Religión y razón: el cristianismo como síntesis

As indicated in Figure 4.7a, it can be seen that Mesh 1 and 2 perform better than Mesh 3. However, Mesh 1 was considered appropriate based on its contributions to the close results predicted by the standard 𝑘 − 𝜀 turbulence model. The mesh density with minimal details

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showed closer results to that obtained during the field experimentation. This indicates that too many details may not be necessary as the indoor conditions of the broiler building become complicated (higher number of indoor equipment). This also suggests that it is unnecessary for ventilation engineers to increase the number of cells in the prism layers when simulating the airflow in the broiler occupied zones so as to improve the predictive capability of the turbulence model used during the CFD simulation.

For better understanding, Mesh 1, which is considered to be appropriate, was separated from other mesh densities for further discussion (Figure 4.7b). As shown in Figure 4.7b, there is no significant difference (p < 0.05) between the prediction of standard 𝑘 − 𝜀 and the field

experiment at all locations except at the centre of the building (9 m from the sidewall) where the standard 𝑘 − 𝜀 turbulence model predicted higher air velocity in the broiler occupied zone. Similar to the previous study (Blanes-Vidal et al., 2008), this study has shown that CFD could be used as an engineering tool to give an estimation of indoor conditions of sidewall inlet and roof exhaust ventilated broiler building which could direct further field experiments.

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Figure 4.7: Validation of air velocity predictions of standard 𝑘 − 𝜀 turbulence model (a) all the volume mesh densities [Mesh 1 (red line), Mesh 2 (green line), Mesh 3 (purple line) with the field experiment (blue line) and (b) Mesh 1 (red line) and field experiment (blue line).

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4.4 Conclusion

This study has shown through various verifications that inlet configurations used in the CFD simulation have an important role in the prediction capability of turbulence models. It has also been found out that it is important to consider indoor equipment in the broiler building when simulating the airflow conditions inside the building with the CFD. In like manner, this study has supported the earlier reports on the assumption that airflow through the sidewall inlets (right and left) into the mechanically ventilated livestock buildings is similar and that measurements from one of the two sides could be used to represent the airflow from the sidewall inlets. In order to further understand how the inlet-outlet alignment could influence indoor airflow across the broiler building, this study has shown that measurements obtained on any measurement plane irrespective of its location from the same origin are similar.

Airflow in the broiler occupied zones, within an empty broiler building, was validated with the field experiment. The results of this study have shown that an estimation of the indoor air velocity of the sidewall inlet and roof exhaust ventilated broiler building could be predicted by using CFD simulation and that standard 𝑘 − 𝜀 turbulence model showed better results

compared to other turbulence models (realisable 𝑘 − 𝜀 and SST 𝑘 − 𝜔) considered in this study. However, in order to simulate airflow in an empty broiler building, it is advisable to increase the mesh density during the surface and volume discretisation so as to improve the prediction capacity of the CFD modelling.

Further study with an occupied broiler building was conducted to evaluate the impact of current inlet opening technique used during the hot weather conditions by the commercial poultry farmers. The standard 𝑘 − 𝜀 turbulence model averagely performed well in predicting the airflow distributions in the occupied zones of broiler chickens when validated with the results of field experiment. However, comparing the mesh densities of occupied broiler

building with that of the empty broiler building, this study has shown that the higher number of cells in the prism layer may be avoided due to the design complexity and longer computation time. With lesser design details of broiler building occupied with broilers, the CFD could accurately predict the airflow distributions in the broiler occupied zones when the building is occupied with broiler chickens.

This study, in conjunction with the report findings of Albright (1990) has shown that the current method used in the sidewall inlet and roof exhaust ventilated broiler building needs to be re-evaluated. It has clearly shown that the method may not provide a better airflow in the broiler occupied zones where higher air movement is needed during hot weather periods. Therefore, this study suggests that the ventilation engineers need to investigate other

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appropriate hot weather ventilation system for broiler production so as to alleviate the heat stress challenges faced by broiler chickens during hot weather periods.

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CHAPTER FIVE

DESIGN, DEVELOPMENT AND EVALUATION OF AN ALTERNATIVE HOT WEATHER VENTILATION SYSTEM FOR BROILER PRODUCTION 5.1 Introduction

Control over temperature, humidity and airflow is essential during intensive broiler production. It is well known that the distributed environment has consequences on the welfare and

productivity of the confined birds (Dawkins et al., 2004; Jones et al., 2005). Raising birds in an environment that would prevent them from exhibiting their normal behaviours such as feeding, drinking and normal distribution, could impair their welfare and production. As a result, there should be a balance between the indoor condition and the thermal comfort of the birds. An ideal thermal condition will allow the birds to expend minimum energy to produce heat by physiological processes (Pereira and Nääs, 2008). Otherwise, the bird would resort to using dietary energy for body temperature maintenance, and this could affect their meat yield, meat quality, body weight gain, muscle growth and activities (Quinteiro-Filho et al., 2010; Ruzal et al., 2011; Mack et al., 2013).

An important airflow characteristic that is yet to be considered in the design of the ventilation system of broiler building is the higher inlet turbulence (that is inlet air fluctuation). Many studies have indicated the importance of an air fluctuation in increasing the convective heat transfer of different objects (see chapter two). Integrating air fluctuation into the hot weather ventilation system in broiler production could significantly increase the heat transfer of poultry birds and also shift heat transfer from latent (panting) to sensible (convective and radiative) heat transfer (Yahav et al., 2005). This integration could also provide broiler chickens with an opportunity to reduce the energy they expend on body maintenance, acid/ base and body water balances and also improve the thermal comfort of birds during hot weather periods (Yahav et al., 2005).

In the built environment, studies (Hua et al., 2012; Huang et al., 2012; Zhu et al., 2015) have shown that air fluctuation with −5⁄₃ power spectrum exponent (a parameter for analysing the fluctuation characteristics of airflow) could provide desirable thermal comfort. Heat loss from food products was increased with higher air fluctuation (Ghisalberti and Kondjoyan, 1999). Li et al. (2016a) simulated with computational fluid dynamics (CFD) and reported that an increase in the turbulence intensity within the pig unit from 0.15 to 0.30 improved the heat loss of pig models by 2.6 % at an air velocity of 3.3 m s-1_{. Presently in the typical commercial}

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operated based on the assumed ventilation required within the building. The air turbulence intensity provided at the air inlets in the broiler building is usually 0.1 (Bustamante et al., 2013; Li et al., 2016). To improve air distribution within the broiler building, there is a need for the development of an alternative ventilation system capable of generating higher inlet turbulence so as to improve airflow distributions in the broiler occupied zones during hot weather periods.

Therefore, the objectives of this study were: (1) to design and develop an alternative hot weather ventilation system for broiler production; (2) to evaluate the performances of an alternative hot weather ventilation system and (3) to develop predictive models for air velocity and turbulence intensity of the system.

5.2 Materials and methods

5.2.1 The design and development of an alternative ventilation system for broiler