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In this work, the effect of using baffles and vortex generators on the cooling performance of a gas turbine combustion chamber is numerically investigated. The RNG k-ɛ model is utilized in order to simulate the flow turbulence. The effects of baffles and vortex generator pitch, hydraulic diameter and bypass ratio on the Nusselt number and friction coefficient at different Reynolds number are studied. The cooling performance of applying baffles and vortex generators are also evaluated and compared based on the Performance Evaluation Criterion (PEC). The numerical results are verified with available experimental data. The results show that the pitch increment results in the decrement of the Nusselt number and the wall friction coefficient due to the lower vortices generation and the turbulence kinetic energy dissipation. Also, the Nusselt number is increased by increasing both the bypass ratio and the hydraulic diameter. It is also found that vortex generators and baffles improve the cooling performance of the gas turbine combustion chamber by 18.8% and 26% respectively through decreasing the external wall temperature.

The MARS code has been assessed for the prediction of onset of flow instability (OFI) in a vertical channel. For assessment, we built an experiment database that consists of experiments under various geometry and thermal-hydraulic condition. It covers pressure from 0.12 to 1.73 MPa; heat flux from 0.67 to 3.48 MW/m2; inlet sub-cooling from 39 to 166 °C; hydraulic diameters between 2.37 and 6.45 mm of rectangular channels and pipes. It was shown that the MARS code can predict the OFI mass flux for pipes reasonably well. However, it could not predict the OFI in a rectangular channel well with a mean absolute percentage error of 8.77%. In the cases of rectangular channels, the error tends to depend on the hydraulic diameter. Because the OFI is directly related to the subcooled boiling in a flow channel, we suggest a modified subcooled boiling model for better prediction of OFI in a rectangular channel; the net vapor generation (NVG) model and the modified wall evaporation model were modified so that the effect of hydraulic diameter and heat flux can be accurately considered. The assessment of the modified model shows the prediction of OFI mass flux for rectangular channels is greatly improved.

The microchannel is one of the essential components for the construction of various micro systems. However, it has been reported that the flow and heat transfer behavior in a microchannel deviates from predictions based on the conventional assumption generally accepted in macro-scale channels. Frictional characteristics of nitrogen and helium flows in three different microchannels (hydraulic diameter range 3-10 w m) have been investigated experimentally. The frictional resistance of gaseous flow in a trapezoidalcross-section microchannel was observed to be smaller than that in the conventional-sized channel. The reduced frictional resistance in microchannels is caused by the rarefaction effect due to extremely small dimensions of flow passages. By using Maxwell's first-order slip boundary condition, we can well predict the mass flow rate through microchannels and the friction constant.

The present paper reports the thermal behavior of flat and curved surfaces with impinging jets employing circular and elliptical nozzle for identical equivalent diameter (de). Tests are performed w...

In this study, an experimental evaluation on the use of Al2O3 nanoparticles in a circular structure of minichannel heat sink is conducted for heat dissipation from electronic components such as Central Processing Unit (CPU). The experiments are prepared for various hydraulic diameter of channels and different values of coolant flow rates. After a hydro-thermal analysis on the obtained data, as a main outcome, findings indicate that decreasing the channel diameter and increasing the flow rate of Al2O3-water as working fluid are the most effective approaches to improve the cooling performance of heat sinks. An optimization study using Response Surface Methodology (RSM) based on Central Composite Design (CCD) is performed due to complex effect of channel size, nanofluid volume flow rates and channel numbers on pressure drop and heat transfer to reach the best operating design.

The suction force on high-sphericity seeds is important to the design of air-suction seed-metering devices. However, little systematic research has been conducted on the suction force. A self-designed suction force measurement device and idealised model were used to conduct CFD simulation, single factor experiments, and orthogonal experiments to improve the model of the suction force on seeds with sphericity over 90.34% and equivalent diameter 6.63–7.16 mm under the following conditions: suction hole diameter 4–6 mm, suction hole vacuum 3–5 kPa, seed-filling angle ±π/8, and horizontal distance from the seed centre to the suction hole 3.5–5.5 mm. The verification experiment conducted using the seeds of soybean, pea, and Panax notoginseng showed that the accuracy was higher for the improved suction force model. Simulation of flow behaviours under different factors revealed that the changes in the air velocity gradient and pressure gradient are the main causes of the change in the suction force. The relationship between the drag force model and the suction force model was studied by comparing the predicted value of the drag force and the measured value of the suction force under the same conditions.

This work is aimed at investigating the effects of the refrigerant charge, expansion device restriction, compressor speed, and their interactions on the performance of a household refrigerator. To this end, a micrometric valve was installed in series with the capillary tube of a frost-free refrigerator to vary the expansion restriction within a range equivalent to capillary tubes with inner diameters spanning from 0.55 to 0.85 mm. The refrigerant charge was manually changed from 35 to 65 g whereas the compressor speed was adjusted between 2500 and 4500 rpm. In total, 294 steady-state energy consumption tests were conducted, being 147 at a surrounding temperature of 32 °C, and the rest at 16 °C. It was noticed that low energy consumptions can be achieved for several combination of refrigerant charge and expansion restriction, albeit the minimal energy consumption figures were always achieved for the highest charges and restrictions. It was also verified that the refrigerator operates in a sub-optimum region so that increasing the charge from 42 g to 52 g while decreasing the capillary tube diameter from 0.64 mm to 0.60 mm led to a 3% decrease on the energy consumption. It was also found that a single combination of refrigerant charge and equivalent diameter provided satisfactory performance levels regardless of the compressor speed. Finally, a method to reduce the number of tests was proposed, in such a way that only 9 datapoints are required to generate a full energy consumption map for a given compressor speed and surrounding temperature.

