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..
Turbine blade temperature calculation and life estimation - a sensitivity analysis
Abstract The overall operating cost of the modern gas turbines is greatly influenced by the durability of hot section components operating at high temperatures. In turbine operating conditions, some defects may occur which can decrease hot section life. In the present paper, methods used for calculating blade temperature and life are demonstrated and validated. Using these methods, a set of sensitivity analyses on the parameters affecting temperature and life of a high pressure, high temperature turbine first stage blade is carried out. Investigated uncertainties are: (1) blade coating thickness, (2) coolant inlet pressure and temperature (as a result of secondary air system), and (3) gas turbine load variation. Results show that increasing thermal barrier coating thickness by 3 times, leads to rise in the blade life by 9 times. In addition, considering inlet cooling temperature and pressure, deviation in temperature has greater effect on blade life. One of the interesting points that can be realized from the results is that 300 hours operation at 70% load can be equal to one hour operation at base load.