er cu ressu ann - rren ure dr nular - ethesis

This thesis examines the film thickness model in gas-liquid two-phase annular flow as well as pressure drop estimation in annular geometry such as fuel bundles and spacers. The pressure drop across the spacer is noticeable and constitutes a noticeable percentage of the total pressure drop in the fuel cluster.

LIST OF TABLES

INTRODUCTION

BACKGROUND

FLOW PATTERNS IN VERTICAL GAS-LIQUID TWO PHASE FLOW A flow regime is a geometrical configuration taken up by the gas and liquid in a
ANNULAR FLOW
INTERFACIAL WAVES

COUNTER CURRENT FLOW PHENOMENON
PRESSURE DROP: ROD BUNDLE & SPACERS

COMPONENTS OF PRESSURE DROP
SPACERS

OBJECTIVE & ORGANIZATION OF THESIS

A falling annular film represents the fundamental limiting case of the annular flow regime of two-phase gas-liquid flows. Some of the above applications require correlations for single-phase and two-phase currents.

Fig. 1.2: Schematic of two-phase annular flow [2].

LITERATURE REVIEW

THEORETICAL MODELS AND CORRELATIONS

FLOODING MECHANISMS GEOMETRICAL DEPENDENCIES

THEORETICAL MODELS AND CORRELATIONS
FLOODING MECHANISMS

KINEMATIC WAVES
DROP ENTRAINMENT

GEOMETRICAL DEPENDENCIES
PRESSURE DROP: ROD BUNDLE & SPACERS
D5 FUEL CLUSTER

Shown in Fig 2.2 [24], the drift flux jgf only depends on the void fraction if the velocities of the two fluids are known. This theory is based on the belief that the process of flooding originates from the bridging of liquid across the cross section of the channel. Cetinbudaklar [26] makes the case that the shear forces on the liquid interface can only be considered if the wave propagation moves in the same direction as the gas flow due to the magnitude of the velocity.

The Reynolds number of the liquid film affects the CCFL by contributing to the friction factor at the interface. In addition, this friction factor is related to the ratio of film thickness to pipe diameter. Rehme & Trippe [31] performed an analysis of the pressure drop of turbulent flow through bundles of rods.

It has been found that the length of the spacer has a significant influence on the pressure drop across the spacer. Modeling the local spacer pressure drop is required to close the momentum equation.

Fig. 2.1: Flow pattern map for vertical counter current pipe 5 cm in dia., air-water at 25 o C, 0.1MPa

ANALYTICAL STUDY

FLOODING CONDITION

FILM THICKNESS MODEL IN ANNULUS PRESSURE LOSS COEFFICIENT AT SPACER

FILM THICKNESS MODEL IN ANNULUS

In Figure 3.2, liquid falls on the outer periphery of the inner tube at flow rate uL, in a concentric tubular geometry in a vertically downward direction, and air blows from bottom to top in countercurrent into the free annulus. Assuming a stable, laminar one-dimensional flow subject to interfacial shear τi, Navier Strokes' theorem reduces to the form in cylindrical coordinate. 36 ‐ The origin of the coordinates is placed in the center of the bar; r is the radial distance from the.

Putting the value of the constant C1 in equation (3.13) gives the shear stress distribution as. 3.15) The differential pressure drop of gas phase in r-z plane over a control volume of length. Final flow rate, Q has the form as below:. 3.20) The above equation can be further reduced as;. A numerical iterative procedure has been implemented to validate the derived film thickness model.

PRESURE LOSS COEFFICIENT AT SPACER

KPSP= ρ

PRESSURE DROP CALCULATION IN D5 FUEL CLUSTER

The static component of the pressure drop is due to altitude and contributes the major percentage of the total pressure drop in the fuel assembly. The pressure drop in the spacers, the frictional pressure drop along the surface of the fuel pin and the pressure drop due to area change, sudden expansion and contraction, valves, holes, bushing junctions result in the dynamic component of the pressure drop. It has always been an area of research how to minimize coolant pressure drop.

More is the pressure drop; higher the pumping power will be, resulting in reduced overall efficiency. In the D5 fuel cluster, the frictional pressure drop along the fuel pins is calculated using the equivalent hydraulic diameter, De, concept. The flow area for calculation of spacer loss coefficient at and before the spacer in the D5 fuel cluster in terms of diameters is mathematically correlated as;. 3.32) Where, Di = jacket diameter, Dcr = coolant pipe diameter, D = fuel pin diameter.

Where Ds = spacer diameter, Dho = outside diameter of fuel bolt hole, Dhi = inside diameter of fuel bolt hole. The flowchart for calculating the pressure drop in the fuel assembly of fuel group D5 is shown in Figure 3.7 below.

SET UP DETAILS INLET & OUTLET DESIGN

STRUCTURE

This large structure provides both the physical foundation for the test section and instrumentation and also provides the rigidity necessary for both stable operation and safety. Standard fittings are used to connect all components and the structure must be anchored to the concrete floor. The slot channels allow for the attachment of other structural and non-structural components to the frame from two sides of the channel.

