Hot Surface Temperature Research Articles

Thermal Analysis of Montmorillonite/Graphene Double-Layer Coating as a Potential Lightning Strike Protective Layer for Cross-Linked Epoxy by Molecular Dynamics Simulation

Nonreactive molecular dynamics simulations were performed to determine the thermal conductivities and through-thickness temperature profiles of unprotected cross-linked epoxy, as well as protected epoxy with graphene (Gr) and montmorillonite (MMT)/Gr surface coatings against lightning strike damage. Three representative hot surface temperatures of 500, 1000, and 10000 K were used for thermal analysis. The MMT/Gr double-layer coating provided the most efficient thermal shielding of the epoxy sublayer, and the epoxy/MMT/Gr system exhibited a 55% lower thermal conductivity than the neat epoxy. The results imply that the MMT/Gr double-layer coating may be used for lightning strike protection.

High-performance and integrated design of thermoelectric generator based on concentric filament architecture

A concentric thermoelectric filament structure used for radioisotope thermoelectric generator (RTG) is designed to satisfy low-power and high-voltage demands for aerospace microelectronic devices. The thermoelectric filament is proven to have a better output voltage than the traditional thermoelectric structure by using COMSOL. The unbreakable thermoelectric filament and corresponding devices are prepared by employing a simple and easy brush coating process. A single thermoelectric filament obtains an open-circuit voltage (Voc) of 6.0 mV and a maximum power output (Pmax) of 2.0 μW at 398.15 K hot surface temperature. An array of thermoelectric filaments is fabricated for the radioisotope heat source of planar heat surface, which obtains Voc of 83.5 mV and Pmax of 32.1 μW at the hot surface temperature of 398.15 K, thereby verifying the practicability of the concentric filament structure in devices. Another radial thermoelectric filament device is designed for the cylindrical heat source. This device exports 84.5 mV Voc and 42.5 μW Pmax at the hot surface temperature of 398.15 K. These thermoelectric devices could gain larger electrical performance in small space through further series connection and fabrication, which will be a commendable design scheme for the radioisotope thermoelectric generator.

Hot Surface Ignition Temperatures: Their Impact on Electrical Area Classification Plans

For many years, hazardous-area classification (HAC) drawings have been used primarily by the electrical discipline (hereafter referred to as electrical) to determine what type of electrical equipment and materials could be installed in different areas of a facility. There has been a growing trend toward global refineries and petrochemical plants that rely on HAC drawings to determine hazardous equipment ratings and locations, not only for electrical equipment but also for nonelectrical equipment with hot surfaces. This article will examine how hot surface temperatures in classified areas are addressed both in the United States and international communities. A possible approach for implementing a new procedure in the United States is also discussed.

Improved PV Inverter Operating Range Using a Miniboost

In the past two decades, the operating voltage of photovoltaic (PV) installation has increased in order to reduce current ratings and system installation costs. Such a large number of PV panels in series (e.g., 1000–1500 V systems) lead to wide variations of PV voltage due undesirable effects such as shading, soiling/dust, aging, and hot surface temperature. A partial shade would normally shut down solar inverters, unless a boost stage is added to the system input to ensure a proper dc-link operating voltage for the inverter. A boost input stage can double the input voltage operating range to extract maximum power under any possible shading and temperature condition. In this paper, a new PV string boost topology arrangement is proposed in the form of a miniboost used for three-phase grid-connected converters. The string miniboost increases the dc voltage range to extend power extraction under shading and low irradiance conditions and only requires to process a fraction of the rated power. The proposed cost-effective solution is further improved by using the inverter peak power envelope at boundary operation, resulting in expanded energy extraction beyond existing techniques. A design procedure to optimally size the miniboost and the peak-power envelope is presented along with a comparative analysis, under different irradiance levels, to illustrate the advantages in energy extraction obtained with the proposed PV string miniboost solution under low voltage and boundary operation. Furthermore, improved efficiency operation schemes and issues of common-mode current are discussed, and three mitigation design techniques intended for three-phase, three-level inverter transformerless topology are presented. Simulations and experimental results using a dual miniboost dc–dc stage and three-phase three-level neutral point clamped inverter are presented to validate the proposed dc-bus extension range and system design.

