Internal Heating Method Research Articles

P - V - T equation of state of platinum to 80GPa and 1900K from internal resistive heating/x-ray diffraction measurements

The P-V-T equation of state (EOS) of Pt has been determined to 80GPa and 1900K by in situ x-ray diffraction of a mixture of Pt and MgO using a modified internal resistive heating technique with a diamond anvil cell. The third-order Birch–Murnaghan EOS of Pt at room temperature can be fitted with K0=273.5±2.0GPa, K0′=4.70±0.06, with V0=60.38Å3. High temperature data have been treated with both thermodynamic and Mie–Grüneisen-Debye methods for the thermal EOS inversion. The results are self-consistent and in excellent agreement with those obtained by the multianvil apparatus where the data overlap. MgO is taken as the standard because its thermal EOS is well established and based on a wealth of experimental and theoretical data, and because the EOS at room temperature has been determined by a primary method that is completely independent of any assumptions or measurements by other methods. Improvements to previous internal resistive heating methods were made by using a Re gasket that replaces the original gasket composed of diamond and MgO powder. We have thereby extended the P-T range to nearly 80GPa and 1900K. Use of this method in combination with synchrotron radiation has advantages in the study of EOS, phase diagrams, and materials synthesis for a variety of problems in physics, chemistry, geosciences, and material sciences.

High Pressure / Low Temperature Sintering of Nanostructured Titania by Internal Heating Method

The feasibility of an internal heating method for the fabrication of large-scale nanostructured TiO2 samples by high pressure/low temperature sintering is studied. The primary apparatus used is a piston-cylinder type. The arrangement inside the die cavity consists of a circular cylindrical green compact, a graphite furnace to heat the sample, an aluminum container to protect the sample and an aluminum silicate or lava tube for electrical insulation. When the sample inside the mold achieved the desired sintering temperature, the temperature of the thermally insulated mold stayed low enough not to damage the mold itself. An obtained cylindrical sample has dimensions of 12.7 mm (1/2 inch) in diameter by 28.6 mm (1 1/8 inch) long. Its average grain size is 64 nm and the Vicker’s hardness is 5.3 GPa.

Nano-Structure And Results Of Phase Transitions In The Liquid Phase Of Common Materials: Metallic And Non-Metallic Elements And Related Materials

Introduction In the following, experimental data are presented from various laboratories treating the liquid state of common elements [1–7]. The goal of this paper is not only to demonstrate that the scientific world’s picture of the structure of the liquid state is grossly oversimplified, but to suggest certain common features of the structural variability. From the mid-1960s to the mid-1980s, Vezzoli et al. employed volumetric, optical, Xray, and electrical techniques to study the discontinuous changes in the liquid state of low-melting elemental materials including sulfur, selenium, tellurium, lead, tin, bismuth and mercury. As a function of high pressure in the 1—100 kbar range, the studies included the use of Bridgman (opposed) anvil, gas cylinder, diamond cell, pistoncylinder, and hexahedral pressure transmitting systems (both quasi-hydrostatic and purehydrostatic), with various compatible external and internal heating methods. More recently, sophisticated in situ X-ray diffraction techniques have been successfully applied to the liquid phase. These involve either angular dispersion analysis, whereby a monochromatic radiation source is utilized, or energy dispersion analysis, which involves a polychromatic source. The data from both of these methods yield a characteristic scattering pattern of peaks and satellites corresponding to a preferred probabilistic shortrange liquid nanostructure [8, 9, 10]. In situ neutron diffraction studies have yielded confirming results. The data given herein provide the details of research findings on the structure of the liquid state of the elements which have been studied. For simplification, the elemental liquids that are treated herein are divided into metals and non-metals and described ad seriatim. All starting materials were 99.9999 to 99.99999% pure. Details of apparatus and measuring techniques are given in the references [1, 2].

