Sampling isokinetic

Isokinetic sampling is for the direct measurements of particulate mass fluxes or concentrations of aerosols (assuming no slip between aerosols and the gas flow) in gas-solid suspension flows. This is accomplished by inserting a thin-wall tube into the particulate suspension flow to draw samples at the isokinetic condition and by passing the collected particles into a sampling train. Typical 

FIGURE 2.2a Corona charger - ball probe system. 

FIGURE 2.2b Example of phase velocity measurements using corona charger method (Soo etal., 1989). 

FIGURE 2.5 Isokinetic sampling system with cyclone separator (Zhu, 1991). 

FIGURE 2.6 Western precipitation isokinetic sampling train (Cadle, 1975). 

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For sampling particulate matter, one is dealing with pollutants that have very different inertial and other characteristics from the carrying gas stream. It becomes important, therefore, to sample so that the same velocity is maintained in the probe tip as exists in the adjacent gas stream. Such sampling is called isokinetic. Isokinetic sampling, as well as anisokinetic sampling, is illustrated in Fig. 13-3. 

Air-dilute with necessary blowers, flow measurement, and control systems Use isokinetic sampling, refrigerated sample transport, and careful handling to minimize physical or chemical changes... 

With particles, the contaminant concentration in the duct is determined by isokinetic sampling with subsequent laboratory analysis use of a calibrated direct reading instrument. If the concentration distribution in the duct is uneven, a complete survey of the concentration distribution with the corresponding duct velocities and cross-sectional area is required. National and ISO standards provide information on isokinetic sampling and velocity measurements. In the case of particles, the airborne emission differs from the total emission, for example in the case of granular particulate. The contaminant settling on surfaces depends on particle distribution, airflow rates, direction in the space, electrical properties of the surfaces and the material, and the amount of moisture or grease in the environment. 

Particulate emission is sampled at a temperature of 70 °C by an isokinetic sampling nozzle, i.e., the sampling velocity is the same as the gas velocity around the nozzle in the duct. 

Adjust the sample gas flow extracted (isokinetic sampling). 

Isokinetic Sampling I he sample gas partial volume flow must be extracted isokinetically to avoid aerodynamic separation effects and to ensure correct particle size distribution. Isokinetics means that the velocity and direction of the sample gas partial flow at the sample nozzle are the same as at the main gas stream. ... 

For isokinetic sampling, the doer sampling-point gas velocity has to be measured, and the corresponding sample gas flow calculated and adjusted. " Normally, a Pitot static tube is used for the measurement of duct gas velocity. 

Isokinetic sampling The sampling of a gas such that the motion of the gas entering the sampling device is identical to that of the gas being sampled. 

For superheated steam, the sample points should be designed and installed to permit correct isokinetic sampling. A modified multiport nozzle design ensures that the velocity of the steam entering the sample nozzle is the same as the velocity of steam in the header. The design incorporates a small, high-quality water delivery tube, used to inject water and remove superheat before sample extraction. 

If the temperature of the superheated steam exceeds the saturation temperature by 28 to 30 °C (50-54 °F), a thermal sleeve is used to attach the nozzle to the steam line and reduce thermal stresses on the nozzle. Isokinetic sampling is especially important where the steam may contain suspended particles. 

Isokinetic Sampling Collection of samples such that there is no change in the momentum of the particles before they reach the filter. Particularly important to obtain a representative sample when the whole air stream cannot be sampled. Small particles (less than three micrometers) do not require isokinetic sampling as they possess little inertia, but it becomes increasingly important for sampling larger particles. 

Schraub, F. A., 1968, Isokinetic Sampling Probe Technique Applied to Two-Phase Flow, ASME 67-WA/FE-28, Annual Meeting, ASME, New York. (3)... 

Other factors related to sample injection can also be important. It has been shown by Kirkland et al. (27) that the way of injectin the sample, especially by using a syringe, is critical. It seems that isokinetic" sampling is necessary to establish a uniform profile of the sa nple band at the column inlet. Otherwise eddies can form at the needle tip and the resulting multimodal injection yields to band nonuniformities ready at the column inlet. The time during which the sample is injected ia also important and it should be less than a maximum v ue, ts,u> isi eii by the relationship... 

If is not certain, however, that isokinetic sampling is the ic al solution. 

All samples should be collected using isokinetic sampling when determining mass emissions. This means the gas sample should be pulled through the sample probe at the same velocity as the velocity of the process gas. If not, the total particulate catch will not be representative of the gas stream. 

Comparison of Experimental and Theoretical Values of Isokinetic Sampling Efficiency... 

Absolute Values of Isokinetic Sampling Efficiency for Various Cotton Dust Distributions... 

Figure 1. Gold amalgamation isokinetic sampling train for mercury...

The low concentration of mercury in the bottom ash results from one or a combination of the following short retention time in the gas stream, the smaller surface area, and/or the higher temperatures at which it is removed from the system. The mercury concentrations in the filter particulates collected during the isokinetic sampling did not show any direct correlation with the ash studies because the mercury collected on the heated filter was partially revolatilized during sampling and collected in the remaining portions of the train. 

Isokinetic sampling of the stack gas for the mercury and particulate concentrations... 

Isokinetic sampling of the ducts between each ash collection mechanism to determine the particulate loadings at each site... 

Figure 1. Representation of an aircraft aerosol sampling inlet showing flow streamlines for subisokinetic, superisokinetic, and isokinetic sampling. Under subisokinetic conditions large particles will be oversampled under superisokinetic conditions small particles will be oversampled and under isokinetic conditions, the particle size distribution will be preserved.

Figure 2. Diagram of a typical sharp-edged probe for isokinetic sampling of aerosol particles from an aircraft. The probe is sized to provide 500 L/m at a sampling velocity of 50 mis. The 7° expansion of the probe behind the probe tip is to slow the air velocity. The interior of the probe is polished to a mirror...

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