A computer model is presented for the calculation of the steady and
nonsteady behavior of
straw bales subject to surface combustion in cigar burners. The
mathematical formulation is
one-dimensional and the flow of gas through the straw bales is
described by means of Darcy's
law for flow through a porous medium. The computer model is able
to predict flow rate,
temperature and composition of gas and straw as function of axial
length and time. Calculated
results are compared to measurements of temperature and gas composition
profiles within the
burning straw bales. It is observed that the straw bale
temperatures as well as the outlet gas
composition are predicted reasonably well. Calculations have been
carried out in order to assess
the implication of a straw bale feed stop upon combustion in a 3 MW
district heating plant fueled
with Heston straw bales. The results indicate that serious
disturbances may be introduced.
The kinetics of a Sic chemical vapour deposition and infiltration process were studied. Sill and C284 were used as precursors: S i S tg) * 1/2C2a(~-Pi~(s) + 311t(g) The composition and microstructure of the resulting coatings were investigated. Furthermore the deposition rate on the surface as well as in pores of the substrate were studied. To this end, graphite substrates vere used rhac were provided with model pores: cylindrical holes 200-1000 n in diameter. The thickness profile of the Sic coating on the pore wall was measured using Scanning Electron Microscopy. The dependency of this profile on the various process parameters like: temperature, total pressure, gas composition and flow rate was studied. The results obtained in the present investigation vere compared to those obtained by other investigators (Fitzer, van den Brekel, Bossignol) and their respective chemical vapour infiltration models. Apart from this fund~ental approach to the CVI procese, a CVI apparatus is being developed for manufacfuring ceramic/cersmic composites. Fibrous preforms of either graphite or silicon carbide will be densified in this apparatus by CVI. The main goal of the present project is to produce denoe ceramic composite8 in this apparatus using CYK in a combined temperature and pressure gradient accroas the fibrous preform. The resulting C/SiC and SiC/SiC composites will be characterized in terms of their microstructure and porousity, vith special attention being given to the fibre-matrix interface. Furthermore high temperature mechanical and corroeion properties will be determined in various atmospheres.
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