Condensation Regime Research Articles

Study of steam jet characteristics and regime maps for bevelled spray nozzles exhausting into quiescent water

Steam-water direct contact condensation phenomenon is being widely used in industrial applications due to its rapid heat and mass transfer rates. The present experimental study explores the underlying physics of the steam jet characteristics by condensing supersonic steam exhausting from five different bevelled nozzles into quiescent water tank. Based on the image processing approach, the effects of steam pressure, water temperature and nozzle exit inclination angle on the size and shape of the steam jet have been studied. The dimensionless steam jet length and maximum expansion ratio have been found in the range of 1.18–5.64 and 1.03–2.70, respectively. The results show that the dimensionless penetration length increases with the increase of steam pressure and water temperature, and decreases with increase in nozzle exit inclination angle. Similarly, maximum expansion ratio of steam jet increases with steam pressure, water temperature and nozzle exit inclination angle. It was observed that steam jet exhausting from bevel nozzle undergoes deflection from its nozzle symmetry axis. The deflected angle increases with steam pressure and nozzle exit inclination angle. A theoretical model of steam jet length for bevelled nozzle has also been presented whose accuracy is found to be within ±30% of the experimental data. Additionally, condensation regime diagrams have been proposed on the basis of steam pressure, water temperature and nozzle exit inclination angle. Existence of seven different plume shapes in regime maps have been identified.

Experimental investigation on the steam condensation dynamic characteristics at low steam mass flux

An experimental study has been performed to investigate the dynamic characteristics of steam direct contact condensation at low steam mass flux. Visible steam bubble parameters can be identified through the image processing algorithm. The maximum dimensionless diameter of steam bubble is calculated and the analysis model of identifying condensation regime is developed to predict transition boundaries of steam chugging and oscillatory bubble regimes. The pressure oscillation waveforms in pipe and in pool are distinguished. In chugging regime, the pressure pulse wave transforms to continuous wave in pool as water temperature increasing, however, in oscillatory bubble regime, continuous wave becomes pulse wave because of increased bubble pulsation volume. The oscillation frequencies are obtained from four different methods of bubble dynamic parameters, pressure pulse periods, pressure frequency spectrums in pipe and in pool to reveal the oscillation mechanism. The low-frequency component in chugging regime increases with water temperature increasing, while the intermediate-frequency component in chugging regime and the frequency in bubble regime decreases.

Experimental Investigation on Condensation Regimes and Transition Boundary During Bubble Condensation in Narrow Rectangular Channel

Experimental Investigation on Condensation Regimes and Transition Boundary During Bubble Condensation in Narrow Rectangular Channel

Polariton condensation in a microcavity using a highly-stable molecular dye

We have fabricated organic polariton microcavities that exhibit remarkable photostability, even in the condensation regime.

Non-Local Theory of Bose-Einstein Condensate and Stopping of Light

The problem of an adequate description of the transport processes in Bose-Einstein condensates (CBE), including space-temporal evolution of CBE in a gravitational field is considered. The full nonlocal system for the CBE evolution is delivered including particular case and analytical solutions. We show (analytically) that a black hole can evolve in the Bose-Einstein condensate (CBE) regime. At the same time, there are modes in which black hole flickering occurs. Quantization of the black holes flickering is discovered. The corresponding nonlocal hydrodynamic equations indicated for fermions gas.

Subsonic and Supersonic Gas Flows to Condensation Surface

Intense heat-mass transfer in a gas flow to a condensation surface is studied with the consistent atomistic and kinetic theory methods. The simple moment method is utilized for solving the Boltzmann kinetic equation (BKE) for the nonequilibrium gas flow and its condensation, while molecular dynamics (MD) simulation of a similar flow is used for verification of BKE results. We demonstrate that BKE can provide the steady flow profiles close to those obtained from MD simulations in both subsonic and supersonic regimes of steady gas flows. Surprisingly, the elementary theory of condensation is shown with BKE results to have a good accuracy in a wide range of gas flow parameters. MD confirms that a steady supersonic gas flow condensates on a surface at the distinctive temperature after formation of a standing shock front in reference to this surface, which can be interpreted as a permeable condensating piston. The last produces the shock compression but completely absorbs incoming gas flow in contrast to a common impermeable piston. The shock front divides the vapor flow on the supersonic and subsonic zones, and condensation of compressed gas happens in the subsonic regime. The complete and partial condensation regimes are discussed. It is shown that above the certain surface temperatures determined by the shock Hugoniot the runaway shock front stops an inflow gas and condensation is ceased.

