Solid Melting Research Articles

A multizonal numerical combustion model of ammonium perchlorate

Solid rocket motors (SRM) are essential for national defense, satellite launch vehicles for placing spacecraft for communications, resource management, and space exploration. Numerical modeling of composite solid propellants is very helpful for optimizing performance, ensuring safety, and complementing experimental testing. It provides insights into combustion dynamics and allows for precise customization to meet specific mission needs, so modeling compositepropellants will stay important. AP (Ammonium Perchlorate), as a synthetic oxidizer, has been widely utilized in modern composite solid propellants. Therefore, it is crucial to understand the physicochemical processes such as condensed-phase heating and reaction kinetics, the interactions between the condensed and gas phases, and gas-phase combustion. A steady-state numerical simulation model is presented to study the combustion of AP. Zonal modeling is employed to treat the solid phase, melt layer, and gas phase separately with conservation of mass, energy, and species, and the solutions are coupled with appropriate boundary conditions. A simple global reaction is developed, validated, and used for the condensed phase with better surface species profiles than those available in the literature. A detailed reaction mechanism is used in the gas phase combustion. This model considers only liquid as a condensed phase and uses a newly condensed phase mechanism and a premixed AP/HTPB (hydroxyl-terminated polybutadiene) gas phase reaction mechanism instead of AP monopropellant gas phase mechanism. This modeling is a prerequisite for a more sophisticated multi-modal composite propellant model with AP grains and AP/HTPB binder. The predicted burn rate and initial temperature sensitivities for different motor operating pressures match well with experimental and other theoretical data. Also, the simulated melt layer thickness of the present model agrees well with experimental observations. Sensitivity analysis is performed for the melt temperature and activation energy for the condensed phase reaction. The simulation also predicts surface temperature and species profile with reasonable accuracy.

Improvement in an Analytical Approach for Modeling the Melting Process in Single-Screw Extruders.

Most single-screw extruders used in the plastics processing industry are plasticizing extruders, designed to melt solid pellets or powders within the screw channel during processing. In many cases, the efficiency of the melting process acts as the primary throughput-limiting factor. If the material melts too late in the process, it may not be sufficiently mixed, resulting in substandard product quality. Accurate prediction of the melting process is therefore essential for efficient and cost-effective machine design. A practical method for engineers is the modeling of the melting process using mathematical-physical models that can be solved without complex numerical methods. These models enable rapid calculations while still providing sufficient predictive accuracy. This study revisits the modified Tadmor model by Potente, which describes the melting process and predicts the delay-zone length, extending from the hopper front edge to the point of melt pool formation. Based on extensive experimental investigations, this model is adapted by redefining the flow temperatures at the phase boundary and accounting for surface porosity at the beginning of the melting zone. Additionally, the effect of variable solid bed dynamics on model accuracy is examined. Significant model improvements were achieved by accounting for reduced heat flow into the solid bed due to the porous surface structure in the solid conveying zone, along with a new assumption for the flow temperature at the phase boundary between the solid bed and melt film.

Impact of high‐intensity ultrasound, cooling rate, and storage temperature on physical properties and oil binding capacity in fully hydrogenated palm‐kernel lipid matrices

