The self-excited pulsed jet is characteristically efficient and inexpensive. To develop an optimal pulsed jet, the structural and operating parameters affecting its peak hitting power were studied. The optimal range of cavity length and diameter, the areal ratio of the bottom and top nozzles, the bottom nozzle length, and the target distance and working pressure were all determined.
The self-excited pulsed jet, developed on the basis of the theories of fluid mechanics, fluid elasticity, fluid resonance, underwater acoustics, etc., is efficient. The fluids passing through it form a self-excited oscillation within the structure, with no external exciting source, so that the continuous jet becomes pulsed. The instantaneous energy of a pulsed jet is several times higher than that of an otherwise similar continuous jet (Jiang & Liao 1998).
The self-excited pulsed jet has the advantages of a simple structure, easy processing, good sealing properties, high reliability, and low cost, etc. It is small and no additional driving mechanism is needed (Tang & Liao 1989), so, it has been widely used and developed.
The device's performance parameters have been studied using measurement techniques usually applied to flows inside fluid equipment (Yang et al. 2006). The optimal structural and operating parameters are discussed in this paper, which can be used as a reference for pulsed jet selection and design.
TEST APPARATUS AND METHODS
The tests dealt with the structural and operating parameters of the self-excited pulsed jet influencing its hitting power. The structural parameters include, in particular: the diameter of the top nozzle, , (8, 10, 12 mm), the diameter of bottom nozzle, , (16, 17, 18, 20, 22, 24 mm), the length of the self-excited oscillation cavity, , (30, 45, 55, 60, 75, 90 mm), the diameter of the cavity, , (85, 95, 105, 120, 125 mm), and the length of the bottom nozzle, , (40, 55, 80, 100 mm). The operating parameters include: the working pressure, , (0.8, 1.0, 1.2, 1.4, 1.6, 1.8, and 2.0 MPa), and the target distance, , (50, 150, 200, 300, 400, and 500 mm). The maximum and minimum fluid velocities, respectively, were 62.6 m/s and 39.6 m/s, and the maximum and minimum flow rates 43.4 m3/h and 1.72 m3/h.
Many proportioning tests of performance parameters were carried out under differing conditions, and the peak hitting power curves were obtained in relation to different parameter dimensions.
ANALYSIS OF EXPERIMENT RESULTS
Length of self-excited oscillation cavity (Lc)
Oscillation cavity diameter (Dc)
Areal ratio of bottom and top nozzles (m = d22/d21)
Bottom nozzle length (l2)
Target distance (Lf)
There is no clear reason why the curves relating to operating pressures of 1.2 and 1.4 MPa do not fit the general pattern fully, especially at and around what seems to be the optimum target distance. In principle, jets at these pressures should operate in the same way as those pressures both above and below this range. Further work is in hand to try to understand what happens/happened.
Working pressure (P1)
The performance parameters of the self-excited pulsed jet were studied. The results show that an optimal pulsed jet has: cavity length 55 mm, cavity diameter 120 mm, bottom/top nozzle areal ratio between 3.24 and 4.84, and bottom nozzle length 55 mm, when it is operated at a working pressure between 0.8 and 1.8 MPa, and the target distance is between 150 and 200 mm. Now, further work is being studied as to whether the conclusions are suitable for all types of pulsed jets.
This work was supported financially by the National Natural Science Foundation of China (51179152 & 90410019), the Public Industry Scientific Special Fund of Ministry of Water Conservancy of PRC (201201085), and the Foundation of the Education Department of Henan Province (12A570003).