Drying cycle

Improved Hot—Wet Properties. Acryhc fibers tend to lose modulus under hot—wet conditions. Knits and woven fabrics tend to lose their bulk and shape in dyeing and, to a more limited extent, in washing and drying cycles as well as in high humidity weather. Moisture lowers the glass-transition temperature T of acrylonitrile copolymers and, therefore, crimp is lost when the yam is exposed to conditions requited for dyeing and laundering. 

For waterproofing, sodium silicate concentrations below 30% are adequate concentrations between 35 and 70% are used for strength improvement. Grouts having 35 vol % or higher silicate resist deterioration on freeze—thaw or wet—dry cycles. Water permeability of sands can be reduced from 10 to 10 cm/s. Unconfined compressive strengths of stabilized sand can vary from 103 to 4130 kPa (15—600 psi) the normal range is between 690 and 1380 kPa. 

In general, one mechanism predominates at any given time in a solid during drying, but it is not uncommon to find different mechanisms predominating at different times during the drying cycle. 

FIG. 12-102 Semiclosed spray-drying cycle with indirect heating. (NIRO Inc. )... 

Allow for clean application without the need for specialty dispensing equipment or special cure/drying cycles. 

One way to obtain enhanced heat and solvent resistance in SBR-based PSA is sulfur addition. It is difficult to obtain sufficient cure with sulfur during normal drying cycles (2-5 min at 150-180°C). Furthermore, cure via sulfur may continue after leaving the oven, thus degrading adhesion. When used in contact with copper, the sulfur may promote corrosion. The use of phenolic overcomes all of these problems despite the fact that its natural cure speed is also insufficient for the time frame available. This is overcome through addition of one of the accelerators... 

In practice, however, the heat exchanger effectiveness will not be unity for these dry cycles, but the above analysis does suggest that for practical plants ... 

However, the turbine work has been increased because of the extra water vapour flow through the turbine, while the compressor work is unchanged. Thus Eq. (6.17), which is still valid, with turbine work equal to the heat supplied, shows that the thermal efficiency increases compared with the dry cycle. It is important to realise that this efficiency is increased not because of a reduction in the heat rejected (Qa) but because of the increa.se in Wi- The heat rejected is still equal to the compressor work. 

Plots of efficiency against pressure ratio for the full injection EGT plant, for a maximum to minimum temperature 5, are shown in Fig. 6.9, compared with lower values of efficiency in the dry CBTX plant. There are. several points to be noted first that an increase in efficiency is worthwhile, up to 10% secondly that the total water injection is up to over 10% of the air mass flow and thirdly that the optimum pressure ratio increases to about 8, from about 5 for that of the dry cycle. 

Fig. 3.16 showed carpet plots of efficiency and specific work for several dry cycles, including the recuperative [CBTX] cycle, the intercooled [CICBTX] cycle, the reheated [CBTBTX] cycle and the intercooled reheated [CICBTBTX] cycle. These are replotted in Fig. 6.17. The ratio of maximum to minimum temperature is 5 1 (i.e. T nx 1500 K) the polytropic efficiencies are 0.90 (compressor), 0.88 (turbine) the recuperator effectiveness is 0.75. The fuel assumed was methane and real gas effects were included, but no allowance was made for turbine cooling.

The assumptions made by the various authors (viz. polytropic efficiencies, combustion pressure loss and temperature ratio, etc.) are all roughly similar to those used in the calculations of uncooled dry cycles. Some modest amounts of turbine cooling were allowed in certain cases [9] but the effect of these on the efficiency should not be large at max 250°C (see later for discussion of more detailed parametric calculations by some of these authors). 

Multiple desiccant beds are used in cyclic operation to dry the gas on a continuous basis. The number and arrangement of the desiccant beds may vary from two towers, adsorbing alternately, to many towers. Three separate functions or cycles must alternately be performed in each dehydrator. They are an adsorbing or gas drying cycle, a heating or regeneration cycle, and a cooling cycle. 

In the drying cycle, the wet inlet gas first passes through an inlet separator where free liquids, entrained mist, and solid particles are removed. This is a very important part of the system because free liquids can damage or destroy the desiccant bed and solids may plug it. If the adsorption... 

Most adsorbers operate on a fixed drying cycle time and, frequently, the cycle lime is set for the worst conditions. However, the adsorbent capacity is not a fixed value it declines with usage. For the first few months of operation, a new desiccant has a very high capacity for water removal. If a moisture analyzer is used on the effluent gas, a much longer initial drying cycle can be achieved. As the desiccant ages, the cycle time will be automatically shortened. This will save regeneration fuel costs and improve the desiccant life. 

Cjcncraily, as the gas velocity during the drying cycle decreases, the abiliiy of the desiccant to dehydrate the gas increases. At lower actual veiociilfs, drier effluent gases will be obtained. Consequently, it would seem desirable to operate at minimum velocities to fuUy use the desiccant. 

After passing through the aftercooler, the compressed air is usually too cool for deposits to form or catch fire but not always. On one plant an instrument air drier became contaminated with oil and caught fire during the drying cycle. 

The catalyst manufacturers control PSD of the fresh catalyst, mainly through the spray-drying cycle. In the spray dryer, the catalyst slurry must be effectively atomized to achieve proper distribution. As illustrated in Figure 3-10, the PSD does not have a normal distribution shape. The average particle size (APS) is not actually the average of the catalyst particles, but rather the median value. 

Recent interest in weathering steels has stimulated work on accelerated laboratory tests which can be used to investigate the effect of alloy composition on performance. It is well established that a wetting and drying cycle should be an integral part of any laboratory test in which the characteristic properties of weathering steels are revealed , and Bromley, Kilcullen and... 

Batch dryers are normally used for small-scale production and where the drying cycle is likely to be long. Continuous dryers require less labour, less floor space and produce a more uniform quality product. 

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