proceedings of the fourth us water jet conference - Waterjet ...

After each sample had been cut to measure 5 x 7.5 cm it was placed in the holder,
the sample length was adjusted to exceed only slightly the anticipated depth of cut, in
order to provide maximum sample stability. A cutting run was made. The pump was
raised to the required pressure prior to the test, and the traverse conditions were such that
the samples had accelerated to the required velocity before they passed under the jet.
Similarly deceleration did not occur until after the sample carriage had passed beyond the
jet. After cutting, the depth of cut was determined by using a thin metal ruler. On every
specimen between four and seven depth values were taken, the final result was then
obtained by averaging the values measured for these depths.
Where polymer was added to the water, before test, the procedure was slightly
different. The polymer was added to a container full of fresh filtered water. After adding
the liquid polymer the solution was stirred vigorously by hand for between 15 and 20
minutes. The solution was then immediately used, any fluid remaining after the test was
disposed after the experiment. Thus, for every test at a new polymer concentration, a
fresh mixture was prepared.
RESULTS
The results for the experiments were analyzed using the desk-top computer
program Statview 512, available for the Macintosh computer. Several regression models
were considered. Among these the best correlation coefficients were achieved when the
exponential model was used. A general equation of the model can be expressed as below:
where
D = k ⋅ P y ⋅ V z . . . . . . . . . . . . . . . . . . .(1)
D is the depth of cut (cm)
P is the jet pressure (MPa)
V is the traverse speed (cm/sec)
k,y,z are the regression coefficients
For three different foam types and five different nozzle diameters, individual
relations are given in the form above in table 3. A multiple regression on the 375 data
points indicated that the equation correlating jet performance with parameters can be
expressed by the equation
where
D = 16.305 f − 0.97 P 1.15 n 1.44 V −0.3 . . . . . . . . . . . . . . .(2)
f is the foam density in kg/m 3
n is the nozzle diameter measured in mm
The equation had an R-squared value of 0.945. A similar procedure was
developed to analyze the results of Foam #1 when different concentrations of polymer
were used in the feed water. Again a multiple regression equation was generated using
135 data points of the form:
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