Extreme low temperature operations


The primary performance features of synthetic lubricants are outstanding flow characteristics at extremely low temperatures and stabdity at extremely high temperatures. The comparative operating temperature limits of mineral od and synthetic lubricants are shown in Figure 2 other advantages, as weU as limiting properties, are outlined in Table 4. Synthesized hydrocarbons, organic esters, polyglycols, and phosphate esters account for over 90% of the volume of synthetic lubricant bases in use. Other synthetic lubricating fluids include a number of materials that generally are used in low volumes.  [c.263]

It should be remembered dial eryogenie expanders operate at extremely low temperatures and spring-loaded PTFE ( Teflon ) eryogenie bp seals are, therefore, generally used for the expander easing. Properly designed, this highly reliable seal is also pressure aetuated. Therefore, effeetive sealing does not depend on torqueing of ease bolts. Elasto-merie o-rings are used for sealing the eompressor easing and parts not subjeeted to extremely low temperatures.  [c.275]

A survey of 13 drilling contractors operating 193 drilling rigs in northern Canada and Alaska indicated that there is a wide range of experience and operating practices under extremely low-temperature conditions. A sizable number of portable masts failed in the lowering or raising process in winter. Thus the exposure to low-temperature failures focuses on mast lowering and raising operations. Based on reports, however, this operation has been accomplished successfully in temperatures as low as -50°F. While the risk may be considerably greater because of the change in physical characteristics of steel at low temperatures, operators may carry on normal operations even at extremely low temperatures. This may be accomplished by closely controlled inspection procedures and careful handling and operation to reduce damage and impact loading during raising and lowering operations. At present, there seems to be no widely accepted or soundly supported basis for establishing a critical temperature for limiting the use of these oilfield structures. Experience in the operation of trucks and other heavy equipment exposed to impact forces indicates that -40°F may be the threshold of the temperature range, at which the risk of structural failure may increase rapidly. Precautionary measures should be more rigidly practiced at this point. The following recommended practices are included for reference  [c.521]

Extreme Low Temperature. Maximum load ratings shall be established at room temperature and shall be valid down to 0°F (-18°C). The equipment at rated loads when temperature is less than 0°F is not recommended unless provided for by the supplemental requirements. When the equipment is operating at lower temperatures, the lower impact absorbing characteristics of many steels must be considered.  [c.533]

Extreme Low Temperature. Equipment intended for operation at temperatures below 0°F may require special design and/or materials.  [c.542]

Reaction rates often may be improved by using more extreme operating conditions. More extreme conditions may reduce inventory appreciably. However, more extreme conditions bring their own problems, as we shall discuss later. A very small reactor operating at a high temperature and pressure may be inherently safer than one operating at less extreme conditions because it contains a much lower inventory. A large reactor operating close to atmospheric temperature and pressure may be safe for different reasons. Leaks are less likely, and if they do happen, the leak will be small because of the low pressure. Also, little vapor is produced from the leaking liquid because of the low temperature. A compromise solution employing moderate pressure and temperature and medium inventory may combine the worst features of the extremes. The compromise solution may be such that the inventory is large enough for a serious explosion or serious toxic release if a leak occurs, the pressure will ensure that the leak is large, and the high temperature results in the evaporation of a large proportion of the leaking liquid.  [c.263]

The implementation of very effective devices on vehicles such as catalytic converters makes extremely low exhaust emissions possible as long as the temperatures are sufficient to initiate and carry out the catalytic reactions however, there are numerous operating conditions such as cold starting and  [c.258]

These systems have been operated in extremely low quality (and radioactivity contaminated) industrial environments for the past several years without any major equipment or component failures. Utilizing specialized operating/warm-up procedures, they have operated in low grade, out-of-doors, dust ridden, rain-soaked, industrial environments at temperature ranges which greatly exceed the original equipment manufacturers (OEM) specified limits. The systems have been successfully operated at ambient temperatures of minus 10 to plus 103 degrees Fahrenheit without any pre-mature or un-anticipated equipment failures.  [c.612]