Effect of aluminum-foam heat sink on inclined hot surface temperature in the case of free convection heat transfer

The need to more powerful electronic chips cause more heat generation as a consequence. So it leads to apply metal foam heat sink as a powerful cooling methods. The objective of this paper is to experimentally investigate the effect of inclination angle on the temperature of a heated surface with and without metal foam in the case of free convection heat transfer conditions. Experimental modeling has been conducted using an electrical resistor on an aluminum plate with and without aluminum metal foam in different angles with respect to the horizontal direction. The results show that the temperature variations have a linear dependency to the sine of inclination angle up to 45° and 60° for plate with and without metal foam, respectively. The slope of the lines are positive in low power input and negative in high power input. The effect of applying metal foam depends on the input power and inclination angle. In the presence of foam, the surface temperature has a decrease of 16°C with respect to a flat plate. The maximum cooling efficiency using foam is about %17 at 90° inclination angle.

THE UNUSUALLY HIGH HALO CONCENTRATION OF THE FOSSIL GROUP NGC 6482: EVIDENCE FOR WEAK ADIABATIC CONTRACTION

ABSTRACT Although fossil galaxy systems are thought to be very old, and thus should possess above-average halo concentrations, typically fossils have unexceptional concentrations of their masses. We revisit the massive isolated elliptical galaxy/fossil group NGC 6482 for which previous X-ray studies of a modest Chandra observation obtained a very uncertain, but also possibly very high, halo concentration. We present new measurements of the hot gas surface brightness, temperature, and iron abundance using the modest Chandra observation and a previously unpublished Suzaku observation, the latter of which allows the measurements of the gas properties to be extended out to . By constructing hydrostatic equilibrium models of the gas with separate components for the gas, the stellar mass of the large central galaxy (BCG), and the dark matter (DM), we measure and using a Navarro-Frenk-White (NFW) DM profile. For a halo of this mass, the measured concentration c 200 exceeds the mean value (7.1) expected for relaxed ΛCDM halos by in terms of the observational error, and by considering the intrinsic scatter in the ΛCDM c–M relation, which situates NGC 6482 as the most extreme outlier known for a fossil system. We explored several variants of adiabatic contraction (AC) models and, while the AC models provide fits of the same quality as the uncontracted models, they do have the following advantages: (1) lower c 200 that is less of an outlier in the ΛCDM c–M relation, and (2) baryon fractions that agree better with the mean cosmic value. While the standard AC prescriptions yield a BCG stellar mass that is uncomfortably low compared to results from stellar population synthesis (SPS) models, a weaker AC variant that artificially shuts off cooling and star formation at z = 2 yields the same stellar mass as the uncontracted models. These are probably the reasons why our X-ray analysis prefers this weaker AC variant applied to either an NFW or Einasto DM halo. Finally, the stellar mass we measure for the BCG from the hydrostatic analysis strongly favors results from SPS models with a Chabrier or Kroupa initial mass function (IMF) over a Salpeter IMF.

Near-field radiative heat transfer between doped-Si parallel plates separated by a spacing down to 200 nm

Heat transfer between two objects separated by a nanoscale vacuum gap holds great promise especially in energy harvesting applications such as near-field thermophotovoltaic systems. However, experimental validation of nanoscale radiative heat transfer has been largely limited to tip-plate configurations due to challenges of maintaining small gap spacing over a relatively large area. Here, we report measurements of heat transfer near room temperature between two 1 cm by 1 cm doped-Si parallel plates, separated by a vacuum gap from about 200 nm to 780 nm. The measured strong near-field radiative transfer is in quantitative agreement with the theoretical prediction based on fluctuational electrodynamics. The largest measured radiative heat flux is 11 times as high as the blackbody limit for the same hot and cold surface temperatures. Our experiments have produced the highest radiative heat transfer rate observed to date across submicron distances between objects near room temperature.

