Chapter 8 - Soil Temperature - LAWR

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SSC 107, Fall 2001 – Chapter 8 Page 8-6 Heat Capacity ∆Q o Heat capacity = (cal / K) ∆T ∆Q is quantity of heat ∆T is associated T change Heat capacity is dependent upon size of the system. Heat capacity per unit mass is ∆ Q c = m∆t cal g° K c is called specific heat - independent of system size Soil Minerals H 2 O Humus c 0.2 1.0 0.5 cal cal cal g° K g° K g° K
SSC 107, Fall 2001 – Chapter 8 Page 8-7 Volumetric heat capacity Csoil = S X i ρ i c i ∆Q = V∆T cal cm ° K Csoil 3 X i - volume fraction of particular soil constituent Csoil = X m ρ m c m + X o ρ o c o + X w ρ w c w + X a ρ a c a - X m , X o , X w , & X a are volume fractions of mineral matter, organic matter, water, & air - ρ are respective densities - c are respective specific heats ρ ρw therefore ρ 1000 a = a ≈ 0 Csoil = X m ρ m c m + X o ρ o c o + X w ρ w c w ρ m = 2.6 g/cm 3 ρ o = 1.3 g/cm 3 ρ w = 1.0 g/cm 3 Csoil = X m (2.6) (0.2) + X o (1.3) (0.5) + X w (1) (1) = 0.52 X m + 0.65 X o + X w Volumetric heat capacity has units of cal cm -3 soil °K -1 Since Xw is just volumetric water content, X w = θv . The equation using slightly different values for ? and c given by Jury et al. (1991) is C soil = 0.46 (1 - φ - X o) + 0.6 X o + θ v In California soils the X o ≈ 1%, so this term has little influence.
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Chapter 8 - Soil Temperature - LAWR

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