BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI

Bul. Inst. Polit. Iaşi, t. LVIII (LXII), f. 3, 2012 73
The maximum x axis value of the plot is only limited to 65 nodes since
the “visible” propagation distance of the temperature perturbation for the
considered charging period is 65 nodes, which corresponds to 260 mm.
A better image of the temperature field evolution is offered by Fig. 3,
which presents it as a 3-D surface, with horizontal plane axes being the distance
from the outer wall surface in terms of node number, and time. This way, the
evolution of the temperature in each of the nodes can be visualized along the
time axis. In this representation, the node number axis range has been extended
to 80, because it provides a more accurate view of the propagation distance of
the thermal perturbation in the radial direction.
Fig. 4. shows the plot versus time of the heat stored in the ground. Except
for a brief time lapse at the start of the process, the amount of heat stored
exhibits an almost linear growth, the total stored heat representing 33,748.83 kJ,
which is 4.7% of the maximum amount of heat that could be stored if the
temperature of the ground were constant and equal to t HF .
Fig. 3 – 3-D surface representation of the temperature field during the charging process.
Figs. 5 through 7 refer to the heat storage discharging process. Fig. 5
represents the plot versus time of the SSM temperature.
Figs. 6 through 8 refer to the heat storage discharging process. Fig. 6
represents the plot versus time of the SSM temperature.
After stopping the charging process, the discharge of the heat storage
begins immediately. As a result, the initial temperature field (the temperature
distribution at the end of the charging phase) starts to be distorted by the
cooling that extracts heat form the SSM layer in contact with the tube outer
surface. As a result, the temperature plots exhibit a maximum that migrates
radially and concurrently becomes more flattened as the process advances. As