•Visual experimental system is built to study the orientations effect on phase change.•The melting interface is observed in the experiment.•Inclination angle significantly affects heat transfer in ...pure phase change material.•Heat sink is designed using composite PCM without considering installation angle.
Using paraffin as phase change material, the melting behaviors of pure phase change material and phase change material embedded in open-cell metal foams (composite phase change material) at different inclination angles are studied. Experimental system enabling continuous rotating is designed and built to explore the influence of inclination angles on phase interface evolution and temperature responses inside pure and composite phase change materials. Constant wall temperature is applied on one surface while others are thermally insulated. Experiments are carried out at angles of 0°, 30°, 60°, and 90° respectively. The effects of inclination on the melting behavior of phase change materials are analyzed by visualizing the solid-liquid interface and analyzing the temperature responses. Results demonstrate that the inclination angle has a great influence on the formation and development of natural convection during melting of pure phase change material, affecting the solid-liquid interface propagation and heat transfer rate. Compared with the case at 90°, the full melting time is reduced by 12.28%, 22.81% and 34.21% at 0°, 30° and 60°, respectively. However, when phase change material is melted in open-cell metal foam, heat conduction dominates, and inclination angle has little influence. Melting fractions at different inclination angles are the same and temperature curves at given points overlaps with each other.
Solar energy, as a kind of renewable energy, offers a large reserve to be harvested at a reasonably low cost for engineering applications. To decouple the temporal and spatial relevance of the ...continuous energy supply of solar energy, latent heat thermal energy storage can deal with this problem at different temperatures. Aiming to improve energy efficiency, a novel hybrid metal foam-pin fin structure is designed and assessed. Upon conducting measurements on a well-designed experimental bench, the phase change processes of paraffin that is filled in fins, metal foam, and a combination of both (hybrid structure) are evaluated. During the experiments, the transient melting interface is snapshotted and temperature development is documented under five different heat source temperatures of 61 °C, 63 °C, 65 °C, 68 °C, and 70 °C. In the foreground of the novel hybrid structure, each segment of the hybrid is also justified and discussed. Results indicate that the hybrid structure augments marked heat transfer. Compared to pure PCM, complete melting time decreases by 63.4% and simultaneously the temperature response rate increases by 143.9% as implementing the hybrid. Attempts to design hybrid structure find a solution to assess and operate thermal storage applications for solar engineering.
In this study, the rheological behavior of TiO2/ZnO/EG nanofluid at temperature range of 25 °C to 50 °C has been experimentally investigated. The steady and homogeneous suspensions, in volume ...fractions of 0.1% to 1.5%, have been prepared with volume composition of 50% ZnO nanoparticles and 50% TiO2nanoparticles in a specified amount of EG. The viscosities of sample nanofluid have been measured in different shear rates of 6.12 S−1 to 61.2 S−1. The results of viscosity measurement showed that, TiO2/ZnO/EG nanofluid has Newtonian behavior in volume fractions of 0.1%, 0.3% and 0.5% and in all of the considered temperatures and by increasing volume fraction of nanoparticles, the viscosity of nanofluid enhances and also, by increasing the temperature, nanofluid viscosity reduces. While, the sample nanofluid in volume fractions of 1% and 1.5% have non-Newtonian behavior similar with power law model with power coefficient less than 1. For nanofluid samples in 1% and 1.5% volume fractions in all considered temperatures, the power law model coefficients have been calculated by curve-fitting with high accuracy The results indicated that, in general, by increasing volume fraction, the apparent viscosity enhances and by increasing the temperature, the apparent viscosity reduces.
•Produce a new hybrid nanofluid composed of TiO2/ZnO/EG.•Evaluation of sample dynamic viscosity based on empirical results.•Non-Newtonian power law model with temperature and concentration.
•A cryogenic flow electrification test rig has been set up.•The influence of velocity, pipe diameter, material and roughness has been analysed.•A modified semi-empirical correlation for streaming ...current based on our test data has been proposed.
Flow electrification occurs in all fluid flow scenarios involving solid–liquid interfaces. Due to electrostatic safety considerations, extensive research, both experimental and theoretical, has been conducted in the petroleum transportation field. However, research on flow electrification related to cryogenic fluids is relatively scarce, with even fewer experimental studies conducted. With the increasing use of cryogenic fluids such as liquid hydrogen and liquefied natural gas in aerospace and energy fields, there is an urgent need to expand the experimental database on cryogenic fluid flow electrification. In this context, a study focusing on cryogenic flow electrification using liquid nitrogen (LN2) as the working fluid was initiated, accompanied by the establishment of a flow electrification experimental platform capable of capturing ultra-low electrical signals at cryogenic conditions. Three measurement methods were designed and implemented, including charge, potential, and current measurements. By comparing their performance, the streaming charge method was identified as the optimal choice due to the stability and linearity of the raw signal. Subsequently, extensive testing was conducted to analyze the effects of various parameters, including flow velocity, pipe diameter, pipe material, and pipe roughness, on flow electrification intensity. The conclusions drawn include: within the experimental measurement range, the current induced by flow turbulence is on the order of 10−12 A for LN2. Moreover, increasing pipe diameter and roughness exacerbate the charge transported. Among the four materials tested, PTFE exhibits the highest intensity of flow electrification, followed by aluminum and stainless steel, with copper showing the weakest effect. Finally, based on the experimental data obtained, a modified semi-empirical correlation formula for the streaming current was proposed, which can reflect the specific effects of flow velocity, pipe diameter, material, and pipe roughness. Our measurement research has significant implications for the study of flow electrification in LN2 and its applications in aerospace and energy security fields.