Hot Surface Ignition of n-Hexane Mixtures Using Simplified Kinetics

ABSTRACTHot surface ignition is relevant in the context of industrial safety. In the present work, two-dimensional simulations using simplified kinetics of the buoyancy-driven flow and ignition of a slightly lean n-hexane–air mixture by a rapidly heated surface (glowplug) are reported. Experimentally, ignition is most often observed to occur at the top of the glowplug; numerical results reproduce this trend and shed light on this behavior. The numerical predictions of the flow field and hot surface temperature at ignition are in quantitative agreement with experiments. The simulations suggest that flow separation plays a crucial role in creating zones where convective losses are minimized and heat diffusion is maximized, resulting in the critical conditions for ignition to take place.

Estimation of Thermal and Kinetic Parameters of Sugarcane Bagasse and Cotton Stalks Dust Layers from Hot Surface Ignition Tests

ABSTRACTA method to estimate thermal and kinetic parameters of sugarcane bagasse and cotton stalks subject to thermal runaway is presented using the standard and modified ASTM E2021 hot surface ignition test apparatus. These parameters include thermal conductivity (k), activation energy (E), and coupled term (QA). Experimental tests are used to determine the minimum hot surface temperature for dust ignition, ignition temperature of the dust itself, and ignition times. Four different dust layer thicknesses: 6.4 mm, 12.7 mm, 19.1 mm, and 25.4 mm, are tested for each material and their E and (QA) values are calculated by a widely known multiple test method. The average value of estimated k is 0.08 W/m.K and 0.068 W/m.K for sugarcane bagasse and cotton stalks, respectively. For sugarcane bagasse, the activation energy ranges from 178.7 kJ/mol to 181.3 kJ/mol and the corresponding value of (QA) is 3.5 × 106 for this range. For cotton stalks, the activation energy ranges from 147 kJ/mol to 149.8 kJ/mol and the corresponding value of (QA) is 10 × for this range. Results also showed that as the dust layer thickness increases, the minimum hot plate ignition temperature () decreases and the ignition time () increases. Different photographs for ignition of dusts are presented and discussed. Gas emissions during ignition are measured and discussed.

Sensors Based Measurement Techniques of Fuel Injection and Ignition Characteristics of Diesel Sprays in DI Combustion System

Innovative sensor based measurement techniques like needle lift sensor, photo (optical) sensor and piezoresistive pressure transmitter are introduced and used to measure the injection and combustion characteristics in direct injection combustion system. Present experimental study is carried out in the constant volume combustion chamber to study the ignition, combustion and injection characteristics of the solid cone diesel fuel sprays impinging on the hot surface. Hot surface ignition approach has been used to create variety of advanced combustion systems. In the present study, the hot surface temperatures were varied from 623K to 723K. The cylinder air pressures were 20, 30 and 40bar and fuel injection pressures were 100, 200 and 300bar. It is found that ignition delay of fuel sprays get reduced with the rise in injection pressure. The ignition characteristics of sprays much less affected at high fuel injection pressures and high surface temperatures. The fuel injection duration reduces with the increase in fuel injection pressures. The rate of heat release becomes high at high injection pressures and it decreases with the increase in injection duration. It is found that duration of burn/combustion decrease with the increase in injection pressure. The use of various sensors is quite effective, reliable and accurate in measuring the various fuel injection and combustion characteristics. The study simulates the effect of fuel injection system parameters on combustion performance in large heavy duty engines.

