10:45 AM - 12:15 PM
[AHW24-P06] Development of in-situ measurement method of effective thermal conductivity in boreholes (verification by numerical calculation)
Keywords:thermal conductivity, shallow ground source heat exchanger system, finite element method
The thermal conductivity of soil and ground basement is an important thermophysical property in the fields of geoscience, resources, environment, agriculture, civil engineering and construction, and many measurements have been conducted.
In particular, in recent years, heat exchanger systems of shallow subsurface heat energy, one of the renewable energies, have spread in Japan and abroad, and many measurements have been made to recognize the necessity of thermal conductivity in the design and construction of such systems.
Generally, there are two main methods for measuring the thermal conductivity of soil or ground basement. One is to measure thermal conductivity in a laboratory on the ground after collecting samples (indoor measurement), and the other is to measure it in situ at the depth to be measured by inserting a sensor or the like into a well (in-situ measurement). In the field of utilize of shallow heat energy, in-situ measurements are performed by circulating hot water to heat the ground (hot water heating circulation method). However, this method of measurement has its ambitious, such as large measurements and long measurement times. In this study, we propose a new method for in situ measurements that is expected to be used in the field of utilize of shallow ground heat source energy. Its effectiveness is currently being verified by numerical analysis.
In order to measure thermal conductivity in boreholes such as underground heat exchange wells, this method combines a heater part with a cylindrical sheet-like heating element combined with a stretchable rubber sheet, and a measurement part utilizing a packer, and makes them adhere to the wall. We expect to be applied to boreholes of about 150 mm, which are commonly used in heat exchange wells.
In this study, we verified that the thermal conductivity can be measured by this method through numerical analysis using the finite element method. In such verification, the proper amount of heating due to the shape (diameter, etc.) of the well was also evaluated.
In particular, in recent years, heat exchanger systems of shallow subsurface heat energy, one of the renewable energies, have spread in Japan and abroad, and many measurements have been made to recognize the necessity of thermal conductivity in the design and construction of such systems.
Generally, there are two main methods for measuring the thermal conductivity of soil or ground basement. One is to measure thermal conductivity in a laboratory on the ground after collecting samples (indoor measurement), and the other is to measure it in situ at the depth to be measured by inserting a sensor or the like into a well (in-situ measurement). In the field of utilize of shallow heat energy, in-situ measurements are performed by circulating hot water to heat the ground (hot water heating circulation method). However, this method of measurement has its ambitious, such as large measurements and long measurement times. In this study, we propose a new method for in situ measurements that is expected to be used in the field of utilize of shallow ground heat source energy. Its effectiveness is currently being verified by numerical analysis.
In order to measure thermal conductivity in boreholes such as underground heat exchange wells, this method combines a heater part with a cylindrical sheet-like heating element combined with a stretchable rubber sheet, and a measurement part utilizing a packer, and makes them adhere to the wall. We expect to be applied to boreholes of about 150 mm, which are commonly used in heat exchange wells.
In this study, we verified that the thermal conductivity can be measured by this method through numerical analysis using the finite element method. In such verification, the proper amount of heating due to the shape (diameter, etc.) of the well was also evaluated.