Bulk density 406,

Bulk density, or the apparent density, is the total mass per unit of total volume. It is not an intrinsic property of a material since it varies with the size distribution of the particles and their environment. The porosity of the solid and the material with which the pores, or voids, are filled also affect the bulk density. For a single nonporous particle, the true density equals the bulk density. 

A sample of quartz sand weighs 2.65 g and occupies a volume of 2.0 cm3. What is its bulk density Solution 15.4 

Bulk density can give information about a material s porosity. Ceramics and powder metals that are made by compaction and sintering have varying degrees of porosity. In structural parts, porosity is undesirable. However, in powdered metal wear parts, porosity is desired for retention of lubrication. 

To find the percentage void space, we use the following formula  

In soils, the bulk density is an indication of the degree of compaction and also the capacity for holding water, air, and nutrients. Highly compacted soils with low porosity (voids) are desirable for roadbeds and dams, but are not suitable for plant growth. The actual density, or particle density, of soils is determined by the displacement of water of a given mass of soil. 

Bulk density (Dj,) is defined as the mass (weight) of a rmit volume of diy soil. This volume includes both solid and pores. The values for clay, clay loam and silt loam surface soils varies from 1.00 - 1.60 g/cm, for sand and sandy loams from 1.20 - 1.80 g/cm. Fine - texture soils tend to have lower bulk densities and therefore higher porosities in comparison to the coarse textured soils due to loose packing of the clay particles. Bulk density measurement for soils is important since it determines the degree of compactness as a measure for soil structure and is used for calculating pore space of soils. 

Coal type Bulk density (kg/m ) Repose angle (°) 

The void fraction (or percentage) of a bulk can also be of interest if, for example, the gas flow velocity through a coal bed or the pressurization of the coal in sluice systems needs to be evaluated. While the former requires calculation of the void fraction of the bulk from the apparent density, which is the usual case as shown in Equation (3.61), the latter needs to take into accoimt the true density as basis. In both cases the bulk density / i,ujk is used. 

The void fraction is, of course, extremely dependent on the particle size distribution and the capability of small particles to fill the void between larger ones. Hence, the lowest void fractions are reported from mine-run coal with broad particle size distributions aroimd 0.37. In usual particles sizes between 0.1 and 50 mm, the void fraction ranges between 0.38 and 0.60 strongly depending of the individual coal properties [10]. 

Another aspect of the coal bulk density is the storage stabiUty of the coaL Low bulk densities permit air to diffuse quickly into the coal bulk, which can cause losses in heating value, e.g., up to 1.7% in the case of bulk density of850 kg/m [2]. 

Some of the most important properties of the bulk material are the bulk density, the coefficient of friction, and particle size and shape. From these properties, the transport behavior of the bulk material can be described with reasonable accuracy. These properties will be discussed in more detail in the following section. 

Low bulk density materials (Pb 0.2 g/cc) tend to cause solids conveying problems, either in the feed hopper or in the feed section of the extruder. Materials with irregularly shaped particles tend to have a low bulk density examples are fiber scrap or film scrap (flakes). When the bulk density is low, the mass flow rate will be low as well. Thus, the solids conveying rate may be insufficient to supply the downstream zones (plasticating and melt conveying) with enough material. Special devices and special extruders have been designed to deal with these low bulk density materials. A crammer feeder, as shown in Fig. 6.1, is a device used to improve the solids transport from the feed hopper into the extruder barrel. 

Special extruders have been designed with the diameter of the feed section larger than the transition and metering section. Two possible configurations, both found commercially, are shown in Fig. 6.2. 

Two examples of extruders designed to handle low bulk density feed 

Since scrap or regrind is more difficult to handle, it is often blended with the virgin material to reduce the handling problems. 

The volume occupied by the solid plus the volume of voids when divided into the powder mass yields the bulk density. Therefore, when powder is poured into a graduated container, the bulk density is the mass divided by the volume of the powder bed. 

As already stated, a powder is a complex form of solid material and it is made up of a very large number of individuals, each different from its neighbor. Individual, or inherent, properties have been already discussed in the previous section under the common term of primary properties. However, every time a particular powder sample is poured into a receptacle, the individual particles are located in different places from before and the structure of the powder is different. It is clear that it is not possible to predict quantitatively how a powder will behave from a knowledge of the measured properties of individual particles, and so direct measurement of bulk properties is, therefore, necessary. Because each repeated measurement on a sample will be upon a rearrangement of its population, there will be an inevitable scatter of readings. This difficulty has the consequence that the powder should be handled in as identical a manner as reasonably possible each time a measurement procedure is performed. Moreover, it would seem logical that there would be a development of standardized testing and characterization methods, but this has not happened. 

The measurement of the bulk density of powders in no exception to the general situation outlined above, but it is so fundamental to their storage, processing, and distribution that it does merit particular consideration. The bulk density of a powder is its mass divided by the bulk volume it occupies. The volume includes the spaces between particles and the envelope volume of the particles themselves. The spaces between particles are denoted as porosity or voidage, and can be defined as the volume of the voids within the bulk volume divided by the total bulk volume. Bulk density and porosity are related by 

The amplitude of the vibration is set so that the powder will fill the cup in 20-30 s. The excess powder is skimmed from the top of the cup using the sharp edge of a knife or ruler, without disturbing or compacting, the loosely settled powder. 

