Performance of ultrasonic therapy instruments.

Abstract

Heat transfer in fluid flows traditionally is examined in terms oftemperature field and heat-transfer coefficients at non-adiabaticwalls. However, heat transfer may alternatively be considered asthe transport of thermal energy by the total convective-conductiveheat flux in a way analogous to the transport of fluid by the flowfield. The paths followed by the total heat flux are the thermalcounterpart to fluid trajectories and facilitate heat-transfervisualisation in a similar manner as flow visualisation. This hasgreat potential for applications in which insight into the heatfluxes throughout the entire configuration is essential (e.g.cooling systems, heat exchangers). To date this concept has beenrestricted to 2D steady flows. The present study proposes itsgeneralisation to 3D unsteady flows by representing heat transferas the 3D unsteady motion of a virtual fluid subject tocontinuity. This unified ansatz enables heat-transfervisualisation with well-known geometrical methods fromlaminar-mixing studies. These methods lean on the property thatcontinuity ``organises'' fluid trajectories into sets of coherentstructures ( ``flow topology'') that geometrically determine thefluid transport. Decomposition of the flow topology into itsconstituent coherent structures visualises the transport routesand affords insight into the transport properties. Thermaltrajectories form a thermal topology of essentially equivalentcomposition that can be visualised by the same methodology. This thermaltopology is defined in both flow and solid regions and thus describesthe heat transfer throughout the entire domain of interest. The heat-transfer visualisation isprovided with a physical framework and demonstrated by way of representative examples.