Passageways

The refractory used to constmct the hearth can be in the form of bricks, preformed shapes, or monolithic. Often a furnace design utilizes all three. Openings or passageways through the walls are fashioned in the same manner as windows in a brick building. 

Capillary Flow Moisture which is held in the interstices of solids, as liquid on the surface, or as free moisture in cell cavities, moves by gravity and capiUarity, provided that passageways for continuous flow are present. In diying, liquid flow resulting from capiUarity appUes to liquids not held in solution and to aU moisture above the fiber-saturation point, as in textiles, paper, and leather, and to all moisture above the equiUbrium moisture content at atmospheric saturations, as in fine powders and granular solids, such as paint pigments, minerals, clays, soU, and sand. 

Waste disposal Prevention of combustible waste accumulation in corners, passageways or other convenient storage areas... 

Pores of the activated carbon exist throughout the particle in a manner illustrated in Figure 2. The pore structure of activated carbon affects the large surface-to-size ratio. The macropores do not add appreciably to the surface area of the carbon but provide a passageway to the particle interior and the micropores. The micropores are developed primarily during carbon activation and result in the large surface areas for adsorption to occur. 

A type of miniature globe valve, needle valves are used in instrument systems for throttling of small volumes. They have metal to metal seats, but due to the small size, can be used for positive shut-off (Figure 15-8). Needle valves have small passageways that may plug easily and limit their use to very small flow rates. 

Whether a flame is transmitted through a flame arrester depends on the length and aperture size of the arrester, the approach velocity of the flame, the pressure rise, and the temperature of the arrester (Wilson and Flessner 1978). Wilson and Flessner state that the evidence indicates that low-speed flames can be quenched by an array of small passageways placed in a duct, provided that the effective passageway diameter (critical diameter) meets the following criterion ... 

For high-speed flames, which are usually accompanied hy a pressure rise, an array of apertures must have sufficient pressure drop to decelerate the flame, and sufficient length to achieve the heat loss needed to quench the flame. Thus, the diameter criterion is not sufficient and the effective length of the passageway must meet the following criterion (Wilson and Attalah 1975) ... 

For a flame to be quenched the flame arrester passageways must be small enough to extract heat from the flame faster than it can be generated by chemical reactions. The surface to volume ratio of flame arresters is impor-... 

Table 5-2 shows the equations for calculating the hydraulic diameter for various flame arrester passageways. 

Low-speed flames will only be quenched if die passageway diameter is below a certain critical value. This critical diameter can be calculated by the following equation (Mendoza et al. 1996) ... 

A typical Worthington BDC plate valve in closed position. All passageways, lift clearances, springs and plates have been dynamically designed and individually selected for maximum flow efficiencies. The individual spring plate valve offers both efficiency and reliability advantages over valves that have flexing strips or plates. 

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