Thermal Characterization of Solid Structures during Forced Convection Heating

Abstract

By now the forced convection heating became an important part of our every day life. The success could be thanked to the well controllability, the fast response and the efficient heat transfer of this heating technology. We can meet a lot of different types of forced convection heating methods and equipments in the industry (such as convection soldering oven, convection thermal annealing, paint drying, etc.) and also in our household (such as air conditioning systems, convection fryers, hair dryers, etc.). In every cases the aim of the mentioned applications are to heat or cool some kind of solid materials and structures. If we would like to examine this heating or cooling process with modeling and simulation, first we need to know the physical parameters of the forced convection heating such as the velocity, the pressure and the density space of the flow, together with the temperature distribution and the heat transfer coefficients on the different points of the heated structure. Therefore in this chapter, first we present the mathematical and physical basics of the fluid flow and the convection heating which are needed to the modeling and simulation. We show some models of gas flows trough typical examples in aspect of the heat transfer. We discuss the theory of free-streams, the vertical – radial transformation of gas flows and the radial gas flow layer formation on a plate. The models illustrate how we can study the velocity, pressure and density space in a fluid flow and we also point how these parameters effect on the heat transfer coefficient. After it new types of measuring instrumentations and methods are presented to characterize the temperature distribution in a fluid flow. Calculation methods are also discussed which can determine the heat transfer coefficients according to the dynamic change of the temperature distribution. The ability of the measurements and calculations will be illustrated with two examples. In the first case we determine the heat transfer coefficient distribution under free gas streams. The change of the heat transfer coefficient is examined when the heated surface shoves out the gas stream. In the second case we study the direction characteristics of the heat transfer coefficient in the case of radial flow layers on a plate in function of the height above the plate. It is also studied how the blocking elements towards the flow direction affects on the formation of the radial flow layer. In the last part of our chapter we present how the measured and calculated heat transfer coefficients can be applied during the thermal characterization of solid structures. The mathematical and physical description of a 3D thermal model is discussed. The model based