Process cycles, references

Mass Transfer and Useful Capacity. The term useful capacity, also referred to earlier as breakthrough capacity, differs from the equihbrium capacity shown on Figures 9a and 9b. The useful capacity is a measure of the total moisture taken up by a packed bed of adsorbent at the point where moisture begins to appear in the effluent. Thus the drying process cycle must be stopped before the adsorbent is fully saturated. The portion of the bed that is not saturated to an equihbrium level is called the mass-transfer 2one. 

Cog enera.tion in a. Steam System. The value of energy in a process stream can always be estimated from the theoretical work potential, ie, the deterrnination of how much power can be obtained by miming an ideal cycle between the actual temperature and the rejection temperature. However, in a steam system a more tangible approach is possible, because steam at high pressure can be let down through a turbine for power. The shaft work developed by the turbine is sometimes referred to as by-product power, and the process is referred to as cogeneration. 

In most cases models describing biogeochemical cycles are used to estimate the concentration (or total mass) in the various reservoirs based on information about source and sink processes, as in the examples given in Section 4.4. This is often called forward modeling. If direct measurements of the concentration are available, they can be compared to the model estimates. This process is referred to as model testing. If there are significant differences between observations and model simulations, improvements in the model are necessary. A natural step is then to reconsider the specification of the sources and/or the sinks and perform additional simulations. 

We can explain the injection molding process with reference to the molding cycle illustrated in Fig. 13.2. The cycle consists of four stages injection, packing, cooling, and ejection. 

Life cycle" refers to all phases of a chemical manufacturing process-from conceptualization, process research and development (R D), engineering design, construction, commissioning, commercial operation, and major modification to decommissioning. 

The standard process cycle for polymer matrix composites is a two-step cure cycle, as seen in Figure 8.1. In such cycles the temperature of the material is increased from room temperature to the first dwell temperature and this temperature is held constant for the first dwell period ( 1 hour). Afterward, the temperature is increased again to the second dwell temperature and held constant for the second dwell period (2-8 hours). After the second dwell, the part is cooled down to room temperature at a constant rate. Because there are two dwell periods, this type of cure cycle is referred to as a two-step cure cycle. The purpose of the first dwell is to allow gases (e.g., entrapped air, water vapor, or volatiles) to escape and to allow the matrix to flow, which leads to compaction of the part. Thus, the viscosity of the matrix must be low during the first dwell. Typical viscosity versus temperature profiles of polymer matrices show that as the temperature is increased, the viscosity of the polymer decreases until a minimum viscosity is reached. As the temperature is increased further, the polymer begins to cure rapidly and the viscosity increases dramatically. The first dwell temperature must be chosen judiciously so that the viscosity of the resin is low while the cure is kept to a minimum. 

The intrinsic life cycle begins when a female mosquito takes a blood meal. At this time, sporozoites that have matured in the mosquito s salivary glands are inoculated into the blood stream. These sporozoites migrate to the liver where they infect hepato-cytes and progress from early trophozoites to mature schizonts. This process is referred to as the exoerythrocytic cycle. Schizonts in the liver contain thousands of merozoites that are able to infect... 

Nitrogen is returned to its atmospheric form by the action of denitrifying bacteria such as Pseudomonas thiobacillus and Micrococcus denitriflcans. The process is referred to as denitrification and represents the major mechanism of nitrogen loss in the overall nitrogen cycle whereby various forms of nitrogen in the soil revert to the N2 form. The reactions and their energetics are given below ... 

Alternatively, in skeletal muscle, pyruvate can be transaminated to alanine (which affords a route for nitrogen transport from muscle to liver) in the liver alanine is used to regenerate pyruvate, which can then be diverted into gluconeogenesis. This process is referred to as the glucose-alanine cycle. 

Both seawater and freshwater move through Earth s atmosphere, its surface, and below its surface in a process known as the water cycle. You may also see the water cycle referred to as the hydrologic cycle. In this cycle, water continually moves through the environment by the processes of evaporation, condensation, and precipitation. The Sun provides the energy for these processes. Follow Figure 26-10 as you read about the water cycle. 

The amount of work used in a practical oxygen separation process is much greater than this minimum because of irreversibility. Figure 1 illustrates the process flow for one type of oxygen production cycle. The process quantities refer to separation of... 

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