Vent flows

For additional information, see Simpson (Chem. Eng., 75(6), 192-214 [1968]). A critical Fronde number of 0.31 to ensure vented flow is widely cited. Recent results (Thorpe, 3d Jnt. Conf. Multi-phase Flow, The Hague, Netherlands, 18-20 May 1987, paper K2, and 4th Int. Conf. Multi-phase Flow, Nice, France, 19-21 June 1989, paper K4) show hysteresis, with different critical Fronde numbers for flooding and untlooding of drain pipes, and the influence of end effects. Wallis, Crowley, and Hagi (Trans. ASME J. Fluids Eng., 405 13 [June 1977]) examine the conditions for horizontal discharge pipes to run full. 

The treatment of vent flow calculations in most typical relief wstem configurations involves two classes of computation models flow in low-fric tion geometries such as nozzles and frictional flow in pipes and fittings. 

Vents are usually sized on the assumption that the vent flow is ... 

The method includes the mass unit vent flow capacity per unit area. G. This allows using any applicable vent capacity calculation method. The method incorporates the equilibrium rate model (ERM) for vent flow capacity when friction is negligible. Additionally, a coiTection factor is used for longer vent lines of constant diameter and with negligible static head change. ... 

A hand calculation method that can be used to take into account two-phase relief when the materials m the vessel are natural" surface active foamers. To account for disengagement, the vessel void fraction at disengagement should be evaluated (i.e.. the point at which the vent flow ceases to be two-phase and starts to be vapor only). ... 

To attain the total venting (outbreathing) requirements for a tank, refer to tlie appropriate flash point column and add the outbreathing plus the thermal venting flows. 

Once the linear gas velocity of the carrier gas has been set, the splitter vent flow should be adjusted between 15 and 100 ml/min. Use lower values to improve detection and higher values to improve GC resolution and decrease column overload. 

C. will Two Phase Venting Occur One of the key decisions in venting calculations is to determine whether two-phase vent flow will actually occur. 

The pressure difference promoting vertical vent flows are solely due to temperature stratification, and conform to a hydrostatic approximation. In other words, the momentum equation in the vertical direction is essentially, due to the low flows ... 

This horizontal vent flow is nearly one-tenth of that for the same size of vertical vent. Thus, a horizontal vent with such unstable flow, as in a basement or ship fire, is relatively inefficient in supplying air to the fire. 

Emmons, H. W., Vent flows, in The SFPE Handbook of Fire Protection Engineering, 2nd edn (eds P.J. DiNenno et al), Section 2, Chapter 5, National Fire Protection Association, Quincy, Massachusetts, 1995, pp. 2-40 to 2-49. 

By using open or vented cells, data are obtained to determine if the full-scale reactor vent flow will be single or two-phase, and if a tempered or nontempered reaction occurs [192]. A tempered reaction is one that can be controlled through the latent enthalpy of evaporation. 

Venting an emergency flow of vessel contents out of the vessel thus reducing the pressure and avoiding destruction of the unit from over-pressuring the vent flow can be single or multiphase, each of which results in different flow and pressure characteristics. 

Split vent. The sample vapors that do not enter the column are ejected through the split vent. A needle valve on this line regulates the total flow of carrier gas into and from the inlet, generating the split ratio, which determines the portion of sample that enters the column. The split ratio is the ratio of the split vent flow to the column flow and provides a measure of the amount of sample that actually enters the column from the injection. A split ratio of 100 1 indicates that a lpl injection from the syringe results in approximately 10 ml of liquid sample reaching the column. 

Figure 13.2 Photographs of a vent flow diverter for a 63.5 mm diameter extruder a) top view showing the surface that is exposed to the inside of the extruder, and b) oblique view. The recessed areas that allow for the expansion of the resin are shown by the arrows. The outside edge is flush with the inside barrel wall when installed in the extruder. The opening is positioned in the upstream region in the vent while the tapered recess is in the downstream region...

Figure 13.3 Schematic of a vent flow diverter in a two-stage vented extruder...

Vent Flow for a Two-Stage Screw Running a Low Bulk Density PS Feedstock... 

The new diverter was built according to the description presented in Section 13.1, and it was installed in the extruder. Immediately upon startup of the machine, resin flow from the vent did not occur. Thus, resin that expanded outside of the barrel cylinder at the entry of the vent opening was tucked back into the barrel cylinder. Based on the cost savings for the elimination of the vent flow and the installed cost of the diverter, the payback time was estimated at 18 days. 

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