Two-phase Mixture Research Articles

Experimental Investigation and Calculation of Convective Heat Transfer in Two-Component Gas–Liquid Flow Through Channels Packed with Metal Foams

This paper presents a study on heat transfer in two-phase mixtures (air–water and air–oil) flowing through heated horizontal channels filled with open-cell aluminum foams characterized by porosities of 92.9–94.3% and pore densities of 20, 30, and 40 PPI. The research included mass flux densities ranging from 2.82 to 284.7 kg/(m2·s) and heat flux densities from 5.3 to 35.7 kW/m2. The analysis examined the effects of flow conditions, fluid properties, and foam geometry on the intensity of heat transfer from the heated walls of the channel to the fluid. Results indicate that the heat transfer coefficient in two-component non-boiling flow exceeds that of single-phase flow, primarily due to fluid properties and velocities, with minimal impact from flow structures or foam geometry. An assessment of existing methods for predicting heat transfer coefficients in gas–liquid and boiling flows revealed significant discrepancies—up to several hundred percent—between measured and predicted values. To address these issues, a novel computational method was developed to accurately predict heat transfer coefficients for two-component non-boiling flow through metal foams.

Transient behavior of the DYNASWIRL® phase separator during cryogenics tank-to-tank transfer operations

In order to separate gas and liquid from a two-phase mixture in space or earth applications, one can generate a strong artificial acceleration field instead of relying on gravity. This can be achieved by generating a swirl flow in a separator. The DYNASWIRL® phase separator is such a passive device, which had been demonstrated in air/water mixtures in the laboratory and on five reduced gravity NASA parabolic flights. In this work, extensive laboratory testing and numerical simulations are conducted to demonstrate the validity of the DYNASWIRL for phase separation with cryogenics. Liquid nitrogen (LN2) is used for extensive testing involving unsteady tank-to-tank transfer with quenching of separator and piping, liquid boil-off and vaporization, phase separation and recovery. This paper describes the separator and testing setups used. It examines the effects of the liquid (water and LN2), geometric parameters, and their effects on the separation and on the pressure loss across the separator, and analyzes the flow dynamics of the gas removal process. Validated numerical simulations support the experimental results and help explain the effects of the design parameters on the results.

Numerical simulation of unsteady cloud cavitation in an orifice nozzle by a compressible gas-vapor/liquid mixture cavitation model

Abstract Focused on the behaviour of unsteady cloud cavitation in a submerged orifice nozzle, this work presents a numerical investigation by using a compressible gas-vapor/liquid mixture cavitation model. The mean flow of the two-phase mixture is calculated by URANS for compressible fluid and the intensity of cavitation is evaluated by the gas volumetric void fraction considering the effect of fluid compressibility varying with phase change. Water jets issuing from a submerged orifice nozzle are investigated under different cavitation conditions. Computation results are compared with experiment data and the validity of computation is confirmed. The periodical shedding of cavitation clouds is captured reliably. Numerical simulations reveal that a leading cloud principally split by the shear flow and a subsequent cloud detached by the re-entrant jet are successively shed downstream, and they coalesce over the range of approximately x/d ≈ 2∼3. This process is repeated and the flow rate coefficient pulsates periodically under the effect of cavitation clouds.

Relationship of flow pattern, vibration, and noise in automobile refrigerant system and flow pattern identification based on convolutional neural network

In recent years, the flow-induced vibration and noise in automotive refrigerant system gradually become the main factor affecting driving comfort. However, the relationship of flow pattern, vibration, and noise is not clear, and pattern identification is not easy but necessary. In this paper, a series of experiments are conducted to investigate the relationship of flow pattern, flow-induce vibration, and noise near the thermal expansion valve in an automobile refrigerant system. The flow pattern, vibration, and noise are closely related to startup processes. Mist flow, which contains more mist two-phase mixture than transition flow and wispy-annular flow, leads to the largest amplitude of vibration and strong broadband hiss noise. Moreover, the increase in compressor speed promotes the pattern transition and the vibration amplitude in time domain but has no effect on the distribution of vibration peaks in frequency spectrum. Finally, a short-time Fourier transform and convolutional neural network combined method for flow pattern identification is developed based on the relationship of flow pattern and flow-induced noise. After using transfer learning and data augmentation, four trained network architectures show relatively high accuracy above 94% for test set. Among them, ResNet34 not only has the highest accuracy of 98.8% but also can recognize each type of flow pattern. The generalization of this method can help engineers to recognize flow patterns in air conditioning without flow visualization but only need to measure sound signals.

