Motion Of Coolant Research Articles

Features of Motion and Heat Transfer of Swirling Flows in Channels of Complex Geometry

The computational and experimental study results of swirling single-phase coolant motion and heat transfer for the standard operation parameters of a nuclear power plant are presented. The experimental model is a vertical heat exchanger of a “pipe in a pipe” type with the countercurrent movement of coolants. Six different swirlers (three with a constant twist pitch and three with a variable pitch) were considered. The heat exchanger temperature field was measured at various combinations of coolant flow rates, and a channel pressure drop for each swirl was determined. Computational studies were performed using the Omega-based Reynolds stress model and SST model with a correction for curvature streamlines. A good agreement between numerical and experimental data was obtained. Based on the velocity and temperature fields, swirling flow motion features in channels with a variable swirl pitch were discovered. For each intensifier, the effectiveness criterion in comparison with a pipe channel was determined.

Film cooling performance under plasma aerodynamic actuation and spoiler ribs of an internal cooling channel based on Suzen model

In this paper, a plasma actuator (PA), treated by the Suzen model, is introduced into film cooling, and four rows of rectangular ribs are employed in internal cooling. Combined action and individual action of film cooling and internal cooling are then investigated at four blowing ratios (M = 0.25; 0.5; 0.75; 1.0). Results show that (no PA, no ribs) the coolant is ejected from the film hole in a spiral form under the action of internal crossflow, and its distributions are inclined to crossflow direction. When the plasma actuator is opened (no ribs), the strength and scale of the counter-rotating vortex pairs are weakened, and the motion of coolant is accelerated, the average cooling effectiveness shows an increase of 82.4% (M = 0.25), 98.9% (M = 0.5), 33.4% (M = 0.75) and a decrease of 2.1% (M = 1.0), the spanwise cooling effectiveness is raised by 57.3–143.3% for each streamwise position, the flow coefficient is lowered by 1.8–3.2%. Ribs (no PA) interfere with the coolant flow in the internal channel, reducing the rotation degree and exit momentum of the coolant, and greatly eliminate the uneven distribution of coolant along the spanwise direction, resulting in an enhancement of 50.4–162.8% in the spanwise cooling effectiveness and of 59.2% (M = 0.25) and 79.5% (M = 0.5) in average film cooling effectiveness. The effect of combined action (PA plus ribs) is lower than those effects of individual factors, and wall average film cooling effectiveness with PA and ribs exhibits a 62.4% (M = 0.25) and 49.4% (M = 0.5) higher to PA off a case (no PA, no ribs); however, a local or global heat transfer deterioration appears at M = 0.75 and 1.0.

Peculiarities of thermal calculation of cross-flow plate air recuperators

Application of modern energy-saving technologies is the most important task in development of construction industry. In the conditions of exhausting decrease of energy consumption of public, administrative buildings due to reduction of transmission heat losses the implementation of mechanical ventilation with recuperation of exhaust air heat becomes a rational way to increase energy efficiency. One of the key problems in the study of plate-type air recuperators is to find the temperature efficiency of the device. The value of this characteristic is influenced by such parameters as the area of the branched heat exchange surface, initial temperatures of heat carriers, volume flow rates, flow rate ratio, type of fins, etc. The purpose of the study is to compare coefficients of thermal efficiency of outside air as a function of Reynolds number obtained by engineering calculation, mathematical modelling and manufacturer’s data for the recuperator ISIS Recover HR-A-05-V-G4-E-1-60. The article substantiates the calculation method using the existing algebraic dependence describing heat transfer in the cross-flow scheme of coolant motion on the basis of new results. An empirical dependence is obtained, which adequately describes the results of numerical simulation using the ANSYS Fluent solver and engineering calculation.

Reduction of Hydraulic Losses in a Pebble-Bed Reactor for Nuclear Power Propulsion Systems for Advanced Spacecraft

An analysis of various schemes for coolant motion in a nuclear reactor with spherical microfuel elements (coated fuel particles, or pebbles) is presented. The conditions under which it is possible to reduce the pressure losses in the coolant keeping all the advantages of the spherical microfuel elements versus the fuel rods are considered. The rate of coolant flow and the pressure losses in the reactor during its longitudinal-axial and radial motion through the pebble bed are determined. An interchannel scheme of coolant motion is proposed, and the conditions are defined for which it has advantages over the radial scheme.

