Computational and Experimental Analysis of Supersonic Air Ejector: Tubrulence Modeling and Assessemnt of 3D Effects

Refrigerant falling film evaporation review: Description, fluid dynamics and heat transfer

In tune with the falling film evaporation heat transfer test results described in Part 1, flow visualization of the boiling process and intertube flow mode transitions from droplet to column and sheet flows have been observed, and the onset of dryout results were obtained. A new empirical approach to describe falling film evaporation with a dominance of nucleate boiling that takes into account the onset of dryout has been proposed and is applicable to plain and enhanced tubes. The method predicts most of the current local measurements for R-134a to within ±20% for conditions without dryout (the desired design condition) and has also been extended to cover conditions with partial dryout. Furthermore, a criterion for predicting the onset of dryout as a function of heat flux has also been proposed for the four types of tubes.

Falling Films on Arrays of Horizontal Tubes with R-134a, Part II: Flow Visualization, Onset of Dryout, and Heat Transfer Predictions

Recent literature suggests that the droplets that form in horizontal-tube, falling-film absorbers play a major role in the absorption process. The performance of such absorbers is critical to the performance of many absorption heat pump systems. The simulation of droplets of aqueous Lithium Bromide pendant from horizontal tubes was performed by numerically solving the equations of motion on a fixed three-dimensional (3D) grid. The so-called volume of fluid method was used to handle the interface between the liquid and vapor phase. Results are compared with simplified axisymmetric models and with high speed video taken during flow visualization experiments

Simulation of pendant droplets and falling films in horizontal tube absorbers

Experimental study of falling film evaporation heat transfer on superhydrophilic horizontal-tubes at low spray density

Intertube flow modes for falling film condensers and evaporators with plain and enhanced horizontal tube bundles are thought to have a key influence on their tube row effects Three principal types of flow modes are typically observed—droplet mode, column mode, and sheet mode—together with intermediate modes—coexistence of droplet-column modes and of column-sheet modes All act as falling jets from the upper tube onto the tube directly below In a previous study by Roques, Dupont, and Thome [1], the transitions between these intertube flow modes were observed and measured for rows of plain tubes, Thermoexcel–C enhanced condensing tubes, Turbo-Bii enhanced boiling tubes, and 26 fpi (1024 fpm) low-finned tubes for water, glycol, and a 50/50 water-glycol mixture Significant differences were observed in the transition thresholds for these tube surface geometries In the present study, this investigation has been extended to 19 fpi and 40 fpi (748 and 1575 fpm) low-finned Wieland tubes A comparison between p

Jean-Francois Roques

Papers

Falling film transitions between droplet, column, and sheet flow modes on a vertical array of horizontal 19 fpi and 40 fpi low-finned tubes