H.M. Soliman

The mist-annular transition during condensation and its influence on the heat transfer mechanism

Abstract Influence of the mist-annular transition on the heat transfer mechanism during condensation is studied. It is shown that the applicability of annular flow correlations cannot be extended with accuracy to the mist region and that a dimensionless parameter. We can be used in defining the departure from annular flow conditions. A heat transfer correlation is suggested for the mist region and shown capable of good agreement with a data base of different fluids and tube orientations.

Measurement and correlation of the pressure drop in air-water two-phase flow in horizontal helicoidal pipes

Abstract Experimental investigations are conducted for air-water two-phase flow in horizontal helicoidal pipes of varying configurations. The helicoidal pipes are constructed by wrapping Tygon tubing around cylindrical concrete forms. Four different inside diameters of tubing and two different outside diameters of the cylindrical concrete forms are used to make the helicoidal pipe with different configurations. Also, the helix angle of helicoidal pipes varies up to 20 degrees. A total of 32 helicoidal pipes has been tested for the present study. The experiments have been performed for superficial water velocity in the range of U L = 0.008–2.2 m/s and superficial air velocity in the range of U G = 0.2–50 m/s. The pressure drop of the air-water two-phase flow is measured and the data are well correlated. It was found that the pressure drop multiplier relates strongly to the superficial velocities of air or water, and that the helix angle has almost no effect on the pressure drop, although the pipe and coil diameters have certain effects in low rates of flow. Correlation for two-phase flow in the horizontal helicoidal pipes has been established based on the present experimental data.

Two-phase pressure drop and phase distribution of a horizontal tee junction

Abstract Experimental data are presented for the phase distribution and junction pressure drops of low-pressure (1.5 bar) air-water mixtures at a horizontal, equal-sided (37.6 mm i.d.) dividing tee junction. These data correspond to inlet flow regimes of stratified, wavy, slug and annular flow with inlet superficial liquid velocities JLI

Experiments on the onset of gas pull-through during dual discharge from a reservoir

Abstract The phenomenon of gas pull-through is investigated experimentally for the condition of simultaneous discharge from two small orifices (6.35 mm i.d.) located on the side of a high-pressure reservoir containing a stratified air-water mixture. The critical height corresponding to the onset of gas pull-through is found to be a function of the two discharge rates and the vertical distance separating the centrelines of the orifices. Experimental results pertaining to the appearance of the phenomenon and the critical height are presented for a wide range of the aforementioned independent parameters. Based on these results, an empirical correlation is developed for predicting the data with a high degree of accuracy.

Onsets of entrainment during dual discharge from a stratified two-phase region through horizontal branches with centrelines falling in an inclined plane: Part 1 – Analysis of liquid entrainment

Abstract A theoretical investigation has been conducted for predicting the critical liquid height and the location of liquid entrainment during dual discharge from a stratified two-phase region through branches mounted on a vertical wall. The two branches are horizontal and their centrelines fall in a common inclined plane. Two models have been developed; a simplified point-sink model and a more-accurate finite-branch model. Predictions from the two models are shown to be in good agreement for the condition of high flow rates from the branches, while the finite-branch model is necessary for good predictions at low branch flow rates. Influences of the various independent parameters on the predicted onset are presented and discussed. Comparisons with experimental results are shown in Part 2 of this paper.

Numerical analysis of laminar mixed convection in horizontal internally finned tubes

Abstract Steady, laminar, mixed convection in the fully developed region of horizontal internally finned tubes is investigated for the case of uniform heat input axially and uniform wall temperature circumferentially. The fluid flow and heat transfer characteristics are found to be dependent on a modified Grashof number Gr+, Prandtl number Pr, number of fins M and the relative fin height H. Governing differential equations are solved numerically for the parametric range M = 4 and 16, H = 0, 0.2, 0.5 and 0.8, Pr = 7 and Gr+ = 0 to 2 × 106. Computed results include the secondary flow components, axial velocity and temperature distributions, wall heat flux, friction factor and average Nusselt number. Internal finning is found to retard the onset of significant free convective effects and to suppress the enhancements in friction factor and Nusselt number compared to smooth tubes. Satisfactory agreement is obtained between the present numerical results and previous experimental data.

Fully coupled solution of a two-phase model for laminar film condensation of vapor–gas mixtures in horizontal channels

Abstract Detailed results are presented for laminar film condensation of vapor–gas mixtures in horizontal flat-plate channels using a fully coupled implicit numerical approach that achieves excellent convergence behavior. These results correspond to steam–air and R134a–air mixtures over wide ranges of the independent parameters, and they include velocity, temperature, and gas concentration profiles, as well as axial variations of film thickness, pressure gradient and Nusselt number. Effects of the four independent variables (inlet values of gas concentration, Reynolds number and pressure, and the inlet-to-wall temperature difference) on the film thickness, pressure gradient, and the local and average Nusselt numbers are carefully examined. It was found that the condensation of R134a–air corresponds to thicker liquid films, lower heat transfer rates, and lower algebraic values of the pressure gradient when compared with steam–air at the same operating conditions.

Experimental investigation of laminar mixed convection in an inclined semicircular duct under buoyancy assisted and opposed conditions

Abstract Combined free and forced convection is experimentally investigated for laminar water flow in the entrance region of a semicircular duct with upward and downward inclinations within ±20° using the boundary condition of uniform heat input axially. The experiment was designed for determining the effect of inclination (particularly the downward) on the wall temperature, and the local and fully-developed Nusselt numbers at three Reynolds numbers (500, 1000, and 1500) and a wide range of Grashof numbers. For the upward inclinations, Nusselt number was found to increase with Grashof number and the inclination angle (up to 20°), while the effect of Reynolds number was found to be small. For the downward inclination, Reynolds number has a strong effect on Nusselt number and the manner by which it varies with Grashof number. The fully-developed values of Nusselt number agree well in magnitude and trend with theoretical results recently obtained by the authors.

Discharge from a smooth stratified two-phase region through two horizontal side branches located in the same vertical plane

Abstract Experimental data are presented for the mass flow rate and quality of two-phase (air-water) discharge from a stratified region through two side branches (6.35 mm W.) with their parallel centrelines located in a vertical plane. These data correspond to different values of the interface level between the onset of gas entrainment at the upper branch to the onset of liquid entrainment at the lower branch for test-section pressures of 316 and 517 kPa, test-section-to-separators pressure difference ranging from 40 to 235 kPa, branch separating distance to diameter ratio ranging from 1.5 to 8 and different hydraulic resistances of the lines connecting the test section to the separators. Normalized plots are shown to be capable of absorbing the effects of some independent variables within the tested range of operating conditions. Empirical relations were developed for the prediction of the two-phase mass flow rate and quality in terms of normalized parameters. These relations represent the data with a high degree of correlation.

Two-Phase Flow From a Stratified Region Through a Small Side Branch

Experimental data are presented for the mass flow rate and quality of two-phase (air-water) discharge through a small branch (6.35 mm i.d.) located on the side of a large reservoir under stratified conditions. These data correspond to different values of the interface level between the onsets of gas and liquid entrainments for test-section pressures ranging from 316 to 517 kPa, test-section-to-separator pressure differences ranging from 40 to 235 kPa, and different hydraulic resistances of the line connecting the test section and separator. Influences of these independent variables on the mass flow rate and quality are discussed and normalized plots are presented showing that the data can be collapsed for a wide range of conditions. Comparisons are made with previous investigations and new empirical correlations are formulated and shown to be capable of predicting the present data with good accuracy.