“ Trends in the Development of Machinery and Associated Technology ” TMT 2008 , Istanbul , Turkey , 26-30 August , 2008 NUMERICAL ANALYSIS OF THE EFFECT OF OPERATIONAL PARAMETERS OF HEAT TRANSFER SURFACES IN CFBS
The design or scale-up of heat transfer systems in fluidized beds require estimation of the effective heat transfer coefficient on heat transfer surfaces in contact with the fluidized medium. In this study, the effects of operational parameters on bed-to-wall heat transfer in CFBs is investigated such as solids volume fraction, particle diameter, suspension density, superficial velocity and solid circulation rate, using modified cluster renewal model. In the modified cluster renewal model, the gas phase properties are used for the dilute phase and similarly the solid phase properties are used for the cluster phase. The gas phase and the solid phase properties are considered in the control volume which is in the vicinity of the heat transfer surface.
Performance of an Entrained-Particle Heat Exchanger
An experimental investigation was carried out to determine the thermal performance of a heat exchanger operating with vertical upflow of a hot gas loaded with solid particles. Using particles having mean diameters (88-157 μm), the inlet gas velocity was varied from 1.5 to 13 m/s and the inlet temperature was varied from 100 to 600°C. This resulted in mixture densities of 2.0 to 30 kg/m3 for the gas-solid flow. The results showed that thermal performance improved with the addition of solid particles to the gas stream. At a given gas velocity, the gas-side coefficient could be increased by factors of 2 to 4 with the addition of solid particles. The exchanger performance was enhanced with increasing solid loading, decreasing particle size, and increasing gas temperature.
Atmospheric drag effects on the KOMPSAT-1 satellite during geomagnetic superstorms
We examine the atmospheric drag on the low earth-orbiting satellite, KOMPSAT-1 in a sun-synchronous orbit at ~685-km altitude starting in 1999, during a 3-month (October-December) period in 2003. This 3-month interval includes the October 29-30 and November 20 magnetic superstorms and weak to moderate storms. We observed that the daily KOMPSAT-1 drag acceleration transiently responses to transient storm-time disturbances. That is, there is an one-to-one correspondence between the KOMPSAT-1 drag accelerations and the storm events. We find that the drag acceleration correlates strongly with the level of geomagnetic disturbance. This indicates that the trajectory of KOMPSAT-1 is significantly perturbed during extremely disturbed intervals because of atmospheric density increase. The main contributor to the density increase is Joule heating associated with the geomagnetic activity rather than the solar EUV radiation, as reported by previous studies. We suggest that understanding how the upper atmosphere responses to the geomagnetic-associated heating is important to predict space weather impacts on low earth-orbiting satellites.