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Condensation phenomena occur in many industrial applications. In this section the focus is on the determination of the condensation heat transfer coefficient and the overall energy balance is left to the reader. There are two idealized models of condensation (i.e., filmwise and dropwise). The former occurs on a cooled surface which is easily wetted. The vapor condenses in drops which grow by further condensation and coalesce to form a film over the surface, if the surface-fluid combination is wettable; if the surface is non-wetting rivulets of liquid flow away and new drops then begin to form. This review and discussion will mainly deal with filmwise condensation. The phenomena of dropwise condensation results in local heat transfer coefficients which are often an order of magnitude greater than those for filmwise condensation. Even though condensation phenomena can be classified into these categories of dropwise and film condensation the initial period of condensation would evolve into a film and probably would not affect the overall pressure-temperature response unless drop condensation is promoted (Slaughterbeck, 1970). Rates of heat transfer for film condensation can be predicted as a function of bulk and surface temperatures, total bulk pressure, surface and liquid film characteristics, bulk velocity and the presence of noncondensible gases. Even though film condensation has been investigated extensively, the majority of these studies were devoted to laminar film condensation (laminar bulk flow and laminar film). Since the vapor flow in heat exchange equipment may be turbulent, models and recent data are also reviewed for the condensation flux with a turbulent mixture flow. A simple engineering correlation or model is preferred many times for use in engineering design studies and with existing computer system analyses (Schmitt, et al., 1970; Tagami, 1965).

Previous theoretical and experimental investigations are reviewed, in particular, the effects of the presence of noncondensable gases and of the vapor velocity. These effects along with the effects of geometry and scale are of major interest at this time. Because the flow regime for the condensation heat transfer is well defined (stratified flow), the reader will find a much greater propensity for detailed mathematical analyses for simple geometries. Condensation on a vertical or horizontal flat plate, which can be extended to any arbitrary geometry, is the main focus of this discussion, because of its generality. The detailed review for film condensation outside a tube can be found in the work of Lee (1982). The usual modification is to replace the length scale, L, by tube diameter, D, with a slight change in the proportionality constant. Table 1 is provided as a summary of the work on condensation at the present time.

9.1. Basic Processes of Condensation
9.2. Theoretical Developments of Condensation
9.3. Experimental Investigations
9.4. Separate Effects and Large Scale Tests
9.5. Observations
next up previous contents
Next: Basic Processes of Condensation Up: CONDENSATION Previous: Observations

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Last Modified: Wed Sep 3 10:36:15 CDT 1997