Regression Models Utilization to the Underground Temperature Determination at Coal Energy Conversion

The underground coal gasification represents a technology capable of obtaining synthetic coal gas from hard-reached coal deposits and coal beds with tectonic faults. This technology is also less expensive than conventional coal mining. The cavity is formed in the coal seam by converting coal to synthetic gas during the underground coal gasification process. The cavity growth rate and the gasification queue’s moving velocity are affected by controllable variables, i.e., the operation pressure, the gasification agent, and the laboratory coal seam geometry. These variables can be continuously measured by standard measuring devices and techniques as opposed to the underground temperature. This paper researches the possibility of the regression models utilization for temperature data prediction for this reason. Several regression models were proposed that were differed in their structures, i.e., the number and type of selected controllable variables as independent variables. The goal was to find such a regression model structure, where the underground temperature is predicted with the greatest possible accuracy. The regression model structures’ proposal was realized on data obtained from two laboratory measurements realized in the ex situ reactor. The obtained temperature data can be used for visualization of the cavity growth in the gasified coal seam.

Cavitation Growth Phenomena in Pure-Sliding Grease EHD Contacts

This article describes experimental and theoretical studies on the cavitation phenomena in the grease lubrication film under pure sliding elastohydrodynamic contact. In situ observation tests using the optical interferometry technique were conducted, and the growth of cavitation was captured using a high-speed camera. The results showed that the cavity grew in two stages, which was similar to the behavior in the base oil, and that the cavity growth rate in the initial stage was higher than that in the second stage. In the initial stage, the cavity growth time in the grease was longer than that in the base oil, and the cavity length after the growth depended on the base oil viscosity. It was also found in the test using diurea grease that small cavities were formed by the lumps of thickener. The cavity growth in the initial stage was discussed by numerical simulation of pressure distribution based on a simple rheological model.

Cavity Growth Simulation in 2.25Cr–1Mo Steel Under Creep-Fatigue Loading

High temperature components in thermal power plants are subjected to creep-fatigue loading where creep cavities initiate and grow on grain boundaries. Development of a quantitative evaluation method of cavity growth is important for reliable maintenance of these components. In this study, a creep-fatigue test was carried out at 600°C on 2.25Cr–1Mo steel in a scanning electron microscope, and continuous observation of cavity growth behavior during the test was made. Based on the cavity growth observation, existing cavity growth models were modified and the simulated results using the modified model were compared to the observed cavity growth behavior. From the observation, spherical shape cavities initiate and grow up to their length of 2μm on the grain boundaries at the initial stage of damage, and then these cavities change their shape to cracklike and grow until their length reaches around 10μm. Finally, cracklike cavities coalesce with each other to form one microcrack along a grain boundary. It can be concluded that cavity growth rates are controlled by diffusion and power law creep under constrained conditions, based on the theoretical consideration of cavity growth mechanism. Through these discussions, a new cavity growth model was proposed by modifying conventional models. Both spherical and cracklike cavity growth rate equations were derived from the modified cavity growth model. It was indicated that the measured cavity growth rate was well predicted by the growth rate equations, derived from the modified model, and a cavity growth simulation result corresponds to the change in the maximum cavity size with number of cycles under the creep-fatigue loading.

Numerical Analysis of the Effect of Diffusion and Creep Flow on Cavity Growth

In this paper, intergranular cavity growth in regimes, where both surface diffusion and deformation enhanced grain boundary diffusion are important, is studied. In order to continuously simulate the cavity shape evolution and cavity growth rate, a fully-coupled numerical method is proposed. Based on the fully-coupled numerical method, a gradual cavity shape change is predicted and this leads to an adverse effect on the cavity growth rates. As the portion of the cavity volume growth due to jacking and viscoplastic deformation in the total cavity volume growth increases, the initially spherical cavity evolves to V-shaped cavity. The numerical results are physically more realistic compared to results in the previous studies. The present numerical results suggest that the cavity shape evolution and cavity growth rate based on an assumed cavity shape, whether spherical or crack-like, cannot be used in this regime due to transitional coupled growth mechanisms.

