Liquid Fraction Profile Research Articles

Implementation of All-Sky Assimilation of Microwave Humidity Sounding Channels in Environment Canada’s Global Deterministic Weather Prediction System

Abstract Cloud-affected microwave humidity sounding radiances were excluded from assimilation in the hybrid four-dimensional ensemble–variational (4D-EnVar) system of the Global Deterministic Prediction System (GDPS) at Environment and Climate Change Canada (ECCC). This was due to the inability of the current radiative transfer model to consider the scattering effect from frozen hydrometeors at these frequencies. In addition to upgrading the observation operator to RTTOV-SCATT, quality control, bias correction, and 4D-EnVar assimilation components are modified to perform all-sky assimilation of Microwave Humidity Sounder (MHS) channel 2–5 observations over ocean in the GDPS. The input profiles to RTTOV-SCATT are extended to include liquid cloud, ice cloud, and cloud fraction profiles for the simulation and assimilation of MHS observations over water. There is a maximum (35%) increase in the number of channel 2 assimilated MHS observations with smaller increases for channels 3–5 in the all-sky experiment compared to the clear-sky experiment, mostly because of newly assimilated cloud-affected observations. The standard deviation (stddev) of difference between the observed global positioning system radio occultation (GPSRO) refractivity observations and the corresponding simulated values using the background state was reduced in the lower troposphere below 9 km in the all-sky experiment. Verifications of forecasts against the radiosonde observations show statistically significant reductions of 1% in the stddev of error for geopotential height, temperature, and horizontal wind for the all-sky experiment between 72- and 120-h forecast ranges in the troposphere in the Northern Hemisphere domain. Verifications of forecasts against ECMWF analyses also show small improvements in the zonal mean of stddev of error for temperature and horizontal wind for the all-sky experiment between 72- and 120-h forecast ranges. This work was planned for operational implementation in the GDPS in fall 2023.

Quasistatic model for foam fractionation

A simple model is presented for foam fractionation. The basis of the model is that the liquid fraction profile across the foam column is known quasistatically at any instant in time, and only varies gradually as the foam column height itself varies. Using suitable boundary conditions, the model provides a relation between liquid flux through the foam column and instantaneous foam column height. The flux of surface active material through the column can then also be determined. The model makes it possible to explore how design and operational parameters of a fractionation system influence performance. Indeed the model clarifies that tall columns enrich surfactant, but high velocities of air through the column are detrimental to enrichment. Having larger bubbles in the column helps enrichment though, despite reducing specific surface area and thereby despite reducing the total amount of surface active material adsorbed.

Incorporation of phase change materials in fire protective clothing considering the presence of water

When firefighters face a heat exposure, free water may be present in the fire protective clothing (FPC). Recently, the incorporation of Phase Change Materials (PCMs) into FPC has shown great promise to increase thermal performance when in the dry state. However, the presence of water in firefighting garments is expected and how this alters the thermal behavior of a PCM FPC assembly still remains to be discussed in the literature. Hence, this study concerns the effect of free water presence in the outer shell and/or thermal inner of a PCM FPC assembly consisting of 3 layers. A new mathematical model is proposed where the PCM is assumed to be incorporated in the thermal inner. A numerical analysis is performed where PCM textile latent heat, water distribution, and heat flux intensity are varied. Skin temperature, skin heat flux, and PCM liquid fraction profiles are obtained along with second-degree burn times to measure thermal performance. It is found that steam condensation at the skin reduces PCM liquid fraction at second-degree burn time, when compared to the dry case. This study tends to shine a light on the importance of considering moisture management in PCM FPC assemblies so as to promote maximum PCM efficiency.

