Electrothermal Efficiency Research Articles

A superhydrophobic/electrothermal synergistically anti-icing strategy based on graphene composite

Surface icing tends to cause serious problems such as flash over and the following blackout accident. Although electrothermal system is the most widely used method, how to solve the re-freeze problem as the melted ice tend to stay on the surface is still a challenge. Here, we introduced a superhydrophobic/electrothermal synergistically anti-icing strategy based on graphene composite. The superhydrophobicity together with the high electrothermal efficiency let the graphene surface dry and clean in the simulated “glaze ice” condition. Although ice accretion would be formed on the surface when the DC voltage was off, the ice could be rapidly removed within 70 s after applying the voltage of 50 V. To enhance the durability of superhydrophobic surface, the hierarchical structure was constructed by the tri-scale nature of inorganic fillers (graphene, carbon nanotubes and silica nanoparticles). Then the hierarchical structure was partially embedded into the substrate by a dissolution and resolidification method. The coupling effect of partially-embedded structure and hierarchical structure led to the superior robustness, which could withstand sandpaper abrasion (500 g load, 8.00 m), the attack of various corrosive liquids, and low/high temperature treatment without losing superhydrophobicity. More remarkably, this graphene superhydrophobic composite retained deicing property even after 30 icing/deicing cycles.

Description and Characterization of a 114-kWe High-Flux Solar Simulator

Abstract A high-flux solar simulator is essential for evaluating solar thermal components under controlled and adjustable flux input conditions. This study presents a newly built high-flux solar simulator composed of 19 individual units. Each unit includes a xenon short-arc lamp (each consuming up to 6 kW electricity power) coupled with a truncated ellipsoidal reflector, a cooling blower, and a power module. The power module yields a current in the range of 50–160 A. The number of lamps in use is flexible, which allows for a wide range of radiation flux (10%–100%) on the focal plane. The radiation power, peak value, flux distribution on the circular target plane, and conversion efficiency are evaluated based on a flux mapping method. The results indicate that the proposed solar simulator is capable of achieving thermal power of 23.3 kW, peak flux in excess of 1.78 MW/m2, a stagnation temperature exceeding 2360 °C, and average irradiance of 773.4 kW/m2 on the focal plane (diameter of 260 mm). The electro-thermal conversion efficiency of the simulator is 35.7%. A ray-tracing method was employed, and the simulation results were found to be in good agreement with those in the experiments. An experimental test of a volumetric ceramic receiver was conducted, and the results indicate the availability and applicability of the high-flux solar simulator when carrying out studies about solar receivers.

Dynamic Behavior of Arc Voltage and Electro-thermal Efficiency in Atmospheric Pressure Non-transferred Arc Plasma Torches under Different Degrees of Anode Cooling

Unusually, high electro-thermal efficiency, observed under certain cooling rates of the anode boundary layer in a typical non-transferred arc argon plasma torch, is reported. The behavior is reproducible at different arc currents and gas flow rates. To understand the origin of such behavior, total arc voltage, which bears an overall signature of the internal arc dynamics, has been analyzed using tools of dynamical analysis such as frequency space behavior, phase space dynamics, correlation dimension and Lyapunov exponent under different rates of anode cooling. Simultaneous emission spectroscopic investigation of the plasma temperature at the nozzle exit and fast photographic study of the anode boundary layer have been carried out for better insight. Observed significant variation in the dominant frequency components with change in cooling rates gives concrete signature of onset on new dynamics induced by anode cooling. Vivid differences in the dynamics are brought out in phase space representations. True natures of the dynamics are obtained through the estimated values of correlation dimension and Lyapunov exponents.

