Internal energy and exergy recovery in high temperature application absorption heat transformers
Abstract In this paper, the design of a triple absorption heat transformer (TAHT) using the working fluids water and lithium bromide is dissected and reassembled using heat exchange network modelling in order to determine the optimum number and locations of internal heat exchange units within the system. It is found that the conventional design of the TAHT does not employ heat exchangers effectively, and that thus by rearranging these units system COP may be increased by 11.7% while exergy destruction within the system (its irreversibility) can be reduced by 21%. Strategically adding an extra one or two heat exchangers increases the COP by 16.4% and 18.8% while decreasing exergy destruction by 28% and 31.5% respectively compared to a conventional TAHT design.
Energy and exergy analysis of a double absorption heat transformer operating with water/lithium bromide
In the present study, the first and second law of thermodynamics have been used to analyze in detail the performance of a double absorption (lift) heat transformer operating with the water–lithium bromide mixture. A mathematical model was developed to estimate the coefficient of performance (COP), the exergy coefficient of performance (ECOP), the total exergy destruction in the system (ΨTD) and the exergy destruction (ΨD) in each one of the main components, as a function of the system temperatures, the efficiency of the economizer (EFEC), the gross temperature lift and flow ratio (FR). The results showed that the generator is the component with the highest irreversibilities or exergy destruction contributing to about 40% of the total exergy destruction in the whole system, reason why this component should be carefully designed and optimized. The results also showed that the COP and ECOP increase with increase in the generator, the evaporator and the absorber–evaporator temperatures and decrease with the absorber and condenser temperatures. Finally, it was observed that the COP and ECOP are very dependent of the FR and the economizer efficiency (EFEC) values. Also the optimum operating region of the analyzed system is shown in the present study. Copyright © 2009 John Wiley & Sons, Ltd.
The structure of electricity demand in the Brazilian household sector
Abstract The present structure of residential electricity demand is analysed by electricity consumption classes and end-uses. Nearly 70% of households consume less than 150 kWh/month and are responsible for 35% of total residential demand. Other determinants of electricity-use, such as income and place of residence, are also discussed. It is found that electricity demand is increasing faster than income as the country reaches appliances saturation in upper consumption levels. Water heating and refrigeration account for the major part of residential consumption. Residential conservation efforts have started introducing more efficient lighting equipment and refrigerators, but further work will have to be done to speed up the diffusion of efficient technology at costs that can be paid by consumers.