Exhaust Plenum Research Articles

SOME POTENTIAL PROBLEMS FOR MEASURING AMMONIA EMISSIONS FROM FARM STRUCTURES

The ability to accurately measure ammonia emissions from farm buildings is an important issue both forestablishing emissions regulations and for effective evaluation of mitigation techniques. Most techniques for measuringemissions rely on subsampling within a space. This study examines the influence of subsampling under a variety ofconditions on estimated ammonia recoveries. Tests were made using a large environmental chamber with controlled releasesof ammonia from a gas cylinder from one of two positions within the chamber. Ammonia concentrations were measured incontinuous air samples from either a single exhaust duct or a sampling port in the exhaust plenum where exhaust gases werewell mixed. The chamber temperature was maintained at 22.2. C with an airflow of 10.5 air exchanges per hour. Formeasurements made in the exhaust duct, ammonia recoveries were 217% when the release position and the sampling ductwere aligned in terms of chamber airflow, and were 52% when the positions were not aligned. Placing a wooden barrierbetween aligned release and measurement positions only reduced ammonia recoveries to 173%. In contrast, using anoscillating fan to disperse the ammonia release reduced ammonia recoveries to 78%. When measurements were made in theplenum, recoveries were essentially 100%, and placement of a continuously wetted barrier between the release position andthe exhaust ducts did not influence recoveries. It is suggested that measurement of ammonia emissions be restricted to farmstructures with welldefined airflows and a limited number of exhaust openings, and that the most accurate method forestimating ammonia emission rates would be to collect and mix all of the exhaust streams from a structure prior tocontinuously measuring ammonia concentration and airflow.

Performance Prediction and Control-System Design of an Aircraft Skin-Cooling Technique

We describe the steady state and transient thermal response of the aft cabin of an aircraft that is retrofitted with high-power electronic equipment and cooled by heat rejection through the skin. In this skin-cooling design, the outer surface of the fuselage is treated as a heat exchanger. Hot air from an equipment exhaust plenum is drawn into a series of baffled ducts within the fuselage support structure, where heat is rejected and then recirculated into the cabin. The cooler air from the cabin is then drawn into the electronic equipment. The aircraft air-conditioning unit is also modeled to provide chilled air directly Into the cabin. In addition, this paper presents an algorithm and a control-system concept to maintain the temperature of the aft cabin within acceptable limits. Results establish a control-system design, which is being implemented in a CL-600 Challenger aircraft

Development and Validation of a Thermodynamic Model for an SI Single-Cylinder Engine

A multizone quasi-dimensional model that illustrates the intake, compression, combustion, expansion, and exhaust processes has been developed for a single-cylinder four-stroke spark-ignition engine. The model takes into consideration mass and energy conservation in the engine cylinder, intake and exhaust plenums, and crank-case plenum. The model calculates instantaneous variations in gas thermodynamic states, gas properties, heat release rates, in-cylinder turbulence, piston ring motion, blowby, nitric oxide, and carbon monoxide formation. The cycle simulation accounts for the induced gas velocities due to flame propagation in the turbulence model (k–ε type), which is applied separately to each gas zone. This allows for the natural evolution of the averaged mean and turbulent velocities in burned and unburned gas regions. The present model predictions of thermal efficiency, indicated mean effective pressure, peak values of gas pressure, ignition delay, concentrations of nitric oxide, carbon monoxide, and carbon dioxide are proven to be in agreement with experimental data.

Controlling Wood Dust from Orbital Hand Sanders

Abstract One of the woodworking processes most difficult to control is hand sanding. Hand sanders are used in many processes, and although traditional controls reduce the dust emissions somewhat, there are disadvantages. To overcome these problems and control sanding emissions more efficiently, a dust control exhaust plenum was designed and installed on a hand sander. Laboratory experiments compared the wood dust particle amounts generated by the sander with and without the new control operating. The plenum reduced emissions by approximately 90 percent. Field experiments conducted at an industrial hand sanding process showed that the plenum reduced emissions 56 to 83 percent by particle count and 13 to 35 percent by mass, using real-time instruments. Membrane filter samples also collected during the field test indicated an average reduction of wood dust mass of 86 percent. All of the samples collected when the control was operating were well below the former 5 mg/m3 exposure limit set by the Occupational ...