A small amount of water may also be added to improve blending or to assure proper furnish (blended materials) me. Actual amounts of resin and wax used in a specific operation are based on amounts needed to produce the desired strength and water-resistance properties. Wax provides, in addition to water resistance, a small amount of lubricity, which aids in moving the materials through the process. The scavenger, normally urea, is added to react with excess formaldehyde from the resin and prevent excessive formaldehyde emissions from the product. In some cases, resin supphers have been able to formulate resins with extremely low emission potential and thus avoid the additional step of adding an external scavenger. The amounts of catalyst (cure accelerator) and buffer (cure retardant) used must be balanced to meet the requirements of the system. Catalyst is used to hasten the cure of the core adhesive, along with the possible use of small amounts in the surface. Because catalyzed resins are sensitive to temperature, amounts are often changed on a summer-to-winter basis. Careful control is required to balance the need for faster press times and more production, with possible precure of the resin occurring before pressing. Resin durabiUty problems may also be associated with too much catalyst remaining in the board after pressing. Resin supphers also have proprietary catalysts and buffers which can be added during resin manufacture and in some cases can tailor a resin to the specific needs of the mill so that external catalysts and buffers are unnecessary. Moisture content from the blenders after wax and resin addition should be 9—11% for surfaces and 6—8% for core.  [c.392]

A simple direct-flame incinerator may be a refractory-lined furnace arranged for good mixing and fitted with a burner. Such an incinerator is low in capital cost and suitable for periodic or batch burning of a process purge gas during plant shutdown. However, such an incinerator in continuous service on other than a very small vent would have extremely high fuel operating cost. In these cases, sufficient auxiHary fuel must be provided to completely heat the incinerator gas to the ignition temperature and this heat can be further utilized. Steam can be generated if there is a need for process steam. If steam is not needed, moderate to large size incinerators have a heat exchanger between the incoming gases and the hot combustion products to preheat make-up air. Because of the temperatures involved, heat-transfer surfaces are generally of alloy constmction or ceramic materials. The latter can be damaged by thermal shock if sudden step changes in operation occur, whereas alloys may be attacked by corrosive gases such as halogens and sulfates if present.  [c.59]

One of the main advantages of LEDs over other lighting sources is reHabiHty. Radiative recombination is a natural process which does not necessarily damage the crystal. Consequendy, LEDs typically exhibit degradation rates in the range of 5—20% during the first 1000 hours of operation and do not reach half-brightness for more than 100,000 hours. In most cases, LEDs are used in appHcations wherein the output is not sensitive to changes in brightness by a factor of two. The degradation that occurs in LEDs often occurs from the relatively high energy radiation (1—2 e inducing or causing the migration of defects within the crystal. Such degradation is accelerated at high current densities (23). As a result, most conventional style LEDs (Eig. 4) are operated at current densities < 50 A/cm however, small emission area LEDs (Eig. 5) maybe operated at current densities as high as 10 kA/cm. In some materials, eg, AlGaAs, the operation of LEDs at high current densities (>300 A/cm ) may result in the formation of networks of dislocations, called dark line defects, around existing defects in the crystal. These defects act as nonradiative recombination sites, resulting in degradation of the internal quantum efficiency of the device (19). Migration of metal from the ohmic contacts to the active region of the LED can create nonradiative centers or electrical leakage, both of which reduce the internal efficiency of the device. The LED package may also induce degradation. At low temperatures, the encapsulation epoxy contracts and can exert extreme compressive stress on the chip, inducing defects and degradation therein. Also, in outdoor appHcations, the encapsulation epoxy may discolor as a result of exposure to ultraviolet radiation. This discoloration causes a decrease in the light output of the packaged device, yielding yet another form of degradation. Despite these problems, LEDs are some of the most reHable light sources available. Their robustness is a primary reason these devices are employed in many appHcations.  [c.120]

Chlorine. Chlorine [7782-50-5] is used either in the first stage of the sequence or in the stage immediately following an oxygen predelignification stage. Its chief function is to render most of the residual lignin soluble in alkaU, and it is always followed by a caustic extraction stage. The mechanisms by which solubilization occurs include demethylation, alkyl—aryl ether cleavage, aromatic substitution, and oxidation (1). An important variable is pH, which is kept below 2 to avoid excessive hydrolysis of chlorine to hypochlorous acid [7790-92-3] HOCl, which can attack cellulose. A saUent feature of chlorination is its extreme rapidity. In a perfectly mixed system, the bulk of the reaction is complete within seconds and a subsequent slower phase is virtually complete within a few additional minutes (2). This, together with the extreme slowness of diffusion of chlorine in pulp suspensions, makes good mixing very important (3). Accordingly, traditional chlorination stages were conducted at low pulp consistency (3—4% dry fiber on pulp suspension-weight basis), to facihtate good mixing, and at low temperature (5—30°C), to decrease the rate of reaction relative to that of diffusion and to increase selectivity for lignin. Modem chlorination stages are mn at either low or medium (10—12%) consistency and higher temperature (40—60°C). Medium consistency operation has been made possible by the introduction of high shear, fluidizing mixers. High temperature operation is faciUtated by good mixing and also by the selectivity improvement that comes from substituting chlorine dioxide for part of the chlorine used. A retention time of 30—60 min is provided to allow for process upsets and less than perfect mixing. Chlorine is appHed at a rate that is proportional to the lignin content, as measured by "kappa number", of the pulp entering the stage. This can vary widely, depending on whether softwood or hardwood is the raw material, whether a preceding oxygen stage is used, and whether new extended delignification technology is used in the pulping step. Chlorine charges of 3—7% have been common, but an environmentally driven downward trend is evident. This has arisen out of concern over possible environmental effects of chlorinated organic by-products. The formation of these by-products is now commonly reduced by substituting chlorine dioxide for part or all of the chlorine used.  [c.155]