Magnetization dynamics fingerprints of an excitonic condensate t2g4 magnet

The competition between spin-orbit coupling $\lambda$ and electron-electron interaction $U$ leads to a plethora of novel states of matter, extensively studied in the context of $t_{2g}^4$ and $t_{2g}^5$ materials, such as ruthenates and iridates. Excitonic magnets -- the antiferromagnetic state of bounded electron-hole pairs -- is a prominent example of phenomena driven by those competing energy scales. Interestingly, recent theoretical studies predicted that excitonic magnets can be found in the ground-state of spin-orbit-coupled $t_{2g}^4$ Hubbard models. Here, we present a detailed computational study of the magnetic excitations in that excitonic magnet, employing one-dimensional chains (via density matrix renormalization group) and small two-dimensional clusters (via Lanczos). Specifically, first we show that the low-energy spectrum is dominated by a dispersive (acoustic) magnonic mode, with extra features arising from the $\lambda=0$ state in the phase diagram. Second, and more importantly, we found a novel magnetic excitation forming a high-energy optical mode with the highest intensity at wavevector $q\to 0$. In the excitonic condensation regime at large $U$, we also have found a novel high-energy $\pi$-mode composed solely of orbital excitations. These unique fingerprints of the $t_{2g}^4$ excitonic magnet are important in the analysis of neutron and RIXS experiments.

Optical and magnetic control of orbital flat bands in a polariton Lieb lattice

We study the magneto-optical response of exciton polaritons in $p$-orbital flat bands in a two-dimensional Lieb lattice of semiconductor microcavity pillars. At low excitation density, we detail the influence of an external magnetic field on the exciton component, which enables magnetic tuning of the flat-band states. In the high-density regime, one can induce a spin population imbalance by circularly polarized pumping leading to an effective nonlinear Zeeman splitting. We show how the interplay between the symmetry of the orbital wave function, photonic spin-orbit coupling, and real and effective Zeeman splittings gives rise to real-space flat-band patterns with tilted orbital wave functions in the regime of dynamical polariton condensation. These results demonstrate the ability to optically and magnetically manipulate the spatial, spectral, and polarization properties of polariton condensates in the flat energy bands of a Lieb lattice.

Reliability of the Ginzburg–Landau Theory in the BCS-BEC Crossover by Including Gaussian Fluctuations for 3D Attractive Fermions

We calculate the parameters of the Ginzburg–Landau (GL) equation of a three-dimensional attractive Fermi gas around the superfluid critical temperature. We compare different levels of approximation throughout the Bardeen–Cooper–Schrieffer (BCS) to the Bose–Einstein Condensate (BEC) regime. We show that the inclusion of Gaussian fluctuations strongly modifies the values of the Ginzburg–Landau parameters approaching the BEC regime of the crossover. We investigate the reliability of the Ginzburg–Landau theory, with fluctuations, studying the behavior of the coherence length and of the critical rotational frequencies throughout the BCS-BEC crossover. The effect of the Gaussian fluctuations gives qualitative correct trends of the considered physical quantities from the BCS regime up to the unitary limit of the BCS-BEC crossover. Approaching the BEC regime, the Ginzburg–Landau equation with the inclusion of Gaussian fluctuations turns out to be unreliable.

Substrate thermal conductivity-mediated droplet dynamics for condensation heat transfer enhancement on honeycomb-like superhydrophobic surfaces

The efficiency of dropwise condensation heat transfer has been improved significantly by the development of superhydrophobic surfaces, which are usually fabricated by coating a thin superhydrophobic layer on different kinds of substrates (e.g., different metals/alloys). However, the effects of the thermal conductivity of the substrate on condensation heat transfer over such superhydrophobic surfaces remain unclear. In this paper, we investigated experimentally the condensation heat transfer and droplet dynamics on honeycomb-like superhydrophobic (HCLS) surfaces with hierarchical microporous structures, fabricated by an electrochemical method on four metallic substrates with different thermal conductivities, i.e., copper, brass H96, brass H65 and stainless steel SS316. We observed spontaneous droplet jumping on all these HCLS surfaces at a relatively low degree of subcooling. We also demonstrated the interplay between the substrate thermal conductivity and condensation heat transfer performance during the flooding condensation transition (FCT) by numerical simulations. In the jumping-droplet condensation and flooding condensation regimes, the condensation heat flux and heat transfer coefficient were found to be almost unchanged for different substrates. However, the substrate with a higher thermal conductivity leads to a higher condensation heat transfer coefficient as well as a higher droplet departure frequency at moderate degrees of subcooling, indicating the synergistic effect between the substrate thermal conductivity and droplet dynamics during FCT. The substrate thermal conductivity-mediated droplet dynamics enables a way for further enhancing condensation heat transfer on the HCLS surfaces.