Multi-holed Orifices (MOs) are widely used in swirling, cavitating and developing flows to reduce pressure losses. This study focuses on analysis of MOs for developing turbulent flows. A large number of experiments were performed, exploring the number of holes (n), Equivalent Diameter Ratio (EDR), compactness ratio (C), plate thickness ratio (s/d) and upstream developing length (L/D) in the Reynolds number (ReD) range of 24,500–55,500. An empirical correlation of pressure loss coefficient and flow rate is formulated. It is observed that pressure loss coefficient decays with the fourth power of EDR. A comparative study of the experimental data with the literature is presented to ensure consistency and reliability.

A nanoporous graphene membrane is crucial to energy-efficient reverse osmosis water desalination given its high permeation rate and ion selectivity. However, the ion selectivity of the common circular graphene nanopore is dependent on the pore size and scales inversely with the water permeation rate. Larger, circular graphene nanopores give rise to the high water permeation rate but compromise the ability to reject ions. Therefore, the pursuit of a higher permeation rate while maintaining high ion selectivity can be challenging. In this work, we discover that the geometry of graphene nanopore can play a significant role in its water desalination performance. We demonstrate that the ozark graphene nanopore, which has an irregular slim shape, can reject over 12% more ions compared with a circular nanopore with the same water permeation rate. To reveal the physical reason behind the outstanding performance of the ozark nanopore, we compared it with circular, triangular, and rhombic pores from perspectives including interfacial water density, energy barrier, water/ion distribution in pores, the ion-water RDF in pores, and the hydraulic diameter. The ozark graphene nanopore further explores the potential of graphene for efficient water desalination.

Manufacturability without supports in design studies for additive manufacturing (AM) brings many advantages such as time, cost, part surface quality, and design freedom. It is thought that the geometries that can be produced without support will help the more widespread use of AM technologies. In this study, the unsupported manufacturability and efficiency research of conformal cooling channel (CCC) geometries created in cylindrical, wide oval, drop, hexagonal, narrow oval, and pentagonal cross-sections were conducted in the direct metal laser sintering (DMLS) system. The study offers innovation in terms of showing the usability of different channel geometries in CCC applications. The study shows that the pentagon form has the most efficient cooling capacity among the comparatively handled geometries. The results are obtained by a computational fluid dynamics (CFD) analysis study on computer-aided design (CAD) data of the actual state channel geometry obtained by CAD and post-production micro-CT scanning of the design and presented in tables. This research shows that the production-induced sagging problem affects the flow by narrowing the channel hydraulic diameter in channel geometries produced without CCC supports.

A three-dimensional computational model, coupled with the Large Eddy Simulation (LES) model and Volume of Fluid (VOF) multiphase model, was established to investigate the two-phase flow and slag entrainment during steel bloom continuous casting. The influence of the in-mold electromagnetic stirring (M-EMS), casting speed, and submerged entry nozzle (SEN) immersion depth on the flow pattern and slag entrainment were evaluated. The number, size, velocity, and spatial distribution of slag droplets were counted and the location, velocity and probability of the slag entrainment on the meniscus were exported in real time through a user defined function. The result shows that the slag entrainment mainly occurred around the 1/4 width of the mold. The equivalent diameter of most slag droplets was 2–6 mm under the current casting condition. A formula for the equivalent diameter distribution of slag droplets was proposed according to the statistical result.

The evolution of the 3D Fe-rich phases of Al–7.0Si–1.2Fe alloys with different Mn contents was visualized and characterized using synchrotron X-ray computed tomography, and the effect of Fe-rich phases with typical morphologies on the fracture behavior during tensile testing was analyzed. The results showed that the Fe-rich phase changed from platelet-like β-Al5FeSi into α-Al15(FeMn)3Si2 with various morphologies after the addition of Mn. The Mn addition not only significantly reduced the volume fraction, equivalent diameter and interconnectivity of the Fe-rich phase but also greatly increased the sphericity, surface thickness, and distribution of the mean curvature and surface thickness. Furthermore, the equivalent diameter of α-Al15(FeMn)3Si2 had an inverse exponential function relationship with its sphericity. The 3D morphology of α-Al15(FeMn)3Si2 can be summarized as massive and regular polyhedrons, hollow and regular polyhedrons, and multibranched polyhedrons. The fraction of the different 3D morphologies in each alloy is related to the Mn content, where excess Mn increased the number and volume fraction of the large Fe-rich particles with a low sphericity. The ductility of each alloy was significantly improved by the addition of Mn but gradually decreased when the Mn/Fe ratio exceeded 1.2. The increase in large α-Al15(MnFe)3Si2 with a low sphericity was the main reason for the decreased ductility of alloys with a high Mn content.

A comparative analysis of methods for estimating the gray cast iron ultimate tensile strength σu by the hydraulic diameter of interdendritic space DHydIP and the volume fraction of primary austenite dendrites fdc is performed. Almost the same accuracy of cast iron castings σu estimation according to both these parameters DHydIP and fdc of the primary microstructure is shown.

The present investigation deals with the study of pore size of filter fabrics. Theoretical expressions are derived for calculating the pore equivalent diameter of woven, knitted and nonwoven filter fabrics. Experimental results were obtained by using a new simplified apparatus. This apparatus has been designed by the author on the base of bubble-pressure method. The derived relations were found to be fairly close to those observed experimently.

The flow field in a semi-circular duct is simulated by Large Eddy Simulation (LES) and its particle field is simulated by Lagrange particle tracking method. Reynolds number Reb (based on bulk velocity and hydraulic diameter) is 80,000 and Reτ (based on friction velocity and hydraulic diameter) is 3528. Particle diameter dp is chosen as 10, 50, 100, 500 μm corresponding to St as 0.10, 2.43, 9.72, 243.05. The results show that the intensity of the secondary flow near the ceiling is less than that near the floor because the ceiling is curved and able to inhibit the secondary flow. It is found that the difference between the semi-circular duct and the square duct is that the secondary flow in a corner of the semi-circular duct is not symmetrical along the diagonal although they have the same generation mechanism. Regarding the particles, small particles (dp ≤ 10 μm) are found to uniformly distribute in the duct, while large particles (dp ≥ 50 μm) preferentially distribute in the corner and floor center. The maximum particles (dp = 500 μm) fall on the floor quickly and their dispersion mainly depends on the secondary flow near the floor. Particle deposition in the corner depends on particle size due to the effect of secondary flow and gravity. The effect of lift force on particles becomes more significant for 50 and 100 μm particles in comparison with other smaller particles. In the end, the effect of secondary flow is found to be more significant to dominate particle behavior than that of flow fluctuation.

