Interpretation of the exergy equation for steady-flow processes

We define and discuss the terms in exergy equations, with particular reference to the role of chemical terms in the exergy loss for steady-flow processes. Although there is a chemical contribution to exergy, exergy losses of steady-flow processes may be calculated by using a simple expression for the specific exergy, namely, b = h − T*s. No restrictions are found in the material flows involved. The necessity of prescribing a standard chemical reference environment is considered and rejected. Instead, a sign convention for material flows is proposed. Finally, some results of Brzustowski's calculations are reviewed and discussed

The mechanism of char ignition in fluidized bed combustors

Knowledge about ignition processes of coal in fluidized beds is of importance for the start-up and dynamic control of these combustors. Initial experiments in a transparent fluidized bed scale model showed the existence of a considerable induction period for the ignition of char, especially at low bed temperatures (e.g., 800–950K for bituminous coal). This paper focuses on char-ignition delay at these low temperatures. It is shown that temperature rise during ignition is not caused by coal particle diameter shrinkage but rather by an increase in reactivity. Analysis of the thermal ignition process leads to the conclusion that the process is noncritical, causing a gradual temperature rise without Semenov Jump. Consequences of this result for future research are expounded. Calculated values of the maximum inclination of the heat generation curve (heat release versus coal particle temperature) may be of use to the development of an adequate experimental device

On modular homology in projective space

AbstractFor a vector space V over GF(q) let Lk be the collection of subspaces of dimension k. When R is a field let Mk be the vector space over it with basis Lk. The inclusion map ∂:Mk→Mk−1 then is the linear map defined on this basis via ∂(X)≔∑Y where the sum runs over all subspaces of co-dimension 1 in X. This gives rise to a sequenceM:0←M0←M1←⋯←Mk−1←Mk←⋯which has interesting homological properties if R has characteristic p>0 not dividing q. Following on from earlier papers we introduce the notion of π-homological, π-exact and almost π-exact sequences where π=π(p,q) is some elementary function of the two characteristics. We show that M and many other sequences derived from it are almost π-exact. From this one also obtains an explicit formula for the Brauer character on the homology modules derived from M. For infinite-dimensional spaces we give a general construction which yields π-exact sequences for finitary ideals in the group ring RPΓL(V)

Production of charcoal briquettes from cotton stalk in malawi: methodology for feasibility studies using experiences in Sudan

The feasibility of charcoal production from cotton stalks in Malawi was studied based on experience from Sudan. The country relies considerably on biomass fuels. Of the total energy consumption in Malawi of 2.376 MTOE in 1989, 92% was met by biomass (fuelwood: 83.6% and charcoal: 8.3% Petroleum fuels and ethanol contributed 5.4%; electricity, 1.6%; and coal, 1.0%. Most of the energy (84.8%) was consumed in the household sector. The “Malawi Charcoal Project”, which is the main charcoal project carried out in the country, attempted to produce alternative softwood charcoal from the large resource of pine plantations but was not successful because of unacceptability of the product for household use, long transport distances and costs, and the equipment required for industrial uses. Briquetting of uncarbonized sawdust was also carried out by the Wood Industries Corporation (WICO), but failed due to unacceptability of the products and technical problems. The estimated total national demand for cotton stalk charcoal (CSC) briquettes is 15,000 t yr−1 made up of 7000 and 8000 t yr−1 for household and industrial sectors, respectively. The household demand is most substantial in Blantyre (3500 t yr−1) and Lilongwe (2700). t yr−1 Ngabu town was found to be the most appropriate location for a plant to supply the Blantyre market. Of the many plant options that were found financially and economically viable, four, using drum kilns for carbonization, were the most attractive. These were the 800 t yr−1 agglomeration process with seasonal sun drying operation, 2- and 3-shifts, and the 3000 t yr−1 roll process, year round operation, 2- and 3-shifts with financial internal rates of return of 28.1%, 38.3%, 26.6% and 40.0% respectively and a pay-back period of three years. The agglomeration process was overall the most attractive, though not significantly so financially

The Modular Homology of Inclusion Maps and Group Actions

Communictated by the Managing Editors Let 0 be a finite set of n elements, R a ring of characteristic p>0 and denote by Mk the R-module with k-element subsets of 0 as basis. The set inclusion map: Mk Mk&1 is the homomorphism which associates to a k-element subset 2 the sum (2)=11+12+}}}+1kof all its (k&1)-element subsets 1i. In this paper we study the chain 0 M 0 M 1 M 2}}}M k M k+1 M k+2}}} (*) arising from. We introduce the notion of p-exactness for a sequence and show that any interval of (*) not including Mn 2 or Mn+1 2 respectively, is p-exact for any prime p>0. This result can be extended to various submodules and quotient modules, and we give general constructions for permutation groups on 0 of order not divisible by p. If an interval of (*) , or an equivalent sequence arising from a permutation group on 0, does include the middle term then proper homologies can occur. In these cases we have determined all corresponding Betti numbers. A further application are p-rank formulae for orbit inclusion matrices. 1996 Academic Press, Inc. 1