A rotating stone flys off tangentially when we cut the string and not radially. So how does centrifugal force "throw" the fluid outward (i.e radially) in case of centrifugal pumps? Also please explain the reason responsible for outward motion of fluid particle in case of centrifugal pumps.
In circular motion, the reason the particle moves in a circle is because there is a net force acting inwards towards the centre of the circle. The object is accelerating (although its speed remains constant) as its direction of motion is changing. In the case of the string being cut, it travels in a straight line as the resultant force acting on the stone (i.e. the tension in the string) is removed, hence it follows its original direction of motion(i.e. tangential to the circle). In the case of the centrifuge, the reaction force of the walls of the container is what's responsible for the circular motion of the particle, hence the fluid is pressed against the walls of the container.