NiCr Wire Research Articles

Effects of thickness of boiling-induced nanoparticle deposition on the saturation of critical heat flux enhancement

Abstract Pool boiling tests were conducted to determine the effects of nanoparticle coating thickness on critical heat flux in 0.01 vol.% alumina nanofluid under atmospheric pressure using Ni–Cr wire heaters. The thickness of nanoparticles coating layer was controlled by varying the boiling time for pre-coating in the nanofluid. The CHF enhancement curve was acquired with respect to time of pre-coating process. As the result, the CHF enhancement is remained or saturated regardless of boiling time over certain or critical pre-coating time while the CHF sharply increased in relatively shorter pre-coating time. The CHF is gradually decreased after the critical time region. The wetting characteristics and the Taylor wavelengths on the coating surfaces were investigated to explain the trend of CHF regarding the effects of coating thickness. The physical deposition characteristics such as the coating thickness and the porosity were studied to analyze the CHF trend. The porosity is a key parameter to determine the CHF saturated under conditions over a critical coating thickness.

Evaluation on Electrical and Thermal Characteristics of Multi-Stacked HTS Coated Conductor With Various Stabilizers

Transporting large currents through High- Tc (HTS) current leads (CLs) inevitably involves using several HTS tapes in multi-stacked form to obtain a high current density. For safe operation of HTS CLs, the thermal stability of stacked HTS tapes should be considered. In this paper, we investigated electrical and thermal properties of multi-stacked HTS tapes using 2G coated conductor (CC). Three kinds of commercial CC with different specification of stabilizer were used for the experiment. Each stack sample was fabricated by soldering together CC tapes using In-Bi alloy. To verify the effects of a stabilizer on thermal stability for multi-stacked CC tapes, we performed an experiment of minimum quench energy measurements. In addition, transient electrical and thermal behavior were measured as a function of the external heat input energy. Each stack sample has a heater made of nickel-chromium (Ni-Cr) wire to make the external heat disturbance and a type-E thermocouple to measure the temperature. Based on the test results, electrical and thermal characteristics of multi-stacked CC tapes were evaluated.

Polypyrrole/montmorillonite nanocomposite as a new solid phase microextraction fiber combined with gas chromatography–corona discharge ion mobility spectrometry for the simultaneous determination of diazinon and fenthion organophosphorus pesticides

A novel solid phase microextraction (SPME) fiber was prepared and coupled with gas chromatography corona discharge ion mobility spectrometry (GC–CD–IMS) based on polypyrrole/montmorillonite nanocomposites for the simultaneous determination of diazinon and fenthion. The nanocomposite polymer was coated using a three-electrode electrochemical system and directly deposited on a Ni–Cr wire by applying a constant potential. The scanning electron microscopy images revealed that the new fiber exhibited a rather porous and homogenous surface. The thermal stability of the fabricated fiber was investigated by thermogravimetric analysis. The effects of different parameters influencing the extraction efficiency such as extraction temperature and time, salt addition, stirring rate, the amount of nanoclay, and desorption temperature were investigated and optimized. The method was exhaustively evaluated in terms of sensitivity, recovery, and reproducibility. The linearity ranges of 0.05–10 and 0.08–10μgL−1, and the detection limits of 0.020 and 0.035μgL−1 were obtained for diazinon and fenthion, respectively. The relative standard deviation values were calculated to be lower than 5% and 8% for intra-day and inter-day, respectively. Finally, the developed method was applied to determine the diazinon and fenthion (as model compounds) in cucumber, lettuce, apple, tap and river water samples. The satisfactory recoveries revealed the capability of the two-dimensional separation technique (retention time in GC and drift time in IMS) for the analysis of complex matrices extracted by SPME.

Electro-fusion behavior of CF/PPS laminates using Ni-Cr wire resistance heating element

This study aims to reveal the mechanism of electro-fusion joining of CFRTP composites using multiple Ni-Cr wires as resistance heating element. The materials used for electro-fusion joining test are unidirectional CF/PPS and woven CF/PPS laminates. The effects of electro-fusion condition such as applied voltage and fusion time, Ni-Cr wire spacing and PPS film thickness on the fusion behavior of CFRTP composites were investigated experimentally. The welding area and the joining strength were evaluated quantitatively by microscopic observation and single lap shear test. From the results of surface observation, it was shown that the welding area increased with increasing the applied voltage and fusion time, but thermal degradation and deformation were caused by excess conducting. It was also revealed that Ni-Cr wire spacing and PPS film thickness were significant parameters affecting on welding area and thermal degradation. The optimum electro-fusion condition could be obtained respectively for unidirectional CF/PPS and woven CF/PPS laminates because microscopic electro-fusion behavior was influenced by the fiber reinforcement configuration. Though the interlaminar shear strength (ILSS) is resulted in a marked improvement in the optimum electro-fusion conditions, ILSS was decreased significantly by inserting PPS film which can reduce the thermal degradation. Therefore the experimental results suggested that it is essential to avoid the thermal degradation of matrix polymer by heating of Ni-Cr wire.

