Superheated Liquid Research Articles

Numerical Study of Growth of a Vapor Bubble in Superheated Seawater with Time-Varying Pressure

Flash evaporation is used in a wide range of applications from seawater desalination to nuclear and space applications. The fundamental mechanism in flash evaporation is mechanical and thermal non-equilibrium which results in liquid being superheated and subsequent bubble growth. Therefore, study of bubble growth is essential to accurately predict the vapor generation rate during flashing. Accordingly, this article provides a comprehensive numerical study of growth of a single vapor bubble during flash evaporation in seawater. Effects of system pressure, liquid superheat, salt concentration, and time-varying pressure during flash evaporation on bubble growth behavior are studied. The Rayleigh-Plesset equation with energy and salt concentration equations is solved numerically with 4th-order discretization schemes. Excellent agreement between the results of the present study and reported experimental results is found. It is observed that during bubble growth in seawater, salt continuously accumulates at the vapor-liquid interface which consequently reduces the growth rate and degrades thermal performance characterized by Nusselt number. However, it elongates the inertia-controlled regime during which the bubble radius is directly proportional to time. It is shown that properly handling the non-uniform distribution of solute in the liquid boundary layer is key to modeling bubble growth in seawater and binary solutions.

High-performance antireflection nanostructure arrays on aluminum-doped zinc oxide film fabricated with femtosecond laser near-field processing

Transmittance is critical to the performance of optoelectronic devices, and the fabrication of nanostructure arrays with sizes and periods similar to wavelengths on optical surfaces can effectively reduce reflectance and increase transmittance. A method combining a femtosecond laser and the near-field effect of polystyrene (PS) microspheres to prepare integrated high-performance anti-reflective nanostructure arrays on aluminum-doped zinc oxide (AZO) film was proposed in this study. The near-field effect of microspheres with different diameters on a laser light field for several laser wavelengths was simulated with the finite-difference time-domain (FDTD) method. The simulation results showed that a 10-fold improvement of the intensity of a focused laser beam could be obtained with the combination of an 800-nm laser and 1-μm PS microspheres. Nano-craters on the surface of the AZO film were obtained with femtosecond laser irradiation. The depth and the area of these nano craters both increased with the increase of the laser fluences and tended toward saturation when the fluence went from 0.67 to 0.83 J/cm2. Facilitated by the gradient refractive index formed by the nano-craters, the transmittance of the sample treated with 0.83 J/cm2 increased by 8% in the 400–1100 nm band and even by 15% in the 400–600 nm band. The ablation mechanism was revealed by the time-resolved pump-probe technique, which proved that the nano-craters were formed by the phase explosion, and the smooth bottom with fine cracks was induced by the inhomogeneous resolidification of the superheated liquid phase. Our method could endow a photoelectric device with high-performance integrated anti-reflection capability, eliminating the need for additional anti-reflection coating.

Large-scale fluctuations during a boiling crisis and during the boiling up of a superheated liquid jet

Large-scale fluctuations during a boiling crisis and during the boiling up of a superheated liquid jet

Dynamic behaviors of in-tank subcooled liquid with depressurization-induced phase change and the impact on primary breakup of flashing jet

Accidental releases of superheated liquids, such as liquefied petroleum or natural gases, are featured by depressurization across the outlet leading to liquid flashing within the upstream container and the downstream jet. In this work, dynamic behaviors of in-tank liquid with phase change throughout depressurized releases and the influence on the primary breakup of flashing jet were studied with an experimental 20 L tank. In-tank parameters (pressure, temperature, and liquid mass) and downstream jet morphology were characterized. A new nondimensional number (ηp), the ratio between the superheat levels of the saturated states corresponding to liquid temperature and pressure, was developed to describe the liquid's thermodynamic state under both release and ambient conditions. A thermodynamics-determined release rate model was established to characterize flow behaviors at the exit. Results showed a strong correlation between the initial ηp0 and key process parameters I (depressurization and release rates): I = aηp0b, where a and b are constants for a particular I. A ηp0-based criterion was derived to characterize in-tank release dynamics and thermodynamics: ηp0 < 0.25 (subcooled), 0.25<ηp0 < 0.4 (transition from subcooled to superheated), and ηp0 > 0.4 (superheated). Mild evaporation and flash evaporation dominated in-tank pressure recovery when ηp0 < 0.25 and ηp0 > 0.25, inhibiting depressurization. The release rate model agreed well with experiments and demonstrated that flashing happens upstream and chokes the induced two-phase flow when ηp0 > 0.25, decreasing the release rate. The evolving upstream conditions changed the breakup regime both in mechanical and thermodynamic aspects. Moreover, the thermodynamic effect increased as the mechanical effect decreased during depressurization.

