Particle Shutdown of Radiatively Driven Convection

辐射可以驱动浅层流体层中的自然对流，例如湖泊或浅池塘的近岸区域。如果辐射来自上方，当它穿过这一层时，就会被流体吸收，加热这一层的顶部，形成稳定的热分层。如果该层足够浅，一些辐射到达该层的底部并被底部边界吸收。边界会升温，吸收的能量以热流的形式重新释放回流体中。这种热通量可以驱动层内的自然对流。这个系统最近已经过实验检验。如果流体层含有负浮力的颗粒，这些颗粒最初将位于流体层的底部。如果辐射驱动的对流足够强，那么这些粒子就会被提升到气流的主体中。如果这些粒子能够吸收辐射，那么它们将改变气流的平均吸收特性，在气流穿过这一层时吸收更多的辐射，从而潜在地稳定气流。如果气流稳定下来，那么负浮力粒子就会沉降到底部，可能会启动对流和稳定的循环过程。该项目将进行实验室实验，以确定浅层流体层中发生的情况，浅层流体层受到来自上方的辐射的影响，含有黑暗的负浮力粒子。可以通过改变流体的密度（使用盐）来改变颗粒的浮力，并且可以改变流体层的深度。

Radiation can drive natural convection in a shallow fluid layer, such as the near-shore region of lakes or shallow ponds. If the radiation is from above, as it travels through the layer, it is absorbed by the fluid, heating up the top of the layer and creating a stable thermal stratification. If the layer is sufficiently shallow, some radiation reaches the bottom of the layer and is absorbed by the bottom boundary. The boundary will heat up and re-emit the absorbed energy back into the fluid as a heat flux. This heat flux can drive natural convection in the layer. This system has been recently examined experimentally.If the fluid layer contains particles that are negatively buoyant, these will initially sit on the bottom of the layer. If the radiatively-driven convection is sufficiently strong, then these particles are lifted up into the bulk of the flow. If the particles can absorb radiation, then they will change the mean absorption properties of the flow, absorbing more of the radiation as it travels through the layer, potentially stabilising the flow. If the flow is stabilised, then the negatively buoyant particles will settle to the bottom, potentially starting a cyclical process of convection and stabilisation.This project will perform laboratory experiments to identify what occurs in a shallow fluid layer, forced by radiation from above and containing dark, negatively buoyant particles. The buoyancy of the particles can be varied by changing the density of the fluid (using salt) and the depth of the fluid layer can be varied.