Bulk Liquid Temperature Research Articles

Effects of operating parameters on single-stage ultrasonic separation of ethanol from its aqueous solutions

The effects of operating parameters on separation of ethanol from its aqueous solutions using ultrasonic atomization were investigated in a single-stage process. With an experimental setup similar to those used in previous work, we measured the degree of enrichment and the combined molar collection rate of ethanol and water for a single combination of the ultrasound power and frequency at 126 combinations of bulk liquid depth, composition, and temperature; carrier-gas inlet/outlet elevation and flow rate; and collection temperature. Enrichment depends strongly on bulk liquid composition, reaching a maximum at an ethanol mole fraction below 0.1, with the maximum enrichment depending on bulk liquid depth and inlet/outlet elevation. The collection rate depends strongly on inlet/outlet elevation and bulk liquid pool depth, and for high ethanol mole fractions is nearly independent of bulk liquid composition. Enrichment and collection rate increase with increasing bulk liquid temperature and decreasing collection temperature. The fact that increasing the carrier-gas flow rate increases the collection rate and decreases enrichment is interpreted in terms of size-selective transport of drops from the ultrasonically-generated fountain where they are atomized, to the cold trap where they are collected. The results are discussed in terms of operating parameters, transport phenomena (including evaporation and gravitational settling of atomized drops), the ultrasonically-induced fountain, and previously reported drop-size distributions. The duration of the experiments, conducted in batch, was such that the results should be relevant to both batch and continuous-flow operation. The work provides guidance and critical data for process scale-up.

Nonequilibrium liquid-vapor interfaces: Linear and nonlinear descriptions.

While it is often assumed that liquid-vapor interfaces in nonequilibrium processes are in states of local thermodynamic equilibrium, this might not be the case for strong deviations from equilibrium. Clausius-Clapeyron equations for bulk properties yield a consistently defined temperature of the interface that is close to the liquid bulk temperature. The alternative interface temperature defined through the surface tension will be different for stronger nonequilibrium processes. Structural variables are introduced to extend the thermodynamic description of interfaces to a wider range of processes. Interfacial resistivities will depend on interface temperature as well as mass and heat flux through the interface.

Influence of liquid conductance on the temporal evolution of self-organization patterns in atmospheric pressure DC glow discharges

Self-Organized Patterns (SOPs) at plasma-liquid interface in atmospheric pressure plasma discharges refer to the formation of intricate and puzzling structures due to the interplay of electrodynamic and hydrodynamic processes. Studies conducted to date have shown that this phenomenon results in the formation of distinctive patterns such as circular ring, star, gear, dots, spikes, etc., and primarily depends on working gas, electrolyte type, gap distance, current, conductivity, etc. However, an adequate understanding of how these patterns change from one type to another is still not available. This study aims to elucidate the influence of initial liquid conductance (σ i ) on the temporal evolution of SOPs in liquid-anode discharges. The discharge was generated in a pin-to-liquid anode configuration at a constant helium (He) flow rate of 500 sccm and DC applied voltage of 6 kV at a gap distance of 12 mm. Through the gradual increment of σ i from 1.8 μS to 4820 μS, we observe that the trend in the evolution of SOPS takes place as solid discs, spikes, dots, rings, double rings, and stars. The continuous formation of reactive species onto the liquid anode in all conductive solutions results in a decrease in pH, an increase in bulk liquid temperature, and an increase in total dissolved solutes, and these have been confirmed through experimental measurements. Observations using optical emission spectroscopy show that the electrons at the plasma-liquid interface participate in the reduction of cations followed by their excitation & ionization due to which electron density as well as emissions from excited species (mainly hydroxyl radicals & excited nitrogen) decrease with time. Our investigation provides experimental evidence on the presence of cations at the plasma-liquid interface required for SOP formation.