A compact non-explosive separation device for high preload and low shock

In this paper, we present a compact non-explosive actuator device (NEA) that is activated with a thermal cutting method using Ni-Cr wire. Practical applications include the deployment of satellite appendages such as solar array panels and antennae. The pyrotechnic based separation device generates high shock and chemical contaminants, which cause malfunctions of components such as optic cameras and other sensors. The proposed NEA device is designed to generate low shock using unspool mechanism characteristic, and to have compact dimensions and a light mass. In the design process, we formulated equations based on a static analysis to verify that it satisfied the basic requirements. Then we fabricated the device based on a theoretical analysis and carried out pre-tests such as maximum preload and response time tests to verify the results of the theoretical analysis. The pre-test results showed an average maximum preload of 1,000 kgf and a response time of 600 ms. Consequently, we verified the feasibility of an NEA that could be activated within 600 ms under high preload. In order to develop a qualification model for the NEA, various additional tests are planned, including launching and space environment tests based on the European Satellite Agency standard test manual.

Metallic Cellular Materials Produced by 3D Weaving

Although it was developed primarily as a method to produce integral thick preforms for composites, 3D weaving provides an intriguing industrial scale manufacturing path to form cellular metal materials. In typical composites applications, development focused on increasing the volume fraction of fibers (yarns) within the preform. To produce effective cellular materials instead, research must focus on how to create open space within the woven structure. As a demonstration of this manufacturing path, small Cu wires, and then NiCr wires, were woven into several materials with various internal architectures using a non-crimp 3D orthogonal weaving machine. Initially, techniques were developed to weave the individual metal wires with precise placement and minimal twisting. These techniques were then used to create several different 3D woven material architectures with regular interconnected internal open space. Subsequent processes, such as brazing, soldering, and electroplating would be used to bond the nodes where the wires contact each other. In this set of experiments, the materials were 30mm wide, 3-4mm thick and on the order of a meter long. However the techniques should be scalable to meters in width, centimeters in thickness, and tens of meters in length.

전기가열장치를 이용한 연약지반개량

본 논문은 심층연약지반 개량용 전기가열장치를 개발하여 경기도 화성시 인근 연약지반에 적용한 것이다. m당 1 kW의 전기를 소비하는 니켈-크롬선으로 구성된 길이 4.0 m의 전기가열장치를 지표하 3.5~6.5 m 사이에 설치하여 48시간의 지반가열을 2회, 총 96시간 실시하였으며, 온도계와 압력계를 지표하 5.0 m 지점에 매설하여 지반가열에 의한 온도 및 증기압 변화를 측정하였다. 실험결과 가열원으로부터 횡방향 거리의 온도분포 및 선단지지력의 변화는 이차함수를 나타내었으며, 둘 다 R2값은 1로 산정되었다. 또한, 전기가열로 인해 수증기가 배출됨에 따라, 함수비 및 간극수압이 감소함을 관찰할 수 있었다. In this study, we developed the electric heating equipment and applied for soft ground improvement. The developed heat pipe is 4 m-length and consumes 1 kW/m, which is consisted of Ni-Cr wire. It was installed in 3.5~4.5 m below ground surface and heated for 96 hours (48 hours, 2 times). The temperature variation and vapor pressure caused by electric heating was measured by the thermometer and pressure gauge which were installed in the ground (5.0 m), and the tip resistances were measured by static electronic piezo-cone penetration test (CPT). As the results of experiments, 2-order polynomial curve was shown to adjust the variation of tip resistance and the temperature distribution with the horizontal distance from electric heater, whose R2 value is close to 1. In addition, in-situ pore-water pressure and water content was decreased.

