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The paper presents a method of microwave influence on ferrocene C10H10Fe and graphite to obtain multilayer carbon nanotubes (MWCNTs)—designed to improve the electrical and thermophysical properties of Organosilicon elastomer (Silagerm 8020). Diagnostics and characterization of the synthesized MWCNTs were carried out by energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. According to SEM data, it follows that the morphology of the synthesized MWCNTs has the form of filamentous formations intertwined in bundles with a diameter of individual MWCNTs from 40 to 60 nm and a length up to several microns. At the same time, the surface of most of the MWCNTs is covered with a continuous layer of iron (Fe). The EDX method also confirmed the Fe and oxygen content on the surface of the MWCNTs. The XRD method identified the presence of Fe in combination with carbon in the form of Fe3C iron carbide and pure Fe iron at 44.7°. The compound Fe3C is also referred to the active phase of Fe allowing the synthesis of MWCNTs. By increasing the concentration of MWCNTs in the elastomer, an increase in thermal conductivity with percolation transition was achieved at a concentration of 8% MWCNTs. The maximum thermal conductivity of the nanomodified elastomer was 0.48 W/(m °C), which corresponded to the mass concentration of MWCNTs equal to 8 wt %. At the same time, the electrical conductivity of the composite, when the MWCNT concentration was changed from 1 to 8%, increased in the range from 4 × 10–5 to 2.4 S cm–1 and is also due to the percolation of MWCNTs in the elastomer matrix. [ABSTRACT FROM AUTHOR]

The effect of different oxygen concentration conditions on the heat release behaviour of bituminous coal during spontaneous combustion was investigated. Thermal analysis experiments were conducted using differential scanning calorimetry (DSC) and laws governing feature peak changes. Heat flow curves were utilised to identify thermal reaction stages, and the impact of oxygen concentration on heat flows during spontaneous coal combustion (SCC) was assessed. The determinants of heat release rates according to temperature and different oxygen concentration conditions were shown. The heat release process exhibited varying heat proportions at distinct stages. Using the feature point analysis method, the DSC curves could be used to show the apparent activation energy of the total SCC process for different oxygen concentrations. Findings showed a noteworthy influence of oxygen concentration on the overall SCC process. As oxygen concentration increased, the characteristic peak of the heat flow curve appeared earlier, the range of heat release and its heat release temperature rose, and the apparent activation energy also increased. A critical oxygen concentration range, between 7 and 12%, was identified, causing fluctuations in the development process of SCC. This article provided a theoretical basis for further investigation into the SCC process and mechanisms. [ABSTRACT FROM AUTHOR]

The combustion of polystyrene (PS) releases enormous amounts of smoke and heat, which seriously affects individuals and property safety. This research employed a porous metal–organic framework (P-Fe-MOF) with excellent adsorption properties to fix 1,1'-bis(diphenylphosphino)ferrocene (BDF) into its porous channels to form a novel flame-retardant system. The peak heat release rate (PHRR) of the neat PS is reduced by 49.3% (from 1128 to 572 kW m−2) with the addition of 3 mass% of D-Fe-MOF, while the time to reach the peak is delayed form 170 to 250 s. Additionally, there is an obvious enhancement in thermal stability. The temperature at initial mass losses is significantly delayed from 331 °C for bulk PS to 379 °C for PS/D-Fe-3.0. And the char residue at 700 ℃ is increased from 1.27 to 3.24 mass%. Compared with pure PS, the char residue of PS/D-Fe-MOF is continuous and dense due to the excellent catalytic performance of D-Fe-MOF in the combustion of composites. This research presents a new flame-retardant design strategy and reduces the fire risk of PS, which provides valuable enlightenment for broadening the application field of MOF and improving the comprehensive properties of polymers. [ABSTRACT FROM AUTHOR]

Recent developments in water-based open sorption thermal batteries (STBs) have drawn burgeoning attention due to their advantages of high energy storage density and flexible working modes for space heating. One of the main challenges is how to improve heat release performance, e.g., longer stable heat output and effective output temperature. This paper aims to explore the heat release performance of sorption thermal batteries based on wave analysis methods. Zeolite 13X is used for the experimental investigation in terms of the relative humidity of inlet gas, system air velocity, and the length of the reactor. The results demonstrate that the optimal stable temperature output time of the sorption thermal battery experimental rig is 80 min, and heat release per unit volume reaches 115.6 MJ for the most appropriate reactor length. Thus, the optimal heat release time of the STB under the condition of various relative humidity and air velocities is 152 min and 182 min, respectively, and the corresponding stable heat release could reach 161.1 MJ and 136.5 MJ, respectively. Therefore, the heat release performance of STBs could be adjusted by adopting the wave analysis method, which would facilitate the reactor design and system arrangement. [ABSTRACT FROM AUTHOR]

In order to study the combustion characteristics of coal samples with different particle sizes under high temperature conditions, the combustion characteristic parameters of coking coal and its mixed coal samples with particle sizes of 0.200-0.450 mm, 0.125-0.200 mm and 0.097-0.125 mm were tested by cone calorimeter. The combustion efficiency parameters were calculated and the relationship between combustion efficiency parameters and the particle size of coal samples was analyzed. The results show that with the decrease of particle size, the ignition time becomes shorter, indicating that the smaller the particle size of the coal sample, the easier it is to burn; the time required to reach the peak value of heat release rate and the peak value decrease with the decrease of particle size, and the peak value of mixed coal sample is the lowest. When the heat release rate curve tends to be stable, the heat release rate and total heat release increase with the decrease of particle size, and the relationship is 0.097-0.125 mm > 0.125-0.200 mm > mixed coal sample > 0.2000-0.450 mm; the peak value of mass loss rate and the stable mass loss rate increase with the decrease of particle size, and the total mass loss also increases, and the relationship is 0.097-0.125 mm > 0.125-0.200 mm > mixed coal sample > 0.200-0.450 mm. The CO release decreases with the decrease of particle size. With the decrease of particle size, the fire performance index decreases, while the fire spread index increases. The fire performance index of mixed coal sample is the largest, and the fire spread index is slightly higher than that of 0.200-0.450 mm coal sample; the fire risk increases with the decrease of coal particle size, and the fire risk of mixed coal sample is low.