Effects of mold electromagnetic stirring on heat transfer, species transfer and solidification characteristics of continuous casting round billet

In this study, the temperature distribution, species transfer, and solidification behavior in round billet continuous casting with mold electromagnetic stirring (M-EMS) was numerically investigated. The joule heat induced by the M-EMS and the liquid fraction profiles in the mushy zone were observed, whereby it was found that increasing current intensity caused further increase in electromagnetic force, which reduced the impact depth of liquid steel while accelerating the dissipation of superheat. The high liquid fraction in the mushy zone at the exit of the secondary cooling zone were 68.1% (case 1) and 77.1% (case 6). The central carbon contents of the round billets were 0.337 wt% (case 1) and 0.335 wt% (case 6). Moreover, the proportion of solidification microstructure and secondary dendrite arm spacing of the round billet samples were compared, which revealed that increasing the current intensity, casting speed, and cooling intensity, were all conducive to improving the uniformity of carbon distribution and compactness of the solidification structure.

Phase Change Material numerical simulation: enthalpy-porosity model validation against liquid fraction data from an X-ray computed tomography measurement/system

ABSTRACT Nowadays, Latent Thermal Energy Storage systems (LTESs) are becoming the key enabling technology for the achievement of the 2050 EU targets on energy savings and CO2 emission reduction. LTESs are based on Phase Change Materials (PCMs), which, during the liquid-solid phase change, can store and release large amount of thermal energy compared to sensible systems. Several studies have already been conducted to properly design LTESs based on PCMs and many of those aimed at developing reliable numerical tools. The main approach to model the phase change with a Computational Fluid Dynamics (CFD) approach is the enthalpy-porosity method, which has already been successfully validated in several articles, especially against the average PCM temperature. However, due to the experimental complexity, the liquid fraction evolution is hard to be measured and monitored and only symmetrical systems could have been tested so far. X-ray Computed Tomography (CT) is a strong and reliable tool to experimentally evaluate the liquid fraction profile during either the melting or solidification process in real geometries and is extremely useful to validate the numerical models. In the present study, a first attempt to combine the described experimental-numerical approach is proposed: an enthalpy-porosity model was developed and validated against liquid fraction data from a computed tomography system. The liquid fraction profile of an ice cylinder melting at ambient temperature was measured using the CT and then compared against the numerical results. The results show the promising capabilities of the proposed methodology.

Phase Change Material numerical simulation: enthalpy-porosity model validation against liquid fraction data from a computed tomograph

Nowadays, Latent Thermal Energy Storage systems (LTESs) are becoming the key enabling technology for the achievement of the 2050 EU targets on energy savings and CO2 emission reduction. LTESs are based on Phase Change Materials (PCMs), which, during the liquid-solid phase change, can store and release a great amount of thermal energy compared to sensible systems. Several studies have already been conducted to properly design LTESs based on PCMs and many of those aimed at developing reliable numerical tools. The main way to model the phase change with a CFD approach is through the use of the enthalpyporosity method, which has already been successfully validated in several articles, especially against the average PCM temperature. However, due to the experimental complexity, the liquid fraction evolution is hard to be measured and monitored and only symmetrical systems could have been tested so far. Computed Tomography (CT) can become a strong and reliable tool to experimentally evaluate the liquid fraction profile during either the melting, and solidification process in real geometries becoming extremely useful to validate the numerical models. In the present study, a first attempt to combine the described experimental-numerical approach is proposed: an enthalpy-porosity model was developed and validated against liquid fraction data from a computed tomography system. The liquid fraction profile of an ice cylinder melting at ambient temperature was measured using the CT and then compared against the numerical results. The results show the promising capabilities of the proposed method.

Dynamics of phase change of gallium under magnetic field and thermocapillary effects under variable gravity conditions

We have numerically investigated the melting and solidification process of a low melting temperature metallic phase change material, gallium, in a semi-circular enclosure with a hot circumferential wall under the influence of thermocapillarity and externally applied uniform magnetic field for different gravity conditions. The governing equations coupled with the enthalpy porosity method are solved to predict the effects of applied magnetic field direction (0 ≤ θ ≤ 90°), and strength (0 ≤ Ha ≤ 125), Rayleigh number (Ra = 4.656 × 102, 4.656 × 104, 1 × 105, 1 × 10⁶), Marangoni number (Ma = -1.44 × 103, −5 × 103 and −1 × 104) and gravity conditions (0.05g, 0.25g, 0.5g and 1g) on the velocity, temperature and liquid fraction profiles. The predictions of the developed numerical models are compared with the experimental and numerical data reported in the literature and found to be in good agreement. The results reveal that the surface tension gradient driven convection significantly enhances the melting process under the microgravity condition without the magnetic field. Fluctuating behaviour of transient average Nusselt number under normal gravity conditions observed during melting of gallium in the presence of thermocapillary and natural convection is reduced by applying the magnetic field. The complete gallium melting time is increased by 5.48% for the change in Hartmann number from 0 to 25 applied at θ = 45°. The direction of the applied magnetic field marginally increases the complete melting time for θ ≥ 75° and insignificantly affects the complete solidification time. The increase in Rayleigh and Marangoni numbers considerably alters fluid flow patterns and the temperature field.