The secondary atomization of droplets is one of the means to improve the efficiency of diesel fuel injection atomization. As a promising biomass fuel, emulsified biodiesel showed a good prospect in improving the atomization effect of diesel engines. In this study, a high-temperature and pressure-resistant evaporator was designed to simulate diesel-like conditions, and the evaporation and combustion experiments of emulsified biodiesel droplets were carried out. The morphological changes in the droplets were dynamically captured using a high-speed camera. According to the collected images, the evaporation characteristic parameters, the dynamic parameters of droplet motion, and the correlation between the original and secondary droplets were quantitatively analyzed. The gain effect of secondary atomization for droplets on the diesel engine spray was evaluated. The results showed that the emulsified biodiesel underwent nucleation, agglomeration, puffing, and explosion during the evaporation process, while the classic d2 law only meets a few cases of this fuel. The effect of high temperature was reflected in reducing the normalization time of droplet agglomeration and explosion, while the higher pressure inhibited the expansion of the droplets, thus slowing down the expansion rate and restricting the droplet volume. Driven by the water content, the time of droplet explosion was closer to the droplet lifetime. The evaporation process of the secondary droplet was similar to that of the original droplet over a reduced scale of 1-2 orders of magnitude. (Dd /Dd0)2 ≈ 1 was a necessary condition for the secondary droplets to be produced in large quantities. The average equivalent diameter of the droplets was distributed in the range of 80-140 μm, and the secondary atomization caused expansion of the spray range by 20-40%. Expansion of the range of secondary droplets was beneficial to shortening the ignition delay and increasing the combustion rate.

Two-dimensional time-resolved particle image velocimetry (TR-PIV) measurements were carried out in confined and non-confined channels with a backward facing step (BFS) while the inlet flow was an oscillating jet from a double feedback fluidic oscillator. In addition, different Reynolds (Re) numbers in the range of 2500–10,000 were applied (based on the hydraulic diameter and mean velocity of jet throat) and the velocity distribution of the oscillating jet was measured in external domains. The effects of the aspect ratio (AR) of the expanded region and the expansion ratio (ER) were studied. Typical time-averaged structures of velocity statistics and the Proper Orthogonal Decomposition (POD) method were used to analyze the flow dynamics. The results show that the oscillation frequency is independent of the external domain and is almost constant for different ER or AR. In contrast, the spreading angle of the fluidic oscillator is much larger value when increasing Re number or decreasing AR. Additionally, a pair of vortices is induced because of the entrainment effect in confined external domain, and the velocity fluctuations can also be increased. Furthermore, the POD analysis revealed that the first two modes are predominant and represent the main characteristics of the flow.

Flow boiling experiments in microchannels under low mass fluxes have rarely been reported in the literature. In this study, flow boiling critical heat flux (CHF) for a parallel straight copper microchannel heat sink with 41 channels and hydraulic diameter of 420 µm (width: 300 µm; height: 700 µm) is reported under low mass fluxes(< 100 kg/m2s). The flow patterns reveal that the inertial force will be too low to flush the bubble downstream. The heat transfer coefficient was observed to decrease with an increase in the heat flux or vapor quality, which pointed toward convective boiling dominancy inside the channels. When approaching the CHF, the vapor flowed back to the heat sink’s inlet plenum, resulting in a flow blockage, which is the main factor for the CHF occurrence.

In the current study, three-dimensional models were established to simulate the transient formation and dripping of droplets during Electroslag Remelting (ESR) of steel, combining the κ-e two-equation turbulence model, Volume of Fraction (VOF) multiphase model, and Magnetohydrodynamics (MHD) model. The influence of the interfacial tension on the varied size distribution and the transient dripping velocity of droplets were calculated and statistically summarized. The absolute velocity distribution of droplets showed that all the fluid inside the droplet flowed downward, while the relative velocity distribution illustrated a recirculation inside the droplets, indicating that the flow of molten steel inside the droplet have two kinds of motion: a downwards flow due to the gravity and a recirculation inside the droplet which led to the deformation of droplets.With a melting rate of 0.03 kg s−1, the equivalent diameter and the dripping frequency in functions of the interfacial tension were D = 0.0119 σ0.23 and f = 1.45 σ −2.37, respectively.

Numerically investigated the electric double layer (EDL) Effects on the performance of the square microchannel heat exchanger (MCHE) at combined electro-osmotic and pressure-driven flow with compared pure pressure-driven with a hydraulic diameter (10 – 50) μm. We defined at any size (Dh) of microchannel heat exchanger become the impact of EDL very slight with the studied effect of electric double layer thickness λ. The diluted water 1:1 potassium chloride (KCl) solution is used as a working fluid at an ionic concentration , , silicon microchannel at zeta potential of surface -0.2 volt. A three-dimensional (3D) Poisson-Boltzmann equations and Naiver-stoke equations with applied electric field solved by using the finite volume scheme in this work. The results show an increase in pressure drop of the microchannel heat exchanger at combined flow electroosmotic and pressure-driven flow with a percentage of 31.09 % at an ionic concentration and 42.71 % at increase in pumping power, especially at low ionic concentration. Slight enhancement in average heat transfer rate and effectiveness due to an increase in average temperature difference. Decrease in overall performance at combined electroosmotic and pressure-driven flow compared with pure pressure driven.

