Latent Heat Of Solidification Research Articles

Optimization of the production and storage of cold in a mechanical compression solar refrigerator

Design, optimization and realization of high-performance photovoltaic systems are topical issues. Especially in photovoltaic solar refrigeration machines, the cost and the lifetime of electrochemical batteries limit the development of these systems in places well served by solar radiation. The objective of the present study is to limit the action of the electrochemical battery in mechanical compression solar refrigeration systems by cold storage in a phase change material. From the cooling tests on a quantity of water bags, replacing the vaccines, we evaluated the overall energy consumption of the refrigerator, and the effect of the addition of a 24 liter-cold battery, placed inside a 150 liter-refrigerated enclosure. This action significantly reduced the daily energy consumption of the refrigerator from 59 to 34 Ah.d−1, a reduction of 42%. In addition, the thermal energy stored by the cold battery during this process made it possible to maintain the temperature of the water bags between 2°C and 8°C for more than 6.5 days without supplying electrical energy. The cold storage by latent heat of solidification not only improves the internal thermal inertia of the refrigerator, but also replaces a portion of the electrical energy of the photovoltaic generator.

Preparation and properties of porous diatomite-supported multi-walled carbon nanotubes with Na2SO4·10H2O-based phase change energy storage composites

The Na2SO4·10H2O-based phase change energy storage materials (PCMs) were fabricated through vacuum impregnating and adsorbing the oxidized multi-walled carbon nanotubes (MWCNs) with diatomite. The Fourier Transform Infrared Spectroscopy results reveals that the existence of carboxyl and hydroxyl groups in MWCNs can increase its compatibility with PCMs. The vacuum impregnated to obtain the diatomite composite PCMs (PCMs-M-D) crystallize adhering to the treated diatomite (DI-2) observed from the scanning electron microscope. The PCMs-M-D displays negligible supercooling and the thermal conductivity reaches 0.97 W m−1 K−1. Moreover, after 100 cycles of phase change, the melting latent heat loss is 1.43% and the solidification latent heat loss is 11.15%, showing good heat storage performance and chemical stability.

Comparison of approaches to the numerical modelling of pure metals solidification using the control volume method

ABSTRACT The thermal processes proceeding in the casting-mould system are analysed. Solidification process can be described in the different ways. One of them consists in the application of the Fourier–Kirchhoff equation in which the source function controlling the phase change is introduced. In this paper, two approaches to the modelling of pure metals solidification, i.e. the solidification proceeding at the constant temperature and in the artificially introduced interval of temperature are considered. Numerical model used at the stage of computations is constructed using the Control Volume Method in which the principle of conservation of energy (taking also into account the release of latent heat of solidification) is applied to each control volume ensuring the correctness of the model. The use of Voronoi/Thiessen tessellation to the discretization of the casting-mould system can accurately reproduce the shape of each sub-domain. In the final part of the paper, the examples of computations are shown.

Microstructure Formation in Freezing Nanosuspension Droplets.

The structural evolution of suspensions upon freezing is studied with optical microscopy in a suspended droplet configuration. Droplets are of millimeter size and consist of an aqueous mixture of silica particles, while the surrounding phase is hexane. Freeze-thaw cycles are applied to this system, and a two-step freezing mechanism is evidenced. A fast adiabatic growth of dendrites that invade the full droplets is first observed and occurs within a few milliseconds. Then, a slow process lasts for several seconds and corresponds to the release of solidification latent heat into the hexane phase. The striking feature of this work is to evidence that after the first freeze-thaw cycle flocculated microstructures are generated. When a second cycle is performed, microstructures further flocculate and generate, for dense silica suspensions, stable porous spheres of the size of the droplets. A phenomenological description based on repulsion or engulfment of particles by solidifying ice fronts is proposed.

Numerical Simulation of Polysilicon Solid-liquid Interface Transmogrification in Heat Transfer Process

The shape of solid-liquid interface during the directional solidification process, which is difficult to be observed and measured in actual processes, controls the grain orientation and grain size of polysilicon ingot. We carried out numerical calculations of the directional solidification progress of polycrystalline silicon and invested the means to deal with the latent heat of solidification in numerical simulation. The distributions of the temperature field of the melt for the crystallization progress as well as the transformation of the solid-liquid interface were obtained. The simulation results are consistent with the experimental outcomes. The results show that the curvature of solid-liquid interface is small and stability, larger grain sized columnar crystal can be grown in the laboratory-scale furnace at a solidification rate of 10 μm•s-1. It shall provide important theoretical basis for metallurgical process and polysilicon production technology.