Моделирование теплофизических процессов в ядерном реакторе на быстрых нейтронах

The development of reactors on the fast neutrons and nuclear power engineering is generally responsible for its formation. One of them is that the responsibility for the reliability of the reactor equipment, its calculation, creation and operation sharply increases. For the development of projects in the field of nuclear energy, it is necessary to carry out various thermalhydraulic calculations. Using the results of calculations will allow for timely adjustment in the engineering. This work is devoted to the study of the processes of hydrodynamics and heat exchange of reactor on fast neutrons with an electrical power of 600 MW with a volumetric energy release up to 0.494 GW / m3. In the process of work, 3D model of the selected fuel assembly area was created in the program Gambit. Computer modeling was carried out in the ANSYS FLUENT software package as a result of which thermal state of fuel assembly for established mode of heat transfer was defined. The calculations were carried out using the k-ε coolant motion turbulent model. This article presents the results of calculations on hydrodynamics and heat transfer in a segment of the selected fuel assembly of a fast sodium reactor. The non-uniformity of temperature distributions along the height of the active zone in various areas of fuel assemblies, the distribution of the heat carrier velocity, as well as pressure indicators are shown. The analysis of the results obtained shows that the temperatures of the structural elements do not exceed the permissible temperatures; the pressure drop is significantly lower than in reactors of another type.

Model Studies of Coolant Flow Hydrodynamics in VVER-1000 In-Reactor Pressure Channel

The results of the development, construction, and testing of a small-scale model of a pressure channel of coolant motion inside the VVER-1000 vessel from the entry connections to the coolant flow entry into the core are presented. A hydrodynamic bench, a model of in-reactor pressure channel in the VVER-1000, and methods for studying the coolant flow hydrodynamics in the channel model are described. The results of experimental studies and a comparative analysis of the coolant flow velocity distribution along the annular pressure channel from the entry into the channel through the pressure connections to the entry section in the elliptical bottom of the cavity of the model are presented. The experimental results obtained for different flow regimes of the coolant through the pressure connections are presented.

Aerothermal Investigations on Mixing Flow Field of Film Cooling With Swirling Coolant Flow

This paper describes the experimental results of a new film cooling method that utilizes swirling coolant flow through circular and shaped film cooling holes. The experiments were conducted by using a scale-up model of a film-cooling hole installed on the bottom surface of a low-speed wind tunnel. Swirling motion of the film coolant was induced inside a hexagonal plenum using two diagonal impingement jets, which were inclined at an angle of α toward the vertical direction and installed in staggered positions. These two impingement jets generated a swirling flow inside the plenum, which entered the film-cooling hole and maintained its angular momentum until exiting the film-cooling hole. The slant angle of the impingement jets was changed to α = 0 deg, 10 deg, 20 deg, and 30 deg in the wind tunnel tests. The film cooling effectiveness on a flat wall was measured by a pressure sensitive paint (PSP) technique. In addition, the spatial distributions of the nondimensional concentration (or temperature) and flow field were measured by laser-induced fluorescence (LIF) and particle image velocimetry (PIV), respectively. In the case of a circular film-cooling hole, the penetration of the coolant jet into the mainstream was suppressed by the swirling motion of the coolant. As a result, although the coolant jet was deflected in the pitch direction, the film cooling effectiveness on the wall maintained a higher value behind the cooling hole over a long range. Additionally, the kidney vortex structure disappeared. For the shaped cooling hole, the coolant jet spread wider in the spanwise direction downstream. Thus, the pitch-averaged film cooling effectiveness downstream was 50% higher than that in the nonswirling case.

Volumetric maximization of coolant usage in closed self-driven circuits

The present study numerically maximizes the heat transferred in a rectangular loop. The loop or circuit is composed of two superimposed rectangles of different sizes with coolant filling the vacant space between them. Buoyancy forces promote coolant motion, since a constant temperature difference is maintained between the two outer vertical walls of the circuit. The results are presented in terms of two quantities: the heat transfer rate per unit of length and per unit of coolant volume, for several values of the Rayleigh number. The numerical solution is obtained by applying the finite elements method to the two-dimensional numerical domain, here represented by the coolant only. The numerical results show that the relative size of the inner and outer rectangles composing the circuit are important in terms of thermal performance and that the optimal gap size between the inner and outer rectangles decreases as the Rayleigh is increased. The circuit aspect ratio (i.e., height/width) was also investigated revealing to have a positive effect on the overall thermal performance of the system if increased, while the eccentricity of the two rectangles composing the circuit presented an opposite effect. The numerical results were compared with scaling analysis showing good agreement.

