Steam condensing heat transfer

Z-Z Wang and Z-N Zhao, Analysis of Performance of Steam Condensation Heat Transfer and Pressure Drop in Plate Condensers, Heat Transfer Eng., 14, pp. 32-41,1993. 

Steam feed rate appeared to have only slight effect on heat transfer coefficients. Improvement in steam condensation heat transfer due to vibration was, in general, a function of the product of frequency and amplitude. 

For steam side noncondensibles, a proper vent is required. A small amount of noncondensibles can greatly lower the steam side heat transfer coefficient. The improper removal of condensate is another way to reduce... 

Heat transfer. Reactor heat removal preheater, reboiler, and condenser heat transfer areas temperature levels of steam and cooling water... 

In a retort which uses condensing steam the heat transfer coefficient to the can is of the order of 5000-10 000 and therefore the... 

Saturated steam at 100 lb/in2 abs is to be used to heat carbon dioxide in a cross-flow heat exchanger consisting of four hundred 1-in-OD brass tubes in a square in-line array. The distance between tube centers is j in, in both the normal- and parallel-flow directions. The carbon dioxide flows across the tube bank, while the steam is condensed on the inside of the tubes. A flow rate of I lb ,/s of CO at 15 lb/in2 abs and 70°F is to be heated to 200°F. Estimate the length of the tubes to accomplish this heating. Assume that the steam-side heat-transfer coefficient is 1000 Btu/h ft2 °F, and neglect the thermal resistance of the tube wall. 

It can be seen from Fig. 7.17 that the condensing heat-transfer coefficient for a fluid with a Prandtl number of approximately 2 (for instance, steam) is not strongly dependent on flow rate or Reynolds number. For this reason, heat-transfer coefficients for steam condensing on vertical tubes are frequently not calculated, but are assigned a value of 1500 to 2000Btu/(h)(ft2)(°F) [8500 to 11,340 W/(m2)(K)]. 

Most condensers used in steam power plants operate at pressures well below the atmospheric pressure (usually under 0.1 atm) to maximize cycle thermal efficiency, and operation at such low pressures raises the possibility of air (a noncondensable gas) leaking into the condensers. Experimental studies show that the presence of noncondensable gases in the vapor has a detrimental effect on condensation heat transfer. Even small amounts of a noncondensable gas in the vapor cause significant drops in heat transfer coefficient during condensation. Eor example, the presence of less than 1 percent (by mass) of air in steam can reduce the condensation heat transfer coefficient by more than half. Therefore, it is common practice to periodically vent out the noncondensable gases that accumulate in the condensers to ensure proper operation. 

You have probably noticed that water vapor that condenses on a canned drink slides down, clearing the surface for further condensation. Therefore, condensation in this case can be considered to be dropwisc. Determine the condensation heat transfer coefficient on a cold canned drink at 2°C that is placed in a large container filled with saturated steam at 95°C. 

Steam condenses at 50 C on the onter surface of a horizontal lube with an outer diameter of 6 cm. The outer surface of the tube is maintained at 30°C. The condensation heat transfer coefficient is... 

As we have already explained in section 4.1.1., if the condensate does not completely wet the wall, individual liquid droplets form instead of a continuous condensate him. Heat transfer coefficients in dropwise condensation are significantly larger than in film condensation. In the condensation of steam, the heat transfer coefficients measured have been a factor of four to eight times larger. However, it has been shown that all investigated substances, in particular water, which condense on commonly used heating surfaces, will completely wet the surface. This is true as long as the material of the heated surface and the liquid have not been contaminated. This also corresponds to the experience that the formation of a water film is taken to be an indication that laboratory equipment is well cleaned. 

J. Palen, B. Cham, and J. Taborek, Comparison of Condensation of Steam on Plain and Turbotec Spirally Grooved Tubes in a Baffled Shell-and-Tube Condenser, Heat Transfer Research, Inc., Rep. 2439-300-6, HTRI, Pasadena, CA, January 1971. 

FIGURE 14.2 The influence of surface material and operating pressure on the dropwise condensation heat transfer coefficient of steam. (Adapted from Ref 1 and printed with permission from Academic Press, Inc., Orlando, FL.)... 

C. Zhang and Y. Zhang, Sensitivity Analysis of Heat Transfer Coefficient Correlations on the Predictions of Steam Surface Condensers, Heat Transfer Eng., 15, pp. 54-63,1994. 

Remove air and the non-condensable gases since these are poor conductors of heat and can reduce the heat transfer coefficients in the system. They can interfere with contact of steam with heat transfer surface. 

A shell and tube exchanger (one shell pass, two tube passes) condenses steam (0.14 bar). The 130 brass tubes (inner and outer diameters of 0.0134 and 0.0159 m) have a length of 2 m. Coolant (water) enters the tubes at 20°C with an average velocity of 11.25 m/sec. Condensation heat transfer coefficient is 13,500 W/m °K. What are the water outlet temperature, the condensation steam rate and the overall heat transfer coefficient ... 

If, for example, the condenser cooling-water valve opens wider than the steam valve, and if its loading signal is less than 4.2 psig, the summer or balance controller calls for a slightly higher column pressure to increase condenser heat transfer. 

Steam. The steam system serves as the integrating energy system in most chemical process plants. Steam holds this unique position because it is an exceUent heat-transfer medium over a wide range of temperatures. Water gives high heat-transfer coefficients whether in Hquid phase, boiling, or in condensation. In addition, water is safe, nonpolluting, and if proper water treatment is maintained, noncorrosive to carbon steel. 

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