Acoustic power measurement of linear compressors

The linear compressor works as an important driver for high frequency regenerative cryocoolers. The acoustic power output of the compressor is a critical parameter in the design and the optimization of a linear compressor. To measure this parameter, several approaches based on different theories have been developed. In this paper, the RC load approach and the back chamber approach have been applied to a linear compressor to measure the acoustic power output. The results measured by the approaches indicate a good consistency with the theoretical calculation and reveal the connections between different approaches.The difference between the acoustic power at the piston surface and the exit of a linear compressor has been analyzed based on the experimental results from the RC load approach and the back chamber approach. The volume flow rate difference which accounts for the acoustic power difference is studied theoretically. Furthermore, based on the RC load approach, the optimum impedance together with the impedance cloudy map for the linear compressor to reach its highest efficiency has been obtained by analyzing the experimental and the theoretical results.     

The continuous artificial bee colony algorithm for binary optimization

Artificial bee colony (ABC) algorithm, one of the swarm intelligence algorithms, has been proposed for continuous optimization, inspired intelligent behaviors of real honey bee colony. For the optimization problems having binary structured solution space, the basic ABC algorithm should be modified because its basic version is proposed for solving continuous optimization problems. In this study, an adapted version of ABC, ABC_bin for short, is proposed for binary optimization. In the proposed model for solving binary optimization problems, despite the fact that artificial agents in the algorithm works on the continuous solution space, the food source position obtained by the artificial agents is converted to binary values, before the objective function specific for the problem is evaluated. The accuracy and performance of the proposed approach have been examined on well-known 15 benchmark instances of uncapacitated facility location problem, and the results obtained by ABC_bin are compared with the results of continuous particle swarm optimization (CPSO), binary particle swarm optimization (BPSO), improved binary particle swarm optimization (IBPSO), binary artificial bee colony algorithm (binABC) and discrete artificial bee colony algorithm (DisABC). The performance of ABC_bin is also analyzed under the change of control parameter values. The experimental results and comparisons show that proposed ABC_bin is an alternative and simple binary optimization tool in terms of solution quality and robustness.     

Numerical modeling of hydrogen catalytic reactions over a circular bluff body

This paper was intended to delineate numerical research for hydrogen catalytic combustion over a circular cylinder. The wire/rod-type catalytic reactor is a simple geometry reactor with an economical design with less pressure loss. For the single rod in the reaction channel, the flow characteristic and the difference of conversion efficiency between non-gas-phase reaction and gas-phase reaction have been delineated in the present study. The flow field and the chemical reactions were numerically modeled using 2D Large Eddy Simulation combined with the gas-phase and surface reaction mechanisms. The results show that the current numerical simulation has been validated to precisely predict the vortex shedding and its frequency in the cold flows. Despite the variation trends being dominated by the upstream flow, the vortex shedding phenomena were affected by the flue gas generated from the rod surface. It can be seen from the linear relationship between the vortex shedding frequency of reacting flow and Reynolds Number. It is noted that the vortex shedding vanished if the gas-phase reaction was ignited in the reaction channel. In addition, the geometric modified conversion efficiency was proposed to delineate an indicator that could be potential for the optimization of rod-type catalytic reactor. In summary, the fundamental study of a rod in a 2D flow channel can provide information for optimizing the catalytic design or the rod array arrangement in the reactor. Moreover, the rod can also be a partial catalytic flame holder to ignite and stabilize the gas-phase reaction. The obtained results could be the potential for practical applications of rod-type catalytic combustion, catalytic gas turbine, hydrogen generation, partially catalytic reaction flame holder, and other catalytic reactions that can be appreciated.     

A novel 2D-3D conversion method for calculating maximum strain of geosynthetic reinforcement in pile-supported embankments

For design of a geosynthetic-reinforced pile-supported (GRPS) embankment over soft soil, the methods used to calculate strains in geosynthetic reinforcement at a vertical stress were mostly developed based on a plane-strain or two-dimensional (2-D) condition or a strip between two pile caps. These 2-D-based methods cannot accurately predict the strain of geosynthetic reinforcement under a three-dimensional (3-D) condition. In this paper, a series of numerical models were established to compare the maximum strains and vertical deflections (also called sags) of geosynthetic reinforcement under the 2-D and 3-D conditions, considering the following influence factors: soil support, cap shape and pattern, and a cushion layer between cap and reinforcement. The numerical results show that the maximum strain in the geosynthetic reinforcement decreased with an increase of the modulus of subgrade reaction. The 2-D model underestimated the maximum strain and sag in the geosynthetic reinforcement as compared with the 3-D model. The cap shape and pattern had significant influences on the maximum strains in the geosynthetic reinforcements. An empirical method involving the geometric factors of cap shape and pattern, and the soil support was developed to convert the calculated strains of geosynthetic reinforcement in piled embankments under the 2-D condition to those under the 3-D condition and verified through a comparison with the results in the literature.     