Breakup regime of flashing jet under thermal nonequilibrium and mechanical forces and its relationship with jet characteristics during depressurized releases of superheated liquid

Accidental superheated liquid emissions into the atmosphere yield two-phase releases. The resulting flashing jet, driven by thermal nonequilibrium and mechanical forces, breaks up into massive droplets, fostering beneficial conditions for fire, explosion, and toxic diffusion. In this work, a 20 L tank was built to examine two-phase flow behaviors during depressurized releases of superheated liquids via a high-speed camera and phase Doppler anemometry. Different breakup regimes of flashing jet and dimensionless groups that effectively represent thermodynamic (RpJa) and mechanical (WevOh) driving effects were determined. Based on the interaction between the two effects, quantitative criteria to distinguish different regimes were developed. The accompanying jet characteristics, including jet angle (θ), area fraction (fA), droplet diameter (dSMD), and droplet velocity (ud), and their relationship with jet breakup were revealed. Results show that non-flashing (NFB), partially flashing (PFB), and fully flashing (FFB) breakups coincide with RpJa(WevOh)1/7 < 41, 41 ≤RpJa(WevOh)1/7 < 223, and 223 ≤RpJa(WevOh)1/7, respectively. For small-sized nozzles (d≤3 mm), θ2 and fA2 increase within 41 ≤RpJa(WevOh)1/7 < 558 and then keep stable. The difference for large-sized nozzles resides in 223 ≤RpJa(WevOh)1/7 < 558 (early FFB regime), where θ2 and fA2 decrease slightly due to the enhanced droplet evaporation. In 41 ≤RpJa(WevOh)1/7, dSMD2 decreases and ud2 increases, but at an extremely low rate within 558 ≤RpJa(WevOh)1/7.

Kinetics of Nucleation in Superheated Liquid Oxygen-Nitrogen Solutions. 1. Experiment and Classical Homogeneous Nucleation Theory.

The method of lifetime measurement has been used to investigate the kinetics of spontaneous boiling-up of superheated liquid oxygen-nitrogen solutions. Experiments have been conducted at pressures of 0.5 and 1.0 MPa in the range of nucleation rates 104-108 m-3 s-1 in the whole concentration range. The temperature and concentration dependences of the nucleation rate have been determined. The sections corresponding to homogeneous nucleation have been singled out on experimental isobars. At fixed nucleation rates and pressures, the concentration dependence of the attainable-superheat temperature is close to a linear one. A comparison of experimental data with classical nucleation theory (CNT) has revealed systematic discrepancies, which are of qualitatively different character for pure liquids and solutions. In a pure liquid, the surface tension of critical bubbles is less, and in a solution, it is greater than at a flat interface.

