Mechanism and Control of Heat Transfer in Gas-Solid Two-Phase Flow

摘要

This paper discusses the characteristics, heat transfer mechanisms, and heat transfer control options for gas-solid two-phase flow, including solid particles in the gas phase flow from the viewpoint of heat transfer engineering. Gas-solid two-phase flow is a heat transfer medium intended "to bring out only merits of both" for gas phase flow which has inferior thermal conductivity and heat capacity though it has superior flowability, and solid particles that have no flowability though are superior for thermal conductivity and heat capacity. The fundamental heat transfer characteristics of gas-solid two-phase are governed by the exchange (giving and receiving) of thermal energy with solid particles, and heat transportation due to particle motion. Consequently it is possible to control the heat transfer characteristics by controlling the motion of the particles. It is possible to say that this point is much different than for porous and packed bodies which are practical refractory applications. On the other hand, gas-solid two-phase flow is a mixture of gas phase flow and solid particles that have quite different characteristics from both thermal and kinetic points of view and consequently it is unavoidable that the handling becomes difficult compared with that of single phase flow. And also as mentioned above, enhancing the interaction between heat transfer surfaces and solid particles to improve the heat transfer characteristics certainly brings about the problem of corrosion damage of the heat transfer surfaces due to solid particles, from the engineering perspective. Judging from these various situations, it is possible to conclude that gas-solid two-phase flow should be applied in suitable fields as a special medium for heat transfer, although it has the very attractive point of having the similar heat transfer characteristics as that of a liquid even under high temperature conditions. The topic of this paper may be rather different than the other papers in this journal, involving refractories, but the author would greatly appreciate if this paper will provide the readers with valuable data and information in the study of heat transfer within the heating media of gas-solid systems, including porous bodies.