To predict and optimize the temperature distribution of slab continuous casting in steady operational state, a three-dimensional model （named ＂offline model＂） based on the heat transfer and solidification theories...To predict and optimize the temperature distribution of slab continuous casting in steady operational state, a three-dimensional model （named ＂offline model＂） based on the heat transfer and solidification theories was developed. Both heat transfer and flux distribution characteristics of the nozzle sprays on the slab were considered, and the complicated boundary conditions, such as spray cooling, natural convection, thermal radiation as well as contact cooling of individual rolls were involved in the model. By using the calibrated caster dependent model factors, the calculated temperature and shell thickness accorded well with the measured. Furthermore, a dynamic secondary water cooling control system was also developed on the basis of a two-dimensional transient heat transfer model （named ＂online model＂） and incremental PID control algorithm to reduce slab surface temperature fluctuation in unsteady state. Compared with the traditional spray table control method, the present online model and dynamic PID control demonstrate a higher capability and flexibility to adjust cooling water flowrate and reduce slab surface temperature fluctuation when the casting speed is changed.展开更多
Temperature is one of the important loads for designing slab track. The characteristic of slab track tem- perature varies greatly with different regional climates. In this work, a bi-block slab track model was built u...Temperature is one of the important loads for designing slab track. The characteristic of slab track tem- perature varies greatly with different regional climates. In this work, a bi-block slab track model was built under outdoor conditions in Chengdu area; the statistical characteristic of temperature gradient in track slab and the relationship between temperature gradient and surface air temperature were tested and analyzed. The results show that the track slab temperature gradient will vary periodically according to the surface air temperature, and show a clear nonlinearity along the height direction. The temperature gradient distribution is extremely uneven： the temperature gradient in the top part of the track slab is larger than that in the bottom part; the most frequently occurring temperature gradient of the track slab is around -3.5 ℃/m and more than 75 % locates in the level -10 to 10 ℃/m; concrete with a relatively good heat exchange condition with the surrounding air has a narrower band distribution. In addition, the frequency distribution histogram should exclude the time zone from 00：00 to 06：00 because there is almost no traffic in this period. The amplitude of track slab temperature variation is obviously lower than that of the air temperature variation, and the former is approximately linear with the latter.展开更多
The solar climate of our Moon is analyzed using the results of numerical simulations and the recently released data of the Diviner Lunar Radiometer Experiment (DLRE) to assess (a) the resulting distribution of the sur...The solar climate of our Moon is analyzed using the results of numerical simulations and the recently released data of the Diviner Lunar Radiometer Experiment (DLRE) to assess (a) the resulting distribution of the surface temperature, (b) the related global mean surface temperature T<sub>s</sub>>, and (c) the effective radiation temperature T<sub>e</sub> <sub></sub>often considered as a proxy for T<sub>s</sub>> of rocky planets and/or their natural satellites, where T<sub>e</sub> <sub></sub>is based on the global radiation budget of the well-known “thought model” of the Earth in the absence of its atmosphere. Because the Moon consists of similar rocky material like the Earth, it comes close to this thought model. However, the Moon’s astronomical features (e.g., obliquity, angular velocity of rotation, position relative to the disc of the solar system) differ from that of the Earth. Being tidally locked to the Earth, the Moon’s orbit around the Sun shows additional variation as compared to the Earth’s orbit. Since the astronomical parameters affect the solar climate, we predicted the Moon’s orbit coordinates both relative to the Sun and the Earth for a period of 20 lunations starting May 24, 2009, 00:00 UT1 with the planetary and lunar ephemeris DE430 of the Jet Propulsion Laboratory of the California Institute of Technology. The results revealed a mean heliocentric distance for the Moon and Earth of 1.00124279 AU and 1.00166376 AU, respectively. The mean geocentric distance of the Moon was 384792 km. The synodic and draconic months deviated from their respective means in a range of -5.7 h to 6.9 h and ±3.4 h, respectively. The deviations of the anomalistic months from their mean range between -2.83 d and 0.97 d with the largest negative deviations occurring around the points of inflection in the curve that represents the departure of the synodic month from its mean. Based on the two successive passages of the Sun through the ascending node of the lunar equator plane, the time interval between them corresponds to 347.29 days, i.e., it is slightly longer than the mean draconic year of 346.62 days. We computed the local solar insolation as input to the multilayer-force restore method of Kramm et al. (2017) that is based on the local energy budget equation. Due to the need to spin up the distribution of the regolith temperature to equilibrium, analysis of the model results covers only the last 12 lunations starting January 15, 2010, 07:11 UT1. The predicted slab temperatures, T<sub>slab</sub>, considered as the realistic surface temperatures, follow the bolometric temperatures, T<sub>bol</sub>, acceptably. According to all 24 DLRE datasets related to the subsolar longitude ø<sub>ss</sub>, the global averages of the bolometric temperature amounts to T<sub>bol</sub>=201.1k± 0.6K. Based on the globally averaged emitted infrared radiation of F<sub>IR</sub>>=290.5W·m<sup>-2</sup>± 3.0W·m<sup>-2</sup> derived from the 24 DLRE datasets, the effective radiative temperature of the Moon is T<sub>e, M</sub>>=T<sub>bol>1/4</sub>=271.0k± 0.7K so that T<sub>bol</sub>>≅0.742T<sub>e, M</sub>. The DLRE observations suggest that in the case of rocky planets and their natural satellites, the globally averaged surface temperature is notably lower than the effective radiation temperature. They differ by a factor that depends on the astronomical parameters especially on the angular velocity of rotation.展开更多