Hydraulic flushing drilling technology can not only improve the efficiency of high-pressure and low-permeability geological reservoir coalbed methane drainage but also effectively reduce the probability of coal and gas outburst disasters through pressure relief. The main mechanism of this technology is to expand the borehole diameter through hydraulic flushing measures, increase the strain of the coal around the borehole, and increase the development of cracked pores, to improve the permeability of the coal seam and realize the dual reduction of ground and gas pressure. However, in the actual application process, the interaction mechanism among the stress field, the structure field, and the seepage field is still not clear, and there is no clear method to accurately determine the pressure relief range based on the pressure relief mechanism in order to carry out reasonable drilling arrangements. Therefore, this article comprehensively uses laboratory experiments, numerical simulations, and field practices to fully explain the hydraulic flushing pressure relief mechanism and proposes a method to accurately determine the pressure relief range based on the radial line strain law. The results based on radial line strain showed that the effective relief radius expands to 0.86 m once adopting the Φ579 mm hydraulic flushing borehole compared to Φ160 mm; the borehole’s equivalent diameter of drilling field #11 is 2 to 3 times than that of #10 and 1.2 times the average CBM extraction amount. Therefore, as the borehole diameter increases, the permeability and radial line strain of the coal around the borehole increase significantly, but the tendency of the increase in permeability decreases with increasing vertical stress. The findings of this study can help for a better understanding of the pressure relief and permeability enhancement mechanism of hydraulic flushing, and the method of determining the pressure relief range based on radial strain can also provide a new way for other mines to practice ideas.

When a penetrator with enhanced lateral effect (PELE) impacts on a reinforced concrete (RC) target, the target is damaged with a large opening. An understanding of how PELE projectile parameters affect the opening dimension, is essential for effective design of the PELE projectile. In this study, under the condition that the impact velocity and target parameters (strength and thickness) were fixed values, the important influence factors of the PELE (jacket wall thickness B, jacket material strength Y 1 , filling material strength Y 2 and angle of monolithic jacket θ) were determined by a dimensional analysis. Tests and simulations of the PELE penetrating the RC target were conducted to analyze the influence of these factors on opening diameter ( D ¯ , an equivalent diameter under relative kinetic energy). Based on the test and simulation results, it is found that the influence of these factors B, Y1 and θ on the deformation mode of the jacket shows a similar trend: as values of the three factors decrease, the jacket deforms from small bending deformation to large one, and then to curling deformation. This causes the opening diameter to first increase with the decrease of these three factors, and then decreases. It is well known that the bending resistance of the jacket is related to these factors B, Y1 and θ. Therefore, a plastic limit bending moment (M0) of the jacket was quoted to characterize the influence of these factors on the bending deformation of the jacket and the opening diameter of the target. The influence factor Y 2 causes D ¯ to first increase with the increase of Y 2 , and then decreases. A formula was developed to predict the opening diameter, whose influence parameters were considered in a dimensionless way. It has been shown that the dimensionless opening diameter D ¯ / d 1 is dependent on two dimensionless parameters Q = d 1 3 f c M 0 and G = f c Y 2 , where d 1 and f c are the outer diameter of the projectile and the compressive strength of the target, respectively.

In this work, the optimization of a monolith reactor 3-dimensional model is carried out, for a first order reaction, isothermal conditions and fully developed laminar flow. The obtained results are consistent with the optimal reactor design obtained under plug flow conditions, namely a maximum conversion reactor features maximum channel width, minimum hydraulic diameter, and maximum fluid velocity determined by an upper bound that is a function of the channel’s width, height, and the capital cost to compression cost ratio.

The present study focuses on the energy performance, entropy generation, and irreversibility of the use of nanofluid in an industrial Peugeot automobile radiator (size: 250 x 301 x 60.4 mm, channel number: 34 and hydraulic diameter: 1.923 mm) with a louvered fin type. 50:50 EG - water which is widely used in existing automobile radiators and a new generation of EG - water - Al2O3 (0.5%) nanofluid have been compared. In order to examine the effect of variable operating conditions on thermal performance for both fluid mixtures, experiments have been performed at variable air velocity (4-5 m/s), variable coolant flow rate (10-15 - 20 It/min), and an inlet temperature of 95 degrees C (real automobile conditions). Thermohydraulics calculations such as entropy generation, irreversibility, effectiveness, NTU, heat transfer rate, pumping power have been obtained from experimental data. Among conducted experiments, with increasing coolant flow rate, entropy generation increases on the airside, while decreasing on the coolant side. When the entropy generation due to temperature and pressure difference is compared, entropy production due to pressure difference can be neglected. It has been evaluated that the use of nanofluid increases the heat transfer rate by 9.52%, reducing the irreversibility by about 68% at the 4 m/s air velocity and 10 It/min coolant flow. (C) 2020 Karabuk University. Publishing services by Elsevier B.V.

Purpose This study aims to explore the 3 D separated flow fields and heat transfer characteristics at the end wall of a serpentine channel with various turn clearances using topological analysis and critical points principles of three-dimensional vortex flow. Design/methodology/approach This aims to explore the 3 D separated flow fields and heat transfer characteristics at the end wall of a serpentine channel with various turn clearances using topological analysis as well as critical points principles of three-dimensional vortex flow. Findings The endwall heat transfer in the narrow spacing passage is significantly stronger than that in a wide spacing channel. As the gap clearance is kept at 0.87 times of the hydraulic diameter, the endwall heat transfer and thermal performance can be accordingly enhanced with low pressure drops, which is because a relatively strong concentrated impingement flow for the medium gap clearance helps to restrain the downstream fluid flow and enhance the shear effect of the secondary flow. Practical implications The numerical results can be applied in designing sharp turn of serpentine channel in heat exchangers, heat sinks, piping system, solar receiver and gas turbine blades. Originality/value The evolution mechanism of the vortices in the turning region under different gap clearance was analyzed, and thermal enhancement characteristics were predicted innovatively using topological analysis method.