AbstractThe ability of a fat crystal network to entrap liquid oil is known as oil binding capacity (OBC) and is an imperative property in semi‐solid fats for use in confectionary, bakery, and snack products. Understanding the factors that increase the OBC of fats is crucial for developing fat‐based foods that are more resistant to unwanted oil migration. In this study, fully hydrogenated palm‐kernel based (FHPKO) lipid matrices were crystallized under different processing conditions to generate samples with a wide range of physical properties and OBC. Three dilutions were created by combining FHPKO with soybean oil (SBO)—75% FHPKO (containing 25% SBO), 50% FHPKO (50% SBO), and 20% FHPKO (80% SBO) and were crystallized at 33, 30, and 22°C; respectively. All the samples were crystallized using fast (FCR; 4.6°C/min) and slow (SCR; 0.1°C/min) cooling rates, as well as with (w) and without (wo) high‐intensity ultrasound (HIU; 20 kHz). These processing conditions resulted in four different sets of samples—FCR wo HIU, FCR w HIU, SCR wo HIU, SCR w HIU. Immediately after processing, the sample's hardness, solid fat content (SFC), viscoelasticity (G′, G″, δ), microstructure, melting behavior (Tpeak, enthalpy), and OBC using a centrifuge method (labeled OBCc) were analyzed. Samples were then stored at 22 and 5°C for 48 h and the aforementioned properties were measured again as well as OBC using a filter paper method (labeled OBCp). Results show that both OBCc and OBCp were positively correlated with the sample's SFC (rs = 0.912, p < 0.001; rs = 0.777, p < 0.001), storage moduli (G′) (rs = 0.674, p < 0.001; rs = 0.526, p = 0.017), hardness (rs = 0.793, p < 0.001; rs = 0.812, p < 0.001), enthalpy (rs = 0.842, p < 0.001; rs = 0.812, p < 0.001), and the number of crystals (rs = 0.655, p < 0.001; rs = 0.728, p < 0.001); respectively. While no correlation between OBCp and the sample's peak melting temperature and microstructure was recorded, a negative association between the sample's peak melting temperature (rs = −0.782, p < 0.001), phase angle (δ) (rs = −0.801, p < 0.001), and crystal diameter (rs = −0.470, p = 0.004) was documented for OBCc. These results suggest oil binding capacity of palm‐kernel based crystallized fats can be increased by formulating harder fats that are elastic, contain more crystals, and have higher SFC and enthalpy. Additionally, the FCR with HIU processing conditions was the most effective in increasing the OBC.

Capitalism, coronavirus, and war in the digital age: Interview with Radhika Desai

In Spring 2024, I met Radhika Desai for the first time at the London School of Economics and Political Science when we both held visiting positions at the Department of International Development as invited scholarly visitors. Although I had not expected her presence, I immediately recognized her after having been a reader of her works on geopolitical economy when developing my own ideas about the political economy of Chinese media and communications. I introduced myself and started talking with her, first at a coffee shop, then in a small office inside LSE’s Connaught House, and later at the Marx Memorial Library in London for a book launch party. Prompted by my questions rooted in the field of media and communication, Radhika Desai shared ideas from her newly published book, Capitalism, Coronavirus, and War: A Geopolitical Economy (Routledge, 2023), which is being translated into Chinese, her critiques about imperialism, globalization and essentially the world order after decades of neoliberalism, and, furthermore, her hopes for China, BRICS, and, ultimately, for the political left. Now, these conversations are turned into a dialogue piece, and with it I hope Communication and the Public readers will sense my gains from Radhika Desai, that is, to paraphrase from the famous line from the Communist Manifesto, in the digital age when all that is solid melts into ostensibly immaterial communication, man/woman is at last compelled to face with sober senses the real conditions of life and his or her relations with their kind.

An extension of atomic mean square displacement method for calculating melting temperatures in II-VI compounds

Understanding how solids melt and determining their melting temperatures is of great significance for studying the properties of materials. Based on the main idea of Lindemann's melting criterion and the first-principles calculation of density functional theory, we proposed the atomic mean square displacement method to predict the melting temperature of the material. In this paper, the application range of this method for calculating melting temperature is extended. 8 kinds of Ⅱ-Ⅵ compounds were selected as verification objects. The results show the accuracy of our method in predicting the melting temperature of Ⅱ-Ⅵ compounds.

Optical measurements of solid nitrogen solubility in hydrogen at cryogenic temperatures

The solubility of impurities in hydrogen at cryogenic temperatures is essential information for the design of liquid hydrogen plants. However, large data scatter and inconsistent predictions of impurity solubility by thermodynamic models mean that expensive engineering design margins are required to avoid blockages in cryogenic equipment. Here we report the combination of a stereomicroscope, commercial cryocooler and pressure cell to directly visualise solid impurity freeze-out and melting in stirred hydrogen at low temperatures and elevated pressures. Scattered literature data for nitrogen's solubility in hydrogen are compared to new solid-fluid equilibrium (SFE) measurements for a 1000 ppm N2 in H2 mixture at (1.8–5) MPa, and (42–52) K. These results were used to improve solubility models implemented in the ThermoFAST software package, achieving a three-fold decrease in the root-mean-square deviations between the SFE predictions and the data, helping lower the risk of impurity freeze-out in hydrogen liquefaction.