Creep Life Evaluation by Micro-Cavities

As the operation time of a power plant increases, the degradation and the cracks inside of the structure exposed to high temperature will increase gradually. Therefore, degradation rate, crack growth rate and fracture life of the structure can be evaluated according to the level of degradation and the growth of crack length. We performed creep rupture test and crack growth test with stress and temperature changes to evaluate the degradation rate, crack growth rate and fracture life. Degradation rate was evaluated using micro-cavities. The area fraction of the cavities increased with the increasing temperature and life fraction (t/tf). da/dt, the crack growth rate against Ct estimated from the relationship between load line displacement rate and cavity increase rate, was in good agreement with the result of da/dt vs Ct acquired from the test. It shows that the creep crack growth rate can be evaluated by the increase of cavity area fraction. It was also found that the predicted life calculated with the cavity growth rate was in good agreement with experimental results.

Effect of Helium and Aging Treatment on Radiation Damage Behavior in Low Activation Fe-Cr-Mn (W, V) Alloy

The effects of helium and aging treatment on radiation damage behavior in low activation Fe-Cr-Mn ( W, V) alloy were investigated by electron and helium ion dual-beam irradiation in a high voltage electron microscope. Specimens were aged at 673 K, 823 K and 923 K for 1000, 3000 and 10000 hours. Electron and He ion dual-beam irradiations were performed at 627 K to 10 dpa. M23C6 type carbides were precipitated in the aged specimens, and the amount of the precipitates was increased with increasing aging temperature and aging time. He bubbles were formed during dual-beam irradiation in all of the specimens. The cavity swelling under dual-beam irradiations was increased with increasing the aging temperature and aging time. It was suggested that cavity swelling is closely related to the concentration of solutes such as Cr and C in the matrix, namely cavity growth rate becomes higher with decreasing of the solutes in solution.

An Investigation of Cavity Growth Rate in Superplastic Al and Mg Alloys

Fine-grained 5083 Al alloy and AZ91 Mg alloy showed superplastic behavior. The plasticitycontrolled growth rates of cavities during superplastic deformation for the Al alloy and Mg alloy were investigated. The cavity volume fraction for the Mg alloy was larger than that for the Al alloy. However, the cavity growth rate for the Mg alloy was lower than that for the Al alloy.

Cavity Growth Simulation of 2.25Cr-1Mo Steel Under Creep-Fatigue Loading

High temperature components in thermal power plants are subjected to creep-fatigue loading where creep cavities initiate and grow on grain boundaries. Development of a quantitative evaluation method of cavity growth is important for reliable maintenance of these components. In this study, a creep-fatigue test was carried out at 600°C on 2.25Cr-1Mo steel in a scanning electron microscope, and continuous observation of cavity growth behavior on the surface during the test was made. Based on the cavity growth observation, existing cavity growth models were modified and a simulation result by the modified model was discussed by comparing with observed cavity growth behavior. From the observation, spherical shape cavities initiate and grow up to their length of 2μm on the grain boundaries at initial stage of damage, and then these cavities change their shape to crack-like to grow until their length reaches around 10μm. Finally, crack-like cavities coalesce each other to form one micro crack along a grain boundary. It can be concluded that cavity growth rates of these cavities are controlled by diffusion and power law creep under constrained condition based on theoretical consideration of cavity growth mechanism. Through these discussions, a new cavity growth model was proposed by modifying conventional models. Both spherical and crack-like cavity growth rate equations were derived from the modified cavity growth model. It was indicated that measured cavity growth rate was well predicted by the growth rate equations derived from the modified model, and a cavity growth simulation result corresponds to the change in the maximum cavity size with cycles under the creep-fatigue loading.