Heat Transfer In Annular Flow Research Articles

Liquid film parameter measurement based on thermal distribution sensor in horizontal annular flow

Liquid film is an important carrier of mass and heat transfer in annular flow, and the parameter detection of which plays an important role in the energy metering of natural gas production processes and the safe and reliable operation of cooling and heating systems. In this paper, a liquid film velocity equation is derived based on the analysis of the heat balance equation between the liquid film and tube wall. According to the constant power principle, the thermal distributed flow measurement sensor is designed by using the multi-physical field coupling simulation technique According to the momentum balance equation of the Laurinat model, considering the pump mechanism of the disturbance wave and using magnitude comparison and stress balance, a liquid film thickness circumferential distribution model in the horizontal annular flow is proposed. Utilizing the model and designed sensor, the liquid film thickness of four locations (0°, 90°, 180°, 270°) measurements are obtained for 64 horizontal annular flow conditions. Laboratory results indicate that the mean absolute percent error of the model is 32.66% and the 82.81% relative error is within the ±30% error band.

Experimental Investigation of Mechanisms of Droplet Entrainment in Annular Gas-Liquid Flows: A Review

Entrainment of liquid from the film surface by high-velocity gas stream strongly affects mass, momentum and heat transfer in annular flow. The construction of basic assumptions for simplified physical models of the flow, as well as validation of numerical models, requires detailed experimental investigation of droplet entrainment process and the preceding stages of film surface evolution. The present paper analyzes the achievements and perspectives of application of various experimental approaches to qualitative and quantitative characterization of droplet entrainment. Optical visualization in at least two planes simultaneously may provide enough information on transitional liquid structures and detaching droplets, given that the side-view image is not obscured by the wall film. A planar LIF technique is not suitable for this purpose, since real objects are hidden by curved agitated interface and replaced by optical artifacts. To characterize the waves evolving into the transitional liquid structures, film thickness measurements in the plane of the wall are necessary. Such measurements can be achieved by intensity-based optical techniques, such as Brightness-Based LIF, near-infrared or X-ray attenuation techniques, combined with the side-view observations.

Research on the effects of liquid viscosity on droplet size in vertical gas–liquid annular flows

The impacts of the entrained droplet size on the pressure drop and heat transfer in annular flow cannot be ignored. However, literature data on the droplet size for higher liquid viscosities are lacking. This paper presents an in-depth study on the characteristics of droplets in annular flow in a 50-mm-inner-diameter vertical pipe, conducted using a particle dynamic analyzer. Afterwards, the effects of variation in the liquid viscosity from 1 to 30 mPa·s on the droplet size distribution, droplet aggregation and breakup are obtained. The results show that the droplet diameter increases logarithmically with increasing liquid viscosity, first rapidly and then slowly. The initially entrained droplets experience different dynamic events in gas core under different liquid viscosities. Moreover, a new correlation for the Sauter mean diameter of the droplets is proposed via improved numerical fitting of data with higher liquid viscosity, which can be applied to a wider liquid viscosity range.

Interfacial wave behavior and its effect on the flow and condensation heat transfer in a microtube

The transient flow and condensation of R32 in a 0.1 mm microtube were simulated for mass fluxes of 100, 150 and 200 kg m−2 s−1. The model predicted three annular-to-intermittent flow pattern transitions as the mass flux increased that are characterized as injection, injection with wave coalescence, and wave coalescence. The annular flow interfacial waves are transient physical phenomena even though the boundary conditions are steady. The mechanism for their appearance, propagation and growth was investigated. The large interfacial waves squeeze and strongly accelerate the local vapor flow. Oscillations of the radial temperature and velocity gradients cause oscillations of the local heat flux and the wall shear stress in the wavy annular flow which increase the average heat flux and flow friction in the wavy annular flow region. Higher mass fluxes significantly increase the local wall shear stress due to the larger radial velocity gradient at the wall. The radial temperature gradient at the wall is nearly inversely proportional to the liquid film thickness which is independent of mass flux in annular flow, so the local heat fluxes are similar for the three mass flux. The higher mass fluxes weakly enhance the heat transfer in the bubbly and liquid flow region. A new correlation for the local condensation heat transfer in annular flow is proposed, and validated by the simulated data with high agreement.

Large Eddy & Interface Simulation (LEIS) of disturbance waves and heat transfer in annular flows

A numerical method for forced convective boiling in an annulus needs to be developed in order to elucidate the reason for nucleation enhancement by disturbance waves. We first developed a numerical strategy to model the development of disturbance waves in annular flows where the highly turbulent gas core flow drives the laminar liquid flow upwards using advanced CFD tool TransAT. In which, the interface tracking method (e.g. Level-set) combined with a scale-resolving turbulence simulation technique (Large Eddy Simulation) was employed to capture dominant turbulence and interfacial scales. Then, the disturbance wave phenomenon in a vertical steam-water annulus system was investigated and analyzed. The finding reported in the present work provides insight into the evolution of disturbance wave and its influence on the heat transfer in annular flow. The modeling results revealed that locally hot ‘spots’ occurred upstream of disturbance wave. These locally overheated zones could play key roles in activating the nucleation boiling sites. In addition, the inception criteria of disturbance wave were explored by adjusting the mass flux of saturated water. And it was found no disturbance waves occurred at liquid film Reynolds number lower than the critical value, 225.

