Phreatomagmatic (PHM) eruptions develop their energetics through rapid heating of external water. With an energy density about 1/4 of that of TNT, bodies of magma have considerable potential for producing powerful vapor explosions where they heat external water rapidly. The thermodynamics of the heat transfer are not simple, ranging from nearly adiabatic to nearly isothermal expansions of a mixture of heated water and magma +/- rock fragments. KWare PHM is designed to make those calculations to illustrate the wide range of explosive potential that develop depending upon the initial conditions of water/magma contact.
The program begins with panel in which the user can adjust initial conditions, those from surface to deep (underground or underwater) conditions or hydrothermal situations.
Using steam table data extrapolations based upon 4th-order polynomials equations, equilibrium conditions (where water and magma first come to the same temperature just prior to water expansion and vaporization. These conditions are shown in the next illustration.
The calculation follows both an adiabatic expansion path and a "isothermal" one (for which isothermal means that the water and magma fragments continuously exchange heat during expansion, maintaining the same temperature). Results show conversions ratios (the percentage of magma heat energy converted to thermodynamic work), steam and water fractions, and final expanded temperature.
The equilibrium values and final states are useful to graph as functions of various initial conditions. Results can help predict the character of phreatomagmatic products from "dry", widely-spread products of high conversion-ratio eruptions to those wet ones of high water/magma ratios. In addition plots can be shown that include all calculated data for the current session.
The current version only support plots versus R (water/magma mass ratio).
KWare PHM software (LA-CC 01-62; Copyright © 2001 UC) is available as self-installing files for downloading for 32-Bit Windows operating systems.
Download for Windows 9x/ME/NT4/2000/XP/Vista: PHM Install (version 1.05.0055, ~3.5 MB, 23 January 2008)
When using this program remember the old adage of "garbage in, garbage out!"
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