The flexible control in burning rate and stable combustion of solid propellants over a broad range of pressures essentially determine the performance of solid rocket motors. The nanoscale metals and their oxides are usually utilized as the traditional burn rate modifiers in adjusting the combustion behaviors of solid propellants, but the energy characteristics of propellants are greatly compromised owing to the inert nature of additives used. In this paper, a series of metal complexes of triaminoguanidine-glyoxal polymer (TAGP-Ms) with high nitrogen content were synthesized and employed as energetic burn rate inhibitors in tunning the combustion properties of composite modified double-based (CMDB) propellants. The influences of prepared TAGP-Ms on the thermal decomposition and combustion of CMDB propellants were comprehensively investigated based on thermal analysis technique and combustion characterization methods. It was found that the peak temperatures of the second exotherm displayed for the propellants containing TAGP-Ms inhibitors were significantly increased by more than 30°C (except for TAGP-Cu), indicating the TAGP-Ms is capable of suppressing the thermal decomposition of CMDB propellants. More importantly, the heat releases of CMDB propellants were substantially enhanced by 16%~34% determined by DSC analysis. In comparison to the blank reference, the energetic TAGP-Ms inhibitors could promote the heat of combustion for the involved CMDB propellants by 5%~9%. The burning rates of CMDB propellants were notably reduced over a wide range of pressures by adding TAGP-Ms, whereas the calculated pressure exponents at pressures ranging from 10 to ~ 22 MPa appear to be relatively high due to the accelerated HMX decomposition. The measured combustion wave temperatures suggest that the CMDB propellants with TAGP-Ms undergo a three-stage combustion process with the highest temperatures in the range of 2160 ~ 2230°C. [ABSTRACT FROM AUTHOR]

A visible‐light responsive ionic liquid crystalline (LC) system based on gallic ester and tetra‐ortho‐substituted azobenzene is designed and synthesized. All the prepared derivatives exhibit columnar hexagonal mesophases at room temperature either in their pristine form or on cooling from isotropic states. The strategic design of these molecules allows for rapid photoisomerization, which is further aided by the dynamic LC phase. These systems attains photostationary states (PSSs) within 5 min of charging and discharging. The maximum Z conversion on charging in the solid‐state at room‐temperature is ≈80% with a highest temperature rise of 9.1 °C on discharging. This new molecular design enables the efficient working of solar thermal fuels (STFs) even in low sunlight intensity conditions, potentially promoting widespread adoption for mitigating global energy demands. [ABSTRACT FROM AUTHOR]

The secondary combustion between unburnt fuel in rocket plume and ambient air significantly affects the stealth characteristics of rocket motors. In order to reveal the effect of secondary boundary layer combustion of hydrogen on rocket plume heat release characteristics, a two-dimensional axisymmetric model for boundary layer combustion between the rocket plume and air is established. The results identifies significant exothermic effect due to secondary combustion reaction between the plume and air. Compared to the nozzle plume without considering secondary combustion, the average temperature of the plume with secondary combustion increases by 47%. As hydrogen content in the nozzle plume increases from 2.7% to 4.2%, the average temperature of the nozzle plume increases by 17.2% due to enhanced combustion heat release. The secondary combustion process is weakened with the increase of flight altitude. The average temperature of the nozzle plume decreases by 11.8% from 2 km to 8 km of flight altitude. This is because both the pressure and temperature of the ambient air decrease when the flying altitude rises, which leads to lower secondary combustion reaction and heat release rate. Moreover, as the ambient pressure decreases, the hydrogen concentration in the plume decreases due to plume expansion effect. The results indicate that hydrogen content and flight altitude affect secondary combustion by different mechanisms. The hydrogen content directly affects the concentration term of the reaction rate of secondary combustion. However, the flight altitude affects the kinetic rate of secondary combustion by changing both the temperature and partial pressure of oxygen. The present study provides better insight into the interaction mechanism between nozzle plume and ambient air. • Established numerical model for secondary combustion of rocket plume. • Higher hydrogen content enhances secondary combustion process. • Secondary combustion heat release is weakened as flight altitude increases. • Secondary combustion is controlled by shear mixing and heat transfer. [ABSTRACT FROM AUTHOR]

Today, there is a growing shortage of commercial motor fuels in the world. This is due to the tendency to regulate the extraction of hydrocarbons, which are the main raw materials for their production; and, therefore, to reduce the import of oil, alternative types of fuel for diesel engines based on oils and animal fats are becoming widespread today. In this regard, intensive work is underway to convert internal combustion engines to biofuel-based ones both in countries with limited fuel and energy resources and in highly developed countries that have the opportunity to purchase liquid energy carriers. Biodiesel fuel (biodiesel, PME, RME, FAME, EMAG, etc.) is an environmentally friendly type of biofuel obtained from vegetable and animal fats and used to replace petroleum diesel fuel. According to the results of modelling, in the process of using RME B100 biodiesel fuel, we found a reduction in nitrogen dioxide emissions by 21.5% and a reduction in soot emissions by 34.5%. This will positively affect the environmental performance of the Sandvik LH514 loader, which is especially relevant in closed environments such as mines. So, according to the results of studies of the operation of the DD15 engine of the Sandvik LH514 loader on commercial and RME B100 biodiesel fuel, it was established that the use of biodiesel fuel leads to a deterioration of the mixture, due to which heat generation is reduced and, as a result, fuel consumption increases and engine power decreases, but the aspect of environmental indicators constitutes the significant improvement demonstrated by the present work. [ABSTRACT FROM AUTHOR]

Copyright of Power Generation Technology is the property of Power Generation Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Boron is an ambitious fuel in energetic materials since its high heat release values, but its application is prohibited by low combustion efficiency and oxidization during storage. The polydopamine (PDA) was introduced into boron particles, investigating the impact of PDA content on the energetic behavior of boron. The results indicated that the PDA coating formed a fishing net structure on the surface of boron particles. The heat release results showed that the combustion calorific value of B@PDA was higher than that of the raw boron. Specifically, the actual combustion heat of boron powder in B@10%PDA increased by 38.08%. Meanwhile, the DSC peak temperature decreased by 100.65 °C under similar oxidation rate compared to raw boron. Simultaneously, the B@PDA@AP and B@AP composites were prepared, and their combustion properties were evaluated. It was demonstrated that B@10%PDA@AP exhibited superior performance in terms of peak pressure and burning time, respectively. The peak pressure is 12.43 kPa more than B@AP and burning time is 2.22 times higher than B@AP. Therefore, the coating of PDA effectively inhibits the oxidization of boron during storage and enhances the energetic behavior of boron and corresponding composites.

