The measurement of air supply volumes and velocities in cleanrooms

Air supply volumes and velocities in cleanrooms are monitored by airflow measuring hoods and anemometers but these measuring methods can be inaccurate if used incorrectly. It is demonstrated in this article that measuring hoods are accurate if the air supply passes evenly out of the hood, as occurs when the air volume is measured from a four-way diffuser or no air supply diffuser. However, when a swirl diffuser was investigated, the measuring hood gave readings more than 50% greater than the true volume. The reasons for the inaccuracy, and methods to correct it were established. Vane anemometers give inaccurate readings at the face of high-efficiency air supply filters, and it was found that the most accurate reading was found about 15 cm from the filter face. The number of readings required across the filter face to obtain an accurate average velocity was investigated, as was a scanning method using overlapping passes

Removal of microbe-carrying particles by high efficiency air filters in cleanrooms

The removal efficiency of high efficiency air filters against microbe-carrying particles (MCPs) in the air supply of occupied rooms, such as cleanrooms, was determined. Knowing the size distribution of MCPs in the air to be filtered, and the removal efficiency of a filter against individual particle diameters, the overall removal efficiency was ascertained. A variety of filters were investigated, and it was found that a filter 90% efficient, when tested against sub-micrometre particles, used in standard classification methods such as EN 1822, was greater than 99.99% efficient in removing MCPs. The effect of filter efficiency on the quality of the air supply, and the concentration of MCPs in cleanroom air was also studied. No practical improvement in airborne concentrations was obtained by filters that had a removal efficiency greater than 99.99% against MCPs. Use of a filter suitable for removing MCPs, rather than sub-micrometre particles, would give a reduction of about 6 to 8-fold in the pressure drop over a filter, and a substantial reduction in the cost of running a cleanroom

Removal efficiency of high efficiency air filters against microbe-carrying particles (MCPs) in cleanrooms

The removal efficiency of high efficiency air filters was determined against microbe-carrying particles (MCPs) in the air supply to cleanrooms. Knowing the size distribution of MCPs in the air to be filtered, and the filter's removal efficiency against individual particle diameters, the overall removal efficiency was ascertained. The removal efficiency of individual species of microbes with a known size was also obtained. A variety of filters were investigated, and it was found that a filter 90% efficient against the most penetrating particle size (as classified by EN 1822) was greater than 99.99% efficient in removing a MCPs. The effect of filter efficiency on the microbial concentration in both the air supply and the cleanroom air was studied, and no practical improvement in the air quality was obtained by filters that had a removal efficiency greater than 99.99% against MCPs. Use of a filter suitable for removing MCPs, rather than sub-micrometre particles, would give a reduction of about 6 to 8-fold in the pressure differential across the filter, and a substantial reduction in the energy costs of running a cleanroom

Fillet Weld Stress Using Finite Element Methods

Average elastic Von Mises equivalent stresses were calculated along the throat of a single lap fillet weld. The average elastic stresses were compared to initial yield and to plastic instability conditions to modify conventional design formulas is presented. The factor is a linear function of the thicknesses of the parent plates attached by the fillet weld

Approach to rapid mission design and planning

Methods and techniques are described for implementation in automated computer systems to assess parametric data, capabilities, requirements and constraints for planning earth orbit missions. Mission planning and design procedures are defined using two types of typical missions as examples. These missions were the high energy Astronomical Observatory Satellite missions, and Small Applications Technology Satellite missions

Experimental and CFD airflow studies of a cleanroom with special respect to air supply inlets

Investigations were carried out into the airflow in a non-unidirectional airflow cleanroom and its affect on the local airborne particle cleanliness The main influence was the method of air supply A supply inlet with no diffuser gave a pronounced downward jet flow and low levels of contamination below it, but poorer than average conditions in much of the rest of the room A 4-way diffuser gave much better air mixing and a more even airborne particle concentration throughout the cleanroom Other variables such as air inlet supply velocity, temperature difference between air supply and the room, and the release position of contamination also influenced the local airborne cleanliness A CFD analysis of airflow fields in a cleanroom was compared with measured values It was considered that a turbulent intensity of 6%, and a hydraulic diameter based on the actual size of the air inlet, should be used for the inlet boundary conditions and, when combined with a k-epsilon standard turbulence model, a reasonable prediction of the airflow and airborne particle concentration was obtained

Dispersion of microbes from floors when walking in ventilated rooms

The redispersion factor of microbe-carrying particles, which is the ratio of the concentration of floor-derived microbes in room air to those on a floor surface, was determined, as was the percentage of floor-derived microbes in room air. These relationships were shown to vary according to conditions in the room. Equations were derived that allow these relationships to be calculated for a variety of room conditions, including air supply rates, levels of personnel activity, and the effect of gravitational deposition on microbe-carrying particles.<p></p> The redispersion factor in ventilated rooms, such as cleanrooms and operating rooms, when the floor surface concentration was measured by nutrient agar contact dishes, was found to vary from about 1.5 x 10-4 to 7.4 x 10-6, and the percentage of floor-derived microbes in room air from about 0.004% to 10.5%. In a typical cleanroom, the redispersion factor is likely to be about 1.0 x 10-4, and the percentage of floor-derived microbes, 0.7. In a typical operating room, the redispersion factor is likely to be about 5.2 x 10-6 and the percentage of floor-derived microbes, 2.<p></p&gt

Lunar targeting study: Lunar and planetary Ephemeris tapes

The Univac 1108 computer tape data formats are documented for the ephermeris tape generated by the Jet Propulsion Laboratory and the ephemeris tape used by the Quick Response Targeting Program (QRTP). Ephermeris tapes are used as the data source for the position and velocity components of those celestial bodies being considered in an integrated trajectory simulation program. The QRTP ephemeris tape has data only for lunar mission simulations. The JPL ephemeris tape has data for the moon and the nine planets. The ephemeris tapes, the data formats, the coordinate systems, and units are defined. The transformation from the mean-of-1950 coordinate system to the nearest mean Besselian year is given

Asymptotic Spectrum of Kerr Black Holes in the Small Angular Momentum Limit

We study analytically the highly damped quasinormal modes of Kerr black holes in the small angular momentum limit. To check the previous analytic calculations in the literature, which use a combination of radial and tortoise coordinates, we reproduce all the results using the radial coordinate only. According to the earlier calculations, the real part of the highly damped quasinormal mode frequency of Kerr black holes approaches zero in the limit where the angular momentum goes to zero. This result is not consistent with the Schwarzschild limit where the real part of the highly damped quasinormal mode frequency is equal to c^3 ln(3)/(8 pi G M). In this paper, our calculations suggest that the highly damped quasinormal modes of Kerr black holes in the zero angular momentum limit make a continuous transition from the Kerr value to the Schwarzschild value. We explore the nature of this transition using a combination of analytical and numerical techniques. Finally, we calculate the highly damped quasinormal modes of the extremal case in which the topology of Stokes/anti-Stokes lines takes a different form.Comment: 13 pages, 6 figure