Inverse Solubility Research Articles

Long-term simulation of crystallization fouling in a forced circulation crystallizer

Most heat exchangers in wastewater treatment systems and the thermal desalination industry experience the deposition of unwanted materials on their surfaces. One of the primary causes is the supersaturation of salts with inverse solubility near the heat exchanger's heated surfaces. In this paper, a long-term simulation of the crystallization fouling of calcium carbonate by developing an efficient solver in the OpenFOAM software is proposed. The k-ω SST model was used to simulate turbulence, and the level-set model was adopted for high-precision and high-quality capturing of the fouling front inside the heat transfer tubes of a forced circulation crystallizer. The results demonstrated that the developed solver is a promising tool for accurately predicting moving boundary conjugate heat transfer. Upon validation of the results, the dynamic evolution of the fouling front and its sophisticated interactions with hydrodynamics were examined. The crystallization fouling was found to be under reaction control. Furthermore, the relatively slight supersaturation caused delayed front growth, which prolonged the fouling time to several months. Besides, findings demonstrated that the intensive competition between removal and deposition mechanisms at higher inlet velocities resulted in decreased asymptotic thermal resistance. Additionally, the velocity increase had a smaller impact on reducing the deposit's asymptotic resistance.

Mitigation of CaCO3 fouling on heat exchanger surface using green functionalized carbon nanotubes (GFCNT) coating

Deposition of mineral foulants on the heat exchanger surface increases the thermal resistance and shortens the operating service life of heat exchangers. The inverse solubility characteristics of some mineral salts in the cooling water cause intensive mineral fouling on heated heat exchanger surfaces. The formation of fouling deposits starts when mineral salts in water crystallize on the heated surface. In this study, a coating of MWCNT from the suspension of water, gum Arabic and MWCNT was applied on the surface of the heat exchanger to mitigate CaCO3 fouling. A 300 mgL−1 CaCO3 supersaturated solution was prepared and used for the foulant deposition on the heat transfer surfaces and analysis. The Field Emission Scanning Electron Microscopy (FESEM) was used for the investigation of CaCO3 depositions on the heat exchanger surface, its surface morphology, and develop correlation with the crystal growth, morphology and the coating introduced inhibition effect on fouling. The results revealed that the CaCO3 crystal formation can be considerably retarded using MWCNT coating layer as a fouling mitigation approach.

Crystallization fouling of turbo-structured tubes during nucleate pool boiling

The superiority of enhanced boiling on structured heat transfer surfaces over plain surfaces is based on excessive bubble generation and behavior as well as the latent heat of evaporation. The generated bubbles with turbulence of large scale would give rise to profoundly higher heat transfer coefficients. Meanwhile, the very same reasons of bubble formation and behavior may lead to accelerate the fouling of these surfaces for aqueous solutions with inverse solubility. The present study characterizes the fouling behaviour of turbo structured tubes under nucleate pool boiling. Several experiments were conducted for heat fluxes ranging from 50 to 250 kW/m2 and a concentration of 1.6 g/L of CaSO4 aqueous solution. The investigated structured tubes were re-entrant cavity tubes referred to as the Turbo-B type which were compared with plain tubes and low finned tubes of different fin heights and densities. Of these investigated tubes, the Turbo-B showed preferable anti-fouling behaviour. Based on a comparison of anti-fouling performance of the test tubes, the Turbo-B reduced fouling resistance up to ∼27 % and ∼83 % than the finned test tubes of 19 fpi (fins per inch) and 40 fpi, respectively. Most interestingly, the deposition of turbo tubes was of powdery and frail structure which could easily be cleaned. Moreover, the deposit was only formed on top of these tubes while no sign of deposition was observed within the cavities. The deposit structure for plain tubes, on the contrary, was a hard, thick and homogeneous layer under similar operating conditions as those for the turbo tubes.