This system includes a magnetic flow meter, two hand operated rotameters and all associated tubing. The location of the water supply system minimizes the distance to the upper plenum of the test section for all slope angles. All water must be supplied from the building water supply and will be fed directly to the half inch nominal magnetic flow meter.

From the flow meter, the water approaches the rotameters and is thus distributed. Thus, the magnetic flow meter will provide all the necessary flow data, while the rotary meters will allow fine control.

ACRYLIC COMPONENTS

THE AIR OUTLET
UPPER PLENUM
TEST SECTION
LOWER PLENUM
INSTRUMENTS & EQUIPMENTS
DATA ACQUISITION SYSTEM

The upper plenum of the test section provides the means by which the water enters the test section. 51 ‐ room and then go into the test section pipe through radially drilled regular hole of. The test section is the transparent acrylic tube in which CCFL is observed to occur.

At the upper end of the test section, inside the upper plenum, water enters the test section through a series of radially drilled holes with a diameter of 3 mm. The water inlet in the test section directs the current into an annular regime, which alleviates many of the input power problems. This water inlet configuration also allows for symmetrical ingress of water into the test section.

The primary purpose of the lower plenum is as a portable reservoir for water leaving the bottom of the test piece. This provides a good clear chamber for both the water leaving the test section and the exhaust section of the air intake.

Fig. 4.3: Schematic of water entry in the upper plenum of test section.

FILM THICKNESS MODEL VALIDATION SPACER LOSS COEFFICIENT

FILM THICKNESS MODEL VALIDATION

In this validation, a numerical technique was used to obtain the film thickness for a given flux using MatLab. The standard error or target error, throughput, and maximum number of iterations are specified. If, for a given flow, the difference between the left and right sides of equation (3.22) is less than the defined standard error or error target, the iteration stops when the solution converges.

If the difference does not become less than the defined standard error, the film thickness is given a small step that keeps the flow rate constant and the iteration starts until the solution converges, i.e. the difference between the left and right sides of the equation becomes less than the default defined error or error measure, and the iteration continues up to the defined maximum number of iterations by increasing the value of the film thickness until the solution converges. At lower flow rates, the film thickness increases, but the curve tends to become constant at higher flow rates. This happens because at lower flow rates the shear stress at the wall is in balance with the weight of the falling film and the falling film is in a state of free fall, but at higher flow rates due to thickened film, droplets are displaced from the falling film under gravity and film thickness tends to assume a constant value even though the flow rate continues to increase.

At lower flow rates, the increase in film thickness is faster, but at higher flow rates this increase in film thickness decreases and tends to become constant. The values are consistent with those obtained from the theoretical film thickness model and show a positive increasing trend.

SPACER LOSS COEFFICIENT

Variation of loss coefficient with respect to area ratio for different lengths is shown graphically in the plot below (Figure 5.2). But at the same time it increases with the increase in the length of the spacer. Taking into account the circularity of the rod bundle, i.e. D5 fuel cluster, the friction loss coefficient in the rod bundle is calculated using Blassius correlation.

The variation of the beam friction factor with respect to the Reynolds number is shown in Table 5.3 below. The Reynolds number in this case was calculated using the equivalent hydraulic diameter concept [15]. The graph between the beam friction factor and the changing Reynolds number based on the equivalent hydraulic diameter concept is shown in Figure 5.3.

Table 5.2 Spacer loss coefficient for varying spacer length and area ratio.

PRESSURE DROP VERIFICATION

An attempt was made to investigate the gas-liquid countercurrent flow phenomenon in a ring of circular geometry. Furthermore, a theoretical model was developed to evaluate the pressure drop at spacer plate in a D5 fuel cluster. A mathematical model was developed to study the film thickness in a gas-liquid countercurrent flow in a cylindrical annular geometry.

An appropriate numerical technique was adopted to calculate the limit state film thickness of this model. A theoretical correlation based on the flow area ratio was developed to estimate the loss coefficients in the fuel rod bundle. This has been implemented in the D5 fuel assembly to be used in an AHWR (advanced heavy water reactor) to estimate the overall static and dynamic pressure drop across the various components of the fuel assembly.

A program was written in MatLab to estimate the pressure drop in the fuel group. The design of an experimental device for the study of gas-liquid counterflow was proposed along with instrumentation techniques to measure various parameters of gas flow, liquid flow and film thickness.

Table 5.4 Component of individual pressure drop in D5 fuel cluster.

An Experimental Study of the Applicability of Flooding Phenomena to the Dynamic Lubrication Method of Well Control, M.S. Thesis. Comparison between flooding correlations and experimental flooding data for gas-liquid flow in vertical circular tubes. Mechanism and effects of limiting parameters of falling water in vertical countercurrent two-phase flow.

Review and proposal for the best fit of wire-wrapped fuel bundle friction factor and pressure drop predictions using various existing correlations. The influence of fluid properties and inlet geometry on flooding in vertical and inclined tubes.