Round Copper Research Articles

Voltage distribution in inorganic insulation windings for high-temperature motors

Purpose The purpose of this paper is to present a method for computing voltage spikes endured by the insulation of the first coils of high-temperature (HT°) synchronous machines fed by PWM inverters that deliver fast-fronted voltage pulses. Design/methodology/approach The transient state following each steep edge is computed by SPICE using the global high-frequency (HF) equivalent circuit of the motor winding. This equivalent circuit is automatically built using the proposed elementary coil model. Two inorganic HT° technologies are compared: the first one uses a round copper wire insulated by a thin ceramic layer and the second one is made with an anodized aluminum strip. Findings The winding made with an anodized aluminum strip, which has a higher turn-to-turn capacitance, yields a better voltage distribution between coils of the machine. Research limitations/implications The elementary coil equivalent circuit is computed from impedance measurements performed on an elementary coil. Another starting point could be developed with an FE analysis to determine the parameters of the HF equivalent circuit, which would avoid the need for a prototype coil before the machine design. Practical implications For inorganic motors, the insulation layers have poorer electrical characteristics compared with standard organic ones. Therefore, the computation of voltage spikes distribution along the coils of each phase represents a major issue in the design of HT° machines. Originality/value The presented approach is a step toward the design of HT° (400-500°C) actuators fed by PWM inverters based on fast SiC electronic switches.

Experimental high gradient testing of a 17.1 GHz photonic band-gap accelerator structure

We report the design, fabrication, and high gradient testing of a 17.1 GHz photonic band-gap (PBG) accelerator structure. Photonic band-gap (PBG) structures are promising candidates for electron accelerators capable of high-gradient operation because they have the inherent damping of high order modes required to avoid beam breakup instabilities. The 17.1 GHz PBG structure tested was a single cell structure composed of a triangular array of round copper rods of radius 1.45 mm spaced by 8.05 mm. The test assembly consisted of the test PBG cell located between conventional (pillbox) input and output cells, with input power of up to 4 MW from a klystron supplied via a ${\mathrm{TM}}_{01}$ mode launcher. Breakdown at high gradient was observed by diagnostics including reflected power, downstream and upstream current monitors and visible light emission. The testing procedure was first benchmarked with a conventional disc-loaded waveguide structure, which reached a gradient of $87\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ at a breakdown probability of $1.19\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}1}$ per pulse per meter. The PBG structure was tested with 100 ns pulses at gradient levels of less than $90\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ in order to limit the surface temperature rise to 120 K. The PBG structure reached up to $89\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ at a breakdown probability of $1.09\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}1}$ per pulse per meter. These test results show that a PBG structure can simultaneously operate at high gradients and low breakdown probability, while also providing wakefield damping.

Reduction of Screening-Current-Induced Fields in an HTS Tape Winding Using Toroidal Arrangement of Shaking Coil

Screening-current-induced fields (SCFs) in an HTS main coil are experimentally reduced by using a copper shaking coil. The HTS main coil is wound using a Gd-based coated conductor into four double pancakes without a joint between them. The shaking coil is also toroidally wound around the HTS main coil using a round copper wire. Both the HTS and copper coils are immersed in liquid nitrogen, and axial magnetic fields at the center of the HTS main coil are observed using a Hall probe. By applying alternating currents to the copper shaking coil and, therefore, azimuthal AC magnetic fields to the HTS main coil, the SCFs at the center of the HTS coil are reduced successfully.

Simultaneous Effects of Flattening Tube and Adding Nanoparticles on Boiling Heat Transfer