Determining the bubble nucleation efficiency of low-energy nuclear recoils in superheated C3F8 dark matter detectors

The bubble nucleation efficiency of low-energy nuclear recoils in superheated liquids plays a crucial role in interpreting results from direct searches for weakly interacting massive particle (WIMP) dark matter. The PICO Collaboration presents the results of the efficiencies for bubble nucleation from carbon and fluorine recoils in superheated C$_3$F$_8$ from calibration data taken with 5 distinct neutron spectra at various thermodynamic thresholds ranging from 2.1 keV to 3.9 keV. Instead of assuming any particular functional forms for the nuclear recoil efficiency, a generalized piecewise linear model is proposed with systematic errors included as nuisance parameters to minimize model-introduced uncertainties. A Markov-Chain Monte-Carlo (MCMC) routine is applied to sample the nuclear recoil efficiency for fluorine and carbon at 2.45 keV and 3.29 keV thermodynamic thresholds simultaneously. The nucleation efficiency for fluorine was found to be $\geq 50\, \%$ for nuclear recoils of 3.3 keV (3.7 keV) at a thermodynamic Seitz threshold of 2.45 keV (3.29 keV), and for carbon the efficiency was found to be $\geq 50\, \%$ for recoils of 10.6 keV (11.1 keV) at a threshold of 2.45 keV (3.29 keV). Simulated data sets are used to calculate a p-value for the fit, confirming that the model used is compatible with the data. The fit paradigm is also assessed for potential systematic biases, which although small, are corrected for. Additional steps are performed to calculate the expected interaction rates of WIMPs in the PICO-60 detector, a requirement for calculating WIMP exclusion limits.

Bubble growth rate in superheated droplets

Calculations are presented to describe the dynamic of a growing bubble in a single and simple formulation for R(t). The calculations show clearly that the behavior of the growing bubble is exponentially increasing with the time constant τ showing a universal behavior as a function of the reduced superheat. Experimental data from other researchers are used to verify the description and are in good agreement with the results. The main motivation for this study was to find R(t)that is accurate and at the same time uncomplicated enough in solving the dynamic of the bubble growth to calculate the far-field pressure for superheated liquids.

Application of dynamical system scaling to bubble dynamics

Dynamical System Scaling (DSS) provides a useful method for analyzing, categorizing and scaling time-dependent processes. A key feature of DSS is the temporal displacement rate, D, which relates the natural process time to the reference clock time. Because of its property of being invariant under a two-parameter affine transformation, it provides an underlying basis for process scaling. Application of DSS to bubble dynamics serves to elucidate the physical significance of the temporal displacement rate and its role in scaling a variety of bubble dynamics processes. In particular, prior studies in bubble dynamics did not recognize the role that bubble interfacial acceleration has on scaling. It is a central feature in the definition of the temporal displacement rate. This paper shows that the temporal displacement rate consists of the sum of the internal dimensionless groups that govern the bubble dynamics. Preserving the temporal displacement rate and boundary conditions for a prototype and a scaled model results in similitude of the time-dependent normalized bubble size, growth rates and interfacial accelerations for different fluid conditions. For vapor bubble growth in a superheated liquid, it is shown that inertial controlled bubble growth occurs when D = 0 and thermally controlled bubble growth occurs when D = 1.

Study on liquid–vapor interface oscillation characteristics and heat transfer of film boiling during quenching of fuel cladding surfaces

It is very important to understand the heat transfer and flow characteristics of the film boiling during the quenching of fuel cladding under severe accident conditions. In order to investigate the liquid–vapor interface oscillation behavior and heat transfer characteristic of the film boiling, an experimental apparatus was established to simulate the quenching process with different liquid subcooling degrees and test sample materials. The image processing technique and the Fast Fourier Transform (FFT) method were combined to capture the characteristics of vapor film, and the inverse heat conduction problem method was employed to calculate the surface temperature and heat flux of the test sample. The results show that the vapor film thickness becomes thinner and the oscillation of the liquid–vapor interface gradually weakens with increasing liquid subcooling degree and decreasing wall temperature. The change in the vapor film characteristics can be attributed to the combined effects of Kelvin-Helmholtz instability of interface and condensation of vapor film, which respectively correspond to the low dominant frequency oscillation (0–35 HZ) and high dominant frequency oscillation (90 HZ) of the liquid–vapor interface observed during the experiment. Besides, it can be concluded that the heat transfer of film boiling is increased with liquid subcooling degree, but not sensitive to the test sample material and axial elevation. Based on the heat transfer results, a new Nusselt correlation of the film boiling that couples the effects of thermophysical properties of the vapor film, thermophysical properties of the coolant, liquid subcooling degree and wall superheat degree is developed with the average error of 10.41 %. The universality of the improved correlation is verified by the experimental data in literatures.

