Server Consolidation Based on Culture Multiple-Ant-Colony Algorithm in Cloud Computing.

High-energy consumption in data centers has become a critical issue. The dynamic server consolidation has significant effects on saving energy of a data center. An effective way to consolidate virtual machines is to migrate virtual machines in real time so that some light load physical machines can be turned off or switched to low-power mode. The present challenge is to reduce the energy consumption of cloud data centers. In this paper, for the first time, a server consolidation algorithm based on the culture multiple-ant-colony algorithm was proposed for dynamic execution of virtual machine migration, thus reducing the energy consumption of cloud data centers. The server consolidation algorithm based on the culture multiple-ant-colony algorithm (CMACA) finds an approximate optimal solution through a specific target function. The simulation results show that the proposed algorithm not only reduces the energy consumption but also reduces the number of virtual machine migration.

Experimental Research on Combustion, Pyrolysis Characteristics, and Kinetics of Three Different Coal Samples in China.

Coal thermal and kinetic parameters are important for the design of combustion reactors and risk assessment. Two methods were employed to investigate such key parameters of lignite, bituminous, and anthracite coal samples from China. With thermogravimetry (TG) and differential scanning calorimetry (DSC) methods, two distinct transitional stages were found in all coal samples combustion, but reaction intervals shifted to higher temperatures from lignite to anthracite and varied between 317 and 665 °C depending on the sample nature. Compared to the other two coal types, the pyrolysis of anthracite was less sensitive to increasing temperature, and its combustion process occurred at a much higher temperature. The results indicated that anthracite is difficult to ignite but has a considerable heat of reaction of 22.6 kJ/kg if ignited, which is close to that of bituminous. The basket heating method was used to obtain the kinetic data. Sample activation energies varied in the ranges of 38-51 kJ/mol from TG analysis and 49-67 kJ/mol from basket heating tests. Both results were comparable and consistent with the reference data. Due to its higher activation energy, anthracite poses a lower risk of thermal runaway than other coal types. This conclusion was validated by performing a minimum ignition temperature determination of a dust layer (MITL). In contrast, lignite and bituminous should be handled with greater safety precautions in coal-related process industries. The data presented will be used for hazard analysis and for designing more efficient combustion reactors in power plants. The data collected led to an extension of the current data for coal dust, as found in the literature.

Effects of dust dispersibility on the suppressant enhanced explosion parameter (SEEP) in flame propagation of Al dust clouds.

This work presents an overview about the suppressant enhanced explosion parameter (SEEP) phenomenon in aluminum dust explosion moderation. The SEEP phenomenon can be attributed to either the flammable gas produced by decomposition of insufficient chemical suppressant so as to form an explosible hybrid mixture, or to the improvement in dust dispersibility caused by small amounts of thermal inhibitor so as to form better dispersed dust clouds. Aluminum (Al) and four particle sizes of alumina (Al2O3) were used to confirm a physically caused SEEP phenomenon by performing flame propagation experiments. Higher flame spread velocities (FSVs) in Al dust clouds were found in the presence of 5 or 10% <150 and <45-µm Al2O3 powder. Adding micro-sized Al2O3 disrupted inter-particle contact in combustible dusts, decreased inter-particle forces, and formed dust clouds with better dispersibility, thereby decreasing the effective particle size distribution (PSD) of Al dust. A strong thermal effect brought about by 2.5 µm Al2O3 overcame the negative effect of improved dispersion, preventing SEEP from occurring. The addition of 50 nm Al2O3 increased cohesion of powder mixtures, and decreased dust dispersibility. With benefits from both dispersion suppression and the thermal effect, Al flame propagation was well quenched.

Moderation of Al dust explosions by micro- and nano-sized Al2O3powder.

Adding solid inertants to combustible dust is one measure to prevent and mitigate dust explosions. Al2O3 at four particle size distributions was used to determine the minimum ignition energy (MIE) and maximum explosion pressure (Pmax) of aluminum dust and thus examine the effect of particle size on the inerting efficiency. It was interesting to observe that nano-sized Al2O3 powder showed excellent promise as a solid inertant, having inerting efficacy superior to that of micro-sized Al2O3. In addition to thermal inhibition, nano Al2O3 contributed to explosion moderation by binding Al particles together forming larger-sized aggregates that reduce dispersion in the dust clouds, and thus alleviate explosion hazards. Ignition sensitivity increased when micro-sized Al2O3 was admixed at 5 or 10% with 1000-1500 g/m3 Al mixtures, an effect apparently caused by a 20% decrease in effective particle size distribution brought on by the Al2O3 addition. Generally, increasing the amount of admixed Al2O3 increased MIE and decreased Pmax of Al dust clouds, and decreasing the particle size of Al2O3 resulted in better inerting performance on moderating both the likelihood of the ignition and the consequence of the explosion.