Quantum fluids of light in all-optical scatterer lattices

One of the recently established paradigms in condensed matter physics is examining a system’s behaviour in artificial potentials, giving insight into phenomena of quantum fluids in hard-to-reach settings. A prominent example is the matter-wave scatterer lattice, where high energy matter waves undergo transmission and reflection through narrow width barriers leading to stringent phase matching conditions with lattice band formation. In contrast to evanescently coupled lattice sites, the realisation of a scatterer lattice for macroscopic matter-wave fluids has remained elusive. Here, we implement a system of exciton-polariton condensates in a non-Hermitian Lieb lattice of scatterer potentials. By fine tuning the lattice parameters, we reveal a nonequilibrium phase transition between distinct regimes of polariton condensation: a scatterer lattice of gain guided polaritons condensing on the lattice potential maxima, and trapped polaritons condensing in the potential minima. Our results pave the way towards unexplored physics of non-Hermitian fluids in non-stationary mixtures of confined and freely expanding waves.

Investigation of two-phase natural circulation with the SMART-ITL facility for an integral type reactor

A two-phase natural circulation test using SMART integral test loop (SMART–ITL) was conducted to explore thermo-hydraulic phenomena of two-phase natural circulation in the SMART reactor. Specifically, the test examined the natural circulation in the primary loop under a stepwise coolant inventory loss while keeping the core power constant at 5% of the scaled full power. Based on the test results, three flow regimes were observed: single-phase natural circulation (SPNC), two-phase natural circulation (TPNC), and boiler–condenser natural circulation (BCNC). The flow rate remained steady in the SPNC, slightly increased in the TPNC, and dropped abruptly and maintained in the BCNC. Using a natural circulation flow map, the natural circulation characteristic in the SMART–ITL was compared with those in pressurized water reactor simulators. In the SMART–ITL, a BCNC regime appeared instead of siphon condensation and reflux condensation regimes because of the use of once-through steam generators.

Thermodynamic and electromagnetic properties of the eta-pairing superconductivity in the Penson–Kolb model

In the paper, we study the thermodynamic and electromagnetic properties of the Penson–Kolb (PK) model, i.e., the tight-binding model for fermionic particles with the pair-hopping interaction J. We focus on the case of repulsive J (i.e., J<0), which can stabilize the eta-pairing superconductivity with Cooper-pair center-of-mass momentum q→=Q→, Q→=(π/a,π/a,…). Numerical calculations are performed for several d-dimensional hypercubic lattices: d=2 (the square lattice, SQ), d=3 (the simple cubic lattice) and d=∞ hypercubic lattice (for arbitrary particle concentration 0<n<2 and temperature T). The ground state J versus n phase diagrams and the crossover to the Bose–Einstein condensation regime are analyzed and the evolution of the superfluid characteristics are examined within the (broken symmetry) Hartree–Fock approximation (HFA). The critical fields, the coherence length, the London penetration depth, and the Ginzburg ratio are determined at T=0 and T>0 as a function of n and pairing strength. The analysis of the effects of the Fock term on the ground state phase boundaries and on selected PK model characteristics is performed as well as the influence of the phase fluctuations on the eta-pairing superconductivity is investigated. Within the Kosterlitz–Thouless scenario, the critical temperatures TKT are estimated for d=2 SQ lattice and compared with the critical temperature Tc obtained from HFA. We also determine the temperature Tm at which minimal gap between two quasiparticle bands vanishes in the eta-phase. Our results for repulsive J are contrasted with those found earlier for the PK model with attractive J (i.e., with J>0).

