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ParTech
Objective
| Question | Answer |
|---|---|
| determines such properties as density and conductivity. | Composition |
| density is usually expressed by the symbol, ρ, is defined as the mass per unit volume. | True density |
| is the total mass per total unit volume. | Bulk (or apparent) density, |
| is the ratio of density of the material to the density of a reference substance. | Specific gravity |
| is defined as resistance to indentation for certain solids such as metals and plastics. | Hardness |
| refers to the ease with which a substance may be broken by impact. | Brittleness or friability |
| is the inverse quality of toughness | Friability |
| is the property of metals and alloys called impact resistance. | Toughness |
| is the resistance to sliding of one material to another material | Friction |
| Particle shape is expressed in terms of | sphericity |
| is sometimes defined as the diameter of a sphere of equal volume. | Equivalent diameter |
| Dp For fine granular materials, | equivalent to nominal size based on screen analyses |
| Dp For crushed materials, | 0.6- 0.8 |
| Dp For particles rounded by abrasion, | as high as 0.95. |
| Dp For Cubes | 0.81 |
| Dp For Cylinder | 0.87 |
| Unit of Coarse Particles | inches or mm |
| Unit of Fine Particles | in terms of screen size |
| Unit of Very Fine Particles | micrometer or nanometers |
| Unit of Ultrafine Particles | surface area per unit mass |
| Methods in determining particle size | Microscope with movable cross hair Screening Sedimentation Elutriation Centrifugation Magnetic Methods Optical Methods |
| for very small particles | Microscope with movable cross hair |
| simplest method of laboratory sizing | Screening |
| small particles of a given material fall in a fluid at a rate proportional to their size | Sedimentation |
| dependent on the velocity of settling. Particles whose normal falling velocity is less than the velocity of the fluid will be carried upward and out of the vessel. | Elutriation |
| centrifugal force is substituted for the normal force of gravity when the size of very small particles is to be determined. | Centrifugation |
| used if material is paramagnetic | Magnetic Methods |
| the amount of light transmitted depend upon the projected area of the particles | Optical Methods |
| characterized by reluctance to flow through openings. | Cohesive |
| readily flow out of a bin or silo. Example: grain, dry sand, plastic chips | Non- cohesive |
| Coarse solids like gravel and coal are stored outside in large piles, unprotected from the weather | Bulk storage |
| Solids that are to valuable or too soluble to expose in outdoor piles are stored in bins, hoppers, or silos. | Bin Storage |
| tall and relatively small in diameter | Silo |
| not so tall and usually fairly wide | Bin |
| small vessel w/ a sloping bottom for a temporary storage before feeding solids to a process | Hopper |
| a unit operation where a mixture of various sizes of particles is separated into two or more portions, | Screening |
| refers to the treatment of a material containing a natural amount of moisture or a material that has been dried before screening. | Dry Screening |
| refers to an operation where water is added to the material being treated for the purpose of washing and facilitating the passage of the fine material through the screen. | Wet Screening |
| these are used for particulate size control and analytical work. The screens are constructed of wire mesh cloth, where the diameters of the wire and the spacing of the wires are specified | Testing sieves |
| clear space between the individual wires of the screen | Screen Aperture |
| number of apertures per linear inch | Mesh |
| relationship between the successive sizes of screen openings in a series. | Screen Interval |
| this series of screens is based upon a 200 mesh screen with wire 0.0021 in thick and with an opening of 0.0029 in. | Tyler Standard Sieve Series |
| introduced by the National Bureau of Standards differ slightly from the Tyler series being based on a 1-mm opening and varying by 4 2 | United States Sieve Series |
| similar to both but the wires heave different gauges. | International Test Sieve Series |
| The mass or number of fraction in each increment is shown as a function of the average particle size. The result is represented as a histogram. | Differential Screen Analysis or Fractional Plot |
| This plot is obtained by adding consecutively the individual increments, starting with that containing the smallest particles and tabulating or plotting the cumulative sum against the maximum particle diameter in the increment. | Cumulative Analysis |
| indicates how much material a screen can handle. | Capacity Of Screens |
