Minimum vapor velocity

Holes and Smaller With Water or High Surface Tension Liquids > om= Minimum Vapor Velocity Through Holes, ft./sec. 

The weep point is considered to be the minimum vapor velocity that will provide a stable tray operation, pre-... 

Assume a minimum vapor velocity through the holes. 

Assume a minimum vapor velocity through the holes. Calculate Vom (Pv) (minimum)... 

Sieve plate without downcomer, countercurrent vapor and liquid flow through the same openings. Liquid rains in dispersed droplets from tray to tray and sprays when landing on next tray. Minimum vapor velocity must be obeyed to keep a liquid layer on the tray as the heat and mass transfer area. 

Sieve plates with tray openings for the vapor flow and feed or drain appliances. Minimum vapor velocity must be obeyed such that liquid does not rain through the trays. As in the case of sieve slit trays, additional slits can be stamped into the surface of the sieve plate, through which some of the vapor is reflected in the direction of the liquid flow. This is advantageous with large liquid loadings. 

Cross-flow tray with half stamped out slots. The flap opening acts as a nozzle. The vapor jet forms parallel to the tray and forces the liquid to flow across the tray to the downcomer. To avoid draining of the tray a minimum vapor velocity is required. 

This reaction is carried out in tall fluidized beds of high L/dt ratio. Pressures up to 200 kPa are used at temperatures around 300°C. The copper catalyst is deposited onto the surface of the silicon metal particles. The product is a vapor-phase material and the particulate silicon is gradually consumed. As the particle diameter decreases the minimum fluidization velocity decreases also. While the linear velocity decreases, the mass velocity of the fluid increases with conversion. Therefore, the leftover small particles with the copper catalyst and some debris leave the reactor at the top exit. 

N,n = Minimum theoretical stages at total reflux Q = Heat transferred, Btu/hr U - Overall heat transfer coefficient, Btu/hrfP"F u = Vapor velocity, ft/sec U d = Velocity under downcomer, ft/sec VD(js = Downcomer design velocity, GPM/fL Vioad = Column vapor load factor W = Condensate rate, Ibs/hr Xhk = Mol fraction of heavy key component Xlk = Mol fraction of the light key component a, = Relative volatility of component i versus the heavy key component... 

Many of the above factors that affect column operation are due to vapor flow conditions being either excessive or too low. Vapor flow velocity is dependent on column diameter. Weeping determines the minimum vapor flow required while flooding determines the maximum vapor flow allowed, hence column capacity. Thus, if the column diameter is not sized properly, the column will not perform well. Not only will operational problems occur, the desired separation duties may not be achieved. 

Vapor-liquid separators (drums) are used to separate a liquid from a vapor-liquid stream with a minimum of liquid carryover. The separator size is determined by the vapor velocity which depends on the entrainment method used. The working equation is ... 

Turndown ratio is the ratio of the maximum allowable vapor rale at or near flooding conditions (rates) to the minimum vapor rate when weeping or liquid leakage becomes significant it may be termed the minimum allowable vapor velocity [193, 199, 200]. 

Minimum design vapor velocity through the holes may be used as calculated, or if additional safety is required increase the value by 20%. 

These trays will dump liquid excessively through the perforations giving exceeding low efficiencies [47] unless a minimum vapor rate is maintained for a given liquid capacity. The smaller the holes the lower the dump point (vapor velocity). 

Calculate minimum allowable superficial vapor velocity (flooding) for equal vapor and liquid loads, for the X-100 and S-100 packings. 

It is desired to operate the hood of Problem 3-29 so that the vapor concentration in the hood plenum is below the lower explosion limit of 12.5% by volume. Estimate the minimum control velocity required to achieve this objective. The amount of TCE evaporated within the hood is 5.3 lb per hour. The molecular weight of TCE is 131.4. The temperature is 70°F and the pressure is 1 atm. 

In an expediently designed plant, one can expect to reach in the pressure range above 8 10-2 mbar a vapor velocity in the cross-section Fk of between 50 and 80 m/s (l/d = 2.5 to 5) However 90 m/s will be reached only, if the design uses special features, e. g. a funnellike connection between the chamber wall and the location of the valve, slow changes in the outline, and smooth surfaces without sharp edges or holes. It is also recommendable, to clarify the maximal amount of vapor transportable at several pressures in a plant specification, e. g. at pch = 1 mbar a minimum of 3 kg/h and at pch = 0.04 mbar a minimum of 25 g/ h flow of water vapor must be demonstrated during the acceptance test, while the condenser temperature is below -30 °C, respectively below -57 °C. Such measurements can be earned out practically with sufficient accuracy (see e. g. Fig. 2.19 and the related text). 

Eq. (19) depicts the deceleration of a droplet in the vapor stream. It decelerates to the velocity of the carrier. L y. provided that L w is no less than the minimum transport velocity of the droplet, which is generally the case. At L — the droplet will be carried along by the vapor stream at the constant velocity. The deceleration length. 1, during the period from 0=0 to 0=0rt can be calculated by ... 

Commonly their orientation is horizontal. When a small amount of a second liquid phase (for example, water in an immiscible organic) is present, it is collected in and drawn off a pot at the bottom of the drum. The diameter of the pot is sized on a linear velocity of 0.5ft/sec, is a minimum of 16 in dia in drums of 4-8ftdia, and 24 in. in larger sizes. The minimum vapor space above the high level is 20% of the drum diameter or 10 in (Sigales, 1975). 

Schmidt (102) observed that flooding and minimum wetting are caused by two different mechanisms. A low-liquid-rate column may therefore flood even when it operates below the MWR. This is most likely to occur in vacuum systems (where liquid rates are low and vapor velocities are high) and in high-surface-tension, low-viscosity systems. 

The limiting diameter occurs at the bottom of the tower therefore, the minimum diameter based on the maximum allowable vapor velocity is 3.6 ft obtained with the use of Fig. 16-6. 

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