An empirical investigation is performed on boiling heat transfer characteristics of R600a refrigerant flow inside horizontal flattened tubes. Round copper tubes of 8.7 mm inner diameter are deformed into flattened shapes with different internal heights of 6.9, 5.5, and 3.4 mm as the test sections. Effects of different parameters such as mass flux, vapor quality, and internal tube height on the heat transfer coefficient are studied. It is shown that flattening the tube causes significant heat transfer enhancement. The maximum augmentation ratio of 163% is obtained for the flattened tube with the maximum aspect ratio of 3.56. A new correlation is developed based on the obtained experimental data to predict the heat transfer coefficient in flattened tubes; 90% of the acquired data are predicted within. Consequently, the tested flattened tube with maximum heat transfer rate is selected to study the effects of nanoparticles. Experiments are conducted for three different working fluid types including 1) pure refrigerant (R600a); 2) refrigerant/lubricant (R600a/oil); and 3) nanorefrigerant: refrigerant/lubricant/nanoparticles (R600a/oil/CuO). Polyolester oil is used as the lubricant in the two latter cases. In addition, nanorefrigerants (R600a/oil/CuO) are prepared by dispersing CuO nanoparticles with different mass fractions of 0.5, 1, and 1.5% in the baseline mixture (R600a/oil). Thereby, maximum heat transfer enhancement of 79% is achieved compared to the pure refrigerant case. The results of this study provide the platform for designing compact efficient heat exchangers/heat sinks for the emerging thermal engineering applications under high thermal load conditions.

Impact of two-phase distribution systems on the performance of a microchannel evaporator

The design and the performance of an innovative shell-and-tube evaporator using round copper microchannels are presented in this article. This prototype has been designed aiming at the minimization of the refrigerant charge, which can be required by safety or environmental restrictions. Experimental data of heat transfer and pressure drop are reported in the present article. The measurements have been obtained with two different evaporator inlet headers and two different working fluids (i.e., R22 and R410A) to investigate the mutual influence of the design of the distribution system and the refrigerant properties on possible maldistribution issues. A computational procedure implementing different correlations has also been developed and validated against experimental data; this procedure allows the prediction of the performance of the same evaporator with a hydrocarbon, such as propane, and comparison of the prototype to a brazed-plate heat exchanger.

Microstructural changes in quasicrystalline Al–Mn–Be–Cu alloy after various heat treatments

Abstract In this study we investigated the microstructural changes after a variety of heat treatments of the quasicrystalline Al–Mn–Be–Cu alloy. In addition, we report on Vickers microhardness measurements and tensile-test results for the same materials. The samples were produced in a conventional manner, i. e., melting in an electrical resistance furnace in air and a gravitational casting process using a round copper die, which was in the form of a tensile-test specimen with a diameter of 5 mm. After the casting, some of the samples were just solution treated (annealed) and then quenched in water, while others were additionally aged (artificially – T6, or naturally – T4) or directly aged after the casting. In comparison to the as-cast state, the Vickers microhardness values of the aluminum-based matrix and the tensile properties of the samples decreased when just the solution treatment, T4 or T6 treatment was performed. The tensile properties also decreased after the heat treatments. A microstructural inspection revealed that the microstructural changes occurred already during the solution treatment, i. e., the formation of the phases Be4Al(Mn, Cu) and τ1-Al29Mn6Cu4 on the approximant H-Al4Mn and quasicrystalline i-phase particles' edges and the occurrence of precipitates in the αAl matrix. The precipitates that would additionally contribute to the hardening of the alloy did not form. The directly aged samples showed little or no increase in microhardness values in comparison to the as-cast samples, but possibilities of θ″ precipitates being formed from the already saturated matrix after the casting could not be excluded. After all the heat treatments the quasicrystalline i-phase, as a primary and eutectic phase, was preserved.

Experimental study of horizontal flattened tubes performance on condensation of R600a vapor

An empirical setup has been established to study heat transfer and pressure drop characteristics during condensation of R600a, a hydrocarbon refrigerant, in a horizontal plain tube and different flattened channels. Round copper tubes of 8.7mm I.D. were deformed into flattened channels with different interior heights of 6.7mm, 5.2mm and 3.1mm as test sections. The test conditions include heat flux of 17kw/m2, mass velocity in the range of 154.8–265.4kg/m2s and vapor quality variation from approximately 10% to 80%. Results indicate that flattening the tubes causes significant enhancement of heat transfer coefficient which is also accompanied by simultaneous augmentation in flow pressure drop. Therefore, the overall performance of the flattened tubes with respect to heat transfer enhancement considering the pressure drop penalty is analyzed. It is concluded that the flattened tube with 5.2mm inner height tube has the best overall performance. Due to the failure of pre-existing correlations for round tube condensation heat transfer, a new correlation is proposed which predicts 90% of the entire data within ±17% error.