Metal additive manufacturing is increasingly used as a complementary manufacturing technique in industrial settings and slowly moving from pure prototyping applications toward full production. In parallel, there is an emergence of Industry 4.0, where the applicability of concepts such as digital twins of manufacturing machines and components are being investigated. Compared to conventionally manufactured parts, typical quality metrics of metal additively manufactured components such as dimensions, roughness, porosity, and hardness are underperforming in an as-built state. As a mitigation strategy, the build chamber variables are often measured and logged by the metal additive manufacturing system to maintain a stable production environment. Thus, proper insight into the expected responses in part quality from changes in those build chamber variables is important in the pursuit of digital twins and process improvement. This sheds more light on the influence of the gas flow variables, namely gas flow speed, relative pressure, and oxygen content on the metal additive manufacturing quality metrics, specifically channel roughness, bulk porosity, average diameter, the equivalent diameter of the unobstructed cross-sectional area, and hardness of the bulk. A Design of Experiments was implemented on two laser powder bed fusion systems, namely an SLM 280 processing 316L stainless steel and an SLM 500 processing Ti6Al4V. The current work found that surface oxidation of 316L and Ti6Al4V components may be classified based on simple red, green, and blue (RGB) color constituent analysis. The influence of gas flow variables was found to be different in the two investigated SLM systems, suggesting a high dependency on the processed material. Oxygen content in the build chamber had the highest standalone effect on the selected quality metrics, while the gas flow speed had the lowest standalone effect. The second-order effects were found to be, in general, more significant than the main effects. The findings of the current work is a step towards an improved understanding of the interaction effects of gas flow conditions on typical quality metrics of metal additive manufactured components. By the creation of simple but computationally fast response surface models, in-line assessments may be carried out and the effect of process variability on component quality may be evaluated in-situ while being one step away from the full feedback control implementation in the digital twin. Following the methodology of the current work for other laser powder bed fusion systems enables the generation of 3D point cloud visualizations for decision making under uncertainty.

In situ synchrotron x-ray radiography studies on the solidification sequences of non-refined and refined Al-20Zn alloys were carried out. The dendrite growth, porosity evolution, grain densities and growth rates were measured. Without and with 0.05% grain refiner, the solidification sequences appear as columnar dendrite. The average columnar dendrite growth rate of non-refined Al-20Zn alloy is larger than refined by 0.05% grain refiner. The burst growth is happened in columnar dendrite which is the first report and the time interval was about 1.2s. The columnar interdendritic region is prone to form porosities with solidification progress. The equivalent diameter of porosity with time is well fitted by Gaussian function, and the growth velocities of porosities of all sequences are faster in the first seven seconds and fluctuated with time. When the addition level of grain refiner is larger than 0.1%, the solidification sequences appear as equiaxed dendrite. The accumulation of grains of refined Al-20Zn alloys is well fitted by logistic function. The porosities disappeared during solidification with equiaxed grains. The equiaxed dendritic growth velocity, which is ~16μm/s at a cooling rate of 8K/min, is much lower than columnar.

Size and effective density (ρe) are important properties of aerosol particles and are related to their influences on human health and the global climate. The volume equivalent diameter (Dve) is an intrinsic property that is used to evaluate particle size. Three definitions of ρe are generally used to characterize the physical property of a particle as an alternative to particle density, in which only the ρeII, defined as the ratio of particle density (ρp) to a dynamic shape factor (χ), has the characteristic of being independent of particle size. However, it is still challenging to simultaneously characterize the Dve and ρeII of aspherical particles. Here, we present a novel system that classifies particles with their aerodynamic diameter (Da) by aerodynamic aerosol classifier (AAC) and determines their vacuum aerodynamic diameter (Dva) by single-particle aerosol mass spectrometry (SPAMS) to achieve a measurement of Dve and ρeII. The reliability of the AAC-SPAMS system for accurately obtaining Dve and ρeII is verified based on the result that the deviation between the measured and theoretical values is less than 6 % for the size-resolved spherical polystyrene latex (PSL). The AAC-SPAMS system was applied to characterize the Dve and ρeII of (NH4)2SO4 and NaNO3 particles, suggesting that these particles are aspherical and their ρeII is independent of particle size. Finally, the AAC-SPAMS system was deployed in a field measurement, showing that it is a powerful technique to characterize the chemically resolved Dve and ρeII of particles in real time.

This paper discusses the use of volumetric enhancers in ducts of heat exchangers for high-viscosity liquid media, which ensure the transition from a laminar flow to a turbulent one. Small random metal packings with a large free volume and an equivalent diameter of 5 to 25 mm were used as volumetric enhancers. It has been found that volumetric enhancers provide an increase in the heat transfer coefficient by a factor of 15 or more when industrial oil is heated. For a comparative assessment of the thermal hydraulic effectiveness of various packings, a modified expression of the Kirpichev energy coefficient has been obtained, which is associated with the thermal effectiveness of the process. The results of calculations are presented and conclusions are drawn about more effective designs of enhancers and operating modes.

The article presents an experimental study on heat transfer and friction behaviors in a solar air duct fitted with multiple V-shaped ribs on the absorber and delta-grooves on the back plate. Measurements were carried out in the test duct having a cross-section of width, W = 300 mm and height, H = 27 mm. The air flow rate inside the duct was varied to have Reynolds numbers based on the duct hydraulic diameter from about 7000 to 30,000. Two vortex flow devices: rib and groove turbulators, were introduced to generate the vortex flows along the duct. In the test duct, the upper/absorber plate having a constant heat-flux was mounted repeatedly by multiple V-shaped thin ribs with an attack angle (α) of 45° relative to main flow direction while the lower/back plate was grooved periodically in the delta/triangular shape with an attack angle (θ) of 60°. In the present investigation, the geometrical parameters of the ribs included three different rib- to duct-height ratios (e/H = BR = 0.108, 0.162 and 0.217) and three rib-pitch to duct-height ratio (P/H = PR = 1.0, 1.5 and 2.0). The experimental results have shown that the duct with the V-ribbed absorber at BR = 0.217, PR = 1 in conjunction with the delta-grooved back plate has the greatest heat transfer and pressure loss. However, the use of the combined devices with PR = 1, BR = 0.108 leads to the highest thermal performance and also provides greater heat transfer and thermal performance than employing the V-rib or the delta-groove alone.