This study presented the development of a reaction kinetics scheme based on saturates–aromatics–resins–asphaltenes (SARA) fractions to represent the complicated chemical reactions occurring during high-pressure differential scanning calorimetry (HP-DSC) tests. The heat release characteristics during heavy crude oil combustion were analyzed from a set of HP-DSC results. On the basis of this analysis, an improved reaction kinetics model, including low-temperature oxidation (LTO) reactions of SARA fractions, cracking of oxidized asphaltenes, and coke combustion, was established. Following that, this model was incorporated into Computer Modeling Group STARS to simulate the HP-DSC results. Both activation energy and frequency factor of each reaction were continuously tuned until the correct kinetics parameters were obtained by matching the simulation data with the HP-DSC experimental data. The experimental results indicated that the heavy crude oil experienced greater heat release due to LTO rather than high-temperature oxidation at 5 MPa, which differed from the results observed at atmospheric pressure. The simulation results showed that the energy required to activate the oxidation reactions in the HP-DSC experiments was similar to that in the numerical simulation. However, the oil sample was subjected to higher molecular collision frequency in the HP-DSC experiments than in the numerical simulation. Therefore, more attention should be given to adjusting frequency factor when determining the oxidation kinetics parameters in the numerical model. Overall, the SARA-based oxidation kinetics model successfully simulated the exothermic characteristics of the heavy oil during heating. [ABSTRACT FROM AUTHOR]

Solid-state solar thermal fuels (SSTFs) serve as efficient means of storing solar energy as chemical potential energy in a closed loop system and releasing it as heat on-demand. An ideal SSTF requires photoswitchability in visible-region without any external heating as well as extended storage times. However, existing systems often rely on ultraviolet (UV) light or heating for photoswitching, or suffer from low storage times. Addressing this, a novel strategy is presented to obtain visible-light responsive SSTFs designed to operate effectively at room-temperature or sub-zero temperatures by innovatively integrating a tetra-ortho-fluoro/chloro azobenzene arm in triphenylene based liquid crystal (LC) moiety. The resulting compounds exhibit discotic nematic (ND) mesophases till -6.5 °C. These compounds exhibit excellent photocyclability, photostability, and sufficient half-lives of cis states. Achieving up to 77% charging under sunlight with a bandpass filter and 62.4% without it, these systems uniquely demonstrate efficient chargeability and dischargeability at sub-zero temperatures. Upon discharging, temperature rise of up to 6.5 and 29.5 °C occur at room-temperature (25 °C) and sub-zero temperatures (around -6 to -7 °C), respectively. This efficacy is attributed to less-ordered ND phases providing conformational freedom for photoisomerization at low temperatures. [ABSTRACT FROM AUTHOR]

The focus of this paper was Jouguet detonation in an ideal gas flow in a magnetic field. A modified Hugoniot detonation equation has been obtained, taking into account the influence of the magnetic field on the detonation process and the parameters of the detonation wave. It was shown that, under the influence of a magnetic field, combustion products move away from the detonation front at supersonic speed. As the magnetic field strength increases, the speed of the detonation products also increases. A dependence has been obtained that allows us to evaluate the influence of heat release on detonation parameters. [ABSTRACT FROM AUTHOR]

This study aimed to dissect the thermal effects and kinetic behaviors of coal spontaneous combustion (CSC) under different heating rates (5, 10, 15, and 20°C/min). The charred coal, nonstick coal, and gas-fat coal were collected as coal samples, and thermogravimetric (TG)-differential scanning calorimeter (DSC) were performed. First, four characteristic temperatures were determined, and the CSC process was divided into four stages. Second, the characteristic temperatures, reaction stages, mass loss and thermal effects were investigated. The results indicated that as the characteristic temperatures increased, mass loss changed little, the TG-DSC curve peak shifted to high temperature, and the total heat release increased as the increases of heating rates. In addition, kinetic parameters of the conversion rate and activation energy was calculated. The apparent activation energies for the collected coal samples found by the Flynn-Wall-Ozawa method were 104.84, 95.51, and 129.84 kJ/mol, respectively, and those found when using the Kissinger method were 86.75, 78.90, and 110.54 kJ/mol, respectively. The results revealed that CSC occurred more difficultly in gas-fat coal than in charred coal. The results can provide theoretical support for the prediction and prevention of CSC in various applications. [ABSTRACT FROM AUTHOR]

The use of a two-stage combustion system in a hydrogen-fueled engine is characteristic of modern internal combustion engines. The main problem with hydrogen combustion in such systems is knocking combustion. This paper contains the results of research under knock combustion conditions with a single-cylinder internal combustion engine equipped with a turbulent jet ignition system (TJI). A layout with a passive pre-chamber and a variable value of the excess air ratio range λ = 1.25–2.0 with a constant value of the center of combustion (CoC = 4 deg) after top dead center (TDC) was used. Two indicators of knock combustion were analyzed: maximum oscillation of pressure and the Mahle Knock Index. Analyses were also carried out taking into account the rate of heat release and the amount of heat released. As a result of the investigation, it was found that knock combustion occurs intensively at small values of the air excess ratio. Hydrogen knock combustion disappears for λ = 2.0 and greater. The pressure oscillation index was found to be more applicable, as its limiting value (>1 bar) allows easy diagnosis of knock combustion. The Mahle Knock Index is a quantity that allows interval analysis of the knock. The choice of classes and weighting coefficients requires an iterative operation, as they strictly depend on engine characteristics, load, and knock magnitude. [ABSTRACT FROM AUTHOR]