Analytical assessment of hetero-/homogeneous combustion of magnesium particle: Fully explicit formulas for flame characteristics

In this study, by proposing a comprehensive multi-step model, the combustion of magnesium particles in O2-He, O2-Ar, and O2-N2 is scrutinized. In the current model, both the heterogeneous and homogeneous combustions are considered and the process is divided into four stages solid, liquid, and gas combustion and melting. Moreover, the diffusions of oxygen and unreacted magnesium to droplet and infinity together with surface exothermic reaction are considered. The governing equations are analytically solved and then, the formulas are extracted for combustion time and temperature, flame standoff distance, and evaporation rate as the functions of particle diameter, ambient temperature and pressure, oxygen mass fraction, type of inert gas, and Lewis numbers. For 120 µm particle and oxygen content of 0.05, time contributions of homogeneous and heterogeneous combustions are 85.8% and 14.2%, respectively. The burning time has drastic changes at ambient pressures below l atm, so that the burning time variations relative to the pressure in the environments less than 1 atm and greater than it are equal to 1200–1550 and 70–90 ms/atm, respectively. When the oxygen mass fraction is less than 0.29, combustion in helium-oxygen ends earlier than that in O2-Ar and O2-N2, but for the mass fraction greater than 0.35, it has the longest burning time.

Benchmarking the accuracy of higher-order particle methods in geodynamic models of transient flow

Abstract. Numerical models are a powerful tool for investigating the dynamic processes in the interior of the Earth and other planets, but the reliability and predictive power of these discretized models depends on the numerical method as well as an accurate representation of material properties in space and time. In the specific context of geodynamic models, particle methods have been applied extensively because of their suitability for advection-dominated processes and have been used in applications such as tracking the composition of solid rock and melt in the Earth's mantle, fluids in lithospheric- and crustal-scale models, light elements in the liquid core, and deformation properties like accumulated finite strain or mineral grain size, along with many applications outside the Earth sciences. There have been significant benchmarking efforts to measure the accuracy and convergence behavior of particle methods, but these efforts have largely been limited to instantaneous solutions, or time-dependent models without analytical solutions. As a consequence, there is little understanding about the interplay of particle advection errors and errors introduced in the solution of the underlying transient, nonlinear flow equations. To address these limitations, we present two new dynamic benchmarks for transient Stokes flow with analytical solutions that allow us to quantify the accuracy of various advection methods in nonlinear flow. We use these benchmarks to measure the accuracy of our particle algorithm as implemented in the ASPECT geodynamic modeling software against commonly employed field methods and analytical solutions. In particular, we quantify if an algorithm that is higher-order accurate in time will allow for better overall model accuracy and verify that our algorithm reaches its intended optimal convergence rate. We then document that the observed increased accuracy of higher-order algorithms matters for geodynamic applications with an example of modeling small-scale convection underneath an oceanic plate and show that the predicted place and time of onset of small-scale convection depends significantly on the chosen particle advection method. Descriptions and implementations of our benchmarks are openly available and can be used to verify other advection algorithms. The availability of accurate, scalable, and efficient particle methods as part of the widely used open-source code ASPECT will allow geodynamicists to investigate complex time-dependent geodynamic processes such as elastic deformation, anisotropic fabric development, melt generation and migration, and grain damage.

Ternary nano-composite wireless ammonia sensor based on Polyaniline/CuTsPc/AgNPs for food intelligent packaging