The Teaching Value of Defining Iterative Design Projects in Serving Capstone Engineering Undergraduate Education

In the past several years, the traditional fourth year “hands-on” requirement for engineering programs in the U.S. is being satisfied by what is now called the capstone senior design project (herein referred to as CSDP). The engineering CSDP program director sends a call to the local industries within the state for solicitation of project proposals that will be worked on by the interdisciplinary engineering student team. Each industrial participant will have to contribute a preset budget defined by the program to the engineering school for each submitted proposal that has been selected by the student team. Honeywell has been an avid participant in the University of Arizona CSDP program for the past several years. Rather than define a simple CSDP that can be fully completed in the first attempt, the author has sought the value of teaching iterative design to the student team by defining a multiyear CSDP scope, in that after the first year, each successive team learns from the past design and implements its own improvement to the design it inherits. This paper gives an overview of Honeywell's CSDP titled “Measuring Heat Transfer in Annular Flow Between Co-Rotating or Counter-Rotating Cylinders.” Now in its fourth iteration, each wave of student team has been able to understand the complexity of the design, the challenge of testing for structural integrity, the controllability of implementing a balanced system of heat gain and loss to reach steady state operation, the evolution of starting with slip ring temperature measurements and ending at wireless telemetry, DOE testing to rank influencing variables, and heat transfer correlation of the data relating Nusselt versus Reynolds number. Beginning with the first year CSDP team, this paper covers the design approach selected by that team, its results, and the lessons learned as a result of failure in meeting the full requirements, which is then taken on by the next group of students the following year.

MODELING OF HEAT TRANSFER OF UPWARD ANNULAR FLOW IN VERTICAL TUBES

This article presents the modeling of heat transfer of upward annular flow in a smooth tube and a spirally internally ribbed tube. First, analytical models of two-phase flow dynamics and heat transfer of annular flow in flow boiling were derived from the liquid film momentum and energy equations for smooth tubes. Combined with empirical correlations for liquid droplet entrainment and deposition rates in annular flow, modeling of heat transfer of upward annular flow in the smooth tube was conducted. The predicted heat transfer coefficients of annular flow agree with the experimental results very well for the smooth tube. Based on the heat transfer model for smooth tubes, a simplified annular flow heat transfer model for the spirally internally ribbed tube was proposed by modifying the interfacial friction factor. The predicted heat transfer coefficients by the modified heat transfer model for the spirally internally ribbed tube agree with the experimental results to some extent. It is suggested that the heat transfer model for the spirally ribbed tube be further improved by modifying the correlations for liquid droplet entrainment and deposition rates in annular flow, which should describe the feature of annular flow in the spirally internally ribbed tube. Extensive experimental data are needed for this purpose.

Evaporation and condensation of steam-water in a vertical tube

Heat Transfer data have been obtained for water from single-phase flow to two-phase annular flow at 0.07–0.09 MPa in a 9.5 mm vertical bore tube under conditions of evaporation and condensation in the same test section. The main aim of the experiments was to elucidate the mechanism of heat transfer in annular flow by distinguishing between the conventional explanation of a purely convective mechanism at high quality region and the alternative hypothesis in which heat transfer is enhanced by secondary nucleation in the region. To avoid ambiguities in local hydrodynamic conditions the experiments were carried out under the same conditions (namely equilibrium annular flow) for both evaporation and condensation in the same test section. The results indicated a forced convective mechanism of the conventional type rather than the alternative thin film boiling mechanism (secondary nucleation) as suggested by Mesler (AIChE, 23 (1977) 448). The heat transfer coefficients in single-phase flow and annular flow regimes are compared with literature correlations. The results show that the present data are in reasonable agreement with existing correlations.

Characteristics of Refrigerant Film Thickness, Pressure Drop, and Condensation Heat Transfer in Annular Flow

Results are presented for void fraction, pressure drop, and condensation heat transfer for refrigerants R-11, R-12, R-22, and R-134a over a range of mass fluxes, qualities, and tube sizes. General characteristics and trends in void fraction, pressure drop, and heat transfer for different refrigerants are discussed. Annular flow modeling relations are used to develop ratiometric equations for liquid fraction, pressure drop, and heat transfer that allow general trends to be predicted when the operating parameters of a refrigeration system are changed.

A Surface Rejuvenation Model for Turbulent Heat Transfer in Annular Flow With High Prandtl Numbers

Heat transfer for high Prandtl number fluids flowing turbulently in a concentric circular tube annulus with prescribed wall heat flux is investigated analytically. This surface rejuvenation based analysis is restricted to thermally and hydrodynamically fully developed flow with constant properties and negligible viscous dissipation. This formulation leads to predictions for the Nusselt Number that are in basic agreement with predictions obtained on the basis of earlier eddy diffusivity models for 30 ≤ Pr ≤ 1000 and 104 ≤ Re ≤ 106.

A Semi-Theoretical Solution of Asymmetric Heat-Transfer in Annular Flow

A brief account is given of the analogy between the transfer of heat and the transfer of momentum. For asymmetric heat transfer in annular flow, the distributions of friction and thermal flux associated with the transport processes are considered. By simplifying the equations describing these distributions, and using an observed experimental fact concerning the temperature profile, the analogy is modified to apply to the annular flow with a fluid having a Prandtl number equal to 1. The modification results in additional factors in the final form of the conventional heat-transfer equation. These factors are functions of the annulus radius ratio parameter. A comparison is made between the final result and the recommendation of a well known authority.