•Using multi-scale testing experiments to distinguish the aging mechanism and performance transformation.•Molecular dynamics simulation is carried out to explore the microscopic mechanism of the ...aging property transformation.•Corresponding relationship between macroscopic and microscopic performance is determined through comparative analysis.
As a complex mixed system, the aging mechanism of high-energy composite materials involves the aging of each component itself, interactions between components, and transformation of microstructural and thermodynamic properties. The study of a single component or performance parameter has great limitations for elaborating the cognitive complexity of aging processes, making it difficult to reveal the underlying principles of physicochemical property transformation. Thus, it can only be applied as an empirical summary. In view of this, this study comprehensively utilized numerical analysis and experimental detection to explore the evolution of micromolecular conformation and changes in macro aging performance from four aspects of composite systems, including binder aging, plasticizer migration, bond interface debonding, and mechanical property transformation. There was good consistency observed between molecular simulation and thermal aging experiments, indicating that there was basically no post curing process for HTPB propellants using TDI as the curing agent. In the early stage of aging, scission chain was the main process and, in the later stage of aging, oxidation crosslinking the main process. Oxidative crosslinking increased the mean square radius of gyration and glass transition temperature of the binder system, reduced the peak value of radial distribution function, and revealed the reason for the change of propellant hardness and CC and CO double bond content. However, chain degradation increased the number of polar groups, enhanced intermolecular polarity, reduced the solubility parameter, and increased the free volume fraction of the mixed system and the dioctyl sebacate diffusion coefficient. This resulted in an increase in the tangent value of the HTPB propellant loss angle from 0.43 to 0.44° and a decrease in the glass transition temperature from 203.3 to 202.0 K. The binding energy at the interfaces of AP/HTPB and Al/HTPB increased first and then decreased, which was consistent with SEM images of bonding interfaces. The joint effect of binding energy and mechanical properties of the binder system promoted the transformation of the stress-strain curve of aging propellant.
In this paper, the nanofluid dynamic viscosity composed of CeO2- Ethylene Glycol is examined within 25–50 °C with 5 °C intervals and at six volume fractions (0.05, 0.1, 0.2, 0.4, 0.8 and 1.2%) ...experimentally. The nanofluid was exposed to ultrasound waves for various durations to study the effect of this parameter on dynamic viscosity of the fluid. We found that at a constant temperature, nanofluid viscosity increases with increases in the volume fraction of the nanoparticles. Also, at a given volume fraction, nanofluid viscosity decreases when temperature is increased. Maximum increase in nanofluid viscosity compared to the base fluid viscosity occurs at 25 °C and volume fraction of 1.2%. It can be inferred that the obtained mathematical relationship is a suitable predicting model for estimating dynamic viscosity of CeO2- Ethylene Glycol (EG) at different volume fractions and temperatures and its results are consistent to laboratory results in the set volume fraction and temperature ranges.
•Nanofluid viscosity of CeO2-EG is studied.•Effects of temperature and volume fraction on viscosity are considered.•Nanofluid has a newtonian behavior in all solid volume fractions.•Exact formula for nanofluids viscosity is obtained.
Scanning electron microscopy (SEM) of diamond nanoparticles.
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•Two carboxyl based nanoparticles dispersed in water with usage of no surfactant.•Effect of various parameters on ...nanofluids’ properties was evaluated experimentally.•ANFIS, ANN and regression were utilized to forecast nanofluids’ properties.•A detailed equation was concluded to predict properties of nanofluids.•Suggested equation is in great consent with the former works & experimental data.
Viscosity, density and thermal conductivity of Diamond-COOH and MWCNT-COOH nanoparticles dispersed in water was studied without adding any surfactants or additives for a range of 20 °C < T < 50 °C and 0.0 < φ < 0.2 vol%. Accordingly, based on the experimental data, a new correlation was introduced that predicts the nanofluids’ relative thermophysical properties. Besides the non-linear regression for minimum prediction error, an adaptive neuro-fuzzy inference system (ANFIS) and optimal artificial neural network (ANN) were developed. The model was fed by 120 experimental data. 70% of data points were included in the dataset training set and 30% were used as test set. The results of different theoretical models, predicted results and experimental data were compared together.The root-mean-square error (RMSE) and mean absolute percentage error (MAPE) were used to evaluate the results. The models explored the influence of material type, nanoparticle concentration and temperature on the thermophysical properties of nanofluids. As the results show the majority of theoretical models define the thermophysical properties accurately, if correct values of base fluid properties are fed to them. Yet, the current soft-computing methods show less error in comparison to the existing correlations. The ANN is recommended for future studies, as it provides the best fits to the experimental data.
