The work is devoted to an experimental study of individual poorly studied stages of vapor explosion triggering (a dangerous destructive phenomenon that occurs during certain emergency situations in ...nuclear energy, metallurgical, pulp and paper, and other industries). Experiments were carried out to study the propagation of the detonation front after spontaneous explosive boiling (triggering) of water on a molten drop of salt (NaCl) and a vapor explosion stimulated by it on closely spaced neighboring drops of salt and tin. The temperature of the melted drops in the experiments was 850–1100°C and water temperature was room temperature (22–24°C). The main research tool was high-speed video recording of the process (recording frequency up to 50 kHz, exposure up to 5 μs). In order to study the initial stage of triggering associated with local contact of the cooler with a hot substance, experiments were carried out using high-speed video footage of the process of the vapor film coming off on a hot solid sphere, synchronized with fixing the sphere-cooler contact electrically. The footage of the instantaneous (precipitous) mode of vapor film disappearance with a duration of 200–500 μs and gradual (progressive) mode lasting approximately 100 ms on spheres under similar experimental conditions. It is shown that the main influence on the regime of film melting and vapor explosion on molten tin drops is exerted by the pressure pulse from the vapor explosion on a nearby NaCl drop. The characteristic times of the triggering process have been determined: tens to hundreds of microseconds. The value of the primary pressure pulse in the liquid has been established. The decisive role in triggering fine fragmentation of centimeter-long drops of hot liquid by the first contact of cold liquid with their surface has been confirmed.
•The experimental platform provides the hydrothermal behavior data for green roof.•The albedo of the green roof was measured and implemented in the numerical model.•A coupled heat and mass transfer ...model for green roof behavior was validated.•Comparison was undertaken between green and conventional roofing.•Green roofing reduces energy demand and outside air temperature in canyon streets.
In the present work, an experimental urban canyon (scale 1:10) with 4cm concrete wall thickness and full scale green roof was used to evaluate the impact of green roof inside and outside the buildings. The platform was equally used to validate a coupled heat and mass transfer model for green roof behavior. The albedo of the green roof was measured and implemented in the numerical model. The developed model has been coupled to a building thermal code (TRNSYS). Then, simulations were conducted for the experimental urban canyon studied where a comparison was undertaken between green and conventional roofing. A reduction of the maximum roof surface temperature by 20°C was found in summer due to the green roof. Green roof protects the roof membrane from high temperature fluctuations increasing the roof longevity and delay the timing of the peak membrane surface temperature by several hours. Also, the presence of vegetation permits to reduce the outside air temperature of the street canyon by 0.8°C. Hence, green roofing is an effective solution to reduce the total energy demand and to improve the urban microclimate in the street canyon for an oceanic temperate climate.
The numerical investigation of a Casson–Williamson reactive nanofluid species in a moving vertical medium is the subject of this study. The complete exothermic reaction of viscoplastic nanofluid ...material in a cylindrical system is considered using a generalized Arrhenius kinetic. Casson and Williamson fluids are combined to give the fluid its viscoelastic property. In collaboration with the bivariate overlapping multi-domain technique, the spectral quasi-linearization scheme is used to find solutions to dimensionless mathematical nonlinear formulated flow equations. The findings are displayed in tabular and graphical form, demonstrating the sensitivity of the thermofluid parameters. The study indicates that the flow motion is not caused by the activation energy or the material reaction. It was obtained that the magnetic field increased the viscosity of the material and the thermal conductivity of the nanoparticles. Also, Lewis number enhanced the fluid viscoplastic property. Thermal and chemical engineering, as well as nanotechnology development, will benefit from the findings of this investigation.
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•Pressure and chemical potential difference were introduced to decompose MH.•Water-gas-hydrate three-phase in sediment was indirectly distinguished via MRI.•The spatial-decomposition ...behaviors of one side or two side were observed.•Ice generation was eliminated by controlling water flow and depressurization rate.•Higher water flow and depressurization rate are benefit more for MH production.
As one of the most potential unconventional fossil fuels, the safe and efficient production of natural gas hydrates (NGHs) has become a prominent research area worldwide. Water flow erosion, which has been proven to be a powerful methane hydrate dissociation method recently, may be an effective way to mitigate the challenging ice generation problems urgently needed to be solved for depressurization production. In this study, we visually studied the effects of the three depressurization modes combined with water flow erosion on MH decomposition using in-situ magnetic resonance imaging. The time and spatial characteristics of the three-phase water–gas-hydrate during the MH production process are indirectly determined in sediment. Three stages of the energy recovery process are directly observed: the MH stable existing stage, the free gas production stage, and the MH decomposition stage. Our work indicates that all three combination modes effectively eliminate ice generated during the MH production process. Compared with the sudden depressurization method, radial extension appears on one side or two sides of the decomposition trends. In addition, the results denote that the higher water flow rate can efficiently enhance the effect of depressurization on hydrate dissociation. Meanwhile, the MH decomposition rate and formation stability benefit more from a faster water flow rate and depressurization rate.
Theoretical study on hydromagnetic heat transfer in dusty viscous fluid on continuously stretching non-isothermal surface, with linear variation of surface temperature or heat flux has been carried ...out. Effects of Hall current, Darcy porous medium, thermal radiation and non-uniform heat source/sink are taken into the account. The sheet is considered to be permeable to allow fluid suction or blowing, and stretching with a surface velocity varied according to a linear. Two cases of the temperature boundary conditions were considered at the surface namely, PST and PHF cases. The governing partial differential equations are transferred to a system of non-linear ordinary differential equations by employing suitable similarity transformations and then they are solved numerically. Effects of various pertinent parameters on flow and heat transfer for both phases is analyzed and discussed through graphs in detail. The values of skin friction and Nusselt number for different governing parameters are also tabulated. Comparison of the present results with known numerical results is presented and an excellent agreement is found.
