Film Breakdown and Bundle-Depth Effects in Horizontal-Tube, Falling-Film Evaporators

Experimental study on the onset of local dryout in an evaporating falling film on horizontal plain tubes

“…Such a behavior seems to be related to the careful manner in which the liquid from the distributor is supplied to the upper tube while in the lower tubes the liquid feed cannot be controlled and cumulative effects of flow non-uniformities and instabilities are present. This is also in agreement with Lorenz and Yung [19] according to which dryout results on single tubes do not apply correctly to tube bundles. Thus, based on the fact that falling film evaporators contain numerous horizontal rows and that the heat transfer performance of the top horizontal row are not representative of the bundle performance, experimental data obtained for the uppermost heated tube were not considered in the present study for the development of the model.…”

Falling-film evaporation on horizontal tubes—a critical review

“…In a triangular-pitch arrangement, the flow rate distribution tends to be less uniform than in a square-pitch arrangement and thus row-to-row variation is larger [26]. Plain surfaces in a triangular-pitch bundle exhibit a decrease of h from row to row [63,69]. This behavior is noted for low flow rates [63] and high heat fluxes [69].…”

“…6, in which the enhanced-condensation tubes give similar performances, bundles using Turbo-CII provided a performance up to 100% higher than those using GEWA-SC. This behavior can be related to the restriction of the longitudinal liquid movement on GEWA-SC by the fins, resulting in a large variation in the local flow rate that increases in the lower rows, and promotes the formation of dry patches [63,66]. For R-123, the Turbo-B tube provides a better performance than does the Turbo-CII [68].…”

“…Plain surfaces in a triangular-pitch bundle exhibit a decrease of h from row to row [63,69]. This behavior is noted for low flow rates [63] and high heat fluxes [69]. Finned tubes such as GEWA-SC can exhibit maldistribution effects, because the surface structure inhibits the longitudinal movement of liquid [64,67].…”

Development of Falling Film Heat Transfer Coefficient for Industrial Chemical Processes Evaporator Design

“…They observed three kinds of behaviour such as (1) heat transfer coefficient decreases to its minimum value and then increases again, (2) it increases with Reynolds number, and (3) heat transfer coefficient increases to its maximum value and then drops. Lorenz and Yung [22] investigated that film evaporation on a single tube is different to an array of tubes, and it may be due to turbulence of inter-tube evaporation. They also found that critical Reynolds number affects the evaporation heat transfer, and for below 300, the heat transfer coefficient value for a single tube is higher as compared to an array of tubes.…”