Copyright of Chemical Engineering (China) / Huaxue Gongcheng is the property of Hualu Engineering Science & Technology Co Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The present work investigates the regime classification and chemical characteristics of the premixed ammonia combustion in a well stirred reactor (WSR). Three combustion regimes can be classified based on the lowest autoignition and highest extinction temperatures and the reacting temperature increment, which are: (i) flameless combustion (FLC); (ii) high temperature combustion (HTC); (iii) traditional combustion (TC). When introducing the upper limit of NO x emission into the classification, MILD combustion can be defined as a sub-regime of FLC. Relative to the methane counterpart, the ammonia combustion is found to exhibit larger FLC and smaller HTC regimes delimited by the inlet temperature and oxygen fraction. It is also revealed that the MILD combustion of ammonia differs significantly from its burning under other regimes in heat production and NO formation mechanisms. In the MILD combustion, multiple reactions dominate the heat production while the DeNO x route greatly reduces the NO formation. Contrarily, in other combustion regimes, heat is controlled by one or two specific reactions while notably the Extended Zeldovich route dominates the NO destruction. Moreover, the working temperature controls the top reactions for both heat and NO x productions, regardless of different combustion regimes. • Regime classification, heat release and NO formation of NH 3 oxidation are studied. • The NO x emission criterion is introduced into the definition of MILD combustion. • The NH 3 combustion shows a larger flameless region against burning CH 4. • The working temperature controls top reactions for both heat and NO x productions. • The leading NO reduction reactions are distinct in MILD and other regimes. [ABSTRACT FROM AUTHOR]

The initial part of a hydrogen jet exhausting upward from a mm slot and burning in air is studied. The profiles of the streamwise and transverse velocity are determined by means of particle image velocimetry; the local temperature distribution and the composition of stable substances are obtained by the Raman scattering method with the use of a focusing resonator system. Based on experimental data, the contributions of molecular and convective transfer mechanisms to the heat release intensity is determined. It is shown that the maximum intensity of heat release depends mainly on gas-dynamic and thermophysical characteristics of the gas flow during its macroscopic motion. [ABSTRACT FROM AUTHOR]

To maximize the efficiency of freezing, the combinations of using nanoparticles and fins have been utilized in current work. Incorporating nanofluids into solidification processes provides a refined and efficient approach to transitioning materials from a liquid to a solid state. Triangular container involving fins has been implemented. The shape and fraction of nanoparticles were varied in this research. The derived equations were solved via finite element method and the associated code has been validated based on prior article. The reduction of freezing time was presumed as the main goal of research to resource utilization in various industries. As a greater amount of nano-powders is utilized, the conduction becomes stronger and the freezing rate improves about 27%. Also, altering the shape of particles and applying powders with bigger m can lead to a reduction of time of freezing by about 7%.

Researchers always like to find way for improving the performance of system integrated with PCM. In this paper, the container was combined with fins and PCM was mixed with nanoparticles to obtain quicker discharging process. Two significant variables related to second technique are fraction of additives (ϕ) and their shapes (m). To involve these factors in equations, single phase formulation was applied. Low magnitude of velocity of liquid material in freezing leads to simplification of equations of this transient procedure. Galerkin method which was applied for this modeling has good accommodation with previous publication. As ϕ soars, the solidification time declines from 4802.97s to 4244.61s and 3738.37s when blade shape particles were applied. This means that adding additive can enhance the rate of process about 22.16%. Moreover, augmenting the shape factor to higher level causes time to drop about 5.7%. [ABSTRACT FROM AUTHOR]

Solar energy utilization has gained considerable attention due to its abundance and renewability. However, its intermittent nature presents a challenge in harnessing its full potential. The development of energy storing compounds capable of capturing and releasing solar energy on demand has emerged as a potential solution. These compounds undergo a photochemical transformation that results in a high‐energy metastable photoisomer, which stores solar energy in the form of chemical bonds and can release it as heat when required. Such systems are referred to as MOlecular Solar Thermal (MOST)‐systems. Although the photoisomerization of MOST systems has been vastly studied, its back‐conversion, particularly using heterogeneous catalysts, is still underexplored and the development of effective catalysts for releasing stored energy is crucial. Herein we compare the performance of 27 heterogeneous catalysts releasing the stored energy in an efficient Norbornadiene/Quadricyclane (NBD/QC) MOST system. We report the first benchmarking of heterogeneous catalysts for a MOST system using a robust comparison method of the catalysts' activity and monitoring the conversion using UV‐Visible (UV‐Vis) spectroscopy. Our findings provide insights into the development of effective catalysts for MOST systems. We anticipate that our assay will reveal the necessity of further investigation on heterogeneous catalysis. [ABSTRACT FROM AUTHOR]

In this study, crystallization in highly supersaturated aqueous urea solutions was investigated using in situ infrared thermography facilitated by an acoustic levitation apparatus. A notable contribution of this thermographic approach is the identification of a transient heat release signature, particularly pronounced beyond the solubility limit, indicating the enhanced formation of bonds between urea molecules in the supersaturated states. Surprisingly, the temporal evolution of the heat release measurements on an acoustically levitated droplet strongly suggests a two-stage process for urea crystallization. A comprehensive statistical analysis based on classical nucleation theory is used to further investigate the exceptionally high degree of supersaturation and the emergence of prominent heat signatures observed toward the onset of crystallization. [ABSTRACT FROM AUTHOR]

The microcontinuum theories have great potential for modeling structure-sensitive materials. Research into the possibilities of using nonlocal thermomechanics in modeling nanodevices and nanoelectromechanical systems, media with a complex internal micro- and nanostructure is of great interest today. Analysis of such models is associated, as a rule, with overcoming certain difficulties caused by the necessity of numerical solution of integro-differential equations. The possibilities of analyzing mathematical models of a continuous medium can be expanded through the use of variational methods. This paper describes the construction of relations for the dual variational model of a stationary nonlinear heat conduction problem with consideration for the nonlocality effects. It is shown that the conditions of stationarity of the alternative functional coincide with known similar conditions in the absence of nonlocality. A quantitative analysis was carried out using the example of a problem about a plate that is infinite in its plane with active internal heat-release sources. Such problems are typical, for example, of the phenomena of a thermal explosion when exothermic chemical reactions occur in the body material or of thermal breakdown of a dielectric layer under the influence of electrical potentials. The dual variational formulation of the problem allows one not only to obtain an approximate solution to the problem under consideration, but also to estimate the error of this solution, and, if necessary, to reduce this error by selecting approximating functions. [ABSTRACT FROM AUTHOR]

Solving problems of detonation control is associated with obtaining detailed information about the gas dynamics accompanying the detonation process. This paper focuses on the dynamics of real gas flow through a plane detonation wave. The influence of real gas parameters on the Chapman–Jouguet detonation process has been studied. The process is described using the Rankine–Hugoniot system of equations. To model the thermodynamic properties of a real gas, the van der Waals equation of state is used. Equations are obtained to determine the ratio of speeds and pressures during the passage of a wave. The influence of van der Waals parameters on changes in the parameters of the detonation process was elucidated. An increase in parameter A slows down the increase in pressure in the detonation wave, and an increase in parameter B enhances it. Differences in the speed of combustion products for ideal and real gases are shown. For an ideal gas, combustion products flow from the detonation front at a critical (sonic) speed. For a van der Waals gas, the speed of combustion products may be greater than the critical one. Moreover, both factors, additional pressure (A) and additional volume (B), lead to acceleration of combustion products. Effects of heat release on the process parameters were elucidated. [ABSTRACT FROM AUTHOR]

