Storage and flow of solids :(rev. 1980. )

Determination of the Mechanical Properties of Powdered Agricultural Products and Sugar

This paper presents the influence of fat replacement on flow and thermal properties of dairy powders. The research was undertaken by measuring flow properties of four different milk powders (whole milk powder, skim milk powder and two fat-filled milk powders with palm oil at 6.63 g/100 g and 25.5 g/100 g fat content, respectively) by using shear test. Fat content has a major influence on milk powder cohesiveness, with greater content resulting in greater cohesiveness. Fat content and type has also significant influence on flowability of milk powder. Fat-filled spray-dried milk powder is characterized by better flowability than whole milk powder with the same content of fat. The DSC curves showed that milk fat tended to melt in a lower temperature region than vegetable fat.

Effect of fat replacement on flow and thermal properties of dairy powders

A b s t r a c t. The influence of water activity, storage time and consolidation on the flowability of wheat flour were evaluated. Powder flowability was measured using a Jenike shear tester according to the Jenike procedure at four levels of normal consolidating stress within the range of 4.9-17.5 kPa. Flour was placed in a humidity chamber to obtain samples of flour at 0.33 and 0.8 water activity. Instantaneous shear tests were performed at temperature of 20C on each sample, from which the instantaneous flow functions were obtained. Time consolidation tests on the flour at 0.33 and 0.8 water activity were carried out using a Jenike shear cell and consolidating bench for the consolidation time of 1 and 7 days. Temporal flow functions of the flour were determined to quantify the combined effect of moisture content, time and compression stress.

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Wheat flour flowability as affected by water activity, storage time and consolidation**

With an increasing quantity and variety of powders being produced in industry, there is growing need for information about material characteristics important for handling and processing. Knowledge of mechanical properties of food powders is essential for design of industrial equipment, efficient and reliable material processing as well as for estimation of quality of raw material (MOLENDA, STASIAK 2002). The knowledge of physical properties of food powders is also important for quality assessment of final product on-line as well as during later storage, handling and transport. Flow properties of powders influence handling and processing operations, such as flow from silos and hoppers, transportation, mixing, compaction and packaging (KNOWLTON et al. 1994).

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Direct shear testing of flowability of food powders

A b s t r a c t. The strength characteristics of fine milk, agglomerated milk and potato starch were examined. Experiments were performed using the Jenike shear tester according to Euro-code 1 recommendations. The tester was 60 mm in diameter and the displacement velocity was 0.03 mm s -1 . A reference normal stress ranging from 30 to 240 kPa was applied. Experiments revealed a significant effect caused by shear stress vibration resulting from dilatation and hardening of the material during the slow shearing phase of these tests. The frequency of these vibrations were found to decrease with an increase in normal stress. Two components of the total strength were suggested: the physical friction strength and the extra component of strength caused by dilatation.

Strength characteristics and dilatation of food powders

Thestrength characteristics of fine milk, agglomerated milk and potato starch were examined. Experiments were performed using the Jenike shear tester according to Euro- code 1 recommendations. The tester was 60 mm in diameter and the displacement velocity was 0.03 mm s -1 .A reference normal stress ranging from 30 to 240 kPa was applied. Experiments revealed a significant effect caused by shear stress vibration re- sulting from dilatation and hardening of the material during the slow shearing phase of these tests. The frequency of these vibra- tions were found to decrease with an increase in normal stress. Two components of the total strength were suggested: the physical friction strength and the extra component of strength caused by dilatation.

J. Horabik

Papers

Strength characteristics and dilatation of food powders

Strength characteristics and dilatation of food powders