Development of the full Lagrangian approach for modeling dilute dispersed media flows (a review)

Continuum models of media with zero pressure are widely used in various branches of physics and mechanics, including studies of a dilute dispersed phase in multiphase flows. In zero-pressure media, the particle trajectories may intersect, “folds” and “puckers” of the phase volume may arise, and “caustics” (the envelopes of particle trajectories) may appear, near which the density of the medium sharply increases. In recent decades, the phenomena of clustering and aerodynamic focusing of inertial admixture in gas and liquid flows have attracted increasing attention of researchers. This is due to the importance of taking into account the inhomogeneities in the impurity concentration when describing the transport of aerosol pollutants in the environment, the mechanisms of droplet growth in rain clouds, scattering of radiation by dispersed inclusions, initiation of detonation in two-phase mixtures, as well as when solving problems of two-phase aerodynamics, interpretation of measurements obtained by LDV or PIV methods, and in many other applications. These problems gave an impetus to a significant increase in the number of publications devoted to the processes of accumulation and clustering of inertial particles in gas and liquid flows. Within the framework of classical two-fluid models and standard Eulerian approaches assuming single-valuedness of continuum parameters of the media, it turns out impossible to describe zones of multi-valued velocity fields and density singularities in flows with crossing particle trajectories. One of the alternatives is the full Lagrangian approach proposed by the author earlier. In recent years, this approach has been further developed in combination with averaged Eulerian and Lagrangian (vortex-blob method) methods for describing the dynamics of the carrier phase. Such combined approaches made it possible to study the structure of local zones of accumulation of inertial particles in vortex, transient, and turbulent flows. This article describes the basic ideas of the full Lagrangian approach, provides examples of the most significant results which illustrate the unique capabilities of the method, and gives an overview of the main directions of further development of the method as applied to transient, vortex, and turbulent flows of “gas-particle” media. Some of the ideas discussed and the results presented below are of a more general interest, since they are also applicable to other models of zero-pressure media.

Investigation of two-phase flow distribution in the vertical annular distribution header of a variable refrigerant flow heat pump system

The characteristics of two-phase flow distribution from a vertically installed annular refrigerant distribution header to multiple branch ports are investigated, with a specific focus on simulating a real variable refrigerant flow heat pump (VRF HP) system. A test section is fabricated to replicate an actual distribution header for empirical investigation, utilizing an air–water mixture as the working fluid. A series of experiments are conducted to examine distribution characteristics, involving variations in the location of the main inlet port, operational mode, total mass flow rate, and void fraction. The experimental results indicate that the two-phase mixture exhibits a relatively uniform liquid phase distribution to the branch ports when the main inlet port is positioned at the bottom side. However, maldistribution to branch ports is intensified as the inlet void fraction increases and the flow rate of the two-phase mixture decreases. Furthermore, a series of computational fluid dynamics analyses is performed to investigate the distribution characteristics of R410A, the actual working fluid utilized in VRF HP systems. These analyses are conducted under the operational conditions typical of VRF HP systems. Despite identical Reynolds numbers for the two-phase R410A flow and air–water mixture flow, the former exhibits a notably uneven distribution to branch ports owing to the distinct thermophysical properties, particularly density and viscosity. The findings from this investigation enhance the comprehension of two-phase flow distribution characteristics in a vertically installed refrigerant distribution header under real VRF HP system conditions, offering valuable insights into mitigating the maldistribution of refrigerant flow to branch ports.

