The use of liquid crystal thermography and particle image velocimetry in the exploration of heat transfer measurements
Generation of vortices enhances heat transfer by swirl, flow destabilization and development of viscous layers. They may increase heat transfer by several hundred percent. Prior to the use of vortices to influence heat transfer it must be known how different vortices are generated and controlled, and how they interact with the base flow and temperature field. To select the most appropriate vortex generators (VG) for a given task it is necessary to know the heat transfer and flow losses associated with the generation of a specific vortex system. The aim of the paper is to asses the state of art and to encourage exploration of heat transfer control by vortices. Flow visualization and heat transfer experiments were conducted using an open low-speed wind tunnel equipped with Liquid Crystals Thermography (LCT) and Particle Image Velocimetry (PIV). In this work we consider five types of transverse vortex generators (TVGs) which where brought to required temperatures by the hot film method. Heat transfer measurements were carried out by LCT.
Validation of a smooth configuration surface for compact heat exchangers using a numerical method/Validación de la superficie de un intercambiador de calor compacto en configuración lisa utilizando un método numérico
This work determines the thermo hydraulics behavior of smooth configuration surface for a compact heat exchanger by means of numerical simulation. The objective is to use the results as baseline for research in the enhancement of heat transfer and drag reduction, directed to reduce the energy consumption and diminish the environmental impact. The fin tube heat exchanger models described. The constraints used in the implementation of the equation solver are announced. The average heat transfer coefficient and pressure drop obtained from numerical simulation are compare to experimental results presented in literature for models with the same dimensions and configuration. A good agreement between numerical and experimental results is reached. Local mechanisms responsible for the heat transfer and pressure drop are detailed. The study is conducted inside the laminar regime for frontal velocities ranging between 0.5 and 6 m/s..
Onset of natural convection in a cube
The problem of transient natural convection in a cube-shaped cavity is investigated ex- perimentally and numerically. The motion is driven by a sudden temperature difference ap- plied to two opposite side walls of the vessel. The experiments are performed at a Rayleigh number of 1:66 10 5 and a Prandtl number of 1109, inside a 5 5 5cm 3 cavity made of plexiglas, with two isothermal copper walls kept at a prescribed temperature. Numeri- cal simulation has been performed using a nite difference vorticity-velocity model of the Navier-Stokes equation with the Boussinesq approximation. The theoretical predictions are found to be in a good agreement with the experimental results.