Uncertainty and sensitivity analysis of boundary conditions during water droplet phase change regimes

This paper presents the heat and mass transfer model of a liquid droplet in the consistently changing condensation, transit and equilibrium evaporation regimes, and iterative scheme of numerical simulation of the instantaneous temperature of a semi-transparent droplet in the case of complex radiative-convective heating. The whole cycle of the phase transition regimes of medium and large water droplets flowing in the flue gas was modeled, taking into account the application of water spraying into the flue gas of a biofuel furnace. Simulation results expressed as thermal, energy and phase transformation parameters of water droplets are analyzed in the universal Fourier time scale. The factors defining the change of heat transfer regime of a water droplet are termed as the suppression of droplet slipping in flue gas flow at initial phase transformation stage, and the decrease of radiation absorption at the final stage. Particular attention is paid to the evaluation of the influence of parameters defining the interaction of complex transfer processes on the droplet's phase transformations performing the sensitivity analysis of the heat and mass transfer parameters for the “hypothetical” droplet case (the diameter and the slipping velocity in to gas did not change). It is substantiated, that the main parameters defining the sensitivity of water droplets equilibrium evaporation temperature are flue gas humidity, droplets dispersity, flue gas temperature and droplets slipping velocity.The performed statistical uncertainty and sensitivity analysis showed that the uncertainty of heat and mass transfer parameters describing the phase transformations of a water droplet until equilibrium evaporation regime is affected mostly by droplet dispersity, slipping velocity, flue gas temperature and pressure. The size of droplets and their slip velocity in the flue gas flow were identified as very important parameters for the interaction of complex heat and mass transfer processes of a sprayed water. The main uncertainties were defined at the transition from condensing to transit evaporation regime, and it was defined that with a confidence interval of at least 95 % and accepting a tolerance limit with a probability of at least 95 %, the transit evaporation regime starts at the range Fo ≈ (0.02–0.1). The droplet surface temperature, i.e. parameter determining the droplet phase transformations and its dynamics, could be assessed with a mean error of ±10 %, accepting 95 % probability with 95 % confidence level.

Energy relaxation of quantum dot hot electrons in hybrid quantum dot—Bose–Einstein condensate system

The theory of electron energy relaxation in a hybrid structure consisting of quantum dot interacting with a two dimensional exciton gas in Bose–Einstein condensate (BEC) regime is developed. A new type of the relaxation mechanism in the presence of BEC is introduced and theoretically analyzed. It is shown that, in the first order of electron-exciton interaction, two microscopic processes of energy relaxation appear. The first one is related to the emission of a single Bogoliubov excitation (bogolon) by an electron, whereas the second process is associated with the emission of two bogolons. It is shown that the second type processes dominate in the QD electron energy relaxation.

Topological phase transition in an all-optical exciton-polariton lattice

Topological insulators are a class of electronic materials exhibiting robust edge states immune to perturbations and disorder. This concept has been successfully adapted in photonics, where topologically nontrivial waveguides and topological lasers were developed. However, the exploration of topological properties in a given photonic system is limited to a fabricated sample, without the flexibility to reconfigure the structure in situ. Here, we demonstrate an all-optical realization of the orbital Su–Schrieffer–Heeger model in a microcavity exciton-polariton system, whereby a cavity photon is hybridized with an exciton in a GaAs quantum well. We induce a zigzag potential for exciton polaritons all-optically by shaping the nonresonant laser excitation, and measure directly the eigenspectrum and topological edge states of a polariton lattice in a nonlinear regime of bosonic condensation. Furthermore, taking advantage of the tunability of the optically induced lattice, we modify the intersite tunneling to realize a topological phase transition to a trivial state. Our results open the way to study topological phase transitions on-demand in fully reconfigurable hybrid photonic systems that do not require sophisticated sample engineering.

Perovskite semiconductors for room-temperature exciton-polaritonics

Lead-halide perovskites are generally excellent light emitters and can have larger exciton binding energies than thermal energy at room temperature, exhibiting great promise for room-temperature exciton-polaritonics. Rapid progress has been made recently, although challenges and mysteries remain in lead-halide perovskite semiconductors to push polaritons to room-temperature operation. In this Perspective, we discuss fundamental aspects of perovskite semiconductors for exciton-polaritons and review the recent rapid experimental advances using lead-halide perovskites for room-temperature polaritonics, including the experimental realization of strong light-matter interaction using various types of microcavities as well as reaching the polariton condensation regime in planar microcavities and lattices.