Experimental investigation of heat transfer characteristics of polyethylene glycol (PEG) based quench media for industrial heat treatment

Aqueous polymer quenchants are now increasingly used in the quench hardening of steels. The inverse solubility property of polymer media leads to polymer film encapsulation of the quenched component, followed by an instantaneous rupture of the polymer film. The film boiling stage is absent, thus improving heat transfer uniformity. In the present investigation, the effect of molecular weight of Polyethylene glycol (PEG) on heat transfer characteristics of PEG/water quenchants with concentrations of 5, 10, and 20 vol% was studied. The cooling curve analysis is performed to assess the cooling characteristics. Spatially dependent surface heat flux transients are estimated using the inverse heat conduction method. The rewetting kinematics is analyzed by videography and acoustic analysis of polymer film rupture during quenching. The results indicated that an increase in the molecular weight of PEG from 200 to 6000 changed the rewetting kinematics from a local wetting front movement to an instantaneous rupture of the polymer film. The change in the rewetting kinematics is reflected in the surface heat flux, indicating an increased uniformity of heat transfer. The film rupture acoustics showed that the polymer film's instantaneous breakup had a higher sound intensity than the one showing wetting front motion.

Intrinsic Phase Stability and Inherent Bandgap of Formamidinium Lead Triiodide Perovskite Single Crystals.

Understanding the intrinsic phase stability and inherent band gap of formamidinium lead triiodide (FAPbI3 ) perovskites is crucial to further improve the performance of perovskite solar cells (PSCs). Herein, we explored the α- to δ-phase transition and band gap of FAPbI3 single crystals grown by an inverse temperature solubility method. We found that the residual γ-butyrolactone solvents in the inner empty space of the FAPbI3 single crystal accelerate the phase transition at kinetics. By adopting 2-methoxyethanol as the solvent, over 2000 h of stable α-FAPbI3 crystals could be acquired. This proves that although FAPbI3 is regarded as unstable at thermodynamics, it could own excellent kinetic stability without any doping or additives because of the slow solid to solid phase transition instead of the fast phase transition assisted by the solvents. Furthermore, we revealed that the bulk FAPbI3 single crystal with a size above 100 μm can have an inherent band gap of 1.41 eV. Thus, our work provides key scientific guidance for high-performance FAPbI3 -based PSCs.

Intrinsic Phase Stability and Inherent Bandgap of Formamidinium Lead Triiodide Perovskite Single Crystals

AbstractUnderstanding the intrinsic phase stability and inherent band gap of formamidinium lead triiodide (FAPbI3) perovskites is crucial to further improve the performance of perovskite solar cells (PSCs). Herein, we explored the α‐ to δ‐phase transition and band gap of FAPbI3 single crystals grown by an inverse temperature solubility method. We found that the residual γ‐butyrolactone solvents in the inner empty space of the FAPbI3 single crystal accelerate the phase transition at kinetics. By adopting 2‐methoxyethanol as the solvent, over 2000 h of stable α‐FAPbI3 crystals could be acquired. This proves that although FAPbI3 is regarded as unstable at thermodynamics, it could own excellent kinetic stability without any doping or additives because of the slow solid to solid phase transition instead of the fast phase transition assisted by the solvents. Furthermore, we revealed that the bulk FAPbI3 single crystal with a size above 100 μm can have an inherent band gap of 1.41 eV. Thus, our work provides key scientific guidance for high‐performance FAPbI3‐based PSCs.

Analysis of Transient Boiling Processes during Steel Quenching in Water PAG Solutions to Decrease Distortion

The paper discusses results of testing standard cylindrical probe 12.5 mm diameter in water polymer solutions which was additionally instrumented with a surface thermocouple. It is shown that central thermocouple cannot depict many physical phenomena taking place during quenching in polymer solutions such as shoulder formation, self- regulated thermal process establishing, surface temperature transient from film boiling to nucleate boiling process. Moreover, it is shown that experimental data depicted by central thermocouple cannot be used for solving inverse problem to analyze quenching process in liquid media. Along with analyzing film and nucleate boiling processes during quenching, the paper discusses the possibility of quality quench process control via using sonar system. It is established an equation for evaluating duration of transient nucleate boiling process. As an example, the cooling characteristics of fresh and old polyalkylene glycol (PAG) polymer solutions are analyzed. It is shown that with passing time the critical heat flux density of polymer decreases and inverse solubility effect disappears. That is while the method and apparatus were developed to control in industrial condition the quality of quenched steel parts during hardening in liquid media.

