3.2 Experimental Facility and Methodology
123
Fig. 3.2 Schematic of a vertical cut through the test facility (a) and Thermocouple distribution
among the whole pebble bed (b)
of a one-dimensional heat transfer in the radial direction at the middle level, which
means no adiabatic condition is required in the axial or radial direction. Moreover,
on account of the experimental method in this test, the heat flux is not necessary to
determine effective thermal diffusivity and conductivity. It’s an advantage to expand
the experiment to higher temperatures without measuring the exact heat flow.
The black points in Figs. (3.2a, b), show the distribution of 90 sheathed type
K thermocouples in the test section. The thermocouples are placed at three levels
in height, and significant data are obtained by the NI system from the 30 middlelevel thermocouples. The thermocouples are named from C1 to C5 in the azimuthal
direction and from T1 to T6 in the radial direction for a specific description of the
following inverse method, such as C1T1. The nominal positions in the radial direction
are as follows: 0.63 m, 0.918 m, 1.21 m, 1.494 m, 1.78 m, 2.07 m.
3.2.2 Data Processing Algorithm
3.2.2.1 Sampling Processes
A vacuum test is first conducted to measure the effective thermal diffusivity at an
absolute pressure of 20Pa. In the inverse method, the heating power isn’t used in the
heat conduction equation, and the two boundary conditions are the temperatures at
two boundary positions. Besides, the accurate heat flux along the radial direction at
the middle level is difficult to measure at high temperature due to losses of heat from
different directions. The dynamic temperature data of heating and cooling is recorded
by the NI system for the inverse method. The heating process is divided into several
stages to make it rise slowly. The stable heating power and cooling water-flow rate
need be ensured to prevent instantaneous temperature fluctuation in the whole period
of the test, which contributes to generating a better result in the inverse method. The
123
Fig. 3.2 Schematic of a vertical cut through the test facility (a) and Thermocouple distribution
among the whole pebble bed (b)
of a one-dimensional heat transfer in the radial direction at the middle level, which
means no adiabatic condition is required in the axial or radial direction. Moreover,
on account of the experimental method in this test, the heat flux is not necessary to
determine effective thermal diffusivity and conductivity. It’s an advantage to expand
the experiment to higher temperatures without measuring the exact heat flow.
The black points in Figs. (3.2a, b), show the distribution of 90 sheathed type
K thermocouples in the test section. The thermocouples are placed at three levels
in height, and significant data are obtained by the NI system from the 30 middlelevel thermocouples. The thermocouples are named from C1 to C5 in the azimuthal
direction and from T1 to T6 in the radial direction for a specific description of the
following inverse method, such as C1T1. The nominal positions in the radial direction
are as follows: 0.63 m, 0.918 m, 1.21 m, 1.494 m, 1.78 m, 2.07 m.
3.2.2 Data Processing Algorithm
3.2.2.1 Sampling Processes
A vacuum test is first conducted to measure the effective thermal diffusivity at an
absolute pressure of 20Pa. In the inverse method, the heating power isn’t used in the
heat conduction equation, and the two boundary conditions are the temperatures at
two boundary positions. Besides, the accurate heat flux along the radial direction at
the middle level is difficult to measure at high temperature due to losses of heat from
different directions. The dynamic temperature data of heating and cooling is recorded
by the NI system for the inverse method. The heating process is divided into several
stages to make it rise slowly. The stable heating power and cooling water-flow rate
need be ensured to prevent instantaneous temperature fluctuation in the whole period
of the test, which contributes to generating a better result in the inverse method. The