Droplet-particle collision phenomenon in significant in process applications such as fluidized catalytic cracking. Out of many different possible interactions - it may so happen that a smaller hot particle penetrates a larger subcooled droplet completely. In cases, where temperature difference surpasses the minimum boiling boiling temperature, a vapour film forms around the submerging particle which drastically reduces the heat transfer coefficient. In literature, analysis of a stationary sphere undergoing heat transfer in such cases is given however analysis with the sphere in motion is hardly available. Does any one know how to determine heat transfer coefficient in such case?
One approach can be Inverse Calculation by a numerical method. If you have experimental data, numerical data or any sense of the problem, try to put the known model (coefficient for stationary particle) in a numerical iterative code (!D spherical heat transfer model) and solve it to get convergence. Then gradually change the coefficient by a bigger loop so that the converged solution meets your experimental data.
Hi Amin, thanks for your suggestion.
I agree that this is perhaps a viable way to empirically obtain the HTC.
However even determining the temperature profile and hence the HTC for a moving particle seems a challenging task. For such case, a non-intrusive temperature measurement indeed required which we have plan to do by thermal imaging. Again the problem here is the enclosure of the experimental setup which needs to be transparent to infra red waves.
I was actually thinking about approaching the problem from a mathematical perspective whereby a dependency of the vapour film thickness with the particle motion can be theoretically established.
Turton and Levenspiel [14] recently attempted to measure hp directly for very
fine ( ~ 100-μηι ) particles. The y did this by injecting small cold particles into a
hot fluidized bed (~95°C) . Th e characteristic of these particle s is that when cold they are magnetic, but they lose their magnetic properties when heated above 70°C; hence by noting when the bed becomes nonmagnetic , one can tell when the temperature of the particles rises past 70°C
Since the injection of a single 100-μ m particle did not give a strong
enough signal, aclump of particles had to be injected into the bed . Unfortunately, the time needed to disperse the clump into the cool bed was roughly the same as the heating time for the particles (~ 1 s); hence , the two factors were confounded , and the measured coefficients were lower than
would be found if each particle of the clump was well surrounded by only cold bed solids
Nevertheless, their data lay distinctly above all the other reported measurements , which were whole bed measurements . These results suggest that the heat transfer coefficient for particles in a fluidized bed is best represented by
Eq . (31).
FLODIZATION ENGINEERING BY Levenspiel . CHAPTER 11
I have attached a file with a drawing. The arrangement may help you to simulate the situation experimentally.
Regards,
Dr.S.Ravindran
Dear Ali,
Many thanks for the information. I will look into the reference.
Regards,
SM
Dear Dr. Ravindran,
Many thanks.
Appreciate very much your kind help and the suggested drawing.
In fact this setup was used in the well regarded works of Hendricks (1969) and Dhir & Purohit (1978) on the analysis of film boiling heat transfer around a hot sphere.
The physical scenario, however, for my case is little more complex than this. I am looking into the interaction of small heated ceramic particles (
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