  A pellet target produces micro-spheres of different materials, which are used
as an internal target for nuclear and particle physics studies. We will
describe the pellet hydrogen behavior by means of fluid dynamics and
thermodynamics. In particular one aim is to theoretically understand the
cooling effect in order to find an effective method to optimize the working
conditions of a pellet target. During the droplet formation the evaporative
cooling is best described by a multi-droplet diffusion-controlled model, while
in vacuum, the evaporation follows the (revised) Hertz-Knudsen formula.
Experimental observations compared with calculations clearly indicated the
presence of supercooling, the effect of which is discussed as well.