Strengthening the interfacial contact between the reactive components effectively boosts the energy release of energetic materials. In this study, we aimed to create a close-knit interfacial contact condition between aluminum nanoparticles (Al NPs) and Polyvinylidene fluoride-hexafluoropropylene (P(VDF-HFP)) through hydrolytic adsorption and assembling 1H, 1H, 2H, 2H-Perfluorododecyltrichlorosilane (FTCS) on the surface of Al NPs. Leveraging hydrogen bonding between –CF and –CH and the interaction between C–F⋯F–C groups, the adsorbed FTCS directly leads to the growth of the P(VDF-HFP) coating layer around the treated Al NPs, yielding Al@FTCS/P(VDF-HFP) energetic composites. In comparison with the ultrasonically processed Al/P(VDF-HFP) mixture, thermal analysis reveals that Al@FTCS/P(VDF-HFP) exhibits a 57 °C lower reaction onset temperature and a 1646 J/g increase in heat release. Associated combustion tests demonstrate a 52% shorter ignition delay, 62% shorter combustion time, and a 288% faster pressurization rate. These improvements in energetic characteristics stem from the reactivity activation of FTCS towards Al NPs by the etching effect to the surface Al2O3. Moreover, enhanced interfacial contact facilitated by the FTCS-directed growth of P(VDF-HFP) around Al NPs further accelerates the whole reaction process.

Fly ash from Berezovskaya Thermal Power Plant, containing a lot of CaO, in combination with silica fume does not expand and exhibits the properties of a binder. However, the strength of this binder is low. The addition of Ca(NO3)2 significantly increases the strength of the binder. The work aims to study the effect of Ca(NO3)2 additive on the strength, heat of hydration, and phase composition of hydration products of the binder based on high-calcium fly ash and silica fume. The results of X-ray diffraction and Differential Thermal Analysis show that the main phases formed during the hydration of binder with the calcium nitrate additive in various dosages are lime, calcium hydroxide, ettringite, CSH(II) type silicates and calcium aluminosilicates, corresponding to such minerals as gismondine, yugavaralite, goosecreekite. When hardening in water, the residual amount of lime after 7 days is sharply reduced. An increase in the dosage of Ca(NO3)2 from 1.5 to 11.8 % leads to a decrease in the CaO content by almost 2 times. With an increase in the dosage of calcium nitrate, the content of portlandite noticeably decreases, and a significant increase in the amount of calcium hydroaluminosilicates, especially the composition of CAS2H4, is observed. A study of the heat release process showed that calcium nitrate greatly accelerates the process in the first 60 minutes of hydration. However, then the composition with the addition of Ca(NO3)2 is inferior in the rate of heat release to binder without the additive. When testing a mortar with polyfractional sand, the addition of Ca(NO3)2 more than doubled the compressive strength of the mortar.

This work aims to study the effect of MgCl2 additive on the strength, heat of hydration, and phase composition of hydration products of the binder consisting of high-calcium fly ash and silica fume. Fly ash from Berezovskaya thermal power plant, containing a lot of CaOfree, in combination with silica fume does not expand and exhibits the properties of a binder. However, the strength of this binder is low. The MgCl2 additive significantly increases the hardening rate and the final strength of the mix. The compressive strength of 32×32×32 mm specimens from the paste at the age of 7 days is 15.2 MPa and 3.7 MPa with and without the MgCl2 additive, respectively. Exothermic data show that silica fume inhibits CaO hydration from the first minutes of the reaction to 2 days, after which the process accelerates and proceeds evenly. The total value of the thermal effect for 10 days is 500 kJ per 1 kg of binder. The MgCl2 additive does not increase this final value, however, it accelerates the release of heat in the initial periods, excluding the indicated stagnation period. The results of XRD and DTA showed that in the presence of MgCl2, calcium hydrochloraluminate (Friedel's salt) is formed, which was not previously observed in the composition of binder hydration products.

Faced with environmental issues and depleting oil reserves, engine research is venturing into novel paths, such as the dual-fuel engine. This has motivated the development of numerical models that provide highly accurate predictive tools. In this context, 0D/quasi-D modeling is necessary, with a compromise between control of computation time and acceptable prediction level, which will certainly enable the various studies on the dual fuel mode to be explored at reduced cost. The aim of the present study is to develop a combustion model adapted to the hydrogen-natural gas (HNG)/diesel dual fuel engine to ensure 0D/1D simulations over a wide load range and under different gas mixture compositions. This model is based on the separation of the different types of combustion in this mode, by first treating the combustion of the pilot fuel by jet modeling, then the combustion of the gas mixture (HNG) by a mathematical model based on the Gaussian function. This phase separation is carefully combined with a mathematical treatment of the heat release rate, in order to determine ignition delays for both phases and model each of them separately. The modeling approach unveiled in this work is based on a phenomenological aspect, where the distinction between pilot and primary fuel combustion is ensured with phase separation allowing precise monitoring of the combustion sequence with the detection of the start and end of each phase and the contribution of each to the overall heat release rate. The results confirm the predictive power of the model developed with a maximum error of around 2%. This accurate prediction is particularly evident at high loads with high hydrogen enrichment, where the combustion sequence becomes complicated. [ABSTRACT FROM AUTHOR]

