Numerical Simulation of Airborne Disease Spread in Cage-Free Hen Housing with Multiple Ventilation Options.

The current ventilation designs of poultry barns have been present deficiencies with respect to the capacity to protect against disease exposure, especially during epidemic events. An evolution of ventilation options is needed in the egg industry to keep pace with the advancing transition to cage-free production. In this study, we analyzed the performances of four ventilation schemes for constraining airborne disease spread in a commercial cage-free hen house using computational fluid dynamics (CFD) modeling. In total, four three-dimensional models were developed to compare a standard ventilation configuration (top-wall inlet sidewall exhaust, TISE) with three alternative designs, all with mid-wall inlet and a central vertical exhaust. A one-eighth scale commercial floor-raised hen house with 2365 hens served as the model. Each ventilation configuration simulated airflow and surrogate airborne virus particle spread, assuming the initial virus was introduced from upwind inlets. Simulation outputs predicted the MICE and MIAE models maintained a reduced average bird level at 47% and 24%, respectively, of the standard TISE model, although the MIRE model predicted comparable virus mass fraction levels with TISE. These numerical differences unveiled the critical role of centrally located vertical exhaust in removing contaminated, virus-laden air from the birds housing environment. Moreover, the auxiliary attic space in the MIAE model was beneficial for keeping virus particles above the bird-occupied floor area.

Computational Fluid Dynamics Modeling of Ventilation and Hen Environment in Cage-Free Egg Facility.

Poultry facilities are going through an evolution in design due to growing demands for cage-free eggs and egg products without unified guidelines to accommodate these transitions. The goal of this study was to help builders and egg producers assess current ventilation design within cage-free production facilities for conditions that impact hen comfort and welfare. The method of evaluation was simulation of the indoor environment of a hen house via computational fluid dynamics (CFD) modeling with individual hens modeled at a typical stocking density. This paper describes the development of a three-dimensional model of a commercial floor-raised cage-free hen house that is cross-ventilated to document current environmental conditions. A one-eighth section of the barn was modeled at full-scale using existing ventilation schemes with each bird represented by a hen-shaped, heated, solid body. A conventional top-wall inlet, side-wall exhaust (TISE) ventilation configuration was modeled for this study. The simulated ventilation rate for the hen house was approximately 3 m3/h (1.77 ft3/min) per hen resulting in 7092 m3/h (4174 ft3/min) for the 2365 birds, which falls at the higher end of the desired cold weather (0 °C) ventilation range. Contours of airflow, temperature, and pressure were generated to visualize results. Three two-dimensional planes were created at representative cross-sections to evaluate the contours inside and outside the barn. Five animal-occupied zones within each of the model planes were evaluated for practical hen comfort attributes. The simulation output suggested the TISE standard ventilation system could limit air speed to a comfortable average of 0.26 m/s (51 ft/min) and the temperature could be maintained between 18 and 24 °C on average at the bird level. Additionally, the indoor static pressure difference was very uniform averaging -25 Pascal (0.1 inches of water), which falls in the normal range for a floor-raised hen house with negative-pressure ventilation during cold weather conditions. Findings confirmed that CFD modeling can be a powerful tool for studying ventilation system performance at the bird level, particularly when individual animals are modeled, to assure a comfortable indoor environment for animal welfare in poultry facilities.

Operator Exposure to Hydrogen Sulfide from Dairy Manure Storages Containing Gypsum Bedding.

Dairy manure storages containing gypsum-based bedding have been linked anecdotally with injury and death due to presumed dangerous levels of gases released. Recycled gypsum products are used as a cost-effective bedding alternative to improve animal welfare and provide agronomic benefits to manure recycled back to the land. Sulfur contained in gypsum (calcium sulfate) can contribute to hydrogen sulfide (H2S) gas formation under the anaerobic storage conditions typical of dairy manure slurry. Disturbance of stored manure during agitation releases a burst of volatile gases. On-farm monitoring was conducted to document conditions during manure storage agitation relative to gas concentration and operator safety. One objective was to document operator exposure to H2S levels; therefore, each operator wore a personal gas monitor while performing tasks associated with manure storage agitation. Data from three dairy bedding management categories on ten farms were compared: (1) traditional organic bedding, (2) gypsum bedding, and (3) gypsum bedding plus a manure additive thought to reduce H2S formation and/or release. Portable meters placed around the perimeter of dairy manure storages recorded H2S concentrations prior to and during 19 agitation events. Results show that farms using gypsum bedding produced higher H2S concentrations during manure storage agitation than farms using traditional bedding. In most cases, gypsum-containing manure storages produced H2S levels above recognized safe thresholds for both livestock and humans. Farm operators were most at risk during activities in close proximity to the manure storage during agitation, and conditions 10 m away from the storage were above the 20 ppm H2S threshold on some farms using gypsum bedding. Although H2S concentrations rose to dangerous levels, only two of 18 operators were exposed to >50 ppm H2S during the first 60 min of manure storage agitation. Operators who are aware of the risk of high H2S concentrations near gypsum-laden manure storages can reduce their exposure risk by working upwind and away from the H2S plume within a closed tractor cab.