| are used for screening large sizes, particularly of 1 in and over. The large and oversize particles are discharged over the lower right end and the smaller particles pass through the slots between the bars into the hopper directly below | Grizzlies |
| are made of punched metal plates or woven wire mesh, usually set at an angle with the horizontal up to about 60°. Suitable for small scale operation such as screening sand, gravel or coal | Stationary Screens |
| are used where large tonnages are to be treated. They are useful in the chemical and fertilizer industry | Vibrated Screens |
| are characterized by low speed oscillations. Screens in this group are usually used from 1⁄2 inch to 60 mesh | Oscillating Screens |
| are standard equipment processing plants for handling fine separations even down to 300 mesh. Used to handle usually dry, light or bulks materials, light metal powders, powdered foods and granular materials. | Reciprocating Screens |
| consist of a cylindrical screen rotating about its axis. | Trommels or Revolving Screen |
| contains two or more eccentric screening surfaces mounted on the same shaft where the coarser screening surface is the innermost and the finest, the outermost. | Compound Trommels |
| have the shape of a truncated cone and are generally mounted with their axes horizontal. | Conical trommels |
| revolving screens driven at relatively high speed used in flour milling industry and for other light, non- abrasive materials | Reels |
| are box like machines either round or square with a series of screen cloths nested atop one another | Gyratory Screens |
| Industrial Screening Equipment | Grizzlies Stationary Screens Vibrated Screens Oscillating Screens Reciprocating Screens Trommels or Revolving Screen Gyratory Screens |
| involves the production of smaller mass units from larger mass units of the same material. | Size reduction |
| is the generic term for size reduction. | Comminution |
| particle disintegration by two rigid forces | Compression |
| particle concussion by a single rigid force | Impact |
| arising from particles scraping against one another or against a rigid surface | Attrition |
| accomplished by forcing a sharp and thin knife through a material | Cutting |
| which states that “the work required in crushing is proportional to the new surface created” | Rittinger’s Law |
| which states that “the work required to form particles of size Dp from very large feed is proportional to the square root of the surface to volume ratio of the product” | Bond’s Crushing Law |
| states that “energy required for crushing is proportional to the leg of the initial and final diameters” | Kick’s Law |
| consists of a swinging jaw which moves back and forth, working against a stationary surface called the anvil jaw, with which it forms a V-shape chamber. | Jaw Crusher |
| swinging jaw pivoted at the bottom | Dodge Type Jaw Crusher |
| swinging jaw is pivoted at the top | Blake Type Jaw Crusher |
| employs a crushing head in the frame of truncated core, mounted on a shaft | Gyratory Crusher |
| if the hourly tonnage to be crushed divided by the square of the gape in inches is less than 0.115, use a jaw crusher; otherwise, a gyratory.” | Taggart’s Rule states that |
| The coal enters through the chute at the far end, is lifted, falls and is broken by the impact as the cylinder is rotated perforations into the chute below. Combines the two features of breaking and screening | Bradford breaker for coal |
| Breaking by pressure of the teeth against larger lumps of the material | Toothed roll crusher |
| The hammer deliver heavy blows to the feed material while it is in suspension, driving it against a breaker plate until it is fine enough to pass through the openings | Hammer Mill |
| For fibrous materials such as wood blocks and asbestos Two concentric cages rotate in opposite direction The feed is introduced into the inner cage Centrifugal force drives the material into the spaces between the rotating cages where it is torn apart | Squirrel- cage disintegrator |
| Two rolls, one in adjustable bearings, rotate in opposite directions. The clearance between them can be adjusted according to the size of feed and the required size of product | Crushing Rolls |
| Consists of a conical crushing head similar to that of the gyratory crusher. | Cone Crusher |
| The only commonly used crusher of this general type is the one which the pan rotates and the horizontal axis of the grinding wheel is stationary. | Edge Runners |
| Is a steel cylinder lying on its side and rotated about its long axis and containing an appropriate grinding medium. | Pebble Mill |
| Rod mills are similar to pebble mills and ball mills except that the grinding media are steel rods rather than balls. | Rod Mill |
| Consists of a horizontal cylinder whose diameter is roughly equal to its length, lined with heavy liner plates. | Ball Mill |
