculated, based on the contribution of a particular surfactant in the mixture to the reduction of water surface tension. The changes of the aqueous solution ternary surfactants mixture surface tension at the constant concentration of TX100 and CTAB mixture at which the water surface tension was reduced to 60 and 50 mN/m as a function of fluorocarbon surfactant concentration, were considered with regard to the composition of the mixed monolayer at the water-air interface. Next, this composition was applied for the calculation of the concentration of the particular surfactants in the monolayer using the Frumkin equation. On the other hand, the Gibbs surface excess concentration was determined only for the fluorocarbon surfactants. The tendency of the particular surfactants to adsorb at the water-air interface was discussed, based on the Gibbs standard free energy of adsorption which was determined using different methods. This energy was also deduced, based on the surfactant tail surface tension and tail-water interface tension.

As-cast Ni-Al bronze (NAB) was subjected to friction stir processing (FSP). Different processing parameters including rotating rate, traverse speed, and processing passes were selected to investigate their effect on the corrosion and cavitation erosion properties. Polarization curve and electrochemical impedance spectroscopy (EIS) were used to reveal the corrosion behavior. Cavitation erosion tests were conducted with an ultrasonic vibration device, and the eroded surfaces were observed using scanning electron microscopy (SEM). Results showed that cavitation erosion resistance was improved for all the processed NAB compared to the as-cast, and a two-pass processed NAB possessed the best corrosion resistance since it had further homogenized microstructure compared to the single-pass processed ones. Corrosion and cavitation erosion tests were also conducted on samples (Surface, Subsurface, Middle, and Bottom) obtained by machining from different positions of the stirred zone (SZ) in a constant-parameter processed NAB along the plate thickness. The Middle was more corrosion resistant since its equiaxed microstructure contributed to a homogeneous oxide film on the surface. The grains in the Bottom were the finest, so the Bottom was the most cavitation erosion resistant.

Enhanced cavitation erosion resistance of GX40CrNiSi25-20 cast stainless steels by surface TIG re-melting

Cavitation erosion often occurs in fluid machinery and piping systems of industrial plants. The erosion damage causes a reduction of performance, noise and a leak accident of fluid machine. In this study, cavitation erosion tests were carried out for cast iron FC250 and stainless steel SUS304 under the condition of the stationary specimen test method using the vibratory apparatus specified by ASTM G32-03. Test results are compared to our previous paper of S15C and discussed in terms of the maximum depth of erosion, the erosion rate and the eroded shape of test specimen after long exposure. It was found that the erosion rate decreases and the maximum depth increases with erosion time with a power of about 0.5 after long exposure regardless of the kind iron and steel.

Early indicators of radiation injury in the lung: Are they useful predictors for late changes?