Book Synopsis The "Heat-Pipe" Effect in Vapor-Dominated Geothermal Systems by :
Download or read book The "Heat-Pipe" Effect in Vapor-Dominated Geothermal Systems written by and published by . This book was released on 1977 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: White, Muffler, and Truesdell (1971) and Truesdell and White (1973) developed a conceptual model of transport in vapor-dominated geothermal zones. The main theme of the model is that coexisting liquid and vapor phases form a counterflowing convection system similar to that observed in a heat pipe (Dunn and Reay, 1976). It is hypothesized that water evaporates from a deep water table, passes upward through the formation, and condenses at an impermeable cap rock, effectively transferring the latent heat of boiling through the formation. The liquid water then percolates downward, completing the cycle. The physics involved in the flow system is illustrated in an analysis of an idealized one-dimensional, homogeneous, 2 km deep vapor-dominated zone which is bounded below by a water table which has a temperature of 236°C. Flow of water and steam in the system is assumed to be described by Darcy's law for unsaturated porous materials. The liquid water potential, defined as the Gibbs free energy per unit volume of water, is used in place of the liquid pressure in the equation for water because flow in a highly unsaturated medium is to be considered. Comparison of figures 2 and 4 illustrates that the liquid saturation in a two-phase convection system can be much higher than that predicted from a static pressure analysis. As a result, the "vapor pressure lowering" effect expected in a static system disappears. The decrease in P{sub V} at the top of figure 4 is caused by temperature decrease; the relative vapor pressure in the dynamic system is above 99%. However, the permeability used in this example is very low. At higher permeabilities the condensing steam drains out of the system much faster, and the saturation approaches the static profile. 5 refs., 4 figs.