Computer Simulation of the Solidification Process Including Air Gap Formation

Abstract The paper presents an approach of numerical modelling of alloy solidification in permanent mold and transient heat transport between the casting and the mold in two-dimensional space. The gap of time-dependent width called "air gap", filled with heat conducting gaseous medium is included in the model. The coefficient of thermal conductivity of the gas filling the space between the casting and the mold is small enough to introduce significant thermal resistance into the heat transport process. The mathematical model of heat transport is based on the partial differential equation of heat conduction written independently for the solidifying region and the mold. Appropriate solidification model based on the latent heat of solidification is also included in the mathematical description. These equations are supplemented by appropriate initial and boundary conditions. The formation process of air gap depends on the thermal deformations of the mold and the casting. The numerical model is based on the finite element method (FEM) with independent spatial discretization of interacting regions. It results in multi-mesh problem because the considered regions are disconnected.

Enhancement of heat transfer in Czochralski growth of silicon crystals with a chemical cooling technique

The cost of producing single-crystalline silicon with the Czochralski method can be reduced by promoting the crystal size and/or crystal pulling rate. However, more latent heat of solidification needs to be released from the melt-crystal (m-c) interface during the crystal growth process. In this study, the C-CO2 chemical endothermic reaction is proposed as a novel and efficient cooling technique to solve this problem. Compared with the conventional gas cooling method, C-CO2 endothermic reaction method can significantly enhance the heat transfer in the crystal at the m-c interface. It was found that the heat transfer is more enhanced with a chemical reaction of smaller activation energy, and the m-c interface becomes flatter. The influence of the carbon concentration in the chemical reactive gas flow on the heat removal in the crystal at the m-c interface is also investigated. The cooling effect is significantly increased with the increase in the carbon concentration when it is small. However, when the carbon concentration in the reactive gas is high, the cooling effect just increases slightly. The research demonstrates that the proposed chemical endothermic reaction is a promising cooling technique to be applied in CZ-Si crystal growth with large size/high pulling rate.

Phase change characteristics of ethylene glycol solution-based nanofluids for subzero thermal energy storage

Summary Nanofluids, particularly water-based nanofluids, have been extensively studied as liquid–solid phase change materials (PCMs) for thermal energy storage (TES). In this study, nanofluids with aqueous ethylene glycol (EG) solution as the base fluid are proposed as a novel PCM for cold thermal energy storage. Nanofluids were prepared by dispersing 0.1–0.4 wt% TiO2 nanoparticles into 12, 22, and 34 vol.% EG solutions. The dispersion stability of the nanofluids was evaluated by Turbiscan Lab. The liquid–solid phase change characteristics of the nanofluids were also investigated. Phase change temperature (PCT), nucleation temperature, and half freezing time (HFT) were investigated in freezing experiments. Subcooling degree and HFT reduction were then calculated. Latent heat of solidification was measured using differential scanning calorimetry. Thermal conductivity was determined using the hot disk thermal constant analyzer. Experimental results show that the nanoparticles decreased the PCT of 34 vol.% EG solution but minimally influenced the PCT of 12 and 22 vol.% EG solutions. For all nanofluids, the nanoparticles decreased the subcooling degree, HFT, and latent heat but increased the thermal conductivity of the EG solutions. The mechanism of the improvement of the phase change characteristics and decrease in latent heat by the nanoparticles was discussed. The nanoparticles simultaneously served as nucleating agent that induced crystal nucleation and as impurities that disturbed the growth of water crystals in EG solution-based nanofluids. Copyright © 2016 John Wiley & Sons, Ltd.

The effect of Al-5wt%Ti-0.2wt%B on the solidification characteristics of 55wt%Al-Zn-1.6wt%Si alloy in hot-dip coating

Abstract In order to research the mechanism which grain refinement of 55 wt%Al-Zn-1.6 wt%Si alloy by Al-5 wt%Ti-0.2 wt%B (master alloy), the effect of different amount of master alloy on the microstructure and characteristic value of solidification for 55 wt%Al-Zn-1.6 wt%Si alloy were studied using thermal analysis. Important solidification events evaluated using the first and second derivative-cooling curve. The results show that the onset temperature of solidification increased from 560.1 to 572.2 °C, namely, the temperature of nucleation for primary α-Al increased from 560.1 to 572.2 °C after adding master alloy, latent heat of solidification which calculated by Fourier method increased from 168.36 to 185.61 KJ and agreed with the result of phase diagram (CALPHAD) calculation. Then, the microstructure and phase composition of cooling samples was analyzed. The results show that the microstructure was composed of primary α-Al, binary eutectic of Al-Si, ternary eutectic of Al-Zn-Si and agreed with the thermodynamic calculation.

