Jairo Alexander Osorio Saraz

Three-Dimensional Modeling and Simulation of Heat and Mass Transfer Processes in Porous Media: An Application for Maize Stored in a Flat Bin

If the relative humidity and temperature of the air inside a granular mass of stored grain exceeds a certain threshold value, microorganism activity is likely to increase. Lower relative humidity and temperature, when uniformly distributed inside the grain mass, prevent moisture migration and an increase in microorganism activity. To cool down or maintain the temperature of the grain mass below a threshold value, forced ventilation with an appropriate airflow can be used to remove excess moisture or heat generated by grain or microorganism respiration. The objective of this work was to solve the equations that describe the conservation of heat, mass, and momentum in order to predict heat and mass transfer processes in the environment inside a grain mass of maize, stored in a flat bin. Three-dimensional computational fluid dynamics was used to solve the equations. The analysis of heat and mass transfer was performed considering the geometry of a two-ton-capacity bin prototype using a hexahedral mesh for the finite volume analysis. The numerical grid was defined to discretize the physical flow domain of interest to calculate velocity, temperature, and moisture distribution in the bulk of stored grain. The predicted results were compared with experimental data, and the agreement between them was very good.

Modeling and Simulation of the Transient Response of Temperature and Relative Humidity Sensors with and without Protective Housing

Based on the necessity for enclosure protection of temperature and relative humidity sensors installed in a hostile environment, a wind tunnel was used to quantify the time that the sensors take to reach equilibrium in the environmental conditions to which they are exposed. Two treatments were used: (1) sensors with polyvinyl chloride (PVC) enclosure protection, and (2) sensors with no enclosure protection. The primary objective of this study was to develop and validate a 3-D computational fluid dynamics (CFD) model for analyzing the temperature and relative humidity distribution in a wind tunnel using sensors with PVC enclosure protection and sensors with no enclosure protection. A CFD simulation model was developed to describe the temperature distribution and the physics of mass transfer related to the airflow relative humidity. The first results demonstrate the applicability of the simulation. For verification, a sensor device was successfully assembled and tested in an environment that was optimized to ensure fast change conditions. The quantification setup presented in this paper is thus considered to be adequate for testing different materials and morphologies for enclosure protection. The results show that the boundary layer flow regime has a significant impact on the heat flux distribution. The results indicate that the CFD technique is a powerful tool which provides a detailed description of the flow and temperature fields as well as the time that the relative humidity takes to reach equilibrium with the environment in which the sensors are inserted.

Mapping thermal environment inside broiler barns for the diagnosis of cold stress at bird initial growing stage.

Average temperature for the whole air volume within a broiler house may not be representative and in some cases it could mask thermal discomfort situations for broilers, especially in their growing period. At this stage, chicks are susceptible to cold stress, which might lead to developmental disorders that will compromise their overall performance. This study was conducted with the aim of mapping the dry-bulb temperature within the bird influence zone for a negative pressure barn (NPB) and a naturally ventilated barn (NVB), both for broilers, during the first three weeks of age, the investigated barns have an architecture that is usually adopted in warm climate conditions, such as Brazil, i.e. non-insulated and occasionally open by lowering the curtains. The mapping results suggested that the insulation capacity of the NVB was poorer as compared to the NPB, while average temperature during the night period was below thermoneutrality for both barns during most of the time, suggesting that both heating systems were undersized. Temperature maps also suggested that heated air was poorly mixed in the NVB during the first two weeks of age being that during the night period the cold air temperature (also in both cases) exposed the chicks to cold stress situations.