恒热流直管中纳米流体对流传热的实验研究(英文)

In this work, the laminar convective heat transfer performance and the pressure drop of water-based nanofluids containing Al2O3, TiO2 and SiO2 nanoparticles flowing through a straight circular tube were experimen-tally investigated. The experimental results showed that addition of small amounts of nano-sized Al2O3 and TiO2 particles to de-ionized water increased heat transfer coefficients considerably, while the SiO2 nanofluids showed the opposite behavior attracting the authors’ interests. An average of 16%and 8.2%increase in heat transfer coefficient were observed with the average of 28%and 15%penalty in pressure drop for Al2O3 and TiO2 nanofluids.     

A General Hybrid GMDH–PNN Model to Predict Thermal Conductivity for Different Groups of Nanofluids

Theoretical Foundations of Chemical Engineering - In this study, a general model for estimating the nanofluids (NFs) thermal conductivity by using a hybrid group method of data handling polynomial...     

A File Group Data Replication Algorithm for Data Grids

In recent years data grids have been deployed and grown in many scientific experiments and data centers. The deployment of such environments has allowed grid users to gain access to a large number of distributed data. Data replication is a key issue in a data grid and should be applied intelligently because it reduces data access time and bandwidth consumption for each grid site. Therefore this area will be very challenging as well as providing much scope for improvement. In this paper, we introduce a new dynamic data replication algorithm named Popular File Group Replication, PFGR which is based on three assumptions: first, users in a grid site (Virtual Organization) have similar interests in files and second, they have the temporal locality of file accesses and third, all files are read-only. Based on file access history and first assumption, PFGR builds a connectivity graph for a group of dependent files in each grid site and replicates the most popular group files to the requester grid site. After that, when a user of that grid site needs some files, they are available locally. The simulation results show that our algorithm increases performance by minimizing the mean job execution time and bandwidth consumption and avoids unnecessary replication.     

Landscape Degradation Modelling: An Environmental Impact Assessment for Rural Landscape Prioritisation

Landscape Degradation Assessment (LDA) of rural areas can play a crucial role in landscape planning. Japan lacks quantitative and cumulative Environmental Impact Assessment (EIA) methodologies, especially in the area of LDA. Although a decision support system is in place for very large projects (Class-1) in Japan, EIAs for much smaller projects are non-existent, which often results in ambiguity with regard to environmental problems. To improve the transparency of the decision-making process for rural landscape planning, increase the scale of the assessment of project size to a more strategic local level, and enhance effective communication with decision-makers, a new EIA procedure is proposed with the development of a Landscape Degradation Model (LDM) for rural areas in Japan. The procedure is based on the equation, L_D=Σ kI/V, where L_D represents the degradation coefficient of the landscape compartments, Σ kI represents the cumulative impact of human activities, and V quantifies the vulnerability of a habitat. The value of L_D provides a means for supporting decisions aimed at the quantitative prioritisation of working units and developing respective conservation plans. This methodology is a holistic approach to rural landscape reclamation decision support systems where these LDM findings are geared toward sustainability appraisal and where integrated assessment of the economics of a proposal is recommended.     

Effect of interfacial-active elements addition on the incorporation of micron-sized SiC particles in molten pure aluminum

Ceramic particles generally have poor wettability by liquid metal, leading to a major drawback in fabrication of cast metal matrix composites (MMCs). In this work,  the effect of 1 wt. % of Ca, Mg, Si, Ti, Zn and Zr interfacial-active alloying elements was studied on the incorporation of micron-sized SiC particles into the molten pure aluminum using the vortex casting method at 680 °C. The results indicated that Ti, Zr, Zn and Si were not positively effective in improving particulate incorporation, while Ca and especially Mg were very efficient at increasing the incorporation of ceramic particles into the molten Al. Also, it was revealed that Al₃Ti, and Al₃Zr intermetallic phases were formed for samples containing Ti and Zr, making hybrid MMCs with a higher amount of hardness. Finally, it was found that a reaction layer between Al and SiC particles was formed at the Al/SiC interface for all of the samples, expect for the ones containing Si and Ti, indicating that for most of the samples at 680 °C an exothermic reaction took place between the Al and SiC particles.     

Hydraulic design and operation of variable-speed pumps as the water–energy saving strategies in pressurized irrigation systems

Clean Technologies and Environmental Policy - Low efficiencies of irrigation pumping stations usually stem from their improper designing, operation, and maintenance of such systems. In the present...     

Synthesis,characterization and in-vitro behavior of natural chitosan-hydroxyapatite-diopside nanocomposite scaffold for bone tissue engineering

Composite materials based on a combination of biodegradable polymers and bioactive ceramics, including chitosan and hydroxyapatite are discussed as suitable materials for scaffold fabrication. Diopside is a member of bioactive silicates; it is a good choice for hard tissue engineering because of its biocompatibility with host tissue and high mechanical strength. Chitosan and hydroxyapatite were extracted from shrimp shell and bovine bone, respectively and diopside nanoparticles were prepared by the sol-gel method. The present study reports on a chitosan composite which was reinforced by hydroxyapatite and diopside; the scaffolds were fabricated by the freeze-drying method. The so-produced chitosan-hydroxyapatite-diopside (CS-HA-DP) scaffolds were further cross-linked using tripolyphosphate (TPP) to achieve enhanced mechanical strength. The ratios of the ceramic components in composites were 5-58-37, 10-55-35, and 15-52-33 (diopside-hydroxyapatite-chitosan, w/w %). The physicochemical properties of scaffolds were investigated using Fourier-transform infrared spectrometry (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) techniques. The effect of scaffolds composition on bioactivity and biodegradability were studied well. To investigate mechanical properties of samples, compression test was done. Results showed that the composite scaffold with 5% DP has the highest mechanical strength. The porosity of composites dropped from 92% to 76% by increasing the amount of DP. Cytocompatibility of the scaffolds was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, alkaline phosphatase (ALP) activity, and cell attachment studies using human osteoblast cells. Results demonstrated no sign of toxicity and cells were found to be attached to the pore walls within the scaffolds; moreover, results illustrated that the developed composite scaffolds could be a potential candidate for tissue engineering.     

Validation of the heat treatment step used in the production of diaspirin crosslinked hemoglobin (DCLHb) for viral inactivation--effect of crosslinking

During the years 1979-81, three different surgical techniques were used in the treatment of 87 ears with extensive cholesteatoma. All procedures were performed in one stage by the same surgeon. Ten to 13 years after the operations about 70 per cent of ears operated on by the canal wall up technique had developed a new cholesteatoma, which in most cases was recurrent, or a deep retraction pocket. A modification of this technique with mastoid obliteration resulted in a similar failure rate. In contrast, ears operated on by the canal wall down technique (in most cases with mastoid obliteration) had acceptable stability with a long-term recurrence rate of about 15 per cent. Most patients in the canal wall down group had a dry ear without significant cavity problems. Hearing in these patients was as least as good as hearing in patients with a preserved canal wall. We conclude that a meticulous one-stage canal wall down technique in ears with extensive cholesteatoma results in a high percentage of unproblematic, stable ears with satisfactory function. In contrast, if the posterior canal wall is preserved, recurrent cholestealoma is the rule more than the exception.     

A synergistic creep fatigue failure model damage (case of the alloy Z5NCTA at 550 °C)

Creep-fatigue tests have been performed on nickel base alloy Z5NCTA 33-21 grade 1. Hold time varied from 0, 10, 30, 90, 300, 1440 and 10,080 min at two values of strain range. It was found that the number of cycles to failure N_R decreases with holding time t_m, according to a power law:

N_R=1.88×10³·(t_m)^-0.39.