Influence of molecular anisotropy and quadrupolar moment on evaporation

The molecular interactions of numerous real fluids, like argon, nitrogen, or carbon dioxide, are adequately described by the two-center Lennard-Jones plus quadrupole potential. Applying this model class in molecular dynamics simulations, evaporation is investigated systematically. The influence of the molecular anisotropy and quadrupole as well as the boundary conditions, i.e., bulk liquid temperature and evaporation magnitude, is reported. A method for specifying the evaporation magnitude in terms of hydrodynamic velocity is further developed for that purpose. Analyses show that the largest molar flux and energy flux occur for spherical molecules and that anisotropy and quadrupole influence several quantities. Depending on the bulk liquid temperature, the quadrupole predominantly affects the interface temperature, while the anisotropy of the molecule significantly influences the interface temperature as well as both molar and energy fluxes. In addition, the preferred average orientation of the molecules in the interface region is investigated. The evaporation coefficient is determined, and thermodynamic states traversed during the evaporation process are discussed.

Nonequilibrium Scattering/Evaporation Dynamics at the Gas-Liquid Interface: Wetted Wheels, Self-Assembled Monolayers, and Liquid Microjets.

ConspectusWe often teach or are taught in our freshman courses that there are three phases of matter─gas, liquid and solid─where the ordering reflects increasing complexity and strength of interaction between the molecular constituents. But arguably there is also a fascinating additional "phase" of matter associated with the microscopically thin interface (<10 molecules thick) between the gas and liquid, which is still poorly understood and yet plays a crucial role in fields ranging from chemistry of the marine boundary layer and atmospheric chemistry of aerosols to the passage of O2 and CO2 through alveolar sacs in our lungs. The work in this Account provides insights into three challenging new directions for the field, each embracing a rovibronically quantum-state-resolved perspective. Specifically, we exploit the powerful tools of chemical physics and laser spectroscopy to pose two fundamental questions. (i) At the microscopic level, do molecules in all internal quantum-states (e.g., vibrational, rotational, electronic) colliding with the interface "stick" with unit probability? (ii) Can reactive, scattering, and/or evaporating molecules at the gas-liquid interface avoid collisions with other species and thereby be observed in a truly "nascent" collision-free distribution of internal degrees of freedom? To help address these questions, we present studies in three different areas: (i) reactive scattering dynamics of F atoms with wetted-wheel gas-liquid interfaces, (ii) inelastic scattering of HCl from self-assembled monolayers (SAMs) via resonance-enhanced photoionization (REMPI)/velocity map imaging (VMI) methods, and (iii) quantum-state-resolved evaporation dynamics of NO at the gas-water interface. As a recurring theme, we find that molecular projectiles reactively, inelastically, or evaporatively scatter from the gas-liquid interface into internal quantum-state distributions substantially out of equilibrium with respect to the bulk liquid temperatures (TS). By detailed balance considerations, the data unambiguously indicate that even simple molecules exhibit rovibronic state dependences to how they "stick" to and eventually solvate into the gas-liquid interface. Such results serve to underscore the importance of quantum mechanics and nonequilibrium thermodynamics in energy transfer and chemical reactions at the gas-liquid interface. This nonequilibrium behavior may well make this rapidly emergent field of chemical dynamics at gas-liquid interfaces more complicated but even more interesting targets for further experimental/theoretical exploration.

An improved cavitation model with thermodynamic effect and multiple cavitation regimes

