Yuichi Niibori - Academia.edu (original) (raw)

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Papers by Yuichi Niibori

Atomic Energy Society of Japan, Jul 16, 2021

Atomic Energy Society of Japan, Jul 31, 2020

Atomic Energy Society of Japan, Feb 22, 2016

Journal of the Geothermal Research Society of Japan, Oct 27, 2009

A simulator for the geothermal heat pump system considering the groundwater flow has been develop... more A simulator for the geothermal heat pump system considering the groundwater flow has been developed. It is known that the groundwater flow affects the ability of heat extraction such as transient response and recovery of temperature. Therefore, it is necessary to simulate the dynamic behavior of the underground heat extraction system in order to evaluate the heat extraction rate. In this paper, the heat flow in the borehole, U-tube and subsurface layers with groundwater flow have been modeled by using the advective-diffusive equation, and the temporal change of temperature has been calculated based on Finite-Element Method (FEM). We analyzed a thermal response test (TRT) data and have clarified that the tool in this paper can simulate the heat flow in the layers associated with the groundwater flow and also represents the heat exchange between U-tube and layers. It has also been demonstrated that the simulator can examine the relationship between groundwater flow and apparent thermal conductivity, groundwater flow and temperature change of layers with time during heat extraction.

$Research paper thumbnail of Numerical simulations of the anomalous solute transport in a fractured porous aquifer$

$Research paper thumbnail of Characterizing non-fickian transport in fractured rock masses using fractional derivative-based mathematical model$

A fractional advection-dispersion equation (fADE) was employed to describe non-Fickian mass trans... more A fractional advection-dispersion equation (fADE) was employed to describe non-Fickian mass transport in fractured rock masses. A fracture network model based on fractal geometry was utilized to analyze numerical tracer responses in inhomogeneous rock masses composed of a number of natural fractures. The density of the natural fractures was varied in the numerical analyses. It was shown that non-Fickian transport (anomalous dispersion with heavy tails) was observed for lower natural fracture densities and the tracer response could be described by the fADE. It was suggested that the term of fractional time derivative in the fADE was responsible for the variance of travel time in the tracer responses, resulting in the non-Fickian transport. The results obtained in this study may support the use of the fADE for characterizing complex fluid flow in geothermal reservoirs.

Journal of ion exchange, 2021

Sr adsorption behavior of potassium dititanate which is a layered ion exchanger was examined unde... more Sr adsorption behavior of potassium dititanate which is a layered ion exchanger was examined under high Na concentration. Potassium dititanate adsorbed Sr 2+ even if the coexisting Na concentration was high. Moreover, when Na + coexisted above a certain amount, the distribution coefficient of Sr increased with increasing pH, and the adsorbed amounts of Sr 2+ and Na + both increased. From the Sr and Na concentration of the liquid phase before and after Sr adsorption, X-ray diffraction pattern of the solid phase, IR spectrum, Raman spectrum, etc., crystallinity of potassium dititanate reduced because some Ti-O-Ti bonds were broken due to contact with water. However, it was suggested that Sr 2+ was adsorbed between the layers and Na + was adsorbed at the surface hydroxyl groups, although the crystallinity was reduced. The distribution coefficient of potassium dititanate for Sr was 1.7×10 7 mL/g or higher in the region of equilibrium pH 12 and equilibrium Na concentration of 40 mmol/L or higher, showing higher Sr adsorption ability than the previously reported Sr adsorbent.