Mass tran sfer

Glaser and Thodos [Am. Chem. Eng. J., 4, 63 (1958)] give a correlation involving individual particle shape and bed porosity. Kunii and Suzuki [Jnt. ]. Heat Mass Tran.sfer, 10, 845 (1967)] discuss heat and mass transfer in packed beds of fine particles.  [c.1059]

Estimation of fct for Reversible Reactions When the reaction is of the form A B, where B is a nonvolatile product and the equilibrium constant is defined by Cg = K Ca, the expressions for computing /cl become extremely complex. A good discussion of this situation is given in Mass Tran.sfer by Sherwood, Pigford, and Wilke (McGraw-Hill, New York, 1975, p. 317). Three limiting cases are hsted below  [c.1368]

External mass tran.sfer between the external surfaces of the adsorbent particles and the surrounding fluid phase. The driving force is the concentration difference across the boundary layer that surrounds each particle, and the latter is affected by the hydrodynamic conditions outside the particles.  [c.1510]

How can the goal of decreasing carbon dioxide emissions be achieved with a growing world population and commensurate increasing energy needs Fossil fuels are still the predominant source for energy. Whereas clean hydroelectric, solar, wind, and other alternate energy sources would be an answer, they can only amount to a modest part of the world s overall energy use in the foreseeable future. Atomic energy is clean m respect to greenhouse gas emissions but has serious problems. Nevertheless, from what we know today, we will have no choice but to use nuclear fission energy in the twenty-first century on a massive scale. We should, however, make it safer and solve the radioactive waste problem (either by improved disposal methods or by new atomic reactor technology). The needed nuclear fuels (uranium, thorium) are themselves not unlimited, but breeder reactors or eventually even controlled fusion may give mankind its needed long-range energy freedom.  [c.217]

The thermospray inlet/ion source does not produce a good percentage yield of ions from the original sample, even with added salts (Figure 11.2). Often the original sample is present in very tiny amounts in the solution going into the thermospray, and the poor ion yield makes the thermo-spray/mass spectrometer a relatively insensitive combination when compared with the sensitivity attainable by even quite a modest mass spectrometer alone. Various attempts have been made to increase the ion yield. One popular method is described here.  [c.73]

Determination of the required height of contacting zone for the. separation to be made as a function of properiies of the fluid mixtures and ma.s.s-tran.sfer efficiency of the contacting device. This determination involves the calculation of mass-transfer parameters such as heights of transfer units and plate efficiencies as well as equilibrium or rate parameters such as theoretical stages or numbers of transfer units. An additional consideration for systems in which chemical reaction occurs is the provision of adequate residence time for desired reactions to occur, or minimal residence time to prevent undesired reactions from occurring. For equilibrium-based operations, the parameters for required height are covered in the present section.  [c.1350]

Flammable liquids are potentially much more dangerous than flammable gas mixtures because of the greater mass which may be present. This is especially true if the liquids are processed or stored under pressure at a temperature above their atmospheric boiling point. Gases leak at a lower mass flow rate than liquids through an opening of a given size. Flashing liquids leak at about the same rate as a subcooled liquid but then turn into a mixture of vapor and spray. The spray, if fine, is just as hazardous as the vapor and can be spread as easily by the wind. Thus the leak of a flashing liquid through a  [c.256]

When considering how the evolution of life could have come about, the seeding of terrestrial life by extraterrestrial bacterial spores traveling through space (panspermia) deserves mention. Much is said about the possibility of some form of life on other planets, including Mars or more distant celestial bodies. Is it possible for some remnants of bacterial life, enclosed in a protective coat of rock dust, to have traveled enormous distances, staying dormant at the extremely low temperature of space and even surviving deadly radiation The spore may be neither alive nor completely dead, and even after billions of years it could have an infinitesimal chance to reach a planet where liquid water could restart its life. Is this science fiction or a real possibility We don t know. Around the turn of the twentieth century Svante Arrhenius (Nobel Prize in chemistry 1903) developed this theory in more detail. There was much recent excitement about claimed fossil bacterial remains in a Martian meteorite recovered from Antarctica (not since  [c.16]

