Stability of Convective Ventilation after Fan Switching-Off in Mines

Study of the Influence of Thermal Convection on Temperature Measurement in Thermal Control Boreholes during Artificial Ground Freezing

“…Taking into account the data from Table 1, the corresponding Rayleigh numbers range from 6.8 × 10 5 to 5 × 10 7 . The Rayleigh numbers are calculated using a formula from [12]:…”

“…As an example, Figure 1 shows the measured temperature distributions over the depth of two TC boreholes that were used in the construction of the skip shaft of a potash mine in the Republic of Belarus [1]. Free convection in a vertical channel filled with fluid arises at certain critical parameters of the fluid, which are usually expressed in terms of the critical Rayleigh [11][12][13] or Grashof [14,15] numbers. Kazakov et al [12] found that for laminar flows, the critical Rayleigh number is relatively small, with a value of about 100.…”

“…where G is the temperature gradient, °C/m; and R is the borehole radius, m. Thermal convection leads not only to temperature fluctuations relative to the actual temperature of the soil (which could easily be eliminated by averaging over time), but also to a long-term quasi-stationary effect (QSE) [12], which is manifested as a consistent decrease in the temperature gradient relative to its value in the soil. Demezhko et al [17] found that the maximum gradient decrease is observed in the upper and lower parts of the borehole, with an average value of 7.5% over the length of the borehole estimated for Free convection in a vertical channel filled with fluid arises at certain critical parameters of the fluid, which are usually expressed in terms of the critical Rayleigh [11][12][13] or Grashof [14,15] numbers. Kazakov et al [12] found that for laminar flows, the critical Rayleigh number is relatively small, with a value of about 100.…”

“…Demezhko et al [17] found that the maximum gradient decrease is observed in the upper and lower parts of the borehole, with an average value of 7.5% over the length of the borehole estimated for Free convection in a vertical channel filled with fluid arises at certain critical parameters of the fluid, which are usually expressed in terms of the critical Rayleigh [11][12][13] or Grashof [14,15] numbers. Kazakov et al [12] found that for laminar flows, the critical Rayleigh number is relatively small, with a value of about 100. Another important parameter that determines the presence of free convection is the ratio of the thermal conductivities of the fluid and the borehole casing [13].…”