Numerical study on the impact of needle and dryness fraction on two-phase ejector performance under fixed/varied operating pressure

This study investigates the effects of varying needle block degree (blockage area ratio of the primary nozzle throat) and dryness fraction (the ratio of gas mass to mass of two-phase mixture) within the primary and secondary flow on the performance of a two-phase ejector, employing CFD numerical simulations under both fixed and varied conditions. The findings reveal the following: (1) Dryness fraction has a significant impact on the performance of the ejector. ER decreases with the decrease of X1 and increases with the decrease of X2, when X1 = 1 and X2 = 0.4, the ejector performance can be improved by 253.3 % under the optimal area ratio; (2) A higher primary flow dryness fraction and a lower secondary flow dryness fraction are more favorable for enhancing the ejector's performance; (3) When P1 changes, the ejector is most sensitive to changes in P1, slightly less sensitive to changes in An, and least sensitive to changes in dryness fraction; When P2 changes, the ejector is most sensitive to changes in dryness fraction, slightly less sensitive to changes in P2, and least sensitive to changes in An; (4) When varying P1 and P2, the ejector performance is optimal at X1 = 1 and X2 = 0.8 (An); (5) Regardless of changes in AR or operating conditions, the adjustable ejector with the needle can effectively enhance the ejector's performance under certain conditions.

Numerical investigation of grain size effect on velocity-skewed oscillatory sheet flow

Wave-induced sheet flow leads to intense sediment transport. Fine sand and medium/coarse sand exhibit opposite directions of net sediment transport under velocity-skewed oscillatory sheet flows. A newly developed two-phase mixture model is employed to simulate the sediment transport under these conditions. The model accounts for particle stress, two-phase momentum exchange, and turbulence modulation. The effects of grain size on flow characteristics and sediment transport are primarily investigated. The model effectively reproduces the spatial and temporal distributions of two-phase velocities and sediment concentration as well as the periodic distribution of erosion depth. Comparisons between configurations with medium and fine sand demonstrate that the grain size impacts sediment transport in two main ways. First, the grain size influences the periodic variations in erosion depth and the quantity of suspended sediment. A decrease in the grain size increases the phase residual and phase lag, enhancing offshore sediment transport. Second, suspended sediments modulate the flow dynamics within the oscillatory boundary layer. Through the mobile bed effect and density stratification, the grain size affects two-phase velocities, turbulence, and net sediment transport.

Two-phase analysis of heat transfer of nanofluid flow in a wavy channel heat exchanger: A numerical approach

The heat transfer improvement by using CuO/water nanofluid (NF) in a wavy channel is evaluated numerically using the turbulent two-phase mixture and the κ - ε models. The numerical work is a 2-dimensional model created and analyzed in Gambit and Ansys Fluent software, respectively. The flow Reynolds (Re) numbers of 8000 – 40,000, wavelength ranging from 0 – 0.4 m, and solid volume fraction (SVF) of 0 % to 4 % are investigated. In all cases, a constant heat flux of q′′=5000 W/m2 is applied on the outer surface of the heat exchanger. The heat transfer and fluid flow were analyzed by the flow visualization method and heat transfer evaluation indexes. The results show that by increasing the Re number, the vortices increase and more turbulence are generated in the vicinity of the waves near the channel inlet. As the amplitude of the channel waves increased, the velocity at the top of the wave increased, and the resulting pressure gradient behind the wave is intensified and the reverse flow is generated. The improving effect of using NF is more prominent where the effect of other enhancing factors is weak. For wall amplitude of 0.1 m, by increasing the SVF from 1 – 4 % the average Nu number (Nuavg) increased by 35 % and 22 % in Re = 8,000 and 40,000, respectively.

A novel system based on a series of ORCs to recover cryogenic energy from the LNG regasification process for power and freshwater production

Seawater desalination emerges as a feasible solution to solve the issues related to the freshwater scarcity generated by climate change. In the meantime, the energy transition promotes using Liquid Natural Gas (LNG) as a cleaner fuel. Usually, it is stored near marine areas at 113 K, therefore the recovery of part of the exergetic cold potential for freshwater production appears very appealing. In light of this, this study evaluates the energy and exergy performances of an innovative seawater desalination plant supplied by the cryogenic power released in the LNG regasification process. Specifically, three Organic Rankine Cycles (ORCs) arranged in series, operating between the seawater (hot source) and LNG (cold source) thermal levels, are investigated. Seawater releases heat to promote the evaporation of proper low-boiling fluids, cooling down to −5.62 °C and forming a two-phase mixture consisting of 50 wt% of pure ice and brine, so that the same liquid phase is employed for ice transportation in post-treatment devices. Simultaneously, the LNG is preheated by the low-boiling fluids’ condensation heat, allowing for the limitation of the thermal energy required for the phase change. Power generation is obtained by turboexpanders located between vaporizers and condensers. Eighteen different ORC configurations using diverse working fluids were analysed assuming steady-state conditions and ideal transformations. Considering a regasification terminal with a capacity of 8 billion Sm³ per year, the maximum power production amounts to 11.24 MW, recovering 13.33% of thermal exergy and producing 137.5 kg/s of freshwater. When desalination is privileged, 149.9 kg/s of freshwater can be produced, generating a power output of 7.02 MW with an exergetic recovery efficiency of 8.32%.