An organic reagent system for solvent extraction of copper should exhibit (/) extremely low solubiUty in aqueous solutions (2) high solubiUty in diluents such as kerosene (f) low rates of biological or chemical degradation (4) high copper-loading capacity (5) rapid rate of copper extraction (6) low cost (7) good phase-separation characteristics (8) abiUty to extract copper in the 1—7 pH range (7) high selectivity (10) low toxicity and (/ /) low volatility at the operating temperature.  [c.207]

Hostile environments, such as extreme cycling temperature (values from —65 to +150 °C in military 883 specs), high relative humidity (85 to 100%), shock and vibration, and high temperature operating bias are part of real life operation, and the device must survive these operation-life cycles. In addition, encapsulants must also have suitable mechanical, electrical, and physical properties, such as minimal stress and matching thermal expansion coefficient, etc, which are compatible with the IC devices. The encapsulant must have a low dielectric constant to reduce the device propagation delay, and excellent thermal conductivity to dissipate power-hungry, high speed bipolar IC and high density packages which generate tremendous amounts of heat that require special thermal management considerations. Furthermore, since the encapsulation is the final process step and some of the devices are expensive, particularly in high density multichip modules (MCM), it must be easy to apply and repair in production and service. With the proper choice of encapsulant and process, the embedding enhances the reUabiUty of the fragile IC device, and improves its mechanical and physical properties and its manufacturing yields. These are the ultimate goals of the embedding (9—28).  [c.188]

In vacuum processing and drying the objective is to create a large temperature-driving force between the jacket and the product. To accomplish this purpose at fairly low jacket temperatures, it is neces-saiy to reduce the internal process pressure so that the hquid being removed will boil at a lower vapor pressure. It is not always economical, however, to reduce the intern pressure to extremely low levels because of the large vapor volumes thereby created. It is necessaiy to compromise on operating pressure, considering leakage, condensation problems, and the size of the vapor lines and pumping system. Veiy Few vacuum diyers operate below 5 mmHg pressure on a commerci scale. Air in-leakage through gasket surfaces will be in the range of 0.2 kg/(h hnear m of gasketed surface) under these conditions.  [c.1214]

The effect of high or low environmental temperature on skilled performance is important for industrial or service personnel. Operators often have to work in extreme thermal conditions, such as in furnaces or when they need to operate a pump in cold weather at night. Errors of omission are quite often due to the workers trying to minimize the time period they have to be exposed to high or low temperatures. Particular emphasis has been placed on the effects of cold on manual performance. Cold can affect muscular control, reducing such abilities as dexterity and strength.  [c.111]

Although the fuel cell is more efficient than an IC engine, it does produce waste heat at low temperature, and this poses problems from a heat rejection standpoint. Because there are vehicle styling constraints on how large the radiator can be, there is significant research into raising fuel cell stack operating temperatures by up to 10°C. If this can be achieved without degrading the electrolyte s durability, then it may almost halve the temperature differential between waste heat and ambient air in extremely hot conditions, with corresponding reductions in radiator size.  [c.532]

Because of the highly exothermic nature of acrylonitrile polymerization, bulk processes are not normally used commercially. However, a commercially feasible process for bulk polymerization ia a coatiauous stirred tank reactor has beea developed (52). The heat of reaction is controlled by operating at relatively low conversion levels and supplementing the normal jacket cooling with reflux condensation of unreacted monomer. Operational problems with thermal stabiUty are controlled by using a free-radical redox initiator with an extremely high decomposition rate constant. Since the initiator decomposes almost completely in the reactor, the polymerization rate is insensitive to temperature and can be controlled by means of the initiator feed rate. Polymer molecular weight and dye site content are controlled by using mercapto compounds and oxidizable sulfoxy compounds.  [c.280]

