Weakly non-linear stability of stratified natural convection in a vertical cavity with lateral temperature gradient

Stability of free convection is examined in a vertical cavity with a fixed lateral temperature difference on the walls, which is also heated from the bottom by a constant heat flux causing vertical stratification of the base flow. Weakly nonlinear stability equations are derived, under the assumption of fully developed flow conditions. Critical Rayleigh numbers and Landau coefficients are determined in terms of the Prandtl number and stratification parameter. It is found that critical disturbances are always two-dimensional, for stationary and oscillating instabilities as well. Alternatives are considered for the calculation of the Landau coefficient. Analysis reveals that unstationary instability is the preferred mode at the codimension point.     

Optimization of Photovoltaic Reflector System for Indoor Energy Harvesting

This study proposes a solution for optimizing the distance between a solar module and reflector for an indoor energy harvesting system. It is a process in which energy(ambient light) is captured and converted directly into electricity. Inside a building, this energy could be used to supply power to wide range of portable equipment or offset other electrical energy usage and associated costs. The proposed reflector element was designed and tested in a real indoor environment to confirm its effectiveness. A distance-optimization method for the placement of a polycrystalline photovoltaic (PV) module and a mirror was described, and the performance characteristics of the system were investigated qualitatively through visual observation and quantitatively through measuring voltage and ampere values. The solar PV system with a reflector element displayed a 10% increase in voltage when compared with that without. As the distance between PV module and the reflector increased, the voltage and ampere reading decreased, thus the distance was optimized to gain maximum readings. Various studies employing reflectors have also showed increases in voltage readings with different designs, suggesting that reflectors are economically viable optical elements that can boost the voltage output of a PV module. In practice, the distance-optimized PV module can be placed in buildings with extended indoor lighting duration away from disrupting building activity.     

Palmitic Acid-Lauric Acid/Expanded Graphite as Form-Stable Composite Phase Change Material for Low-Temperature Energy Storage Applications

Low thermal conductivity of binary fatty acid mixture of palmitic and lauric acids (PA-LA) within the value range of 0.15-0.17 W/(m·K) restricts its wide utilization as thermal energy storage material in the active regime of solar heating applications at low operating temperatures. Nevertheless, this mixture as phase change material (PCM) has a suitable phase-change temperature and heat of 36 ℃ and 176.3 J/g, respectively. Hence, the objective of this study is to formulate a novel form-stable composite PCM with the PA-LA mixture and expanded graphite (EG) as a thermal enhancer. PA-LA eutectic mixture with varied concentrations of EG was prepared and characterized. The thermal conductivity of PA-LA/EG increased gradually with the mass of EG. Optimum thermal properties were observed in PA-LA/(5% EG) composite, where its melting (T_m), freezing temperature (T_f), latent melting heat and thermal conductivity was 35.53 ℃, 34.84 ℃, 174 J/g, and 1.19 W/(m·K), respectively. Also, the composite PCM is characterized by good chemical-thermal stability and thermal reliability for long-term usage. In conclusion, it can be utilized as a prospective form-stable PCM for thermal energy storage in solar heating systems, overheat treatment systems, and other thermal storage applications at low operating temperatures.     

Prediction simulation of sports injury based on embedded system and neural network

Sports injury prediction is one of the most important parts of the challenge of prevention and harm challenging in motion. Sports injury contemplated wherein a simplified view of the phenomenon to study the reduction unit's cause. A linear analysis is viewed as the unidirectional manner a substantial portion of, and causality. This reduction method depends on the correlation and regression analysis. Despite the extensive efforts to predict sports injuries, the existing method is the inability to identify the predictors that were and have been limited. The risk of the very important element for sports players' injury when developing prevention and risk mitigation strategies for work-related accidents. Some signs can be used in many ways to identify risk factors for injury. However, it can be made from the data and lead to incorrect inferences and difficulty understanding the nuances of different statistical methods. The proposed Neural Network (NN) and the embedded system classify the sports player's injury prediction to solve the problem. The proposed Neural Network (NN) and the embedded system have attracted a simple calculation and interpretation of the reliable results for sports injury prediction. The simulation results show the high performance compared to other existing methods.     

Synthesis of water networks for industrial parks considering inter-plant allocation

Since an industrial park is a cluster of multiple company individuals, there is requirement to develop specific reuse strategies so as to improve the utilization of resources across plants. This article presents a ‘plant-based’ mode respecting to the water allocation problem within industrial parks. In the mode, mixers and splitters are involved to present the mixing, conveying and splitting operations for reusing streams across plants. Such that, the mixing possibilities can also be investigated and many redundant solutions can be avoided by considering the number limit of inter-plant stream connections at the building stage of network superstructures. On base of this mode, both direct and mixed (direct–indirect) integration scenarios are studied in this study. Superstructures are established and mathematically formulated aiming to minimum fresh water consumption as well as the total annualized cost. At last, three integration cases are explored based on an example from literature for illustration.     