Study of DC and AC electric field effect on Pisum sativum seeds growth

In this research the effect of electric field on two groups of wet and dry Pisum sativum seeds growth was studied. To generate the required electric field a parallel-plate capacitor with round copper plates of 30 cm diameter was used. The experiments were performed once in fixed exposure duration of 8 min in variable DC electric field of 0.25–1.5 kV/m. The other experiments were performed in variable fields of 50–125 kV/m in fixed exposure duration of 8 min, in two groups of AC and DC electric fields. The experiments were repeated three times. In each experiment 10 seeds were used and there was a sham exposed group for comparison, too. After application of electric field, the seeds were kept for six days in the same growth chamber with the temperature of 25 ± 1 °C and 12 h light/12 h darkness. On the 6th day length of stems and height of roots were measured. After doing statistical analysis, in low intensities of DC electric field, the highest significant increase of mean growth (The average of stem length and the height of roots) was seen in 1.5 kV/m in wet seeds. In high intensities of DC and AC electric fields, the highest significant increase of mean growth was seen in AC electric field of 100 kV/m in wet seeds.

2중 원형동관의 2축압축 변형특성에 관한 연구

The deformation characteristics of a double round copper pipe and a single round copper pipe under biaxial compression were studied using a horizontal compression die. The change in punch load and in deformation behavior was measured during the experiments using various compressive deformation rates in the range of 10mm/min. ~ 450mm/min. The maximum punch load for both the double round copper pipe and the single round copper pipe decreased with increasing compressive deformation rate. The maximum punch load for the single round copper pipe was twice that of the double round copper pipe. After a 4.0mm stroke, the deformed shape of the single round copper pipe remained rectangular. However the outer tube of double round copper pipe remained rectangular while the inner tube was clover shaped. The stress and strain distributions in the double round copper pipe and the single round copper pipe show clear differences. The results of numerical simulations using Deform-2D are in good agreement with experimental results.

Experimental Study of Flat Format Multichannel Triggered Rail Spark Gap

This paper is concerned with the development and testing of a compact flat format multichannel electrically triggered rail spark gap. It is tested for multichannel discharge under atmosphere for high reliability. Multichannel discharge rail spark gaps can be developed using laser trigger or fast rising trigger voltage pulse . The extra volume and weight added by laser or fast triggering circuits limit the use in pulse power applications. An electrically multitriggered low-inductance spark gap is developed. It is used as a multichannel low-inductance discharging element in a fast rising high-current generation system. The trigger of such rail gap is realized using the set of round copper pins similar to single trigger pin in a field distortion spark gap. In parenthesis, five different trigger pins are located in main trigger plate and these are isolated with high impedance. Therefore, five different trigger signals are generated with time difference of tens of nanoseconds. The major material erosion at five points of both stainless steel main electrodes confirms the multichanneling discharge. The main gap spacing in this switch is 4 mm and the trigger is located close to the ground electrode for reducing the delay time and jitter in delay time. This paper shows the trigger circuit design, main gap voltage, and trigger voltage effect on the closing of the spark gap and picture of electrodes after use.

원형 동관의 2축압축 변형특성 및 조직변화에 관한 연구

The deformation characteristics and microstructure changes in a round copper pipe under biaxial compression was studied using a horizontal compression die. The change of material properties, punch load and deformation behavior were monitored using various compressive deformation rates in the range of 0.5mm/min.~450mm/min. The strains, either tensile or compressive, were estimated from Vickers microhardness test results. The punch load and deformation characteristics of the round copper pipes were found to change greatly at a deformation rate of about 200mm/min. The punch load decreased with increasing compressive deformation rate. The results of numerical simulations agreed well with what was expected from the final microstructure and the hardness profile estimated from the final deformation strains.

