As relatively new and promising members of the wickless heat pipes family, Pulsating Heat Pipes, with their high effective thermal conductivity, construction simplicity, low weight, and potential high power loads may answer the present industry demand of high heat transfer capability, efficient thermal control, flexibility and low cost. Numerous are the attempts to simulate their complex thermal behavior, but none of the existing models is validated for transient operative conditions and under various gravity levels. Thus, a novel lumped parameters model able to compute the steady state as well as the transient performance of PHPs has been developed. It consists of a two-phase separated flow model applicable to a confined operating regime (slug plug flow). A complete set of balance differential equations accounts for thermal and fluid-dynamic phenomena. The main originalities of this tool lay in the suppression of the standard assumption of saturated vapor plugs as well as in the consequent embedding of heterogeneous and homogeneous phase changes. In addition, an experimental work has been carried out with a 16 turns copper capillary PHP filled with FC-72. Therefore, the model has been validated in several operative conditions and under various gravity levels by comparison with these experimental data both in normal and hyper-gravity conditions showing very good prediction capability. (C) 2016 Elsevier Ltd. All rights reserved.