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

本文研究了气固两相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.辐射在流化颗粒层中的穿透。首先，从浸没在流化床中的表面的辐射传递进行了实验研究;单色激光通过表面投射到流化颗粒中，并测量颗粒内激光的强度分布。结果表明，辐射在颗粒乳状液中的穿透深度较小，但辐射几乎不被流化颗粒的“气泡相”散射。这些结果表明，传热表面对流化颗粒的辐射传递受传热表面热边界层厚度与颗粒辐射穿透深度的关系所支配。 关于我们 .传热表面附近流化颗粒的辐射。从与传热表面相邻的流化颗粒发射的辐射通过IR热成像法测量;流化颗粒从传热表面加热，该传热表面对于IR辐射是透明的，并且从颗粒发射的辐射的强度通过IR热照相机测量。结果表明，随着流化气流量的增加，颗粒的红外辐射强度降低，而随着流化气流量的增加，颗粒的红外辐射强度增加。这些结果表明，当颗粒浓度较低且对辐射透明时，高温气固悬浮流中的辐射强化传热效果明显.流化床内辐射传热的实验评价。为了证实上述结果，高温传热表面和流化颗粒之间的辐射传热进行了实验研究;使用三种不同材料的颗粒，以检查颗粒发射率的影响。两个不同的发射率，这是加热到1200 K的传热表面，用于评估从传热表面的辐射传热。实验结果表明，在我们的实验条件下，只有当使用氧化铝颗粒，这是相对透明的红外辐射，观察到明显的辐射传热。这一结果与我们在上述研究中估计的结果吻合得很好。此外，还研究了循环流化颗粒单元的传热，以开发控制传热表面附近流化颗粒空隙率分布的技术，该技术控制来自或到流化颗粒的辐射传热。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