In high pressure processes,the driving force for cavitation and there by a variation in vapor content is the ratio between the local pressure and the static pressure in the bulk fluid (FrancandMichel, 2004). Thus,the vapor content gradually increases with increasing pinlet, due to a continuous increase in fluid velocity and a decrease in local pressure at a constant static pressure of the bulk fluid (Riedel, 1973). In the present case,the inlet pressure is constant and the back-pressure increases,thus the driving force for the mass flow rate and the cavitation tendency decreases. According to the work of McKillop etal.(1955), whore corded visible cavitation in a venturitube,the cavitation pattern in the OAOC are depicted for the first and the second orifice as shadow graphic images(Fig. 3) at a constant pinlet of 100 bar.The images
depict a region of 2 mm in diameter and 10 mm in length of the OAOC right after the orifice exit.The flow direction is left to right