•Solidification in open-cell metal foam is experimentally and numerically investigated.•Porosity rather than pore density dominates solidification process.•Natural convection affects greatly ...solidification front shape and temperature field.•Using composite PCM is profitable with a short payback period.
This study conducted both experimental and numerical investigations on the solidification behavior in a metal foam composite phase change material (PCM) for cold storage. Volume-average-method was adopted with the help of Forchheimer-Darcy equation to model the fluid flow through porous media. Experimental measurements were performed to validate the analytical model and the numerical method, with good agreement achieved. Local thermal equilibrium and non-equilibrium states were justified numerically and experimentally. Effect of pore morphological parameters (porosity and pore density) upon the solidification features of composite PCM were investigated. For the appliance of composite PCM to cold storage, techno-economic characteristics was also assessed. Results demonstrated that the full solidification time for metal foams with a porosity of 0.93 and 0.97 can be saved 87.5% and 76.7% respectively compared with pure water. It indicated that porosity of metal foam played a dominant role in heat transfer enhancement; while pore density seemed to have little influence on phase change behavior according to the results. Local natural convection in the unsolidified phase caused a remarkable promotion of the interface evolution, and the full solidification time with natural convection considered can be saved by 14.3% compared with pure conduction for the case with the same porosity of 0.97. The economic analyses indicated that using composite PCM was profitable with a short payback period less than 2 years.
•Water vapor adsorption of over-mature Longmaxi shales are investigated using gravimetric measurement.•Five classical isotherm models for water adsorption isotherm are evaluated.•Physical meaning ...behind the related parameters in the five classical isotherm models are discussed.•Four parameter double log polynomial (DLP) model is the optimal model to fit WVA isotherm on Longmaxi shale.
Mathematical characterization of water vapor adsorption (WVA) isotherms on organic-rich shale is important for both modeling processes such as water flow and mass transport, and accurate evaluation of moisture content in shale. Although several theoretical and empirical models have been proposed to describe WVA on porous materials (e.g, coal, food and carbon black), the applicability of these proposed models for over-mature gas shale (e.g., >2.0%Ro) is not well understood, which requires both experimental data and a theoretical description of downhole shale. In this work, WVA isotherms were measured at 50℃ (323.1 K) using a dynamic vapor sorption apparatus for four over-mature Lower Silurian Longmaxi shales, the leading gas-producing shale reservoir in the Sichuan Basin, China. To describe water adsorption behavior mathematically, five models, including the Guggenheim-Anderson-de Boer (GAB), double log polynomial (DLP), Oswin, Freundlich, and Frenkel-Halsey-Hill (FHH), for WVA isotherm are evaluated for their ability to match the experimental WVA isotherm data.
In general, all the models are suitable for fitting the experimental data, with R2 values larger than 0.95. However, the transformations of non-linear isotherm equations to their linear forms could implicitly alter the error structure and may violate the error variance and normality assumptions. To address this deficiency, six more statistical parameters (AAD, MSE, SEE, RSS, ARE and χ2) were used to evaluate the goodness-of-fit results for different models. Comparative studies show that the four-parameter DLP model is the optimal to predict the WVA isotherms on Longmaxi shale, with the smallest fitting errors, rather than the most versatile GAB model documented in the literature. Considering the WVA behavior, the distribution of water (free and adsorbed) in hydrophobic and hydrophilic pores in shales was also discussed, which can provide a reference point for theoretical analysis of water flow and retention.
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•The presented procedure records the full crack behaviour in large-scale experiments.•DIC results of the specimen’s surface provide highly accurate crack measurements.•Complex crack ...patters are automatically extracted using 2D image processing methods.•Several sensitivity analyses help in understanding the measurement uncertainty.•Crack measurements are represented with automated data visualisations tools.
The acquisition and evaluation of the crack behaviour in experiments on quasi-brittle materials, such as concrete, mortar, or masonry is essential for understanding their structural behaviour. This publication presents a fully automated procedure to detect cracks and measure crack kinematics in laboratory experiments instrumented with digital image correlation (DIC). Crack lines are extracted using well-established image processing methods showing excellent agreement with the physical crack pattern. In contrast to most existing crack detectors that rely on pixel intensities of true images, the presented crack detection is based on the DIC principal tensile strain field what allows the extraction of much finer cracks and more reliable crack locations. The crack widths and slips are measured using the DIC displacement field accounting for local rotations of the specimen. Additionally, automated visualisations of the crack kinematic measurements including data smoothing are presented. Several sensitivity analyses evaluating the performance and the uncertainty of the crack detector and the crack kinematic measurements have been conducted. These analyses show that the obtained results depend on the DIC configuration and that the procedure is limited in the case of very closely spaced cracks. With appropriate DIC parameters, the procedure allows detecting crack locations with high precision and measuring crack kinematics very accurately even in large-scale experiments with complex crack patterns.
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