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Cooling curves for the four temperature monitoring points for each of the four heat transfer cases studied. The inlet diffusor cone angle was 45°. The heat transfer mechanisms in the inlet diffusor are a conduction only, b conduction and radiation, c conduction and natural convection and d all three heat transfer mechanisms
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This paper presents a computational study of the static cooling of a catalytic converter with a monolith system. Under conditions without gas flow, the converter cools by convection and radiation to the surroundings. Internally, heat transfer occurs by conduction, natural convection and radiation. The monolith has a high initial temperature and is...
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Citations
... Important heat transfer phenomena within an EAT device include heat conduction within the substrate wall and heat convection between the gas flow and the substrate. Radiative heat transfer is rarely included in EAT models [226], although it can be an important process above 600 • C which can be encountered during uncontrolled regeneration [227]. ...
This thesis presents the development and application of a computational model for optimisation and investigation of rare behaviours of exhaust after-treatment systems. Firstly, the performance of the model is critically assessed for various after-treatment devices against literature data, including a diesel oxidation catalyst (DOC), a selective catalytic reduction (SCR) device and a diesel particulate filter (DPF). The model is then applied to study the impact of the configuration of a multi-device after-treatment system. An after-treatment design case study for a heavy-duty diesel engine is performed. The case study showed that the DOC-DPF-SCR layout can lead to better fuel economy in the engine than the DOC-SCR-DPF layout. The commonly claimed promotional effect of the DOC on the SCR performance in the SCR-front layout is not observed in the case study. A flux analysis is performed which explains why the DOC-SCR-DPF configuration is less preferable for the particular SCR catalyst employed. Transient particulate emission from an active regenerating DPF is investigated using the model. The filtration model is extended based on experimentally observed non-uniform combustion of the soot cake layer and a reduction in filtration efficiency of the filter wall at high temperature. The extended model is shown to be able to better describe the elevated particulate emission during active regeneration in both the timing of particle breakthrough and the final steady filtration efficiency of the hot regenerated DPF. The viability of thermal treatment as an ash management strategy for ash-contaminated particulate filters is investigated. The model is applied to simulate the deposition of soot and ash particles in order to estimate the spatial distribution of ash deposits within the particulate filters. The introduction of phenomenological sintering and cracking models for ash deposits shows good agreement between model predicted and experimentally measured pressure drop of thermally treated filters. Crack formation in the ash layer is identified to be the most important phenomenon for a successful thermal treatment.
... Finally, radiation can play a significant role in the static cooling of monoliths, that is, under conditions of no flow. [28] A summary of radiation techniques can be found in our book. [3] We should note that current commercial modelling software, such as COMSOL and Fluent, incorporate complex radiation models, so accounting for it is more straightforward. ...
The honeycomb type monolith reactor dominates the field of catalytic automotive exhaust gas after treatment systems and is increasingly being used in other applications. Advanced computational modelling of such systems can provide valuable insight into their operating characteristics and be used as a design tool. This reactor provides an excellent example of a multi-scale modelling challenge with many complexities. This paper provides a perspective on the development and use of computational modelling tools in this context over the last 30 years, with an emphasis on the work published by the researchers at the University of Alberta. This paper covers all aspects of model development, including single channel and full-scale reactor models and inter and intra mass and heat transfer effects, with the latter including radiation.
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