The work reviews the research and development status of magnesium alloy, with more attention to the methodologies and technologies adopted to improve the properties of AZ91 alloy. The drive force of ...utilizing magnesium alloys for automotive and biomedical application is light weightiness and biocompatibility respectively. However, the softness and high activity of magnesium alloys result in high wear and high corrosion rate respectively. One of the essential factors influencing the properties of magnesium alloy is its microstructure. Consequently, the grain size, morphology and distribution of phase constituents influence the properties of magnesium alloys. The modification of microstructure through processing route (hot working and cold working), heat treatment, and alloying elements improves the mechanical, corrosion, biocompatible, and tribological properties of magnesium alloys. Besides microstructural modification processes, addition of reinforcements, and coatings improves the properties of magnesium alloys. This article emphasis on the recent research on the technologies to improve the microstructure, hardness, tensile strength, ductility, yield strength, wear resistance, and corrosion resistance of magnesium alloy AZ91. Moreover, this review addresses the key issues hindering the applications of magnesium alloys for structural and biomedical applications.
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This paper reported a review based study into the Indirect Evaporative Cooling (IEC) technology, which was undertaken from a variety of aspects including background, history, current status, concept, ...standardisation, system configuration, operational mode, research and industrialisation, market prospect and barriers, as well as the future focuses on R&D and commercialisation. This review work indicated that the IEC technology has potential to be an alternative to conventional mechanical vapour compression refrigeration systems to take up the air conditioning duty for buildings. Owing to the continuous progress in technology innovation, particularly the M-cycle development and associated heat and mass transfer and material optimisation, the IEC systems have obtained significantly enhanced cooling performance over those the decade ago, with the wet-bulb effectiveness of greater than 90% and energy efficiency ratio (EER) up to 80. Structure of the IEC heat and mass exchanger varied from flat-plate-stack, tube, heat pipe and potentially wave-form. Materials used for making the exchanger elements (plate/tube) included fibre sheet with the single side water proofing, aluminium plate/tube with single side wicked setting (grooved, meshed, toughed etc), and ceramic plate/tube with single side water proofing. Counter-current water flow relevant to the primary air is considered the favourite choice; good distribution of the water stream across the wet surface of the exchanger plate (tube) and adequate (matching up the evaporation) control of the water flow rate are critical to achieving the expected system performance. It was noticed that the IEC devices were always in combined operation with other cooling measures and the commonly available IEC related operational modes are (1) IEC/DEC system; (2) IEC/DEC/mechanical vapour compression system; (3) IEC/desiccant system; (4) IEC/chilled water system; and (5) IEC/heat pipe system. The future potential operational modes may also cover the IEC-inclusive fan coil units, air handle units, cooling towers, solar driven desiccant cycle, and Rankine cycle based power generation system etc. Future works on the IEC technology may focus on (1) heat exchanger structure and material; (2) water flowing, distribution and treatment; (3) incorporation of the IEC components into conventional air conditioning products to enable combined operation between the IEC and other cooling devices; (4) economic, environment and social impacts; (5) standardisation and legislation; (6) public awareness and other dissemination measures; and (7) manufacturing and commercialisation. All above addressed efforts may help increase the market ratio of the IEC to around 20% in the next 20 years, which will lead to significant saving of fossil fuel consumption and cut of carbon emission related to buildings.
This paper focuses on researching the various factors that influence the material melting rate during the hot air melting process. To achieve this purpose, the paper proposes a melting model for ...Acrylonitrile-Butadiene-Styrene (ABS) plastic under hot air heating based on Computational Fluid Dynamics (CFD). Orthogonal experiments were conducted based on the parameter range of each factor obtained in the pre-experiment. The results showed that the outlet distance, hot air velocity, hot air temperature, and their interaction items are important factors that affect the melting rate of ABS materials. Based on the simulation results, a multiple nonlinear regression model was constructed to predict the melting rate under different parameters. Comparing the simulation values with the predicted values of the multiple nonlinear regression model, the error between the two was no >10%, indicating the effectiveness of the prediction model. The research results can help guide the hot air welding melting process for different materials and characteristics, and provide a certain reference value for the development of hot air welding technology.
•Welding of airbag labels was performed using hot air welding technology;•Realizes real-time monitoring of melt quality during the material melting process•Using CFD modeling to study the effects of outlet distance, hot air velocity, and hot air temperature on the melting rate.
Spectral methods are ubiquitous in the analysis of dynamically evolving fluid flows. However, tools like Fourier transformation and dynamic mode decomposition (DMD) require data that satisfy the ...Nyquist–Shannon sampling criterion. In many fluid flow experiments, such data are impossible to acquire. We propose a new approach that combines ideas from DMD and compressed sensing to accommodate sub-Nyquist-rate sampling. Given a vector-valued signal, we take measurements randomly in time (at a sub-Nyquist rate) and project the data onto a low-dimensional subspace. We then use compressed sensing to identify the dominant frequencies in the signal and their corresponding modes. We demonstrate this method using two examples, analyzing both an artificially constructed dataset and particle image velocimetry data from the flow past a cylinder. In each case, our method correctly identifies the characteristic frequencies and oscillatory modes dominating the signal, proving it to be a capable tool for spectral analysis using sub-Nyquist-rate sampling.
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