Airflow apparatus

The release of pheromone from hollow fibers as described by Brooks (6) is dependent upon several factors including the movement of air past the open end of the fiber. In the mini-airflow apparatus the open end of the fiber is in a stream of constantly moving air so that any released pheromone is immediately swept away from the end. In the static air apparatus the only air movement across the open end will be as a result of diffusion. Consequently the concentration of pheromone is more likely to build up at the open end of a fiber in a static air apparatus than at the open end of a fiber in an airflow apparatus with the result that the release rate is lowered in the static air apparatus. Work is now in progress to evaluate the effect of air speed on release rates. 

A common principle for the prt)duction of smoke for this purpose is to cvat>-orate a mineral oil by electrically hearing it and to mix the vapor into air. The oil will then condense and form a mist. Different such apparatus can be found on the market. Some of them are aimed for the visualization t f airflow but others are intended lor special effects in theaters, discotheques, etc. Figure 12.3 shows one such apparatus commonly used for this purpose. 

Assmann psychrometer An apparatus which uses a clockwork or electrical fan located above wet and dry bulb thermometers, positioned in a cylinder to provide a set airflow rate over the thermometer bulbs for accurate temperature readings of both bulbs. 

As the need for accurate data that can be statistically reduced develops, automated sampling systems are used. The elements of an automated system include the airflow-handling system, sensors, data transmission storage, display apparatus, and data processing facility. The overall system is no more valuable than the weakest link of this chain. 

Results such as those reported in Table I are clearly unacceptable. It was decided that the airflow method would ultimately be the most accurate and the most versatile so the attempts at improving the methodology began with a critical examination of the apparatus pictured in Figure I. 

To determine the versatility of the apparatus for measuring release rates in general, the release of (acetyl-l-1 C)-gossy-plure was measured from rubber septa, a pheromone release device frequently used in field experiments. After 21 days of measurements, the septa were extracted and any residual activity in the apparatus was measured. The average recovery, detailed in Table II, was 97% indicating that the usefulness of the mini-airflow device was not limited to hollow fibers alone. 

Weather resistance in an accelerated test is defined as the resistance of plastics towards changes caused by simulated open-air weathering (simulation of global radiation by means of filtered xenon arc radiation and periodic rain). After the weathering (measured by the product of intensity and duration), defined properties of the test sample are compared with those of an identical unweathered sample. Properties should be considered which are of practical importance, such as color or surface properties. For standards, see Table 1.1 ( Weathering in apparatus ). Apparatus test chamber, rain and air humidification equipment, airflow equipment, radiation measuring equipment. 

ASTM C 522 covers the measurement of airflow resistance and the related measurements of specific airflow resistance and airflow resistivity of porous materials that can be used for the absorption and attenuation of sound. The method describes how to measure a steady flow of air through a test specimen, how to measure the air-pressure difference across the specimen, and how to measure the volume velocity of airflow through the specimen. The airflow resistance, R, the specific airflow resistance, r, and the airflow resistivity, rQ, may be calculated from the measurements. The apparatus includes a suction generator or positive air supply arranged to draw or force air at a uniform rate through the specimen. A flowmeter is used to measure the volume velocity of airflow through the specimen, and a differential-pressure-measuring device measures the static-pressure difference between the two faces of the specimen with respect to atmosphere. 

The airflow permeability can be used to gain an insight into the structural or physical properties of the cellular materials. The apparatus used is shown in Fig. 16. It comprises a cell into which the specimen can be placed and a method by which a steady flow of air through the specimen can be achieved. This steady airflow can be controlled to give different values, and hence K can be deduced. 

Filtration of oxidizable materials can constitute a serious fire hazard. The ignition source can be a burning particle from the dryer or the static charge carried by the dust particle. Because of this, bag-house systems should be equipped with automatic devices for closing off the airflow in case of fire, should be provided with adequate sprinklers or chemical fire control apparatus, and vents should be provided on the side containing the dust particles. 

Figure 11.1. Chemical heat release rate for a 100-mm diameter and 25-mm thick horizontal slab of polypropylene exposed to 50 kW/m of external heat flux in normal air, under well-ventilated condition, in the ASTM E2058 Apparatus [31]. Airflow rate 2.9 X 10 m /s. Data up to about 900 s are for the combustion with very small bubbles formed at the surface of the solid slab of PP. Beyond about 1150 s, the data are for the combustion with deep liquid pool over the solid slab of PP. Data were measured in our laboratory.

These data were measured in the ASTM E2058 Fire Propagation Apparatus under quiescent airflow conditions for about 100 mm and 25-mm thick slab of polymethylmethacrylate (PMMA), with surface coated black [39], The experimental TRP value, TRPexp, is taken as the inverse of the slope of the linear relationship between (1/hg) / and g", for black coated surface (a = 1.0). 

Third, since it is impossible to avoid some turbulent air patterns inside the hood, any apparatus inside the hood should be placed on 2-inch blocks to allow better airflow, and all work should be at least 6 inches inside from the front of the hood. This wiU help minimize the chance of vapors escaping through the face of the hood. 

Since chemical hoods are so well ventilated, it sometimes becomes a pretty common practice to store chemicals inside hoods. This is a very bad practice since the volume of storage usually accumulates to inhibit good airflow in the hood, particularly when some apparatus is then constructed in this crowded space. This compromises the function of the hood and the ability to use the hood safely. Furthermore, as Incident 7.1.4.1 describes, a crowded hood makes it difficult to use the hood all of the time and this inevitably leads to experiments being conducted on open benches instead of inside hoods. 

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