Browsing by Subject "Heat transfer"

This dissertation shows the use of Constructal law to find the relation between the morphing of the system configuration and the improvements in the global performance of the complex flow system. It shows that the better features of both flow and heat transfer architecture can be found and predicted by using the constructal law in energy systems. Chapter 2 shows the effect of flow configuration on the heat transfer performance of a spiral shaped pipe embedded in a cylindrical conducting volume. Several configurations were considered. The optimal spacings between the spiral turns and spire planes exist, such that the volumetric heat transfer rate is maximal. The optimized features of the heat transfer architecture are robust. Chapter 3 shows the heat transfer performance of a helically shaped pipe embedded in a cylindrical conducting volume. It shows that the optimized features of the heat transfer architecture are robust with respect to changes in several physical parameters. Chapter 4 reports analytically the formulas for effective permeability in several configurations of fissured systems, using the closed-form description of tree networks designed to provide flow access. The permeability formulas do not vary much from one tree design to the next, suggesting that similar formulas may apply to naturally fissured porous media with unknown precise details, which occur in natural reservoirs. Chapter 5 illustrates a counterflow heat exchanger consists of two plenums with a core. The results show that the overall flow and thermal resistance are lowest when the core is absent. Overall, the constructal design governs the evolution of flow configuration in nature and energy systems.

The problem of inadequate sanitation in less developed countries has dire health consequences such as diarrheal diseases. A household-scale sanitation system consisting of an anaerobic digester, heat exchanger, and biogas-powered heater, was developed to provide a simple, potentially low cost and low carbon-footprint solution to this problem. A conceptual model was developed to predict the effectiveness of the heat sterilization system in reaching the appropriate temperatures to significantly inactivate pathogens such as E. coli, helminthe ova, and viruses. Lab experiments with a stainless steel heater and exchanger were used to establish model parameters and to verify the model. Though the model sometimes predicts higher or lower values than the experimental data, probably due to uncertainties in pathogen decay constants and in the different heat transfer coefficients, the model adequately predicts temperature across the heat exchanger and heater, and can provide a preliminary estimate of pathogen inactivation within the system. Both disinfection experiments showed the system reduces E. coli concentrations to below the WHO limit, which was predicted by the model.