Reduction In Average Density Research Articles

Experimental and numerical study of fluid dynamic parameters in a jetting fluidized bed of a binary mixture

The solid circulation pattern, the voidage profile, and the jet penetration height have been investigated experimentally and computationally in a cold-flow model of jetting fluidized beds (JFBs) of a binary mixture in this paper. This rectangular two-dimensional bed is 0.30 m wide and 2.05 m high with a central jet and a conical distributor, which roughly stands for the ash-agglomerating fluidized-bed coal gasifier. A video camera and coloured particle tracer method were employed to explore the fluid dynamics in the bed. In terms of the average physical properties of binary mixtures, a hydrodynamic model describing the gas–solid flow characteristics in a jetting bed is resolved by using a modified Semi-Implicit Method for Pressure-Linked Equation (SIMPLE) algorithm. This paper focuses on three features of the fluid dynamics—solid circulation pattern, voidage profile, and jet penetration height. The solid circulation pattern is composed of three regions: the jetting region, the bubble street, and the annular region. Above the central nozzle the time-averaged isoporosity contours are almost elliptic, while near the walls of the bed, the voidage in high solid concentration region is approximately equal to that at the minimum fluidization state. The jet penetration height increases with increasing jet gas velocity and with decreasing average particle diameter. The increase in weight percentage of the lighter component in the binary system reveals that reduction of average density causes the enlargement of jet penetration height. The simulated results show good agreement with the experimental data.

Simple models for the impact of rabbit calicivirus disease (RCD) on Australasian rabbits

Models are described for simple epidemics of rabbit calicivirus disease (RCD) and for its longer-term effect on non-seasonal or seasonally varying rabbit populations, assuming direct transmission or indirect transmission via free-living virus. The additional effect of juvenile immunity is examined, in which young of a certain age are immune for life if exposed. The models are parameterised from European and Australian data and used to demonstrate the relationships between disease parameters and epidemic intensity and velocity. Disease cannot persist locally, given direct transmission and the rapid epidemics observed. Given indirect transmission, disease persistence depends on the decay rate of virus in the environment and the basic reproductive rate of the disease, R 0. Again, the model suggested that local disease persistence is unlikely given the observed rapidity and intensity of epidemics, particularly in Australia, and given that a proportion of susceptibles survive exposure. If the criterion for the speed of the initial epidemic is relaxed, the models allowed persistent disease with 2-yearly outbreak patterns, as observed in European rabbit populations. Damped 2-yearly cycles in rabbit density were an intrinsic property of the rabbit/RCD system, but adding seasonally varying reproduction caused the biennial cycles to persist indefinitely. When juvenile immunity was added, disease persistence was enhanced and yearly epidemics were more likely than 2-yearly ones. In terms of RCD as a control, persistent disease generally gave around a 75% reduction in average density, while non-persistent disease gave about a 60% reduction if introduced every 3 years. The timing of introduction, whether within or outside the breeding season, appeared to have little effect on suppression and recovery.

Basic Density of Jack Pine Wood Influenced by Fertilization and Thinning

Basic wood density was measured at eight bole positions within and below the green crown in a jack pine (Pinus banksiana, Lamb.) fertilization and thinning trial near Chapleau, Ontario. Analysis showed a 6% reduction of average density in wood laid down during the first 5 years following treatment. A significant height × fertilizer interaction was noted during the same period indicating that bole density gradients specific to fertilized trees should be used to calculate biomass gains from fertilization if substantial underestimates of response are to be avoided. The portion of the bole where the wood changed most rapidly from low density, juvenile-type to higher density mature-type wood appeared to be just beneath the base of the green crown.