Assembly of carbon nanodots in graphene-based composite for flexible electro-thermal heater with ultrahigh efficiency

A high-efficiency electro-thermal heater requires simultaneously high electrical and thermal conductivities to generate and dissipate Joule heat efficiently. A low input voltage is essential to ensure the heater’s safe applications. However, the low voltage generally leads to low saturated temperature and heating rate and hence a low thermal efficiency. How to reduce the input voltage while maintaining a high electro-thermal efficiency is still a challenge. Herein, a highly electrical and thermal conductive film was constructed using a graphene-based composite which has an internal three-dimensional (3D) conductive network. In the 3D framework, cellulose nanocrystalline (CNC) phase with chiral liquid crystal manner presents in the form of aligned helix between the graphene oxide (GO) layers. Carbon nanodots (CDs) are assembled inside the composite as conductive nanofillers. Subsequent annealing and compression results in the formation of the assembled GO-CNC-CDs film. The carbonized CNC nanorods (CNR) with the helical alignment act as in-plane and through-plane connections of neighboring reduced GO (rGO) nanosheets, forming a conductive network in the composite film. The CDs with ultrafast electrons transfer rates provide additional electrons and phonons transport paths for the composite. As a result, the obtained graphene-based composite film (rGO-CNR-CDs) exhibited a high thermal conductivity of 1,978.6 W·m−1·K−1 and electrical conductivity of 2,053.4 S·cm−1, respectively. The composite film showed an outstanding electro-thermal heating efficiency with the saturated temperature of 315 °C and maximum heating rate of 44.9 °C·s−1 at a very low input voltage of 10 V. The freestanding graphene composite film with the delicate nanostructure design has a great potential to be integrated into electro-thermal devices.

MEMS Thermal Flow Sensors— An Accuracy Investigation

The geometric structure of a low-power thermal micro-hot film sensor has been investigated and optimized, using both computational and experimental methods. The response and accuracy of eight CMOS designs with different heater and membrane sizes were studied and found to vary considerably with geometry. It is found that reducing the heater length causes an improved electro-thermal efficiency and that a large reduction in accuracy was seen when reducing the membrane size. Our simulations suggest that this effect is due to higher temperature gradients causing localized stronger natural convective flows above the measuring resistor. However, the reduced accuracy disappears as flow rate increases due to a higher proportion of forced convection compared with natural convection. We believe that this paper will help in the design of a new generation of high accuracy MEMS thermal flow sensors for low-cost, low-power application.

Discharge and electrothermal efficiency analysis of capacitive discharge plasma synthetic jet actuator in single-shot mode

Gas discharge plasma techniques have been applied successfully in a wide range of fields. As one of these techniques, plasma synthetic jet (PSJ) actuator shows promising application in high-speed flow control. However, for practical application to aircraft, the capacity of the power source is very limited. So the energy efficiency optimization of PSJ actuator is vital to its longtime effective performance. The overall efficiency of PSJ actuator can be divided into three parts: discharge efficiency, electrothermal efficiency and exhaust efficiency. In this paper, discharge and electrothermal efficiencies of a home-designed and manufactured two-electrode PSJ actuator working in single-shot mode and normal atmosphere are evaluated experimentally. The influence of circuit parameters and actuator configurations are investigated and analyzed as a reference for optimization. The results show that, discharge efficiency is basically determined by the resistance ratio of the RLC circuit. The parasitic resistance of the circuit has a great influence on discharge efficiency due to the very short length and low resistance of the plasma arc (O (100 mΩ)). Electrothermal efficiency seems to be less affected by the circuit parameters and actuator configurations compared to discharge efficiency. The variation extent of electrothermal efficiency is around 50–70% for the tested conditions. Smaller discharge chamber volume produces PSJ with higher speed, but will reduce electrothermal efficiency. For a certain overall input energy required, a design of smaller capacitance and wider anode-to-cathode distance is highly recommended to increase both discharge efficiency and electrothermal efficiency.