A reduced-order model of mould heat transfer in the continuous casting of steel

A reduced-order model (rom) of mould heat transfer in the continuous casting of steel is presented and demonstrated for several commercial mould geometries. The rom relies on a physically-based solution of the one-dimensional heat-conduction equation. The up-front cost of the rom is a single three-dimensional finite-element calculation of a small representative portion of the exact mould geometry, which is used to calibrate the geometric parameters of the rom. Specifically, the rom exactly matches the average hot and cold surface temperatures of the mould as computed in the snapshot model. Other features of the rom, namely predictions of the cooling water temperature change and thermocouple temperatures, are derived in a manner consistent with the one-dimensional solution. Combined with models of solidification and mould-metal interfacial phenomena, this accurate and efficient modelling tool can be applied to enable deeper insight into many different aspects of heat transfer and related phenomena in the continuous casting process.

Study on blast furnace cooling stave for various refractory linings based on numerical modeling

Cooling technology for refractory lining of blast furnace is very important for the metallurgical industry, because it can substantially increase output and operation life of furnaces. A three dimensional mathematical model for the temperature field of the blast furnace stave cooler with refractory lining has been developed and analyzed. The temperature and heat dissipated by stave cooler is examined by using the finite element method. The cast steel stave is studied and computational analysis is made to know the effect of the cooling water velocity, temperature, and the lining material on the maximum temperature of the stave hot surface. The refractory lining materials, which are used in this experiment, are high alumina bricks with different stave materials (copper, aluminum and cast iron). The obtained numerical calculations are compared with that obtained from experiments performed at Rourkela Steel Plant, Odisha taking a stave in belly zone having maximum heat load shows very good agreement.

Hot surface ignition of n-hexane in air

An experimental investigation is conducted to analyze hot-surface ignition of n-hexane-air mixtures. The experimental setup, equipped with temperature diagnostics and schlieren imaging, utilizes a glow plug to initiate ignition in a flammable mixture. The hot-surface temperature at the point of ignition is measured for equivalence ratios ranging from 0.6 to 3 and chamber pressures varying from 25 to 100 kPa. The hot-surface temperature resulting in ignition is found to be weakly sensitive to equivalence ratio with a mean value of 980 K for mixtures with equivalence ratios between 0.75 and 3 at 100 kPa. Chamber pressure has a stronger influence with ignition temperature increasing to about 1140 K at 25 kPa. The experimental trends were reproduced in numerical simulations utilizing detailed chemistry of n-heptane as a surrogate for n-hexane given their similar ignition and flame propagation characteristics. The simulations further predict a two-stage ignition process resulting from an initial breakdown of the fuel with a small increase in temperature followed by a main ignition event accompanied by fuel depletion. Reaction rate analysis of the sequence of events leading to ignition conducted using a reduced order kinetic model suggests that the second-stage ignition event is caused primarily by the decomposition of hydrogen peroxide which occurs at temperatures above 900 K. The two-stage ignition process observed here is significantly different from that observed in previous studies due to the presence of convective and diffusive processes as well as the continuous increase in hot-surface temperature. These arguments are used to explain the insensitivity of ignition temperature to equivalence ratio, its decrease with increasing chamber pressure, and the location of the ignition kernel observed in experiments and simulations.

Transition into a Hothouse World at the Permian–Triassic boundary—A model study

The Permian–Triassic boundary (PTB, ~252.3Ma) marks the largest mass extinction of the Phanerozoic, with a loss of more than 90% of marine organisms, and is characterized by lethally hot surface temperatures. The PTB global warming has been linked to greenhouse gas emissions from the Siberian Traps and associated coal-bed intrusions and likely led to severe environmental consequences, such as ocean acidification, a decline in the marine productivity, and extensive hypoxia. In order to understand these changes, feedbacks in the climate system have been explored with sensitivity climate simulations and compared to temperature proxies from the sedimentary record. The response of the PTB ocean circulation to an atmospheric perturbation of ~5000PgC, comparable to Earth's total fossil fuel inventory, leads to a global temperature increase by 3–4°C and an increase in ocean stratification. The pole-to-equator temperature gradient decreases by 2°C with an increase in CO2-radiative forcing, predominately due to snow albedo feedbacks over Gondwana. The greenhouse-induced warming would have led to a weakening of the Hadley cell and an associated decrease in the trade winds and equatorial primary productivity. These climatic changes might have been amplified by cloud-feedback processes. A reduced concentration of cloud condensation nuclei due to a biologic decline of dimethylsulfide caused by the temperature stress or changes in airborne mineral particles could have reduced the cloud albedo, particularly in high latitudes. Results from a climate simulation with reduced cloud albedo suggest a polar warming of up to 7°C and a reduction of the pole-to-equator temperature gradient by ~4°C in addition to the reduction caused by the increase in greenhouse-induced radiative forcing. The scenario with reduced cloud albedo further leads to an increase in ocean stratification and widespread low-oxygen concentrations in the Panthalassa during the Early Triassic.