Strength of Normal Concrete Using Metallic and Synthetic Fibers

Based on the laboratory experiment, cube and cylindrical specimens have been designed with metallic and non-metallic groups of fibers. In metallic fibers, steel fibers of hook end with 50, 60 aspect ratio and crimped round (copper coated) of 52.85 aspect ratio containing 0% and 0.5% volume fraction were used without adding admixtures. In synthetic fibers category, fibrillated polypropylene fibers of 15 mm, 20 mm and 24 mm cut length at 0.4% by weight of cement were used without adding admixtures. Total 63 specimens were casted and tested for the work. Comparing the results of fiber reinforced concrete with plain concrete, this paper validated the positive effect of steel fibers with different aspect ratios and fibrillated polypropylene fibers with different cut length in compression and splitting strength improvement of specimen at 7 and 28 days, analyzed the sensitivity of different fibers to concrete with different strength.

Numerical simulation of horizontal continuous casting process of round copper billet with electromagnetic stirring

In this paper, a comprehensive three-dimensional mathematical model is built to investigate the effect of rotating electromagnetic stirring on the solidification process of copper round billet during horizontal continuous casting. The electromagnetic field was simulated by ANSYS software, and the thermal flow field was simulated by FLUENT software. The coupling between the electromagnetic field and the thermal flow field was implemented by a user defined subroutine. The simulation results match with the experiment ones. The influence of current frequency and current intensity on the flow field of molten melt was investigated. The optimum current intensity and frequency are found to be 40 A and 10 Hz when the maximum magnetic flux density and the time average electromagnetic force are 100 mT and 72×10−3 N respectively on the surface of the round copper billet.

Numerical and experimental analysis of a point focus solar collector using high concentration imaging PMMA Fresnel lens

A high concentration imaging Fresnel solar collector provided with different cavity receivers was developed and its behavior was investigated. Round copper pipes winded into different spring shapes were used as receiver by placing in the cylindrical cavity to absorb concentrated solar energy and transfer it to a heat transfer fluid (HTF). The collector efficiency factor and collector heat removal factor were derived for the cavity receivers to find out heat transfer mechanism and to propose an effective way for evaluating the performance of Fresnel solar collector and determining the optimal cavity structure. The problem of Fresnel solar collector with synthetic heat transfer oil flow was simulated and analyzed to investigate heat loss from different cavity receivers. Solar irradiation as well as convection and heat transfer in the circulating fluid and between the internal surfaces of the cavity and the environment are considered in the model. The temperature distribution over its area as well as the collector thermal efficiency at nominal flow rate was used in order to validate the simulation results. It was found that the simulated temperature distribution during operation and the average collector efficiency are in good agreement with the experimental data. Finally, the optimal shape of solar cavity receiver, as well as its thermal performance, are deeply analyzed and discussed.

Simulation Study on Horizontal Continuous Casting of Round Copper Billet with Electromagnetic Stirring

In this paper, a comprehensive three dimensional mathematical model is built to investigate the effect of electromagnetic stirring (EMS) on continuous casting process of copper round billet. The electromagnetic field is simulated by ANSYS software and the thermal-flow field is simulated by FLUENT software. The coupling between electromagnetic field and thermal-flow field is implemented by user-defined subroutines. The simulation results have good agreement with the experiment ones. The results show that electromagnetic frequency and current intensity have significant influence on the fluid velocity, temperature gradient and sump depth. The optimum current intensity and frequency are found to be 40A and 10Hz respectively.

Performance evaluation of flattened tube in boiling heat transfer enhancement and its effect on pressure drop

An experimental investigation has been carried out to study heat transfer and pressure drop characteristics of R-134a flow boiling inside a horizontal plain tube and different flattened tubes. Round copper tubes with an inner diameter of 8.7 mm were flattened into an oblong shape with an internal height of 6.6 mm, 5.5 mm, 3.8 mm, and 2.8 mm. The test apparatus was basically a vapor compression refrigeration system equipped with all necessary measuring instruments. Analysis of the collected data showed that, by flattening the round tube, the heat transfer coefficient and pressure drop increased simultaneously. The performance of these tubes from the point of view of heat transfer enhancement and pressure drop increasing were evaluated. It was concluded that, the tube with an internal height of 5.5 mm has the best performance compared with the other flattened tubes. Finally, based on the present experimental pressure drop data, a correlation was developed to estimate the pressure drop in flattened tubes. This correlation predicts the experimental data of the present study within an error band of ± 20%.

