Optimization of Heat Transfer Systems and Use of the Environmental Exergy Potential - Application to Compact Heat Exchangers and Heat Pumps

Abstract

In this thesis, the optimization of forced convection heat sinks and groundwater-source heat pumps is addressed with the purpose of improving energy efficiency. Parallel ducts heat sinks are considered under constrained (fixed) pressure drop, pumping power and heat transfer rate. The intersection-of-asymptotes method is employed together with numerical simulations and relationships for determining optimum hydraulic diameter are put forward. An optimal design emerges under fixed heat transfer rate, which matches that found through the joint minimization of pressure drop and pumping power. With regard to heat pumps optimization, the relation between coefficient-of-performance and air-to-ground exergy potential is established, showing that energy saving as compared to air-to-air systems depends on the square root of that potential. The exergy potential in the Evora region is estimated, and exergy analysis of groundwater-source systems helps identifying distinct conditions of operation: maximum/null net exergy output and best trade-off between environmental exergy utilization and power input.