Study of flow and heat transfer characteristics of saturated flow film boiling over two inline cylinders

In this article, a numerical investigation carried out on saturated flow film boiling over two cylinders placed in an inline arrangement has been discussed. Water at near critical condition, p/pc = 0.99, is considered for all simulations, where pc is the critical pressure of water. In this study, buoyancy assisted flow is considered. The effects of different liquid Reynolds number ReD and wall superheat on heat transfer rates are studied for different spacings between the two cylinders. Interface structures and their modes of evolution greatly vary for different cases investigated. For some cases, especially for those with lower spacing between the cylinders, a steady vapor column connecting both cylinders in the gap region between them is formed. At higher flow rates, the vapor column in the gap region is unstable. At some cases where re-circulation zones are formed, the vapor column breaks off. The heat transfer rate from the rear cylinder is significantly affected by the modes of the phase-interface evolution and the types of flow structures formed in the gap region between the cylinders. It is found that the flow structures and the phase-interface evolution are strongly dependent on the distance between the two cylinders for a given Reynolds number and a non-dimensional wall superheat.

Experimental study on single bubble growth of R32 + R1234yf binary mixtures during saturated pool boiling

R32 + R1234yf mixtures are considered highly promising refrigerants. Understanding the bubble growth characteristics of mixtures is vital for understanding their boiling heat-transfer performance. In this study, pool boiling experiments were conducted to investigate the single-bubble growth characteristics of R32, R1234yf, and their binary mixtures. The bubble growth curves for each test refrigerant were obtained in the superheat range of 1.3–6.2 K. The results showed that the asymptotic bubble growth rates of the pure refrigerants were slower than those predicted using previous theoretical models, which were developed for isolated bubbles growing in an infinite superheated liquid. The bubble growth constants of the mixtures were lower than those of the pure components, whereas the growth exponents were greater than the “ideal growth exponent.” The sudden decrease in the effective wall superheat and sharp increase in mass transfer resistance slowed the initial bubble growth rate. In the late stage of growth, the microlayer that had not yet dried out provided stable heat input to the bubble, resulting in a higher asymptotic growth rate than that of pure components. A set of dimensionless correlations for the bubble growth rate of mixtures is proposed, and they predicted the data in this study within a ± 15% deviation band.

Mechanistic critical heat flux model development for subcooled flow boiling based on superheated liquid sublayer depletion

Critical heat flux (CHF) refers to the limit of boiling transfer systems, and crossing this limit may jeopardize system safety. However, a clear understanding of the physical mechanisms of CHF is still lacking. In this study, a new CHF prediction model based on superheated sublayer depletion was established for subcooled flow boiling in an upward vertical tube at low pressure. The model is characterized by its developed determination of the superheated liquid sublayer thickness, net vapor generation location, forced convection heat transfer and liquid supplement caused by bubble turbulent fluctuations. The proposed CHF model was validated by a database covering the low pressure subcooled operational ranging over P = 0.1–2.15 MPa, G = 0.7–35 Mg/m2s, ΔTin = 11–183.16 K, D = 0.7–12 mm, L/D = 4.2–115.55, and xeqout = −0.2673–0.0843. The model can accurately predict the trend of thermal-hydraulic and geometric factors’ effects on the CHF. The prediction results have good prediction accuracy with an root-mean-square error (RMSE) of 15.21%, and overall error of ±25%. The proposed model also shows good adaptation to a non-water (refrigerant 113 and liquid nitrogen) system.

