Gas Flow Methods

Additionally, it should be noted that continuous SSP can also be carried out in vacuo, as reported by Buxbaum [30], Some of the previous problems regarding the tightness of the bucket wheels (rotary valves) and other parts of the equipment could be solved in the meantime however, it seems that this technology has lost its attractiveness owing to the success of the commonly preferred gas-flow method. 

Mixing. Mixing can be accomplished by mechanical recirculation, agitation or by controlled gas flow methods. The practice is desired to facilitate on intimate contact between methane forming bacteria and their substrate and to prevent the formation of surface scum in the digester. 

Gas flow method. The above methods have a common characteristic. That is, they do not discriminate between the active pores and the "passive" pores. For separation applications, only the "active" pores arc most relevant. A nondestructive technique for inferring the pore size distribution of a membrane is the gas flow method. Having been developed and tested at Oak Ridge Gaseous Diffusion Plant [Fain. 1989], it departs greatly from the above methods in that the pore size distribution is based on gas flow... 

Gas permeability method. Like the gas flow method, this technique is also based on the measurement of the flow rate of a gas through a porous medium such as a membrane. The flow rate is monitored as a function of the pressure drop across the thickness of the membrane. But unlike the gas flow method, the gas used in this method is a pure, nonadsorbable and noncondensable gas. 

Figure 4.14 Pore size distributions by gas flow method of (a) two similar sol-gel alumina membranes and (b) two distinctively different anodic alumina membranes [Fain 1989]...

For a further check on the practical applicability of the theory, we may for any point, e.g., the fitted point, calculate the effective diffusivity Dell of this catalyst from the observed value of rj, the particle size ro, and the actual reaction velocity k, (obtained from measurement on fines). This diffusivity was then compared to the diffusivity measured directly by a gas flow method as described in Section IV.5. 

Two gas flow methods These methods apply to larger specimens, up to 9 X 50 cm x board thickness for our apparatus. Board edges may be sealed. The aldehyde is driven off by nitrogen flow, recovered in water, and determined photometrically with chromotropic acid. The chosen methods are ... 

The FESYP Gas flow method, using nitrogen at 60 C, 3% relative humidity, 120 L/hour nitrogen. The result Is expressed in HCHO ug/kg board x hour (, and... 

The absence of any correlation between the three methods can be seen immediately. In particular, if we compare the results obtained with the perforator and the gas flow method at 23 C, 55% RH which is close to normal use conditions, we note the inconsistent results shown in Figure I. In fact, if we calculate the ratio, perforator rate to gas flow rate, we obtain the following approximate ratios ... 

The gas flow method would permit the evaluation (under certain conditions) of the risk that we may expect from a board. 

The saturated vapour pressure of a-CdSe was measured in the temperature range 1016 to 1170 K using a gas flow method. Values for the entropy and the enthalpy of formation of a-CdSe at 298.15 were derived using the second law and an estimated heat capacity of a-CdSe. The experimental results were therefore re-evaluated by the review using both the second and the third law, the selected thermodynamic functions of selenium, the data for Cd in [89COX/WAG], the selected heat capacity of a-CdSe, and the selected entropy of a-CdSe in the case of the third law. The vaporisation was assumed to occur according to the reaction a-CdSe Cd(g) + The results were... 

The apparent vapour pressure of a-HgSe was measured in the temperature range 613 to 753 K using a gas flow method. The thermodynamic quantities were evaluated by the review because no values were reported in the original paper. 

Porosities of char samples were calculated from the particle density and true density. The particle density was determined by Ergun s gas flow method (3), which we shortened by making measurements with only three rates or flow at each of two bed densities. The estimate of the standard deviation from 21 duplicate determinations was 7%. We determined true density by helium displacement in a Beckman air pycnometer. 

A crystal of l-I was mounted on an X-ray diffractometer and cooled below 80 K using the cold-nitrogen gas-flow method [15], The intensity data were collected and the structure was analyzed. The molecular structure of l-I is shown in Fig. 8.1. Then the crystal was irradiated with 365 nm light using a high-pressure Hg lamp in combination with a band-path filter at 80 K for 2 h. The intensity data were collected under the same conditions as those before the photo-irradiation. 

With catalysts, sintered products and porous materials the Ergun gas flow method can determine a particle density of porous material regardless of particle size and porosity because the external gas flows around the porous particles and does not penetrate the porous interstructure of the particle (see Section 1.4.4). 

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