Moving text associated with \underbrace downward

Question

Is there a way to move the text associated with an \underbrace{} downward? I've attempted to depict what I mean in the marked-up image below. The text "Thermal Conduction" does not need to be contained with in the left and right parentheses, nor the square braces. The goal is to reduce the overall height of the actual equation by moving the text outside the parentheses.

In case it is helpful, here is the raw latex used to generate the heat transport equation in porous media (shown below):

\begin{equation*}
\underbrace{\left( 1+ \frac{1- \phi}{\theta} \frac{C_{P_{s}}}{C_{P_{w}}} \frac{\rho_s}{\rho_w} \right) \frac{\partial \left( \theta T \right) }{\partial t}}_\text{change in stored energy}=\frac{\partial }{\partial x_i} \left[ \theta \left( \underbrace{\frac {k_{T_{bulk}}}{\theta C_{P_{w}} \rho_w}}_{\text{Thermal} \atop \text{Conduction}} + \alpha \frac{\mathrm{q}}{\theta} \right) \cdot \frac{\partial T}{\partial x_j} \right] - \frac{\partial }{\partial x_i} \left( \theta v_i T \right) + q'_s T_s + \frac{\theta \gamma_w }{C_{p_{w}}} + \frac{ \left( 1 - \phi \right) \gamma_s }{C_{p_{w}}} \frac{\rho_s}{\rho_w}
\end{equation*}

Answer 1

If you're able to update the raw LaTeX code provided, you can manually choose the appropriate delimiter height with \biggl...\biggr pairs:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\noindent Original equation:
\begin{equation}
  \underbrace{
    \left(
      1 + \frac{1 - \phi}{\theta} \frac{C_{P_s}}{C_{P_w}} \frac{\rho_s}{\rho_w}
    \right)
    \frac{\partial \left( \theta T \right)}{\partial t}}\text{change in stored energy}
    =
    \frac{\partial}{\partial x_i}
    \left[
      \theta
      \left(
        \underbrace{
          \frac{k{T_{bulk}}}{\theta C_{P_w} \rho_w}
        }{\text{Thermal} \atop \text{Conduction}}
        +
        \alpha \frac{\mathrm{q}}{\theta}
      \right) \cdot \frac{\partial T}{\partial x_j}
    \right]
    -
    \frac{\partial}{\partial x_i}
    \left(
      \theta v_i T
    \right)
    + q'_s T_s + \frac{\theta \gamma_w}{C{P_w}} + \frac{\left( 1 - \phi \right) \gamma_s}{C_{P_w}} \frac{\rho_s}{\rho_w}
\end{equation}
\noindent Modified equation:
\begin{equation}
  \underbrace{
    \biggl(
      1 + \frac{1 - \phi}{\theta} \frac{C_{P_s}}{C_{P_w}} \frac{\rho_s}{\rho_w}
    \biggr)
    \frac{\partial ( \theta T )}{\partial t}}\text{change in stored energy}
    =
    \frac{\partial}{\partial x_i}
    \biggl[
      \theta
      \biggl(
        \underbrace{
          \frac{k{T_\text{bulk}}}{\theta C_{P_w} \rho_w}
        }{\substack{\text{thermal} \ \text{conduction}}}
        +
        \alpha \frac{\mathrm{q}}{\theta}
      \biggr) \cdot \frac{\partial T}{\partial x_j}
    \biggr]
    -
    \frac{\partial}{\partial x_i} (\theta v_i T)
    + q'_s T_s + \frac{\theta \gamma_w}{C{P_w}} + \frac{(1 - \phi) \gamma_s}{C_{P_w}} \frac{\rho_s}{\rho_w}
\end{equation}
\end{document}

Other minor changes include:

• Removal of unnecessary \left...\right combinations
• \text{bulk}
• \substack{\text{thermal} \\ \text{conduction}}
• Consistent use of P_w