Simulation of a photovoltaic/thermal heat pump system having a modified collector/evaporator

A new photovoltaic/thermal heat pump (PV/T-HP) system having a modified collector/evaporator (C/E) has been developed and numerically studied. Multi-port flat extruded aluminum tubes were used in the modified C/E, as compared to round copper tubes used in a conventional C/E. Simulation results suggested that a better operating performance can be achieved for a PV/T-HP system having such a modified C/E. In addition, using the meteorological data in both Nanjing and Hong Kong, China, the simulation results showed that this new PV/T-HP system could efficiently generate electricity and thermal energy simultaneously in both cities all-year-round. Furthermore, improved operation by using variable speed compressor has been designed and discussed.

Superhydrophobic Copper Tubes with Possible Flow Enhancement and Drag Reduction

The transport of a Newtonian liquid through a smooth pipe or tube is dominated by the frictional drag on the liquid against the walls. The resistance to flow against a solid can, however, be reduced by introducing a layer of gas at or near the boundary between the solid and liquid. This can occur by the vaporization of liquid at a surface at a temperature above the Leidenfrost point, by a cushion of air (e.g. below a hovercraft), or by producing bubbles at the interface. These methods require a continuous energy input, but a more recent discovery is the possibility of using a superhydrophobic surface. Most reported research uses small sections of lithographically patterned surfaces and rarely considers pressure differences or varying flow rates. In this work we present a method for creating a uniform superhydrophobic nanoribbon layer on the inside of round copper tubes of millimetric internal radius. Two types of experiments are described, with the first involving a simultaneous comparison of four tubes with different surface finishes (as received, as received with hydrophobic coating, nanoribbon, and nanoribbon with a hydrophobic coating) under constant flow rate conditions using water and water-glycerol mixtures. The results show that the superhydrophobic nanoribbon with a hydrophobic coating surface finish allows greater flow at low pressure differences but that the effect disappears as the pressure at the inlet of the tube is increased. The second experiment is a simple visual demonstration of the low-pressure behavior using two nominally identical tubes in terms of length and cross-section, but with one tube possessing a superhydrophobic internal surface finish. In this experiment a reservoir is allowed to feed the two tubes with open ends via a T-piece and it is observed that, once flow commences, it preferentially occurs down the superhydrophobic tube.

Mould Heat Transfer in the Continuous Casting of Round Billet

Mould heat transfer behaviors during the continuous casting of round billets are elucidated in this paper. Round copper moulds were instrumented with 72 thermocouples and mould temperature together with heat flux were monitored simultaneously with mould powder lubrication during continuous casting of a diameter 178 mm round billets. The profiles of the temperature and heat flux were analyzed based on the longitudinal and circumferential monitoring data under different installation status of moulds. The influences of steel carbon content, casting speed, and mould oscillation frequency on heat transfer have been discussed especially at position 70–110 mm below the meniscus where the heat transfer was the highest and most sensitive to operational parameters. Eventually, the correlation coefficient, defined as the correlation of local heat flux and temperature (CCHT) in the hot face of mould around the mould circumference at the same mould height, has proved to be a good characteristic parameter for analyzing the influence of scale on abnormal heat transfer in quantity.

An experimental investigation of tool wear in electric discharge machining

In this study, the variations of geometrical tool wear characteristics – namely, edge and front wear – and machining performance outputs – namely, workpiece removal rate, tool wear rate, relative wear and workpiece surface roughness – were investigated with varying machining parameters. Experiments were conducted using steel workpieces and round copper tools with a kerosene dielectric under different dielectric flushing conditions (injection, suction and static), discharge currents and pulse durations. The experiments have shown that machining parameters and dielectric flushing conditions had a large effect on geometric tool wear characteristics and machining performance outputs. Additionally, published research on tool wear is presented in detail in this study.