Horizontal tubes, condensation

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. 

In horizontal condensers (outside tubes), for N tubes in a vertical row, with the condensate flowing uniformly from one tube to the one below without extensive splashing, the mean condensing coefficient, h j, for the entire row of N tubes (per Knudsen in reference 94A) is related to a film coefficient for the top, h, single tube by ... 

Unless specified, all water is untreated, brackish, bay or sea. Notes H = horizontal, fixed or floating tube sheet, U = U—tube horizontal bundle, K = kettle type, V = vertical, R = reboiler, T=thermosiphon, v = variable, HC = hydrocarbon, C) = cooling range At, (Co) = condensing range At. 

On a single horizontal tube r = condensation rate per unit length of tube... 

Heat-transfer coefficient in condensation Mean condensation heat-transfer coefficient for a single tube Heat-transfer coefficient for condensation on a horizontal tube bundle Mean condensation heat-transfer coefficient for a tube in a row of tubes Heat-transfer coefficient for condensation on a vertical tube Condensation coefficient from Boko-Kruzhilin correlation Condensation heat transfer coefficient for stratified flow in tubes Local condensing film coefficient, partial condenser Convective boiling-heat transfer coefficient... 

These data must be carefully interpreted to obtain overall heat-transfer coefficients for condenser tube bundles, e.g., horizontal condensers. Based on for a single tube, the condensing heat-transfer coefficient for a bundle, can be found from Eq. 3.4.6-22 of Ref. [2] ... 

A horizontal condenser uses a 4 X 4 array of tubes that have an outer diameter of 5.0 env and length 2.0 ru. Saturated steam at 101.3 kPa condenses on tlie outside tube surface held at a temperature of 80°C. Calculate itie steady rate of steam condensation in kg/h. 

Shown in Fig. PlO-95 is the tube layout for a horizontal condenser that is used for liquefying 900 kg/h of saturated ammonia vapor at 37"C. There are 14 copper tubes, each with inner diameter L>i = 3.0 cm and outer diameter f), = 3.8 cm. A coolant flows through the tubes at an average temperature of 20°C such that it yields a heat transfer coefficient of 4.0 kW/m K. For this condenser, estimate (a) the average value of the overall heat transfer coefficient and (b) the tube length. 

On perfectly horizontal tubes a condensed film will increase its thickness towards the bottom of the tube (Fig. 15.2). Some of the condensed liquid will fall onto lower tubes, increasing the liquid load, and decreasing the heat transfer coefficient on those tubes. Even a slight inclination of the tube is sufficient to cause the condensate to drain in the direction of the slope. A horizontal shell and tube condenser is likely to be baffled so as to force the vapor to flow horizontally across the tubes. Other flow arrangements are, however, possible. 

For shell-and-tube condensation related topics include evaporation (Section 16.11.4.1) and distillation (Section 16.11.4.2). Prefer condensation outside horizontal tubes use vertical tubes when condensing immiscible liquids to subcool the condensate. Assume pressure drop of 0.5 of the pressure drop calculated for the vapor at the inlet conditions. Baffle spacing is 0.2 to 1 times the shell diameter with the baffle window about 25%. Limit pressure drop for steam to 7 kPa on the shell side. U = 0.5 to 0.85 kW/m °C. 

Perfluoro(5-propyl-l,3,4-dioxazol-2-onc) (14.36 g. 56.3 mmol) was added over a period of 15 min to a 100-mL flask packed with stainless steel sponge (flash arrestor) and connected to a horizontal stainless steel tube heated to 285 -312 C. During the addition, the tube and flask were evacuated to 30 Torr. and the pyrolysate that passed through the tube was condensed in successive traps cooled with dry icc/acctone and liquid N2. The flask containing the stainless steel Sponge was heated periodically to ensure complete volatilization of the dioxazolone. The liquid N, cooled trap contained solid C02. The dry ice cooled trap contained a liquid, which was distilled to give the product yield 12.45g (93%) colorless liquid bp 25.5 26 C. 

The elemental sulfur that is formed in the primary reactor system is condensed in a horizontal shell-and-tube steaming condenser (17). This represents over 40% of the total recovered sulfur. The process gas stream then enters the first stage (18) of a two-stage Claus reactor system where the following exothermic reaction occurs ... 

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