The singular limits of the Riemann solutions as pressure vanishes for a reduced two-phase mixtures model with non-isentropic gas state

We study the cavitation and concentration phenomena of the Riemann solutions for a reduced two-phase mixtures model with non-isentropic gas state in vanishing pressure limit. We solve the Riemann problem by constructing the regions in (p, u, s) coordinate system. Then we obtain the limiting behaviors of the Riemann solutions and the formation of δ-shock waves and vacuum as pressure vanishes. We conclude that, as pressure vanishes, the limit of Riemann solutions is the Riemann solutions of the reduced 2-dimensional pressureless gas dynamics model. Finally, we present numerical simulations which are consistent with our theoretical analysis.

Numerical research on refrigerant injection for motor cooling of screw compressor for heat pump with large temperature lift

In the screw compressor for heat pump with large temperature lift, the large load on the motor makes the motor heat up severely. The stability and safety of the motor directly affects the operation of the compressor. High motor temperatures or strong impact on winding will destroy the insulating coating on the copper wires of the motor winding, which could cause the motor to burn out. Refrigerant injection for motor cooling is an effective way of motor cooling. There is a lack of research on this method. In this paper, a computational fluid dynamics model containing evaporation–condensation and conjugate heat transfer is developed. In order to reasonably simulate the evaporation–condensation process, the physical parameters varying with temperature of the refrigerant are taken into account. The temperature field of the screw compressor by refrigerant injection for motor cooling is predicted, and the accuracy of the model is verified through experiments of an R134a heat pump with large temperature lift. The maximum discrepancy between the simulation results and the experimental results under four working conditions does not exceed 3.0%. Next, the effects of the injection pressure and the injection position on motor cooling, impact caused by refrigerant injection and temperature uniformity are investigated. The results show that by adjusting the injection pressure to make the refrigerant two-phase mixture, the impact caused by refrigerant injection is reduced by 57.0%, while the cooling effect is reduced by only 9.0%. By choosing the injection position appropriately, the cooling effect is increased by 12.0% and the impact caused by refrigerant injection is reduced by 21.2%. In addition, the temperature in the middle of the motor is the highest before refrigerant injection, so the motor temperature sensor should be arranged in the middle of the motor winding.

Analysis of nanofluid and nano-enhanced phase change material (NEPCM) in a heat exchanger for thermal management of electronic devices

Thermal management of high-power electronic devices is essential to control their enormous heat generation, which is usually the cause of their damage. Scientists have found several solutions for cooling electronic devices, but a counter-current heat exchanger has never been used. In the same context, numerical research on the thermal performance of a proposed new cooling system based on a counterflow heat exchanger combined with a heat sink is conducted in this article. Cu-H2O nanofluid, n-Docosane nano-enhanced phase change material, and water were selected as coolants, and they are compared in terms of temperatures, Nusselt number, heat transfer coefficient, pressure drop, friction factor, and performance enhancement coefficient using a two-phase mixture transient model based on Finite Volume method. Two cases of the proposed system are studied to find the optimal distance between heat exchanger pipes and the hot surface. Results are compared with previous experimental data to demonstrate that the system under study is accurate. They revealed that integrating the heat exchanger with the heat sink using Cu-H2O nf as a coolant maintained the hot surface temperature below 308 K with improved heat transfer by 31.22% compared to water. 0.25 mm is the optimum distance to find the highest thermal performance of the cooling system.

