Sieve holes vapor

The major factors that determine the amount of entrainment are plate spacing, depth of liquid on the tray, and vapor velocity in the space between the plates. Slot or sieve-hole vapor velocity and liquid flow rate have some effect on the entrainment, but they are not of major importance. 

Fig. 4.3 Liquid velocity profiles obtained by using different modes, operation condition Z = 38 mm, Fs = 1.464 m/s (kg/m ) -, L = 6.94 x 10 m /s a based on superficial vapor velocity mode and b based on sieve hole vapor velocity [17]...

Vapor bubbles up through the sieve holes, or valve caps, on the tray deck, where the vapor comes into intimate contact with the liquid. More precisely, the fluid on the tray is a froth or foam—that is, a mix-... 

When vapor flows through a tray deck, the vapor velocity increases as the vapor flows through the small openings provided by the valve caps, or sieve holes. The energy to increase the vapor velocity comes from the pressure of the flowing vapor. A common example of this is the pressure drop we measure across an orifice plate. If we have a pipeline velocity of 2 ft/s and an orifice plate hole velocity of 40 ft/s, then the energy needed to accelerate the vapor as it flows through the orifice plate comes from the pressure drop of the vapor itself. 

Figure 2.2 shows a simple sieve tray, with a single hole. Why is it that the liquid flows over the 3-in outlet weir, rather than simply draining down through the sieve hole It is the force of the vapor (or better, the velocity of the vapor), passing through the sieve hole, which prevents... 

Vg = velocity of vapor or gas flowing through the sieve hole, ft/s... 

Vc = linear velocity of gas in riser, reversal area, or annulus of bubble cap (maximum value) or in sieve hole, ft/s = maximum allowable superficial linear velocity of gas (based on net cross-sectional area of tower for vapor flow), ft/s, see Eq. (3)... 

The mass-transfer devices may be sieves (holes), fixed valves, moveable valves, or bubble caps. Fig. 2 shows a selection of mass-transfer devices. The purpose of the device is intimate mixing of the vapor and liquid on the tray deck. An ideal device has high capacity, high flexibility, low leakage, low pressure drop, and low cost. 

As the art becomes more of a science, designers become more confident and innovative. Thus we are now seeing applications involving mixed-mode equipment, that is, trays that have valves plus sieve holes, and columns that have alternate sections of grids and packing, or mesh and trays. These mixed-mode devices are particularly useful in the not-uncommon situation where liquid and vapor loads vary appreciably over the length of the apparatus. 

Many towers equipped with valve or sieve trays do not operate efficiently at low feed rates. This is due to tray-deck leakage. As the pressure drop of the vapor flowing through the sieve holes falls below the weight of the liquid on the tray deck (as determined by the height of the weir), the tray will start to leak. 

Liquid passes down a slot and spills onto a sieve plate. Vapor bubbles through holes in the sieve plate and creates a froth, which increases the amount of liquid-vapor interface. The amount of frothing can be increased by adding bubble caps to the sieve holes, shown in Figure 5.27. Bubble caps also decrease leakage of preequilibrated... 

Vapor bubbles up through the sieve holes, or valve caps, on the tray deck, where the vapor comes into intimate contact with the liquid. More precisely, the fluid on the tray is a froth or foam—that is, a mixture of vapor and liquid. In this sense, the function of a tray is to mix the vapor and liquid together to form a foam. This foam should separate back into a vapor and a liquid in the downcomer. If the foam caiuiot drain quickly from a downcomer onto the tray below, then the foamy liquid or froth will back up onto the tray above. This is caWed flooding. 

When vapor flows through a tray deck, the vapor velocity increases as the vapor flows through the small openings provided by the valve cajjs, or sieve holes. The energy to increase the vapor velocity comes... 

Sieve trays are simple flat plates with a large number of small holes. Vapor flows up through the holes, preventing the liquid from falling through. Liquid... 

As the vapor velocity leaving the sieve holes is much higher than the superficial and sometimes even forming jet flow, such influential effect cannot be ignored, especially under the condition of high F factor. Referring to Fig. 4.2, the three-dimensional vapor velocities leaving the sieve hole can be expressed as follows [11] ... 

Fig. 4.25 Formation of vapor bubbles from sieve holes in different zones...

Experimental work shows that the main form of vapor in this layer is jetting. The diameter of the vapor jet dj, which is related to the liquid height /jl and the diameter of sieve hole was correlated by Hai [25] ... 

The vapor fraction py in this layer for sieve hole smaller than 2 mm can be estimated by equation below... 

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