Solidification Enhancement in a Triple-Tube Latent Heat Energy Storage System Using Twisted Fins

This work evaluates the influence of combining twisted fins in a triple-tube heat exchanger utilised for latent heat thermal energy storage (LHTES) in three-dimensional numerical simulation and comparing the outcome with the cases of the straight fins and no fins. The phase change material (PCM) is in the annulus between the inner and the outer tube, these tubes include a cold fluid that flows in the counter current path, to solidify the PCM and release the heat storage energy. The performance of the unit was assessed based on the liquid fraction and temperature profiles as well as solidification and the energy storage rate. This study aims to find suitable and efficient fins number and the optimum values of the Re and the inlet temperature of the heat transfer fluid. The outcomes stated the benefits of using twisted fins related to those cases of straight fins and the no-fins. The impact of multi-twisted fins was also considered to detect their influences on the solidification process. The outcomes reveal that the operation of four twisted fins decreased the solidification time by 12.7% and 22.9% compared with four straight fins and the no-fins cases, respectively. Four twisted fins improved the discharging rate by 12.4% and 22.8% compared with the cases of four straight fins and no-fins, respectively. Besides, by reducing the fins’ number from six to four and two, the solidification time reduces by 11.9% and 25.6%, respectively. The current work shows the impacts of innovative designs of fins in the LHTES to produce novel inventions for commercialisation, besides saving the power grid.

Numerical analysis of nanomaterial-based sustainable latent heat thermal energy storage system by improving thermal characteristics of phase change material.

Thermal energy conversion and storage plays a vital role in numerous sectors like industrial processing, residential and mass cooking processes, thermal management in buildings, chemical heating, and drying applications. It will also useful in waste heat recovery operations in industrial/thermal power stations. The effect of Al2O3 nanoparticle volume fraction (0%, 2%, and 5%) in a paraffin phase change material (PCM) and heater location (Bottom and Sidewall) in a 2D square thermal energy storage system have been numerically analyzed in this study. Transient thermal analysis has been carried out in ANSYS Fluent R18.1 for 500, 1000, and 3000 s. Laminar flow conditions with an enthalpy porosity model are used to study the solidification and melting behavior of nano-PCM. A Grid independence test has been conducted and selected an optimum number of elements as 115538. The results revealed that the addition of nanoparticles in PCM improves its thermal characteristics. The variation of liquid fraction and temperature profile with time has been recorded, and this is due to Rayleigh-Benard convection. At a given time, the melting rate increases with an increase in nanoparticle concentration up to 2% insertion after that the melting fraction reduces for both bottom wall and sidewall heating. This is mainly due to viscous domination with the increase in physical characteristics like density and viscosity of the fluid. Also, the melting rate in the case of sidewall heating augmented more than the bottom wall heating due to negligible buoyancy effects in former than later. The outcome of this analysis helps to find out the optimum volume concentration of nanoparticles to maximize the thermal energy storage applications.

