1、Designation: D7743 12Standard Test Method forMeasuring the Minimum Fluidization Velocities of FreeFlowing Powders1This standard is issued under the fixed designation D7743; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year o
2、f last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes the apparatus and procedureneeded for determining the minimum fluidization velocity ofGel
3、dart Group A powders and the minimum fluidization orcomplete fluidization velocity of Geldart Group B powders.1.1.1 This test method is for powders that are readily oreasily fluidizable and fall into the category of Group A and Bof the “Geldart” classification. The fluidization of GeldartGroup C pow
4、ders will be addressed in another standard. Thistest method could apply to Geldart Group D particles but thefocus of this document is towards Group and A and Bmaterials.1.1.2 Geldart classification of powders is often defined bycomparing the Sauter mean particle size with the differencebetween the p
5、article density and the density of the fluidizinggas, as illustrated in Fig. 1(1).21.1.2.1 Group A powders are easily fluidized but there is adifference between the gas velocity where the bed is initiallyfluidized and the velocity where bubbles are first observed. ForGroup A powders, bed expansion c
6、an be considerable beforeany bubbles are observed. Group B powders are also easilyfluidized; but there is no difference between the velocity wherethe bed is fluidized and the velocity at the onset of bubbling.The minimum gas velocity, where all of the particles are fullysupported by the gas for Grou
7、p B powders, is often referred toas the “complete fluidization velocity” instead of minimumfluidization velocity. Group C powders are cohesive and can bedifficult to fluidize.1.1.2.2 Group A powders can be distinguished from GroupB powders by the response to deaeration. Group A powdersdeaerate relat
8、ively slowly whereas Group B powders deaeratealmost instantaneously in fluidized beds.1.1.2.3 Group A Powders that lie near or on the Group A/Cboundary may be tested by this method. However, if thepowders do not fluidize freely, test results should be consideredinvalid.1.1.2.4 Temperature, moisture
9、(water) content, particle sizedistribution, particle shape and sometimes other variablesinfluence the Geldart classification of a powder. Deaerationtesting specified in 1.1.2.2 is a more definitive test than simplyusing particle size and density differences as described in 1.1.2.NOTE 1A Standard Pra
10、ctice for deaeration testing is under develop-ment.1.2 This test method should be performed in a laboratoryunder controlled conditions of temperature and humidity.1.3 All observed and calculated values shall conform to theguidelines for significant digits and rounding established inPractice D6026.1.
11、3.1 The procedures used to specify how data are collected/recorded or calculated, in this standard are regarded as theindustry standard. In addition they are representative of thesignificant digits that generally should be retained. The proce-dures used do not consider material variations, the purpo
12、se forobtaining the data, special purpose studies, or any consider-ations for the users objectives; and it is common practice toincrease or reduce significant digits of reported data to becommensurate with these considerations. It is beyond the scopeof this standard to consider significant digits us
13、ed in analysismethods for engineering design.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D
14、18.24 on Characterizationand Handling of Powders and Bulk Solids.Current edition approved June 1, 2012. Published August 2012. DOI: 10.1520/D7743-12.2The boldface numbers in parentheses refer to a list of references at the end ofthis standard.Copyright ASTM International, 100 Barr Harbor Drive, PO B
15、ox C700, West Conshohocken, PA 19428-2959. United States11.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bili
16、ty of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3D653 Terminology Relating to Soil, Rock, and ContainedFluidsD2216 Test Methods for Laboratory Determination of Water(Moisture) Content of Soil and Rock by MassD3195 Practice for Rotameter CalibrationD3740 Practice f
17、or Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD6026 Practice for Using Significant Digits in GeotechnicalData3. Terminology3.1 Definitions:3.1.1 For common definitions of technical terms in thisstandard, refer t
18、o Terminology D653.3.1.2 complete fluidization velocity, Ucf, nin powders andbulk solids, the superficial gas velocity at which all particles inthe bed are fully suspended by the gas.3.1.3 fluidized bed, nin powders and bulk solids, a bed ofparticulate matter fully suspended by a gas or liquid (liqu
