## 3 CFD Applied to Compost-Bedded Pack Barn Systems
### Considerations for Future Studies  
Potentially, some simplifications conducted to reduce the complexity of the computational domain and of the collections for CFD models validation of animal facilities can cause divergences between modeled and experimental results. In this context, based on the literature, some important considerations that can be applied to CFD modeling of CBP systems in future studies were addressed as follows:  
* If the facility has pillars and/or walls inside, these constructive elements must be considered in the computational domain. Normally, there is a reduction in air velocity in the regions where these elements are located, and, consequently, there is a tendency for the concentration of temperature, humidity, and gases, which is not going to be predicted in the CFD model if they are not considered in the computational domain [36]. * In the case of CBP systems with open sides, if there are other buildings nearby, these must be included in the computational model since they can influence the air flow and the environmental conditions inside the facility [31]. The same is valid for variations in topography in the external region of the facility, which can influence the air flow when they are large scale [48]. If there is variation in the speed and direction of natural air flow through the inlet side of the facility due to variations in terrain and other obstacles, whenever possible, these variations should be included in the computational model, using relevant approaches, so that divergences do not occur in relation to the real situation [36]. * Whenever possible, it is recommended that housed animals be included in the computational domain with uneven distribution according to the places where there is a tendency for their concentration [29]. In this way, the simulation can return results closer to those of the physical (real) system, unlike the cases in which the AOZ is assumed to be a uniform porous medium [14; 31], which disregards the fact that the animals tend to concentrate in certain facility regions, such as near feeders, drinkers, salt troughs, sprinkler lines, etc. Additionally, it is important to highlight that when the animal's presence is not represented in the computational domain, as observed in some CFD studies carried out in animal facilities [16; 30; 44], the results achieved will not represent a typical production situation. * It is important to include momentum source terms due to the animal's presence and building elements, as well as heat source terms due to animal metabolism and the bedding composite process. These terms must be calculated considering adequate approaches, according to the pressure, energy, and metabolic loss mechanisms that occur in each case and included together with the momentum and energy conservation equations [36; 48]. * As there is variation in the spatial distribution of bedding temperature, as reported in some studies [17; 18], due to ventilation conditions and bedding management, it is of interest to establish distribution models of the bedding surface temperature, as performed by [PERSON] et al. [29]. If the bedding surface temperature is considered constant throughout the area, deviations from real situations may occur. As there is the transfer of chemical species, such as moisture and water vapor due to the accumulation of animal feces/urine and bedding composite, it is also important to include transport models for these and other chemical species present in CBP systems. If this is not considered in the CFD modeling, the results achieved may differ from the physical systems, given that the mass balance will not faithfully represent the real situation. Above, only the main considerations for the proper application of the CFD technique to the CBP systems modeling were highlighted.