The integration of gas sensing unit and low-cost wireless communication equipment enables real-time detection of various environmental gases, which is of great significance for food safety, medical diagnosis and environmental monitoring. In this study, copper phthalocyanine powder (CuTsPc) was prepared by high temperature solid phase melting technology. Ternary ammonia sensors with exceptional sensitivity to ammonia and conductivity were successfully fabricated by growing polyaniline/copper phthalocyanine/silver nanoparticles (PANI/CuTsPc/AgNPs) composites on polyethylene terephthalate films by in-situ polymerization. The morphology and composition of the films were characterized by FTIR, XRD and SEM, respectively. The ammonia sensing performance of the films at room temperature was systematically investigated. It is found that the flexible PANI/CuTsPc/AgNPs gas sensor exhibited rapid response time (61 s), fast recovery time (19 s), low theoretical detection limit (0.234 ppm), high response value (3.6 towards 500 ppm NH3), and excellent stability at room temperature. These remarkable response characteristics can be attributed to the synergistic effect between protonic acid-doped PANI, CuTsPc derivatives with an electron-withdrawing group, and AgNPs possessing both chemical sensitisation and electron sensitisation. Finally, the sensor material was transformed into a label antenna pattern as well as sensor transducer through series and parallel antenna loop access methods to create a wireless sensor system based on near-field communication (NFC). This system can offer real-time sensing and monitoring of changes in food packaging environment by non-contact recognition way, making it highly promising for future applications in intelligent packaging.

Design, fabrication and experiment of soft fingers with double-chamber based on layer jamming

PurposeThe purpose of this paper is to propose a casting process for the production of double-chamber soft fingers, which avoids the problems of air leakage and fracture caused by multistep casting. This proposed method facilitates the simultaneous casting of the inflation chamber and the jamming chamber.Design/methodology/approachAn integrated molding technology based on the lost wax casting method is proposed for the manufacture of double-chamber soft fingers. The solid wax core is assembled with the mold, and then liquid silicone rubber is injected into it. After cooling and solidification, the mold is stripped off and heated in boiling water, so that the solid wax core melts and precipitates, and the integrated soft finger is obtained.FindingsThe performance and fatigue tests of the soft fingers produced by the proposed method have been carried out. The results show that the manufacturing method can significantly improve the fatigue resistance and stability of the soft fingers, while also avoiding the problems such as air leakage and cracking.Originality/valueThe improvement of the previous multistep casting method of soft fingers is proposed, and the integrated molding manufacturing method is proposed to avoid the problems caused by secondary bonding.

State diagram of freeze-dried sardines (Sardinella longiceps, Valenciennes)

State diagram is used to determine the stability of dried and frozen foods during their processing and storage. In this study, state diagram of sardine was developed by measuring the freezing curve, glass line, solids melting line, and maximal-freeze-concentration conditions. Glass transition temperature decreased with the increase in water content and it was adjusted using a modified Gordon-Taylor equation. The glass transition of dry-solids and critical temperature were 184.1 and 12.5oC, and the model parameter of the modified Gordon-Taylor equation was estimated as 4.2, respectively. Solids melting temperature was modeled by Flory-Huggins equation; and dry-solids melting temperature and Flory-Huggins solids-water interaction parameter were determined as 199.4oC and 0.956, respectively. Freezing point of fresh sardine was observed as −1.3oC with ice melting enthalpy of 186.3 kJ/kg, and it decreased with the increase of solids due to the freezing point depression with solutes. Freezing point was adjusted by Chen equation based on Clausius-Clapeyron equation. The ultimate maximal-freeze-concentration temperatures, (Tm′)u and (Tg′′′)u were determined as −18.6 and −25.1oC, respectively and maximal-freeze-concentration solids were estimated as 0.90 g solids/g sample (i.e. un-freezable water 0.10 g water/g sample). This indicated that frozen sardines could be most stable if stored below −25.1oC, and dried fish stored below its glass transition.

Induced Aggregation, Solvent Regulation, and Supracluster Assembly of Aluminum Oxo Clusters.