Mechanical feed pumps in organic Rankine cycle (ORC) power plants can suffer from cavitation to lose their normal feeding performance or even damage. Cavitation models for organic fluids in ORC systems are lacking presently. Hence, a new cavitation model with thermodynamic effect was proposed. Surface tension-controlled, inertia-controlled, intermediate and heat transfer-controlled cavitation regimes, and two key elements: vapour bubble growth rate and vapour bubble number density are included in the model. A known air or non-condensable gas concentration in the liquid was employed to determine cavitation nuclei number density. The model was coded in ANSYS CFX as user defined model and validated with cavitating flows of organic fluid R114 in a venturi, liquid nitrogen and liquid hydrogen on a tapered hydrofoil and warm water around a hydrofoil NACA 0015 in cavitation tunnels based on visualised cavity length. Two model constants, temperature depression, and minimal cavitation number were correlated to bulk liquid temperature, Reynolds number, and Jakob number. The temperature and pressure profiles of liquid nitrogen and hydrogen on hydrofoil surface were examined against the experimental data. The model was applied to simulate unsteady cavitating flows of organic fluid R245fa in a diaphragm pump. It was shown that the temperature depression and minimal cavitation number cannot be correlated to bulk liquid temperature, Reynolds number and Jakob number. Two model constants can be correlated fairly to Reynolds number. The model underestimates the thermodynamic effect by 43% for R114, 18.6% for liquid nitrogen and 32.6% for liquid hydrogen based on temperature depression. The predicted temperature and pressure profiles on hydrofoil surface agree with the experimental data for liquid nitrogen. The model can produce an expected curve of mean pump flow rate against net positive suction head available.

Mechanistic modelling of bubble growth in sodium pool boiling

This work presents a mechanistic model to simulate the growth of a sodium bubble from nucleation to departure in sodium pool boiling. A previously developed and validated heat transfer sub-model is coupled to a force balance sub-model to predict the growth rate and departure radius of a sodium bubble. The model accounts for the change in the contact angle of a bubble as it grows, and the shrinkage of the bubble base prior to departure. The developed model is used to quantify and analyse the heat transfer from different regions, i.e. the microlayer, the macrolayer, the thermal boundary layer and the bulk liquid surrounding the bubble. In addition, bubble growth rate and departure radius are calculated for different values of wall superheat, rate of change of contact angle and bulk liquid temperature. It is found that the departure radius of a sodium bubble is on the order of a few centimetres and the wall superheat has a significant influence on the shape of a sodium bubble at departure.

Heat transfer modelling of an isolated bubble in sodium pool boiling

Sodium tubular boiler receivers in concentrated solar thermal power plants are a viable option to provide near-isothermal heat for industrial applications. Accurately predicting the boiling behaviour in the receivers is imperative to improve the performance of these plants. A physics-based reduced-order bubble growth model is developed in this work to gain a fundamental understanding of the boiling process in the receiver. The model predicts the growth rate of an isolated bubble in a sodium pool based on heat transferred from the microlayer, the macrolayer, the thermal boundary layer and the bulk liquid surrounding the bubble. A transient 2D conduction equation is solved to model the cooling of the wall below the bubble due to evaporation of the microlayer and the macrolayer. The model is used to study the growth of a sodium bubble in a liquid pool and analyse the relative contribution of different heat transfer mechanisms to the growth process. It is found that the microlayer heat transfer is the dominant mechanism controlling bubble growth in sodium. Furthermore, a parametric study of the effect of wall superheat, contact angle and temperature of the bulk liquid on the bubble growth process in sodium shows that the bubble size increases with increasing superheat, contact angle and bulk liquid temperature.

Thermal imaging – A novel method for gas-liquid Interface conditions determination

We suggest monitoring of the interfacial mass transfer activity over the surface of the packing under distillation conditions by a thermal camera. Such a study should reveal zones with imperfect hydrodynamics and decreased mass-transfer intensity, enabling quantification of the fraction of the packing geometrical area, which is ineffective in the interfacial mass exchange.The objective of the present study is to validate that the temperature of a liquid surface measured by the camera is truly the temperature of the interface, which can substantially differ from the liquid bulk temperature under the non-zero heat and mass-transfer conditions. Validation experiments are performed using a water-air system with zero net mass transfer across the interface and non-zero heat transfer induced by cooling of the liquid phase and heating of the gas phase. The interface temperature is indirectly determined from the partial pressure of water in the air above the liquid level.The results show that the temperature reading of the thermal camera is up to 92% determined by the temperature of the interface. Its measurement opens the possibility of determining not only effective interfacial area but also local distribution of the mass-transfer and heat-transfer resistances between the phases.