Intense Quench Process in Slow Agitated Water Salt and Polymer Solutions

In the paper it is shown that quenching in slow agitated water salt solution of optimal concentration and in low concentration of inverse solubility polymers is intensive quenching creating maximal temperature gradients at the beginning of cooling. The evidence to support such idea were collected by analyzing quenching process in liquid media where any film boiling process was completely absent. In this case, surface temperature at the beginning of cooling drops closely to saturations temperature of a liquid within the interval 1–2 seconds, independently on nature of water solution, and then during transient nucleate boiling process maintains at the level of boiling point of a liquid which is often called self–regulated thermal process. The computer modeling of such cooling processes provided Kondrat’ev numbered Kn which are strongly linear function of time. At the beginning of cooling Kondrat’ev number is almost equal to 1 while average Kondrat’ev number Kn≥0.8. According to US Patent, intensive quenching starts when Kn=0.8. Based on achieved results, it is possible to perform intensive quenching in slow agitated of low concentration water salt and polymer solutions, usually initiated by hydrodynamic emitters. Along with liquid agitation, emitters generate resonance wave effect which destroys film boiling processes making cooling very uniform and intensive. The proposed IQ process works perfectly when martensite starts temperature Ms>Ts. If saturation temperature Ts≥Ms, intensive austempering process via cold liquids can be successfully performed to replace slow cooling of molten salts and alkalis by intensive quenching in liquid media.

Highly In-Plane Polarization-Sensitive Photodetection in CsPbBr3 Single Crystal

The fully inorganic perovskite lead cesium bromide single crystal (CsPbBr3 SC) is considered as an excellent candidate semiconductor for photodetectors because of its superior humidity resistance, thermal stability, and light stability compared with organic-inorganic hybrid perovskites as well as its photoelectric properties such as large light absorption coefficient and ultralong carrier migration distance. In this Letter, we utilize the inverse temperature solubility of CsPbBr3 in ternary solvents to grow large-sized CsPbBr3 SCs. By the use of the (101) plane, CsPbBr3 SC-based photodetectors are fabricated, which exhibit excellent polarized light response characteristics. The photocurrent relies on the polarization angle in a sinusoidal fashion and shows strong anisotropic optoelectronic properties. The photodetection performance perpendicular to the y axis is significantly higher than that parallel to the y axis, and the dichroic ratio under 405 nm illumination at a bias voltage of 1 V reaches 2.65. The experimental results are consistent with the results of first-principles calculations.

Mechanism of Film Boiling Elimination and IQ Process Design for Hardening Steel in Low Concentration of Water Polymer Solutions

The paper considers a mechanism of the elimination of the film boiling process during intensive quenching (IQ) of steel parts in water polymer solutions of low concentration. The use of the IQ process results in improvement of material mechanical properties and steel part performance characteristics. Evaluation of ways of eliminating of the film boiling process using a modern physics point of view allows significant improvement of the IQ equipment making it less costly and more efficient. All of this cardinally simplifies the implementation of the IQ technology in heat treat practice. The paper shows how creation of a thin insulating surface layer during quenching of steel parts in low concentration of inverse solubility polymers results in eliminating of film boiling processes that makes the quench process intensive. Historically in heat treating industry, an effective heat transfer coefficient was widely used for evaluating of the nucleate boiling process. And quenching during the nucleate boiling mode of heat transfer was considered as slow cooling.

Uniform and Intense Cooling During Hardening Steel in Low Concentration of Water Polymer Solutions

The possibility of decreasing water polymer concentration, decreasing alloy elements in steel, decreasing distortion of steel parts, and increasing service life of machine components and tools during quenching is widely discussed in this paper based on achievements of modern physics. Instead of quenching alloy steel in oils or high concentration of water polymer solutions, the accelerated quench process of optimal hardenability steel in water low concentration of inverse solubility polymers is proposed. Physics of the new approach and new technologies is explained by the author. The creation of a thin polymeric insulating layer during quenching steel in low concentration of inverse solubility polymers decreases initial heat flux density below its critical value that is reason for absence the film boiling process. Due to this fact, full film boiling during quenching is completely absent allowing use optimal hardenability steel instead of alloy steels containing costly alloy elements. Accelerated cooling provided by low concentration of water polymer solution results in creation of high surface compression residual stress, and super strengthening of material that in turn increases service life of machine components and tools. It is underlined in the paper that along with the use of a thin polymeric insulating layer, the resonance effect can be used for destroying the full film boiling process based on implementation different kinds of hydrodynamic emitters. The proposed new technology saves materials, increases service life of steel parts, and improves environment condition in heat treating industry. The patented technologies and processes can be used by engineers and scientists. and can bring great benefits if widely implemented in the practice.

