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Three-Dimensional Buoyant Turbulent Flows in a Scaled Model, Slot-Ventilated, Livestock Conhnement Facility

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Three-Dimensional Buoyant Turbulent Flows in a Scaled Model, Slot-Ventilated, Livestock Conhnement Facility THREE-DIMENSIONAL BUOYANT TURBULENT FLOWS IN A SCALED MODEL, SLOT-VENTILATED, LIVESTOCK CONHNEMENT FACILITY S. J. Hoff, K. A. Janni, L. D. Jacobson MEMBER MEMBER MEMBER ASAE ASAE ASAE ABSTRACT influences the velocity and temperature distributions A three-dimensional turbulence model was used to throughout the space. determine the effects of animal-generated buoyant forces Little information exists on velocity and temperature on the airflow patterns and temperature and airspeed distributions throughout a ventilated space beyond the distributions in a ceiling-slot, ventilated, swine grower inlet-jet-affected region. Spatial conditions generally have facility. The model incorporated the Lam-Bremhorst been described qualitatively based on overall airflow turbulence model for low-Reynolds Number airflow typical patterns. The microclimate of the animal, as a function of of slot-ventilated, livestock facilities. The predicted results the inlet conditions for winter conditions when the from the model were compared with experimental results potential for animal chilling is the greatest, is of prime from a scaled-enclosure. The predicted and measured concern. results indicated a rather strong cross-stream recirculation Mixed-flow ventilation research related to animal zone in the chamber that resulted in substantial three- confinement facilities has attempted to characterize the dimensional temperature distributions for moderate to desired inlet conditions based on the inlet jet behavior as it highly buoyancy-affected flows. Airflow patterns were enters the ventilated space. In the past, recommendations adequately predicted for Ar^ > 40 and J values < 0.00053. specified that the desired inlet velocity be maintained For Ar^ < 40 and J values > 0.00053, the visualized between 4.0 and 5.0 m/s. Recent research highlighted the patterns indicated that the jet separated from the ceiling importance of air-mixing and the effect of buoyant forces before the opposing end-wall. This discrepancy was on the behavior of the inlet jet as it enters the confinement attributed to variations in the experimental and numerical facility (Barber et al., 1982; Leonard and McQuitty, 1986). inlet flow development assumptions. The effect of buoyant forces on inlet jets were summarized KEYWORDS. Animal housing. Ventilation, Airflow. by Randall and Battams (1979) using the inlet corrected Archimedes Number (Ar^). The application of mathematical models to simulate INTRODUCTION airflow in livestock facilities has been pursued before. inter ventilation of livestock confinement Timmons et al. (1980) applied an inviscid two-dimensional facilities is characterized by low ventilating rates model to a slot-ventilated livestock facility. Janssen and Win relatively large spaces and high animal Krause (1988) applied a two-dimensional model that densities. The animals produce a substantial amount of described velocity, temperature, and contaminant sensible and latent heat, >yhich, combined with low distributions in slot-ventilated livestock facilities. The ventilating rates, can produce non-uniform temperature model used an augmented laminar viscosity to account for distributions and air velocities within the ventilated space. turbulence effects in the building. Choi et al. (1987, 1988, The goal of the engineer is to distribute this limited amount 1990) applied the isothermal fully turbulent k-£ model to a of fresh inlet air as efficiently as possible and to provide an two-dimensional slot-ventilated enclosure. They acceptable microclimate near the animals that maintains investigated the distributions of velocity and contaminants well-being. with and without obstructions and found very reasonable A typical arrangement has fresh air entering the agreements with experimental results. ventilated space through a slot-diffuser adjacent to the Many questions exist regarding the relation between the ceiling along one wall. Fans in the opposing wall provide Ar^ and the spatial variability of temperature and velocity, the required pressure differential necessary for the desired which ultimately affects the thermal comfort of the fresh-air exchange rates. The resulting ceiling jet confined animals. Animals can be adversely affected at some levels and combinations of velocity and temperature (Riskowski and Bundy, 1990). Current computing Article was submitted for publication in August 1991; reviewed and resources and modeling equations and techniques make it approved for publication by the Structures and Environment Div. of possible to address questions regarding velocity and ASAE in February 1992. Published as Paper No. 19,254 of the