Fluid Properties. A great variety of equipment exists for measuring clean, low viscosity, single-phase fluids at moderate temperatures and pressures. Fluid-related factors that are normally considered are operating pressure, temperature, viscosity, density, corrosive or erosive characteristics, flashing or cavitation tendencies, and fluid compressibiHty. Any extreme fluid characteristic or condition, such as a corrosive nature or high operating temperature, gready reduces the range of available equipment and should be given first consideration in any selection procedure. Other fluid properties important for use of certain meter types are heat capacity, an important consideration for thermal meters, and fluid electrical conductivity, requited for magnetic flow meter operation. In some cases particular fluid requirements may limit the metering choices. An example of this is the requirement for the sanitary design of meters used in food processing (qv).  [c.55]

Gas Lubrication. Despite severe limitations, gas lubrication of bearings has received intensive consideration for its resistance to radiation, for high speeds, temperature extremes, and use of the working fluid (gas) in a machine as its lubricant. A primary limitation is, however, the very low viscosity of gases (Fig. 16 (68)) which leads to a limiting load of only 15—30 kPa (2.2—4.4 psi) for most self-acting (hydrodynamic) gas bearings and up to 70 kPa (10 psi) for operation with external gas-lifting pressure in hydrostatic operation.  [c.252]

In the mbber and printing industries, carbon black is used to enhance the mechanical properties of mbber and to provide pigments for printing inks. The production of carbon black involves the partial combustion of feedstock oil in a high temperature, low pressure environment. Fuel oil is injected into the reactor using air- or steam-assisted atomizers. The key issues relating to the processes of carbon black production include the protection of refractory lining, spray impingement by the quenching nozzles, and carbon buildup. In more recent years, manufacturers continue to add new grades of carbon blacks for product improvement and competition. The control of spray droplet size, size distribution, and spray angle becomes extremely important to obtain the desired quaUty. Typical carbon black furnaces utilize either pressure- or air-assisted (internal or external) atomizers. The choice is largely deterrnined by the type of black being produced, flow rate, available fuel and air pressure, fuel properties, and fuel preheating capabiUty. A typical plant handles fuel flow capacity between 500 to 3000 L/h and fuel pressure from 0.3 to 1.5 MPa (3—15 bar). The atomizing air can range from 18.9 to 37.8 L/s (40—80 SCFM) with air pressure about 700 kPa (7 bar). If the atomizing medium is steam, the flow capacity can mn between 180 to 350 kg/h using a line pressure up to 1.5 MPa. A typical mean droplet size for this type of operation is around 100 p.m.  [c.335]

Mining of the Athabasca tar sands presents two principal issues in-place tar sand requires very large cutting forces and is extremely abrasive to cutting edges, and both the equipment and pit layouts must be designed to operate during the long Canadian winters at temperatures as low as —40° C.  [c.357]

Boiling Point Elevation. Boiling point elevation may also be beneficial in heat transfer appHcations. As engine power increases, the heat given off by the engine also increases. This increase in engine operating temperature increases engine efficiency by making more heat available to power the engine. However, if too much heat remains in the engine, overheating of both the engine and the oil may occur and engine efficiency decreases. The extra cooling required can be suppHed either by increasing the cooling system capacity, or by enabling the coolant to accept more heat. An increase in the capacity of the cooling system is a cosdy alternative that can require physical changes to the system. Enabling the coolant to remove more heat most often requires no capital changes, and can be achieved by either increasing the flow rate of the coolant, or increasing the system pressure, and thus the boiling point of the coolant, which would allow the coolant to circulate at a higher maximum temperature. Today, most engines operate slightly pressurized to increase the maximum use temperature of the coolant and thus eliminate boiling of the coolant under extreme operating conditions. Under these operating conditions, the very low vapor pressure of glycol-based coolants significantly reduces the evaporative losses of the coolant, when compared to high vapor pressure hquids such as methanol and ethanol.  [c.188]