Inverse solubility of chitin/chitosan in aqueous alkali solvents at low temperature

The low-temperature dissolving mechanism of chitin/chitosan in the alkali (LiOH, NaOH and KOH) aqueous solvents has not been well established yet. As revealed by our XRD and NMR methods, the prepared deacetylated chitins can be categorized as chitin (DA = 0.94–0.74), chitosan I (DA = 0.53–0.25) and chitosan II (DA < 0.25). Aqueous alkali exhibits fully different dissolving power in the above three regions, i.e., KOH > NaOH >> LiOH for chitin, KOH ≈ LiOH ≈ NaOH for chitosan I, and inverse LiOH >> KOH > NaOH for chitosan II. While in the two-alkali mixed solvent, NaOH or KOH can destroy the interaction of LiOH with D9 (chitosan II region) in the order of NaOH >> KOH, but LiOH cannot destroy the interaction of KOH with raw chitin. The varied solubility of chitin/chitosan in alkali solvent is suggested to be from the cation’s preferential interaction rather than OH− ion and low temperature.

Synthesis of Well-Defined Pyrrolidone-Based Homopolymers and Stimulus-Responsive Diblock Copolymers via RAFT Aqueous Solution Polymerization of 2-(N-Acryloyloxy)ethylpyrrolidone.

Poly(N-vinylpyrrolidone) (PNVP) is a well-known, highly polar, nonionic water-soluble polymer. However, N-vinylpyrrolidone (NVP) usually exhibits strongly non-ideal behavior when copolymerized with methacrylic or styrenic monomers. Moreover, NVP is not particularly well-controlled under living radical polymerization conditions. For these reasons, alternative pyrrolidone-based monomers have been investigated. For example, the reversible addition–fragmentation chain transfer (RAFT) polymerization of 2-(N-methacryloyloxy)ethylpyrrolidone (NMEP) has been recently investigated using various polymerization formulations. However, PNMEP homopolymers are significantly less hydrophilic than PNVP and exhibit inverse temperature solubility in aqueous solution. In the present work, we studied the RAFT aqueous solution polymerization of 2-(N-acryloyloxy)ethylpyrrolidone (NAEP) using either AIBN at 70 °C or a low-temperature redox initiator at 30 °C. PNAEP homopolymers are obtained in high yield (>99%) with good control (Mw/Mn < 1.20) for target degrees of polymerization (DP) of up to 400 using the latter initiator, which produced relatively fast rates of polymerization. However, targeting DPs above 400 led to lower NAEP conversions and broader molecular weight distributions. 2-Hydroxyethyl acrylate (HEA) and oligo(ethylene glycol) methyl ether acrylate (OEGA) were chain-extended using a PNAEPx macro-CTA via RAFT aqueous solution polymerization, yielding double-hydrophilic acrylic diblock copolymers with high conversions (>99%) and good control (Mw/Mn < 1.31). In addition, a PNAEP95 macro-CTA was chain-extended via RAFT aqueous solution polymerization of N-isopropylacrylamide (NIPAM) at 22 °C. Dynamic light scattering (DLS) analysis indicated that heating above the lower critical solution temperature of PNIPAM led to so-called “anomalous micellization” at 35 °C and the formation of near-monodisperse spherical micelles at 40 °C. Finally, 2-(diethylamino)ethyl methacrylate (DEA) was polymerized using an N-morpholine-functionalized trithiocarbonate-based RAFT chain transfer agent and subsequently chain-extended using NAEP to form a novel pH-responsive diblock copolymer. Above the pKa of PDEA (∼7.3), DLS and 1H NMR studies indicated the formation of well-defined PDEA-core spherical micelles.