| Fine Size Reduction | Pebble Mill Rod Mill Ball Mill |
| Intermediate Size Reduction | Crushing Rolls Cone Crushers Edge Runners |
| Coarse Size Reduction for Soft Materials | Bradford Breaker for Coal Toothed roll crusher Hammer Mill Squirrel- cage disintegrator |
| Coarse Size Reduction for Hard Materials | Jaw Crusher Gyratory Crusher |
| the condition at which the balls are carried over due to very high speed | Centrifuging |
| the speed at which centrifuging occurs | Critical Speed |
| is a unit operation where fine particles are assembled to form bigger agglomerates. | Agglomeration |
| often makes use of agglomeration process in order to produce granules and is often carried out in a mixing device. | Granulation |
| which are attributable to Brownian movement can therefore occur even in a static fluid. | Perikinetic processes |
| occur where the perikinetic process is supplemented by the action of eddy currents which may be set up in stirred vessels or in flowing systems. | Orthokinetic process |
| in which fresh particles are formed, generally by attrition. | Nucleation |
| is deposited on the surfaces of the nuclei, this increasing both the size and total mass of the particles | Layering or Coating |
| which results in an increase in particle size but not in the total mass of particles | Coalescence |
| which results in degradation and the formation of small particles, thus generating nuclei that re-enter the cycle again. | Attrition |
| particle size is largely determined by the size of the droplet of liquid or suspension. | Spray Drying |
| relatively coarse droplets are introduced into the top of a tall, narrow tower and allowed to fall against an upward flow of air. Produces somewhat larger particles than in spray dryers. | Prilling |
| an atomised liquid or suspension is sprayed on to a bed of hot fluidised particles and layers of solid build up to give enlarged particles. | Fluidised beds |
| particles are tumbled in an open cylinder with roughened walls and subjected to a combination of gravitational and centrifugal forces. | Drum and pan agglomerators |
| impart a complex kneading action that is a combination of ribbing and shearing and mixing. | Pug Mills and Extruders |
| agglomeration may be achieved by heating which results in softening in the surface layers. | Elevated temperatures |
| a material is subjected to very high compaction forces. | Pressure compaction |
| If a body is released from its position of rest, the falling body consists of two period | Periods of Settling |
| In this period, the velocity increases from zero to its terminal velocity. It is very short, usually in the order of tenths of a second or less | short period acceleration |
| at which particle is at its terminal velocity | period |
| The particles settle at a constant rate and are assumed to be moving at terminal velocity. The movement of particles is not affected by the presence of other particles. | Free Settling |
| is the partial separation or concentration of suspended solids from a liquid based on the motion of particles through fluids. | Sedimentation |
| increase concentration of suspended solids | Thickening |
| to remove a relatively small quantity of suspended particles and produce a clarified effluent | Clarification |
| is a mechanical process of separating multi – phase mixture with the use of centrifugal force. | Centrifugation |
| A given particle in a given fluid settles under gravitational force at a fixed maximum rate. | CENTRIFUGAL SEDIMENTATION |
| the diameter of that particle which just reaches one- half the distance between r1 and r2. | Cut point |
| Flow of fluid is caused by centrifugal force instead of impressed pressure difference. | CENTRIFUGAL FILTRATION |
| deals with their movement over relatively short distances. | HANDLING OF SOLIDS |
| involves movement of materials over short distances, usually not exceeding 10 ft, and only when the quantity does not exceed 4 to 5 tons. | Unassisted manpower |
| is recommended when the radius of work is increases to 100 to 200 ft to lift loads weighing more than 100 to 150 lbs, various mechanical devices are employed to amplify the force exerted by the workman. | Assisted manpower |
| it pertains to the characteristics of the material, physical as well as chemical, and its quantity. It practically answers the question “WHAT” | Material |
| it indicates the scope of movement, the distance that must be covered from source to destination, the frequency of transfer, the speed or rate and the type of route involved. Answers the question “WHERE” and “WHEN” | Movement |
| it pertains to the choice of manpower (assisted or unassisted), choice of an appropriate device or equipment to be used. | Method |
