Studies on the dielectrophoretic force and its effects on boiling bubble dynamics and heat transfer in terrestrial and microgravity environments

One of the main effects an electric field has on the boiling process is the addition of a dielectric polarization force (the dielectrophoretic force) on the generated vapor bubbles. This force can drastically change the bubble dynamics and the resulting boiling heat transfer rates in both terrestrial and microgravity environments. First, the development of the facilities to support the electric-field boiling research is presented. This includes the design, construction, and calibration of the drop tower, and the other experimental measurement devices. Aside from this, a chapter is also devoted to the feasibility of utilizing a thin gold-film heater with thermochromic liquid crystals which provides an instantaneous average surface temperature with the resistometry technique and a color/temperature map. Second, a numerical study is performed which shows that the capability of an electric field to enhance boiling in terrestrial gravity or microgravity is greatly dependent on the electrode geometry. Among other things, high-gradient electric fields result in larger forces which are inherently more localized, while low-gradient electric fields result in smaller forces which are more evenly distributed in space. Third, with the use of the numerical results, a uniform dielectrophoretic force is placed across a platinum heater wire. An effective gravity is defined which accounts for the relative dielectrophoretic and buoyancy forces, and boiling curves are performed while varying the effective gravity. It is shown that the heat transfer will be enhanced if the effective gravity holds the bubbles near the heater surface, while at the same time permitting access of the liquid to the surface to prevent dryout. Also, it was discovered that a quarter power dependence appears to be a reasonable engineering approximation for the increase in CHF with effective gravity. Fourth, a flat surface-boiling gold-film heater and a single-bubble heater are used with three electrode geometries--a diverging-plate, a flat-plate, and a pin electrode. It is shown that each of these geometries are effective in driving the boiling process in microgravity, however, the effectiveness is dependent on the heat flux with respect to the high voltage strength. The results are presented in terms of a boiling map which can account for the transient heat transfer coefficients observed in some circumstances. The bubble diameter at the time of detachment was found to vary inversely as the effective gravity to the...