Condensation tubes, outside

A modified Hahn condenser, a form of partial condenser, is illustrated in Fig. VI, 12, 1 it is best constructed of Pyrex glass. The dimensions given are only approximate and may be varied slightly. The inside clearance should be approximately 0-3 cm. a water jacket should be fitted over the central portion of the side arm by moans of rubber stoppers. Alternatively, the side arm may have a length of about 10 cm. and a condenser fitted to this in the usual manner. An approximately 1 cm. layer of absolute alcohol is placed in the inner condensing tube and the top of the tube is connected to a reflux condenser. The outside of the condenser below the side arm should be insulated with asbestos cloth or paper. The refluxing mixture boils the ethyl alcohol in the inner tube, most of the isopropyl alcohol is returned to the flask and the acetone distils over. 

Figure 8.6 Severe grooving by ammonia-containing condensate on an admiralty brass condenser tube. Condensate flowed down the tube sheet and collected at the tube end, cutting an annular groove. Note the perforation just outside the tube roll.

For single pure vapors Kem recommends the following, due to the splashing of condensed liquid (outside) from horizontal tubes as it drips/splashes to and off of the lower tubes in the bundle ... 

W = flowrate, Ib/hr, condensate Do = outside diameter of tubes, ft Nj = total number of tubes in bundle used for condensation... 

Figure 10-71. Condensing steam film coefficients for vertical surfaces or horizontal tubes. G 7n,/ restricted to < 1,090. For theoretical h , for horizontal tubes, use and multiply results by 0.8. G = condensate mass flow per unit tube outside circumference, vertical tubes, lb/(hr) (ft). (Used by permission Devore, A. Petroleum Refiner, V. 38, No. 6, 1959. Gulf Publishing Company, Houston, Texas. All rights reserved.)...

Go = condensate mass flow per unit tube outside circumference, vertical tubes, lb./(hr) (ft)... 

The small condensing surface required by a domestic appliance such as a deep-freeze may allow the use of the outside metal skin of the appliance itself as a surface condenser. In such a construction, the condenser tube is held in close mechanical contact with the skin, so that heat is conducted through to the outside air, where it is lost by natural convection. This system is restricted to a few hundred watts. 

Note that the propane vapor is still condensing to propane liquid at 120°F. The condensed liquid is in intimate contact with the propane vapor, as it drips off the outside surface of the colder condenser tubes. The saturated propane vapor condenses directly to saturated propane liquid at 120°F. The saturated, or bubble-point, liquid then drips from the condensation zone of the condenser into the subcooling zone of the condenser. This is the zone where the tubes are submerged in liquid. 

The tower overhead vapor, shown in Fig. 13.6, condenses to a liquid on the outside of the cold condenser tubes. The liquid drips off the tubes. These droplets of liquid are in close contact with the saturated vapor in the condenser shell. This means that the liquid is in equilibrium with the vapor. The condensed liquid is therefore, initially, at its bubble-point temperature. This liquid accumulates in the bottom of the condenser s shell. The submerged tubes then must subcool this liquid. Part of the surface area of the condenser is hence devoted to subcooling liquid, and part is devoted to condensing vapor. 

Condensation may be performed inside or outside tubes, in horizontal or vertical positions. In addition to the statements made in the previous section about the merits of tube side or shell side When freezing can occur, shell side is preferable because it is less likely to clog. When condensing mixtures whose lighter components are soluble in the condensate, tube side should be adopted since drainage is less complete and allows condensation (and dissolution) to occur at higher temperatures. Venting of noncondensables is more positive from tube side. 

Figure 1. Tube furnace laser vaporization apparatus used by Haufler et al. (1991) to produce high yields of C 0F. The 532 nm doubled Nd YAG pulse vaporizes C from the rotating graphite target into the inert carrier gas stream. The fullerenes condense just outside the oven on the tube wall.

When the action has started make sure the condensing tube end is in the collecting bottle along with an end of the tubing leading outside. Press modelling clay around the two tubes so no fumes escape into the kitchen. Now you are ready to distil the ammonia. 

A diagram of the apparatus is shown in Figure E4-2, p. 512. Although two ring stands are sufficient, three are recommended to reduce equipment breakage. The condenser tubing should be wired in place. Tape a spare fuse to the outside of the variable transformer and be sure that you do not add boiling chips to a hot solution. 

Carnavos [155] reported typical overall improvements that can be realized with a variety of commercially available enhanced horizontal condenser tubes. The heat flux for single 130-mm-long tubes, in most cases with outside diameters of 19 mm, is plotted in Fig. 11.22 against AT/m for 12 tubes qualitatively described in the accompanying table. The overall heat transfer performance gain of the enhanced tubes over the smooth tube is as high as 175 percent. Internal enhancement is a substantial contributor to the overall performance, since the more effective external enhancements produce a large decrease in the shell-side thermal resistance. 

Film-condensation coefficients outside horizontal cylinders. The analysis of Nusselt can also be extended to the practical case of condensation outside a horizontal tube. For a single tube the film starts out with zero thickness at the top of the tube and increases in thickness as it flows around to the bottom and then drips off. If there is a... 

The steam-side condensing coefficient outside the tubes can be estimated using Eqs. (4.8-20H4 8-26). The resistance due to scale formation usually cannot be predicted. Increasing the velocity of the liquid in the tubes greatly decreases the rate of scale formation. This is one important advantage of forced-circulation evaporators. The scale can be salts, such as calcium sulfate and sodium sulfate, which decrease in solubility with an increase in temperature and hence tend to deposit on the hot tubes. 

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