The brownie mix was scooped into the trough and the scraping tool was then used to evenly distribute the powder throughout the trough. After recording the sample weight and entering it into the software, a standard flow function test and then a wall friction test were run. Time required for each test was 35 minutes and 20 minutes respectively.
Baking mix for brownies.
Instrument: Powder Flow Tester (PFT)
Trough Lid Type: 30 cc, 6-inch diameter
Vane Lid, 304 s/s, 33cc, 6-inch diameter (Flow Function)
Wall Lid, 304 s/s, 2B finish, 6-inch diameter (Wall Friction)
Type of Test: Flow Function Test, Wall Friction Test Temperature Room Temperature (70-72° F) Humidity 48%
Flowability Very Cohesive
Wall Friction 45º to 25º
Bulk Density 475 kg/m³ (fill density) to 660 kg/m³
Hopper Shape Conical
Arching Flow Factor 1.40
Critical Arching Dimension 108.6mm (4.28 inches)
Rathole Diameter Dependent on bin diameter
Figure 1 shows the flowability of the brownie mix at different levels of consolidating stress. These results show that the brownie mix is generally very cohesive throughout the different levels of consolidating stress-es.
Note: The Flow Function data is indicated by the red line. The other lines are references (or “Standard Flow Indices”), which distinguish the different types of flow behavior, ranging from “non-flowing” to “free flowing”.
Figure 2 represents the angles of wall friction at different levels of normal stress. Angles of wall friction rep-resent the friction between the sliding powder and the wall of the hopper or chute at the onset of flow. In this test a stainless steel lid was used, illustrating what the friction would be like if the brownie mix was in a stainless steel hopper. At a low normal stress of about .5 kPa, the angle of wall friction is about 45º and goes down to about 25º at higher levels of normal stress (4.75 kPa). Wall friction angles above 20º are considered high.
Figure 3 shows the bulk density of the material at di erent levels of consolidating stress. This graph tells us that the brownie mix has a ll density of about 475 kg/m3 and rises to about 660 kg/m3 at around 4.75 kPa of consolidating stress. In general, a free flowing powder will show very small changes in bulk density, while a cohesive or poor flowing powder will generally show a large increase in bulk density. This brownie mix shows a large increase in bulk density which is another indicator that this powder is very cohesive.
The brownie mix is a very cohesive powder at all levels of consolidation stress. This means that the brownie mix may experience flowability issues if proper precautions are not taken. Possible problems include arching (when the powder forms a cohesive bridge over the outlet) and ratholing (when the powder flows out only from the center leaving the rest of the material static against the walls).
The critical arching dimension of 108.6 mm (4.28 inches) provides a conservative estimate to prevent arching from happening, provided the minimum outlet dimension of the hopper exceeds this value. The critical ratholing dimension is dependent on the diameter of the bin. If the bin diameter is known, the software can automatically calculate the rathole dimension.
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