Ignition hazard of non-metallic dust clouds exposed to hotspots versus electrical sparks.

Non-metallic combustible dusts contribute to more than 50% of dust explosion accidents. Almost 38% of dust explosion accidents relate to mechanical malfunction. Compared to electric sparking as an ignition source, the ignition hazard of non-metallic dust clouds exposed to simulated hotspots during mechanical malfunction has received little attention in the literature. Minimum ignition temperature of hotspots (MITH) for corn starch, wood dust, and polymethyl methacrylate (PMMA) dust fall within a narrow range from 710 to 745 °C although large differences in minimum ignition energy (MIE) were evident. A much narrower dust concentration range (around 1500 g/m3) was observed for MITH than for MIE. A longer ignition delay time when exposed to hotspots also indicated lower ignition hazard compared to ignition by electric sparking. Whether exposed to hotspots or electric sparks, average flame spread velocity (FSV) of PMMA dust was much higher than that of corn starch and wood dust. Once a dust cloud was ignited, pulsating flame propagation was similar for hotspots and electric sparking, but average FSV was higher for hotspots than for electric sparks, due to continuous radiation from the ignition source. At higher dust loadings, layer fires could occur due to sedimentation of many ignited and unburned particles exposed to hotspots.

Fire hazard of titanium powder layers mixed with inert nano TiO2 powder.

Metallic dust layers are highly sensitive to ignition from common ignition sources, even when mixed with high percentages of inert solids. In turn, dust layer fires are a potential ignition source for dust explosions or other damaging fires. Flame spread velocity (FSV), as a potential parameter for evaluating fire hazard, was investigated for titanium powder layers mixed with inert nano TiO2 powder in both natural convection and in forced airflow conditions. Increased mass percentage of nano TiO2 powder decreased FSV of Ti powder mixtures as expected. The mixing ratio of nano TiO2 to fully suppress layer fires was 80% and 90% for micro and nano Ti powder, respectively. Mechanisms governing flame spread across a layer of nano Ti powder differed from those of a layer of micro Ti powder. FSV in no airflow conditions was higher than in aided airflow for micro Ti powder because conduction was the dominant heat transfer mechanism. However, FSV in no airflow was lower than in opposed airflow for nano Ti powder because convection/radiation was the dominant heat transfer mechanism. A fly fire phenomenon contributed to greater FSVs and higher fire hazard with nano Ti powder mixtures under aided airflow conditions.

Explosion risk evaluation during production of coating powder.

Powder coating is widely used in industry to prevent equipment corrosion. More than 600 companies produce coating powder in China, but most do not understand the explosion hazard of such products. In the present investigation the explosibility parameters of a coating powder were determined. Results showed that the coating powder is explosible, though the ignition energy is higher than those of normal dusts such as coal powder and corn starch. Based on these experimental findings, a systematic explosion protection method is proposed, with explosion isolation and explosion venting being adopted as the main protective methods.

Minimum ignition temperature of nano and micro Ti powder clouds in the presence of inert nano TiO2 powder.

Minimum ignition temperature (MIT) of micro Ti powder increased gradually with increases in nano-sized TiO2 employed as an inertant. Solid TiO2 inertant significantly reduced ignition hazard of micro Ti powder in contact with hot surfaces. The MIT of nano Ti powder remained low (583 K), however, even with 90% TiO2. The MIT of micro Ti powder, when mixed with nano Ti powder at concentrations as low as 10%, decreased so dramatically that its application as a solid fuel may be possible. A simple MIT model was proposed for aggregate particle size estimation and better understanding of the inerting effect of nano TiO2 on MIT. Estimated particle size was 1.46-1.51 µm larger than that in the 20-L sphere due to poor dispersion in the BAM oven. Calculated MITs were lower than corresponding empirically determined values for micro Ti powder because nano-sized TiO2 coated the micro Ti powder, thereby decreasing its reaction kinetics. In the case of nano Ti powder, nano-sized TiO2 facilitated dispersion of nano Ti powder which resulted in a calculated MIT that was greater than the experimentally determined value.