Vortex generation using fin-slot structures and a submerged nozzle at a wall-injected cylinder

The internal flows of solid rocket motors are not yet fully understood. Several cold-air flow experiments that simulated combustion gas flow with compressed gas wall injections have been conducted to observe the behavior of internal flows and acoustic phenomena. Direct visualization, however, has rarely been performed due to the non-transparency of the wall-injecting media. In this study, novel techniques were employed to visualize the internal flow of the cold-flow model of a solid rocket motor. The smoke, which was generated using a heated Ni–Cr wire, was used as a flow tracer, and a light penetrated through an acrylic nozzle. The head-end of the test model was made with a transparent acrylic window to record the visualized flow using a high-speed CCD camera. The results of the visualization at the nozzle entrance region showed the symmetric vortex tube structures and the transient behavior of the circumferential flow. The vortex tube generation mechanism was explained with reference to the inlet vortex phenomenon of an aircraft engine. Also, it was observed that the interaction between the adjacent vortex tubes created the circumferential flow.

Experimental study of a universal CHF enhancement mechanism in nanofluids using hydrodynamic instability

Pool boiling tests were designed and performed to confirm the relation between the enhancement of critical heat flux (CHF) in nanofluids and the development of a hydrodynamic instability on the test heater surface from the deposition of nanoparticles during boiling. These pool boiling experiments were carried out under atmospheric pressure using a 0.49mm diameter cylindrical Ni–Cr wire as a heating element with ZnO, SiO2, SiC, Al2O3, graphene oxide and CuO nanoparticles at 0.01% volume concentration. The test fluids are distilled water and R-123. The CHF value for each nanofluid is obtained and compared with the measured Rayleigh–Taylor wavelength. Higher CHF results have shorter Rayleigh–Taylor wavelengths in all cases. We propose a modified theoretical model for hydrodynamic instability that incorporates these effects and fits experimental results.

스택의 채널 수에 다른 열음향파의 특성 비교 연구

The conversion of solar energy into acoustic waves is experimentally studied. Measurements were made on the Sound Pressure Level(SPL), onset time and the temperature gradient across the stack, with the Cell Per Square Inch(CPSI) of stack changed. A pyrex resonance tube is used with a honey-comb structure ceramic stack along with Ni-Cr and Cu wires. An AL1 acoustical analyzer was used to measure the SPL and frequency of acoustic waves whereas K-type thermocouples were hired to estimate temperature gradients. As a result, when the supply electric power was 25W, maximum SPLs of 104.1 dB, 109.4 dB and 112.8 dB were detected for the stacks of 200, 300 and 400 CPSI and their respective stack positions of 70mm, 60mm and 50mm from the closed end.

The effect of pressure on the critical heat flux in water-based nanofluids containing Al2O3 and Fe3O4 nanoparticles

Water-based nanofluids are colloidal dispersions of nanoparticles in pure water and have significantly higher critical heat flux (CHF) values compared to pure water at atmospheric pressure. This paper describes the effects of pressure on the CHF in a pool of water-based nanofluids of magnetite (Fe3O4) and alumina (Al2O3) nanoparticles using Ni–Cr wire. To evaluate the effect of pressure on the CHF enhancement of water-based nanofluids, pool boiling CHF experiments using pure water were first conducted at 101kPa (atmospheric pressure) to 1100kPa of absolute pressure. The CHF values for pure water increased with increasing system pressure, as expected. The results for pure water were compared with the CHF correlations and were found to be well matched. Based on the results for the pure water case, pool boiling CHF experiments using magnetite water nanofluid (MWNF) and alumina water nanofluid (AWNF) were performed at higher pressures within the same range as those used for the pure water case. It was found that the CHF using water-based nanofluids also can be enhanced at high pressures in a pool. Based on the obtained results, several methods (i.e., analyses of the bubble dynamics during nucleate boiling, of the contact angle with a droplet of pure water, and of the weight of deposited nanoparticles on the heating surface after CHF) were used to investigate the mechanism of CHF occurrence and the effect of pressure on the CHF in water-based nanofluids. The bubble frequency in the nanofluids was approximately 2 times higher than that for pure water. Due to the higher frequency of departing bubbles, the opportunity to rewet the hot spots on the heating surface was increased. The contact angles of the nanofluid were lower than that for the pure water cases at all ranges of pressure tested. The weight of the deposited nanoparticles on the heating surface decreased as the system pressure was increased. We discuss the effect of pressure on the surface characteristics in detail based on these analyses.

Method and apparatus for pyrolysis—Porous layer open tubular column—Cryoadsorption headspace sampling and analysis

In previous work, dynamic headspace vapor collection on short, porous layer open tubular (PLOT) capillary columns maintained at low temperature was introduced. In this paper, that metrology is extended with the introduction of a small in situ pyrolysis platform that provides for rapid heating and rapid vapor capture for a wide variety of samples. The new approach is referred to as pyro-PLOT-cryo. The pyrolysis platform is made from two small copper lead wires that hold a basket formed from small diameter, high resistance stainless steel or NiCr wire. The basket is formed to accept a small sample, the mass of which can typically range from 0.2 to 0.05mg. The pyrolysis is performed by use of a resistor capacitor circuit of the type used in spot welders. We have provided examples of the application of this technique with the analysis of facial cosmetics, plastic explosives, organometallic gasoline additives, polymers, and in micro scale chemical reactions. Additional modifications and future work are also discussed.