Natural and mixed convection in a vertical water-flow chamber in the presence of solar radiation

Natural and mixed convection in a vertical plane channel in the presence of solar radiation are analytically studied. The physical problem under consideration simulates water flow and heat transfer in a chamber with transparent rigid boundaries exposed to solar radiation. The intensity of the volumetric heat source across the channel declines exponentially as described by the Beer–Lambert law for light absorption in near-infrared and visible spectra. The flows are assumed laminar and fully-developed. The properties of the liquid are considered constant except for the variation of density defining the Boussinesq term in the momentum equation. For both natural and mixed convection it is possible to observe one, two or no reverse flows and the conditions for the existence of reverse flows are derived. Heat fluxes across the chamber as well as the power outlet and the bulk liquid temperature are calculated for values of the Reynolds number between zero and 500 and the Prandtl number for water. It is shown that the solar heat source in combination with the liquid heating from the chamber walls has a pronounced effect on the flow behavior and the heat transfer.

A full mechanistic and kinetics analysis of carbon tetrachloride (CCl4) sono-conversion: Liquid temperature effect

In this study, a model of CCl4 sono-pyrolysis inside an acoustic bubble is used to provide a novel mechanistic and kinetics study of CCl4 conversion. The impact of fluid temperature (10–50 °C) on CCl4 conversion and the resulted products is illustrated for various aqueous CCl4 concentrations and acoustic intensities (0.7–1.5 W/cm2). With a concentration less than 3 × 10−3 M, 1 W/cm2 is sufficient for the complete degradation of CCl4 at 20 °C. However, at 10 °C, 1.5 W/cm2 is much than enough to degrade CCl4 completely, regardless of its concentration in solution. The generation of reactive chlorine species (RCS) increased proportionately with the temperature rise when the intensity was 0.7 W/cm2. In contrast, between 1 and 1.5 W/cm2, increasing the liquid temperature from 10° to 40 °C has a beneficial effect on the sonolytic activity of the cavity. However, this positive impact continues to be observed only for·OH radicals when the bulk liquid temperature is greater than 40 °C (the yield of RCS, H·, HCl, and HOCl is amortized). According to the simulation results, it was concluded that the rapid sono-degradation of nonvolatile pollutants in the presence of CCl4 was mainly due to the RCS and·OH radicals generated at the efficient bubble collapse.

Evaporation driven by conductive heat transport

Molecular dynamics simulations are conducted to investigate the evaporation of the truncated () and shifted Lennard–Jones fluid into vacuum. Evaporation is maintained under stationary conditions, while the bulk liquid temperature and the thermal driving force gradient are varied over wide ranges. It is found that the particle flux and the energy flux solely depend on the interface temperature. Both of these quantities are correlated to estimate their values for macroscopically large systems. The latter is analysed by a hydrodynamic energy balance, considering conductive heat transport by Fourier's law. Following the Hertz–Knudsen approach, the evaporation coefficient is determined and found to be in good agreement with literature data based on the kinetic equation for fluids and molecular dynamics.

Velocity distribution function of spontaneously evaporating atoms

Numerical solutions of the Enskog-Vlasov (EV) equation are used to determine the velocity distribution function of atoms spontaneously evaporating into near-vacuum conditions. It is found that an accurate approximation is provided by a half-Maxwellian including a drift velocity combined with different characteristic temperatures for the velocity components normal and parallel to the liquid-vapor interface. The drift velocity and the temperature anisotropy reduce as the liquid bulk temperature decreases but persist for relatively low temperatures corresponding to a vapor behaviour which is only slightly non-ideal. Deviations from the undrifted isotropic half-Maxwellian are shown to be consequences of collisions in the liquid-vapor interface which preferentially backscatter atoms with lower normal-velocity component.