ConspectusRecent years have witnessed the development of cluster materials as they are atomically precise molecules with uniform size and solution-processability, which are unattainable with traditional nanoparticles or framework materials. The motivation for studying Al(III) chemistry is not only to understand the aggregation process of aluminum in the environment but also to develop novel low-cost materials given its natural abundance. However, the Al-related clusters are underdeveloped compared to the coinage metals, lanthanides, and transition metals. The challenge in isolating crystalline compounds is the lack of an effective method to realize the controllable hydrolysis of Al(III) ions. Compared with the traditional hydrolysis of inorganic Al(III) salts in highly alkaline solutions and hydrolysis of aluminum trialkyl compounds conducted carefully in an inert operating environment, we herein developed an effective way to control the hydrolysis of aluminum isopropanol through an alcoxalation reaction. By solvothermal/low melting point solid melting synthesis and using "ligand aggregation, solvent regulation, and supracluster assembly" strategies, our laboratory has established an organic-inorganic hybrid system of aluminum oxo clusters (AlOCs). The employment of organic ligands promotes the aggregation and slows the hydrolysis of Al(III) ions, which in turn improves the crystallization process. The regulation of the structure types can be achieved through the selection of ligands and the supporting solvents. Compared with the traditional condensed polyoxoaluminates, we successfully isolated a broad range of porous AlOCs, including aluminum molecular rings and Archimedes aluminum oxo cages. By studying ring expansion, structural transformation, and intermolecular supramolecular assembly, we demonstrate unique and unprecedented structural controllability and assembly behavior in cluster science. The advancement of this universal synthetic method is to realize materials customization through modularly oriented supracluster assembly. In this Account, we will provide a clear-cut definition and terminology of "ligand aggregation, solvent regulation, and supracluster assembly". Then we will discuss the discovery in this area by using a strategy, such as aluminum molecular ring, ring size expansion, ring supracluster assembly, etc. Furthermore, given the internal and external pore structures, as well as the solubility and modifiability of the AlOCs, we will demonstrate their potential applications in both the solid and liquid phases, such as iodine capture, the optical limiting responses, and dopant in polymer dielectrics. The strategy herein can be applied to extensive cluster science and promote the research of main group element chemistry. The new synthetic method, fascinating clusters, and unprecedented assembly behaviors we have discovered will advance Al(III) chemistry and will also lay the foundation for functional applications.

Tribo-mechanical and structural characterizations of LLDPE matrix bio-composite reinforced with almond shell micro-particles: effects of the processing methodology

Abstract The objective of this research work is to examine the effect of mixing operation in the reinforcement of linear low density polyethylene (LLDPE) with almond shell powder (ASP). Two groups of bio-composites mixed in solid state and melt extrusion state were developed by the standard thermo compression molding process. For each group of bio-composites developed, the mass percentage of ASP was varied from 5 % to 40 %. Tensile and friction tests and micro structural analyzes were carried out. The main results show that the addition of ASP particles: decreases the maximum tensile stress and increases the rigidity of the two types of bio-composites produced. A significant improvement was observed in terms of maximum stress and Young’s modulus of the bio-composites mixed in the molten state compared to those mixed in the solid state. Microscopic observations concluded that the melt-blended ASPs were better covered by the LLDPE matrix and the dispersion was successfully achieved. Friction tests have shown an improvement in tribological performance thanks to the addition of an optimal percentage of ASP equal to 20 % in the case of bio-composites mixed in the molten state. From this research work, it can be concluded that the LLDPE/ASP homogenization method influences the mechanical and tribological properties of bio-composites.

Anomalous electromagnetic wave absorption of MAX phase ceramic powder achieved through high entropy solid solution and melt pool heat transfer preparation method

Anomalous electromagnetic wave absorption of MAX phase ceramic powder achieved through high entropy solid solution and melt pool heat transfer preparation method

All that is solid melts into air (Salton Sea), 2017

This paper is an analysis of the artist Sadia Sadia’s 5’54” filmed loop three channel digital video and surround sound installation ‘all that is solid melts into air (Salton Sea)’ filmed at the Salton Sea, Coachella Valley, California in 2017. Integrating a practice that has included music production, sound design and fine art filmed installation, the artist examines the Salton Sea as a site of ecological devastation undergoing drought amplified by the climate crisis. The drying lake exposes ‘Salton Sea dust’ which contains a mix of arsenic, selenium, chromium, zinc, lead and DDT as a consequence of industrialised agricultural activity. The filmed installation employs aesthetic ‘methodologies of transcendence’ to initiate sublime, transcendent and epiphanic states, grounded in practice-based artistic research as well as existing sociological, psychological and neuroscientific research. Through an examination of the filmed installation work, the artist interrogates whether there is an element of the sacred that can be found in ecological devastation and whether the redemptive power of awe can lead from individual epiphany through to meaningful collective change. The submission is of a creative work of practice-based research with an accompanying expository text by a practicing artist and filmmaker.