Heat transfer enhancement in latent heat thermal energy storage using copper foams with varying porosity

Latent Heat Thermal Energy Storage (LHTES) is a promising solution to alleviate the supply-demand mismatch in the field of energy utilization. LHTES relies on high-quality phase change materials (PCMs) for high thermal capacity and narrow temperature variation. As an important class of PCMs, paraffin shows advantages of safe, non-corrosive, low-cost, but has limited applications because of relatively low thermal conductivity. The heat transfer performance of LHTES could be remarkably improved by embedding metal foams into PCMs. In the present work, water, paraffin (RT54HC) and copper foam were used to study the heat transfer enhancement, which acted as heat transfer fluid (HTF), PCM and heat transfer enhancer, respectively. The non-thermal-equilibrium energy model was applied in the numerical investigation. The liquid fraction profile was compared between pure PCM and composite PCM. The melting process, interface evolution and the average heat flux density under copper foams with different porosity changing modes were investigated. Results indicated that the incorporation of copper foams into PCM significantly increased the heat transfer performance of LHTES. The full melting time was reduced by 73.7% compared to that of pure PCM. The average heat flux density was improved from 96.38 W to 330.16 W. The optimal method was that dividing the copper foam into upper and lower parts, where the porosity increased separately along with the positive x-direction and positive y-direction. Compared with fixed porosity, the full melting time and average heat flux density were reduced by 6.78% and increased by 4.26%, respectively.

Reduced complexity solidification models

The solidification of a binary alloy, flowing between two cooled parallel plates is considered. A two-dimensional model for this system, involving the conservation equations of heat, solute, mass, and momentum, is constructed – the hi-fidelity model. Through a depth integration, a Reduced Complexity Model (RCM), in terms of one-dimensional advection equations, expressing the transient conservation of heat and solute, is obtained– the transient- RCM. For thermo-physical data, consistent with a dilute Al-Cu binary alloy, numerical predictions from the transient- RCM are shown to be in close agreement with predictions obtained from a numerical solution of the hi-fidelity model. The RCM is reduced further, to a model formed as a single initial value problem, predicting the steady-state axial temperature and liquid fraction profiles between the plates – the steady-RCM. Analysis and numerical solutions of the transient- RCM and steady-RCM, provide a means of modeling, evaluating, and illustrating the role of solid phase motion in the timing and pattern of a binary alloy solidification.

Modeling of water evaporation from a shrinking moist biomass slab subject to heating: Arrhenius approach versus equilibrium approach

Liquid moisture evaporation and pyrolysis of a biomass fuel slab subject to heating were computationally investigated in a one-dimensional domain where the fuel shrinkage was accounted for. The evaporation dynamics was separately represented by equilibrium and Arrhenius models. The equilibrium model describes evaporation as a thermodynamic process whereas the Arrhenius model treats it as a chemical reaction. For calculations, Gpyro, a pyrolysis computational framework, was used after its source code was revised to include the equilibrium model. By default, Gpyro is only capable of operating with the Arrhenius model. In the present study, also, a continuum description of mass and energy conservation for a pyrolyzating, shrinking porous medium was provided in the form of integral-differential equations. Such a description in the previous Gpyro works was lacking for shrinking objects and the Gpyro documents only provided a numerically discretized equation form. Here, the approximations made to develop this form from the integral-differential equations were clarified. The model was validated against experimental data of cone calorimeter experiments. Two fuel moisture contents (FMC) of 26% and 100% (on dry basis) representing dead and living fuels, respectively, were examined. The living fuel is characterized by a high FMC although the difference between dead and living fuels is not limited to this parameter. The evaporation rate, liquid moisture mass fraction and temperature profiles obtained by using the equilibrium model exhibited abrupt changes at the evaporation front whereas those obtained by using the Arrhenius model showed a smooth behavior throughout the slab. The drying dynamics described by the equilibrium model was more consistent with the underlying physics of evaporation. The equilibrium model demonstrated a distinct evaporation front, did not result in evaporation below the normal boiling point of water and more accurately exhibited the impact of the initial FMC on the drying dynamics. Simulation results showed that the thermochemical evolution of living fuel was appreciably more sensitive to the evaporation model.

Liquid fraction profile in a liquid foam under an applied voltage

Liquid transport in a dry foam, a deformable porous material, in the presence of an applied electric field, is computed in the limits of rigid and mobile interfaces. The evolution of the liquid distribution is diffusive-like and significantly affected by the hydrodynamic boundary conditions.

