Effects of Properties and Behavior of Particles Laden with High Temperature Gas Flow on the Heat Transfer Augmentation and Control

在本研究项目中，研究了气固悬浮流中颗粒的性质和行为对辐射换热的影响。主要研究结果如下：1.辐射在流态化颗粒层中的穿透。首先，实验研究了浸没在流态化床中的表面的辐射传递，通过表面向流态化颗粒投射单色激光，并测量了激光在颗粒内的光强分布。结果表明，粒子乳状液中的辐射穿透深度较小，但流态化粒子的“气泡相”对辐射几乎没有散射。这些结果表明，表面热边界层厚度与颗粒辐射穿透深度之间的关系决定了从受热面到流态化颗粒的辐射传递。2…更多。从靠近换热表面的流态化颗粒发出的辐射。用红外热像仪测量了靠近换热表面的流态化颗粒的辐射，流态化颗粒从对红外辐射透明的换热面加热，并用红外热像仪测量了颗粒发出的辐射强度。结果表明，受热颗粒的辐射强度随着流态化气体流量的增加而减小，即流态化颗粒的含气率越高，辐射强度越大。这些结果表明，当颗粒稀薄且对辐射透明时，高温气固悬浮流中辐射对换热的强化作用是明显的。沸腾床内辐射换热的实验评价为了验证上述结果，对高温换热表面与流态化颗粒之间的辐射换热进行了实验研究，并使用三种不同材料的颗粒来考察颗粒发射率的影响。对加热到1200K的两种不同发射率的换热表面进行了辐射换热计算。实验结果表明，在本实验条件下，只有当氧化铝颗粒对红外辐射相对透明时，才能观察到明显的辐射换热。这一结果与我们在上述研究中估计的结果很好地吻合。此外，还对循环流态化颗粒槽的传热进行了研究，以期开发出控制流态化颗粒在传热面附近的空泡率分布的技术，而空泡率分布是流态化颗粒辐射换热的主导因素。较少

In the present research project, effects of the properties and behavior of the particles laden with a gas-solid suspension flow on the radiation heat transfer were examined. The results are summarized into the followings :1. Penetration of Radiation within a Fluidized Particle Layr. First of all, radiation transfer from a surface immersed in a fluidized bed was experimentally examined ; a monochromatic laser light was projected into the fluidized particles through the surface, and intensity distributions of the laser light were measured within the particles. The results showed that the radiation penetration depth in the particle emulsion is relatively small, but that the radiation is hardly scattered by the "bubble phase" of fluidized particles. These results suggests that the radiation transfer from a heat transfer surface to fluidized particles is dominated by the relation between the thickness of thermal boundary layr on the surface and the radiation penetration depth of particles.2 … More . Radiation Emitted from the Fluidized Particles Adjacent to the Heat Transfer Surface. Radiation emitted from the fluidized particles adjacent to a heat transfer surface was measured by means of IR thermography ; fluidized particles were heated from a heat transfer surface, which was a transparent for the IR radiation, and intensity of the radiation emitted from the particles was measured by a IR thermo-camera. The results showed that the radiation emitted from the heated particles decreases with increasing the fluidizing gas flow rate, i.e. void fraction of the fluidized particles, and that the intensity of radiation increases as the fluidized particles become "black" for IR radiation. These results mean that the heat transfer augmentation due to radiation in a high-temperature gas-solid suspension flow is evident when the particles are dilute and transparent for radiation.3. Experimental Evaluation of Radiation Heat Transfer in a Fluidized Bed. In order to confirm the results described above, radiation heat transfer between a high-temperature heat transfer surface and fluidized particles was experimentally examined ; particles of three different materials were used so as to examine the effects of particle emissivity. Heat transfer surfaces of two different emissivity, which were heated upto 1200 K, were used for evaluating the radiation heat transfer from the heat transfer surface. The experimental results showed that, under our experimental conditions, evident radiation heat transfer was observed only when the alumina particles, which are relatively transparent for IR radiation, were used. This result coincides well with the ones estimated in our stury described above. In addition to these, heat transfer of a circulating fluidized particle cell was examined so as to develop the control technique for void fraction distribution of the fluidized particles adjacent to the heat transfer surface, which dominates the radiative heat transfer from or to the fluidized particles. Less