Experimental and analytical studies on the flexible, low-voltage electrothermal film based on the multi-walled carbon nanotube/polymer nanocomposite

This paper presents multi-walled carbon nanotube (MWCNT)/poly(m-phenylene isophthalamide) (PMIA) nanocomposite films as electrothermal elements, which offer advantages in flexibility, low energy consumption and rapid temperature growth. The electrical properties, electrothermal behavior and thermal stability of the films were investigated as a function of MWCNT content. The percolation behavior analysis revealed MWCNTs built a continuously conductive network in PMIA matrix at the corresponding percolation threshold of ∼0.06 wt%. The electrothermal behavior of the MWCNT/PMIA film was investigated by considering temperature response rapidity and electrothermal efficiency under different ambient conditions. For the film with 7.0 wt% MWCNTs under different ambient conditions, the film worked at a high heating rate of 1.0–8.2 °C s−1 and cooling rate of 0.75–7.0 °C s−1 under a low voltage of 3–12 V, due to the low electrical resistivity (4.5 Ω cm) of the film. The prepared MWCNT/PMIA films supported more outstanding heating performance than conventional PI-Kanthal film, including good heating uniformity, higher electrothermal efficiency and heating/cooling rate. Moreover, the improved thermomechanical properties of the nanocomposite were observed by dynamic thermomechanical analysis.

Enhanced electrothermal efficiency of flexible graphene fabric Joule heaters with the aid of graphene oxide

Flexible fabric Joule heaters reflect a broad prospect due to their wearable substrate, low cost and easily compatibility to garment. In this paper, graphene-based fabric Joule heaters were fabricated with spraying coating method, the as-prepared fabrics possessed bilayer structure corresponding to the inner graphene/polyurethane layer and the outer graphene oxide layer respectively. The morphology and electrothermal performance of the fabric Joule heaters were accomplished by scanning electron microscopy and infrared camera. The outer graphene oxide could dramatically promote the electrothermal efficiency of the fabric Joule heaters with the steady-state temperature (162.6 °C) and the maximum heating rate (8.4 °C/s) under 10 V applied voltage, which was much higher than the heaters without GO layer with the steady-state temperature 70.1 °C and the maximum heating rate 2.61 °C/s. Therefore, the existence of GO layer was first demonstrated to observably enhance the electrothermal efficiency of flexible fabric Joule heaters.

Influence of the Shroud Gas Injection Configuration on the Characteristics of a DC Non-transferred Arc Plasma Torch

The characteristics of the plasma jet emanating from a dc non-transferred plasma torch is affected by many factors including arc current, type of gas, gas flow rate, gas injection configuration and torch geometry. The present work focuses on experimental investigation of the influence of shroud gas injection configuration on the I–V characteristics and electro-thermal efficiency of a dc non-transferred plasma torch operated in nitrogen at atmospheric pressure. The plasma gas is injected into the torch axially and shroud gas is injected through three different nozzles such as normal, sheath and twisted nozzles. The effects of flow rates of plasma/axial gas and arc current on I–V characteristics and electro-thermal efficiency of the torch holding different nozzles are investigated. The I–V characteristics and electro-thermal efficiency of the torch are found to be strongly influenced by the shroud gas injection configuration. The effect of arc current on arc voltage decreases with increasing the axial gas flow rate. At higher axial gas flow rate (> 45 lpm), the I–V characteristics of the plasma torch are similar irrespective of the nozzle used. The variation of electro-thermal efficiency with arc current is almost similar to that of arc voltage with arc current. As expected, the electro-thermal efficiency is increased when the axial gas flow rate is increased and at higher axial gas flow rate, it is not influenced by the arc current and shroud gas configuration. The plasma torch with normal nozzle may be better in the range of operating conditions used in this study.

Mask-less deposition of Au–SnO2 nanocomposites on CMOS MEMS platform for ethanol detection