Numerical Modeling of Heat and Specie Transfer in a Diffusion Dominated Continuum Model of Binary-Alloy Castings

A numerical modeling of diffusion-controlled heat and specie transfer using a source base method to determine evolution of liquid/solid fraction from energy equation both for constant densities in the phases and variable densities as a function of temperature and concentration was developed to predict macro-solute redistribution in binary alloy system. From the results, it is observed that there was a solute depleted zone near the chill surface and that, the source base method can be effectively implemented without the need for setting a large arbitrary value in determining the derivative of liquid fraction-temperature function . The cooling curve and the liquid volume fraction versus temperature profile shows a smooth transition from fully liquid to mushy zone and then to fully solid state, hence, adequate handling of the jump discontinuity was ensured. The liquid fraction-temperature relation outlined in this work is suitable for tracking the liquid/solid interface.

Solidification enhancement in a triplex-tube latent heat energy storage system using nanoparticles-metal foam combination

Thermal storage systems utilizing Phase Change Materials (PCMs) are known to exhibit slow thermal response. This is mainly due to the relatively low thermal conductivity of most PCMs used in the systems. Thus packing the PCMs in better performing containment vessels and/or employing heat transfer enhancement additives is required for improved performance of these systems. Nanoparticle-metal foam combination as a compound enhancement approach along with triplex-tube heat exchanger as a modified exchanger design were used in this study to improve the PCM solidification rate. A mathematical model based on the thermal equilibrium assumption which takes into account the non-Darcy effects of porous foam and the Brownian motion of nanoparticles was formulated and validated with previous related experimental studies. The influence of nanoparticle volume fraction and metal foam porosity on the evolution of the solid-liquid interfaces, distribution of isotherms, and liquid-fraction profile over the whole solidification process was studied. Results show that dispersing nanoparticles in the presence of metal foams results in total time saving up to 96% depending on foam structure and volumetric nanoparticle concentration.

Melting enhancement in triplex-tube latent heat energy storage system using nanoparticles-metal foam combination

Phase change material (PCM) energy storage systems have relatively low thermal conductivity values which greatly reduces the systems’ performance. In this study, a compound porous-foam/nanoparticles enhancement technique was used to significantly improve melting of a phase change material (PCM) in a triplex-tube heat exchanger applicable to liquid desiccant air-conditioning systems. A mathematical model that takes into account the non-Darcy effects of porous foam and Brownian motion of nanoparticles was formulated and validated with previous related experimental studies. The influence of nanoparticle volume fraction and metal foam porosity on the instantaneous evolution of the solid-liquid interfaces, distribution of isotherms, and liquid-fraction profile under different temperatures of the heat transfer fluid (HTF) were investigated. Results show that dispersing nanoparticles in the presence of metal foams results in melting time savings of up to 90% depending on the foam structure and volumetric nanoparticle concentration. Although the melting time decreases as the porosity decreases and/or volume fraction increases, high-porosity metal foam with low volume-fraction nanoparticles is recommended. This ensures minimal PCM volume reduction and promotes positive contribution of natural convection during the melting process.

Effect of volume expansion on the melting process’s thermal behavior

This paper presents a numerical model for melting of wax in a vertical cylinder. Two different approaches are investigated, one of them does not simulate the volumetric expansion of wax during the melting process, an average value of actual solid and liquid density was used as a model density for liquid and solid phase like most previous works made, and this is called in the present work as approach-I. The second model involves the volumetric expansion of wax during melting process into account by using the actual values of liquid and solid density and this model was remarked as approach-II. The numerical model has been verified through the comparison between its predicted results and those obtained from referenced experimental work. The results of the comparison show a good satisfaction between both results in terms of prediction of liquid fraction profile. Another comparison was conducted between the two different approaches to shed the light on the effect of wax expansion during the melting process. The comparison has been carried out at different heating boundary conditions. The comparison shows a significant difference between the results obtained from the two different approaches only at low Biot number.

