Condensers material selection

When condensing explosive gases, the temperature of the bath and the effect on the reactant gas of the condensing material selected must be determined experimentally (see Chapter 6, section 6.D). Very small quantities should be used because detonations may occur. A taped and shielded Dewar flask should always be used when condensing reactants. Maximum quantity limits should be observed. A dry ice solvent bath is not recommended for reactive gases liquid nitrogen is recommended. (See also Chapter 3, section 3.D.3.I.)... 

As many emissions involve chlorinated compounds, corrosion is a major problem in many control methods. The corrosion of columns and surface condensers can be prevented or reduced by the correct material selection. However, corrosion remains a constant threat to the interior of incinerators. Additional pollution control equipment such as scrubbers may also be required to remove acidic compounds from treated gases before discharging into the atmosphere. 

H.A.Todhunter, Material Selection for Condenser Tubes, Corrosion, 11, 39 4 (1955). 

The size of the particles is determined by the particular material selected and the vapor concentration used. In practice, limited variation in particle size can be achieved for a particular aerosol material because conditions for stable aerosol formation require a particular set of thermal and vapor concentration conditions. The monodispersity of the aerosol can be improved by revaporization and recondensation. In systems in which the condensation occurs in a container with a high ratio of volume to surface areas, relatively monodisperse particles can be obtained (frg 1.1). Otherwise, the particle size varies with the proximity to the wall. In cylindrical or tubular systems, such as in the condensation aerosol generator developed by Liu et al. [10] or the falling-film generator, the particle size that is produced varies radially (see Ref. [3]). A more monodisperse aerosol can be produced by extracting the central portion of the flow, which is less subject to wall effects. Liu et al. [10] found that the monodispersity improved from a ug value of 1.35 to 1.15 by using only the central 5% of the aerosol flow. A commercial version of a modified Sinclair-LaMer generator is available with particle size control suited for inhalation studies [11]. 

Studies of aerosol size distributions in power plant plumes clearly show that gas-Co-panicle conversion is an important source of submicron aerosol. Condensable material is formed primarily by the oxidation of SOi to sulfates and NOj, to nitrates, both usually present as ammonium salts. It is somewhat easier to analyze plume aerosol dynamics than urban aerosol behavior because (in selected cases) the plume aerosol originates from a single source and is sufficiently well-defined to follow many kilometers downwind. By using ground-based mobile laboratories and/or suitably instrumented aircraft, the aerosol and associated gasc.s can be measured. 

Material selection is extremely important, not only because of system requirements (i.e., temperatures, pressures, etc.) but also because of material cost considerations. In an HVAC module, the heater core and evaporator core reside within the module, which usually comprises nylon 66 or a filled polypropylene. Refrigerant flows through the evaporator core and condenser and will vary in a range from 9 to 115°C. Engine coolant flows through the heater core and reaches temperatures up to 120°C. Valves and seals within the HVAC module must withstand temperature cycling combined with pressure extremes. 

Among the simple catalysts that have been proposed oxides of zinc,09 cadmium, lead, bismuth, silicon, aluminum, titanium may be mentioned.5,0 Alkaline materials as sodium or calcium carbonates have also been claimed. The zinc oxide catalyst is prepared by spraying a solution of zinc nitrate, alone or with nitrates of other metals, on pumice and then heating the product in air. In practice the phthalic anhydride is simply steam dis-stilled into the reaction chamber and the products separated by fractional condensation or selective solution. 

Source Outgassing Data for Selecting Spacecraft Materials, NASA Publication 1124. CVCM collected volatile condensable materials TML total mass loss WVR weight volatile residue. 

Normally, the analyses mentioned previously are performed on the residual materials. However, there is nothing to prevent measurements being made on the separated fractions or on condensate materials. In the case of samples containing water, be aware that the condensate will be enriched with water. An interesting approach to the controlled evaporation of materials is to use the combined techniques of thermogravimetric analysis and infrared. Although this technique is typically used for the determination of thermal decomposition products, it may also be used for controlled and reproducible selective removal of volatile components, with on-line monitoring of the volatile components. 

Tubular or box shapes should be used whenever possible to minimize edges and inside corners. If possible, the metallic materials selected should have the best resistance to corrosive attack or be alloyed to enhance coatings performance. A particular attention to design should be made to minimize the dwelling time of atmospheric condensation and provide special attention to surfaces shaded from the sun [5]. Large enclosed spaces that have not been totally sealed, such as the insides of box girders, should be coated, or ventilated, with fans if necessary. Decisions on coatings should not be left to the casual attention of inexperienced personnel. It is quite clear that... 

Selective condensation occurs when one or more of the components in the feed stream condenses in the pores of the membrane (Rao and Sircar, 1993b). Once the pores are filled, the condensed material diffuses across the membrane. The pore size required for selective condensation is generally larger than 30 A. Very high selectivity can be achieved if one of the components is noncondensible (Sakata and Yamamoto, 1986), but the separation is limited by the condensation partial pressure of the components, which is a function of pore size and shape. Therefore, this mechanism is difficult to control and is rarely used in carbon membranes. 

The efficiency of the Rankine cycle itself can be increased by higher motive steam pressures and superheat temperatures, and lower surface condenser pressures in addition to rotating equipment selection. These parameters are generally optimized on the basis of materials of constmction as well as equipment sizes. Typical high pressure steam system conditions are in excess of 10,350 kPa (1500 psi) and 510 °C. 

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