On the mechanism responsible for unconventional thermal behaviour during freezing

Abstract

Mean-field kinetic theory approach to Langmuir evaporation of polyatomic liquids

The evaporation of polyatomic liquids into near-vacuum conditions is investigated by using the Enskog–Vlasov model. Molecules are approximated as classical rigid rotators, and the collisional energy exchanges between the translational and rotational degrees of freedom are dealt with by the Borgnakke–Larsen method. The distribution function of evaporated molecules and the evaporation coefficient are evaluated in a wide range of liquid bulk temperatures and inelastic collision fractions. It is found that the translational velocity distribution function is well approximated by a drifted bi-Maxwellian, while the rotational energy follows the Boltzmann distribution at a temperature that varies between the separation and the parallel temperatures as the inelastic collision fraction increases. The evaporation coefficient based on the separation temperature turns out to be independent of the inelastic collision fraction and only mildly dependent on the liquid bulk temperature.

Study on Forced Convective Heat Transfer of FC-72 in Vertical Small Tubes

Abstract This paper presents an experimental investigation of the forced convective heat transfer of FC-72 in vertical tubes at various velocities, inlet temperatures, and tube sizes. Exponentially escalating heat inputs were supplied to the small tubes with inner diameters of 1, 1.8, and 2.8 mm and effective heated lengths between 30.1 and 50.2 mm. The exponential periods of heat input range from 6.4 to 15.5 s. The experimental data suggest that the convective heat transfer coefficients increase with an increase in flow velocity and µ/µw (refers to the viscosity evaluated at the bulk liquid temperature over the liquid viscosity estimated at the tube inner surface temperature). When tube diameter and the ratio of effective heated length to inner diameter decrease, the convective heat transfer coefficients increase as well. The experimental data were nondimensionalized to explore the effect of Reynolds number (Re) on forced convection heat transfer coefficient. It was found that the Nusselt numbers (Nu) are influenced by the Re for d = 2.8 mm in the same pattern as the conventional correlations. However, the dependences of Nu on Re for d = 1 and 1.8 mm show different trends. It means that the conventional heat transfer correlations are inadequate to predict the forced convective heat transfer in minichannels. The experimental data for tubes with diameters of 1, 1.8, and 2.8 mm were well correlated separately. And, the data agree with the proposed correlations within ±15%.

Validation and Uncertainty Quantification for Two-Phase Natural Circulation Flows Using TRACE Code

The work presents validation of the TRAC/RELAP Advanced Computational Engine (TRACE) code for natural circulation two-phase flow in a vertical annulus. Natural circulation experiments were recently conducted for a vertical internally heated annulus at the Multiphase Thermo-Fluid Dynamics Laboratory at the University of Illinois. The experimental matrix consists of 107 experiments with system pressure in the range of 145 to 950 kPa and heat flux up to 275 kW/m2. Void fraction, gas velocity, and interfacial area concentration were measured in five axial locations along the test section with six measurements of bulk liquid temperature and pressure. To validate the capability of the TRACE code under natural circulation flow conditions, a complete model of the experimental facility was created and validated using forced convection and single-phase natural circulation data. Sensitivity and uncertainty quantification were performed. The sensitivity to important simulation parameters was studied using Sobol’s variance decomposition and the Morris screening method. The sensitivity of boundary conditions on void fraction measurement was investigated. The sensitivity study has shown significant differences in model sensitivity between different experimental conditions. With heat flux being the most influential parameter for high-pressure cases without flashing and pressure, temperature and heat flux have a combined strong effect in the case of low-pressure experiments when flashing occurs. Additionally, higher uncertainty in void fraction prediction was observed for experimental conditions at low pressure with flashing.