In a typical hot molding operation to form a 1.7 m diameter billet 1.3 m long, approximately 7200 kg of mix at 160°C is introduced into a steam heated mold without cooling. The platens of the press compact the mix at ca 5 MPa (49 atm), holding this pressure for 15—30 min. The cooling step for pieces of this size is the most critical part of the forming operation. Owing to the low thermal conductivity of pitch, 0.13 W/(m-K) (7), and its relatively high expansion coefficient at 25—200°C (4.5 x lO " /°C) (8), stresses build rapidly as the outer portions of the piece soHdify. If cooling is too rapid, internal cracks are formed that are not removed in subsequent processing steps. As a result, a cooling schedule is estabUshed for each product size and is carefully followed by ckculating water of various temperatures through the mold for specified time periods. When the outside of the piece has cooled sufficientiy, it is stripped from the mold and the cooling operation continued by dkect water spray for several hours. If cooling is stopped too soon, heat from the center of the piece warms the pitch binder to a plastic state, resulting in slumping and distortion. The cooled piece is usually stored indoors prior to baking in order to avoid extreme temperature changes that may result in temperature gradients and damage to the stmcture. Bulk density of the green billet is usually 1.65—1.70 g/cm.  [c.503]

In service, graphite electrodes operate at up to 2500 K and are subject to large thermal and mechanical stresses and extreme thermal shock. Graphite is unique in its abiUty to function in this extreme environment. The relatively low electrical resistance along the length of the electrode minimizes the power loss owing to resistance beating and helps keep the electrode temperature as low as possible. This characteristic is most important in ultrahigh power furnaces where the approximately 30% lower electrode resistivity of premium-grade electrodes is usually essential for successful operation. A high value of the thermal shock parameter is also important (Table 2) this parameter is improved by high strength and high thermal conductivity combined with low elastic modulus and low coefficient of thermal expansion. The ability of graphite electrodes to withstand thermal shock has been increased significantly in the past decade as a consequence of enhancement in the elastic modulus and coefficient of thermal expansion resulting from improved raw materials and advanced manufacturing technology.  [c.518]

Plasticity. Although even at elevated temperatures mechanical failure of ceramics is dominated by britde fracture, plastic deformation mechanisms often precede brittle fracture. Plastic deformation is also important because of the role it plays in net shape forming operations such as extmsion, which require extremely high strain rates ia a deformation regime known as superplasticity (37). At low and high temperatures plastic deformation of crystalline ceramics can occur by sHp, but it is not usually observed, except under special conditions, because the required stress levels are usually much higher than those required for brittle fracture. At elevated temperatures plastic deformation can also occur by grain boundary sliding and softening of secondary phases such as glass.  [c.322]

Osaka University and the University of Wales are coUaborating on a research project aimed at the recovery of electrical power from waste heat from commercial processes (20). This is a low (80°C) temperature low (- 60° C) AT process that makes use of very thin thermoelements and very large area heat exchange devices. The initial costs could be quite high, but the low temperature operation should result in extremely long life times to depreciate the costs effectively. Because this system is using only waste heat from another process, electrical power is gained without additional poUution of any sort. The efficiency of these systems is rather low compared to other devices operating over wider temperature ranges, but because it is piggybacking on other processes that take care of the economic investment, it is a promising approach to alleviating any energy cmnch in the future.  [c.509]

Temperature The operating temperature of a biofilter is primarily controlled by the inlet gas temperature. The recommended operating temperature range for high destruc tion efficiency is between 20° to 40° C, with an optimum temperature of 37° C (98° F). At lower temperatures, the bacteria growth will be limited, and at extremely low temperatures the bacteria coiild possibly be destroyed. At temperatures above the recommended range, the bacteria s activity is also impaired. Extremely high temperatures will destroy the bacteria within the filter bed.  [c.2192]

In the 1990s, significant efforts have gone into the development of transmission lines made from superconductors, which are materials that have essentially no resistance when operating at extremely low temperatures. Wliile a significant amount of energy is required to operate the cryogenic systems, the reduction 111 power loss and the increase in power transfer capability have made the technology appealing. Several prototype installations in various stages of design and preparation have provided encouraging prelimmai y results, but as of the end of the twentieth century, no full-scale applications have been deployed.  [c.437]

Lasers have been used to both modify and probe surfaces. When operated at low fluxes, lasers can excite electronic and vibrational states, which can lead to photochemical modification of surfaces. At higher fluxes, the laser can heat the surface to extremely high temperatures in a region localized at the very surface. A high-power laser beam produces a very non-equilibrium situation in the near-surface region, during which the effective electron temperature can be extremely high. Thus, lasers can also be used to initiate thenual desorption. Laser-induced thenual desorption (LITD) has some advantages over TPD as an analytical teclmique [36]. When a laser is used to heat the surface, the heat is localized in the surface region and tlie temperature rise is extremely fast. It is also possible to produce excitations that involve multiple photons  [c.311]

