A Visual Study of Two-Phase Flow While Evaporating in Horizontal Tubes

1964 ◽  
Vol 86 (3) ◽  
pp. 417-429 ◽  
Author(s):  
W. R. Zahn
Keyword(s):  
Air Conditioning ◽  
Horizontal Tube ◽  
Volume Flow ◽  
Flow Instabilities ◽  
Review Of The Literature ◽  
Two Phase ◽  
Horizontal Tubes ◽  
Commercially Pure ◽  
Actual Operation ◽  
Number Flow

A review of the literature shows no data for horizontal two-phase one-component flow with evaporation; therefore, visual studies have been made of the flow patterns of evaporating R-22 (commercially pure dichloro-difluoro-methane) inside horizontal tube sections under pressure, temperature, flow, and heat load conditions simulating actual operation of a small air-conditioning coil. Description of the patterns observed are given along with data to use in checking with volume flow fraction, Froude number flow regime maps and with maps using Baker’s [1] parameters. A discussion on the qualitative relation between coefficients, the type of flow, effect of return bends, and flow instabilities is included.

Theoretical Model of the Mixture-Vapor Transition Point Oscillations Associated With Two-Phase Evaporating Flow Instabilities

1974 ◽  
Vol 96 (2) ◽  
pp. 138-144 ◽  
Author(s):  
G. L. Wedekind ◽  
B. T. Beck
Keyword(s):  
Theoretical Model ◽  
Transition Point ◽  
Horizontal Tube ◽  
Rayleigh Distribution ◽  
Flow Instabilities ◽  
Statistical Characteristics ◽  
Two Phase ◽  
Proposed Model ◽  
Complete Vaporization ◽  
Liquid Film Dryout

A horizontal tube evaporator in which complete vaporization takes place can be divided into three distinct regions—a subcooled, a two-phase, and a superheat region. The mixture-vapor transition point corresponds to the liquid film dryout point, and when entrainment is negligible, it represents the boundary between the two-phase and superheat regions. Experimental evidence indicates that during what is conventionally accepted as steady flow conditions, the motion of the mixture-vapor transition point is of an oscillatory nature. Furthermore, not only are the oscillations random, but their statistical characteristics can be represented by a modified Rayleigh distribution. This paper presents the formulation of a theoretical model which incorporates various deterministic mechanisms, while at the same time includes the existence of a random phenomenon. The model has the capability of predicting the influence of evaporator heat flux and inlet flow quality on the statistical characteristics of the transition point oscillations. Perhaps, the most significant potential of the proposed model is that it represents a first step toward the formulation of some of the fundamental mechanisms associated with two-phase evaporating flow instabilities on a statistical basis; a basis which appears to be consistent with many of the experimental observations currently available.

COMPARISON OF THE EFFECTS OF DIFFERENT TYPES OF TUBE INSERTS ON TWO-PHASE FLOW INSTABILITIES

2013 ◽  
Vol 20 (2) ◽  
pp. 179-194 ◽  
Author(s):  
Gokhan Omeroglu ◽  
Omer Gomakh ◽  
Sendogan Karagoz ◽  
Suleyman Karsli
Keyword(s):  
Two Phase Flow ◽  
Flow Instabilities ◽  
Phase Flow ◽  
Two Phase ◽  
Different Types

TWO-PHASE FLOW INSTABILITIES ANALYSES IN BOILING WATER REACTOR

2016 ◽  
Author(s):  
Antonella Lombardi Costa ◽  
WILMER ARUQUIPA COLOMA ◽  
Antonella Lombardi Costa ◽  
Claubia Pereira ◽  
Maria Veloso ◽  
...  
Keyword(s):  
Two Phase Flow ◽  
Boiling Water ◽  
Flow Instabilities ◽  
Boiling Water Reactor ◽  
Phase Flow ◽  
Two Phase ◽  
Water Reactor

The effect of two-phase flow regime on hydrodynamics and mass transfer in a horizontal-tube gas-liquid reactor

1985 ◽  
Vol 50 (3) ◽  
pp. 745-757 ◽  
Author(s):  
Andreas Zahn ◽  
Lothar Ebner ◽  
Kurt Winkler ◽  
Jan Kratochvíl ◽  
Jindřich Zahradník
Keyword(s):  
Mass Transfer ◽  
Pressure Drop ◽  
Flow Regime ◽  
Liquid Flow ◽  
Horizontal Tube ◽  
Liquid Holdup ◽  
Two Phase ◽  
Flow Rates ◽  
Type Relation ◽  
Good Agreement

The effect of two-phase flow regime on decisive hydrodynamic and mass transfer characteristics of horizontal-tube gas-liquid reactors (pressure drop, liquid holdup, kLaL) was determined in a cocurrent-flow experimental unit of the length 4.15 m and diameter 0.05 m with air-water system. An adjustable-height weir was installed in the separation chamber at the reactor outlet to simulate the effect of internal baffles on reactor hydrodynamics. Flow regime maps were developed in the whole range of experimental gas and liquid flow rates both for the weirless arrangement and for the weir height 0.05 m, the former being in good agreement with flow-pattern boundaries presented by Mandhane. In the whole range of experi-mental conditions pressure drop data could be well correlated as a function of gas and liquid flow rates by an empirical exponential-type relation with specific sets of coefficients obtained for individual flow regimes from experimental data. Good agreement was observed between values of pressure drop obtained for weirless arrangement and data calculated from the Lockhart-Martinelli correlation while the contribution of weir to the overall pressure drop was well described by a relation proposed for the pressure loss in closed-end tubes. In the region of negligible weir influence values of liquid holdup were again succesfully correlated by the Lockhart-Martinelli relation while the dependence of liquid holdup data on gas and liquid flow rates obtained under conditions of significant weir effect (i.e. at low flow rates of both phases) could be well described by an empirical exponential-type relation. Results of preliminary kLaL measurements confirmed the decisive effect of the rate of energy dissipation on the intensity of interfacial mass transfer in gas-liquid dispersions.

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