Poured density is widely used, but the measurement is often performed in a manner found suitable for the requirements of the individual company or industry. In some cases the volume occupied by a particular mass of powder is measured, but the elimination of operation judgment, and thus possible error, in any measurement is advisable. To achieve this, the use of a standard 

The compacted bulk density would refer to the density of a powder compacted over and above what can be attained by tapping. There are no standard procedures for determining the compacted bulk density, other than the rather specialized soil compaction tests and density determinations, quoted in a British Standard for soils (British Standards Institution, 1975). 

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The formation density log is the main tool for measuring porosity. It measures the bulk density of a small volume of formation in front of the logging tool, which is a mixture of minerals and fluids. Providing the rock matrix and fluid densities are known the relative proportion of rock and fluid (and hence porosity) can be determined. 

The bulk density measured by the logging tool is the weighted average of the rock matrix and fluid densities, so that ... 

The formation bulk density (p ) can be read directly from the density log (see Figure 5.51) and the matrix density (p J and fluid density (p,) found in tables, assuming we have already identified lithology and fluid content from other measurements. The equation can be rearranged for porosity ((])) as follows ... 

Polyurethane is pulverized to iacrease its bulk density, mixed with 30—80% of a thermoplastic mol ding material, gelled, and then granulated to give coated urethane foam particles 0.1 to 0.15 mm in size (48). The particle bulk density is three times that of the polyurethane, while the volume is 15% less. This material may be injection molded or extmsion molded into products (49). Other technologies for recycling polyurethanes have also been reported. 

A higher density sol—gel abrasive, produced by the introduction of seed crystaUites formed by wet-milling with high alumina media or by introduction of submicrometer a-alumina particles, was patented (28) and designated Norton SG. The microstmcture of this abrasive consists of submicrometer a-alumina crystals (Fig. 1) and its bulk density approaches that of fused alumina. Norton SG has proven to be an exceptional performer in coated and bonded abrasive products it was awarded the 1989 ASM Engineering Materials Achievement Award (29). 

Polyoxymethylene is obtained as a finely divided soHd. The bulk density of the product, which is very important for ease of handling in subsequent manufacturing steps, is influenced by many reaction variables, including solvent type, polymerisation temperature, and agitation. 

Sodium carbonate monohydrate crystals from the crystallizers are concentrated in hydroclones and dewatered on centrifuges to between 2 and 6% free moisture. This centrifuge cake is sent to dryers where the product is calcined 150°C to anhydrous soda ash, screened, and readied for shipment. Soda ash from this process typically has a bulk density between 0.99—1.04 g/mL with an average particle size of about 250 p.m. 

V. Milan and co-workers. The Preparation of High Bulk Density Nitroguanidine, Rpt. 3037, NAVORD, Washington, D.C., 1957. 

Typical bulk density, loose, 881—929 kg/m angle of repose, 28—32 degrees. 

The properties of fillers which induence a given end use are many. The overall value of a filler is a complex function of intrinsic material characteristics, eg, tme density, melting point, crystal habit, and chemical composition and of process-dependent factors, eg, particle-si2e distribution, surface chemistry, purity, and bulk density. Fillers impart performance or economic value to the compositions of which they are part. These values, often called functional properties, vary according to the nature of the appHcation. A quantification of the functional properties per unit cost in many cases provides a vaUd criterion for filler comparison and selection. The following are summaries of key filler properties and values. 

Bulk Density. Bulk density, or the apparent density, refers to the total amount of space or volume occupied by a given mass of dry powder. It includes the volume taken up by the filler particles themselves and the void volume between the particles. A functional property of fillers in one sense, bulk density is also a key factor in the economics of shipping and storing fillers. 

When determining bulk density, a distinction should be made between loose bulk density and tap density, eg, ASTM B527-81. The latter is a measure of the influence of settling on filler volume at constant mass. 

Sodium Antimonate. Sodium antimonate [15593-75-6] Na SbO, another antimony synergist of commercial importance, has an antimony content of 61—63 wt % and a bulk density of 39.4—46.4 kg/m. Properties are given in Table 2. It is made by oxidizing antimony trioxide using sodium nitrate and caustic. It is a white powder and has a pH of around 9—11 when dissolved in water. 

Solid Density. SoHds can be characterized by three densities bulk, skeletal, and particle. Bulk density is a measure of the weight of an assemblage of particles divided by the volume the particles occupy. This measurement includes the voids between the particles and the voids within porous particles. The skeletal, or tme soHd density, is the density of the soHd material if it had zero porosity. Fluid-bed calculations generally use the particle... 

The light weight of these products reduces user s shipping costs and conserves energy in transportation. These products are reusable, a key property from economic, ecological, and energy conservation standpoints. Most products are available in bulk densities of 4.0 to 4.8 kg/m (0.25 to 0.30 lb/fT). Average price is about 1.50 per pound from the manufacturer. 

Physical Properties. Physical properties of waste as fuels are defined in accordance with the specific materials under consideration. The greatest degree of definition exists for wood and related biofuels. The least degree of definition exists for MSW, related RDF products, and the broad array of ha2ardous wastes. Table 3 compares the physical property data of some representative combustible wastes with the traditional fossil fuel bituminous coal. The soHd organic wastes typically have specific gravities or bulk densities much lower than those associated with coal and lignite. 

Fuel Specific gravity Bulk density, kg/m Moisture content, wt %... 

Specific gravity is the most critical of the characteristics in Table 3. It is governed by ash content of the material, is the primary deterrninant of bulk density, along with particle size and shape, and is related to specific heat and other thermal properties. Specific gravity governs the porosity or fractional void volume of the waste material, ie. 

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