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Internal Energy Balance and the Richards Equation
Author(s) -
Sposito Garrison,
Chu ShuYuan
Publication year - 1982
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1982.03615995004600050001x
Subject(s) - richards equation , energy balance , first law of thermodynamics , internal energy , partial differential equation , work (physics) , balance equation , water potential , balance (ability) , water balance , thermodynamics , mathematics , soil water , environmental science , geotechnical engineering , physics , soil science , mathematical analysis , geology , medicine , statistics , markov model , markov chain , physical medicine and rehabilitation
The energy concept of soil water introduced by Buckingham and developed by Richards is employed to derive a differential balance equation for the partial specific internal energy of water in an unsaturated soil. This equation is shown to comprise both heat flux and chemical work terms, in correspondence with the first law of thermodynamics. For the case of isothermal water flow through a rigid, homogeneous soil, the balance law for internal energy reduces to the Richards Equation with the soil water matric potential as the dependent variable. This result, which does not require the conventional direct appeal to the law of mass balance, demonstrates that the energy concept of soil water provides a self‐consistent method for obtaining the Richards Equation. Either the energy balance concept or the traditional mass‐balance approach can be used to establish the macroscopic physical foundations of the Richards equation.