A Nonisothermal Wellbore Model and Its Application in Well Testing

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper IPTC 18152, “A Nonisothermal Wellbore Model With Complex Structure and Its Application in Well Testing,” by Shiyi Zheng, SPE, London South Bank University, and Yiqun Zhang, SPE, Heriot-Watt University, prepared for the 2014 International Petroleum Technology Conference, Kuala Lumpur, 10–12 December. The paper has not been peer reviewed. Although the wellbore is in a nonisothermal environment, heat transfer between the fluid in the wellbore and the formation is often ignored and temperature is usually assumed constant in data interpretation, which will lead to misunderstanding of the pressure profile. In this work, wavelet transform and a nonlinear-regression-analysis method were used to study the relationships between downhole temperature, pressure, and flow rate. A nonisothermal wellbore model was established that is capable of predicting temperature, pressure, flow rate, and liquid-fraction profiles under multirate and multiphase production scenarios. Introduction In order to monitor the downhole production and injection conditions, as well as make decisions for well-performance optimization, the dynamic temperature data acquired from permanent downhole gauges (PDGs) and distributed-temperature sensors (DTSs) are often interpreted widely. In this paper, first, the relationships among bottomhole-pressure (BHP), -temperature (BHT), and flow-rate data were analyzed briefly by use of wavelet transform and nonlinear regression. Next, a nonisothermal wellbore model with complex structure was derived theoretically step by step. Then, the wellbore model was coupled with an existing reservoir model through BHT. After that, several synthetic cases were simulated to verify the wellbore model. Finally, on the basis of the coupled wellbore/ reservoir model, the transient temperature behavior during flowing and shut-down periods was drawn out for well-testing analysis and some typical thermodynamic parameters were estimated by use of a set of field data. BHT, BHP, and Flow-Rate Relationships It is worth noting that formation pressure and temperature emerged in many similar characteristics. First, temperature and pressure meet the same diffusion equation. Second, at the junction between formation and well, near-wellbore damage should be considered for pressure. At the same time, on the temperature side, heat loss should also be considered, located in the formation, casing, tubing, and cement. Third, wellbore storage is compared with heat-capacity coefficient in wells. Fourth, constant-pressure and impermeable boundaries have been set for pressure boundaries, but the temperature boundary is always regarded as infinite ground. Analyses of the measured PDG data show that the temperature can also be used to provide reservoir information.

냉각수 및 전기 가열 방식에 따른 요소수 해동 특성에 관한 수치해석 연구

A Urea-SCR(Selective Catalytic Reactor) system, which converts nitrogen oxides into nitrogen and water in the presence of a reducing agent, creates a major exhaust gas aftertreatment system for NOx reduction among other compounds. With regard to vehicle applications, a urea solution was chosen based on its eutectic composition of a 32.5  urea-water solution. An important advantage of this eutectic composition is that its melting point of -11.7 is sufficiently low to avoid solidification in cold °C environments. However, the storage tanks must be heated separately in case of low ambient temperature levels to ensure a sufficient amount of liquid is available during scheduled start ups. In this study, therefore, a numerical investigation of three-dimensional unsteady heating problems analyzed to understand the melting processes and heat transfer characteristics including liquid volume fraction, temperature distributions, and temperature profiles. The investigations were performed using Fluent 6.3 commercial software that modeled coolant and electric heater models based on a urea solution. It is shown that the melting performance with the electric heater is higher than a coolant heater and is more efficient. Corresponding Author, manykim@jbnu.ac.kr 2016 The Korean Society of Mechanical Engineers C

Drainage in a rising foam.

Rising foams created by continuously blowing gas into a surfactant solution are widely used in many technical processes, such as flotation. The prediction of the liquid fraction profile in such flowing foams is of particular importance since this parameter controls the stability and the rheology of the final product. Using drift flux analysis and recently developed semi-empirical expressions for foam permeability and osmotic pressure, we build a model predicting the liquid fraction profile as a function of height. The theoretical profiles are very different if the interfaces are considered as mobile or rigid, but all of our experimental profiles are described by the model with mobile interfaces. Even the systems with dodecanol are well known to behave as rigid in forced drainage experiments. This is because in rising foams the liquid fraction profile is fixed by the flux at the bottom of the foam. Here the foam is wet with higher permeability and the interfaces are not in equilibrium. These results demonstrate once again that it is not only the surfactant system that controls the mobility of the interface, but also the hydrodynamic problem under consideration. For example liquid flow through the foam during generation or in forced drainage is intrinsically different.