Mechanics of submerged jet cavitating action: material properties, exposure time and temperature effects on erosion

Abstract

Experimental setup with a submerged cavitating jet has been used for the study of influences of material, exposure time and working fluid temperature on the erosion process. Each of the parameters has been varied separately, and the results of erosion are analyzed in detail. Additionally, comparison of experiments with nitrated and non-nitrated material has been made in order to study the enhancement (mostly reflected as the prolonged incubation time) of erosion resistance achieved by nitrating the specimen surface. List of symbols σ cavitation number-defined as σ = p ref − p v 1 2 ρ×u 2 ref p ref reference (downstream) pressure (bar) p v (T ) saturation (vapour) pressure (bar) ρ L (T ) density of the liquid (kg/m 3 ) T temperature ( • C) L stand-off distance (mm) A nozzle outlet cross-section area (m 2 ) D in inlet nozzle diameter (mm) u ref reference velocity − exit jet velocity (m/s) = Q/A = V j p 1 upstream pressure (bar) (absolute) p 2 downstream pressure (bar) (absolute) W weight loss (mg), ρ m density of the eroding material (kg/m 3 ), t exposure time (h, s) Q K× √ ( p 1 − p 2 ) flow rate (m 3 /s) K constant = 4.78E-09 for divergent; (m 3 /s/Pa 1/2 ) = 6.17E-09 for convergent nozzle D out outlet nozzle diameter (mm)

The ability of using the cavitation phenomenon as a tool to modify the surface characteristics in micro- and in nano-level

“…The details of the chamber are shown in Fig. 1(a), the details of the test rig is published in a previous work [4]. The cavitating jet impinged on the specimen at 90 degrees to its surface, as shown in Fig.…”

“…In addition, the cavity structure composed of bubbles was investigated and their light emission (sono-luminescence) was studied for various temperature and various hydrodynamic conditions. The published results clarified the dynamics of cavitation clouds and highlighted the important parameters related to the control the phenomenon [4,[25][26][27]. …”

“…The Al-alloy target has a disc shape with 14 mm in diameter and 2.98 mm in thickness as can be seen in Fig.3. The full description of experimental setup for cavitation damage testing is given in details elsewhere [4,25]. The specimens were polished using a classical procedure including grinding papers and diamond pastes.…”

“…Following the first observation of surface erosion (which is assumed to be analogous to the crack initiation step) deeper erosion will be triggered within many rings (depending on the depth of the pits). In our current paper we focus on the plastic deformation phase, more details regarding the erosion stage can be found in our previous publication [4].…”

“…3) The cavitation intensity can be easily controlled by the hydraulic and geometrical parameters. 4) There is no thermal effect to the target surface (compared for example to laser polishing methods). 5) The cavitating jet can be used to selectively pattern the target surface.…”