Mass flow, minimum

There are two mechanisms by which arching can occur particle interlocking and cohesive strength. The minimum outlet size required to prevent mechanical interlocking of particles is directly related to the size of the particles. The diameter of a circular outlet must be at least six to eight times the particle size, and the width of a slotted outlet must be at least three to four times the particle size. These ratios normally only govern the outlet size of mass flow hoppers if the particles are at least 0.6 cm or larger. 

An alternative to traditional mass flow bin design is to use a patented BINSERT, which consists of a hopper-within-a-hopper below which is a single-hopper section (Fig. 15). The velocity pattern in such a unit is controded by the position of the bottom hopper. A completely uniform velocity profile can be achieved which results in an absolute minimum level of segregation. Alternatively, by changing the geometry at the bottom of the hopper, a velocity profile can be developed in which the center section moves faster than the outside, thus providing in-bin blending of the materials (7). 

Fig. 7. Phase or state diagram for horizontal conveying where represents a particular mass flow rate, line AB corresponds to the pressure drop for air alone flowing in the system, Gq = 0, and ( is the minimum pressure line where saturation occurs. Other points ate explained in text.

An expander performanee map of shaft power versus mass flow with lines of eonstant inlet temperature and pressure shall be provided. There shall be a minimum of four eonstant pressure lines with inerements of approximately 5 psi and a minimum of four eonstant temperature lines with inerements of approximately 100°F. The map shall be valid for rated speed with normal exhaust pressure and gas eomposition. The normal operating point shall be indieated on the map. 

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. 

If = dimensionless friction factor for shellside cross-flow = mass flow, lb/ (hr) (ft of cross section at minimum free area in cross-flow)... 

The minimum detectable level is commonly given in terms of the mass flow rate in grams per second. 

If the heat capacities of streams are such that it is not possible to make a match at the pinch without violating the minimum temperature difference condition, then the heat capacity can be altered by splitting a stream. Dividing the stream will reduce the mass flow-rates in each leg and hence the heat capacities. This is illustrated in Example 3.16. 

A plant handling substantial quantities of flammable toluene is located 1000 ft from a residential area. There is some concern that a sizable leak of flammable vapors will form a flammable cloud with subsequent ignition in the residential area. Determine the minimum mass flow rate of toluene leakage required to produce a vapor cloud in the residential area with a concentration equal to the LFL. Assume a 5 mph wind and D atmospheric stability. 

The outlet size required to overcome no-flow conditions depends highly on the flow pattern that develops. If mass flow develops, the minimum outlet diameter. Be, to overcome arching is (4) ... 

If funnel flow develops instead of mass flow, the minimum outlet diameter is given by the tendency for a stable rathole to occur, because this diameter is usually larger than that required to overcome arching. In this case, the minimum outlet diameter is... 

The heat pipe achieves its high performance through the process of vapor state heat transfer. A volatile liquid employed as the heat-transfer medium absorbs its latent heat of vaporization in the evaporator (input) area. The vapor thus formed moves to the heat output area, where condensation takes place. Energy is stored in the vapor at the input and released at the condenser. The liquid is selected to have a substantial vapor pressure, generally greater than 2.7 kPa (20 mm Hg), at the minimum desired operating temperature. The highest possible latent heat of vaporization is desirable to achieve maximum heat transfer and temperature uniformity with minimum vapor mass flow. 

At specified mass flow rate and inlet conditions Py and V), Eq. (6.68) predicts a relation between the area ratio A2IAX and the pressure ratio P-JPy when isentropic flow prevails. It turns out that, as the pressure falls, the cross section at first narrows, reaches a minimum at which the velocity becomes sonic then the cross section increases and the velocity becomes supersonic. In a duct of constant cross section, the velocity remains sonic at and below a critical pressure ratio given by... 

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