Burden and Spacing

The blast hole pattern used at any particular site will be the result of a certain amount of trial and error. Konya and Walter (1990) suggest using Equation (4.3)  

SG = specific gravity (g/cm3) of the explosives SGtf = specific gravity (g/cm3) of the rock De = diameter of the explosive charge, in. 

However, the Atlas Powder Co. suggests the following empirical relationship see Equation (4.4)  

The value for the ratio of burden to hole diameter, for average rock using an explosive such as ammonium nitrate-fuel oil (ANFO), has been suggested as 25 (Hustrulid, 1999). The spacing of the blast holes will be related to burden by an empirical ratio. The Atlas Powder Co. has suggested that the spacing should be between 1.0 and 1.8 times the burden. 

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With respect to contributions of other mobile sources to the atmospheric burden of trace metals, very few data are available. The National Aeronautics and Space Administration in 1974 published calculated annual average ambient concentrations at or near airports of 49 trace elements attributable to aircraft most values were less than numbers. Of interest, however, are the estimates for the environmentally important metals, titanium, vanadium, and cadmium these were given as 24 ng/m , 0.12 ng/m and < 14 ng/m , respectively (56). EflForts to characterize aircraft emissions and to develop emissions factors by means of dynamometer tests are under way. One such experiment is being performed at Pratt and Whitney under contract to the Environmental Protection Agency results from this study should be available in mid-1978 (57). 

Burden to spacing ratio from 0.8 to 1.2 is appropriate for wall-control blasting. Weak planes act as free faces and its position determine amount of back break. 

Limits for several parameters such as mass and volume were still being developed in parallel vwth other reactor and space ship design efforts. Although precise values were not defined, failure to address the limits indicated would result in a design which would overly burden the rest of the vehicle and could even make design of a viable spaceship untenable. 

Radiative Heat Transfer Heat-transfer equipment using the radiative mechanism for divided solids is constructed as a table which is stationary, as with trays, or moving, as with a belt, and/or agitated, as with a vibrated pan, to distribute and expose the burden in a plane parallel to (but not in contacl with) the plane of the radiant-heat sources. Presence of air is not necessary (see Sec. 12 for vacuum-shelf dryers and Sec. 22 for resubhmation). In fact, if air in the intervening space has a high humidity or CO9 content, it acts as an energy absorber, thereby depressing the performance. 

The burden must have a definite sohdification temperature to assure proper pickup from the feed pan. This limitation can be overcome by side feeding through an auxiliary rotating spreader roll. Apphcation hmits are further extended by special feed devices for burdens having oxidation-sensitive and/or supercoohng characteristics. The standard double-drum model turns downward, with adjustable roll spacing to control sheet thickness. The newer twin-drum model (Fig. ll-55b) turns upward and, though subject to variable cake thickness, handles viscous and indefinite solidification-temperature-point burden materials well. 

Disposable The opposite of a cleanable filter, which after collecting a certain dust burden is thrown away. Dry cell panel A dry filter mounted in a rigid frame. In the past these were manufactured from woven fabrics and felts however, synthetic fibers are replacing these. They have fiber diameters of 20 pm with average spacing of 300 pm and allow air velocity in the 2 m s-1 range. 

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