A numerical study on heat transfer enhancement and design of a heat exchanger with porous media in continuous hydrothermal flow synthesis system

The aim of this study is to use a new configuration of porous media in a heat exchanger in continuous hydrothermal flow synthesis(CHFS)system to enhance the heat transfer and minimize the required length of the heat exchanger.For this purpose,numerous numerical simulations are performed to investigate performance of the system with porous media.First,the numerical simulation for the heat exchanger in CHFS system is validated by experimental data.Then,porous media is added to the system and six different thicknesses for the porous media are examined to obtain the optimum thickness,based on the minimum required length of the heat exchanger.Finally,by changing the flow rate and inlet temperature of the product as well as the cooling water flow rate,the minimum required length of the heat exchanger with porous media for various inlet conditions is assessed.The investigations indicate that using porous media with the proper thickness in the heat exchanger increases the cooling rate of the product by almost 40% and reduces the required length of the heat exchanger by approximately 35%.The results also illustrate that the most proper thickness of the porous media is approximately equal to 90% of the product tube's thickness.Results of this study lead to design a porous heat exchanger in CHFS system for various inlet conditions.

Bio-Diesel Based Additive for Enhancing Flow of Emulsion in Pipeline

Emulsions are difficult to transport in the oil and gas industry due to its water content and high viscosity property, thus a need arises to break these emulsions down into lighter emulsions that would make it a lot more suitable for transportation. In this research, biodiesel was synthesized and used to break down relatively viscous emulsion samples into lighter emulsion samples. An apparatus was designed with the aim of determining the flowrate of four different samples in different proportions and compositions: 80% oil and 20% water (sample A), 90% sample A + 10% of biodiesel by volume (sample B), 75% of sample A + 25% of biodiesel by volume (sample C), 60% of sample A + 40% biodiesel by volume (sample D). The results showed that it was possible to significantly increase the flow of emulsions by injecting biodiesel, which was acted as a surfactant, resulting in the lowering of the surface tension of the emulsion sample. The relevance of this research work is validated as it proffers a solution to the transportation of heavy oil and emulsions from all over the world possessing the non-Newtonian flow behavior, which results in serious problems related to its transportation.

Improved Soft Abrasive Flow Finishing Method Based on Turbulent Kinetic Energy Enhancing

Soft abrasive flow（SAF） finishing can process the irregular geometric surfaces, but with the matter of low processing efficiency. To address the issue, an improved SAF finishing method based on turbulent kinetic energy enhancing is proposed. A constrained flow passage with serration cross-section is constructed to increase the turbulence intensity. Taking the constrained flow passage as the objective, a two-phase fluid dynamic model is set up by using particle trajectory model and standard k-ε turbulence model, and the flow field characteristics of the flow passage are acquired. The numerical results show that the serration flow passage can enhance the turbulence intensity, uniform the particles distribution, and increase the particle concentration near the bottom wall. The observation results by particle image velocimetry（PIV） show that the internal vortex structures are formed in flow passage, and the abrasive flow takes on turbulence concentrating phenomenon in near-wall region. The finishing experiments prove that the proposed method can obtain better surface uniformity, and the processing efficiency can be improved more 35%. This research provides an abrasive flow modeling method to reveal the particle motion regulars, and canoffer references to the technical optimization of fluid-based precision processing.

Mechanism of Electromagnetic Flow Control Enhanced by Electro-Discharge in Water

Pulsed discharge utilized to achieve large current density in the electromagnetic flow control is numerically studied. A mathematic discharge model is established to calculate the plasma channel, and an actuator is designed to generate the Lorentz force in the micro plasma channel. During the discharge process, the resistance in the channel decreases rapidly and a large current density appears between the discharge electrodes. After the actuator is applied in the leading edge of a flat plate, the separation region and downstream turbulent boundary layer on the plate disappear. Meanwhile, a skin-friction drag force reduction is achieved.

Control water molecules across carbon-based nanochannels

It is important to know the mechanisms of water molecules across carbon-based nanochannels, which is not only beneficial for understanding biological activities but also for designing various smart devices. Here we review the recent progress of research tbr water transfer across carbon-based nanochannels. In this review, we summarize the recent methods which can affect water molecules across these nanochannels. The methods include exterior factors （i.e., dipolar molecules and gradient electric fields） and interior factors （namely, cone-shaped structures, nonstraight nanochannels, and channel defects）. These factors can control water permeation across nanochannels efficiently.

Flow Range Enhancement by Secondary Flow Effect in Low Solidity Circular Cascade Diffusers

High-pressure ratio and wide operating range are highly required for compressors and blowers. The technical issue of the design is achievement of suppression of flow separation at small flow rate without deteriorating the efficiency at design flow rate. A numerical simulation is very effective in design procedure, however, cost of the numerical simulation is generally high during the practical design process, and it is difficult to confn＇m the optimal design which is combined with many parameters. A multi-objective optimization technique is the idea that has been proposed for solving the problem in practical design process. In this study, a Low Solidity circular cascade Diffuser （LSD） in a centrifugal blower is successfully designed by means of multi-objective optimization technique. An optimization code with a meta-model assisted evolutionary algorithm is used with a commercial CFD code ANSYS-CFX. The optimization is aiming at improving the static pressure coefficient at design point and at low flow rate condition while constraining the slope of the lift coefficient curve. Moreover, a small tip clearance of the LSD blade was applied in order to activate and to stabilize the secondary flow effect at small flow rate condition. The optimized LSD blade has an extended operating range of 114 % towards smaller flow rate as compared to the baseline design without deteriorating the diffuser pressure recovery at design point. The diffuser pressure rise and operating flow range of the optimized LSD blade are experimentally verified by overall performance test. The detailed flow in the diffuser is also confirmed by means of a Particle Image Velocimeter. Secondary flow is clearly captured by PIV and it spreads to the whole area of LSD blade pitch. It is found that the optimized LSD blade shows good improvement of the blade loading in the whole operating range, while at small flow rate the flow separation on the LSD blade has been successfully suppressed by the secondary flow effect.

