Tube bundles, tubes vaporizers

Shklover and Gerasimov [215] used an interesting baffling technique to create a spiraling motion in the vapor condensing outside a tube bundle. With vapor velocities approaching... 

Kettle-type reboilers, evaporators, etc., are often U-tube exchangers with enlarged shell sec tions for vapor-liquid separation. The U-tube bundle replaces the floating-heat bundle of Fig. 11-36. ... 

The kettle reboiler is shown in Fig. ll-3.5ishell-side, this common design provides adequate dome space for separation of vapor and hquid above the tube bundle and surge capacity beyond the weir near the shell cover. 

Most vapors condense inside tubes eooled by a falling curtain of water. The water is eooled by air circulated through the tube bundle. The bundles ean be mounted directly in a cooling tower or submerged in water. 

Any part of the reboiler tube bundle that may be exposed to the vapor phase... 

Ketde horizontal reboilers consist of either a U-bundle or a shell and tube bundle inserted into an enlarged shell. The enlarged shell provides disengaging space for the vapor outside and above the liquid, which is usually held by level control at the top level of the tube bundle or possibly a few in. below the top of the tubes. The heating medium is inside the tubes. 

In tube bundles, if the disengaging space between the bundle and the kettle is small and insufficient to allow the vapor bubbles to break-free of the liquid and thus tend to blanket the upper tubes with gas, heat transfer will be restricted. For best design the superficial vapor velocity should be in the range of 0.6-1.0 ft/sec to prevent the bubbles from blanketing the tube through the bundle and thereby preventing liquid contact with the tubes. When the maximum heat flux is approached, this condition can occur, so the 1.0 ft/sec vapor velocity is recommended. 

The vapor composition at the top of the condenser (Y,i) is different from that at the bottom (Y, ). The condenser may be compared to a fractional distillation problem in reverse. Butane, having a higher boiling point, will condense out faster than the propane, although both are condensing at the same time. Thus, the vapor and liquid mol fractions from the top to the bottom of the condenser tube bundle are always changing. Proceed as follows The vapor at the top has the same composition as the gas leaving the evaporator. Therefore, Y,. = Y,. 

It should be noted that the shell diameter will be around 40% greater than that of the tube bundle to allow for vapor disengagement. 

For the CHF condition for two-phase crossflow on the shell side of horizontal tube bundles, few investigations have been conducted. Katto et al. (1987) reported CHF data on a uniformly heated cylinder in a crossflow of saturated liquid over a wide range of vapor-to-liquid density ratios. Recently, Dykas and Jensen (1992) and Leroux and Jensen (1992) obtained the CHF condition on individual tubes in a 5 X 27 bundle with known mass flux and quality. At qualities greater than zero, they found that the CHF data are a complex function of mass flux, local quality, pressure level, and bundle geometry. 

On being pumped to the next stage, the liquid flashes through the nozzle and the mixture travels down the tube bundle as it did in the first stage. Vapor from the first-effect separator provides the heat for evaporation in the second stage. 

Figures 6.11 and 6.12 show the input screen and the output answers for the tube section pressure loss. Please note that the pressure loss for only one tube is analyzed, since all 920 tubes are assumed to have equal flow and vaporization. Thus, the pressure profile made for one tube will be the same for the full tube bundle.

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