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.
Exergy analysis of a heat transformer for water purification increasing heat source temperature
Abstract In the present study, the first and second laws of thermodynamic have been used to analyse in detail the performance of a heat transformer used for water purification. The heat delivered in the auxiliary condenser is recycled into the system increasing the heat source temperatures and therefore the coefficient of performance (COP) and the exergy coefficient of performance (ECOP). Plots of COP, ECOP, the improvement potential (IP) and the cycle irreversibility (ICYCLE) are shown against the main operating temperatures of the system, the gross temperature lift (GTL), the flow ratio (FR) and the effectiveness of the economiser (EFEC). In order to found the components of the system with the highest irreversibilities, plots of the irreversibilities for each one of the main components of the system are reported against the main temperatures and operating parameters of the heat transformer. The results showed that the highest irreversibilities occurred in the absorber contributing with more than the 30% of the irreversibilities of the entire system, followed by the auxiliary condenser with about the 25%. The lowest irreversibilities were found in the pumps which are almost negligible and in the economiser which were in general lower than 5%.
Laminar heat or mass transfer in rectangular channels and in cylindrical tubes for fully developed flow: comparison of solutions obtained for various boundary conditions
Abstract A comparison is made of results obtained with various boundary conditions at the wall of the channels. By comparing blood Sherwood numbers for finite wall resistance with those for constant concentration boundary condition only a small variation is found for various points along the blood channel.