The term nebulizer is used generally as a description for any spraying device, such as the hair spray mentioned above. It is normally applied to any means of forming an aerosol spray in which a volume of liquid is broken into a mist of vapor and small droplets and possibly even solid matter. There is a variety of nebulizer designs for transporting a solution of analyte in droplet form to a plasma torch in ICP/MS and to the inlet/ionization sources used in electrospray and mass spectrometry (ES/MS) and atmospheric-pressure chemical ionization and mass spectrometry (APCI/MS).  [c.138]

A representation of atomic structure. The various spheres are not drawn to scale. The lump of iron on the left would contain almost a million million million million (10 ) atoms, one of which is represented by the sphere in the top center of the page. In turn, each atom is composed of a number of electrons, protons, and neutrons. For example, an atom of the element iron contains 26 electrons, 26 protons, and 30 neutrons. The physical size of the atom is determined mainly by the number of electrons, but almost all of its mass is determined by the number of protons and neutrons in its dense core or nucleus (lower part of figure). The electrons are spread out around the nucleus, and their number determines atomic size but the protons and neutrons compose a very dense, small core, and their number determines atomic mass.  [c.336]

The primary VOCs in hair sprays are lower order alcohols and propellants. In nonaerosols, with typical VOC levels of 88—92%, a drop to 80% can be accomphshed with total water addition of about 15%, which causes an increase in solution viscosity and a heavier, wetter spray. In aerosols with typical VOC level of 93—98%, a much bigger decrease is needed. The propellant amount is fixed, requiring an even greater percent of the concentrate to be water, about 23%. This in turn causes difficulties in spraying and may require the use of dimethyl ether as a component of the propellant system. Significant discontinuities occur when 55% VOC levels are attempted. Polymer suppHers are working to develop new materials which may be adaptable to these high water content formulas with the overall goal of approaching the performance standards of anhydrous fixative sprays.  [c.455]

Hinder or Repel, registered under the Eederal Insecticide, Eungicide, and Rodenticide Act (EIERA) Section 24C, a state registration for special local need only, repels deer and rabbits from fmit trees, vines, vegetables, field crops, forage and grain crops, ornamentals, nursery stock, and noncrop areas. It is best apphed before damage occurs as an aqueous spray or by painting and is claimed to last 3—8 weeks. Hinder contains 15% ammonium soaps of higher fatty acids (1.5% ammonia and 13% mixed rosin and fatty acids) and 85% inert ingredients (81). The material is sold in the western United States as Hinder and in the eastern United States as Repel or Sticker-spreader 268. Chaperone is the only material as of this writing (1996) approved by EPA in Elorida as a repeUent for deer, mice, and rabbits. About 10 materials have been registered in Georgia in 1982, usuaUy containing 4—22% thiram (29) (82).  [c.121]

Entrainment Flooding. The vapor capacity of a column is limited, by excessive entrainment, usually called flooding. A flooding condition can be observed when the holdup of Hquid becomes excessive, the pressure drop increases dramatically, and the mass-transfer efficiency falls precipitously. Estimates of the vapor velocity for a flooding condition may be made from the chart in Figure 18 (53). The abscissa term E/G(P /is called a flow parameter and its value can indicate several things about the character of the aerated mass on the plate. For example, a very low value can indicate a phase inversion in which the vapor flow is continuous (spray flow) whereas a high value can indicate a bubbly mass (emulsion flow). The value of the flow parameter is easily determined from the stage calculations (reflux and boilup ratios) and densities of the phases. The ordinate value in Figure 18 leads to a value of the flooding velocity, and pmdent design calls for limiting actual flows to 70—80% of this velocity.  [c.169]

At higher vapor loads, the kinetic energy of the vapor rather than the bubble burst supphes the thrust for jets and sheets of hquid that are thrown up as well as the energy from breakup into spray. This yields much higher levels of entrainment. In distillation trays it is the most common limit to capacity.  [c.1413]

Health Hazards Information - Recommended Personal Protective Equipment Self-contained breathing apparatus (SCBA) acid-type canister mask goggles and face shield, rubber gloves and chemical protective clothing. Symptoms Following Exposure Inhalation causes irritation of the nose and throat pulmonary edema may develop following severe exposure. Contact with skin or eyes causes sever bums. Ingestion causes sever burns of mouth and stomach. General Treatment for Exposure Seek immediate medical attention following all exposures to this chemical. INHALATION Remove victim to fresh air if breathing has stopped, start mouth to mouth resuscitation. EYES Flush with clean running water for at least 15 minutes. Do not use any oils or ointments. SHIN Flush with water wash with soap and water. INGESTION Give victim large amounts of milk or water. Do not induce vomiting. If victim begins to vomit, give milk or beaten eggs at one-hour intervals. Toxicity by Inhalation (Threshold Limit Value) No data Short-Term Exposure Limits No data Toxicity by Ingestion No data Late Toxicity No data Vapor (Gas) Irritant Characteristics No data Liquid or Solid Irritant Characteristics No data Odor Threshold No data.  [c.39]