A LOCAL EXHAUST VENTILATION SYSTEM TO REDUCE AIRBORNE RIBAVIRIN CONCENTRATIONS

A local exhaust hood was designed and built to capture and contain aerosol emissions of ribavirin during drug administration. The newly designed over-the-head hood is similar to the single hood currently used to administer the drug. This new hood was surrounded by an exhaust plenum to form a compound hood configuration. The exhaust plenum was connected to a filtered local exhaust air system to remove the waste aerosol. The compound hood and local exhaust ventilation system were evaluated for leak rate and inside hood aerosol concentration as a function of exhaust flow rates. This hood reduced the leak rate from an average of 98% with the traditional head hood to an average of less than 1% with the compound hood with exhaust port. The compound hood did not perform quite as well when not in use (set aside during infant caretaking) with the nebulizer remaining on. The leak rate was found to increase from an average of less than 1% to an average of 12% when trials were conducted that used a doll as a simulated patient versus trials without a doll, respectively. As regards therapeutic dose inside the hood, the system's performance may lead to an 18% to 25% decrease in inside hood concentration of aerosol entering the hood. Optimum hood operating parameters were identified. An exhaust flow rate in the range from 1.0 Lpm below to 1.0 Lpm above inlet flow rate from the small particle aerosol generator (SPAG nebulizer) reduced the leak rate to an average of less than 1%.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Ceiling Height on Determining Calculated Intake Air Velocities for Biological Safety Cabinets

Abstract A potential problem exists with the certification of Class II, Type A, biological safety cabinets using the standard method for deriving cabinet intake velocity. It has been found that the cabinet air flow balance is affected by low ceiling height over the cabinet exhaust opening. Two different Class II, Type A, cabinets and two air flow measuring methods were compared as a false ceiling apparatus was positioned from 5.2 to 35.6 cm (2–14 in.) above the cabinet exhaust opening. The results showed that a ceiling height as low as 5.2 cm (2 in.) above the exhaust plenum had no effect on actual cabinet air flow. Results also indicated two measuring methods yielded different results throughout the range of ceiling heights. Both measuring methods demonstrated a strong negative correlation (-0.9) for derived cabinet intake air velocity as a function of increased ceiling height. The precisely determined, yet inaccurate, operational setpoint (with the low ceiling in place) versus the actual operational set...

Solvent Vapor Transfer across an Enthalpy Energy System

A study was done on an enthalpy heat transfer wheel (heat wheel) because there was suspected excessive contamination from the exhaust side of the wheel into the building supply side. A quantitative test was done with a fluorocarbon vapor during which the concentration was measured almost simultaneously in the supply and exhaust plenums. The results showed a significant carry-over of the vapor into the supply.

A Bench-Scale Aerosol Test Chamber

Abstract This paper describes the design and evaluation of a bench-scale aerosol test chamber. Although originally designed for respirator testing, the chamber has broad applications for industrial hygiene research, testing, and calibration. The 109 L chamber includes a top mixing section, a honeycomb flow laminator section, a 52 L transparent plastic aerosol test section, and a bottom exhaust plenum. Overall chamber dimensions are 0.6 × 0.6 × 1.5 m high. Airflow velocity was uniform within ± 20% of the mean throughout the test section. A uniform aerosol concentration was achieved in the test section by opposed jet mixing in the mixing section. Test aerosol concentrations in the chamber were uniform within ± 15%, and concentration was stable to within ± 5% for more than one hour. Measurements were made with a GCA Model RAM-1 instrument and based on perpendicular 8-point traverses. Similar uniformity (within ± 5%) was found for 12 μm and 24 μm monodisperse particles. Chamber pressure can be controlled from...