Comments on paper EHT 2006-049 “Pilot scale particle…” by A.Indarto et al. submitted to EHT
This paper reports an investigation of drying of fluidized particles. A nice feature of the paper is that it combines experiments and modelling. However, the results are not very convincing since the residence time is not correctly predicted, which directly impacts on the drying efficiency calculation. On the whole, the paper needs serious revisions. The work should be presented with much more clarity and details. The text should be much more consistent. In addition there are some concerns of fundamental nature as regards the particle force balance. Thus, although the paper is not uninteresting, I would be inclined to recommend rejection of the paper. Some more specific comments are given below, however, so as to help the authors if they are willing to improve significantly their paper. Comments: 1. Title is not adequate. Title should reflect that drying of fluidized particles is the subject of paper. 2. Expression used for FB should be given explicitly. Considering the buoyancy forces as a significant contribution sounds very odd for big particles (on the order of 200 µm and more) of density at least 1000 times greater than the surrounding gas. Hence this part of the paper should be clarified. 3. The local gas velocity is not computed. The flow is probably turbulent. Thus the computation of residence time is quite simplified. The average gas velocity probably varies along the dryer, etc. The fluid mechanics part of the problem is therefore overly simplified. This may explain in part the discrepancies with experiments. The authors should comment on these points in the paper. 4. The method used for solving Eq.(1) must be given 5. Nomenclature is not complete, for example what does ∆TLMTD represent in Eq.(13) ? kf in Eq.(14), etc 6. Analysis of forces (Figure 3b) is not convincing if one does not accept the buoyancy forces as a significant contribution. 7.
Fig3c vertical axis: should be umf and not ug
8. How is the particle temperature measured (p.9 right above Eq.(15) 9. The English needs serious improvements. 10. There are many typos