In low temperature fuel ceUs, ie, AEG, PAEC, PEEC, protons or hydroxyl ions are the principal charge carriers in the electrolyte, whereas in the high temperature fuel ceUs, ie, MCEC, SOEC, carbonate and oxide ions ate the charge carriers in the molten carbonate and soHd oxide electrolytes, respectively. Euel ceUs that use zitconia-based soHd oxide electrolytes must operate at about 1000°C because the transport rate of oxygen ions in the soHd oxide is adequate for practical appHcations only at such high temperatures. Another option is to use extremely thin soHd oxide electrolytes to minimize the ohmic losses.  [c.577]

Several studies have chosen to focus on the volatiHty of the alkyltin stabilizers and their by-products of PVC stabilization, alkyltin chlorides, during the calendering operation because this process presents a worst case scenerio for PVC processing relatively high stabilizer levels, very high exposed surface area of hot PVC melt, and high processing temperatures. In two of these studies conducted by the NATEC Institute in Germany, extremely low levels of volatilized alkyltin compounds were observed (30). Similar studies conducted by Morton International confirmed these results (31). AH of these studies demonstrate that the level of volatile tin compounds in the air during PVC processing operations are significandy below the TLV of 0.1 mg /m for tin compounds estabHshed for the United States workplace.  [c.549]

Polya.cryla.mid.es. Polyacrjiamide gels were designed to obtain the advantages of the performance of acrylamide-based gels while substantially avoiding exposure to acrylamide monomer (15,16). Low molecular weight polyacrylamides, which form low viscosity solutions in water, are cross-linked on demand to form insoluble gels (see Acrylamide polymers). An early product developed by Dow, but withdrawn in the mid-1980s, comprised a mixture of 20% polyacrylamide and 40% glyoxal (5,17). Cyanagel 2000 Chemical Grout (Cytec Industries) is an anionic polyacrylamide grout in which gel formation is based on complex formation between anionic (carboxylate) sites on the polymer and ferric ions, generated by oxidation of ferrous ions with a mixture of sodium chlorate and sodium bromate. Gel rates increase with increasing bromate chlorate ratio. As with acrylamide grouts, ethylene glycol can be added to protect against extremes of temperature and repeated wet—dry cycles. This system forms gels similar to those obtained with acrylamide grout and can thus be operated with equipment designed to handle the latter.  [c.228]

Asbestos-Based Organic Materials. The primary appHcations of asbestos-based organic frictional materials and thek requkements are (/) primary dmm brake linings providing high and stable friction at all temperatures and pressures (2) secondary and nonservo dmm brake linings providing stable friction and wear resistance (J) Class A disk pads providing friction levels of 0.35—0.45, nonabrasive wear properties, quiet operation, and rotor compatibihty (4) Class B disk pads providing higher (0.45—0.60) friction and high temperature wear resistance at the expense of some low temperature wear resistance, noise properties, and rotor compatibihty (5) Class C friction materials consisting of both disk pads and block-type friction materials for extremely heavy-duty operations providing high (>0.50) friction and minimal fade at the expense of other brake characteristics such as wear resistance, rotor compatibihty, and noise properties and (6) clutch friction materials providing stable friction, good wear properties, quiet operation, and rotor compatibihty combkied with high strength properties. Class A friction materials were more common on vehicles built ia North America Class Bs were common ia Europe and Asia.  [c.272]

Sinee the design of turbomaehinery is eomplex, and effieieney is direetly related to material performanee, material seleetion is of prime importanee. Gas and steam turbines exhibit similar problem areas, but these problem areas are of different magnitudes. Turbine eomponents must operate under a variety of stress, temperature, and eorrosion eonditions. Compressor blades operate at relatively low temperature but are highly stressed. The eombustor operates at a relatively high temperature and low-stress eonditions. The turbine blades operate under extreme eonditions of stress, temperature, and eorrosion. These eonditions are more extreme in gas turbine than in steam turbine applieations. As a result, the materials seleetion for individual eomponents is based on varying eriteria in both gas and steam turbines.  [c.411]