Scientific Journal Series of the temperature distributions in confinement livestock Minnesota Experiment Station. This research was conducted under facilities. Minnesota Agricultural Experiment Project No. 12-076 and with support The purpose of this project was to develop and verify a from the University of Minnesota Supercomputer Institute. three-dimensional, turbulent-buoyant, numerical model for The authors are Steven J. HofT, Assistant Professor, Agricultural and the analysis of slot-ventilated, livestock confinement Biosystems Engineering Dept., Iowa State University, Ames; Kevin A. Janni, Associate Professor, and Larry D. Jacobson, Associate Professor, facilities. Existing turbulence models and solution Agricultural Engineering Dept., University of Minnesota, St. Paul. techniques were used to develop a three-dimensional VOL. 35(2): MARCH-APRIL 1992 © 1992 American Society of Agricultural Engineers 0001-2351 / 92 / 3502-0671 671 numerical model for the analysis of slot-ventilated result in acceptable air mixing conditions in the ventilated livestock confinement facilities. The numerically predicted space. The air-mixing criteria is summarized in a Jet airspeed and temperature distributions were compared with Momentum Number (J) (Barber et al., 1982). data from a 1/5 scale-model slot-ventilated swine Three dimensionless parameters were used to identify growing/finishing facility. The numerical model's the ventilating conditions for this non-isothermal capabilities for analyzing ventilating airflow in livestock arrangement. The Jet Momentum Number (J) confinement facilities was assessed. (Barber et al., 1982) was used to describe the momentum This study makes frequent reference to a 1/5 scale- of the entering jet and is defined as (all variables defmed in model facility. The 1/5 scale-model is similar to that used nomenclature section): in the study of Barber and Ogilvie (1984). That is, the air chamber used to verify the turbulence model is geo­ metrically 1/5 the size of a typical swine growing/finishing J = QH^ (1) facility. gv BUILDING DESCRIPTION AND GOVERNING The inlet corrected Archimedes Number (Ar^) defmed as (Randall and Battams, 1982): PARAMETERS A schematic of the building studied is shown in figure 1. ^^, Cd g AsWH(W H- H) (Ts - TO This facility represents a 1/5 scale-model swine (2) growing/Hnishing facility identical in size to the apparatus Q^(546.+ Ts+Ti) reported in Barber and Ogilvie (1984). This facility had a single port exhaust located at the center of the exhaust was used to estimate the buoyant forces on the incoming end-wall. Ventilating air entered the building through a chilled jet. It has been widely used for livestock facilities continuous end-wall slot located adjacent to the ceiling. (Barber et al., 1982; Leonard and McQuitty, 1985, 1986). The chamber was 2.40 m long, 2.00 m wide, and 0.64 m Finally, the Raleigh Number (Ra^) based on building high. The building was empty, with a uniformly heated height (H); floor simulating a dense population of animals. The building was symmetrical with respect to the X-Y plane R^,,PgPCrs~TOH^ located through the exhaust fan center-line. Only data from (3) one-half the chamber is reported. It is shown in Hoff (1990) that symmetry did exist in the experimental apparatus. was used to estimate the natural (or free) convection effects expected in the building as a result of the heat from the DiMENSIONLESS PARAMETERS simulated animals. Recent research projects have characterized the desired These three parameters defined key elements of this inlet-jet conditions in terms of how the inlet buoyant and ventilation arrangement. Jet Momentum describes the inertial forces affect the trajectory of the inlet jet. The ratio anticipated level of air-mixing, the Archimedes Number between inlet buoyant and inertial forces characterizing the describes buoyancy affects on the inlet jet, and the Raleigh inlet-jet can be summarized in terms of an inlet-corrected Number describes the overall buoyancy effects in the Archimedes Number (Ar^.). building. Winter inlet design recommendations also were For well-mixed, non-drafty flows, the Jet Momentum developed to create a horizontally stable jet pattern upon should be kept between 0.(KX)75 and 0.0015 (Barber et al, entrance to the ventilated space (Randall and Battams, 1982; Ogilvie et al., 1988). Minimizing buoyancy affects 1979; Barber et al., 1982; Leonard and McQuitty, 1986). requires that the Archimedes Number be kept below 50.0 Recommendations were given for inlet conditions that (Leonard and McQuitty, 1986), and minimizing natural or free-convection effects requires the Raleigh Number based on building height to be kept at or below 4.0 x 10^ (Torrance and Rocket, 1969). For this project, the J values varied between 0.00029 Symmetry and 0.00126, the Ar^, values varied between 13.2 and 88.5, and the Ran varied between 1.1 x 10^ and 4.0 x 10^. Thus, it
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