Nearly isothermal compression characteristics of the helium oil-flooded scroll compressor

The helium compressor is a crucial component in cryocooler refrigeration systems. Oil-flooding is a promising technique to solve the cooling and leakage challenges in helium scroll compressors, facilitating nearly isothermal compression. In this paper, the validated numerical model is employed to investigate the nearly isothermal compression characteristics of the two-phase mixture of helium and oil in a scroll compressor. Results indicate that the discharge temperature can be remarkably lowered from 455 °C to approximately 64 °C with the injection of an appropriate amount of oil into the working chamber. Moreover, the sealing effect of oil enhances the volumetric efficiency from approximately 66 % to 93.6 %. These advantages of oil flooding ensure an internal indicated efficiency that exceeds 100 % and results in superior isothermal efficiency. However, the polytropic exponent during the nearly isothermal compression process is smaller than the theoretical value, which imposes higher requirements on the built-in volume ratio for the helium oil-flooded scroll compressor.

Microstructure and phase evolution of Fe-20Ni-20W foams during high-temperature redox cycling

Freeze-cast Fe-20Ni-20 W (at%) foams suitable for high-temperature redox cycling show excellent microstructural stability and regenerative porosity formation, but they exhibit slower reduction kinetics as compared to previously studied Fe-25 W foams. The Fe-20Ni-20 W lamellar foams, after initial hydrogen reduction, consist of a two-phase mixture of µ-Fe7W6 and γ-Fe(Ni,W), with significant microporosity due to the sintering inhibition of W. During oxidation by steam at 800 °C, these phases are oxidized to a three-phase mixture of (Fe,Ni)WO4, Fe3O4, and γ-Ni(Fe); upon subsequent reduction by H2, the foams return to their initial composition. The chemical vapor transport reduction of FeWO4 results in the formation of submicron pores during each reduction half-cycle which accelerate subsequent reaction and limit sintering in the reduced state. The reduction of mixed oxide is relatively sluggish, which is likely due to the increased stability of the (Fe,Ni)WO4 phase brought on by the substitution of Ni in Fe sites in FeWO4.

Numerical simulation and geometric optimization of a desalination system using solar energy using two-phase mixing method with alumina nanoparticles

This research paper presents 2D numerical simulations of a single-slope solar desalination system from a nanomaterial science perspective, utilizing the two-phase mixture method. Alumina nanoparticles with a volume percentage of 0.1 % are introduced into the water storage tank for thermal analysis. The system features a trapezoid-shaped glass wall to harness solar energy. Key variables studied encompass ambient temperature, glass wall angle, front wall height, glass wall temperature, and air temperature inside the system. Temperature and velocity contours within the system are obtained through numerical simulations. To enrich the analysis, artificial intelligence techniques and response surface methodology are employed to examine the maximum and minimum temperatures. The results indicate that, at medium ambient temperatures, the lowest maximum air temperature inside the desalination system occurs at a front wall height of 0.2 m and a glass angle of 45°. Additionally, the lowest air temperature is observed at an ambient temperature of 10 °C and a front wall height of 0.05 m, corresponding to a glass angle of 27.5°. On the other hand, the highest maximum air temperature is recorded at a front wall height of 0.125 m, with a glass angle of 45° and an ambient temperature of 55 °C. Increasing the ambient temperature from 10 °C to 55 °C for a wall height of 0.2 m leads to a 26.81 °C rise in the air temperature inside the system, equivalent to a 9 % increase. The findings provide valuable insights for optimizing the design and performance of single-slope solar desalination systems integrated with alumina nanoparticles from the perspective of nanomaterial science.

Experimental and numerical analysis of heat transfer mechanisms for two-phase oil-refrigerant flow process in the cylinder of rotary compressor

Investigating the heat transfer mechanisms in rolling piston type rotary compressors is crucial for improving their operational efficiency. A thermal test platform was established and steady-state temperature fields of key components were measured under various conditions, revealing a correlation between these temperatures and crank angles, except near the angle of 54° for the cylinder head-up. It provided important boundary conditions for simulation research. A novel three-dimensional fluid–solid-heat coupled simulation method was proposed, calculating heat transfer coefficients at fluid–solid interfaces. The two-phase heat transfer characteristics post oil–gas miscibility was studied, arising from the injection of lubricating oil into the working chamber. Two-phase oil-refrigerant mixtures, compared to single-phase refrigerant, increased heat transfer coefficients by 2.35 % in the suction channel and 2.99 % in the cylinder head-up, but decreased by 5.85 % in the cylinder head-down, 17.42 % in the piston, and 5.63 % in the cylinder. Oil injection was found to significantly enhance convective heat transfer in the suction chamber, increasing suction superheat in the cylinder by up to 29 K and reducing temperature of the compression chamber by up to 17 K. These results provide novel insights into the complex heat transfer in rotary compressors.

