h i j k for velocity and c 39 d 39 h 39 i 39 j 39 k 39 for pressure correspondingly at the mandrel inlet section the fluid velocity sharply increases b c because the inner diameter of the mandrel is less than tubing 1 and the pressure decreases in accordance with the bernoulli law b 39 c 39 there is the same condition at the nozzle inlet section d e for increasing velocity and d 39 e 39 for decreasing pressure in the narrowing section of the nozzle 12 the flow velocity rapidly increases e f and achieves its maximum in the throat 13 f and then decreases f g in the diffuser 14 accordingly to the bernoulli law pressure inside nozzle section 12 decreases e 39 f 39 reaches its minimum in throat 13 and increases f 39 g 39 in the diffuser 14 in the narrowing nozzle passage 12 the static pressure is converted into kinetic energy by acceleration of the flow then the opposite occurs in the expanding area 14 wherein the kinetic energy is converted into the static pressure by the slowing down of the flow velocity at the nozzle outlet the flow velocity sharply decreases g h and the pressure increases g 39 h 39 correspondingly because the flow cross section sharply expands the same condition occurs at the mandrel outlet section i j for decreasing flow velocity and i 39 j 39 for increasing pressure u03b4p2 is the difference between pressure.