Unveiling the physical properties predictive of oil binding capacity in an interesterified palm‐based fat

AbstractThis paper identifies physical properties of an interesterified palm‐based fat (EIEPO) that predict oil binding capacity (OBC). A 100% EIEPO sample, 50% EIEPO sample diluted with 50% soybean oil (SBO), and a 20% EIEPO sample diluted with 80% SBO were used to test how saturation level impacts OBC. All samples were crystallized using either a fast (6.4°C/min) or slow (0.1°C/min) cooling rate as well as with or without the application of high‐intensity ultrasound (HIU; 20 kHz) to generate a wide range of physical properties. Immediately after crystallization, the sample's physical properties, including crystal microstructure, solid fat content (SFC), viscoelasticity (G′, G″, and δ), melting behavior, hardness, and OBC (centrifuge method) were quantified. The samples were then stored for 48 h at 22 and 5°C and the aforementioned physical properties were measured again, with one additional measurement for the samples stored at 5°C—OBC using a filter paper method (OBCp). The results indicate that OBC can be optimized in a palm‐based fat by modifying the physical properties which was achieved via the processing conditions. Both measurements of OBC were significantly correlated with SFC, hardness, δ, and enthalpy. A model was developed to predict a sample's OBCc using the following dominant variables—SFC, hardness, peak temperature, enthalpy, and the number of crystals. These results suggest that OBC can be predicted using a sample's SFC, hardness, peak temperature, enthalpy, and number of crystals and that SFC, hardness, and enthalpy are main drivers of OBC.

Functional properties of cream and butter oil from milk of Holstein cows abomasally infused with increasing amounts of high-oleic sunflower fatty acids.

This research paper addresses the hypothesis that there is an optimal amount of intestinally available oleic acid (provided via abomasal infusion) to produce higher-oleic acid milk fat with satisfactory functional characteristics of cream and butter oil. A control and four increasing doses of free fatty acids from high oleic sunflower oil (HOSFA) were infused into the abomasum of four lactating dairy cows in a crossover experimental design with 7-d periods. Treatments were: (1) control (no HOSFA infused), (2) HOSFA (250 g/d), (3) HOSFA (500 g/d), (4) HOSFA (750 g/d), and (5) HOSFA (1000 g/d). All treatments included meat solubles and Tween 80 as emulsifiers. Viscosity, overrun and whipping time as well as foam firmness and stability were evaluated in whipping creams (33% fat). Solid fat content (from 0 to 40°C), melting point and firmness were determined in butter oil. Whipping time of cream increased linearly and viscosity decreased linearly as infusion of HOSFA increased. Overrun displayed a quadratic response, decreasing when 500 g/d or more was infused. Foam firmness and stability were not affected significantly by HOSFA. For butter oil, melting point, firmness, and solid fat content decreased as HOSFA infusion increased. Changes in 21 TG fractions were statistically correlated to functional properties, with 6-10 fractions showing the highest correlations consistently. Decisions on the optimal amount of HOSFA were dependent on the dairy product to which milk fat is applied. For products handled at commercial refrigeration temperatures, such as whipping cream and butter oil, the 250 g/d level was the limit to maintain satisfactory functional qualities. Palmitic acid needed to be present in at least 20% in milk fat to keep the functional properties for the products.