Here we report on the mask-less deposition of Au–SnO2 nanocomposites with a silicon-on-insulator (SOI) complementary metal oxide semiconductor (CMOS) micro electro mechanical system (MEMS) platform through the use of dip pen nanolithography (DPN) to create a low-cost ethanol sensor. MEMS technology is used in order to achieve low power consumption, by the employment of a membrane structure formed using deep reactive ion etching technique. The device consists of an embedded tungsten micro-heater with gold interdigitated electrodes on top of the SOI membrane. The tungsten micro-heater is used to raise the membrane temperature up to its operating temperature and the electrodes are used to measure the resistance of the nanocomposite sensing layer. The CMOS MEMS devices have high electro-thermal efficiency, with 8.2 °C temperature increase per mW power of consumption. The sensing material (Au–SnO2 nanocomposite) was synthesised starting from SnO nanoplates, then Au nanoparticles were attached chemically to the surface of SnO nanoplates, finally the mixture was heated at 700 °C in an oven in air for 4 h. This composite material was sonicated for 2 h in terpineol to make a viscous homogeneous slurry and then ‘written’ directly across the electrode area using the DPN technique without any mask. The devices were characterised by exposure to ethanol vapour in humid air in the concentration range of 100–1000 ppm. The sensitivity varied from 1.2 to 0.27 ppm−1 for 100–1000 ppm of ethanol at 10% relative humid air. Selectivity measurements showed that the sensors were selective towards ethanol when they were exposed to acetone and toluene.

Synergistic effect of siloxane modified aluminum nanopowders and carbon fiber on electrothermal efficiency of polymeric shape memory nanocomposite

The present study reports an effective approach of significantly enhancing electrothermal efficiency and shape recovery performance of shape memory polymer (SMP) nanocomposite, of which shape recovery was induced by electrically resistive heating. Metallic aluminum (Al) nanopowders synthesized from Al3+ solution were chemically grafted onto carbon fiber. Siloxane groups were grafted onto surfaces of the Al nanopowders to enhance the interfacial bonding between the carbon fiber and SMP matrix via van der Waals force and covalent bond, respectively. The siloxane modified Al surfaces could improve both the electrically induced shape recovery performance and electrothermal efficiency through facilitating the electrically resistive heating from carbon fiber into the SMP matrix. Effectiveness of the synergistic effect between siloxane modified Al surface and carbon fiber was demonstrated to achieve the electrical actuation for SMP nanocomposites at a low electrical voltage below 4.0 V.

The electrical properties and snow melting of graphite slurry infiltrated steel fiber concrete

The conductivity property of graphite slurry infiltrated steel fiber concrete (GSIFCON) was investigated by the four-probe method. The experimental results show that the electrical resistivity of GSIFCON decreases significantly at a specific concentration of graphite, i e, the percolation concentration. A model was accordingly developed to explain its conductive mechanism, where graphite particles could be served as bridge for conductive network between unconnected fiber chains. For an application, snow melting test of GSIFCON was carried out and a simple heating power analysis was performed. The results reveal that the thermal energy produced by GSIFCON makes snow melting effectively and the electrothermal efficiency can reach approximately 20%.

Effect of critical plasma spray parameter on properties of hollow cathode plasma sprayed alumina coatings

A 20 kW hollow cathode plasma spray torch was manufactured and its performances were examined by spraying alumina coatings on mild steel substrates with different critical plasma spray parameters (CPSP: 0.12, 0.24, 0.36, 0.48). CPSP is defined as the ratio between the torch input power and primary plasma forming gas flow rate. The effects of CPSP on the microstructure, porosity, microhardness, surface roughness, sliding wear and erosive wear properties of the coatings were investigated. The electrothermal efficiency and the excitation temperature of the plasma jet were also investigated for different CPSP. The microstructure and phase composition of the alumina coatings were examined using scanning electron microscope and X-ray diffraction (XRD) analysis respectively. XRD analysis revealed that alumina particles during plasma spraying reach sufficient melting state prior to the impact on the substrate with a velocity comparable to that of conventional plasma spraying. The experimental results have shown that the CPSP has significant influence on the microstructure and other properties of the deposited alumina coating. It also showed that the hollow cathode plasma spray torch is a suitable tool to coat the dense ceramic materials with low input power levels.

