Operating temperature effects

Duthie X, Kentish S, Powell C, Nagai K, Qiao G, Stevens G. Operating temperature effects on the plasticization of polyimide gas separation membranes. J Membr Sci 2007 294(l-2) 40-9. 

Fig. 3. Comfort 2ones at 6% of population predicted dissatisfied from ref 4. RH lines are valid only when the air temperature equals the average temperature of the surfaces, (a) Operative temperature range where ET is effective temperature as defined in text, (b) Comfort 2one detail. To convert...

Steps such as the substitution of low sulfur fuels or nonvolatile solvents, change of taw materials, lowering of operation temperatures to reduce NO formation or vo1ati1i2ation of process material, and instaHion of weU-designed hoods (31—37) at emission points to effectively reduce the air quantity needed for pollutant capture are illustrations of the above principles. 

The fuels Hsted in Table 2 are generally representative of fuels to be encountered over the range of industrial furnaces and, depending on the type (cooled or refractory wall), exhibit operating temperatures considerably different from adiabatic values. The choice of fuel is dependent upon a number of factors including cost, availabiUty, cleanliness, emissions, reflabiUty, and operations. Small furnaces tend to bum cleaner, easier to use fuels. Large furnaces can more effectively use coal. 

When the operating temperature exceeds ca 93°C, the catalytic effects of metals become an important factor in promoting oil oxidation. Inhibitors that reduce this catalytic effect usually react with the surfaces of the metals to form protective coatings (see Metal surface treatments). Typical metal deactivators are the zinc dithiophosphates which also decompose hydroperoxides at temperatures above 93°C. Other metal deactivators include triazole and thiodiazole derivatives. Some copper salts intentionally put into lubricants counteract or reduce the catalytic effect of metals. 

Heat Sensitivity. The heat sensitivity or polymerization tendencies of the materials being distilled influence the economics of distillation. Many materials caimot be distilled at their atmospheric boiling points because of high thermal degradation, polymerization, or other unfavorable reaction effects that are functions of temperature. These systems are distilled under vacuum in order to lower operating temperatures. For such systems, the pressure drop per theoretical stage is frequently the controlling factor in contactor selection. An exceUent discussion of equipment requirements and characteristics of vacuum distillation may be found in Reference 90. 

Now refer to Figure 28.13(a) to obtain the skin effect ratio Ffac/ffdc- Consider the cross-sectional curves for EIE-M grade of flat busbars at an operating temperature of 85°C for a cross-sectional area of 6.45 cm and determine the Ffac/ dc ratio on the skin effect curve having... 

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