Performance Limits of Oscillating Heat Pipes: Theory and Validation

Oscillating heat pipes have been the subject of significant research since 1990, but to allow their entry into broad application, it is important to understand their operational limitations. This paper presents analytical and experimental investigations of the various performance limits of oscillating heat pipes. The Bond number limit, vapor inertia limit, heat flux limit, viscous limit, sonic limit, and limitations on heated length are discussed in detail and developed with analytical tools for prediction. These limits are then tested against experimental studies. It is found that the Bond number coefficient can be as high as 2.4-2.74, rather than the typically reported 1.8-2.0. The established vapor inertia, heat flux, viscous, and sonic limits show good agreement with published experimental data sets, as well as controlled experiments run specifically to test these limits. Finally, it was determined that longer evaporator lengths result in a reduction of overall heat transport capability. An analytical approach is presented to predict this performance loss, showing good agreement with experimental results.