Averaging equations

Volume averaging for the three components (two solid and one fluid) yields

- p_AK_A = B<>u_A - _A(1-_A),  

- p_BK_B = B<>u_B - _B(1-_B),   and

- p_fK_f = B<>u_f + .   These three equations should be compared to (solids) and (fluidf). Now, to provide some further insight, notice that the left hand side of (uA) is equal to $\delta[V_A(1-\phi_A)]/V_A(1-\phi_A)$, while the right hand side is $\delta V_A/V_A - \delta\phi_A/(1-\phi_A)$.