scholarly journals МОДЕЛЮВАННЯ ДУГОВОГО РОЗРЯДУ НА МІДНОМУ КАТОДІ ДЛЯ ГЕНЕРАЦІЇ НАНОСТРУКТУР

2021 ◽  
pp. 62-76
Author(s):  
Ю. В. Широкий ◽  
Г. І. Костюк
Keyword(s):  
Plasma Concentration ◽  
Specific Gravity ◽  
Transfer Coefficient ◽  
Current Density ◽  
Ionic Current ◽  
Initial Pressure ◽  
Working Fluid ◽  
Cathode Potential ◽  
Plasma Generation ◽  
Cathode Temperature

The paper considers the model of processes acting in the ionization layer of the cathode assembly during plasma generation of nanostructures. In the given model the processes in electrodynamic and gas - dynamic layers of plasma and their coordination are rather densely considered. Therefore, the solution of the model allows to adequately determine the magnitude of the cathode potential jump in the electrodynamic layer, which allows to compensate for all energy losses during the generation of nanostructures, and the magnitude of ion and electron fluxes at the cathode. The calculations were performed at a constant value of the elongation of the ionization layer, because it has little effect on the change in the ion current density along the length of the cathode layers. Also, the calculations confirmed a non-significant dependence of the initial pressure from the ionization layer on the temperature of the electrons. The obtained dependences, the fraction of ionic current at the cathode and the cathode potential drop from the current density at different cathode temperatures, showed that the change in the proportion of ionic current makes it possible to compensate for energy costs to maintain the cathode temperature. And consideration of the equation of energy balance allowed to establish the range of losses of the working fluid at which it is possible not to take into account the energy of evaporation of the working fluid and steam heating. To determine the current density at the cathode, the dependence of the thermoemission current on the cathode temperature and the dependence of the current density on the cathode on the plasma concentration at different cathode drops and different representations of electric field strengths were obtained. This allowed to determine the cathode temperature due to the ionic current density and to estimate the plasma concentration. Depending on the plasma concentration, the electric transfer coefficient for different emission mechanisms and cathode drops is obtained. All this allowed us to determine the dependence of the specific gravity leaving the cathode per unit time per unit area, on the cathode temperature and heat flux density for the copper cathode. Determining the specific gravity and the transfer coefficient makes it possible to determine the life of the cathode during plasma generation of nanostructures.

ENSURING QUALITATIVE-ACCURACY CHARACTERISTICS DURING RESTORING OF VEHICLE PARTS

2021 ◽  
Vol 3 (144) ◽  
pp. 116-121
Author(s):  
Nikita A. Pen’kov ◽  
◽  
Oleg A. Sidorkin ◽  
Sergey Yu. Zhachkin ◽  
Anatoliy I. Zavrazhnov ◽  
...  
Keyword(s):  
Wear Resistance ◽  
Current Density ◽  
Hydraulic Drive ◽  
Research Purpose ◽  
Working Fluid ◽  
Agricultural Machinery ◽  
Servo Valve ◽  
Contact Points ◽  
Drive Systems

One of the most common reasons for the failure of hydraulic drive systems for agricultural machinery is the working fluid leak in the contact points of the rubbing surfaces of hydraulic blocks. The application of composite coatings based on chromium on the contacting surfaces allows you to restore the defect in the shape of the part caused by wear, as well as reduce the friction coefficient at the contact points, which positively affects the wear resistance of the part. (Research purpose) The research purpose is in developing technologies for restoring parts of agricultural machinery with predetermined operational properties. (Materials and methods) A servo valve, widely used in various hydraulic drive systems, was used as an experimental sample. Its working surface was restored with a composite coating applied by electroplating to increase the wear resistance of the servo valve. (Results and discussion) Authors conducted a series of direct measurements under the same conditions. The article presents the de-pendence of the microhardness on the parameters of the electrolysis mode and the thickness of the applied coating using the method of least squares. The nature of changes in microhardness and residual stresses was evaluated to determine the quality of the coatings. The article presents the dependences of these indicators on various control parameters (current density, temperature, tool pressure). The equations of the regression of the main qualitative and accuracy characteristics of the parts were deter-mined using the apparatus of the theory of experimental planning. (Conclusions) The article presents the method for predicting coatings of a given quality, taking into ac-count the influence of the current density and the temperature of the electrolyte during electrolysis on the nature of the precipitation obtained. The influence of the tool pressure on the depth of deformation of the formed layers was estimated. This approach allows us to evaluate the nature of the stress distribution in the formed coating and the quality of the restored parts.