The processing of biological materials and employing biological agents such as cells, enzymes, or antibodies are the principal domain of biochemical engineering. Biochemical reactions involve both cellular and enzymatic processes and the principal differences between the biochemical and chemical reactions lie in the nature of the living systems. Small living creatures known as microorganisms interact in many ways with human activities. Microorganisms play a primary role in the capture of energy from the sun. Additionally, their biological activities also complete critical segments of the cycles of carbon, oxygen, nitrogen, and other elements necessary for life. The cell is the unit of life, and cells in multi-cellular organism function together with other specialized cells. Generally, all cells possess basic common features. Every cell contains cytoplasm, a colloidal system of large biochemicals in a complex solution of smaller organic molecules and inorganic salts. The use of cells or enzymes taken from cells is restricted to conditions at which they operate, although most plant and animal cells live at moderate temperatures but cannot tolerate extremes of pH. In contrast, many microorganisms operate under mild conditions, some perform at high temperatures, others at low temperatures and also pH values, which exceed neutrality. Some can tolerate concentrations of chemicals that can be highly toxic in other cells. Thus, successful operation depends on acquiring the correct organisms or enzymes while preventing the entry of foreign organisms, which could impair the process.  [c.830]

This transition cannot be directly explained. However, we may rationalize this transition if we consider the factors limiting the operation of Frank-Read sources for these two types of dislocations. At low temperatures the (110) sources are blocked due to the extremely high Peierls stress of edge dislocations, and the (111) sources start to operate if a sufficiently high stress level is reached. As temperature increases, the Peierls barrier can eventually be overcome with the help of thermal activations and the line tension limits the operation of corresponding sources. Our calculations of the line energies, including dislocation core energies, result in a lower line tension for the (110) than for the (111) dislocations [19]. Consequently, at sufficiently high temperatures the activation of (110) sources should overtake the (111) sources.  [c.353]

Turboprop types of aircraft proved more reliable and cheaper to operate than piston-engined airplanes for short hauls and more fuel-efficient than turbojets in such use. Overall airline patronage shot up dramatically after 1960. Since the 1980s, air express has boomed as well. Thus most aviation fuel used today is well-distilled kerosene, with a small portion of antifreeze for the extremely low ambient temperatures at high altitude. High-octane gasoline powers much of the general aviation sector of private aircraft, where piston engines are still the norm for planes of up to four or five passengers.  [c.1159]

Resin (Resinoid). The resinoid bond, originally called BakeHte, was named for its inventor, Leo Baekeland (see Phenolic resins). Baekeland s original patent was issued in 1909, but it was not until the 1920s that this type of bonding was perfected for use in abrasives. The resin consists basically of phenol and formaldehyde. It is thermosetting in nature, making it particularly suitable for tough grinding and cutting-off operations at high speeds. Resin bonds cure at temperatures of 150 to 200°C. Thus there are no problems with grain reactivity and fiberglass or metal reinforcements may be molded in to make a much safer product for high speed grinding. Additionally, this low processing temperature allows the use of inert fillers to strengthen the bonded product, or of "active" fillers to increase the efficiency of grinding. Active fillers include such materials as cryoHte, pyrites, potassium fluoroborate, sodium and potassium chloride, 2inc sulfide, antimony sulfide, and tin powder. Such materials, alone or in combination, aid grinding by acting as extreme pressure lubricants or as reactants for the metal being ground this prevents rewelding of the chips being removed. Lead and lead compound fillers are stiU used in Europe for some cut-off wheels (special marking required) but are not used in the United States for health reasons.  [c.14]

Molybdenum. Molybdenum is the most readily available and widely utili2ed refractory metal. Most engineering appHcations of this metal utili2e the high melting temperature, high strength and stiffness, resistance to corrosion in many environments, or high thermal and electrical conductivity. However, molybdenum must be coated if exposed to air above 535°C. The melting point of 2610°C, over 1000°C higher than for most high temperature superaHoys, permits molybdenum to be used in inert atmosphere furnace equipment. Furnace hardware and heat shields also perform well under extreme temperature conditions. The high thermal and electrical conductivity of molybdenum, as well as its inertness to molten glasses, permits it to be used for electrical heating or heat booster electrodes in commercial continuous glass making operations. Molybdenum also is used in a wide range of electronic and thermionic devices as well as crystal growing devices, x-ray tubes, magnetism and thyristors, and resistance weld electrodes. Other characteristics of molybdenum are its low thermal expansion, high stiffness, and the abiUty to take a high surface finish. Molybdenum is usehil for high temperature laser mirror components such as those to be used in fusion power systems (see Fusionenergy Lasers).  [c.127]

