Vapor Shear Effects on Falling-Film Mode Transitions Between Horizontal Tubes
نویسندگان
چکیده
A liquid falling between horizontal tubes can take the form of droplets, jets, or a continuous sheet mode, depending on the flow rate. The so-called falling-film flow regime is important to heat and mass transfer, and to maintaining wetted-surface conditions in a falling-film tube bundle, and the performance of such tube bundles is important in many air-conditioning systems. In this paper, we review prior work on falling film mode transitions between horizontal tubes and investigate vapor shear effects on the mode transitions. It is shown that vapor shear effects on mode transitions depend on liquid properties. Mode transition hysteresis is reduced by an increasing gas flow velocity. It is also found that the liquid feeding length can have an impact on falling-film mode transitions.
منابع مشابه
A Thermodynamic Basis for Predicting Falling-Film Mode Transitions
Horizontal-tube, falling-film heat exchangers are used in many air-conditioning and refrigeration systems. Depending on the geometry, flow rate and fluid properties, when a liquid film falls over a series of horizontal tubes several distinct flow patterns can be manifested: the droplet mode, the jet mode, and the sheet mode. A thermodynamic analysis is undertaken to predict the transitions betw...
متن کاملFlow Patterns and Mode Transitions for Falling-Film on Flat Tubes
The transitional Reynolds numbers for different patterns are available and a proposed transitional map is also provided in this paper. The transition of falling-films on flat tubes is studied in this work. Water and ethylene glycol are used as working fluids, for falling-film experiments conducted under adiabatic conditions, without an imposed vapor flow. The flow patterns are recorded using a ...
متن کاملDominant Flow Mechanisms in Falling-Film and Droplet Mode Evaporation Over Horizontal Rectangular Tube Banks
Flow visualization with high-speed video of evaporating water films falling over flat horizontal tubes, representative of the external surfaces of microchannel tubes, is presented. Experiments were conducted with 1.4 mm thick and 27 mm tall tubes over a film Reynolds number range of 23 < Re < 126. In addition to a qualitative description of the flow mechanisms, this work quantifies key droplet ...
متن کاملTurbulent Film Condensation on a Horizontal Elliptical Tube with Variable Wall Temperature
An analytical model has been developed for the study of turbulent film condensation from downward flowing vapors onto a horizontal elliptical tube with variable wall temperature. The interfacial shear at the vapor condensate film is evaluated with the help of Colburn analogy. The condensate film flow and local/or mean heat transfer characteristics from a horizontal elliptical tube with nonunifo...
متن کامل