In present work, numerical simulation has been performed using the volume of fluid method under steady-state condition to find the effect of various operating parameters, viz. mass flux, vapor quality and effective thermal conductivity on heat transfer coefficient using refrigerants R1234ze and R1234yf. The numerical simulation has been carried out using various turbulence models, viz. the standard k − e model, the standard k − ω model and the low-Re SST k − ω model. The model having minimum deviation with experimental results is considered for subsequent study. The hydraulic diameter and length of mini-channel considered are 1.085 and 420 mm, respectively. The vapor quality has been varied from 0.14 to 0.95, and mass flux has been varied from 200 to 800 kg/m2 s keeping saturation temperature of 313 K. The heat transfer coefficient results of hydrofluoroolfine refrigerants R1234yf and R1234ze have been compared with hydrofluorocarbons refrigerant R134a in order to check the suitability of new hydrofluoroolfine refrigerants as a replacement to hydrofluorocarbons refrigerant. It has been observed from the flow regime map proposed by Sardesai et al. (Chem Eng Sci 36:1173–1180, 1981) that majority results of heat transfer coefficient for refrigerants R1234ze and R1234yf fall in the annular flow regime. It has been observed that the effective thermal conductivity may play vital role in the local heat transfer rate compared with the liquid film thickness.

An important physical property in environmental samples is particle size distribution. Several processes exist to measure particle diameter, including change in electrical resistance, blocking of light, the fractionation of field flow and laser diffraction (these being the most commonly used). However, their use requires expensive and complex equipment. Therefore, a digital microscopic imaging application (DMIA) method was developed adapting the algorithms used in the helminth egg automatic detector software coupled with a neural network (NN) and Bayesian algorithms. This allowed the determination of particle size distribution in samples of waste activated sludge (WAS), recirculated sludge (RCS), and pre-treated sludge (PTS). The recirculation and electro-oxidation pre-treatment processes showed an effect in increasing the degree of solubilization, decreasing particle size and breakage factor with ranges between 44.29%, and 31.89%. Together with a final NN calibration process, it was possible to compare results. For example, the 90th percentile of equivalent diameter value obtained by the DMIA with the corresponding result for the laser diffraction method. DMIA values: 228.76 μm (WAS), 111.18 μm (RCS), and 84.45 μm (PTS). DMIA processing has advantages in terms of reducing complexity, cost and time, and offers an alternative to the laser diffraction method. HIGHLIGHTS Adaptation of HEAD software algorithms, image processing techniques, and neural network fitting, allowed the evaluation of the particle size distribution.; Electro-oxidation pre-treatment improves the subsequent anaerobic digestion process.; Larger sludge particles are the most affected by the electro-oxidation process.

To clarify some of the inconsistencies in the research of equivalent diameter of PVDs, we constructed 3-D consolidation models of PVDs and sand drains using ABAQUS and compared models with and without sand drain resistance. When the sand drain resistance was included in the model, the equivalent diameters of the sand drains were 30, 65, 78, and 100 mm (for a 100-mm-wide, 4-mm-thick PVD) corresponding to PVD drainage depths (or soft soil layer thickness) of 2, 5, 8, and 10 m. Except for the depth of 2 m, the other results were higher than the values found in previous studies. The equivalent diameters increased with increasing consolidation depths. When the well resistance was ignored, the equivalent diameters were 20 mm for all the ground consolidation depths, which was less than the value in most previous research findings.

Urban road dust was collected from Vellore City, Tamil Nadu, India, and analyzed. Scanning electron microscopy (SEM) was used to examine road dust from nine sampling locations in the study region. SEM image analysis was used to identify various shape factors of collected dust particles. The equivalent spherical diameter of most particles was between 10 μm and 30 μm. Fine particles had greater concentrations at locations with higher traffic flow. Particles were categorized into four classes based on their shape factors, viz., spherical, mineral, elongated, or irregular. Spherical particles had the smallest mean equivalent diameter (1.95 μm) and mineral particles had the largest diameter (33.3 μm). Spherical particles made up the smallest portion of road dust (0–12%) in the study region and mineral particles made up the largest (45–65%). Elongated and irregular particles, each made up 23–30% of road dust. Electron dispersive X-ray spectroscopy analysis was used to identify the elemental composition of dust particles. Spherical particles were mostly from combustion sources and mineral particles were largely of crustal origin. No individual source was found for irregular and elongated particles. Biological debris was the major source of irregular particles.

Permeating behaviour is one of the most important factors of porous ceramics used for gas/liquid filters or membrane/catalysis supporters. Insufficient research has reported on the effect of raw particle size on permeating behaviour and the relationship between particle size and pore size of fabricated porous ceramics. In this work, porous SiC ceramics were fabricated with raw SiC particles of different grit designations and the effect of particle size on the permeating behaviour and equivalent pore size of the resulting porous ceramics were investigated. Due to oxidation of the SiC particles during the firing process, resulting materials with finer raw particles exhibited higher mass gain and lower bulk and true density. When the grit designation changed from 2000# to 120#, the strength of the resulting materials declined, and the Darcy permeability k1 increased from 6.65 × 10−15 to 4.85 × 10−13 m2. The ratio of the hydraulic equivalent diameter of pores to raw particle size in the resulting materials decreased from 0.25 to 0.11, indicating that the hydraulic equivalent pore size did not increase proportionally with the particle size increase. Further measures should be employed to enlarge pore size in porous ceramics to enhance its permeability.