다양한 사전하중에 적용할 수 있는 Ni-Cr wire와 Kevlar rope를 이용한 위성 분리장치

본 논문에서는 기존의 복잡한 구조를 가지는 비폭발식 분리장치를 단순화시켜 니크롬 와이어와 케블라 로프를 이용한 새로운 개념의 비폭발식 분리 메커니즘을 설계/제작하고 기초성능 평가(사전하중, 분리시간, 충격 실험 등)를 위한 실험을 수행하였다. 그 결과 니크롬 와이어의 회전횟수에 따라 다양한 사전하중 하에서 작동이 가능한 것을 확인하였고, 최대 6.0kN의 사전하중 하에서 110G의 충격을 발생시키며 680ms의 짧은 시간에 분리되는 것을 확인하여 제안된 분리장치의 유용성을 확인하였다. 추후 발사환경 및 우주환경 시험을 통하여 제안된 분리장치의 우주인증을 수행하고 다양한 사전하중에서 작동 신뢰도를 확보하여 태양 전지 패널의 전개뿐만이 아니라 페어링 분리 등 다양한 용도에 사용이 가능하도록 개발하고자 한다. We present a kevlar rope based Non-Explosive Actuator(NEA) device which has simple structure and is activated by burning Ni-Cr wire. Through performance test, we find it can be operated under various pre-load by simply changing turn number of Ni-Cr wire. It shows release time of 680ms and shock level of 110G under pre-load of 6.0kN. Launching environment and space environment tests are planned to verify performance of the NEA based on European Satellite Agency test manual. Conclusively, we expect the proposed NEA can be applicable to release solar panel and fairing separation.

Flow Visualization, Critical Heat Flux Enhancement, and Transient Characteristics in Pool Boiling Using Nanofluids

Abstract This paper presents the experimental outcome of a study of the pool boiling heat transfer characteristics of alumina and CuO nanofluid in distilled water using a 0.19 mm diameter NiCr wire. A series of experiments were conducted in order to visualize the flow, critical heat flux (CHF) enhancement, and transient characteristics of nanofluid. The boiling phenomenon was visualized using a 0.1 g/l concentration of alumina nanofluid. The average bubble diameter was measured and was found to increase with increased heat flux. The average bubble contact angle decreased from 69° during the initial stages of boiling to 33° at CHF. Massive vapour bubbles were observed on the test heater surface near the CHF, inducing vapour blankets and forming hot/dry spots. The increase in the CHF could be well explained by the hot/dry spot theory. Pool boiling experiments conducted using low volume concentrations of CuO-water nanofluid at atmospheric pressure in distilled water showed an increase in the CHF by 30 % at a 0.3 g/l concentration. The transient behaviour of nanofluid, examined by exposing the heater surface at a constant heat flux of 700 kW/m2, indicated CHF enhancement of 5.21 % to 6.77 % for the two time durations. Based on the experimental investigations, it was concluded that the CHF enhancement is due to nanoparticle coating, which changes the thickness of the surface as a function of time and surface wettability and corroborates the hot/dry spot theory.

태양열 적용을 위한 열음향 레이저의 특성 비교 연구

The conversion of solar energy into acoustic waves is experimentally studied. Measurements were made on the Sound Pressure Level (SPL), frequency, onset time and the temperature gradient across the stack. A pyrex resonance tube is used with a honey-comb structure ceramic stack along with Ni-Cr and Cu wires. An AL1 acoustical analyzer was used to measure the SPL and frequency of acoustic waves whereas K-type thermocouples were hired to estimate temperature gradients. For a resonance tube of 100 mm, no acoustic waves were generated with a power input of 25W. By increasing its length to 200 mm, however, maximum SPLs of 96.4 dB, 106.3 dB and 112.8 dB were detected for the tubes of 10mm,20mm and 30mm in IDs and their respective stack positions of 70mm, 60mm and 50mm from the closed end.