Technology for safe and energy-efficient storage of liquefied petroleum gas at strategic facilities

A technology for safe and energy efficient storage of liquefied petroleum gas (LPG) at strategic facilities has been proposed. A strategy for controlling the technological parameters of the process of condensation of LPG vapors and regasification of the liquid phase has been developed. The peculiarity of the technology lies in the use of a vapor compression heat pump as a source of alternative energy with stabilization of temperature regimes, preventing LPG losses and providing a given regasification performance when supplied to the consumer. The compressor of the heat pump allows to provide the required degree of compression in the operating temperature range in the heat pump condenser, and throttling of the refrigerant through the thermostatic valve ensures the stabilization of the required pressure corresponding to the set range of values of the boiling points of the refrigerant in the evaporator. The regulation of these parameters under conditions of random disturbances caused by external factors creates conditions for the complete condensation of LPG vapors of various compositions formed as a result of its self-evaporation, and also maintains the productivity of the regasification process in the range of specified values, regardless of the climatic zone. The proposed automatic control will ensure the accuracy and reliability of control by reducing the spread of controlled parameters, ensuring their variation in a given range, which is a significant reserve for the intensification of thermal processes while reducing the magnitude of the fire risk and increasing the environmental safety of the environment, including through the use of harmless, non-flammable, non-explosive refrigerant. The use of operational information from the control object to regulate the temperature regimes of condensation of vapors of liquefied hydrocarbon gas in the evaporator and its regasification in the condenser of a vapor compression heat pump within the specified values creates optimal conditions for storing and dispensing gas in large-capacity tanks with minimal energy costs.

Full scale test facility for operability verification of tokamak pressure suppression system at sub-atmospheric conditions

The reliable and safe operation of tokamak fusion reactors is mainly based on radioactive contaminants confinement, achieved preserving the integrity of robust barriers, among which the Vacuum Vessel (VV) performs an essential role. The VV protection against postulated over pressurization events is guaranteed by the safety functions implemented in the Pressure Suppression System (PSS), in which steam from VV is discharged and Direct Contact Condensation (DCC) occurs at sub-atmospheric conditions. Aiming to verify the VVPSS performance of ITER machine (i.e. steam condensation efficiency at different DCC regimes with/without non-condensable), in steady state and transient conditions relevant for fusion reactor postulated events, and contribute to fill the knowledge gap regarding sub-atmospheric condensation, an extensive experimental research activity is ongoing with the Large and Full Scale Test Facility (LSTF and FSTF): designed, assembled, instrumented and commissioned at Laboratory B. Guerrini at DICI University of Pisa. This facility is mainly composed of a Steam Generator (up to 500 g/s, about 1.8 MW), three different steam lines for wide mass flowrate regulation, two air lines for mixed condensation characterization, Experimental Test Tank (92 m3, where steam condensation is investigated adopting two different spargers, scaled and full scale with 100 and 1000 holes, respectively), Auxiliary Tank (10 m3 for plant conditioning), Vacuum Pump, Chiller and Water Storage Tank (15 m3). Two Steam Storage Tanks (15 m3 each) allow to accumulate and provide the foreseen steam peak flowrate value (of 5 kg/s) in the postulated accident. FSTF is highly instrumented (81 thermo-resistances, 28 thermocouples, 35 pressure transmitters, 18 strain gauges and 4 vortex flow meters) and fully remotely controlled (64 on-off and control valves) by a dedicated Data Acquisition and Control System (DACS). Six video cameras and 4 led lights assure steam injection video-recording, for detailed characterization of condensation regimes. Preliminary results are shown for 50 g/s of steam injected through the scaled sparger into water pool at 30 °C with cover gas at 0.1 bar absolute, providing a condensation efficiency of about 100% and verifying instable chugging condensation regime.

Condensation of SIP Particles and Sticky Brownian Motion

We study the symmetric inclusion process (SIP) in the condensation regime. We obtain an explicit scaling for the variance of the density field in this regime, when initially started from a homogeneous product measure. This provides relevant new information on the coarsening dynamics of condensing interacting particle systems on the infinite lattice. We obtain our result by proving convergence to sticky Brownian motion for the difference of positions of two SIP particles in the sense of Mosco convergence of Dirichlet forms. Our approach implies the convergence of the probabilities of two SIP particles to be together at time t. This, combined with self-duality, allows us to obtain the explicit scaling for the variance of the fluctuation field.