Experiments are conducted to study the heat transfer and friction in a rectangular duct roughened by arrays of alternate ribs (square-, triangle-. and circle-shaped ribs). The Reynolds number Re based on duct hydraulic diameter rages from 12.000 to 60.000. whereas the rib pitch-to-height ratio (P/h) varies from 6 to 18. To understand the mechanism of heat transfer enhancement the measurements of streamwise mean velocities are also conducted in the square-ribbed duct. The results show that the flow of air through the ribbed duct becomes periodically fully developed after the third rib from the duct inlet. The data indicate also that the triangular type ribs have a substantially higher heat transfer performance than any other ribs in the studied range. The experimental results show that the heat transfer enhancement factors are greater than the friction factor ratios associated with the use of rib-turbulators in the rectangular ducts. Also, the rib conductivity affects significantly on the heat transfer enhancement factor. Correlations for friction and heat transfer in square-ribbed ducts are developed to account for rib spacing to height ratio and flow Reynolds number.

This paper is focussed on investigating into some key aspects relating to design of an integrated proton exchange membrane fuel cell. Analysis of all currently utilised storage mediums was undertaken. High and low inlet operating conditions were studied by determining the distributions of over potentials, velocity distribution, and pressure. At entrance and exit, a triangle channel flow-field was predicted to have better polarization performance and regular velocity distribution, whereas for rectangular that was performance differences among four serpentine flow-fields for hydrogen and air. The pressure in the triangle channels were monitored to have periodically similar plots and showed important low pressure drop. Considering low pressure drop of rectangular channel has mid effect between triangles and rectangular for the same dimension that depends on the hydraulic diameter, these flow-fields would be beneficial for the larger inlet channel area. The study found that the triangular channels produced a better performance than their square flow path counterparts.

The current study is based on the DEM computer simulation of three experimental test devices with different dimensions to determine the difference in the results of the formation of shear and repose angles that the particles experience when grouped under the action of the gravitational force. In this respect, the experimental test devices with different height, width, and depth were geometrically modeled with iron pellet particles using morphology and a granulometric variation from 6 mm to 9 mm of equivalent diameter in its spherical shape. Depending on the results obtained, a reliable size of the experimental test device will be available to obtain the necessary data for a correct adjustment of the calibration parameters for the DEM simulation of mining-metallurgical processes that use granulated material of iron pellet.

The article presents measurements and calculations of selected gas phase parameters in a liquid metal-gas flow in a magnetic field. The gas phase were argon bubbles, while the liquid metal was the GaInSn eutectic. The flow velocities of the gas bubbles, their equivalent diameter, and drag coefficient values were calculated for different argon inlet nozzles. The boundaries between the rise of individual bubbles and the chain flow were also indicated. The ultrasonic pulse echo method was chosen as the measurement method.

In order to design a more compact small nuclear reactor, liquid metal gallium can be selected as the reactor coolant. Gallium is rarely used in reactor as liquid metal coolant, however, due to its excellent thermal conductivity and low melting point, research on the flow and heat transfer characteristics of liquid metal gallium in channels can provide a theory basis for nuclear reactor design optimization and relax reactor safety limits. The flow heat transfer characteristics of liquid gallium are obtained by calculating the surface heat transfer coefficient of liquid gallium in various thermal and structural parameters. The calculation results show that the heat transfer between liquid gallium and the pipe wall can be enhanced by the increase of the inlet flow velocity, the increase of the wall heat flux density, or the reduction of the pipe size. When the hydraulic diameter of each pipe is the same, the heat exchange effect of liquid gallium flow in tubes is: triangle tube>square tube>round tube. The flow heat exchange effect of liquid gallium is better than that of lead-bismuth fluid.

The goal of this work was to determine which standard particle size metric derived from optical analysis most closely approximates the sieved weight percent of irregularly shaped powder intended to be used for directed energy deposition. In this investigation, equivalent circle diameter, maximum diameter, minimum diameter, and perimeter were used as metrics to “virtually sieve” the particles in samples of irregularly shaped powder into the following particle size bins: 150 µm. The percentage in the 45 µm – 150 µm bin were then compared to the weight percent of the powder mechanically sieved into this size range. The absolute difference between the virtually sieved percentage and the mechanically sieved percentage was assessed for 81 samples of mechanically-generated stainless steel 316L powder, all produced under different processing conditions in an oscillation ball mill. This difference was found to be on average, the least with the minimum diameter assessed as an area percentage, followed by the equivalent diameter assessed as an area percentage, and then the maximum diameter assessed as a percentage of the total number of particles ranked third. These findings and the methodology used to obtain them may be used by powder production process engineers and quality assurance personnel to assist in process control as more diverse additive manufacturing feedstocks become utilized.

In this work, flow and heat transfer in a channel having oval trench dimples were investigated numerically. 3-D channel flow with a cross-section of 300-mm width and 32-mm height were created using Computational Fluid Dynamic (CFD) with ANSYS, Fluent (V.15.0). Five oval trench dimples with 3-mm depth, 10.0-mm width and 45-mm length arranging with a single row and in-line configuration were located on the bottom surface of the channel. Reynolds number based on hydraulic diameter of the channel were fixed at Re=20,000 whereas a dimple inclined angle defined as the angle of dimple centreline to the mainstream was varied at 0, 15, 30 and 45 degrees. SST turbulent model was used to solve governing Equations. The result show that longitudinal vortex flow occurred at ?=15° to 45° which would be enhance heat transfer on the surface. When inclined angle became larger, the areas of Nusselt number and high total pressure coefficient took place at dimple edge in +Z direction. The peak of average spanwise Nusselt numbers took place for the case of ?=45°. Moreover, the area of high spanwise average Nusselt numbers (>100) for the case ?=30° was the largest.