19、idsuspensions are not covered in this method).3.1.4 minimum bubbling velocity, Umb, nin powders andbulk solids, the superficial gas velocity at which gas bubblesare first observed in a bed of powder.3.1.5 minimum fluidization velocity, Umf, nin powders andbulk solids, the superficial gas velocity at
20、 which the bed isinitially suspended by the fluid (or liquid).NOTE 2At minimum fluidization, the pressure drop or differentialpressure across the bed becomes relatively constant with additional gasvelocity. The pressure drop at minimum fluidization corresponds to themass of the bed times the gravita
21、tional constant divided by the bed crosssectional area.3.1.6 superficial gas velocity, nin powders and bulk sol-ids, the calculated gas velocity if no particles were present, i.e.,the gas volumetric flow rate divided by the cross sectional areawith respect to the bed diameter.3.1.7 Sauter mean parti
22、cle size, nin powders and bulksolids, the diameter of a sphere that has the same volume tosurface area ratio as the particles being measured.3.2 Definitions of Terms Specific to This Standard:3.2.1 differential pressure, nthe static pressure at onelocation referenced to the static pressure at anothe
23、r locationseparated by a known distance.3.2.2 particle density, nthe density of a particle includinginternal voids and pores.3.2.3 pressure drop, nthe same as differential pressure forthis application.4. Summary of Test Method4.1 Fluidize the specimen to eliminate any internal stressesthat may have
24、developed during filling, then terminate thefluidizing gas and allow the bed to deaerate naturally.4.2 Incrementally increase the gas flow rate and recordvalues of pressure drop as a function of gas flow rate.4.3 Once the specimen is fully fluidized, incrementallydecrease the gas flow rate and recor
25、d values of pressure drop.NOTE 3The final asymptotic pressure drop at full bed suspensioncorresponds to the bed density or bulk density times the bed height and theacceleration of gravity.5. Significance and Use5.1 The data from this test can be used to determine thesuperficial gas velocity required
26、 to suspend a bed of powder inthe fluidized state and the resulting pressure drop.NOTE 4The quality of the results produced by this standard isdependent on the competence of the personnel performing it, and thesuitability of the equipment and facilities used. Agencies that meet the3For referenced AS
27、TM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.FIG. 1 Geldart Classification of ParticlesD7743 122criteria of Practice D3740 a
28、re generally considered capable of competentand objective testing/sampling/inspection/etc. Users of this standard arecautioned that compliance with Practice D3740 does not in itself ensurereliable results. Reliable results depend on many factors: Practice D3740provides a means of evaluating some of
29、those factors.Practice D3740 was developed for agencies engaged in the testing orinspection or both of soil and rock. As such it is not totally applicable toagencies performing this standard. However, users of this standard shouldrecognize that the framework of Practice D3740 is appropriate forevalu
30、ating the quality of an agency performing this standard. Currentlythere is no known qualifying national authority that inspects agencies thatperform this standard.6. Apparatus6.1 The test unit is shown schematically in Fig. 2.NOTE 5The fluidization chamber consists of a plenum, a bed ofpowder and a
31、freeboard. A plenum consists of an expansion chamber forincoming gas and a porous media for gas distribution. The bed of powderis contained within a right circular cylinder. Any cylinder shape cantheoretically be used, but the gas needs to be uniformly distributed. Sincethis is most easily accomplis
32、hed using a right circular cylinder, this testmethod is limited to this apparatus. The freeboard is used to disengageentrained or elutriated particles (or at least provide an opportunity forthem to disengage). The outlet port in the freeboard region should beequipped with filtering media to prevent
33、the loss of powder to theenvironment.6.2 Select porous media based on anticipated bed height andpowder properties.6.2.1 Select the pore size of the porous media to be smallenough to prevent particle weepage into pores of the porousmedia.NOTE 6Porous media such as glass or quartz frits or sintered me
34、taldiscs are commonly used. The pore size does not have to be smaller thanthe smallest size of the test specimen.6.2.2 Seal the porous media to the plenum and fluidized bedchamber to ensure gas does not bypass the porous media.NOTE 7Typically, this can be done with adhesives or by welding.6.3 Ensure