| Used to keep gravity slides free by giving the slide a vibration in the direction of flow. | Vibrators |
| – is the angle of minimum slope measured from the horizontal at which any loose material will flow | Angle of slide |
| – is the angle of maximum slope measured from the horizontal at which a heap of loose material will stand without sliding | Angle of repose – |
| Mechanical conveyors may move materials by a scraping action or by a carrying action | MECHANICAL CONVEYOR |
| Consists of a steel shaft having a spiral or helical fin fastened to the shaft in a trough without touching the trough. | Screw or Helical Flight conveyors |
| is a special type of screw conveyor I which the center portion of the helical fin is absent. Suitable for sticky or gummy liquids | Ribbon conveyor |
| Consists of one or two endless chains passing through a trough or a set of guides. | Flight Conveyors |
| Consist of endless belts, suitably supported and driven, which carry or transport solids from place to place | Belt Conveyors |
| Simplest and most dependable unit for vertical or lifting movement of solids | Bucket Elevators |
| – for grain and other dry, pulverized material | Minneapolis Type |
| for wet or sticky materials | Flatter buckets |
| for large lumps and heavy materials | Stamped- steel bucket – |
| Similar to belt conveyors since solids are also moving by a moving trough | Apron Conveyors |
| in which groups of particles are moved from one position to another | Convective mixing, |
| where the particles are distributed over a freshly developed interface | Diffusion mixing, |
| where slipping planes are formed | Shear mixing, |
| Used to blend viscous liquids or light pastes (e.g. food processing or paint manufacture) | Change Can Mixer |
| Used to mix deformable or plastic solids. It involves squashing the mass flat, | Kneaders, Dispersers and Masticators |
| can handle light to fairly heavy materials. | Continuous Kneaders |
| The mix is cut and folded while in the mixing chamber and subjected to additional shear as it flows through the die. | Mixer Extruders |
| Subjects pastes and deformable solids to intense shear by passing them between smooth metal rolls turning at different speeds. | Mixing Rolls |
| Mulling is a smearing or rubbing action similar to that in a mortar and pestle. | Muller Mixers |
| Mixing is done by blades and knives set in a helical pattern on a horizontal shaft turning in an open through or closed cylinder. | Pug Mills |
| Consists of a horizontal trough containing a central shaft and a helical ribbon agitator. Mixing results from the turbulence induced by the counteracting agitators | Ribbon Blenders |
| Used to mix free – flowing grains and other light solids. | Internal Screw Mixers |
| Consists of a container rotating about a horizontal axis | Tumbling Mixers |
| The material is blended continuously be spreading them out in a thin layer under centrifugal action. | Impact Wheels |
| is the removal of solid particles from a fluid by passing the fluid through a filtering medium, or septum, on which the solids are deposited. | Filtration |
| added in order to increase the porosity of the cake to permit passage of the liquor at a reasonable rate. | Filter Aids |
| are used to separate relatively large amounts of solids as a cake of crystals or sludge | Cake filters |
| are used to remove small amounts of solids to produce a clean gas or sparkling clear liquids. | Clarifying filters |
| are used by allowing the feed suspension to flow under pressure at a fairly high velocity across the filter medium. | Crossflow filter |
| the particles from the suspension, which usually has a high proportion of solids, are deposited on the surface of a porous septum which should ideally offer only a small resistance to flow. | Cake filtration |
| the particles penetrate into the pores of the filter medium, where impacts between the particles and the surface of the medium are largely responsible for their removal and retention. | Depth or deep-bed filtration |
| is a special example of flow through a porous media in which the resistances to flow are constant. | Filtration |
| The pressure drop is held constant and the flow rate allowed to fall with time | CONSTANT – PRESSURE FILTRATION (CPF) |
| The pressure drop is progressively increased | CONSTANT – RATE FILTRATION (CRF) |
| The washing of a cake after the filtration cycle takes place by displacement of the filtrate and by diffusion. | Rate of Washing |
| The wash liquid travels through a cake twice as thick and area half as large as in filtering so, | Plate and frame filter plate |
| The plate – and – frame filters suffers from the disadvantages common to all batch processes and cannot be used for large capacity processes. | Continuous filtration- Rotary Filter |
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