A Numerical Investigation Into the Interaction Between Current Flow and Fuel Consumption in a Segmented-in-Series Tubular SOFC

2009 ◽  
Vol 6 (3) ◽  
Author(s):  
B. A. Haberman ◽  
A. J. Marquis
Keyword(s):  
Density Distribution ◽  
Fuel Consumption ◽  
Current Density ◽  
Current Flow ◽  
Flow Direction ◽  
Ionic Current ◽  
Leading Edge ◽  
Current Density Distribution ◽  
Fuel Flow ◽  
In Series

A typical segmented-in-series tubular solid oxide fuel cell (SOFC) consists of flattened ceramic support tubes with rows of electrochemical cells fabricated on their outer surfaces connected in series. It is desirable to design this type of SOFC to operate with a uniform electrolyte current density distribution to make the most efficient use of the available space and possibly to help minimize the onset of cell component degradation. Predicting the electrolyte current density distribution requires an understanding of the many physical and electrochemical processes occurring, and these are simulated using the newly developed SOHAB multiphysics computer code. Of particular interest is the interaction between the current flow within the cells and the consumption of fuel from an adjacent internal gas supply channel. Initial simulations showed that in the absence of fuel consumption, ionic current tends to concentrate near the leading edge of each electrolyte. Further simulations that included fuel consumption showed that the choice of fuel flow direction can have a strong effect on the current flow distribution. The electrolyte current density distribution is biased toward the upstream fuel flow direction because ionic current preferentially flows in regions rich in fuel. Thus the correct choice of fuel flow direction can lead to more uniform electrolyte current density distributions, and hence it is an important design consideration for tubular segmented-in-series SOFCs. Overall, it was found that the choice of fuel flow direction has a negligible effect on the output voltage of the fuel cells.

A Loop Thermosyphon With Hydrophobic Spots Evaporator Surface

2018 ◽  
Author(s):  
Hongbin He ◽  
Biao Shen ◽  
Sumitomo Hidaka ◽  
Koji Takahashi ◽  
Yasuyuki Takata
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Nucleate Boiling ◽  
Working Fluid ◽  
Immersion Method ◽  
Two Phase ◽  
Coating Materials ◽  
High Heat Transfer ◽  
Coated Surface

Heat transfer characteristic of a closed two-phase thermosyphon with enhanced boiling surface is studied and compared with that of a copper mirror surface. Two-phase cooling improves heat transfer coefficient (HTC) a lot compared to single-phase liquid cooling. The evaporator surfaces, coated with a pattern of hydrophobic circle spots (non-electroplating Ni-PTFE, 0.5∼2 mm in diameter and 1.5–3 mm in pitch) on Cu substrates, achieve very high heat transfer coefficient and lower the incipience temperature overshoot using water as the working fluid. Sub-atmospheric boiling on the hydrophobic spot-coated surface shows a much better heat transfer performance. Tests with heat loads (30 W to 260 W) reveals the coated surfaces enhance nucleate boiling performance by increasing the bubbles nucleation sites density. Hydrophobic circle spots coated surface with diameter 1 mm, pitch 1.5 mm achieves the maximal heat transfer enhancement with the minimum boiling thermal resistance as low as 0.03 K/W. The comparison of three evaporator surfaces with same spot parameters but different coating materials is carried out experimentally. Ni-PTFE coated surface with immersion method performs the optimal performance of the thermosyphon.

A Fundamental View of the Flow Boiling Heat Transfer Characteristics of Nano-Refrigerants

2012 ◽  
Author(s):  
Lorenzo Cremaschi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Phase ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Working Fluid ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow Boiling Heat Transfer