Goals in Hquid crystal synthesis include the design of room temperature thermotropics which are stable, colorless Hquid crystalline over a wide range of temperature, and operate at low voltage and power levels. The number of compounds of commercial importance is actually not very large representative ones are shown in Table 3 (26). Extended mesomorphic temperature ranges are obtained by using eutectic mixtures, since obtaining a wide room temperature Hquid crystal phase in a single compound is extremely difficult. Large positive dielectric anisotropy is achieved by attaching strongly dipolar terminal groups, although the effect is often reduced due to antiparallel association between pairs of molecules. Large negative dielectric anisotropy is much more difficult to obtain, due to difficulties in reducing the longitudinal dipole moment, the fact that the electric field points along all directions perpendicular to the long axis of the molecules, and strong dipole moments from lateral substituents frequently affect the stabiHty and viscosity adversely. The birefringence can be controUed by adjusting the number of aromatic rings and TT-bonded terminal or linking groups. As a rule, molecules with low polarity and polari2abiHty, with short terminal groups and no lateral substituents, have the lowest viscosity and are best suited for nematic displays.  [c.199]

The heavy-duty sigma blade batch mixer is used widely for the process of flushing in the preparation of pigment dispersions, primarily for offset inks. For some products, it is also used to disperse dry pigments in Hquid vehicles of a wide range of viscosity and in thermoplastic resins with relatively low melting points. The finished dispersion from the flusher can be discharged as a soHd or Hquid with a wide range of viscosities. The mixer offers a wide operating range of pressures, temperatures, and speeds of blades. This processing flexibiHty makes it an extremely versatile machine for processing a wide range of dispersions and explains its popularity for producing pigment dispersions for offset inks, despite its high installation and operating costs. The mixers are routinely available to 3774-L (1000-gal) capacity and can process up to 3200 kg of finished dispersion. The choice of constmction material ranges from carbon steel and chrome-plated carbon steel to various stainless steel alloys. Often the mixers are hydraulically driven to operate under constant torque and permit operation with variable speeds at different stages. Due to very specialized constmction, close tolerances, and large drive motors, the installations require high capital investments. The process is batch-type and can take several hours to complete. Considering the high capital and operating costs, alternative continuous processing systems have been explored to produce similar dispersions. There are, however, few successful commercial installations.  [c.512]

There are several important, specialized appHcations for siHcone PSA tapes. Platers tapes mask selected areas of parts during etching or plating operations. Masking tapes are also used as protective coatings against high temperatures, radiation, harsh chemical environments, or moisture. These tapes are used frequendy in the manufacture of printed circuit boards (409). Splicing tapes are used to join plastic films. SiHcone PSAs are often used to spHce low surface energy materials or to provide high cohesive strengths at temperature extremes. Plasma or flame spray tapes are used to protect selected metal surfaces during sandblasting or flame spraying operations. SiHcone PSAs are particulady usefH as the adhesive for electrical insulating tapes. A common appHcation is as a wire wrap in motor coils. SiHcone PSAs are also used in medical appHcations, notably as an adhesive for bandages and transdermal dmg dehvery systems (410).  [c.57]

A significant development occurred in the mid-1980s with the introduction of the heat recovery system (HRS) developed by Monsanto Enviro-Chem (127,128). In the HRS process, absorbing towers operate at temperatures as high as 220°C, recovering the sensible heat of the gas stream and the heat of reaction as steam with pressures up to 1140 kPa (150 psig). This achieves thermal efficiencies of 90—95% compared to about 55% for plants in the early 1970s. A number of HRS plants have been built or retrofitted, including at least two in excess of 3000 t/d. The HRS process uses conventional stainless alloys and was made possible by the discovery that above 99% acid, a number of alloys have very low corrosion rates at temperatures as high as 200°C. The HRS process requites extremely careful control of acid concentration. Catastrophic corrosion rates can result if tower concentrations are significantly outside of the prescribed range. This requites rapid and proper response to boiler or other leaks that can introduce water to the process.  [c.189]

The dominant process in modem methanol manufacture is the ICI low pressure process (58). Because of the potentially huge market for methanol as an automotive fuel, this technology is an extremely important appHcation for supported catalysts. The ICI process uses a catalyst typically formed as 5 mm X 5 mm cylinders containing copper, 2inc, and aluminum precipitated simultaneously as the oxides. The copper oxide must be reduced to copper metal prior to use, and in order to obtain a high copper surface area, reduction is carried out slowly using hydrogen diluted with an inert gas at temperatures <300°C. A copper content of about 60 wt % is optimum. To avoid the loss of copper surface area by processes similar to sintering during operation, the temperature limit for use of this type catalyst is about 270°C.  [c.199]


See pages that mention the term Extreme low temperature operations : [c.23]    [c.578]    [c.136]    [c.208]    [c.265]   
Standard Handbook of Petroleum and Natural Gas Engineering Volume 1 (1996) -- [ c.0 ]