Microwave-heating laboratory experiments for planetary mantle convection
Microwave-heating laboratory experiments for planetary mantle convection
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DOI：
10.1017/jfm.2015.347
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发表时间：
2015-08-01
影响因子：
3.7
通讯作者：
Jaupart, C.
中科院分区：
文献类型：
--
作者：
Limare, A.;Vilella, K.;Jaupart, C.
由于放射性同位素的衰变，地球上行星的热演化主要受长期冷却和内部加热的控制，从对流动力学的观点来看，这两个过程是等价的。在从上方冷却和体积加热的流体中，对流是由顶部边界层的不稳定性决定的，内部热结构是非等熵的。在这里，我们介绍了创新的实验室实验，其中利用微波辐射在高普兰特数(>；300)和高瑞利-罗伯茨数(从10(4)到10(7))的流体中产生均匀的内部热，适合于行星地幔对流。非侵入性技术被用来确定温度和速度场。我们通过在三维笛卡尔几何中进行数值模拟，再现了实验条件，成功地验证了实验结果。对于刚性边界条件和自由滑移边界条件，建立了热边界层的主要特征，即其厚度和温降与Rayleigh-Roberts数之间的标度定律。一个可靠的结论是，对于刚性边界条件，内部温度显着高于自由滑移边界条件。我们的标度定律，再加上合理的物理参数输入瑞利-罗伯茨数，使我们能够计算地球和金星的地幔潜在温度，这两个地球行星在其表面具有不同的机械边界条件。
Thermal evolution of telluric planets is mainly controlled by secular cooling and internal heating due to the decay of radioactive isotopes, two processes that are equivalent from the standpoint of convection dynamics. In a fluid cooled from above and volumetrically heated, convection is dominated by instabilities of the top boundary layer and the interior thermal structure is non-isentropic. Here we present innovative laboratory experiments where microwave radiation is used to generate uniform internal heat in fluids at high Prandtl number (>300) and high Rayleigh-Roberts number (ranging from 10(4) to 10(7)), appropriate for planetary mantle convection. Non-invasive techniques are employed to determine both temperature and velocity fields. We successfully validate the experimental results by conducting numerical simulations in three-dimensional Cartesian geometry that reproduce the experimental conditions. Scaling laws relating key characteristics of the thermal boundary layer, namely its thickness and temperature drop, to the Rayleigh-Roberts number have been established for both rigid and free-slip boundary conditions. A robust conclusion is that for rigid boundary conditions the internal temperature is significantly higher than for free-slip boundary conditions. Our scaling laws, coupled with plausible physical parameters entering the Rayleigh-Roberts number, enable us to calculate the mantle potential temperature for the Earth and Venus, two telluric planets with different mechanical boundary conditions at their surface.