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Powdered milk boasts excellent flowability: using standard flow function and wall friction tests, it was determined that powdered milk is generally free flowing through it was determined all levels of consolidating stress.

A Brookfield Powder Flow Tester, equipped with Powder Flow Pro soft-ware for automated instrument control and data acquisition, was used to test a name-brand powdered milk. The powdered milk was scooped into the trough and the scraping tool was used to evenly distribute the powder throughout the trough. The flow tester's trough measures 230 c [m.sup.3] with a 6" diameter. After recording the sample weight and entering it into the software, a standard flow function test, lasting 35 min, and a wall friction test, lasting 20 min, were both conducted. The experiment was done at room temperature (70 to 72 F) with 25.4% humidity

Analysis and results

Parameters measured include: flowability: easy flowing; wall friction: 10 [degrees]; and bulk density: 335 kg/m3 (fill density) to 385 kg/[m.sup.3] (9.5 kPa). Analysis was done with a conical hopper, an arching flow factor of 1.40 and a critical arching dimension of 0.464" (11.6 mm).

Figure 1 shows the flowability of the powdered milk at different levels of consolidating stress. These results show that the powdered milk was generally free flowing throughout all levels of consolidating stress.




Figure 2 represents the angles of wall friction at different levels of normal stress. Angles of wall friction represent 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 powdered milk was in a stainless steel hopper. At all levels of consolidating stress, the powdered milk exhibited an effective angle of wall friction of about 10 [degrees].

Figure 3 shows the bulk density of the material at different levels of consolidating stress. This graph illustrates that the powdered milk has a fill density of about 335 kg/[m.sup.3] and rises to about 385 kg/m3 at around 4.5 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.


The powdered milk is an easy flowing powder throughout all consolidation stress levels. This powder should not exhibit many flowability problems. The critical arching dimension, of 0.464" (11.6 mm) provides a conservative estimate to prevent arching, provided the minimum outlet dimension of the hopper exceeds this value.

The critical ratholing dimension is dependent on the diameter of the bin. Brookfield's Powder Flow Pro can automatically calculate the rathole diameter once the bin diameter is entered.


For more information, call Brookfield Engineering at 508-946-6200, or visit


* A Brookfield Powder Flow Tester was used in an experiment to test the flow-ability of a name-brand powered milk.

* Experiment results showed that the flowability of the powdered milk was generally free flowing.

* Results also indicated an excellent angle of wall friction of about 10 [degrees].

by Brookfield Engineering Laboratories, Inc., Middleborro, Mass.

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Title Annotation:FOOD& BEVERAGE LABS
Publication:Laboratory Equipment
Date:Jan 1, 2012
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