Study of ignition characteristics of microemulsion of coconut oil under off diesel engine conditions

The increasing awareness of the depletion of fossil fuel resources and the environmental benefits motivates the use of vegetable oils, however there is little known information about ignition and combustion characteristics of vegetable oil based fuels under off diesel engine conditions. These conditions are normally reached either during starting or when the engine is sufficiently worn out. A fuel was prepared by co-solvent blending of coconut oil with 20% butyl alcohol and was analysed. An experimental study of the measurement of ignition delay (ID) characteristics of conical fuel sprays impinging on hot surface in cylindrical combustion chamber was carried out. The objective of the study was to investigate the effect of hot surface temperatures on ignition delays of microemulsion of coconut oil at various ambient air pressures and temperatures which would have reached under off diesel engine conditions. An experimental set-up was designed and developed for a maximum air pressure of 200 bar and a maximum temperature of 800 °C with the emphasis on optical method for the measurement of ignition delay. Hot surface temperature range chosen was 300–450 °C and ambient air pressure (inside the combustion chamber) range chosen was 10–25 bar. Present study shows that at fixed injection pressure and fixed ambient (hot surface) temperature, at higher ambient air pressure (25 bar) inside the combustion chamber, ignition delay of diesel and microemulsion of coconut oil are comparable and therefore are having matching combustion characteristics. Although a pressure of 25 bar is much less than the precombustion pressure of most diesel engines but again conclusively establish that combustion characteristics are same despite lower air pressure, temperature and lower injection pressure. At higher injection pressure ignition delay of microemulsion of coconut oil and pure diesel attains the lower value at the same ambient air pressure inside the combustion chamber. It can also be seen that at fixed injection pressure and higher ambient temperature conditions, ignition delay variations of microemulsion of coconut oil with chamber pressure show approximate same trend as that of conventional diesel fuel.

Computational Modeling of Blast Furnace Stave Cooler Based on Steady State Heat Transfer Analysis

The technology of the furnace cooling is very important for the metallurgical industry, because it can substantially increase output and operation life of furnaces. A three dimensional mathematical model for the temperature field of the blast furnace stave cooler has been developed and analyzed. The temperature and heat dissipated by stave cooler is examined by using the finite element method. The cast steel stave is studied and computational analysis is made to know the effect of the cooling water velocity, temperature, and the lining material on the maximum temperature of the stave hot surface. The refractory lining materials, which are used in this experiment, are high alumina bricks with different stave materials (copper, aluminum and cast iron). The obtained numerical calculations are compared with that obtained from experiments performed at Rourkela Steel Plant, Odisha taking a stave in belly zone having maximum heat load shows very good agreement.

Dynamic behavior and micro-explosion characteristics of impinging droplets on a high-temperature surface

The dynamic behavior and micro-explosion characteristics of impinging droplets on a hot surface were examined experimentally. A 2.3 mm sized, de-ionized water droplet was made through a 31G injection needle. A sapphire plate was heated up to 300 oC on a hotplate. Two high-speed cameras at a frame rate of 4,000 fps were used for visualization. The Weber number was changed from 5 to 117 by changing the initial height of the droplet from 10 to 210 mm. The hydrophobic characteristics were observed when the temperature of hot surface was over the Leidenfrost point. Dynamic behavior was strongly dependent on the Weber number, and a splashing phenomenon occurred when the Weber number was higher than 50. A micro-explosion was observed at high Weber number under Leidenfrost conditions before splash. From the PIV measurement, the micro-droplets after the explosion jetted at a considerably high speed compared to the impinging velocity.