Spectral analysis of dispersed multiphase flows in the presence of fluid interfaces

Spectral analysis of dispersed two-phase flows is highly desirable to reveal the interplay of the various flow scales, much larger or much smaller than the size of the dispersed bodies. This is a challenging task as the matching conditions at the body interfaces generate singularities in the fields describing the two-phase mixture. The nature of these singularities and their consequences on the spectra are theoretically analyzed for bubble or droplet flows. Results of direct numerical simulations are reported and spatial spectra of the mixture velocity, the flow forces and their power are examined. The regular part of the spectral densities of energy production, dissipation and transfers between scales are separated from their singular part. The resulting spectral energy balance, free of the footprint of the singularities, is found in agreement with coarse-grained simulations where the interfaces are filtered out before solving the Navier–Stokes equations. These results pave the way for the spectral analysis of more complex turbulent dispersed flows.

Thermal and Entropic analyses of free convection of nanofluid in a partially heterogeneous porous chamber using the two-phase mixture model

Entropy generation and convection heat transfer in a partially porous chamber with different side wall temperatures using CuO–H2O have been investigated. The importance of this issue is wide application of the results in solar collectors, thermal extrusion systems, heat exchangers, bio-medicine, nuclear waste disposal, etc. The innovation of the present work is related to the investigation of fluid and heat fields and entropy generation by using a matrix with subordination of porosity to the vertical axis and permeability, thermal conductivity, and viscosity with subordination of porosity. To obtain accurate results, the two-phase mixture model was used, and thermal conductivity and viscosity of nanofluid were simulated by experimental models by temperature and volume fraction dependence. Governing equations are solved by the FVM. The main findings indicate that the best and worst optimization factor will occur in the porous matrix ε = ε(y2) and ε = -ε(y2), respectively, which is 113 % and 86 % of NH of the homogeneous matrix, respectively. Also increasing the filling of the cavity, highly improves NH, so that the NH will reach from 1.19 to 1.82 with the increase of S from 0.25 to 1.

An approach for topology optimization of heat sinks for two-phase flow boiling: Part 1 – Model formulation and numerical implementation

Two-phase flow boiling in heat sinks and cold plates is attractive for various thermal management applications due to high effective heat capacity rates and high heat transfer coefficients compared to single-phase operation. In addition, multi-physics topology optimization is sought for generation of high performance thermal management components. Yet, the design of heat sinks using topology optimization has been restricted to single-phase flow physics, due to incompatibility between available two-phase flow models and traditional single-phase topology optimization approaches. Interface-capturing two-phase flow models are too computationally expensive for optimization; mixture and two-fluid models that treat the liquid and vapor phases as an interpenetrating continuum with interfacial transport phenomena captured through empirical correlations are computationally tractable for heat-sink-scale optimization. However, the penalization approaches commonly used to define the structures formed during topology optimization results in arbitrary fin and channel geometries for which a universal two-phase flow correlation is not available. To enable coupling with two-phase mixture models, this work leverages a homogenization approach to topology optimization wherein heat sink designs are represented using spatially varying microstructures with optimized dimensions. A predefined microstructure geometry is chosen for which two-phase flow correlations exist and therefore topology optimization can be performed. This work is the first to develop a topology optimization algorithm using a mixture model for simulating two-phase flow boiling to design heat sinks and cold plates. Part 1 of this study develops and implements the algorithm to investigate topology optimized heat sinks at various heat inputs, topology optimization grid sizes, and maximum vapor quality constraints. Topology optimized heat sinks designed for single-phase versus two-phase flow are compared. There are significant differences in hydraulic and thermal responses of the single-phase and two-phase designs due to high effective heat capacity rates and high heat transfer coefficients of flow boiling. A companion paper (Part 2) focuses on manufacturing, model calibration, and experimental validation of the topology optimized heat sinks under two-phase flow boiling. The algorithm demonstrated in this work extends the capabilities of topology optimization to two-phase flow physics, and thereby enables the design of various two-phase flow components such as evaporators, condensers, heat sinks, and cold plates.