Vapor condensation on plate during horizontal motion of coolant

An analytical study is made of heat transfer during vapor condensation on a vertical plate. An engineering method of verifying the heat transfer calculations is also shown.

A Numerical Model of Reactor Fuel and Coolant Motions Following Pin Failure

The computer code EPIC models fuel and coolant motion that results from internal fuel pin pressure (from fission gas or fuel vapor) and/or from the generation of sodium vapor pressures in the coolant channel subsequent to pin failure in a liquid-metal fast breeder reactor. The modeling includes the ejection of molten fuel from the pin into a coolant channel with any amount of voiding through a clad rip which may be of any length or which may expand with time. One-dimensional Eulerian hydrodynamics is used to model both the motion of fuel and fission gas inside a molten fuel cavity and the mixture of two-phase sodium and fission gas in the channel. Motion of molten fuel particles in the coolant channel is tracked with a particle-in-cell technique.

Recent results from treat tests on fuel, cladding and coolant motion

Transient in-pile tests in the TREAT reactor are showing dispersive fuel movement and substantiate use of mechanistic modeling of such movements in Liquid Metal Fast Breeder Reactor (LMFBR) safety analyses. Test conditions are selected to mock-up the thermal histories calculated for hypothetical LMFBR accidents, and include use of previously irradiated fuel with various fuel structures. These test data are used in analyzing the consequences of LMFBR fuel failure under a range of hypothetical accident conditions and possible accident scenarios, as well as guiding descriptions of the extended fuel motion leading into the transition phase between the immediate post-accident configuration and the final stable, coolable configuration. Status of these experiments as of Spring 1974 was reviewed in three papers at the 1974 American Nuclear Society topical meeting on fast reactor safety: one on studies of transient overpower accidents (Rothman et al., 1974), one on loss-offlow accident studies directed toward behaviour of irradiated fuel (Deitrich et al., 1974), and one on loss-of-flow accident studies with fresh fuel using direct simulation of key axial LMFBR dimensions (Grolmes et aL, 1974). Since those reports, new data on cladding and fuel movement have been obtained from post-mortem examinations on those tests. Also, additional experiments have been run with the primary aims of clarifying the phenomena producing fuel motion, and of assessing the role of cladding motion as it might limit or otherwise affect fuel movement.

The Recovery of Coolant Flow Following Rapid Release of Fission Gas from a Postulated Multiple Pin Failure in a Liquid-Metal Fast Breeder Reactor Subassembly

A previous single-bubble model describing the coolant motion within an oxide fuel subassembly of a liquid-metal fast breeder reactor due to rapid gas release from multiple pin failure has been extended to include the description of coolant motion following the release of fission gas into the exit coolant plenum. The present model supplements the previous model in that it follows the motion of the lower gas-liquid interface by allowing for the expansion of gas in the exit plenum in the form of a spherical bubble, and by allowing it to detach and form another bubble in its place. The model assumes that the motion of the liquid surrounding the expanding bubble can be described by potential flow theory and that the motion of lower liquid slug in the subassembly can be described by one-dimensional continuity and momentum equations for incompressible flow model. The model also considers the translation of the center of the plenum bubble during its expansion. It is demonstrated that the behavior of the first bubble (i.e., when the difference between bubble pressure and the pressure of the surroundings is large) is analogous to that of the high-pressure bubble formed under large depths of water,and the behavior of those bubbles formed subsequently resembles that of the bubbles due to orifice bubbling above a gas chamber of finite volume. The sample calculations for a Fast Flux Test Facility reactor subassembly indicate that the recovery of coolant flow, even with a nearly simultaneous breach of all 217 pins in the sub-assembly, is very rapid, and the total transient time is not long enough to cause any significant overheating of the coolant and the cladding.