Ramadas Narayanan

Theoretical Modelling of Silica Gel Desiccant Wheels

Desiccant evaporative cooling system is a potential environment-friendly alternative to conventional vapour compression chillers. A desiccant wheel is the heart of this heat driven cooling system and it uses a solid desiccant for dehumidification with silica gel being most widely used. The desiccant material is coated, impregnated or formed in a place on the supporting rotor structure. The matrix consists of multiple channels in the direction of axis of rotation of the wheel. Proper design of the wheel is very important for the successful operation of the system and theoretical models are very useful tool in predicting the performance and design optimization. One of the major difficulties in numerical modelling of the desiccant wheel is the lack of knowledge of adsorption equilibrium of porous medium.In this paper, adsorption equilibria of the silica gel is studied and the different theories existing to characterize the adsorption process and different equations for prediction of adsorption equilibria are compared and used in a theoretical model predicting the wheel performance. The results of the different models are compared with experimental data and conclusions are drawn.

Heat-Driven Cooling Technologies

Heat-driven air-conditioning systems are systems that use low-grade thermal energy like solar energy and waste heat rather than electricity to cool the air. These systems can produce significant energy savings, have low global warming and ozone depletion potential, and also ensure higher indoor air quality. This chapter aims to disseminate the fundamentals of the technologies of heat-driven air conditioning to the wide spectrum of people and to review the latest developments in this area. At first, the heat driven technology is introduced and then different classes of heat-driven chillers such as closed cycle systems and open cycle systems are elaborated. Absorption and adsorption chillers come under the first category, whereas liquid and solid desiccant evaporative cooling systems are open cycle systems. So this chapter has sections on absorption chillers, adsorption chillers, liquid desiccant evaporative cooling system, solid desiccant evaporative cooling systems, desiccant wheel, and developments in this field.

Defining Knowledge Constituents and Contents

While it appears that a consensus is crystalising with regard to the hierarchy of concepts such as “knowledge”, “definition” and “information”, there is an increasing urgency for improving definitions of these terms. Strategies such as “knowledge extraction” or “data mining” rely on the increasing availability of digital (electronic) records addressing almost any aspect of socio-economic realm. Information processors are invaluable in the capacity of turning large amount of data into information. However, a new problem emerged on the surface in this new information environment: numerous concepts and terms are blurred by ambiguous definitions (including the concept of ‘definition’ itself). This triggered a need for mitigating hindrances such as homonymy and synonymy, leading further to demands on the decoding software complexity of which equals the artificial intelligence applications. Information technology presumably copes with this diversity by providing the information decoding ‘tools’. This opens a never-ending opportunity for further permutations of tasks and service abilities. The solution, however, is to address the causes rather than indulge in multiplying the superficial remedies. Clearly, the multiplicity of definitions for the same concepts, false synonyms and so forth show that there is a need for introducing definitions of sufficient dimensionality. In this article, a number of examples of important concepts are presented first to point at the ambiguities associated with them, and then to propose their disambiguation. The minimum intent is to demonstrate how these key terms can be defined to avoid ambiguities such as pleonasm, homonymy, synonymy and circularity. KEywoRDS Ambiguity, Concept, Knowledge