Airflow techniques

Fig. 10.3 Approaches available for the preparation of honeycranb-structured porous films via (i) solvent casting (ii) spin-coating (iii) dynamic airflow technique (iv) dip-coating, and (v) on-water surface spreading. Reprinted with permission fi-om ref [27]...

Airflow Technique An alternative method, the airflow technique, measures the flow of air passing through the membrane surface. Several variations of this test method are available from the various membrane suppliers, and the test is usually automated. This test may involve applying a constant feed-side gas pressure below the bubble point of the selected size hole. The operator then measures the diffused gas filtrate flow or the displaced water from the membrane. 

Analytical design techniques, which predict the magnitude of local airflow and provide a basis for sizing exhaust systems, are not immediately available for... 

TTie ability of the ventilation system to protect the worker efficiently can readily be determined by personal samples. The PIMEX method (see Chapter 12) can be used to determine the worker s exposure during various work phases. The capture efficiency as well as the supply air fraction can be measured using tracer gas techniques. Simple evaluation is carried out visually with smoke tube or pellet tests. Daily system evaluation is recommended using airflow or static pressure measurements at appropriate parts of the system. The air velocities, turbulence intensities, air temperature, mean radiant temperature, and air humidity should also be measured to provide an assessment ol thermal comfort. 

In some texts guidance is given to estimate and evaluate the leakage of buildings and building components. The multizone airflow model can also be used to adjust the assumed conductances to an overall building leakage, measured by blower door technique, for example. 

All three experimental approaches are presented in this chapter visualization of airflow and contaminant dispersion (Section 12.2), measurement techniques including laser-based-techniques (Section 12.3), and scale model experiments (Section 12.4). 

The reasons for using airflow or contaminant dispersion visualization techniques may be divided into purely technical and pedagogical, both with the purpose to give a base for the design and proper use of a contaminant control technology for workplaces with a good air quality. 

In this chapter the most common and/or well-evaluated techniques for the visualization of airflow and contaminant dispersion are described. The strategy for its use as a pedagogic tool is not included this can be found elsewhere. To separate the different methods according to either airflow or contaminant dispersion studies is meaningless and not always possible. For example, smoke may many times be used for both purposes. The emitted smoke acts like a substitute for the contaminant in question and visualizes its dispersion to, e.g., the... 

As said earlier in this chapter, the use of properly arranged ilkunination will improve the visibility of the smoke markedly. Extra light should be arranged so that the light beams ace directed almost directly into the eyes of the observer or into the lens of a camera. Direct dazzling must be avoided with tlie help of some shield. The use of a laser beam expanded to a sheet makes it possihle to isualize the airflow in a special layer in the room. This technique makes it possible to study the airflow in more detail, e.g, near an enclosure or around a machine. ... 

For the investigation of airflow, air-particle and air-droplet systems (dusty and humid air), and the related technical equipment, laser-based techniques fulfill the following experimental demands ... 

S. B. Riffat, M. Holmes. Measurement of airflow in HVAC systems using tracer-gas techniques. In Proceedings of the 11th AIVC Conference, vol, 1, 1990, pp. 195-214. 

Flow Rate. The values for volumetric or mass flow rate measurement are often determined by measuring pressure difference across an orifice, nozzle, or venturi tube. Other flow measurement techniques include positive displacement meters, turbine flowmeters, and airflow-measuring hoods. 

Aseptic manipulations should be performed in the sterile air of a laminar airflow unit. Speed, accuracy and simplicity of movement, in accordance with a complete understanding of what is required, are essential features of a good aseptic technique. 

Branches I-V and II-V were sized to provide an approximate 35%-65% split-up in airflow, respectively (i.e., using pressurebalancing techniques)... 

COPD is a chronic, slowly progressive disorder characterized by airways obstruction (FEVi < 80% predicted FEViA C ratio < 70%) which does not change markedly over several months. The airways obstruction is largely fixed but may be partially reversible by bronchodilator therapy. Unlike asthma, airflow limitation in COPD can never be returned to normal values. The diagnosis of COPD is usually suggested by symptoms. A firm diagnosis can only be made by objective measurement of airways obstruction with spirometric tests, which may be enhanced by radio diagnostic techniques (Table 4). 

L)lnterferometer Camera. E.Mach and his son L.Mach were the first to apply interferometer techniques to study of ballistic problems (Ref 1, p 275), The camera devised by them was improved by Zehnder and became known as "Mach -Zehnder Interferometer (Ref 2,p 173 Ref 18,p 141 and Addnl Ref dd). Bennett et al (Addnl Ref cc)gave the theory of interferometric analysis and described the procedure used at BRL(Ballistic Research Laboratories), Aberdeen, Md for analysis of airflow around projs in flight. The app of... 

To improve interwell communication further, a hydraulic fracturing treatment was performed at a depth of 79 to 84 ft in well 5 to ensure the displacement and detonation of the 300-qt charge of NG1. The effectiveness of the three fracturing techniques was determined by measuring airflow rates between selected wells before and after each test. 

Further, pelletized TNT performed satisfactorily in wellbore shots in wells 150-385 ft deep. Fractures were created between wells as indicated by airflow tests, but numerous other evaluation techniques did not indicate the extent of rock fragmentation. 

Foam fractionation is a promising technique for concentrating proteins because of its simplicity and low operating cost. One such protein that can be foamed is the enzyme cellulase. The use of inexpensively purified cellulase may be a key step in the economical production of ethanol from biomass. We conducted foam fractionation experiments at total reflux using the cellulase component P-glucosidase to study how continuous shear affects P-glu-cosidase in a foam such as a fermentation or foam fractionation process. The experiments were conducted at pH 2.4, 5.4, and 11.6 and airflow rates of 3,... 

One operating concern for a rich combustor is the occurrence of high combustor wall temperatures. In a fuel-rich combustor, air cannot be used to film-cool the walls and other techniques (e.g., fin cooling) must be employed. The temperature rise of the primary combustor coolant was measured and normalized to form a heat flux coefficient which included both convective and radiative heat loads. Figure 7 displays the dependence of this heat flux coefficient on primary combustor equivalence ratio. These data were acquired in tests in which the combustor airflow was kept constant. If convective heat transfer were the dominant mechanism a constant heat flux coefficient of approximately 25 Btu/ft -hr-deg F would be expected. The higher values of heat flux and its convex character indicate that radiative heat transfer was an important mechanism. 

In the light of the poor efficiency of broadcast applications of pheromones in air permeation techniques the alternative practice of scattering or placing a limited number of release points at suitable distances apart over the treated area merits consideration. Since each point will then act as an individual source the treated area will be permeated by a set of individual plumes of pheromone vapor whose direction will vary with airflow through the crop or woodland. Large... 

---