Effect of Ce melt treatment on solidification path of ZA8 alloy

The solidification path of ZA8 alloy with Ce addition was characterized using Newtonian technique of thermal analysis. The solidification events were determined using cooling curve and its first derivative curve. The microstructure and chemical composition of various phases in the alloy were studied using EDS, SEM and XRD techniques. It was found that the addition of Ce did not cause formation of new phases. However, it hinders the nucleation of stable β dendrites in the alloy. The presence of Ce promotes the eutectoid phase transformation and increases the hardness of the alloy. Latent heat of solidification and heat of eutectoid transformation were found to increase on Ce addition. The upward solidification of the alloy against Cu chill was analysed. Chilling had significant influence on solidification parameters, and caused refinement of the microstructure. The addition of Ce to the melt had no effect during chill casting of the alloy.

Assessment of Latent Heat and Solid Fraction of Al-22Si Alloy Using Newtonian and Fourier Analysis Techniques

Computer aided cooling curve analysis (CACCA) is an online prediction tool for the determination of solidification characteristics of metals or alloys. The results of CACCA can be used to accurately determine latent heat and solid fraction needed for modeling of the solidification process. Newtonian and Fourier analysis techniques adopt a data base line fitting technique to the first derivative curve for calculation of the solid fraction and latent heat of solidification. This paper describes the theoretical and experimental procedures involved Newtonian and Fourier analysis techniques with reference to an Al-22% Si alloy. The correlations between the solid fraction and temperature/time for the alloy were determined.

Every Snowflake is Not Unique

This article discusses various aspects of snowflake architectures. It is certain that every snowflake conforms to only one architecture: a flat star with six fishbones connected at the center. The latent heat of solidification, which is released by the water vapor that becomes solid at the bead surface. There comes a critical time when the spherical bead is no longer an efficient architecture for dissipating heat. The principle calls for design change, toward faster heat release and solidification. The growth of ice morphs abruptly into a ball continued in one plane by needles. Because of the configuration of the water molecule, the needles grow in six directions. The flat star transfers heat to the surroundings more easily than a spherical bead with the same diameter. In order to give credit to the view that every snowflake is unique, the actual configuration depends on many secondary effects, which are of random origin.

Thermal and Kinetic Analysis of the solidification of a near eutectic Al-Cu Alloy

ABSTRACTIn this work the thermal and kinetic analysis of the cooling and solidification of a near eutectic Al-Cu alloy is performed using inverse thermal and solidification kinetics analysis. The Fourier thermal analysis is applied to experimental cooling curves to obtain data on solid fraction evolution and latent heat of solidification. Inverse thermal analysis is applied to calculate the global heat transfer coefficients that allow correct simulation of the cooling of experimental probes. The free growth method is used to obtain the eutectic growth coefficients. All the obtained parameters are feed into a heat transfer-solidification kinetics model to validate the methodology and results generated from this work. It is found a relatively good agreement between experimental and predicted cooling curves which suggest that this methodology could be used to generate useful information needed to simulate eutectic solidification.

Microstructure and grain orientation evolution of a specially shaped shroud during directional solidification process

The microstructure and the grain orientations of one shroud prepared by directional solidification process have been investigated using metallographic method and electronic backscatter diffraction (EBSD). The results indicate that the solidification process of the tested shroud is composed of three steps: dendritic branching, the break-up and drift of the dendrite arms and the solidification of the residual liquid. Misoriented grains were formed between the primarily solidified dendrite stems during the process of recalescence which was caused by the accumulation of the solidification latent heat. A low angle grain boundary of 6° was produced across the impinging dendrite fronts.

An Investigation on the Effect of S and Al on the Austenite Growth Morphology in Gray Cast Iron, Using Thermal Analysis and Etching Technique

The austenite nucleation and growth morphology was investigated through experiments by inoculation with pure Al in a controlled environment using DTA furnace and H.F furnace. The austenite volume fraction and the dendrite growth orientations were affected by the addition of Al to the melt. Thermal analyses were performed to study the effect of sulfur content on austenite volume fraction and growth morphology using DSC. The possibility of austenite nucleation by MnS particles was analyzed. Different sulfur contents in the alloys were resulting in change in the latent heat of solidification and the rate of austenite formation. Austenite volume fraction was measured with four methods, colour etching, DSC thermal analysis, lever rule, and using LH calculated by Thermo-Calc data base, and a comparison was made among them.

