A Study of Computational Fluid Dynamics Assumptions and Their Role in the Evaluation and Design of Targeted Cooling Strategies for Dairy Operations Validated Through Experimentation.

摘要

Heat stress represents a significant cost to the dairy industry. To alleviate these loses, dairy producers have invested into designing and installing ventilation and cooling systems for their dairy cows. The design of dairy barns is usually (for new barns) based on the cooling requirements for the dairy cows, which vary significantly with breed and region. New systems are beginning to cool the cow itself, rather than the whole barn in order to increase efficiency. The present work evaluates two dairy cow cooling systems: a positive pressure tube ventilation, using experimental data as computational modeling; and a conduction cooling heat exchanger using experimental data. Testing these systems at production scale is expensive and time consuming for producers. In order to alleviate these costs, computational fluid dynamic models can be used to estimate the systems performance before they are installed. However, there is a need to understand how accurately the cow should be represented within these models. Therefore this study evaluates six different cow analogs, three primitives (sphere, cylinder, rectangular prism) and three realistic (six-cylinder cow, low polygon cow, high polygon cow) geometries in order to compare and contrast their applicability in computational modeling. The study discusses the ability of computational fluid dynamics models to evaluate positive pressure tube ventilation. The ability of conduction cooling to maintain cows cool during high temperatures and humidity is discussed in detail. Furthermore, the different cow geometries are evaluated and suggestions as to when each is to be used are provided. The low polygon cow representation is then used to evaluate the animal occupied zone as porous media assumptions within the holding area of the barn.