Driven by higher energy efficiency targets and industrial needs of process intensification and miniaturization, nanofluids have been proposed in energy conversion, power generation, chemical, electronic cooling, biological, and environmental systems. In space conditioning and in cooling systems for high power density electronics, vapor compression cycles provide cooling. The working fluid is a refrigerant and oil mixture. A small amount of lubricating oil is needed to lubricate and to seal the sliding parts of the compressors. In heat exchangers the oil in excess penalizes the heat transfer and increases the flow losses: both effects are highly undesired but yet unavoidable. This paper studies the heat transfer characteristics of nanorefrigerants, a new class of nanofluids defined as refrigerant and lubricant mixtures in which nano-size particles are dispersed in the high-viscosity liquid phase. The heat transfer coefficient is strongly governed by the viscous film excess layer that resides at the wall surface. In the state-of-the-art knowledge, while nanoparticles in the refrigerant and lubricant mixtures were recently experimentally studied and yielded convective in-tube flow boiling heat transfer enhancements by as much as 101%, the interactions of nanoparticles with the mixture still pose several open questions. The model developed in this work suggested that the nanoparticles in this excess layer generate a micro-convective mass flux transverse to the flow direction that augments the thermal energy transport within the oil film in addition to the macroscopic heat conduction and fluid convection effects. The nanoparticles motion in the shearing-induced and non-uniform shear rate field is added to the motion of the nanoparticles due to their own Brownian diffusion. The augmentation of the liquid phase thermal conductivity was predicted by the developed model but alone it did not fully explain the intensification on the two-phase flow boiling heat transfer coefficient reported in previous work in the literature. Thus, additional nano- and micro-scale heat transfer intensification mechanisms were proposed.

Flow Boiling Heat Transfer in a Silicon Microchannel Heat Sink Using Liquid Crystal Thermography

2008 ◽  
Author(s):  
Ayman Megahed ◽  
Ibrahim Hassan ◽  
Tariq Ahmad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Microchannel Heat Sink

The present study focuses on the experimental investigation of boiling heat transfer characteristics and pressure drop in a silicon microchannel heat sink. The microchannel heat sink consists of a rectangular silicon chip in which 45 rectangular microchannels were chemically etched with a depth of 295 μm, width of 254 μm, and a length of 16 mm. Un-encapsulated Thermochromic liquid Crystals (TLC) are used in the present work to enable nonintrusive and high spatial resolution temperature measurements. This measuring technique is used to provide accurate full and local surface-temperature and heat transfer coefficient measurements. Experiments are carried out for mass velocities ranging between 290 to 457 kg/m2.s and heat fluxes from 6.04 to 13.06 W/cm2 using FC-72 as the working fluid. Experimental results show that the pressure drop increases as the exit quality and the flow rate increase. High values of heat transfer coefficient can be obtained at low exit quality (xe < 0.2). However, the heat transfer coefficient decreases sharply and remains almost constant as the quality increases for an exit quality higher than 0.2.

Computer Simulation of Mixed Convection of Alumina-Deionized Water Nanofluid Over Four In-Line Electronic Chips Embedded in One Wall of a Vertical Rectangular Channel

2019 ◽  
Vol 12 (4) ◽  
Author(s):  
Nalla Ramu ◽  
P. S. Ghoshdastidar
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Mixed Convection ◽  
Transfer Coefficient ◽  
Base Fluid ◽  
Rectangular Channel ◽  
Working Fluid ◽  
Al2o3 Nanoparticles ◽  
Enhancement Factors

Abstract This paper presents a computational study of mixed convection cooling of four in-line electronic chips by alumina-deionized (DI) water nanofluid. The chips are flush-mounted in the substrate of one wall of a vertical rectangular channel. The working fluid enters from the bottom with uniform velocity and temperature and exits from the top after becoming fully developed. The nanofluid properties are obtained from the past experimental studies. The nanofluid performance is estimated by computing the enhancement factor which is the ratio of chips averaged heat transfer coefficient in nanofluid to that in base fluid. An exhaustive parametric study is performed to evaluate the dependence of nanoparticle volume fraction, diameter of Al2O3 nanoparticles in the range of 13–87.5 nm, Reynolds number, inlet velocity, chip heat flux, and mass flowrate on enhancement in heat transfer coefficient. It is found that nanofluids with smaller particle diameters have higher enhancement factors. It is also observed that enhancement factors are higher when the nanofluid Reynolds number is kept equal to that of the base fluid as compared with the cases of equal inlet velocities and equal mass flowrates. The linear variation in mean pressure along the channel is observed and is higher for smaller nanoparticle diameters.

