DISJOINING PRESSURE EFFECT ON THE WETTING CHARACTERISTICS IN A CAPILLARY-TUBE

A mathematical model capable of predicting the wicking height formed b y a wetting liquid in a vertical, heated capillary tube was developed. The model incorporates the disjoining pressure, the fluid flow and he at transfer in the thin film region, and the thermocapillary effects. Evaluation of the modeling predictions indicates the meniscus radius o f curvature at the vapor-liquid interface increases significantly with increasing heat flux, resulting in an increase in the contact angle d ue to the surface tension variation, disjoining pressure, and fluid fl ow in the el aporafing thin film. The increase in the contact angle is shown to be the principal reason that the static wicking height in ca pillary tubes is typically greater than the dynamic wicking height obs erved during dynamic flow conditions. In addition to the individual co ntributions of the dynamic flow effect and the contact angle variation , both of these parameters are presented and discussed as a function o f the tube diameter In order to verify the analytical model, compariso ns with previously obtained experimental data are made. The verified a nalytical model presented and developed here provides a better underst anding of the wetting phenomena occurring in a heated capillary tube a nd has applicability in a wide range of applications.