In the past, the planetary radiation balance served to quantify the atmospheric greenhouse effect by the difference between the globally averaged near-surface temperature of and the respective effective radiation temp...In the past, the planetary radiation balance served to quantify the atmospheric greenhouse effect by the difference between the globally averaged near-surface temperature of and the respective effective radiation temperature of the Earth without atmosphere of resulting in . Since such a “thought experiment” prohibits any rigorous assessment of its results, this study considered the Moon as a testbed for the Earth in the absence of its atmosphere. Since the angular velocity of Moon’s rotation is 27.4 times slower than that of the Earth, the forcing method, the force-restore method, and a multilayer-force-restore method, used in climate modeling during the past four decades, were alternatively applied to address the influence of the angular velocity in determining the Moon’s globally averaged skin (or slab) temperature, . The multilayer-force-restore method always provides?the highest values for , followed by the force-restore method and the forcing method, but the differences are marginal. Assuming a solar albedo of , a relative emissivity , and a solar constant of and applying the multilayer-force-restore method yielded and for the Moon. Using the same values for α, ε, and S, but assuming the Earth’s angular velocity for the Moon yielded and quantifying the effect of the terrestrial atmosphere by . A sensitivity study for a solar albedo of commonly assumed for the Earth in the absence of its atmosphere yielded , , and . This means that the atmospheric effect would be more than twice as large as the aforementioned difference of 33 K. To generalize the findings, twelve synodic months (i.e., 354 Earth days) and 365 Earth days, where , a Sun-zenith-distance dependent solar albedo, and the variation of the solar radiation in dependence of the actual orbit position and the tilt angle of the corresponding rotation axis to the ecliptic were considered. The case of Moon’s true angular velocity yielded and . Whereas Earth’s 27.4 times higher angular velocity yielded , and . In both cases, the effective radiation temperature is ,?because the computed global albedo is . Thus, the effective radiation temperature yields flawed results when used for quantifying the atmospheric greenhouse effect.展开更多
基金supported by the National Natural Science Foundation of China (No.50174031)
文摘To predict and optimize the temperature distribution of slab continuous casting in steady operational state, a three-dimensional model （named ＂offline model＂） based on the heat transfer and solidification theories was developed. Both heat transfer and flux distribution characteristics of the nozzle sprays on the slab were considered, and the complicated boundary conditions, such as spray cooling, natural convection, thermal radiation as well as contact cooling of individual rolls were involved in the model. By using the calibrated caster dependent model factors, the calculated temperature and shell thickness accorded well with the measured. Furthermore, a dynamic secondary water cooling control system was also developed on the basis of a two-dimensional transient heat transfer model （named ＂online model＂） and incremental PID control algorithm to reduce slab surface temperature fluctuation in unsteady state. Compared with the traditional spray table control method, the present online model and dynamic PID control demonstrate a higher capability and flexibility to adjust cooling water flowrate and reduce slab surface temperature fluctuation when the casting speed is changed.
基金supported by the National Key Basic Research Program of China (973 Program) (2013CB036202)the National Natural Science Foundation of China (51008258)Fundamental Research Funds for the Central Universities (SWJTU12CX065)
文摘Temperature is one of the important loads for designing slab track. The characteristic of slab track tem- perature varies greatly with different regional climates. In this work, a bi-block slab track model was built under outdoor conditions in Chengdu area; the statistical characteristic of temperature gradient in track slab and the relationship between temperature gradient and surface air temperature were tested and analyzed. The results show that the track slab temperature gradient will vary periodically according to the surface air temperature, and show a clear nonlinearity along the height direction. The temperature gradient distribution is extremely uneven： the temperature gradient in the top part of the track slab is larger than that in the bottom part; the most frequently occurring temperature gradient of the track slab is around -3.5 ℃/m and more than 75 % locates in the level -10 to 10 ℃/m; concrete with a relatively good heat exchange condition with the surrounding air has a narrower band distribution. In addition, the frequency distribution histogram should exclude the time zone from 00：00 to 06：00 because there is almost no traffic in this period. The amplitude of track slab temperature variation is obviously lower than that of the air temperature variation, and the former is approximately linear with the latter.