Shape effect on solid melting in flowing liquid

Iceberg melting is a critical factor for climate change. However, the shape of an iceberg is an often neglected aspect of its melting process. Our study investigates the influence of different ice shapes and ambient flow velocities on melt rates by conducting direct numerical simulations of a simplified system of bluff body flow. Our study focuses on the ellipsoidal shape, with the aspect ratio as the control parameter. We found the shape plays a crucial role in the melting process, resulting in significant variations in the melt rate between different shapes. Without flow, the optimal shape for a minimal melt rate is the disk (two-dimensional) or sphere (three-dimensional), due to the minimal surface area. However, as the ambient flow velocity increases, the optimal shape changes with the aspect ratio. We find that ice with an elliptical shape (when the long axis is aligned with the flow direction) can melt up to 10 % slower than a circular shape when exposed to flowing water. Following the approach considered by Huang et al. (J. Fluid Mech., vol. 765, 2015, R3) for dissolving bodies, we provide a quantitative theoretical explanation for this optimal shape, based on the combined contributions from both surface-area effects and convective-heat-transfer effects. Our findings provide insight into the interplay between phase transitions and ambient flows, contributing to our understanding of the iceberg melting process and highlighting the need to consider the aspect-ratio effect in estimates of iceberg melt rates.

Molecular Spectroscopic (FTIR and UV-Vis) Analysis and In Vitro Antibacterial Investigation of a Deep Eutectic Solvent of N,N-Dimethyl Urea-Citric Acid

The intriguing pursuit of environmentally friendly solvents with tailored properties for diverse applications is a focal point of numerous studies, encompassing precursor selection, thorough characterization, and the exploration of potential applications. The study aims to assess the physicochemical properties and antimicrobial activity of deep eutectic solvents (DES) produced from N,N-dimethyl urea (DMU) and citric acid (CA), highlighting differences from their individual precursors. Various mass ratio variations of (DMU, solid) and (CA, solid) (DMU:CA = 1.0:1.0; 1.0:1.5; 1.0:2.0; 2.0: 1.0; 1.5:1.0) have been tested to make DES solvents through the melt process. Both types of blends generally melt at a temperature of 80°C. The overall liquid resulting from the melting of solids was generally clear in color. Molecular analysis using an infrared spectrophotometer showed some insignificant shifts from one product to another, compared with DMU and CA as precursors. Likewise, analysis using a UV–Vis spectrophotometer, when the entire sample was dissolved in demineralized water (2 mg/mL), showed no difference in the spectrum. In addition, functional group analysis using a spectrophotometer showed some minor changes, mainly shifts in peaks due to changes in the DMU:CA ratio. This may be due to the interaction of the hydrogen donor and the hydrogen acceptor in DES. All samples showed absorption peaks in the ultraviolet region of 202-210 nm. The resulting DES application showed growth inhibitory activity for Staphylococcus aureus and Escherichia coli bacteria in all products produced. The same analysis of the two types of precursors used showed that only CA had activity, but DMU did not have similar activity.

Experimental study on the melting heat transfer characteristics of a phase change material under mechanical agitation

Phase change materials (PCMs) are extensively employed for the thermal management of electronic devices, but their low thermal conductivity often results in slow heat absorption and release in practical applications. Existing improvement measures primarily focus on enhancing heat conduction, while research from the perspective of convection is scarce. Therefore, an experimental study on the melting heat transfer characteristics of n-docosane under mechanical agitation (0–1600 RPM) was conducted at 4.7–34 kW/m2. Upon agitation, the heating wall temperature (Tw) rapidly decreases, while the PCM temperature, heat transfer coefficient and Nusselt number significantly increase, and their variation amplitude is positively correlated with the rotation speed. This can be attributed to enhanced liquid PCM convection and accelerated solid PCM melting. At 8.5 kW/m2, the Tw at 1600 RPM is approximately 27 °C lower than that at 0 RPM, leading to a fourfold increase in the Nusselt number. Tw decreases with increasing rotation diameter, especially at lower rotation speeds. From 30 to 50 mm, the temperature decreases by approximately 13 and 10 °C at 800 and 1600 RPM, respectively. Tw changes slightly with increasing rotation height. Agitation can reduce the increase in Tw caused by a higher heat flux. Agitation can quadruple the upper limit of heat flux from 8.5 to 34 kW/m2 while maintaining consistent thermal control requirements. The power consumption of agitation increases as the rotation speed and diameter increase, peaking at 10.1 W. Moreover, after considering the minimum start-up time, Tw, and power consumption, the optimal configuration is determined: a rotation height of 10 mm and a rotation diameter of 40 mm for 1600 RPM and 50 mm for 800 RPM. These findings hold significant implications for PCM-based thermal management, particularly in terms of incorporating active convection enhancement.