Tube bundles condensation

Example 4.2 In a tube bundle condenser, like that sketched in Fig. 4.11, 7 103kg/h saturated vapour of refrigerant R22, at a pressure of 1.93 MPa is to be condensed. Cooling water is available at a temperature of 18 °C, and this can be heated by 10K. Copper tubes of length 1.5 m, 16 mm outer diameter and 1 mm wall thickness are to be used in the construction of the condenser. 

Example 4.3 In a tube bundle condenser made up of 200 vertical tubes each with 25 mm inner diameter, Mq = 8 kg/s of saturated toluene vapour at a pressure of 0.1 MPa is to be condensed. The tubes will be cooled from outside by Mw = 60 kg/s of water flowing countercurrent, fed into the condenser at a temperature of 45 °C. The overall heat transfer coefficient of the cooling water up to the tube wall is k m = 2500 W/m2K. Calculate the required tube length. 

Several studies considered commercial deep spirally fluted tubes for horizontal singletube and tube-bundle condensers [152-154]. Commercially available configurations bear some resemblance to the Gregorig profile shown in Fig. 11.21. The derived condensing coefficients (envelope basis) range from essentially no improvement to over 300 percent above the plain-tube values. 

Improved and redesigned rotors of modem compressors save considerable power. The ethylene fractionator and the propylene refrigeration condensers can be replaced with extended surface tube bundles instead of conventional tube bundles. 

Impingement Baffle The tube bundle is customarily protected against impingement by the incoming fluid at the shell inlet nozzle wmen the shell-side fluid is at a high velocity, is condensing, or is a two-phase fluid. Minimum entrance area about the nozzle is generally equal to the inlet nozzle area. Exit nozzles also require adequate area between the tubes and the nozzles. A full bundle without any provision for shell inlet nozzle area can increase the velocity of the inlet fluid by as much as 300 percent with a consequent loss in pressure. 

Depropanizer overhead condenser, top row of tubes, middle of tube bundle... 

A routine inspection of the tube bundle during a plant outage revealed fine cracks of the type shown in Fig. 9.11. Scattered longitudinal cracks were observed along the lengths of most tubes. The external surface was covered with a thin film of black copper oxide and deposits. The bundle had been exposed to ammonia levels that produced 14 ppm of ammonia in the accumulated condensate. 

Specimen Location Surface condenser tube, main condenser bundle... 

If I ever have to design an amine plant I will know, for example, that the temperature of the lean amine solution entering the absorber should be about 10°F higher than the inlet gas temperature to prevent hydrocarbon condensation and subsequent foaming, that the reboiler tube bundle should be placed on a slide about six inches above the bottom of the shell to provide good circulation, that about two percent of the total circulating flow should pass through the carbon towers, and many other necessary requirements. 

Air cooled heat exchangers are used to transfer heat from a process fluid to ambient air. The process fluid is contained within heat eonducting tubes. Atmospherie air, whieh serves as the eoolant, is caused to flow perpendicularly across the tubes in order to remove heat. In a typical air cooled heat exchanger, the ambient air is either forced or induced by a fan or fans to flow vertically across a horizontal section of tubes. For condensing applications, the bundle may be sloped or vertical. Similarly, for relatively small air cooled heat exchangers, the air flow may be horizontal across vertical tube bundles. 

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. 

Just inside the shell of the tube bundle is a cylindrical baffle F that extends nearly to the top of the heating element. The steam rises between this baffle and the wall of the healing element and then flows downward around the tubes. This displaces non-condensed gases to the bottom, where they are removed at G. Condensate is removed from the bottom of the heating element at H. This evaporator is especially suited for foamy liquids, for viscous liquids, and for those liquids which tend to deposit scale or crystals on the heating surfaces. Vessel J is a salt separator. 

Rohsenow and Hartnetti present Nusselt s relation for the heat transfer average for horizontal tubes in a bundle condensing vertically from tube to tube, top to bottom tube ... 

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,. 

For purposes of standardisation, 19 mm outer diameter tubes of 1.65 mm wall thickness will be used, and these may be 2.5, 3-6, or 5 m in length. The film coefficient for condensing pentane on the outside of a horizontal tube bundle may be taken as 1.1 kW/m2 K, The condensation is effected by pumping water through the tubes, the initial water temperature being 288 K. 

Some sub-cooling of the condensate will usually be required to control the net positive suction head at the condensate pump (see Chapter 5, and Volume 1, Chapter 8), or to cool a product for storage. Where the amount of sub-cooling is large, it is more efficient to sub-cool in a separate exchanger. A small amount of sub-cooling can be obtained in a condenser by controlling the liquid level so that some part of the tube bundle is immersed in the condensate. 

Bench-scale tests were conducted to determine design parameters and operability of Che distillation process for the pilot plant. The column, reboller, and condenser used in the bench-scale system were constructed of fiberglass-reinforced ethylene-chlorotrifluoroethylene. The heat exchangers were spaghetti tube bundles constructed of fluorinated ethylene-propylene copolymer. 

Translate the heat-transfer area determined above into corresponding tube bundle dimensions. If different from those assumed in step (2), repeat steps (2) through (8) until satisfactory agreement is reached. The s-IVm method cannot be appHed to cases in which U varies along the tube length or the stream temperature profile is not smooth, ie, boiling or condensation is included. 

Once the steam pressure in the channel head of Fig. 8.4 falls to the pressure in the condensate collection header, the steam trap can no longer pass condensate. Water will back up in the channel head, and water-log the lower tubes in the tube bundle. This will lead to unstable steam flow control. This is especially true if the steam supply pressure is less than 20 psig higher than the maximum condensate collection header pressure. 

---