Testing flow properties

The actual process materials should be used if possible. If substitute materials must be used, they should have the same mixing charac teristics. Tests with differently colored but otherwise identical beads can be misleading, and so can tracers. The reason is that the flow properties of the specific materials to be mixed in the plant may not be the same as these demonstration materials. Regardless of how the mixer contents appear to be moved around, the properties of the actual batch ingredients may cause segregation or other problems. 

Flow Property Tests Flowahility of the produc t granules can be charac terized by unconfined yield stress and angle of friction by... 

The standard melt flow index machine is often used for characterising the flow properties of polypropylene and to provide a rough measure of molecular weight. Under the conditions normally employed for polyethylene (2.16 kg load at 190°C) the flow rate is too low for accurate measurement and in practice higher loads, e.g. 10 kg, and/or higher temperatures are used. It has been found that a considerable pressure drop exists in the barrel so that the flow towards the end of a test run is higher than at the beginning. 

Plastic Viscosity and Yield Point. Plastic viscosity and yield point measurements are obtained from a direct indicating viscometer. Due to the temperature effect on the flow properties of oil-base mud, the testing procedure is modified. The mud sample in the container is placed into a cup heater [23]. The heated viscometer cup provides flow property data under atmospheric pressure and bottomhole temperature. 

The pour point of a crude oil or product is the lowest temperature at which an oil is observed to flow under the conditions of the test. Pour point data indicates the amount of long-chain paraffins (petroleum wax) found in a crude oil. Paraffinic crudes usually have higher wax content than other crude types. Handling and transporting crude oils and heavy fuels is difficult at temperatures helow their pour points Often, chemical additives known as pour point depressants are used to improve the flow properties of the fuel. Long-chain n-paraffins ranging from 16-60 carhon atoms in particular, are responsible for near-ambient temperature precipitation. In middle distillates, less than 1% wax can be sufficient to cause solidification of the fuel. ... 

Flow Tests. One foot long sand packs using Wilmington oil field unconsolidated sand were prepared for each of the flow tests. Porosity and permeability of all the sand packs were within 30-35% and 100-300 md, respectively. All core packs were evacuated to about 1 mm of mercury (Hg) before saturating them under gravity to assure complete water saturation. Table III gives the core and fluid properties for the flow tests. The properties of the cores were chosen so that they are close to the field conditions reported by Krebs(15). 

The range of application of shear cell testing methodology is seen in Tables 2-6. Table 3 relates the flow properties of mixtures of spray-dried lactose and bolted lactose. These mixtures, in combination with the excipients tested, cover a broad range of flow. Tables 4 and 5, for example, show lot to lot variations in the flow properties of several materials, and Table 6 shows the variation in flow properties of bolted starch, sucrose, and phenacetin at different relative humidities (RH). Figure 8 presents the yield loci of sucrose at four different consolidation loads. Also shown in the figure are the shear indices determined at each consolidation load. 

Too little has been published about the flow properties of PET as a criterion for processing. The results of melt flow index (MFI) testing conditions do not correlate with the processing behavior in the case of PET. This may be caused by the discrepancy between the shear rates in testing and processing. MFI is defined as the amount of polymer melt (in g) extruded within 10 min through an orifice of specified diameter at a standard load and temperature. In the case of PET, this method was not very popular until recently due to the sensitivity of this material to hydrolytic degradation. 

The melt Index test measures the flow property at a fixed wall shear stress In the capillary. The shear stress depends on the load specified for the condition and it is provided in Table 3.8. The apparent shear rate at the capillary wall that the resin experiences depends on the Ml value measured, and it can be calculated using a modification of Eq. 3.33 as follows ... 

Activity Measurements. To test catalytic properties of various samples partial oxidation of methanol to formaldehyde was studied in a flow micro-reactor operating under normal atmospheric pressure (10). For each run about 0.2 g of catalyst sample was used and the activities were measured at 173 C in the absence of any diffusional effects. The feed gas consisted of 72, 2 and by volume of nitrogen, oxygen and methanol vapor respectively. Reaction products were analysed with a 10% Carbowax 20 M column (2m long) maintained at 60 C oven temperature. 

This wax can accumulate on fuel filter media and can lead to plugging of small orifices and lines. This plugging temperature can be measured and is commonly referred to as the filter plugging temperature. Testing methods utilized to predict the filter plugging temperature and the low-temperature flow properties of distillate fuel are listed in TABLE 4-5. 

The pour point test is used to determine the lowest temperature at which a fuel can be effectively pumped. However, the pour point value can be misleading, especially when it is used to determine the low-temperature handling characteristics of residual fuel oil and other heavy fuels. Low-temperature viscosity measurements are considered more reliable than pour point values for determining the flow properties and pumpability of these oils. 

Controlled optimal particle size and size distribution ensures superior flow properties of coprocessed excipients and reduced reliance on addition of glidants. The volumetric flow properties of SMCC were studied in comparison with those of the physical mixture of its parent excipients (42). The particle size range of the two test samples was found to be similar, but the flow of coprocessed excipient was better than that of the physical mixture. A comparison of the flow properties of Cellactose with its parent excipients was also performed (5) by measuring the angle of repose and Hausner ratio, and Cellactose was found to have better flow characteristics than lactose or a physical mixture of cellulose and lactose. The spray-dried coprocessed product had a spherical shape and even surfaces, which resulted in improved flow properties. On similar terms, mechanically coating the 2% CSD over microfine cellulose powder resulted in improving its flow properties (43). 

In order that a wax be accepted for use as a desensitizer in an expl compn, it must not only meet the requirements of Specification Ml L-W-20553, it must also be found acceptable in use tests. Such tests include characterization of a wax in the specific expl compn for incorpora-bility, possibility, sensitivity, physical compatibility, flow properties, cast shrinkage, etc. Examples of Army qualificationworkis contained in Refs 63,87,92 99. The qualification test procedures required by the Navy are spelled out in Ref 95. Specification MIL-W-20553D, paragraph 6.4.2 cites NWS TR-1 and TR-2 for qualification of waxes for Composition B and H-6 and D-2, respectively, and WS 13574, OD 45295 and WS 13564, OD45001 for qualification of Compn A-3... 

Molecular theories of flow behavior are applied on the assumption that the macroscopic velocity field can be considered to apply without modification right down to the molecular scale. In continuum theories the components of relative velocity in an arbitrarily small neighborhood of any material point are taken to be linear functions of the spatial coordinates measured from that point, i.e., the flow is assumed to be locally homogeneous. The local velocity field is calculated from the macroscopic velocity field. This property of local homogeneity of flow is an obvious prerequisite for any meaningful macroscopic analysis, and perhaps the fact that analyses are at all successful and that flow properties can be determined which are independent of apparatus geometry constitutes a fair test of the assumption. 

With a number of plastimeters in common use, it is inevitable that there is a demand to know the relationship between the readings obtained with them. From the foregoing discussion emphasising the dependence of plasticity results on the shear rate and other conditions of test, it must be clear that the question is not really a sensible one. Any relationship found between two different instruments can only be valid for the compounds used and the particular conditions of test, simply because the flow properties of rubber cannot be defined by a single parameter. 

---