\(\frac{\partial\left(\rho_{G}\varepsilon_{G}u_{G}\right)}{\partial t}+\nabla.\left(\rho_{G}\varepsilon_{G}u_{G}u_{G}-\mu_{G}\varepsilon_{G}\left(\nabla u_{G}+\left(\nabla u_{G}\right)^{T}\right)\right)=-\varepsilon_{G}\nabla p+M_{G,L}+\rho_{G}\varepsilon_{G}g\). (4)