Thermal wear comfort for workwear clothing plays a vital role in maintaining comfortable water- and moisture-vapor-permeable properties while wearing clothing. In particular, thermal wear comfort measured using a thermal manikin is required in the protective workwear clothing market because their use provides objective data concerning the actual wearing performance of the clothing. This paper investigated the thermal wear comfort properties of various ceramic-embedded composite fabrics for workwear clothing worn in gas and oil industries produced from new schemes. The thermal insulation rate (Clo value) of Al2O3(Aluminum oxide)/graphite, ZnO(zinc oxide)/ZrC(zirconium carbide) and ZnO/ATO(antimony tin oxide)-embedded clothing was greater (25.5, 24.7 and 16.9%, respectively) than that of regular clothing (control), which was in accordance with the results (15.0, 13.8 and 11.3% higher, respectively) of the heat retention rate (I) of fabric specimens. It revealed that ZnO- and ATO-embedded yarns mixed with ZrC particles enhanced thermal wear comfort and had superior anti-static and UV-protective properties. Considering UV-protective and anti-static protective clothing worn in gas and oil industries and cold weather regions, it can be concluded that ZnO/ZrC-incorporated fabric is suitable because it showed superior thermal wear comfort with excellent UV-protective and acceptable anti-static properties. Meanwhile, assuming high functional performance for protective clothing worn in winter and factories, ZnO/ATO-incorporated fabric is pertinent to fabricating protective clothing for cold weather regions. [ABSTRACT FROM AUTHOR]

This work examines the transition from kinetic to diffusion combustion using optical diagnostic methods. Experimental data were obtained on the temperature fields, composition and velocity of gas near the leading edge of a hydrogen flame flowing from a 2×20 mm slit into the air. The distribution of the rate of combustion product formation, the intensity of heat release and pressure was obtained using the method of balances in equations of energy, momentum, and mass transfer. It is shown that during the transition to diffusion combustion, heat release along the flame length decreases more slowly than the rate of water formation. [ABSTRACT FROM AUTHOR]

In this article, we discuss the importance of the analysis of indicator diagrams and indicated parameters in operational diagnostics of marine engines. An innovative method was devised to improve the effectiveness of diagnostics based on this information. It consisted of the elimination of harmful measurement spaces during cylinder pressure measurements as well as an in-depth analysis of the resultant indicator diagrams based on the functions of heat release. This research demonstrated a negative impact on the quality of indicator diagrams and the values of the parameters indicated by cylinder pressure measurements with sensors mounted on indicator cocks. The elimination of the indicator cock and measuring channel in the cylinder pressure measurements affected the quality of the indicator diagrams and, based on the calculated heat-release functions, allowed the emergence of new (additional) diagnostic symptoms. This could significantly improve the effectiveness of diagnostics performed in operating conditions and, as a result, the effective, trouble-free, and ecological operation of marine engines, thus meeting the growing environmental and operational safety requirements. [ABSTRACT FROM AUTHOR]

Building fires can spread through surface combustion of both combustible and interior finishing materials. Recently, the use of foam blocks as interior materials for high-rise residential buildings has increased. However, as foam blocks are primarily composed of polyethylene, they are not flame-retardant and can readily burn and the fire can spread, leading to large-scale damage. Herein, the fire hazard and diffusion characteristics of foam blocks were compared with those of flame-retardant and general wallpapers to confirm the risk of fire. The fire risk of the foam blocks was confirmed using flammability, cone calorimetry, and spread-of-flame analyses. Based on a comparative analysis of the fire risk of foam blocks, the average total heat release was 11.2 MJ/m. This is approximately three times higher than the average heat release rate of the flame-retardant wallpaper and approximately two times higher than that of the general wallpaper. The foam blocks ignited rapidly owing to fire and generated large amounts of combustion gas and heat. To prevent such a fire, 5 wt% montmorillonite (MMT) was simply coated after surface modification to suppress the occurrence of fire. Various flame-retardant materials, surface modifications, and fire safety systems must be developed to prevent fire hazards. [ABSTRACT FROM AUTHOR]

In the present study, the microstructure, mechanical properties, and stored energy of an aluminum alloy containing iron-rich fine precipitates, subjected to severe plastic deformation through equal-channel angular pressing (ECAP), were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. Up to four passes through ECAP resulted in significant nanometer-scale grain refinement, as well as the accumulation of lattice defects, such as dislocations and mesoscopic shear planes. This resulted in a noticeable enhancement in the Vickers microhardness and the flow stress after ECAP. Differential scanning calorimetry results showed that the ECAP'ed material exhibited two exothermal peaks at 222 ± 2 °C and 362 ± 2 °C, with total thermal effects of ΔH = 4.35 and 6.5 J/g, respectively. Slight increases in the ECAP'ed material microhardness and flow stress were observed at 200 °C. The heat release, at a relatively low temperature, and the slight improvement in the mechanical properties were attributed to the evolution of low- and high-angle misorientation, with the strain and the pinning of tangled dislocation caused by the existing fine particles. The second peak was attributed to grain growth, resulting in a significant softening of the material. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2) is widely used in the prevention and control of spontaneous coal combustion. In this manuscript, three low-rank coals with different metamorphic degrees were selected as the research objects. The temperature-programmed experiments, in situ infrared cooling experiments, simulation of the competitive adsorption of CO2 and oxygen (O2) in coal pores, and simulation study of the CO2 inhibition of the coal oxygen composite reaction were used to obtain the role and effect of CO2 in preventing oxygen adsorption in coal at the low-temperature oxidation stage. It was concluded that CO2 can displace the O2 near the pore wall to physically prevent the adsorption of O2. Through the changing law of heating rate and a kinetics analysis, it was found that CO2 can increase its activation energy by 5.3–108.3% during the slow heating stage of coal and reduce its heat rate. At around 120 °C, coal loses the protective effect of CO2. From the changes in functional groups, it can be seen that when coal was cooled in the CO2 atmosphere, mainly pyrolysis and condensation reactions occurred due to the lack of O2. In addition, CO2 can also inhibit the chain reaction of the chemical adsorption of oxygen in coal. This work provides a theoretical basis for CO2 prevention and the control of spontaneous coal combustion. [ABSTRACT FROM AUTHOR]

The focus of this paper was Jouguet detonation in an ideal gas flow in a magnetic field. A modified Hugoniot detonation equation has been obtained, taking into account the influence of the magnetic field on the detonation process and the parameters of the detonation wave. It was shown that, under the influence of a magnetic field, combustion products move away from the detonation front at supersonic speed. As the magnetic field strength increases, the speed of the detonation products also increases. A dependence has been obtained that allows us to evaluate the influence of heat release on detonation parameters.

