## 3 CFD Applied to Compost-Bedded Pack Barn Systems
### Boundary Conditions and Simulation Schemes
\begin{table}
\begin{tabular}{c c c c c} \hline
**No.** & **Location** & **Type** & **Specifications** & **References** \\ \hline \multicolumn{5}{c}{**Compost-Bedded Pack Barn Systems with Open Sides**} \\ \hline
1 & Fans & Inlet & Establish air velocity and turbulent & \\  & & & intensity in air flow directions & \\
2 & Roof, pillars, floors of food and & & Non-slip condition, isothermal, with & \\  & & service alleys, walls, etc. & & temperatures specified per & [PERSON] et al. [29] \\  & & & experimental conditions & [PERSON] et al. [15] \\
3 & Bedding surface & Wall & Non-slip condition, with variable & \\  & & & temperature according to & \\  & & & experimental measurements & \\
4 & Inlet region of natural & & Air speed established according to & \\  & & air currents & & experimental measurements & \\
5 & Region opposite to the entry of & & Outlet & Static pressure set to zero & Pakari and Ghani [16] \\  & & natural air currents & & Entrainment, with relative pressure & \\
6 & Side openings & Opening & established according to & \\  & & & experimental conditions & \\ \hline \multicolumn{5}{c}{**Closed Compost-Bedded Pack Barns systems**} \\ \hline
1 & Evaporative pad cooling inlet & Opening & Entrainment, with relative pressure & \\  & & & established according to & \\  & & & experimental conditions & \\
2 & Evaporative pad cooling output & Outlet & Air speed established according to & \\  & & & experimental measurements & \\  & & & Roof, side curtains, deflectors, & \\
3 & pillars, doors, floors of food and & Wall & Non-slip condition, isothermal, with & \\  & & & temperatures specified per & \\  & & & experimental conditions & \\  & & & [PERSON] et al. [15] \\
4 & Bedding surface & Wall & Non-slip condition, with variable & \\  & & & temperature depending on the & \\  & & & distance from the pad cooling & \\
5 & Side curtains & Symmetry & & \\
6 & Exhaust fans & Outlet & Establish air velocity and turbulent & \\  & & intensity in air flow directions & \\ \hline \end{tabular}
\end{table} 
Table 1: Boundary conditions applicable to Computational Fluid Dynamics modeling in Compost-Bedded Pack Barns systems with open and fully enclosed sides. favorable convergence, reasonable accuracy, and lower computational cost compared to the others [13; 15; 16; 31; 37; 42; 47; 77; 80]. This model adds extra stress (Reynolds stress) to the viscosity (\(\mu_{\text{T}}\)), relating the turbulent kinetic energy (k) to its dissipation (\(\varepsilon\)) [28; 36; 72]. In modeling animal facilities, the standard k-\(\varepsilon\) model is usually used in conjunction with an improved treatment (refinement) near the walls [19; 20; 29; 45]. In some studies, the k-\(\varepsilon\) RNG (Renormalization Group) model has been used to model the airflow in the internal and external environments of the facilities and, according to the authors, this model can improve the results achieved due to the inclusion of the additional terms for dissipation rates modeling [37; 45; 78]. This turbulence model differs from standard k-\(\varepsilon\) in that it considers the small scales of fluid motion that contribute to turbulent diffusion [84]. When modeling animal facilities, it is important to also consider buoyancy forces, especially when working with natural and/or natural ventilation systems combined with mechanics [38]. In this case, the thermal buoyancy caused by the heating and/or air cooling must also be modeled, and, therefore, the state equation must relate the air density with its thermodynamic state (temperature and pressure). Methods that can be used to describe changes in air density due to thermal buoyancy are the Boussinesq approximation and treating air as an ideal gas [23; 37]. The Boussinesq approximation considers only dry air as the fluid medium and is not commonly used in CFD studies in animal facilities, as most flows in these facilities have a mixture of dry air and moisture.