Electrothermal efficiency, temperature and thermal conductivity of plasma jet in a DC plasma spray torch

A study was made to evaluate the electrothermal efficiency of a DC arc plasma torch and temperature and thermal conductivity of plasma jet in the torch. The torch was operated at power levels from 4 to 20 kW in non-transferred arc mode. The effect of nitrogen in combination with argon as plasma gas on the above properties was investigated. Calculations were made from experimental data. The electrothermal efficiency increased significantly with increase in nitrogen content. The plasma jet temperature and thermal conductivity exhibited a decrease with increase in nitrogen content. The experiment was done at different total gas flow rates. The results are explained on the basis of dissociation energy of nitrogen molecules and plasma jet energy loss to the cathode, anode and the walls of the torch

Characterization of a spray torch and analysis of process parameters

Anode for a non-transferred DC plasma spray torch was designed to improve electrothermal efficiency. A theoretical calculation was made for the electrothermal efficiency in a DC plasma torch operating with argon at atmospheric pressure with power level in the range of 5.2–20 kW using energy balance equations. ANOVA for the two level factorial design was done. Plasma gas flow rate, current intensity, nozzle diameter and length were found to influence the efficiency. The efficiency was found to decrease with increase in current intensity and nozzle length and to increase with increase in nozzle diameter and gas flow rate. The overall energy balance calculations showed that the heat transfer to the plasma-forming gas decreases with increase in arc current and the same was more significant at higher flow rates. Plasma jet velocity for different flow rates, input to the torch and nozzle dimensions was calculated from the gas enthalpy. It was found that the velocity increased with increase in the power input to the torch and gas flow rate and decreased with increase in nozzle length and diameter. The current–voltage characteristics of the torch operating with argon gas were studied for different gas flow rates. The Nottingham coefficients were calculated using least – square method.

Prediction of electrical characteristics of anon-transferred arc-plasma torch using principles ofdynamic similarity

The theory of dynamic similarity has been used to construct a generalized current-voltage characteristic (CVC) of a non-transferred, straight polarity, solid electrode arc-plasma torch. The enthalpy number obtained from the energy equation has been found to significantly influence the characteristics of the electric arc. The generalized CVC developed has been found to match with experimental parameters of other torches having the same basic principle of design and used elsewhere. The electrothermal efficiency of the plasma torch has been determined and put in the form of a generalized correlation using dimensionless numbers. The use of the theory of dynamic similarity to obtain a generalized correlation has been therefore found to be more appropriate.

Characterization of DC plasma spray torch using energy balance technique and thermo-fluid dynamical consideration

Abstract A non-transferred plasma torch is characterized. Electrothermal efficiency of the plasma torch and the stagnation enthalpy of the plasma jet were calculated using the energy balance technique. Argon and argon + 10% nitrogen mixture were the plasma forming gases. Average electrical conductivity of the plasma jet at the nozzle was calculated from the arc characteristics. The temperature, velocity, thrust, density and the degree of ionization of the plasma jet were also calculated from the thermofluid dynamical method. In addition the heat transfer from plasma jet to the solid wall was also considered. In all the calculations the experimental values of the parameters were used. The calculated efficiency ranged from 59-65%. Efficiency was found to increase with addition of nitrogen. The temperature and the degree of ionization were found to be in the range 1400-7500 °K and 0.4-5 × 10−3 respectively. The results are explained and discussed qualitatively.

Efficiency of a 50-Hz 100-kW plasma torch

The electrothermal efficiency of a recently developed 50-Hz continuous operation plasma torch has been established. A new electronic system for measuring arc power input was developed. Using it as a reference standard, the relative errors were evaluated which arise if thermal or dynamometer wattmeters are used for this power input measurement. The thermal output was measured by a specially developed parallel-flow self-jacketed calorimeter. The salient observation is that this torch has an electrothermal efficiency greater than 60 percent. This is higher than previously reported figures for ac plasma torches intended for continuous operation.

Measuring the Electrothermal Efficiency of a 50-Hz Plasma Torch

This study concerns the measurement of electrothermal efficiency in an ac plasma torch. It was found that the best method of measuring arc input power was an electronic system involving multiplication and integration although thermal wattmeters could be used with a slight loss of accuracy. A self-jacketed parallel flow calorimeter was found best for measuring the heat content of the torch output. The flow-dependent thermal efficiency of this torch was found to exceed 60 percent. For established designs of torch the electrode losses can be used to establish the input power to the arc, and thus eliminate the need for an electrical measurement.