RESEARCH ON USE OF LOW CONCENTRATION INVERSE SOLUBILITY POLYMERS IN WATER FOR HARDENING MACHINE COMPONENTS AND TOOLS

There is an optimal water concentration of inverse solubility polymers ( 1 %) where in many cases film boiling is absent. Based on accurate experimental data of French and data of authors, it was shown that during quenching from 875 oC in cold water solutions of optimal concentration film boiling is completely absent for those steel parts initial heat flux densities of which are below critical value. It is established that initial heat flux density decreases with increase sizes of tested samples. Initial process of quenching (formation of boundary boiling layer), which makes further history of cooling, is not investigated deeply and widely yet enough. When film boiling is absent, mathematical model includes only transient nucleate boiling process and convection. In this case, cooling time within the transient nucleate boiling process can be calculated using average effective Kondratjev numbers Kn. They were evaluated for inverse solubility polymers depending on their concentration and sizes of tested samples. As a result, an improved technology of hardening large gears and bearing rings is proposed by authors. Its essence consists in interruption of accelerated cooling or turning off agitation of quenchant when dissolving of surface polymeric layer starts. Examples of performing improved technology are provided by authors. Developments can be used by engineers to switch from carburized large gears quenched in oil to gears made of optimal hardenability steel and quenched in water solutions of optimal concentration.

COOLING INTENSITY OF INVERSE SOLUBILITY POLYALKYLENE GLYKOL POLYMERS AND SOME RESULTS OF INVESTIGATIONS FOCUSED ON MINIMIZING DISTORTION OF METAL COMPONENTS

Poly(Alkylene Glycol) polymers of inverse solubility (PAG) provide ideal uniform cooling for minimizing distortion and preventing crack formation during hardening machine components and tools. However, in spite of ideal cooling, from time to time, a big distortion takes place during hardening process. A reason for a big distortion development during hardening in PAG solutions is explained and an idea how to fix the problem is suggested. It is shown that at the end of cooling coating can be locally dissolved by a cold water flow creating local open area where martensite transformation starts first. Due to greater specific volume of martensite, it creates a big distortion. To solve the problem, one should interrupt cooling process or stop agitation before insulating coating is dissolved. To perform correctly proposed technology, cooling intensity of inverse solubility PAG polymers of 1–20 % were investigated on the basis of use of regular thermal condition theory. As a result, dimensionless effective numbers Kn were obtained for recipes development. A technique for solving the problem is proposed by author. Examples of calculations are provided.

Pressure inverse solubility and polymorphism of an edible γ-cyclodextrin-based metal-organic framework.

A very exceptional effect of pressure-induced dissolution has been revealed for an edible metal-organic framework, γ-CD-MOF-1, formed using γ-cyclodextrin and KOH base. In addition, a new polymorph of γ-CD-MOF-1 has been obtained. The trigonal structure is a symmetry sub-group modification of the cubic form. The pressure-induced dissolution of γ-CD-MOF-1 and its polymorphism are shown to be closely related and regulated by adsorption in the pores, as well as the guest framework interactions.

Modeling of CaSO4 crystallization fouling of finned tubes during nucleate pool boiling

The thermal superiority of nucleate boiling over convective heat transfer can greatly be compromised if crystallization fouling occurs on heat transfer surfaces for aqueous solutions with inverse solubility. The change of surface structure, such as finned tubes, though, is shown to have profoundly retarded the deposition process. There is not, nonetheless, a sound model in the open literature to predict fouling of structured surfaces, i.e. finned tubes. The present study proposes a new phenomenological model for finned tubes during nucleate pool boiling at different heat fluxes where CaSO4 solution was used as foulant. The proposed model can predict the supersaturation in the microlayer beneath the bubbles, which are formed on the surface during nucleate pool boiling, as a function of geometry. The fouling resistances predicted from the model were compared with the experimental data, and good quantitative/qualitative agreement was achieved.