Effects of liquid structure transition on solidification by the Newton thermal analysis method

This paper is to explore the effects of the liquid structure transition (LST) on the solidification kinetics of Sn-30 wt% Sb alloy by the Newton thermal analysis (NTA) method and the solidified microstructure analysis. Influence of the cooling rate on solidification behavior and microstruc- ture was also concerned. With a self-designed sand mold, the cooling curves of five points were collected automatically in the process of solidification by a HYDRA. In the case of the liquid structure transition and a faster cooling rate, the mod- ification melt treatment will lead to a higher undercooling of nucleation and an increased solidification latent heat in cen- tral part of solidifying castings, then the eventual grain size was evidently refined.

Phase Field Simulation of Solidified Multiple Grains

A phase-field model based on the Ginzburg-Landan theory and KKS model is used to simulate the dendrite growth of multiple grains for Al-Cu alloy. The influence of solidification latent heat and undercooling on the growth of equiaxed dendrite, solute distribution and temperature distribution were studied. The results show that the dendrite has well-developed and the competitive growth between grains more intense with the increasing of undercooling. The release of solidification latent heat restrain dendrite growth to a certain extent, which led to the less developed growth of dendrite solidified in non-isothermal conditions than that in isothermal conditions.

Thermal stability and thermal property characterisation of Fe–14.4Cr–15.4Ni–2.4Mo–2.36Mn–0.25Ti–1.02Si–0.042C–0.04P–0.005B (mass%) austenitic stainless steel (Alloy D9I)

High temperature measurements of enthalpy increment (ΔHT°) and lattice parameter have been carried out on Alloy D9I by means of drop calorimetry and high temperature X-ray diffraction techniques, respectively. In addition, the thermal stability during heating and cooling from the melting range has been investigated by differential scanning calorimetry. It is found that under near equilibrium cooling conditions (3Kmin−1), Alloy D9I exhibits L→γ austenite→L+γ+δ ferrite→γ+δ→γ solidification mode. However, the phase fraction of δ ferrite and the temperature region of γ+δ two phase domain are found to be small. The on-cooling liquidus and solidus temperatures are found to be 1684 and 1631±5K, respectively. The latent heat of solidification is found to be in the range, 190–220Jg−1. The thermal analysis study has revealed that solution treated Alloy D9I exhibits an endothermic dissolution of Ti(C,N) particles at about 1323±2K, with an associated heat effect of 16–20Jg−1. The specific heat Cp and coefficient of linear thermal expansion αl at 298.15K are estimated to be 486Jkg−1K−1 and 1.15×10−5K−1, respectively. The measured temperature dependencies of Cp and αl for Alloy D9I are in good agreement with the general trend exhibited by many austenitic steels. Further, an empirical linear correlation has been found between the measured temperature dependent molar volume and molar enthalpy values. The measured thermal property data have been modelled through Debye–Grüneisen formalism to obtain an integrated and self-consistent estimate of thermal properties in a comprehensive temperature domain ranging from 0 to 1400K.

Effect of Latent Heat to Solidification Process of Phase Change Material

The heat transfer characteristics of heat storage unit are analyzed by many researchers from both theoretical and experimental in solidification heat release. Most theoretical models define the initial temperature of the phase change materials is equal to the phase transition temperature, in fact, thermal storage unit in the application, its initial temperature is not equal to the phase transition temperature. Many theoretical models have not considered the impact of latent heat of solidification. In this paper, homemade inorganic hydrated salt material is used as heat storage media, packaging with a cylindrical container. The phase change heat transfer process was analyzed both from theoretical and experimental. The effect of initial temperature and the latent heat of the heat transfer material were both considered.

Determination of solid fraction–temperature relation and latent heat using full scale casting experiments: application to corrosion resistant steels and nickel based alloys

Casting simulation results are only useful to a foundry if they reflect reality, which requires accurate material datasets for the alloys being simulated. Material datasets include property data such as density, specific heat and thermal conductivity as functions of temperature, as well as latent heat of solidification and a solid fraction–temperature relation. Unfortunately, there are a significant number of commonly used metal alloys for which no reliable material data are available. The present study focuses on five such corrosion resistant alloys: superaustenitic stainless steel CN3MN, duplex stainless steels CD3MN and CD4MCuN and nickel based alloys CW6MC and N3M. Initial alloy material datasets are generated using thermodynamic simulation software. Comparisons of temperatures measured in full scale sand castings made from these alloys with temperatures predicted in computer simulations revealed that these initial datasets are inadequate. Therefore, an iterative method is developed to adjust the datasets (in particular the solid fraction–temperature relation and latent heat) in order to match measured and predicted temperatures and cooling rates. Uncertainties in the simulation are effectively eliminated through parametric studies. Although more tedious, the present iterative method to determine the solid fraction–temperature relation and latent heat is believed to be more accurate than traditional cooling curve analysis using small experimental castings.