Preliminary Investigation of Copper Joints Soldered with Sn58Bi

In recent years, intensive studies have been carried out to find an alternative for Tin (Sn)-Lead (Pb) solder alloys with increasing demand over lower temperature solder alloys in current electronic packaging industry. High temperature operational solder alloys seem to produce drawback to other components on the printed circuit board (PCB). Low melting temperature Sn58Bi substrate as a potential replacement was investigated in this paper based on the melting properties, wettability, and shear strength. The Sn58Bi was soldered at a temperature below 200 ℃ on the Cu substrate, and the shear strength and contact angle were calculated. A peak temperature (melting temperature, TM) of 144.83 ℃ was identified. Single lap joint method was performed at a strain rate of 0.1 mm/min and an average shear strength of 23.4 MPa was found from three samples. The contact angle (wettability) was calculated to study the solder joint behaviour at reflow temperature of 170 ℃. The contact angle of the Sn58Bi was found to be 32.4 ° and considered to be desired value since the angle is less than 50 °. The low temperature soldering provides a preliminary result to allow further application on the real PCB.     

Improved strength-impairing contact damage resistance of Ti3Si(Al)C2/SiC composites

The resistance of Ti₃Si(Al)C₂-based materials to strength-impairing contact damage was investigated using the Hertzian indentation method. Microstructural analysis indicated that for the three types of testing materials the contact damage was governed by multiple grain slip, crushed grains, and intergranular shear failure. No cone cracking or other macro-cracks were visible on or beneath the contact damage surfaces. Bending tests on the specimens containing single-cycle contact damage revealed that the resistance of Ti₃Si(Al)C₂ to strength degradation was significantly improved by incorporating SiC particles into the matrix. The mechanism of the improvement is ascribed to the increased shear resistance and the fact that the hard SiC particles inhibit the downward extent of the contact damage through restricting the slip and deformation of the Ti₃Si(Al)C₂ grains.     

Methyl Ester Sulfonate: A High-Performance Surfactant Capable of Reducing Builders Dosage in Detergents

The detergency performance of α-sulfo fatty-methyl ester sulfonate (α-MES) under different water hardness conditions was compared against the dominant workhorse in Home Care products, linear alkylbenzene sulfonate (LAS). Results demonstrate that α-MES has a higher soil removal index and its detergency performance is not drastically affected by water hardness, compared to that of LAS. The addition of α-MES to LAS also shows an improved cleaning performance and better water hardness resistance, due to the structural characteristics of α-MES, which allow the molecules to be relatively insensitive toward polyvalent ions such as Ca²⁺ and Mg²⁺. The washing performance of α-MES, α-MES/LAS, and LAS with different builders at various dosages was studied, and the results indicated that the dosage of builders in the detergent product could be reduced up to 33% with the application of α-MES, while the detergency is not sacrificed.     

Cleaning Ability of Mixed Solutions of Sulfonated Fatty Acid Methyl Esters

Here, we present results from a systematic study on cleaning of oily deposits from solid surfaces (porcelain and stainless steel) by solutions of fatty acid sulfonated methyl esters (SME), sodium salts. The zwitterionic dodecyldimethylamine oxide (DDAO) has been used as a cosurfactant. As representatives of the vegetable and mineral oils, sunflower seed oil and light mineral oil have been used. The process of oil drop detachment from the solid substrates (roll-up mechanism) has been monitored. In the case of porcelain, excellent cleaning of oil is achieved by mixed solutions of SME and DDAO. In the case of stainless steel, excellent cleaning (superior than that by linear alkylbenzene sulfonate and sodium lauryl ether sulfate) is provided by binary and ternary mixtures of SME, which may contain also DDAO. For the studied systems, the good cleaning correlates neither with the oil/water interfacial tension, nor with the surfactant chainlength and headgroup type. The data imply that governing factors might be the thickness and morphology of admicelle layers formed on the solid/water interface. The results indicate that the SME mixtures represent a promising system for formulations in house-hold detergency, having in mind also other useful properties of SME, such as biodegradability, skin compatibility, and hard water tolerance.     

Development of a new in situ test method to measure the air permeability of high performance concretes

Although several in situ techniques, including the Autoclam Permeability System, are available to examine normal concretes (NCs) for this purpose, none are sufficiently sensitive to quantify and distinguish relative high performance concrete (HPC) performance. Therefore, to assess the HPC performance characteristics using the Autoclam air permeability test methodology, two key modifications were investigated and a new test protocol developed. The first modification considered a reduced volume of compressed air applied to the test area (named LV test), and the second an increased test area (named A-75). The reliability of the proposed modifications was investigated by comparing against a laboratory-based gas permeability test method (RILEM air permeability test). Surface resistivity and relative humidity were assessed to evaluate the influence of moisture conditions on in situ air permeability test results. A strong correlation between LV test and RILEM air permeability test results was found when the free moisture near concrete surface regions (up to 20 mm) was removed. It was concluded that the LV test exhibits strong potential to become an established method for assessing in situ HPC permeability.