The objective of this research is to study flame structure and heat transfer characteristics for the premixed flame jet from the swirling chamber. In this study, LPG and air was utilized as gas fuel and oxidizer for a premixed flame. The equivalence ratios () of LPG and air were considered at 0.8, 1.0, and 1.2 under a Reynolds number Re = 4,000. The swirl flame was generated by double tangential inlets in cylindrical chamber. The diameter of chamber was fixed at D = 20 mm and the hydraulic diameter of the inlet was Dh = 5 mm. In this study, the effect of chamber geometry on flame structure was investigated by varying the chamber from H = 2.2Dh to 7.0Dh. The structures and temperature of the free flame jet was recorded with camera and measured with a thermocouple. The heat transfer rate of impinging flame jet was also measured at distance from chamber outlet to flame impingement surface varying from L = 4Dh to 10Dh. The results show that the maximum of flame temperature occurs at =1.2. Impinging flame jet for case of chamber height at H = 4.6Dh and impingement distance at L = 4Dh give the highest heat transfer for all equivalence ratios due to the reaction zone of combustion reached to approach near the heat transfer surface.

An experimental investigation of thermohydraulic performance characteristics of a packed bed solar air heater is done in the present work. The packed bed is generally used to enhance the heat transfer area, increase the turbulence in the flow and for the storage of thermal energy. The experimental investigation has been carried out on a low porosity packed bed solar air heater. The investigation covers a particular range of design and operating parameters. Design parameters take account of the equivalent diameter of packing material (1.55 mm), packing density (250 g per 0.075 m3) and colour of the packed bed material (Black) while the operating parameters take account of the mass flow rate ranging from 0.01 to 0.04 kg/s. It is observed that the efficiency of the air heater increases with increase in mass flow rate. It is also found that the impact on the overall efficiency due to frictional loss is much less in a low porosity packed bed solar air heater.

We performed experiments to measure a single-phase upward flow in a 5 × 5 rod bundle with spacer grids using a particle image velocimetry, focusing on the crossflow. The Reynolds number based on the hydraulic diameter and the bulk velocity is 10,000. The ratio of pitch between rods and rod diameter is 1.4 and spacer grid is installed periodically. The turbulence in the rod bundle results from the combination of a forced mixing and natural mixing. The forced mixing by the spacer grid persists up to 10Dh from the spacer grid, while the natural mixing is attributed to the crossflow between adjacent sub-channels. The combined effects contribute to a sinusoidal distribution of the time-averaged streamwise velocity along the lateral direction, which is relatively weak right behind the spacer grid as well as in the gap. The streamwise and lateral turbulence intensities are stronger right behind the spacer grid and in the gap. Based on these findings, we newly defined a modified mixing coefficient as the ratio of the lateral turbulence intensity to the time-averaged streamwise velocity, which shows a spatial variation. Finally, we compared the developed model with the measured data, which shows a good agreement with each other.

The aim of this work is at investigating the applicability of electronic expansion valves (EEVs) in domestic refrigerators. To this end, a valve with an orifice of 0.19 mm of hydraulic diameter was installed in a conventional refrigerator to correlate the flow restriction with the overall energy consumption spanning different operating conditions. Tests with the same refrigerator mounted with a capillary tube were also performed. Also, a mathematical model was devised to simulate the effect of the refrigerant charge and the expansion device restriction on the system performance. More than a thousand different conditions were simulated. The results revealed that zero superheating is not necessarily the best-case scenario in terms of energy consumption. In addition, it was noticed that the lowest energy consumptions were achieved for the highest refrigerant charges and expansion restrictions. Furthermore, it was observed that, when the surrounding temperature or the compressor speed were changed, the energy consumption could be reduced by varying the restriction of the expansion device. The system with the EEV, nonetheless, presented higher energy consumptions than the system with the capillary tube for most conditions, which was mostly related to the extra thermal load generated by the valve. Nevertheless, by increasing the internal heat exchanger length and mitigating the heat dissipated by the EEV, it was found that the system with the EEV consumed between 4 and 9% less energy than the system mounted with capillary tube under operating conditions different from that the capillary tube has been sized for.

To solve the problem of non-uniform refrigerant distribution among multi-tubes of micro-channel heat exchangers (MCHXs), a novel embedded-clapboard distributor is presented in this study, in which the embedded clapboards have a spray hole to transform the irregular flow pattern of inlet refrigerant into a dispersed bubble flow, and to form a cyclic channel to maintain the regular layout of dispersed bubble flow. The design method for the distributor is illustrated, including the calculation method for the spray hole diameter deduced from the transition criteria of dispersed bubble flow at both the horizontal and the vertical installations, and the calculation method for the hydraulic diameter of cyclic channel deduced based on the Bernoulli Equation for the circulation of dispersed bubble flow. The validation of refrigerant distribution performance includes the comparison of two-phase flow pattern between the proposed distributor prototype and conventional distributor prototype manufactured with transparent material, and the test of distribution unevenness among the outlet tubes for these two types of distributor prototypes. The experimental results show that the embedded-clapboard distributor forms the regular dispersed bubble flow at all installation patterns, and the average unevenness of the proposed distributor at the vertical, the sloped and the horizontal installations is 42.5%, 45.9% and 41.4% lower than that of the conventional cylinder-type distributor, respectively.

Nowadays, there is a large demand for many electronic devices such as the laptop, and cell phone. The heat generated by such electronic component increases due to continuous functioning. Implementing microchannel could be a good solution despite the heat from microminiature refrigerators, microelectronics, micro heat pipe spreader, fuel processing biomedical, and aerospace. Therefore, several investigations have been done to improve the performance of such continuous operating electronic devices by dissipating heat with the use of microchannels. In this study, an experimental and numerical investigation is done for the circular microchannel having the hydraulic diameter of 253 µm and 63 mm in length under the condition of constant wall temperature by submerging the microchannels in the oil at constant temperature and water is forced to pass through total 5 microchannels. Experimental conducted for various flow rates shows that the microchannel has a significant impact on the heat transfer rate for the considered flow rate. Numerical results through COMSOL 5.1 software show good agreement with the experimental results. It is observed that the heat transfer coefficient increases with the Reynolds number whereas friction factor decreases with Reynolds number. Based on numerical and experimental results, empirical correlations for friction factor and Nusselt number are suggested to provides a reasonable estimate of heat transfer in the microchannel.