Experimental study on explosive boiling mechanism of superheated liquid containing ethanol impurities under rapid depressurization

In this study, a small visualization device was used to research the dynamic evolution of pressure reactions and bubble nucleation in tanks under rapid decompression. The effect of ethanol impurities on the mechanism of superheated boiling of liquids was investigated. The effect of ethanol impurities on the superheated boiling of liquids under different storage conditions is discussed by studying the pressure characteristic parameters. The experimental results show that ethanol impurities can reduce the bubble nucleation radius, leading to a sharp increase in the number of bubbles and more severe boiling during leakage. Besides, there is a saturation concentration which maximizes the promotion of superheated boiling of the liquid. Under the present experimental conditions, the boiling intensity of ethanol impurities saturates at 3.53%, and this saturation concentration decreases slightly with increasing initial leakage pressure. Ethanol impurities also promote boiling of superheated liquids at different initial liquid levels. This study can provide ideas for the investigation, analysis and prevention of related accidents.

A Comprehensive Model for Single Bubble Nucleate Flow Boiling

Abstract The single bubble dynamics and local thermal effects in a rectangular channel are investigated in this paper under subcooled nucleate flow boiling conditions. A combined effect of Marangoni and microlayer evaporation in flow boiling regimes has rarely been reported in open literature. Therefore, a comprehensive boiling model that combines the three submodels, namely, phase change model, microlayer evaporation model, and Marangoni model, is developed that accounts for small-scale physics such as evolution of superheat layer during bubble growth, microlayer evaporation, and scavenging of the superheated liquid during the bubble departure. The verification of model has been carried out through detailed flow and temperature field validation exercises of various bubble stages with recent experimental data reported in the literature. The effects of varying subcooled conditions and Reynolds number on bubble dynamics and the associated heat transfer rates have been examined. The study reveals a decreasing trend in the bubble diameter with increasing Reynolds number and degree of subcooling. It has also been observed that the bubble shape is affected by the Marangoni phenomena. Bubble shape slightly flattens during inception, gradually becomes spherical while sliding, and later elongates after liftoff. The individual contribution of microlayer heat flow (Qmicrolayer) is estimated to be around 22–40% for flow boiling conditions and it is the second-highest heat transfer contributor after the latent heat transfer. The results obtained from the proposed model show a good match with published data and indicate the significance of microlayer in the single bubble flow boiling heat transfer.

Numerical simulation of bubble dynamics and segregation in binary heptane/dodecane mixtures

A mathematical model for the simulation of spherical bubble dynamics in binary alkane mixtures is presented. Detailed heat and mass transfer and phase transition are resolved, and air absorption and desorption are considered. As example mixtures, high-volatile heptane and low-volatile dodecane are investigated. The low-volatile component shows a convective counter-intuitive mass transport opposite to the diffusion flux. A staggered mass flux of heptane and dodecane is associated with a local segregation of mixture components in the surrounding liquid and a distinctive species distribution within the bubble. A comparative study with a pseudo-fluid where alkane species interdiffusion is absent and whose components cannot segregate reveals that for an oscillating bubble, the local segregation hardly affects bubble dynamics, while for a continuously growing bubble in a superheated liquid, the growth rate is considerably affected, particularly for a low heptane mixture percentage. This study demonstrates limitations of treating mixtures by a single-component surrogate fluid and may serve as a starting point for the development of multi-component cavitation models for computational fluid dynamics applications in real fluid mixtures as, e.g. fuels or hydraulic oils.

Experimental research on the two-phase explosive boiling mechanism of superheated liquid under different leakage conditions

In this study, a 17 L cube vessel was designed to simulate the explosive boiling of high-pressure liquefied gas after the leakage of the storage tank. The influence of leakage conditions such as crack position, crack diameter, and initial liquid fill level were investigated. Results indicate that when the crack is at the gas phase and gas-liquid interface, the rapid boiling of the liquid is caused by the leakage and significant pressure rebound is occurred. What’s more, cracks located under the gas-liquid phase may also cause a significant rebound in pressure. As the crack diameter increases, the two-phase flow boiling intensity first increases and then decreases, and it reaches the maximum when the diameter is 30 mm. Furthermore, a concept of the critical liquid level difference was proposed, and its influencing factors were studied. Under the experimental conditions in this article, BLEVE will not occur if the height between the liquid level and the crack is above the critical liquid level difference.

