This paper describes existing numerical techniques used for simulating heat pipe operation, and the development of a simplified numerical model for normal wicked/wickless heat pipes based on the analysis of current modelling methods. Vapour flow was treated as a two-dimensional flow. Heat transfers through the liquid-wick region and wall region were computed by solving a one-dimensional heat conduction equation. Flow in the liquid-wick region was treated as a one-dimensional problem. The liquid and vapour flows were Coupled using a set of governing equations, incorporating thermal compressibility, hydrodynamical and capillary relationship, as well as geometrical correlation. The finite-difference method was employed to carry out the numerical analysis, and FORTRAN language was used to develop a computer program. The model was used to investigate the operating characteristics of a long 'wicked' heat pipe, including variation of cross-sectional area, axial/radial velocity, pressure and temperature of liquid/vapour flows with height position above the liquid level. To validate the modelling predictions, a test rig was constructed to carry out experimental testing. This included measurement of surface temperatures and heat flow associated with heat-pipe heat transfer. The results from tests were found to be in general agreement with the numerical predictions when the test conditions were close to the simulation assumptions. Copyright (C) 2004 John Wiley Sons, Ltd.