Proc. Heat Tran.sfer Fluid Mech., ASME, pp. 89-98, June 22-24 [1949]) and Cleeves and Boelter Chem. Eng. Prog., 43, 123-134 [1947]).  [c.647]

Software for these procedures is supplied, for example, by Constan-tinides (Applied Numerical Methods with Personal Computers, McGraw-Hill, 1987, pp. 577-614, with diskette) and by the commercial product SimuSolv (Mitchell and Gauthier Associates, 200 Baker Street, Concord, MA 01742). These do the integration, find the constants and their statistical criteria, and make the plots. SimuSolv is claimed to provide maximum efficiency in problem solving with minimum involvement in computational procedures. Since the computer does the work, many possibilities may be considered. For the reaction cyclohexanol to cyclohexanone, 36 experiments at 6 temperature levels were made and more than 50 rate equations were tested (Hofmann, inde Lasa, Chemical Reactor Design andTechnology, Martinus Nijhoff, 1986, p. 72). A rate equation for methanol from CO9 and H9 was selected from 44 possibilities by Beenackers and Graaf (in Cheremisinoff, Handbook of Heat and Ma.s.s Tran.sfer, vol. 3, Gulf Pubhshing, 1989, pp. 671-699). They used a spinning basket reactor like the item shown in Fig. 23-29c.  [c.707]

Outlook. Organic materials could provide much cheaper solar cells, since crystalline or epitaxially grown inorganic materials are cosdy. Also, deposition of organic compounds in vacuum could provide for large-area or custom shaped cells. Recent advances have greatly improved the efficiency of polymer-based solar cells, though they still suffer from a lower efficiency than inorganic-based devices. Also, the polymers suffer from photostabiUty problems that must be overcome. However, they still could see near-term use in appHcations which do not require exposure to powerful light sources.  [c.245]

Dimensiona.1 Ana.Iysis. Dimensional analysis is a mathematical technique that proceeds from the general principle that physical laws must be independent of the units of measurement used to express them. If one quantity is related to a group of other quantities, the quantities comprising the group must be related in such a manner that the net units or dimensions of the group are the same as those of the dependent quantity. A dimensionless group can then be formed immediately by division. A useful tool, the Pi theorem, asserts that the number of dimensionless groups needed to describe a situation is equal to the total number of variables less the number of fundamental dimensions needed to express them. Fundamental dimensions are generally taken to be length, time, mass, temperature, and heat content. The Pi theorem is a powerful tool because it limits the amount of experimental work needed to estabUsh a general relationship. For example, consider the problem of determining the drag force on a smooth sphere around which a Newtonian fluid is flowing. The diameter of the sphere and the fluid viscosity, density, and velocity may vary. Each of the five variables can be expressed using various combinations of the three dimensions mass, length, and time (force = mass times length per the square of time). The Pi theorem leads immediately to the conclusion that only two dimensionless numbers are needed to describe the relationship. These may be taken to be a drag coefficient 2F / AppV and a Reynolds number DV pj p. An accurate set of measurements for one sphere in one fluid provides a universal relationship between these numbers that is appHcable to all spheres in all Newtonian fluids.  [c.106]

To record a complete mass spectmm, a very fast frequency sweep of the voltage appHed to the transmitter plates is performed. The induced image currents are detected as a time—domain signal. This signal is then converted into a frequency—domain signal by the appHcation of a fast Fourier transform (fft). Very high (<10 ) resolution spectra can be obtained as long as the source pressure is low (<10 Pa (<10 torr)) enough. Therefore, the interfacing of high pressure techniques such as high performance Hquid chromatography (hplc) to ftms has required the development of external source machines. A high pressure ion source outside the magnet is used to produce ions that are injected through a differentially pumped transfer line into the analy2er cell, which is maintained at the low pressure needed for high resolution. Because this is an ion storage device, like the ion trap, complex (ms) experiments are possible. Like ion traps, ftms instmments also suffer from space—charge effects which result in perturbation of the ion motion, and this in turn limits the system s dynamic range. These systems have benefited from the continual reduction in price of the powerful computers needed for system control and data processing.  [c.542]

