# Development of Predictive Equations for Thermal Conductivity of Compost Bedding
## 3 Results and Discussion
### Thermal Properties of Composts in Different Moisture Contents and Static Compaction Degrees
[PERSON] and [PERSON] [41] reported that the \(k\) of the dry compost (dairy manure and sawdust mix) was 0.051 W m\({}^{-1}\) K\({}^{-1}\) and 0.096 W m\({}^{-1}\) K\({}^{-1}\) with 57% moisture. As noted by [PERSON] et al. [21], the values of \(k\) of composting material (dairy manure and sawdust mix), with moisture content ranging from 0 to 44.2%, showed values between 0.05 and 0.202 W m\({}^{-1}\) K\({}^{-1}\), respectively. The response surfaces presented in Figure 5 were quadratic due to the adjusted polynomial regression models, showing good correlation between the adjusted data for the different depths evaluated (R\({}^{2}\) > 91%), and the parameters of the models were significant (\(p\) < 0.05). For all compost materials tested (Figure 5), \(k\) values increased as MC and SC increased. The composting material with low moisture content presented low thermal conductivity due to the presence of a relatively high fraction of air, thereby reducing heat propagation with uniform temperature distribution across layers of bedding material. Since water, air, and solid materials have their own specific thermal property values, the thermal properties of compost materials vary with the proportion of these three materials, changing the water content, apparent density, and particles [42; 43; 44; 45]. Usually, materials that have a low density also have a low thermal conductivity; consequently, these materials are poor for heat storage. In other words, the thermal conductivity of a bedding material is generally characterized by its dependence on particle density, as the void space is reduced, the filler particles begin to contact each other, and a continuous path is formed through the volume of the sample, increasing the heat and mass transfer with the environ  
Figure 5: Response surface of moisture content (MC) and static compaction (SC) on thermal conductivity (\(k\)) of bed compost materials at different depths: H1 (**a**), H2 (**b**), and H3 (**c**). observed in the field, as when stirring the pack in a CBP barn, the fast exchange of heat and mass is observed between the bedding material and the environment. In Figure 5, it is also possible to observe that the behavior of \(k\) as a function of SC is slightly different in depth H1 in relation to the other depths tested (H2 and H3). This difference was shown by the polynomial model when presenting in Equation (2) a linear term (0.1838-SC) that was not significant in Equations (3) and (4). According to [PERSON] et al. (2009), the thermal conductivity of porous media shows a greater significant difference between the degrees of compaction and depths tested. This could be due to the fact that heat conductivity is controlled by all three phases (solid/liquid/gas) of the material, thus influencing the \(k\) values along the evaluated depth. In addition, the properties of a porous medium itself such as material texture, the insulating properties of any organic layers, and material compaction enhancing the decrease in porosity may endogenously affect material thermal properties ([PERSON] et al., 2011; [PERSON] et al., 2012).