Development and Simulation of a Magnetohydrodynamic Solar Generator Operated With NaCl Electrolyte Solution

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Steffanie Jiménez-Flores ◽  
J. Guillermo Pérez-Luna ◽  
J. Joaquín Alvarado-Pulido ◽  
Antonio E. Jiménez-González
Keyword(s):  
Current Density ◽  
Check Valve ◽  
Electrical Energy ◽  
Solar Thermal ◽  
Working Fluid ◽  
Thermal System ◽  
Mhd Generator ◽  
Solar Generator ◽  
Neodymium Magnets ◽  
Solar Thermal System

Abstract A magnetohydrodynamic (MHD) generator is a device that generates electrical energy through the interaction between a conductive fluid and a magnetic field. This method of direct energy conversion allows the use of a renewable energy source such as solar energy and represents an alternative to tackle the greenhouse effect. This paper presents the development of an MHD solar generator, which is constituted by a solar thermal system and an MHD cell. The solar thermal system consists of a set of tubes with copper fins, connected in parallel and placed inside of a 1 m2 panel. In which, an electrolytic mixture of H2O and NaCl at 20% vol. was introduced as a working fluid. In order to increase the kinetic energy of the fluid, the panel was exposed to solar radiation, where it reached temperatures above 373 K and pressures above 96 kPa. This solar thermal system operates in closed cycle conditions by including a check valve in its inlet–outlet junction; in this way, the fluid travels through the MHD generator. The MHD cell was composed of a block of polytetrafluoroethylene, two cylindrical stainless-steel electrodes, and four neodymium magnets. For simulation purposes, comsol multiphysics was used to reproduce the current density produced by the MHD solar generator. Pressure and temperature quantities obtained experimentally in the MHD cell were employed as boundary conditions. The experimental maximal current density obtained corresponds to 4.30 mA/m2, and the comparison between theoretical and experimental results shows that the model fits fairly well.

scholarly journals Heat transfer aspects of condensation during vapour phase soldering on aligned PCB-based surfaces

2020 ◽  
Vol 32 (4) ◽  
pp. 247-252 ◽  
Author(s):  
Daniel Straubinger ◽  
István Bozsóki ◽  
Balazs Illes ◽  
Oliver Krammer ◽  
David Bušek ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Vertical Wall ◽  
Initial Pressure ◽  
Vapour Phase ◽  
Circuit Board ◽  
Pressure Measurements ◽  
Transfer Coefficients ◽  
Content Type

Purpose The paper aims to present an investigation on heat transfer in a vapour phase soldering (VPS) oven, focusing on the differences of horizontally and vertically aligned Printed Circuit Board (PCB) surfaces. The investigation can help develop a better understanding of the process and provide information for future modelling of the process. Design/methodology/approach For the investigations, flame retardant grade 4 (FR4) PCB plates and sealed plate–based boxes were immersed into saturated vapour of an experimental oven. The temperature and resulting heat transfer coefficients were analysed according to the sample boxes and the surface orientations. In addition, the boxes’ vapour consumption was investigated with pressure measurements. Findings The horizontal top- and bottom-side heating shows very similar results. In addition, the sides of a box were heated in a manner similar to the top and the bottom sides, but there was a slight increase in the heat transfer coefficient because of the vertical wall alignment. The pressure measurements reveal the dynamic changes in vapour after immersion of the boxes. Practical implications The findings may help to show differences on different surface orientations, pointing to more precise, explicit and multiphysics simulation results. Originality/value The experiments present an aspect of heat transfer coefficient differences in VPS ovens, also highlighting the effect of initial pressure drop inside the workspace of an oven.

Two Phase Heat Transfer of Ammonia in a Mini/Micro Channel

2010 ◽  
Author(s):  
M. Hamayun Maqbool ◽  
Bjo¨rn Palm ◽  
R. Khodabandeh ◽  
Rashid Ali
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Experimental Results ◽  
Working Fluid ◽  
Internal Diameter ◽  
Vapour Quality ◽  
The Heat Transfer Coefficient

Experiments have been performed to investigate heat transfer in a circular vertical mini channel made of stainless steel (AISI 316) with internal diameter of 1.70 mm and a uniformly heated length of 245 mm using ammonia as working fluid. The experiments are conducted for a heat flux range of 15 to 350 kW/m2 and mass flux range of 100 to 500 kg/m2s. The effects of heat flux, mass flux and vapour quality on the heat transfer coefficient are explored in detail. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux while mass flux and vapour quality have no considerable effect. Experimental results are compared to predictive methods available in the literature for boiling heat transfer. The correlations of Cooper et al. [1] and Shah [3] are in good agreement with our experimental data.

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