Comparison of interfacial heat transfer correlations for high-pressure subcooled boiling flows via CFD two-fluid model

Heat transfer processes using two-phase boiling flows are often found in the industry, due to the high-efficiency heat removal, with a minimum difference of temperature between the heated surface and fluid. Moreover, the use of computational fluid dynamics to solve safety issues related to nuclear reactors has increased rapidly, but a complete validation is still being carried out. Therefore, this study aims the assessment of different sub-models of the interfacial heat transfer coefficient which is used as a closure relation in the two-fluid multiphase model. As a manner to validate the numerical results, the set of experimental conditions of Bartolomei and Chanturiya (Therm Eng 14:123–128, 1967) were applied to an upwards flow in a circular channel, under high water saturation pressures. The interfacial sub-models were implemented into an axisymmetric simulation domain, using the Eulerian two-fluid approach. Three different saturation pressures and two uniform heat fluxes were considered in the simulation runs. Fixed mass flux and subcooled degree of 900 kg/m2 and 60 K were applied, respectively. A satisfactory agreement was achieved for the estimation of the heated wall temperature, the liquid bulk temperature and the onset of saturated boiling. Different heat transfer closure relations promoted different vapor volume fraction along the channel, indicating the importance of an adequate interfacial heat transfer correlation to predict the flow boiling phenomena.

Liquid depth effect on the acoustic generation of hydroxyl radical for large scale sonochemical reactors

Abstract Liquid depth (z) is one of the most critical factors that influence the sonochemical activity, particularly for large-scale sonoreactors. This factor is one of the missing links between lab-scale sonoreactors and industrial-scale sonoreactors. Herein, computer simulations of depth effect (z = 0–8 m) on the acoustic generation of free radicals were conducted at various parameters of frequency (355–1000 kHz), acoustic intensity at the source (In,0 = 1–5 W/cm2) and bulk liquid temperature (10–40 °C). The computations were made with and without taking into account the attenuation of the ultrasound wave to concretize the influence of this event on the overall impact of depth toward the chemical activity of imploding cavities. The production of free radicals at the collapse was found to be diminished with increasing depth up to 8 m. The ultrasound wave attenuation contributed substantially in the overall reductive event, particularly at higher z and frequency and lower intensity and liquid temperature. The overall reductive effect of depth was strongly operating conditions-dependent. It was more pronounced at higher frequency (1000 kHz) and lower acoustic intensity (1 W/cm2) and bulk liquid temperature (10 °C). Depending on cavitation conditions, the attenuation of the sound wave may suppress completely the production of free radicals at small depths. All these findings were interpreted and discussed through comparison with results of previous experimental observations. In conclusion, the present computation study may furnish important data for understanding cavitation process in big-scale sonoreactors, in which attenuation of the sound wave with depth could inhibit significantly the intensity of the sonochemical process.

Infrared analysis of the two phase flow in a single closed loop pulsating heat pipe

A Single Loop Pulsating Heat Pipe (SLPHP) filled at 60% vol. with pure ethanol, having an inner diameter of 2 mm, is designed with two sapphire tubes mounted between the evaporator and the condenser. Being the sapphire almost transparent in the infrared spectrum, such inserts allow simultaneous high-speed visualizations and infrared analysis of the fluid regimes. Two highly accurate pressure transducers measure the pressure at the two ends of one of the sapphire inserts. Three heating elements are controlled independently, in such a way to vary the heating distribution at the evaporator. It is found that particular heating distributions promote the slug/plug flow motion in a preferential direction, allowing to establish a self-sustained circulatory motion. It is demonstrated that a direct infrared visualization of the two-phase flow passing through the sapphire inserts is a valuable technique to measure the liquid slug bulk temperature after a proper calibration of the camera, with uncertainty of 1.5 °C (99.7% confidence level). Additionally, the fluid infrared visualization allows to appreciate the liquid film dynamics (wetting and dewetting phenomena) during the device operation, and to map the temperature gradients of liquid slugs thanks to the high-sensivity of the infrared measurements (0.05 K).