PEM Fuel Cell Stack Cold Start Thermal Model

AbstractFor passenger fuel cell vehicles (FCVs), customers will expect to start the vehicle and drive almost immediately, implying a very short system warmup to full power. While hybridization strategies may fulfill this expectation, the extent of hybridization will be dictated by the time required for the fuel cell system to reach normal operating temperatures. Quick‐starting fuel cell systems are impeded by two problems: (i) the freezing of residual water or water generated by starting the stack at below freezing temperatures and (ii) temperature‐dependent fuel cell performance, improving as the temperature reaches the normal range. Cold start models exist in the literature; however, there does not appear to be a model that fully captures the thermal characteristics of the stack during sub‐freezing startup conditions. Existing models lack the following features: (i) modeling of stack internal heating methods (other than stack reactions) and their impact on the stack temperature distribution and (ii) modeling of endplate thermal mass effect on end cells and its impact on the stack temperature distribution. Unlike a lumped model, which may use a single temperature as an indicator of the stack's thermal condition, a model considering individual cell layers can reveal the effect of the endplate thermal mass on the end cells, and accommodate the evaluation of internal heating methods that may mitigate this effect. This paper presents and discusses results from simulations performed with a new, layered model.

Polymer electrolyte fuel cell stack thermal model to evaluate sub-freezing startup

For passenger fuel cell vehicles (FCVs), customers will expect to start the vehicle and drive almost immediately, implying a very short system warmup to full power. While hybridization strategies may fulfill this expectation, the extent of hybridization will be dictated by the time required for the fuel cell system to reach normal operating temperatures. Quick-starting fuel cell systems are impeded by two problems: (1) the freezing of residual water or water generated by starting the stack at below freezing temperatures and (2) temperature-dependent fuel cell performance, improving as the temperature reaches the normal range. Cold start models exist in the literature; however, there does not appear to be a model that fully captures the thermal characteristics of the stack during sub-freezing startup conditions. Existing models lack the following features: (1) modeling of stack internal heating methods (other than stack reactions) and their impact on the stack temperature distribution and (2) modeling of endplate thermal mass effect on end cells and its impact on the stack temperature distribution. The focus of this research is the development and use of a sub-freezing thermal model for a polymer electrolyte fuel cell stack. Specifically, the work has focused on the generation of a model in which the fuel cell is separated into layers to determine an accurate temperature distribution within the stack. Unlike a lumped model, which may use a single temperature as an indicator of the stack's thermal condition, a layered model can reveal the effect of the endplate thermal mass on the end cells, and accommodate the evaluation of internal heating methods that may mitigate this effect.

Natural Convection Heat Transfer in Two-Dimensional Semicircular Slice Pool

This paper presents results from the Mini-SIGMA (Simulation of Internal Gravity-driven Melt Accumulation) tests concerned with high Rayleigh number turbulent natural convection in a molten pool. Tests are conducted to check on functionality of a custom-designed heater and to obtain correlations in terms of the Rayleigh and Nusselt numbers. The internal heating method is adopted in the tests utilizing the cable-type heater. This study concentrates on the thermal load, angular heat flux distribution, and temperature distribution inside the molten pool. The test section is a two-dimensional slice whose diameter, height, and thickness are 250 mm, 125 mm, and 50mm, respectively. The pool's curved wall, with a 23 mm thick copper plate, is cooled by a regulated water loop. A water-cooling system is used to maintain the temperature of water surrounding the test section as constant as practicable with time. Four thin cable-type heaters, each with a diameter of 2.4 mm and a length of 900 mm, are used to simulate internal heating in the pool. They are uniformly distributed in the semicircular section to supply a maximum of 1 kW power to the pool. The Rayleigh number is obtained from these test data up to 1010.

Natural Convection Heat Transfer in Two-Dimensional Semicircular Slice Pool

This paper presents results from the Mini-SIGMA (Simulation of Internal Gravity-driven Melt Accumulation) tests concerned with high Rayleigh number turbulent natural convection in a molten pool. Tests are conducted to check on functionality of a custom-designed heater and to obtain correlations in terms of the Rayleigh and Nusselt numbers. The internal heating method is adopted in the tests utilizing the cable-type heater. This study concentrates on the thermal load, angular heat flux distribution, and temperature distribution inside the molten pool. The test section is a two-dimensional slice whose diameter, height, and thickness are 250 mm, 125 mm, and 50mm, respectively. The pool's curved wall, with a 23 mm thick copper plate, is cooled by a regulated water loop. A water-cooling system is used to maintain the temperature of water surrounding the test section as constant as practicable with time. Four thin cable-type heaters, each with a diameter of 2.4 mm and a length of 900 mm, are used to simulate internal heating in the pool. They are uniformly distributed in the semicircular section to supply a maximum of 1 kW power to the pool. The Rayleigh number is obtained from these test data up to 1010.