Migrant populations moving from areas with low prostatic cancer incidences to areas of high incidence have been shown to suffer increased rates, approaching those of the host country, suggesting that environmental factors may be involved aetiologically. For example, age-standardised rates of prostate cancer in different Japanese regions between 1983 and 1987 were between 6.6 and 10.0 per 100 000, while the rate among migrant Japanese in Hawaii was approximately four-fold higher at 34 per 100 000. In turn this is only about half the rate among white Hawaiians (63 per 100 000). It has been argued, however, that the incidence of this condition in Japan is actually much higher than it appears owing to regional differences in diagnostic practice. After adjustment for differences between USA and Japan in the proportion of latent prostate carcinoma and of localised tumours among all carcinomas of the prostate, the incidence rate was estimated as between 25 and 33 per 100 000 population.This would suggest that clinically significant prostate cancer may be over-diagnosed in the USA, and migration may not play as significant a role as previously reported. Notwithstanding this possibility, Japanese men have low mortality rates from prostatic cancer with small latent carcinomas only infrequently developing into clinically apparent disease. The high levels of dietary isoflavones and lignans consumed throughout the lifetime of Japanese men have been suggested as being protective against disease progression. Thus, it is suggested that high levels of isoflavones may influence the growth of cancer cells, slowing the development of the latent carcinomas. In Finland, despite a high fat intake, the incidence of prostate cancer is much lower than in the USA (although higher than in Japan), and this has been suggested to be due to the high production of lignans in their gut resulting from the relatively high intake of whole-grain products (particularly rye bread).  [c.122]

The original Gleiter method of making nanostructured solids is fine for research but not a feasible commercial method of making substantial quantities, for instance of a nanostructured cermet such as Co-WC. A whole range of chemical methods has now been developed, as described in the Edelstein/Cammarala book. These methods are mostly dependent on colloidal precursors, often using the so-called sol-gel approach. A sol is a colloidal liquid solution, often in water on evaporation or other treatment, a sol turns into a gelatinous gel which in turn can be converted into a nanostructured solid. A range of organometallic colloidal precursors can be converted into oxide ceramics by such an approach. Spray pyrolysis or conversion via an aerosol (a suspension of colloidal particles in air or other gas) offer other potentially large-scale routes to make nanostructured materials, and yet another route, chemically sophisticated, is by stabilising metal clusters with ligands , chemical radicals which bind to and coat the clusters to stabilise them against agglomeration. This approach allows a population of uniformly sized clusters to be made, but it is not appropriate for conversion into continuous solid materials.  [c.401]

Epoxy-phenolic (EP) blends are among the best adhesives for long-term high-temperatures service ([198], pp. 25-39). They were developed around 1955 [208]. Temperatures as high as 260°C for periods of up to thousands of hours are available. Extended exposures to temperatures above 260°C result in oxidative degradation [211]. EP adhesives such as Bloomingdale s HT-424 are capable of withstanding exposure to temperatures exceeding 530°C for short periods, making these adhesives useful for construction of supersonic jet aircraft [211]. Shear and tensile strengths are good across a wide temperature range, making them far superior to most unmodified epoxies in this respect. HT-424 retains about 1000-psi (7 MPa) tensile shear strength at 530°C. It also shows tensile shear strength of over 3000 psi (21 MPa) at —218°C [211]. The general RT range of tensile shear strengths for EP resins is 2000-3200 psi (14-22 MPa) [212]. Some EP adhesives are rated to —260°C service temperature [212]. Resistance to weathering, aromatic fuels, glycol, hydrocarbons, and water is high. High cost and poor peel and impact strengths detract from performance. The materials are useful in metal, glass, phenolic composite, and ceramic bonding. The metals include aluminum, stainless steel, copper, copper alloys, titanium, galvanized iron, and magnesium ([198], pp. 25-39 [212]). EP finds much use in honeycomb and metal sandwich constructions for aircraft. Epoxy curing is a low shrinkage process in general. Better thermal stability is seen on aluminum than on stainless steel or titanium [211].  [c.931]

