In a cryogenic propellant tank, the liquid always continuously changes into gas which pressurizes the tank. To pressurize the tank more we can run the liquid through the pipes along the outer wall and because of heat transfer the temperature of liquid increases and it changes into gas, which is known as self-pressurizing. This mechanism is mostly used for pressure fed systems.
How much can we rely on self-pressurizing, while we do it for the tanks in the rockets?
Is it better to use external tanks than self-pressurizing to pressurize the cryogenic propellant tanks in the rockets?
Will it lead to flashing of the stored cryogenic liquid?