Progress in phase angle thermography

Phase angle thermography is basically spatially multiplexed photothermal radiometry. It provides images for remote detection and imaging of damage. For energy deposition one can use external heat sources (e.g., light or convective heating) or internal heat generation (e.g., electric current, microwaves, eddy current, or elastic wave). More complete information about defects is obtained by combining information from external and internal heating methods: Effects of intact thermal structure can be distinguished from defect specific thermal signatures. Our recent results relate to multifrequency excitation allowing for depth profiling from one lock-in-thermography measurement and, additionally, to modulated ultrasound frequency burst phase angle thermography where effects of standing elastic waves are eliminated. This way the applications for nondestructive evaluation become more reliable and faster.

Internal Heating Effect and Application of Microwaves with Fluidization of Electrically Conductive Particles in the Ceramic Drying Process

AbstractIn the ceramic drying process, it takes a long time to completely remove internal moisture from molded ceramics due to large resistance of internal migration. Microwave heating is an effective internal heating method and will promote the moisture movement rate inside ceramics due to the elevation of vapor pressure. The effect of internal uniform heating on the ceramic drying behavior is first studied by theoretical analysis. The effectiveness and problems of drying of a slab heated by microwaves were evaluated experimentally and compared with hot air heating. The drying proceeded successfully and quicker than hot air heating when the internal temperature could be controlled below 380 K, by introducing intermittent heating or low power irradiation of microwaves. Additionally, a technique for improving uniformity of the microwave field by fluidization of electrically conductive particles was proposed. The distribution of the microwave field became successively uniform by the diffuse reflection of microwaves in a fluidized bed of plastic foam particles wrapped in aluminum foil.

A Hybrid Heating Method for the HT-7U Coils during Vacuum-Pressure Impregnation

The HT-7U superconducting tokamak is a full-superconducting magnetically confined fusion device, The toroidal magnet system of HT-7U is a very important part of the device. In VPI (Vacuum-Pressure Impregnation) process the magnet coils must be heated and degassed before impregnating and must be heated to the gel temperature and then the curing temperature, and keep the two kinds of temperatures for a long period of time after impregnating. Thus the heating method of VPI is critical. In this paper, a hybrid method of combining the internal and external heating for the coils is analyzed, especially the possibility of the internal heating method is proved.

Predictive and Diagnostic Simulation of In Situ Electrical Heating in Contaminated, Low-Permeability Soils

By in situ heating, contaminants can be mobilized by vaporization, modified into a harmless chemical state, or entrapped by soil vitrification. However, effective heating may be difficult or impossible by depending solely upon conduction of heat externally applied to a contaminated target layer. Heating a layer internally by passing an electric current through it has been employed in several different in-situ remediation field experiments. The authors present a three-dimensional computer model of groundwater flow and transport in an electrically heated, partially saturated, porous regime. Simulations are used to show that the uniformity of heating can be enhanced by increasing the number of electrical phases employed in supplying current to the electrodes. However, a more serious concern for the field-scale application of this internal heating method is the nonuniform heating of the target layer because of large heating-rate differences between the near-electrode region and the center of the array. Finally, for a dissolved solvent like TCE, the authors show that ohmic heating is exceptionally effective at clearing the layer by vapor-phase partitioning. Once expelled from the low-permeability layer, the solvent that is not already thermally destroyed by a pyrolytic reaction is available for extraction. (A)

Pyrolysis of coconut shells in a concentric three tubes reactor

To improve energy efficiency, coconut shells were pyrolyzed in a concentric three tubes reactor using a combination of external and internal heating method. Coconut shells were oxidized partially at the bottom of the reactor, and the gas rised through the redhot charcoal packing to be cracked to smaller compounds and burnt by the air. The hot gas diverged outward and flowed down along the outside wall of the second tube before it left the reactor. The higher the temperature and the longer the time of pyrolysis, the less charcoal and light oil, but the more tar were produced. The charcoal obtained was in between that produced from external and internal heating procedures. Under the optimum time of 95 minutes and temperature of 579°C, the products were 19.53% charcoal, 5.22% tar, and 0.16 % light oil.