Condensate inundation

During shell-side condensation in tube bundles, neighboring tubes disturb the vapor flow field and create condensate that flows from one tube to another under the action of gravity and/or vapor shear stress forces. The effects of local vapor velocity and condensate inundation must, therefore, be properly accounted for when calculating the average heat transfer in the bundle. Marto and Nunn [53], Marto [54], and Fujii [55] provide details of these phenomena. 

Effect of Condensate Inundation. In a condenser with quiescent vapor, there is no vapor shear, and condensate flows by gravity onto lower tubes in a bundle. This extra condensate falling on the lower tubes increases the average condensate film thickness around these tubes, and the condensation heat transfer coefficient therefore decreases as one goes further down the bundle. 

Combined Effects of Vapor Shear and Inundation. In tube bundles, a strong interaction occurs between vapor shear and condensate inundation, and data for these combined effects are limited [54]. The simplest way of handling both phenomena is to separate them and calculate the local heat transfer coefficient for the Mh row as ... 

Tube Bundles. The average heat transfer coefficient in a bundle of finned tubes is influenced by both vapor shear and condensate inundation, although the effects are not as large as for smooth tubes [88,102-107]. At low vapor velocities, Webb and Murawski [107] express the local coefficient for the Mh row in terms of the local film Reynolds number ... 

C. M. Chu and J. M. McNaught, Condensation on Bundles of Plain and Low-Finned Thbes— Effects of Vapor Shear and Condensate Inundation, Proc. 3rd UK Heat Transfer Conf, IChemE Symp. Series 129,1, pp. 225-232,1992. 

Film condensation in tube bundles (more commonly used in shell-and-tube heat exchangers) characterize more complex physical conditions compared to condensation on a single tube. The gravity-controlled and surface-shear-stress-influenced condensate films must be modeled in different ways to accommodate combined influences of condensate drain to lower tubes (i.e., condensate inundation) and shear effects. Such a correlation, the fourth correlation from the top of Table 17.24, was proposed by Kern and modified by Butterworth [81]. 

By distillation she returns to the earth the moisture of which vegetation, or heat, have deprived it. Sublimation is made by the elevation of vapours in the air, where they are condensed into clouds. The second is made by rain and dew. Fair weather succeeds rain, and rain fair weather, alternately a continual rain would inundate everything perpetual fair weather would wither all. Rain falls drop by drop, because if poured down too abundantly it would destroy all, as a gardener who would water his grains by bucket full. Thus Nature distributes her benefits with weight, measure and proportion. 

Armbruster and Mitrovic [62] observed that liquid falls from tube to tube in three patterns discrete droplets, jets or columns, and sheets, depending on the flow rate (i.e., film Reynolds number) and fluid properties. In addition, depending on the tube arrangement and spacing, the condensate may cause ripples, waves, and turbulence to occur in the film splashing may occur, as well as nonuniform rivulet runoff of condensate because of tube inclination or local vapor velocity effects. As a result, it is impossible to arrive at an analytical expression to describe these complex bundle phenomena. In general, the effect of inundation may be accounted for using... 

One way of preventing inundation of condensate on lower tubes is to incline the tube bundle with respect to the horizontal. As the inclination angle increases, a critical value is reached where the condensate no longer drips off the tube but instead clings to the tube and flows to its base. Shklover and Buevich [66] conducted an experimental investigation of steam condensation in an inclined bundle of tubes and recommend an inclination angle of 5°. 

D. W. Nobbs and Y. R. Mayhew, Effect of Downward Vapor Velocity and Inundation on Condensation Rates on Horizontal Tube Banks, Steam Turbine Condensers, National Engineering Laboratory Report No. 619, East Kilbride, Glasgow, pp. 39-52,1976. 

The location of electrical circuits and electrically operated equipment in a room should be such that they are unlikely to become wet and they should not be in an area susceptible to condensation or where a user might be in contact with moisture. As unlikely as it may appear, instances have been observed where equipment has been located and electrical circuits have been installed where water from deluge showers would inundate them. For some equipment, such as refrigerators, freezers, dehumidifiers, and air conditioning units, moisture is likely to be present due to condensation, and these equipment items must be well grounded. 

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