Retardation of heat exchanger surfaces mineral fouling by water-based diethylenetriamine pentaacetate-treated CNT nanofluids

Mineral scale deposition on heat exchanging surfaces increases the thermal resistance and reduces the operating service life. The effect is usually intensified at higher temperatures due to the inverse temperature solubility characteristics of some minerals in the cooling water. Scale formation build up when dissolved salt crystallize from solution onto the heated surface, forming an adherent deposit. It is very important for heat transfer applications to cope with the fouling problems in industry. In this present study, a set of fouling experiments was conducted to evaluate the mitigation of calcium carbonate scaling by applying DTPA-treated MWCNT-based water nanofluids on heat exchanger surfaces. Investigation of additive DTPA-treated MWCNT-based water nanofluids (benign to the environment) on fouling rate of deposition was performed. 300mgL−1 of artificially-hardened calcium carbonate solution was prepared as a fouling solution for deposit analysis. Assessment of the deposition of calcium carbonate on the heat exchanger surface with respect to the inhibition of crystal growth was conducted by Scanning Electron Microscope (SEM). The results showed that the formation of calcium carbonate crystals can be retarded significantly by adding MWCNT-DTPA additives as inhibition in the solution.

RAFT Aqueous Dispersion Polymerization of N-(2-(Methacryloyloxy)ethyl)pyrrolidone: A Convenient Low Viscosity Route to High Molecular Weight Water-Soluble Copolymers.

RAFT solution polymerization of N-(2-(methacryoyloxy)ethyl)pyrrolidone (NMEP) in ethanol at 70 °C was conducted to produce a series of PNMEP homopolymers with mean degrees of polymerization (DP) varying from 31 to 467. Turbidimetry was used to assess their inverse temperature solubility behavior in dilute aqueous solution, with an LCST of approximately 55 °C being observed in the high molecular weight limit. Then a poly(glycerol monomethacylate) (PGMA) macro-CTA with a mean DP of 63 was chain-extended with NMEP using a RAFT aqueous dispersion polymerization formulation at 70 °C. The target PNMEP DP was systematically varied from 100 up to 6000 to generate a series of PGMA63–PNMEPx diblock copolymers. High conversions (≥92%) could be achieved when targeting up to x = 5000. GPC analysis confirmed high blocking efficiencies and a linear evolution in Mn with increasing PNMEP DP. A gradual increase in Mw/Mn was also observed when targeting higher DPs. However, this problem could be minimized (Mw/Mn < 1.50) by utilizing a higher purity grade of NMEP (98% vs 96%). This suggests that the broader molecular weight distributions observed at higher DPs are simply the result of a dimethacrylate impurity causing light branching, rather than an intrinsic side reaction such as chain transfer to polymer. Kinetic studies confirmed that the RAFT aqueous dispersion polymerization of NMEP was approximately four times faster than the RAFT solution polymerization of NMEP in ethanol when targeting the same DP in each case. This is perhaps surprising because both 1H NMR and SAXS studies indicate that the core-forming PNMEP chains remain relatively solvated at 70 °C in the latter formulation. Moreover, dissolution of the initial PGMA63–PNMEPx particles occurs on cooling from 70 to 20 °C as the PNMEP block passes through its LCST. Hence this RAFT aqueous dispersion polymerization formulation offers an efficient route to a high molecular weight water-soluble polymer in a rather convenient low-viscosity form. Finally, the relatively expensive PGMA macro-CTA was replaced with a poly(methacrylic acid) (PMAA) macro-CTA. High conversions were also achieved for PMAA85–PNMEPx diblock copolymers prepared via RAFT aqueous dispersion polymerization for x ≤ 4000. Again, better control was achieved when using the 98% purity NMEP monomer in such syntheses.

DESIGNING OF ADVANCED AND ORIGINAL AUSTEMPERING PROCESSES BASED ON THERMAL SCIENCE AND ENGINEERING PHYSICS APPROACHES

In the paper, a small concentration of inverse solubility polymers in water and other liquid media is recommended to eliminate film boiling by means of reducing initial heat flux density. Quenching steel parts and tools in a small concentration of water solutions under pressure allows performing austempering process just using cold liquids. Its essence consists in coinciding martensite start temperature MS with the average temperature of self-regulated thermal process during nucleate boiling mode and further immediate transferring steel parts for tempering at the temperature which exceeds value MS. The new technology increases the service life of austempered workpieces by more than two times, saves alloy elements, is suitable for larger metallic components, improves environmental conditions, since instead of melted salts and alkali, plain water and water salt solutions can be used. The new austempering process can be used in forging shops to obtain super-strengthened materials in order to switch from alloy steel to plain carbon steels. And it can be also widely used for obtaining nano - bainitic structure in plain carbon steels resulting in saving alloy elements and improving mechanical characteristics of materials.