Criticality of the thorium burnup in equilibrium state

The effective neutron multiplication factor (k_eff) as a function of burnup for different volume coolant (CoR) and fuel (FR) to cell ratio is presented. Additionally the Conversion Ratio (CR) of Th-232 to U-233, concentration of U-233, fissile and fission products calculation as a function of burnup are presented. The assembly is a critical reactor which makes volumes of coolant and fuel changes possible. In addition, an analytical model of calculation of k_eff as a function of U-233 and a poison concentration in equilibrium state are presented. One can achieve the criticality of Thorium Breeder Reactor (TBR) for enough high average neutron energy which one can obtain in Fast Breeder Reactor (FBR) only. The maximal value of CR and burnup for case of k_eff ≥ 1 achieves 1.4 and 360 GWd/MTU, correspondently. The calculations were done with a MCNPX 2.7 code using F₂Be, Na and Pb coolants.     

Effect of sol–gel MgO spin-coating on the performance of TiO2-based dye-sensitized solar cells

This paper is concerned with the improvement of dye-sensitized solar cell (DSSC) efficiency upon MgO post-treatment of the TiO₂ electrode. A simple sol–gel technique, involving magnesium acetate as precursor, ethanol as solvent and nitric acid as stabilizer, is applied to prepare a solution of suspended MgO nanoparticles. A single drop of MgO sol at 0.1 M precursor concentration was spin-coated at 3000 rpm for 30 s onto the TiO₂ electrode and sintered at 500 K for 1 h. Dye-loading using N3-dye was applied for 6 h. An increase in the average efficiency of the DSSC from 2.5% to 3.9% (over 50% enhancement) was recorded. Measurements of the dark I–V characteristics, the open circuit voltage decays, the SEM images and the dye absorbance spectra, for both uncoated and MgO-coated electrodes were examined. The improvement of the DSSC efficiency was attributed to an upward shift of the TiO₂ flat band energy and a reduction of the rate of back-transport and recombination.     

Biomass boiler conversion potential in the eastern United States

The U.S. is the world's leading consumer of primary energy. A large fraction of this energy is used in boiler installations to generate steam and hot water for heating applications. It is estimated there are total 163,000 industrial and commercial boilers in use in the United States of all sizes.This paper characterizes the commercial and industrial boilers in the 37 states of the Midwest, Northeast, and Southern regions of the U.S. in term of number of units, unit capacity, aggregate capacity, and fuel type. A methodology is developed for evaluating and ranking the potential for converting from existing fossil-fuel boilers to biomass boilers in these states.In total, 3495 oil and coal boiler units in industrial and commercial buildings, and 1067 major wood energy facilities in the 37 eastern states were identified. These represent a subset of existing and potential conversions from fossil fuels to woody biomass. Based on this sample and energy consumption data from the Energy Information Administration (EIA), we estimate that there are currently 31,776 oil, coal, and propane boiler units over 0.5 MMBtus/hour capacity in these 37 states, representing a total energy consumption of 1.7 quadrillion Btus, or roughly the equivalent of 287 million barrels of oil. Were these units all converted to woody biomass fuel, they would consume a total of 121 million dry tons of wood per year, about three times the most recent US DOE estimates of woody biomass availability in those regions. Since only the most economical conversions typically occur, the reality of woody biomass market availability combined with thermal fossil-fuel consumption patterns suggests that roughly one-third of all potential projects could be achieved under sustainable utilization of existing biomass feedstocks in the three regions.Analysis of the results indicates that a targeted response to wood-conversion initiatives will yield the most successful program of fossil-fuel replacement in thermal applications. A ranking index developed in this study through analysis of existing boiler installations and availability of wood feedstocks suggests that the top ten states in the eastern United States on which to focus future messaging, feasibility studies, and policy development for potential woody biomass conversions are:1. Maine, 2. Texas, 3. New York, 4. Florida, 5. Georgia, 6. Alabama, 7. South Carolina, 8. North Carolina, 9. Arkansas, 10. Pennsylvania.     

Modelling the compaction curve of fine-grained soils

A theoretical model for the compaction curve of fine-grained soils at various compaction efforts for the entire range of water content is presented in this study. The prediction method is based on the assumption that the compaction curve represents the state surface at the yield state in an unsaturated condition. Thus, for each applied compaction effort, the compaction curve relates to one yielding point on the saturated normal consolidation line (NCL). For a given soil, the model requires the NCL, S_rc, and one point from any compaction curve to predict the compaction curves for different compaction efforts. Moreover, the lines of equal suctions on the compaction curves can be determined if the SWCC, the wetting path, is known. The model introduced here provides additional theoretical understanding of the soil׳s volume change behavior of the compaction curve. The model was verified in two ways: first it was verified quantitatively, by experimental results, and second it was verified qualitatively, by examining the relationships from other models in the literature. The model was further applied to experimental data reported in the literature on previous static and dynamic compaction tests. The results show that the model fits the experimental data very well. Finally, a simple chart, based on this model and using only liquid limits, is presented to estimate γ_dmax and OMC quickly.     

Epitaxial p-type SiC as a self-driven photocathode for water splitting

Solar-to-hydrogen conversion efficiencies of water-splitting photochathodes using epitaxially grown p-type 4H-, 6H- and 3C-SiC were estimated in a two-electrode system without applying any external bias. By using electrode materials with small oxygen overpotentials as counter electrodes, the photocurrent became comparable to that observed in a three-electrode system with a suitable bias. Estimated efficiencies seem to depend on the bandgap of the SiC polytypes. For the 3C-SiC, the obtained efficiency was 0.38%, which is so far the highest value reported for SiC. We confirmed that the hydrogen volumes estimated from the photocurrent were almost the same as actual volumes observed by gas chromatography.