文摘The solar climate of our Moon is analyzed using the results of numerical simulations and the recently released data of the Diviner Lunar Radiometer Experiment (DLRE) to assess (a) the resulting distribution of the surface temperature, (b) the related global mean surface temperature T<sub>s</sub>>, and (c) the effective radiation temperature T<sub>e</sub> <sub></sub>often considered as a proxy for T<sub>s</sub>> of rocky planets and/or their natural satellites, where T<sub>e</sub> <sub></sub>is based on the global radiation budget of the well-known “thought model” of the Earth in the absence of its atmosphere. Because the Moon consists of similar rocky material like the Earth, it comes close to this thought model. However, the Moon’s astronomical features (e.g., obliquity, angular velocity of rotation, position relative to the disc of the solar system) differ from that of the Earth. Being tidally locked to the Earth, the Moon’s orbit around the Sun shows additional variation as compared to the Earth’s orbit. Since the astronomical parameters affect the solar climate, we predicted the Moon’s orbit coordinates both relative to the Sun and the Earth for a period of 20 lunations starting May 24, 2009, 00:00 UT1 with the planetary and lunar ephemeris DE430 of the Jet Propulsion Laboratory of the California Institute of Technology. The results revealed a mean heliocentric distance for the Moon and Earth of 1.00124279 AU and 1.00166376 AU, respectively. The mean geocentric distance of the Moon was 384792 km. The synodic and draconic months deviated from their respective means in a range of -5.7 h to 6.9 h and ±3.4 h, respectively. The deviations of the anomalistic months from their mean range between -2.83 d and 0.97 d with the largest negative deviations occurring around the points of inflection in the curve that represents the departure of the synodic month from its mean. Based on the two successive passages of the Sun through the ascending node of the lunar equator plane, the time interval between them corresponds to 347.29 days, i.e., it is slightly longer than the mean draconic year of 346.62 days. We computed the local solar insolation as input to the multilayer-force restore method of Kramm et al. (2017) that is based on the local energy budget equation. Due to the need to spin up the distribution of the regolith temperature to equilibrium, analysis of the model results covers only the last 12 lunations starting January 15, 2010, 07:11 UT1. The predicted slab temperatures, T<sub>slab</sub>, considered as the realistic surface temperatures, follow the bolometric temperatures, T<sub>bol</sub>, acceptably. According to all 24 DLRE datasets related to the subsolar longitude ø<sub>ss</sub>, the global averages of the bolometric temperature amounts to T<sub>bol</sub>=201.1k± 0.6K. Based on the globally averaged emitted infrared radiation of F<sub>IR</sub>>=290.5W·m<sup>-2</sup>± 3.0W·m<sup>-2</sup> derived from the 24 DLRE datasets, the effective radiative temperature of the Moon is T<sub>e, M</sub>>=T<sub>bol>1/4</sub>=271.0k± 0.7K so that T<sub>bol</sub>>≅0.742T<sub>e, M</sub>. The DLRE observations suggest that in the case of rocky planets and their natural satellites, the globally averaged surface temperature is notably lower than the effective radiation temperature. They differ by a factor that depends on the astronomical parameters especially on the angular velocity of rotation.
文摘In the past, the planetary radiation balance served to quantify the atmospheric greenhouse effect by the difference between the globally averaged near-surface temperature of and the respective effective radiation temperature of the Earth without atmosphere of resulting in . Since such a “thought experiment” prohibits any rigorous assessment of its results, this study considered the Moon as a testbed for the Earth in the absence of its atmosphere. Since the angular velocity of Moon’s rotation is 27.4 times slower than that of the Earth, the forcing method, the force-restore method, and a multilayer-force-restore method, used in climate modeling during the past four decades, were alternatively applied to address the influence of the angular velocity in determining the Moon’s globally averaged skin (or slab) temperature, . The multilayer-force-restore method always provides?the highest values for , followed by the force-restore method and the forcing method, but the differences are marginal. Assuming a solar albedo of , a relative emissivity , and a solar constant of and applying the multilayer-force-restore method yielded and for the Moon. Using the same values for α, ε, and S, but assuming the Earth’s angular velocity for the Moon yielded and quantifying the effect of the terrestrial atmosphere by . A sensitivity study for a solar albedo of commonly assumed for the Earth in the absence of its atmosphere yielded , , and . This means that the atmospheric effect would be more than twice as large as the aforementioned difference of 33 K. To generalize the findings, twelve synodic months (i.e., 354 Earth days) and 365 Earth days, where , a Sun-zenith-distance dependent solar albedo, and the variation of the solar radiation in dependence of the actual orbit position and the tilt angle of the corresponding rotation axis to the ecliptic were considered. The case of Moon’s true angular velocity yielded and . Whereas Earth’s 27.4 times higher angular velocity yielded , and . In both cases, the effective radiation temperature is ,?because the computed global albedo is . Thus, the effective radiation temperature yields flawed results when used for quantifying the atmospheric greenhouse effect.