Analysis of the non-uniform thermal behavior in slab continuous casting mold based on the inverse finite-element model

A full finite-element model of a mold, including four copper plates, nickel layer and water slots of different depths, was developed to reveal the complex thermal behavior of molds in slab continuous casting. An inverse algorithm was applied to calculate the heat flux and combined with the temperatures measured using thermocouples that were buried in different positions of the mold. The temperature distributions of the four copper plates are not symmetric, reflecting the non-uniform nature of heat transfer and the necessity of building a full model. The maximum hot surface temperature of the mold occurs in the region 70–100mm below the meniscus. At heights 100mm below the meniscus, the average temperature of the deep water slot root is higher than that of the shallow water slot by approximately 10°C. In the off-corner regions, the hot surface temperature differences between the narrow face and wide face near the corners are approximately 20–30°C 100mm below the meniscus. It will provide a helpful tool for further improving the casting parameters and operations.

Improvement Vortex Cooling Capacity by Reducing Hot Tube Surface Temperature: Experiment

A vortex tube is a cooling device in which an air can be used as a working medium; thus, the vortex cooling system is environmentally friendly. Thermal separation flow studied and preliminary tests suggest that reducing the temperature of an external surface at the hot tube section of the vortex tube could increase the vortex cooling capacity. In this paper, a thermoelectric module is employed to extract heat from the hot tube surface and then release it to environment. In other words, a temperature difference is used to generate power by the thermoelectric generator as thermal energy harvester. A test rig is designed and constructed, in the laboratory, for the experiment on the vortex cooling system incorporating the thermoelectric module. Test parameters are the cold fraction from 0 to 1 and an inlet air pressure of 1.5 bars. The results show that the cooling capacity and efficiency increase when the thermoelectric module is used to extract heat from the hot tube surface of the vortex tube and electricity is generated as by product. The cooling capacity and efficiency of the vortex tube is increased by 4.3% and 9.6% respectively.

Experimental Analysis of Minimum Ignition Temperature of Coal Dust Layers in Oxy-fuel Combustion Atmospheres

An experimental investigation into the hot surface ignition of coal dust layers has been undertaken in oxy-fuel combustion atmospheres, with the oxygen mole fractions in the range of 21-50 vol. % (21%, 30%, 40% and 50%). Three coals were used to determine the minimum layer ignition temperature (MLIT) with a hot surface ignition apparatus according to the European EN50281-2-1 norm. In addition, thermal and kinetic parameters were also determined. Layer thicknesses of 5, 12.5, 15, 20 and 30mm were investigated. Firstly, 5 and 12.5mm thick coal dust layers were used to investigate the influence of the oxygen mole fraction on the MLIT, and the steady state dust layer temperature profile of a 30mm thick coal dust layer was used to estimate the thermal conductivity (k) at a low hot surface temperature. Secondly, the South African coal was used in this study to determine the kinetic parameters on the basis of the Frank-Kamenetskii theory. Results show that oxygen concentration has a significant influence on the MILT, (i.e., MLIT decreases with increasing oxygen concentration). It also shows that replacing N2 in the combustion air with CO2 a small increase of the MLIT will occur. The estimated k of the coal dust samples is respectively 0.1, 0.11 and 0.1 W·m-1·K-1 for South African coal, Sebuku coal and Pittsburgh coal. The region of the kinetic parameters of South African coal changes when there is a shift in the test from air to oxy-fuel combustion atmospheres,which means that the reaction mechanism of self-heating or ignition changed somewhat.