Pressure drop Condensing vapors

This is satisfactory, although a 2-in. nozzle would have a velocity of 34.3 ft/sec. Because this condenser has entering vapors at the dew point, entrainment of some particles is always a real possibility therefore, a low inlet velocity is preferred. Also, overhead vapor lines should have low pressure drop for vapor at its dew point and a 3-in. line might he indicated when this line is checked. 

The frictional pressure drop for vapors condensing inside tubes can be predicted as below ... 

The pressure drop together with the vapor flow settles virtually instantaneously. The pressure drop consists of the diy and wet pressure drop. Tlie vapor flow depends on the energy balance. Roughly, the leaving vapor flow equals the arriving vapor flow minus condensation due to heat losses. 

The pressure drop through conventional coil-in-box condensers in which complete condensation occurs (but no cooling of liquid) is one-third to one-half of the pressure drop Uiat would occur if no condensation took place The pressure drop of vapors through straight pipe (vapor lines, pipe coils, etc.) can be estimated from Fig. 13-6 and Eqs. (13-9) and (13-10), Chap. 13. 

Fig. 3. Solvent-processing equipment using partial condenser. Level a on the water overflow line to the receiver should be about 3 cm below level b on the solvent-return line. Dimension b—c must be great enough to overcome pressure drop in the vapor piping, condenser, solvent piping, and rotameter. In a 4 m (1000-gaI) ketde, dimension b—c would be at least 1.25 m. The volume of the piping described by the dimension c—d—e should contain twice the volume of dimension b—c, thus providing an adequate Hquid seal against normal ketde operating pressures.

For condensing vapor in vertical downflow, in which the hquid flows as a thin annular film, the frictional contribution to the pressure drop may be estimated based on the gas flow alone, using the friction factor plotted in Fig. 6-31, where Re is the Reynolds number for the gas flowing alone (Bergelin, et al., Proc. Heat Transfer Fluid Mech. Inst., ASME, June 22-24, 1949, pp. 19-28). 

Baffles in a horizontal in-shell condenser are oriented with the cuts vertical to facilitate drainage and eliminate the possibility of flooding in the upward cross-flow sections. Pressure drop on the vapor side can be estimated by the data and method of Diehl and Unruh [Pet. Refiner, 36(10), 147 (1957) 37(10), 124 (1958)]. 

Pressure drop on the condensing side may be estimated by judicious application of the methods suggested for pure-component condensation, taking into account the generally nonlinear decrease of vapor-gas flow rate with heat removah... 

Sudden vapor condensation in the pool may cause water hammer if the holes are too big and the pressure drop is too low Sonic hole velocity is desirable to avoid this problem. 

Condensation reduces the volume of the vapor present and can be assumed to occur at a constant pressure drop. 

An innovation is a direct-contact condenser mounted on the vapor body. A short piece of vertical pipe connects the vapor body with the condenser to minimize piping and pressure drop. This design also eliminates structural steel for support of a separate condenser. For cooling tower applications, the hotwell is elevated to permit gravity flow of water from the hotwell to the top of the cooling tower, thus eliminating the need for a pump. 

Because flashing steam-condensate lines represent two-phase flow, with the quantity of liquid phase depending on die system conditions, these can be designed following the previously described two-phase flow methods. An alternate by Ruskin [28] uses the concept but assumes a single homogeneous phase of fine liquid droplets dispersed in the flashed vapor. Pressure drop was calculated by the Darcy equation ... 

A distillation column is operating at 27.5 inches mercury vacuum, referenced to a 30-inch barometer. This is the pressure at the inlet to the ejector. Due to pressure drop through a vapor condenser and trays of a distillation column, the column bottoms pressure is 23 inches vacu-... 

It is essential to realistically establish the condensing conditions of the distillation overhead vapors, and any limitations on bottoms temperature at an estimated pressure drop through the system. Preliminary calculations for the number of trays or amoimt of packing must be performed to develop a fairly reasonable system pressure drop. With this accomplished, the top and bottom column conditions can be established, and more detailed calculations performed. For trays this can be 0.1 psi/actu-al tray to be installed [149] whether atmospheric or above, and use 0.05 psi/tray equivalent for low vacuum (not low absolute pressure). 

Water vapor leaving cooler condenser at 104°F and an assumed 31 psia, allowing 3 psi for pressure drop through unit. 

Pressure drops from Dowtherm A heat transfer media flowing in pipes may be calculated from Figure 10-137. The effective lengths of fittings, etc., are shown in Chapter 2 of Volume 1. The vapor flow can be determined from the latent heat data and the condensate flow. With a liquid system, the liquid flow can be determined using the specific heat data. 

From Figure 26.7 it can be seen that for equal duties and flows the temperature difference for countercurrent flow is lower at the steam inlet than at the outlet, with most of the steam condensation taking place in the lower half of the plate. The reverse holds tme for co-current flow. In this case, most of the steam condenses in the top half of the plate, the mean vapor velocity is lower and a reduction in pressure drop of between 10-40 per cent occurs. This difference in pressure drop becomes lower for duties where the final approach temperature between the steam and process fluid becomes larger. 

Sometimes insufficient differential across the regenerated catalyst slide valve is not due to inadequate pressure buildup upstream of the valve, but rather due to an increase in pressure downstream of the slide valve. Possible causes of this increased backpressure are an excessive pressure drop in the Y or J-bend section, riser, reactor cyclones, reactor overhead vapor line, main fractionator, and/or the main fractionator overhead condensing/cooling system. 

The pressure drop across the reactor cyclones, reactor vapor line, main fractionator, and main column overhead condensing/cooling system can be too high. The pressure drop is primarily a function of vapor velocity. Any plugging can increase the pressure drop. 

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