The use of a two-stage combustion system in a hydrogen-fueled engine is characteristic of modern internal combustion engines. The main problem with hydrogen combustion in such systems is knocking combustion. This paper contains the results of research under knock combustion conditions with a single-cylinder internal combustion engine equipped with a turbulent jet ignition system (TJI). A layout with a passive pre-chamber and a variable value of the excess air ratio range λ = 1.25–2.0 with a constant value of the center of combustion (CoC = 4 deg) after top dead center (TDC) was used. Two indicators of knock combustion were analyzed: maximum oscillation of pressure and the Mahle Knock Index. Analyses were also carried out taking into account the rate of heat release and the amount of heat released. As a result of the investigation, it was found that knock combustion occurs intensively at small values of the air excess ratio. Hydrogen knock combustion disappears for λ = 2.0 and greater. The pressure oscillation index was found to be more applicable, as its limiting value (>1 bar) allows easy diagnosis of knock combustion. The Mahle Knock Index is a quantity that allows interval analysis of the knock. The choice of classes and weighting coefficients requires an iterative operation, as they strictly depend on engine characteristics, load, and knock magnitude.

Butanol has a high potential as a renewable substitution for gasoline in spark-ignition direct-injection (SIDI) engines. Different butanol isomers showed various flame characteristics that are strongly related to their molecular structure. However, there has been limited research on the implications of the butanol isomer's molecular structure on SIDI engine combustion, performance, and emissions. This study investigated butanol isomers as gasoline substitutes in SIDI range extender engines, with a focus on the effects of isomer molecular structures. This work employed a single-cylinder optical SIDI research engine and a high-speed camera to examine engine performance, flame kernel stability, flame propagation, and particle number (PN) emissions. The investigated blends comprised 70% toluene reference fuel (TRF) and 30% butanol isomers (1-butanol (n), 2-butanol (s), isobutanol (i), and tertbutanol (t)). Experimental tests are carried out at a 1000 rpm engine speed and a load of 5.7 bar IMEP, while the fuel condition is kept stoichiometric.The results elucidate that adding 1-butanol makes the flame kernel more stable and reduces COVimep compared to pure TRF. On the other hand, TRF-i, TRF-s, and TRF-t decrease flame initiation stability and increase COVimep. 1-butanol exhibited the highest apparent flame speed, IMEP, and peak in-cylinder pressure, followed by TRF, TRF-i, TRF-s, and TRF-t. Over half of the TRF-t cycles exhibited either no or a delayed flame kernel. Flame circularity improved with 1-butanol and diminished with the other blends. Diffusion flame intensity and PN emissions were higher for TRF, TRF-n, and TRF-t compared to TRF-s and TRF-i. In conclusion, linear chain butanol isomers with more internal C-H bonds and terminal C-OH bonds provide a more stable flame kernel and superior engine performance than branched isomers featuring internal C-OH bonds. The results from this study can be useful for expanding the practical applications of butanol isomers as a renewable fuel replacement in SIDI engines.

Thermal behavior and fire reaction properties of aerial glass fiber (GF)/bismaleimide (BMI) composites were tested using thermogravimetric analysis (TGA), thermogravimetric coupled with Fourier transform infrared spectroscopy (TG-FTIR), cone calorimeter, limiting oxygen index, and smoke density chamber. The results showed that the pyrolysis process was one stage in a nitrogen atmosphere with the prominent volatile components of CO2, H2O, CH4, NOx, and SO2. The release of heat and smoke increased with the increase in heat flux, while the time required to reach hazardous conditions decreased. The limiting oxygen index decreased monotonically from 47.8% to 39.0% with increasing experimental temperature. The maximum specific optical density within 20 min in the non-flaming mode was greater than that in the flaming mode. According to the four kinds of fire hazard assessment indicators, the greater the heat flux, the higher the fire hazard, for the contribution of more decomposed components. The calculations of two indices confirmed that the smoke release in the early stage of fire was more negative under flaming mode. This work can provide a comprehensive understanding of the thermal and fire characteristics of GF/BMI composites used for aircraft. [ABSTRACT FROM AUTHOR]

To regulate emissions and reach efficiency values closer to theoretical limits in heavy and medium-duty vehicles the incremental improvement of the combustion engine is necessary as other options, like electrical powertrains, remain in the early stages of their development for such load demands. The objective of this work is to evaluate the effect on emissions and performance of three different injectors – with two flow rates (1300 and 1500 cm3/min) and three different hole numbers (7, 9, and 10) – coupled with two levels of swirl ratio (1.81 and 1.05) under experimental stationary conditions. Following this, a merit function strategy is developed and used to determine the hardware combination that provides the best advantage regarding the tradeoff between emissions and fuel consumption based on criteria that considers prospective regulations and the current performance of the hardware. The results obtained from this work indicate that a low flowrate injector, coupled with a cylinder-head that achieves a swirl ratio of 1.81 performs the best among the tested hardware combinations, providing reductions of at least 2 g/kWh of indicated specific fuel consumption while NOx emissions are comparable with the other tested hardware combinations and soot emissions have almost negligible values (under 6 mg/kWh for all operating conditions). [ABSTRACT FROM AUTHOR]

Thermogenesis is a physiological activity of releasing heat that originates from intracellular biochemical reactions. Recent experimental studies discovered that externally applied heat changes intracellular signaling locally, resulting in global changes in cell morphology and signaling. Therefore, we hypothesize an inevitable contribution of thermogenesis in modulating biological system functions throughout the spatial scales from molecules to individual organisms. One key issue examining the hypothesis, namely, the “trans-scale thermal signaling,” resides at the molecular scale on the amount of heat released via individual reactions and by which mechanism the heat is employed for cellular function operations. This review introduces atomistic simulation tool kits for studying the mechanisms of thermal signaling processes at the molecular scale that even state-of-the-art experimental methodologies of today are hardly accessible. We consider biological processes and biomolecules as potential heat sources in cells, such as ATP/GTP hydrolysis and multiple biopolymer complex formation and disassembly. Microscopic heat release could be related to mesoscopic processes via thermal conductivity and thermal conductance. Additionally, theoretical simulations to estimate these thermal properties in biological membranes and proteins are introduced. Finally, we envisage the future direction of this research field.

In order to obtain the effects of different amounts of metakaolin on the physical, mechanical properties and hydration characteristics of concrete, basic physical and mechanical tests of metakaolin concrete and concrete hydration performance tests were carried out. The results show that the proper addition of metakaolin instead of concrete cement admixture can better improve the mechanical properties and working performance of concrete. However, with the increasing content of metakaolin, the cement content inside the concrete will decrease and the chemically bound water inside the concrete will decrease. So that the heat and rate of hydration are reduced, and the content of calcium hydroxide generated by the hydration reaction is reduced. By combining the XRD pattern analysis of metakaolin after hydration, it can be known that the peak value of the XRD pattern of ettringite is the most significant when the content of metakaolin is 15%. This is consistent with the content of metakaolin that is obtained in the early stage to achieve the best mechanical properties of concrete.