Iodine s use as a water purification method emerged after World War 2, when the U.S. military was looking for a replacement for Halazone tablets. Iodine was found to be in many ways superior to chlorine for use in treating small batches of water. Iodine is less sensitive to the pH and organic content of water, and is effective in lower doses. Some individuals are allergic to iodine, and there is some question about long term use of iodine. The safety of long-term exposure to low levels of iodine was proven when inmates of three Florida prisons were given water disinfected with 0.5 to 1.0 ppm iodine for 15 years. No effects on the health or thyroid function of previously healthy inmates was observed. Of 101 infants born to prisoners drinking the water for 122- 270 days, none showed detectable thyroid enlargement. However, 4 individuals with preexisting cases of hyperthyroidism became more symptomatic, while consuming the water. Nevertheless, experts are reluctant to recommend iodine for long term use. Average American iodine intake is estimated at 0.24 to 0.74 mg/day, higher than the RDA of 0.4 mg/day. Due to a recent National Academy of Science recommendation that iodine consumption be reduced to the RDA, the EPA discourages the use of iodized salt in areas where iodine is used to treat drinking water. Iodine is normally used in doses of 8 PPM to treat clear water for a 10 minute contact time. The effectiveness of this dose has been shown in numerous studies. Cloudy water needs twice as much iodine or twice as much contact time. In cold water (Below 41 ° F or 5° C) the dose or time must also be doubled. In any case doubling the treatment time will allow the use of half as much iodine. These doses are calculated to remove all pathogens (other than cryptosporida) from the water. Of these, giardia cysts are the hardest to kill, and are what requires the high level of iodine. If the cysts are filtered out with a microfilter (any model will do since the cysts are 6 fim), only 0.5 ppm is needed to treat the resulting water.  [c.38]

To demonstrate the application of the above scheme, results obtained using the SOPR-KKR are presented in the following. Fig. 1 gives the orbital magnetic moment as deduced from experiment [15] and calculated using the SPR-KKR (without OP) for pure bcc-Fe, fcc-Co and fcc-Ni. Obviously for Fe and Co the theoretical moments are much too small. Performing LMTO calculations that account for SOC in the variational step and incorporate the OP-term (LMTO-SOC-OP) this discrepancy could more or less be removed. This was demonstrated by Eriksson et al. [16] for the ASA as well as by Trygg et al. [17] for the full potential construction. As can be seen in Fig. 1 using the SOPR-KKR-method one gets nearly the same results. However the great advantage compared to the LMTO-SOC-OP is that one has not to rely on the pseudo-perturbational treatment of SOC. Even more important seems the property that the  [c.458]

Although rail costs are route specific and vary tremendously, shipping by double-stack container is usually the most economical option, largely reflecting the energy savings. The energy-relcrted advantage of the double-stack over the piggyback trailer comes from more cargo weight per rail car ("leaving the wheels behind," stacking, and lighter cars). As a result, a train can carry more cargo without increasing length (more cargo per 6,000 ft. of train). Trains also suffer less air resistance since double-stack sits lower, However, when droyage (local trucking) is expensive (up to 4.00 per mile in some areas), much of the economic advantage of intermodal shipping using double-stack containers is negated.  [c.516]

Superior surface utilization in mass and heat transfer, allowng shorter packed bed heights. Turn-down performance is superior over 2-in. and 3) -in. Pall rings.  [c.305]

Major uses of the ferritic steels have been on motor vehicles as trim and in domestic equipment such as cutlery and hollow ware, but use has also been made in refrigerators, washing machines and on sinks and similar fittings. Some types would no doubt find much wider application in the chemical field and other fields where their superior corrosion resistance would be a considerable advantage if it was not for the fact that the austenitic types have advantages (sometimes considerable) in fabrication. However, the availability of the low interstitial weldable types and the super ferritics is increasing in scope.  [c.557]

Our final form for the Boltzman equation is then obtained by substituting these last two expressions for the gain and loss terms into equation 9.29 and adding the term Vijf x, v, t) to the LHS for the case where there is an external force F Vjj is the gradient operator with respect to v and m is the hard-sphere mass)  [c.477]

See pages that mention the term Mass tran sfer : [c.1635]    [c.368]    [c.244]    [c.647]    [c.737]    [c.220]    [c.199]    [c.70]    [c.75]    [c.317]    [c.725]   
Refrigeration and Air Conditioning (2000) -- [ c.11 ]