Investigation of the kinetics of spontaneous boiling-up of superheated n-pentane in a glass tube with defects of the inner surface. I. Monitoring the liquid-vapor surface tension

The paper studies the kinetics of spontaneous boiling-up of superheated n-pentane in a thermostated glass tube at a pressure of 0.10 MPa in the temperature range from 70.2 to 125.3°C (superheatings from 34.1 to 89.2°C). Experiments were conducted by the method of lifetime measurement of a superheated liquid both with and without two glass capillaries joined by fluoroplastic. It has been found that under the action of repeated boiling-ups, the boundary of attainable superheating may increase stepwise by 10°C. This effect is reversible. Monitoring the surface tension as the property determining the kinetics of spontaneous boiling-up was realized right in the experimental setup. It is shown that in the temperature range from 61.1 to 170.0 °C, this value does not depend on the number of boiling-ups of a superheated liquid and is in good agreement with reference data.

Morphological characteristics and flashing mechanism of superheated liquid jets released from rectangular breaches

The leakage of liquefied gases such as liquefied hydrocarbons and liquid chlorine is usually accompanied by an intense phase transition that results in two-phase release. This two-phase release will lead to fire, explosion, toxic diffusion and other major dangerous accidents, seriously endangering the safety of personnel and ecological environment, resulting in inestimable losses. To deepen the understanding of such accidents, a 20L tank was used to simulate the accidental release of superheated liquid and study its accident behavior. This work simulated different breaches by using different shapes of nozzles with equal cross-sectional area and more focused on rectangular nozzles. Besides, the influence of initial temperature (110–130 °C) and pressure (6–16 bar) was also taken into account. A high-speed camera was used to record the external morphological characteristics of the superheated liquid jets released from the nozzles. The jet angle and half-width were extracted as the quantitative characterization of the external morphology by threshold processing algorithm. The results revealed that the rectangular nozzle jet (RNJ) has a different external morphology from the circular nozzle jet (CNJ) due to the presence of vortex and axis-switching phenomena. Aspect ratio plays an important role in the determination of external morphology of the RNJ and there is a critical aspect ratio AR = 3. In addition, this study also demonstrates that the rectangular nozzle has a different flashing mechanism from the circular nozzle, which is the underlying reason for the different external morphologies. In summary, compared to the traditional circular breach, rectangular breach has a significant promotion effect on the jet flashing, and the industrial medium released from the slit breach will have a greater impact range, resulting in more serious consequences of accidents.

Thermophysical Properties of Liquids in Not Fully Stable States—From the First Steps to the Current Trends

The present article marks the 95th anniversary of the birth of Vladimir P. Skripov, author of the classic study of superheated and supercooled liquids. It presents a discussion based on the early work carried out by Skripov and his research team in Ekaterinburg during the 1950s and 1960s. Due to their pioneering nature, these works laid the foundation for the study of metastable liquid states. For various reasons, although they remain relevant to this day, these groundbreaking works remain unknown to most non-Russian-speaking readers. As well as elucidating the behavior of the heat capacity of a solution in the liquid–liquid critical region, the presented research also concerns the characteristic features of light scattering and free-convective heat transfer in the liquid–vapor critical region of a one-component system, discussing two options for the position of the superheated liquid spinodal on the phase diagram of water, including the area of supercooled states and negative pressures. The issues involved in the discussion are united by the fluctuating nature of such phenomena. Indeed, the very possibility of their experimental study is due to a significant increase in the scale of fluctuations of the corresponding quantities when approaching the critical point or spinodal. The ongoing development of the approaches proposed in these papers for solving contemporary problems in the thermophysics of superheated liquids is discussed.