5.5 Further Issues
387
Fig. 5.128 The transient response of high particle temperature in the decay heat removal process
of HTR-PM
0.8 [7]. Under such conditions, the transient temperature response is shown in Fig.
5.128. The highest temperature of the packed bed increases significantly with time
and reaches its maximum at about 12h. Then the temperature decreases with time.
The highest temperature is about 1,307.2
◦ C under 1.0 P d and 1,549.4
◦ C under 2.0
P d . The possible highest temperature is still under the design limitation of 1,600
◦ C
[160] of nuclear-packed pebble bed.
5.5.4 Short Summary
The black radiation model, the uniform radiation model, the local radiation model,
and the particle-scale radiation model are proposed herein for a comparative study
of modeling densely packed beds of high-temperature particles. Thermal radiation
heat transfer of gray-body surface has been studied in full integral scales. For the
black surfaces in the granular system, the black radiation model was proven valid and
agreed with existing correlations and models. The effective thermal conductivity of
the pebble bed of HTR-10 was directly proportional to the third power of temperature,
and the radiation exchange factor was 1.03.
From the experimental results and correlations in a packed bed, the radiative
effective thermal conductivity increased significantly with the particle emissivity.
However, the Asakuma radiation model [134], the two-flux model, and the local
radiation model were almost independent of particle emissivity. The explanation
was that the uniform assumption of q r,i (r i ) for every particle without a heat source
387
Fig. 5.128 The transient response of high particle temperature in the decay heat removal process
of HTR-PM
0.8 [7]. Under such conditions, the transient temperature response is shown in Fig.
5.128. The highest temperature of the packed bed increases significantly with time
and reaches its maximum at about 12h. Then the temperature decreases with time.
The highest temperature is about 1,307.2
◦ C under 1.0 P d and 1,549.4
◦ C under 2.0
P d . The possible highest temperature is still under the design limitation of 1,600
◦ C
[160] of nuclear-packed pebble bed.
5.5.4 Short Summary
The black radiation model, the uniform radiation model, the local radiation model,
and the particle-scale radiation model are proposed herein for a comparative study
of modeling densely packed beds of high-temperature particles. Thermal radiation
heat transfer of gray-body surface has been studied in full integral scales. For the
black surfaces in the granular system, the black radiation model was proven valid and
agreed with existing correlations and models. The effective thermal conductivity of
the pebble bed of HTR-10 was directly proportional to the third power of temperature,
and the radiation exchange factor was 1.03.
From the experimental results and correlations in a packed bed, the radiative
effective thermal conductivity increased significantly with the particle emissivity.
However, the Asakuma radiation model [134], the two-flux model, and the local
radiation model were almost independent of particle emissivity. The explanation
was that the uniform assumption of q r,i (r i ) for every particle without a heat source