In this paper, numerical approach has been implemented to depict the promising efficacy of dispersion of alumina nanoparticles for expedition of freezing. The fraction and volume of powders were assumed as variables to evaluate the performance of system. The tank has sinusoidal shape and triangular cold surface has been applied as origins of solidification. The use of adaptive grid leads to better capturing the regions with higher gradient of scalar which gives higher accuracy of modeling. The precision of simulation was checked with associating the outcomes with previous data and good accommodation was reported. As alumina added in water, the period of process declines around 41.18% and optimized size of powder with highest concentration has been utilized. The time changes from 197.25 s to 157.91 s if the d p changes from 30 nm to 40 nm. By changing the radius of powder from 15 nm to 25 nm, the required time augments around 19.33% when ϕ = 0. 0 4. [ABSTRACT FROM AUTHOR]

Wood, as a naturally green and environmentally friendly material, has been widely used in the construction and decoration industries. However, the flammability of wood poses serious safety problems. To improve the fire resistance of wood, In this study, it is proposed to use calcium chloride (CaCl2) and disodium hydrogen phosphate (Na2HPO4, DSP) to impregnate wood for multiple cycles. The experimental results show that phosphate mineral precipitation can be deposited on the surface of the wood. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) are used to analyze the micromorphology of mineral precipitation and use the MIP test to analyze the treated wood pore structure. The results show that with the increase in the number of cycles, the phosphate deposited on the surface of the wood increases, and the cumulative pore volume and water absorption rate of the wood after 10 cycles are 54.3% and 13.75% lower than that of untreated wood respectively. In addition, the cone calorimeter (CONE) confirmed that the total heat release (THR) and total smoke production (TSP) of wood treated in 10 cycles have decreased by 48.7% and 54.2% respectively compared with the untreated wood. Hence, this treatment method not only improves the mechanical properties of wood. It also improves fire resistance. [ABSTRACT FROM AUTHOR]

This paper analyzes the mechanisms of entropy production that stem from exothermic chemical reactions in laminar, premixed flames. This paper is particularly motivated by the problem of indirect combustion noise, where acceleration of entropy fluctuations through a nozzle leads to acoustic fluctuations. In general, entropy generation in reacting systems occurs through molecular transport and chemical reaction, with the reaction terms being dominant in combustion systems. However, there are multiple mechanisms for entropy production from exothermic reactions, including heat release, change in number of moles of species, and changes in species. Most past analyses of indirect combustion noise have equated the heat release term with the flames entropy production, implicitly neglecting the other reaction-induced entropy sources. This paper shows the decomposition of the chemical source term from the entropy equation into three sub-terms, and then use detailed kinetic calculations from a one-dimensional reacting flow solver to calculate their magnitudes. Illustrative results are presented in the paper for several different fuels with varying thermodynamic properties methane, propane, octane, n -dodecane and hydrogen. Calculations are also performed for both air and oxygen as an oxidizer as well as at different parameter sweeps, in order to vary the flames fractional molar production and levels of product dissociation. These results show that heat release is by far the dominant production term in air-fueled flames. However, in oxygen fired systems, heat release has comparable magnitude as the other reaction terms. An important practical implication of this result is that indirect combustion noise source terms can be equated with the heat release terms for air-breathing systems but cannot be for rockets. [ABSTRACT FROM AUTHOR]

Utilizing one triangular cold wall and one wavy adiabatic wall creates new container which is utilized in current modeling research. Inside the container is filled with water and to improve the solidification rate, nano-powders were added into PCM with low concentration. Unsteady process of freezing inside the domain was simulated based on Galerkin method and empirical data were utilized for verification. Concentration of nano-powder and its size were assumed as variables. Homogeneous formulation for NEPCM was utilized to involve the nanoparticle effects in governing equations. This process is mainly supported by conduction and existence of cold region at bottom side makes the impact of buoyancy negligible. With augmenting the concentration of copper oxide, the conductivity augments and speed of solid front increases and lower time needs for full freezing process. Size of nano-powders can affect the process because of its effect of feature of NEPCM. With rise of dp, at first the conduction increases but further increment makes conduction becomes weaker due to sedimentation. When dp = 40 nm, increase of φ leads to reduction of time about 18.04%. With augment of dp from 30 for 40 and then 50 nm, the freezing time at first decreases about 20.01$ and then it augments about 35.48%. When φ = 0.04, dp = 40 nm, the fast process occurs and full solidification takes place after 457.60 s. [ABSTRACT FROM AUTHOR]

Internal combustion engines face increased market, societal, and governmental pressures to improve performance, requiring researchers to utilize modeling tools capable of a thorough analysis of engine performance. Heat release is a critical aspect of internal combustion engine diagnostic analysis, but is prone to variability in modeling validity, particularly as engine operation is pushed further from conventional combustion regimes. To that end, this effort presents a comprehensive open-source, zero-dimensional equilibrium heat release model. This heat release analysis is based on a combined mass, energy, entropy, and exergy formulation that improves upon well-established efforts constructed around the ratio of specific heats. Furthermore, it incorporates combustion using an established chemical kinetics mechanism to endeavor to predict the global chemical species in the cylinder. Future efforts can augment and improve the chemical kinetics reactions for specific combustion conditions based on the radical pyrolysis of the fuel. In addition, the incorporation of theoretical calculations of energy and exergy based on the change in chemical species allows for cross-checking of combustion model validity. [ABSTRACT FROM AUTHOR]

In this study, crystallization in highly supersaturated aqueous urea solutions was investigated using in situ infrared thermography facilitated by an acoustic levitation apparatus. A notable contribution of this thermographic approach is the identification of a transient heat release signature, particularly pronounced beyond the solubility limit, indicating the enhanced formation of bonds between urea molecules in the supersaturated states. Surprisingly, the temporal evolution of the heat release measurements on an acoustically levitated droplet strongly suggests a two-stage process for urea crystallization. A comprehensive statistical analysis based on classical nucleation theory is used to further investigate the exceptionally high degree of supersaturation and the emergence of prominent heat signatures observed toward the onset of crystallization.