Variation in channel diameter is investigated as a means of enhancing heat transfer in a pulsating heat pipe with capillary wick using the model presented here. The model is one-dimensional with slug flow where the momentum equation is solved for each liquid slug. The number and mass of liquid slugs are allowed to vary throughout a simulation. The energy equation is solved both in the wall and wick and in the working fluid. The effects of diameter profile, gravity, fill ratio, and heating and cooling schemes can be studied with the model. Results yield similar trends to what has been experimentally observed. Results also indicate that heat transfer call be enhanced when the diameter of the channel is varied along the channel length, thereby providing increased range of heat load capability, less sensitivity to gravity, and in some cases smaller temperature differentials. (c) 2005 Elsevier Ltd. All rights reserved.