Online Design Aid for Evaluating Manure Pit Ventilation Systems to Reduce Entry Risk.

On-farm manure storage pits contain both toxic and asphyxiating gases such as hydrogen sulfide, carbon dioxide, methane, and ammonia. Farmers and service personnel occasionally need to enter these pits to conduct repair and maintenance tasks. One intervention to reduce the toxic and asphyxiating gas exposure risk to farm workers when entering manure pits is manure pit ventilation. This article describes an online computational fluid dynamics-based design aid for evaluating the effectiveness of manure pit ventilation systems to reduce the concentrations of toxic and asphyxiating gases in the manure pits. This design aid, developed by a team of agricultural engineering and agricultural safety specialists at Pennsylvania State University, represents the culmination of more than a decade of research and technology development effort. The article includes a summary of the research efforts leading to the online design aid development and describes protocols for using the online design aid, including procedures for data input and for accessing design aid results. Design aid results include gas concentration decay and oxygen replenishment curves inside the manure pit and inside the barns above the manure pits, as well as animated motion pictures of individual gas concentration decay and oxygen replenishment in selected horizontal and vertical cut plots in the manure pits and barns. These results allow the user to assess (1) how long one needs to ventilate the pits to remove toxic and asphyxiating gases from the pit and barn, (2) from which portions of the barn and pit these gases are most and least readily evacuated, and (3) whether or not animals and personnel need to be removed from portions of the barn above the manure pit being ventilated.

Mid-infrared spectroscopy for gases and liquids based on quantum cascade technologies.

In this paper we present two compact, quantum cascade laser absorption spectroscopy based, sensors developed for trace substance detection in gases and liquids. The gas sensor, in its most integrated version, represents the first system combining a quantum cascade laser and a quantum cascade detector. Furthermore, it uses a toroidal mirror cell with a volume of only 40 cm(3) for a path length of up to 4 m. The analytical performance is assessed by the measurements of isotope ratios of CO2 at ambient abundance. For the (13)CO2/(12)CO2 isotope ratio, a measurement precision of 0.2‰ is demonstrated after an integration time of 600 s. For the liquid sensor, a microfluidic system is used to extract cocaine from saliva into a solvent (PCE) transparent in the mid-infrared. This system is bonded on top of a Si/Ge waveguide and the concentration of cocaine in PCE is measured through the interaction of the evanescent part of the waveguide optical mode and the solvent flowing on top. A detection limit of <100 µg mL(-1) was achieved with this system and down to 10 µg mL(-1) with a simplified, but improved system.

Temperature dependence of the frequency noise in a mid-IR DFB quantum cascade laser from cryogenic to room temperature.

We report on the measurement of the frequency noise power spectral density in a distributed feedback quantum cascade laser over a wide temperature range, from 128 K to 303 K. As a function of the device temperature, we show that the frequency noise behavior is characterized by two different regimes separated by a steep transition at ≈200 K. While the frequency noise is nearly unchanged above 200 K, it drastically increases at lower temperature with an exponential dependence. We also show that this increase is entirely induced by current noise intrinsic to the device. In contrast to earlier publications, a single laser is used here in a wide temperature range allowing the direct assessment of the temperature dependence of the frequency noise.

Photodetectors based on intersubband transitions using III-nitride superlattice structures.

We review our recent progress on the fabrication of near-infrared photodetectors based on intersubband transitions in AlN/GaN superlattice structures. Such devices were first demonstrated in 2003, and have since then seen a quite substantial development both in terms of detector responsivity and high speed operation. Nowadays, the most impressive results include characterization up to 3 GHz using a directly modulated semiconductor laser and up to 13.3 GHz using an ultra-short pulse solid state laser.

Microfluidic tuning of distributed feedback quantum cascade lasers.

In this Letter, we report the tuning of the emission wavelength of a single mode distributed feedback quantum cascade laser by modifying the mode effective refractive index using fluids. A fabrication procedure to encapsulate the devices in polymers for microfluidic delivery is also presented. The integration of microfluidics with semiconductor laser (optofluidics) is promising for new compact and portable lab-on-a-chip applications.

Continuous wave operation of a mid-infrared semiconductor laser at room temperature.

Continuous wave operation of quantum cascade lasers is reported up to a temperature of 312 kelvin. The devices were fabricated as buried heterostructure lasers with high-reflection coatings on both laser facets, resulting in continuous wave operation with optical output power ranging from 17 milliwatts at 292 kelvin to 3 milliwatts at 312 kelvin, at an emission wavelength of 9.1 micrometers. The results demonstrate the potential of quantum cascade lasers as continuous wave mid-infrared light sources for high-resolution spectroscopy, chemical sensing applications, and free-space optical communication systems.