New Developments in Reboilers and Evaporators

Abstract

A prototype cooling tower was used to explore the potential of using cooling towers compared with radiator cooling systems with 3 MW diesel engines. The working parameters were the water mass flow rate, water inlet temperature, air mass flow rate, and humidity ratio. The water mass flow rate was relatively the most effective. Three methods of calculation were used to evaluate performance—namely, heat and mass balance, psychrometric chart, and the heat and mass transfer method. The first was the best in comparison with experiments. The economic analysis of both the cooling tower and radiator systems showed that it would be more economical in the long run to use cooling towers for diesel engines.     

Higher dimensional problems in the discrete calculus of variations †

The purpose of this paper is to formulate a calculus of variations for certain discrete systems which are governed by second order partial difference equations. This is accomplished by deriving necessary conditions for a multiple sum to be extremal. The procedure used to obtain the necessary conditions yields boundary terms which in turn load to natural boundary conditions and conservation laws for the discrete system.     

A heuristic approach to the hierarchical control of multivariable serially connected dynamical systems

A heuristic approach is developed for the control of serially connected dynamical systems with and without time delays between the subsystems. The approach enables near optimal control to be achieved and has particularly modest computational requirements. This is illustrated in a number of examples where the overall optimal and the heuristic strategy are compared by digital simulation. Finally, a method is developed for calculating bounds on the suboptimality of the strategy and a numerical example illustrates the approach.     

Adaptive min-max filtering in spread-spectrum channels with very fast frequency-hop disturbances

A min-max filtering technique is presented which uses a semi-adaptive policy to filter out a narrowband jammer in a spread-spectrum channel. This technique is compared with adaptive whitening and is shown to be superior because of its reduced computational requirements and its improved signal-to-noise ratio for cases of very fast frequency-hop jamming where there is insufficient time for adequate signal identification as required for least-squares whitening filters.     

Information extraction from remotely sensed data.

Digital image processing is now widely available for users of remotely sensed data. Although such processing offers many new opportunities for the user (or analyst) it also makes heavy demands on the acquisition of new skills, if the data are to yield useful information efficiently. In deciding on the best approach for image classification the user faces a bewildering array of choices, many of which have been poorly evaluated. It is clear, however, that the use of both internal and external contextual information can be of great value in improving classification performance. The ultimate use of information extracted from remote sensing data is strongly affected by its compatability with other geographic data planes. Problems in achieving such compatibility in the framework of automated geographical information systems are discussed. The success of image analysis and classification methods is highly dependent on the relationships between the abilities of sensing systems themselves and the character of the phenomena being studied. This is illustrated by reference to the capabilities of future high resolution satellite systems.     

Migratory bird habitat monitoring through remote sensing

Abstract

Unsupervised classification of Landsat-TM data was employed to identify habitats important for migratory birds in Costa Rica. The overall habitat classification accuracy was 70 per cent (Kappa correction). Mature forest could be identified with high accuracy (93 per cent) but Landsat-TM classification accuracy for major successional stages was low. Habitat availability and conversion rates from 1976 to 1986 were derived from multidate Landsat imagery supplemented with interpretation of historical air photos to document the specific types of habitat change. The major trend in habitat conversion between 1976 and 1984 was forest clearing followed by establishment of permanent pasture. Some of the pasture land was converted to perennial tree crops by 1986. The implication of habitat modification on groups and species of migrant land birds are discussed.