Critical heat flux characteristics of nanofluids based on exfoliated graphite nanoplatelets (xGnPs)

In this paper, nanofluids containing xGnPs and xGnPs oxide were prepared due to superb thermal properties and low cost. Pool boiling experiments were performed for different particle concentrations. The critical heat flux (CHF) of nanofluids when boiled over a NiCr wire increased with increasing concentrations of xGnP and xGnP oxide particles in the base fluid. We determined that the xGnP oxide nanofluids with 0.005vol% dispersed particle concentration had the most enhanced CHF. Although the largest CHF enhancement was observed for the nanofluid with 0.005vol% xGnP oxide, no reduction was observed in the contact angle.

The experimental research and analysis on the quench propagation of YBCO coated conductor and coil

Quench propagation characteristics of YBCO tapes and coils were studied in this paper. Quench propagation in each test was initiated by a NiCr wire heater mounted on the sample tape and coil. Quench propagation velocity was measured through voltage taps and temperature sensors across different zones of the tapes and coil. Voltage taps and temperature sensors are arranged in longitudinal and radial direction of the coil. The thermal stability margin, the longitudinal quench propagation velocity for the tape and coil, radial quench propagation velocity for coil and the minimum propagation current were measured. In this study, we investigated the relationship between heat inputs and normal zone propagation velocities and the impact of operating currents on normal zone propagation velocities. We also compared the longitudinal quench propagation velocity and the radial quench propagation velocity. Furthermore, we performed numerical simulations by using a computer program based on a one-dimensional heat flow equation model for YBCO tape. The temperature longitudinal distributions of YBCO tape were simulated. The simulation results also prove the relation between heat input and normal zone propagation velocities and agree with the experimental results.

Experimental study on the pool boiling CHF enhancement using magnetite-water nanofluids

This paper described the effects of a magnetite-water nanofluid (MWNF) on the critical heat flux (CHF) enhancement using an Ni–Cr wire in pool boiling. All experiments were performed at a saturated condition under atmospheric pressure. The CHF values between the MWNF and the other nanofluids with several volume concentrations were compared to evaluate the effect of the MWNF on the CHF enhancement. The CHF values of the MWNF were enhanced from approximately 170% to 240% of pure water as the nanoparticle concentration increased. In addition, the CHF for the MWNF showed the highest value among the evaluated nanofluids. In this paper, three methods were introduced to elucidate the mechanism underlying CHF enhancement. First, scanning electron microscope (SEM) images were obtained to explain the CHF enhancement mechanism due to the deposited nanoparticles, which is related to the surface wettability of the heating surface during the pool boiling. Second, bubble formation in pool boiling was analyzed using image processing to demonstrate the relationship between bubble dynamics and CHF enhancement. Finally, the magnetic field was analytically calculated using the Biot–Savart law to evaluate the effects of the magnetic field on the CHF.

Experimental studies on CHF enhancement in pool boiling with CuO-water nanofluid

Critical heat flux enhancement (CHF) in pool boiling with CuO nanofluids was experimentally studied using a 36 gauge NiCr wire at atmospheric pressure. Experimentation included (1) subjecting the wire surface to multiple heating cycles with constant volume concentration of CuO nanofluid and (2) subjecting the wire surface to a single heating cycle with different volume concentrations of CuO nanofluid. Boiling of nanofluid in both the cases resulted in nanoparticle deposition and subsequent smoothing of the wire surface. To substantiate the nanoparticle deposition and its effect on critical heat flux, investigation was done by studying the surface roughness and SEM images of the wire surface. The experimental results show the evidence of nanoparticle deposition on the wire surface and its effect on CHF enhancement.

Experimental study on CuO nanoparticles in distilled water and its effect on heat transfer

The pool boiling characteristics of dilute dispersions of CuO nanoparticles in water were studied using a 36 gauge NiCr wire at atmospheric pressure. Significant enhancement in critical heat flux (CHF) can be achieved at modest nanoparticle concentrations (< 0.1% by volume) without facing any problem of agglomeration and fouling. During experimentation and subsequent inspection, formation of a porous layer of nanoparticles on the heater surface was observed. Boiling of nanofluid resulted in nanoparticle deposition smoothing the surface at lower concentration. To substantiate the nanoparticle deposition and its effect on critical heat flux, investigation was done by measuring the surface roughness and SEM images of the wire surface. While SEM images revealed particle coating, measurement of surface roughness indicated surface modification. Formation of the porous layer on the heater surface as revelled by SEM images provided an excellent location for nucleation sites and subsequent bubble formation. Flow visualisation of the CuO nanofluid (0.1 g/l) up to critical heat flux gave an idea of bubble growth. The experimental results showed the evidence of nanoparticle deposition on the wire surface enhancing critical heat flux.