35、 that the inside diameter of the cylinder is at least150 mm, preferably 200 mm or larger.NOTE 8Smaller columns can be used, but the column diameter needsto be noted in the report. Inner diameters of less than 150 mm may haveresults affected by wall friction.6.3.1 Construct the cylinder of any materi
36、al suitable for theenvironment in which the experiment is to be conducted.NOTE 9Typically, lab-scale units are constructed of Plexiglas,acrylic or glass. Many of these materials are relatively brittle, so pressurerelief devices need to be considered.6.4 Ensure that the freeboard height is at least t
37、he same asthe bed height when fully fluidized.6.4.1 Ensure that the freeboard inside diameter is the sameor larger than the inside diameter of the bed.NOTE 10In some instances, a freeboard region of greater diameterthan the bed can be used to lower the superficial gas velocity to reduce theparticle
38、entrainment rate. The expanded freeboard region needs to besufficiently above the bed such that an expanded bed does not move intothis expanded freeboard region. For typical minimum fluidization testing,an expanded freeboard is not needed.6.4.2 Choose for the filtering media for the outlet port in t
39、hefreeboard region a fibrous cartridge, cellulose thimble, sinteredmetal filter, etc.NOTE 11Cyclone(s) can also be used if sized correctly.6.4.3 Consider a pressure relief device in the freeboardassembly.NOTE 12Pressure relief can be done with pressure frangible, pressurerelief disk, pressure relief
40、 valve or static fluid column, depending on thepressure drop across the filter media (pressure in the freeboard withrespect to the ambient pressure).FIG. 2 Schematic of Test Apparatus for Measuring the Minimum or Complete Fluidization Velocity of Geldart Groups A and B PowdersD7743 1236.5 Select app
41、ropriate flow control and measuring devices.6.5.1 Regulate the flow rate of the gas upstream from theplenum by either a rotameter or a mass flow controller.6.5.2 Ensure that the rate of gas flowing into the material, Q,can be measured to a precision of 6 3 % of full scale.NOTE 13An example of a devi
42、ce is an electronic mass flow metersuch as thermal mass flow or Coriolis mass flow meter.6.5.3 Ensure that the flow measuring device is sized suchthat flow rates needed for minimum or complete fluidization donot exceed 90 % of the devices maximum capability.NOTE 14Minimum fluidization and minimum bu
43、bbling velocities canbe estimated using available correlations in the literature such as Wen andYu (2) for minimum fluidization velocity and Abrahamsen and Geldart(3)for minimum bubbling velocity.6.5.4 Install a pressure measuring device on the compressedgas supply between the plenum and gas flow me
44、asuring device.6.5.5 Choose a pressure gauge or transducer that is ratedwith respect to the maximum pressure rating on the com-pressed gas supply or the pressure regulator (if a regulator isbeing used).NOTE 15The gauge or transducer is used in conjunction with flowmeasurement instrument to establish
45、 the flow at recorded temperature andpressure.6.5.6 Install a differential pressure measuring device tomeasure the pressure drop across the fluidized bed.6.5.6.1 Use a fast response, low volume differential pressuretransducer or manometer.6.5.6.2 Connect the device to two ports in the fluidizingcham
46、ber, one port in the lower part of the bed of powder justabove the distributor (at 10 but no more than 50 mm), and theother port located high in the freeboard region.6.5.6.3 Use snubbers (fittings equipped with sintered metalfilters) on each port to prevent the backfilling of powder intothe differen
47、tial pressure lines.6.5.6.4 Ensure that one of the two snubbers will be in thebed when the specimen is added.6.6 Ensure that the correct fluidizing gas is available. See7.1.6.6.1 Ensure that the compressed gas supply is pulsationfree, has sufficient volumetric capacity at all anticipated flowrates,
48、is dry and oil free, and is capable of at least 200 6 5 kPaabsolute pressure.7. Hazards7.1 WarningSome powders may have a tendency toexplode, catch fire, are toxic or are hazardous when used withthe fluidization gas.7.1.1 Dust explosions can occur when some powders areairborne in an oxidizing enviro
49、nment with an ignition source.Materials such as flour, coal, cellulose material, sugar, etc. havecaused devastating dust explosions.7.1.2 Pyrophoric material such as many reduced metals andnitrated organic materials, can cause fire and explosions whenexposed to an oxidizing environment. An ignition source is notneeded.7.1.2.1 Fluidizing pyrophoric material with air could be asafety risk.7.1.2.2 Fluidizing pyrophoric material with nitrogen andthen exposing the bed to air could be a safety risk.7.1.3 Fluidizing oxidized material that has been reduced innitr
copyright@ 2008-2019 麦多课文库（www.mydoc123.com）网站版权所有
备案/许可证编号：苏ICP备17064731号-1