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Research Papers: Multiphase Flows

Detection of Cavitation in a Venturi Injector With a Combined Method of Strain Gauges and Numerical Simulation

[+] Author and Article Information
Yuncheng Xu

College of Water Resources
and Civil Engineering,
China Agricultural University,
Beijing 100083, China
e-mail: ycxu1990@gmail.com

Yan Chen

College of Water Resources
and Civil Engineering,
China Agricultural University,
Beijing 100083, China
e-mail: caihua2008@yeah.net

Jianqiang He

College of Water Resources
and Architectural Engineering,
Northwest A&F University,
Shaanxi 712100, China
e-mail: mythbird@hotmail.com

Haijun Yan

College of Water Resources
and Civil Engineering,
China Agricultural University,
Beijing 100083, China
e-mail: yanhj@cau.edu.cn

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received March 29, 2013; final manuscript received February 17, 2014; published online May 15, 2014. Assoc. Editor: Olivier Coutier-Delgosha.

J. Fluids Eng 136(8), 081302 (May 15, 2014) (8 pages) Paper No: FE-13-1210; doi: 10.1115/1.4026879 History: Received March 29, 2013; Revised February 17, 2014

Abstract

The fertilizer suction capability of a Venturi injector is dependent on the vacuum pressure in the throat portion. As the vacuum level drops below the saturation vapor pressure, the pressure decreases to a particular value corresponding to the maximum pressure difference (Δpmax) between inlet and outlet pressures, and critical cavitation is likely to occur, leading to an unstable suction flow rate and low fertilization uniformity. A new method of using strain gauges to detect cavitation in Venturi injectors was explored experimentally and verified numerically under various operating conditions. The standard deviation (SD) of the measured strain values and the simulated values of the vapor-phase volume fraction (Vf) were used to evaluate the influence of cavitation. The results showed that both the rate of increase $(ηm)$ of the average SD and the average growth rate (AGR) of the simulated cavitation length reach relatively large values at the maximum pressure difference (Δpmax), where the measured suction flow rate simultaneously reaches a maximum. In addition, SD and Vf shared similar variation trends at pressure differences larger than the corresponding Δpmax under various conditions. This new cavitation detection method has been proved to be feasible and reliable. It helps to determine accurately the value of Δpmax at different inlet pressures and to ensure that the Venturi injector runs in a safe operating-pressure range.

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Figures

Fig. 1

Internal structure of the Venturi injector with strain gauges attached to its surface. Dimensions in millimeters (mm).

Fig. 2

Schematic diagram of experimental device for cavitation detection in a Venturi injector, including valves (components 1, 2, 3, 9, and 10), turbine flow meters [4,8], pressure gauges [5,7], a Venturi injector with strain gauges attached [6], and a dynamic strain indicator [11]. Dimensions in millimeters (mm).

Fig. 3

Schematic views of volume–throat and volume–diffusion domains. The blue volumes represent the computational domains of the two spherical volumes.

Fig. 4

Relationship between SD of strains at the throat portion of the Venturi injector and the pressure differences (Δp) under seven different inlet pressures. Vertical lines of Δp1, Δp2, and Δp3 correspond to an inlet pressure of 0.45 MPa.

Fig. 5

Relationship between the SD ratio (SDm/SD1) at the throat portion and the diffusion portion and the pressure difference (Δp) at an inlet pressure of 0.40 MPa. Three eigenvalues, Δp1, Δp2, and Δp3. Maximum pressure difference Δpmax.

Fig. 6

Relationship between SD of strain values at the throat portion and suction flow rate (Q3) at inlet pressures of (a) 0.30–0.45 MPa and (b) 0.15–0.25 MPa

Fig. 7

Relationship between maximum pressure difference (Δpmax) and inlet pressure (p1)

Fig. 8

Schematic diagram of internal flow in a Venturi injector for the section Z = 0, inlet pressure of 0.40 MPa, and outlet pressure of 0.011 MPa

Fig. 9

Distributions of vapor-phase volume fraction (Vf) at an inlet pressure of 0.40 MPa

Fig. 10

Variation of cavitation length with pressure difference (Δp) at inlet pressures (p1) of 0.40 and 0.30 MPa. The diffusion portion starts from X = 2 mm (dashed horizontal line).

Fig. 11

Variation of simulated vapor-phase volume fraction (Vf) and SD of strain values at (a) the throat portion and (b) the diffusion portion at an inlet pressure of 0.40 MPa

Fig. 12

Relationship between simulated vapor-phase volume fraction (Vf) and SD of strain values at inlet pressures of 0.30, 0.35, 0.40, and 0.45 MPa

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