Experimental Investigations Of Flow And Heat Transfer Characteristic Of Honeycomb Catalyst Monoliths

In recent years, with the increased awarence of energy and environment impacts, nearly all the countries have payed a great attention on energy shortage and environment pollution in their development project. Catalyst monolith, as a high-tech product, is widely used in combustion and exhaust emission control. However, traditional flaming combustion of fuels, with low combustion efficiency, often wastes energy. The emissions of pollutants are NOx, UHC and CO. They produce serious environment impacts. Catalytic combustion technology can solve the above problems. This technology makes use of the catalyst, which is coated on the surface of the catalyst monoliths, to reduce activation energy during combustation. In this way, the combustion efficiency is improved and the pollutant emission is reduced. The most difficult problem in the process of catalytic combustion is that catalyst can be easily aged and thus the catalytic capability decreased. The aging of catalyst has a close relationship with its structure as well as the heat and mass transmission characteristics. Therefore,the study of how to reduce the catalyst monoliths temperature, choose proper monolith, and find its inner heat and mass transfer characteristics have great importance to reduce the emission of NOx, enhance combustion efficiency and prolong the service life of catalyst.The convective heat transfer characteristics of honeycomb monoliths were investigated experimentally and the convertion heat transfer coefficient was obtained. The geometrical properties of honeycomb substrate, such as length, cell density and porosity were analyzed accordingly. The results showed that shorter carrier had a high heat transfer coefficient because of Thermal Entrance Effect, but when the air flow is in the fully develop, heat transfer coefficient kept stable. The study also found that the carrier with the same length and porosity, the larger cell density had smaller cell diameter and bigger specific surface area, thus heat transfer coefficient was higher; that with the same cell density and length, the larger porosity had bigger cell diameter and low heat transfer coefficient.The fluid flow characteristics of the honeycomb monoliths were also investigated and both press drop and friction factor were obtained. Our experimental results showed that pressure loss had close relationship with the monolith length, cell-diameter and cell density. Pressure loss increases with the monolith length. Meanwhile, affected by Entrance Effect, the pressure loss was much greater. For the same porosity and length, the shorter diameter had large cell density, poor circulation properties, thus much pressure loss; for the same cell density and length, carrier with larger porosity had long diameter, and good circulation properties, thus less pressure loss.Finally, based on the above experiments, the dimensionless experimental correlation and monolith friction factor experimental correlation were obtained.