The purpose of this study is to investigate basically the mechanism of heat transfer by the resolution of complex fluid flow inside a sophisticated designed screw dryer for the treatment of sewage sludge by using numerical analysis and experimental study. By doing this, the result was quite helpful to obtain the design criteria for enhancing drying efficiency, thereby achieving the optimal design of a multiple screw type dryer for treating inorganic and organic sludge wastes. One notable design feature of the dryer was to bypass a certain of fraction of the hot combustion gases into the bottom of the screw cylinder, by the fluid flow induction, across the delicately designed holes on the screw surface to agitate internally the sticky sludges. This offers many benefits not only in the enhancement of thermal efficiency even for the high viscosity material but also greater flexibility in the application of system design and operation. However, one careful precaution was made in operation in that when distributing the hot flue gas over the lump of sludge for internal agitation not to make any pore blocking and to avoid too much pressure drop caused by inertial resistance across the lump of sludge. The optimal retention time for rotating the screw at 1 rpm in order to treat 200 kg/hr of sewage sludge was determined empirically about 100 minutes. The corresponding optimal heat source was found to be 150,000 kcal/hr. A series of numerical calculation is performed to resolve flow characteristics in order to assist in the system design as function of important system and operational variables. The numerical calculation is successfully evaluated against experimental temperature profile and flow field characteristics. In general, the calculation results are physically reasonable and consistent in parametric study. In further studies, more quantitative data analyses such as pressure drop across the type and loading of drying sludge will be made for the system evaluation in experiment and calculation.
The purpose of this study was to evaluate the healing process of collagen-apatite composite (CAC) at the titanium-bone interface in animal model. Small gaps (0.5 or 1.0 mm-sized wells) were prepared in the epoxy-resin block implants coated with pure titanium. The gaps were filled with CAC or demineralized freeze-dried bone (DFDB). The titanium-coated epoxy-resin block implants were inserted in the tibia of rabbit for 4 weeks or 8 weeks. The microscopic features of bony healing process in the grafted gaps were examined and analyzed. In the histomorphometric analysis, CAC group showed higher fraction of newly-formed bone than DFDB group in both 0.5 and 1.0 mm gap subgroup at 4-week specimen (P < 0.05). In the transmission electron microscopic examinations, osteoblasts of the newly-formed bone of CAC group showed more cellular activity than that of DFDB group. From the results, it was expected that CAC had more beneficial property on early bony healing process than DFDB at the titanium-bone interface.
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