Metropolitan Emblems or Symbols in Globalization？ Both for the Future of Metropolises and Their Citizens

This research concerns on ＂metropolis and metropolisation＂： what is new with the symbols of city local life and the emblems of global competition？ From New York, Rome, Barcelone, Paris and Bordeaux, the same question demands specific answers： can we live and appreciate urban and metropolitan symbols and emblems together or on their own？ That is the question for towns and the future of their citizens. Confrontation of urban sites and observed places with the plural points of view of their establishment, their designers and urban skills, and their inhabitants and citizens. The combination of these several points of view always make a richer discovery than their disciplinary partition and monopoly.

A Hemodynamic Study of the Effect of Neuromuscular Electrical Stimulation on Enhancing Popliteal Venous Flow

Neuromuscular electrical stimulation has been studied to be a method of prophylaxis for deep venous thrombosis by activating the calf muscle pump. However, there is little evidence of the effects of different stimulating parameters on hemodynamics and comfort levels. The objective of this paper is to compare the effects of different stimulating parameters(current amplitude, pulse-width) on hemodynamic alterations of the popliteal vein and the comfort levels in a group of fourteen healthy subjects. Doppler ultrasound detection of peak venous velocity and blood volume were taken from baseline, twelve sequential electrical stimulations and foot dorsiflexion for each subject. A visual analogue scale was used to assess the subjects' pain perception of neuromuscular electrical stimulation. The results showed that peak venous velocity and blood volume augmented as current amplitude and pulse-width increased while pain level also increased. A compromise was reached that parameters consisting of an amplitude of 10 m A and a pulse-width of 500 μs would obtain a high-peak venous velocity and blood flow volume with a relatively comfortable perception. In addition, parameters consisting of an amplitude of 20 m A and a pulse-width of 300 μs were also shown to be a promising choice. However, further studies need to be done to validate and enrich these findings.

ERFC:An Enhanced Recursive Flow Classification Algorithm

Packet classification on multi-fields is a fundamental mechanism in network equipments,and various classification solutions have been proposed.Because of inherent difficulties,many of these solutions scale poorly in either time or space as rule sets grow in size.Recursive Flow Classification（RFC） is an algorithm with a very high classifying speed. However,its preprocessing complexity and memory requirement are rather high.In this paper,we propose an enhanced RFC（ERFC） algorithm,in which a hash-based aggregated bit vector scheme is exploited to speed up its preprocessing procedure.A compressed and cacheable data structure is also introduced to decrease total memory requirement and improve its searching performance.Evaluation results show that ERFC provides a great improvement over RFC in both space requirement and preprocessing time.The search time complexity of ERFC is equivalent to that of RFC in the worst case; and its average classifying speed is improved by about 100%.

Experimental Study on Flow Boiling Heat Transfer Characteristics of Microencapsulated Phase Change Material Suspension

Due to its core phase change characteristics,microencapsulated phase change material(MPCM)can make many base fluids have better heat transfer characteristics.In this paper,the flow boiling heat transfer characteristics of fluorinated liquid-based microencapsulated phase change material suspension(MPCMS)through vertical transparent quartz channel were studied.The effects of MPCM core phase change temperature and suspension flow velocity on boiling heat transfer coefficient and critical heat flux were discussed,respectively.The results show that the appropriate concentration of MPCMS can enhance both the boiling heat transfer coefficient and the critical heat flux.The strengthening effect becomes weak with the increase of suspension flow velocity.The maximum strengthening rates of critical heat flux appear at 0.05 m/s,which are 25%(MPCMS(70℃)),16%(MPCMS(58℃))and 10%(MPCMS(28℃)).The phase change temperature of the MPCM core has important effects on the boiling heat transfer coefficient and the critical heat flux.The results showed that the MPCM with core phase change temperature higher than the boiling temperature of base fluid has the best enhancement effect.Different bubble behavior in vertical tube with different heat flux can be observed by high-speed photography system.The particle core phase change in MPCMS inhibits the aggregation of bubbles and forms many small bubbles to enhance heat transfer.The work lays a foundation for further exploring the industrial application of MPCMS.

Global Search of a Three-dimensional Low Solidity Circular Cascade Diffuser for Centrifugal Blowers by Meta-model Assisted Optimization

A three-dimensional blade of a low solidity circular cascade diffuser in centrifugal blowers is designed by means of a multi-point optimization technique. The optimization aims at improving static pressure coefficient at a design point and at a small flow rate condition. Moreover, a clear definition of secondary flow expressed by positive radial velocity at hub side is taken into consideration in constraints. The number of design parameters for three-dimensional blade reaches to 10 in this study, such as a radial gap, a radial chord length and mean camber angle distribution of the LSD blade with five control points, control point between hub and shroud with two design freedom. Optimization results show clear Pareto front and selected optimum design shows good improvement of pressure rise in diffuser at small flow rate conditions. It is found that three-dimensional blade has advantage to stabilize the secondary flow effect with improving pressure recovery of the low solidity circular cascade diffuser.