ABSTRACT
This chapter discusses enhanced extended surface geometries for the plate-and-fin heat exchanger geometry, which is shown in Figure 5.1. Normally, at least one of the fluids used in the plate-and-fin geometry is a gas. In forced convection heat transfer between a gas and a liquid, the heat transfer coefficient of the gas is typically 5 to 20% that of the liquid. The use of extended surfaces will reduce the gas-side thermal resistance. However, the resulting gas-side resistance may still exceed that of the liquid. In this case, it will be advantageous to use specially configured extended surfaces, which provide increased heat transfer coefficients. Such special surface geometries may provide heat transfer coefficients 50 to 150% higher than those given by plain extended surfaces. For heat transfer between gases, such enhanced surfaces will provide a substantial heat exchanger size reduction. There is a trend toward using enhanced surface geometries with liquids for cooling electronic equipment. Data taken for gases may be applied to liquids if the Prandtl number dependency is known. Brinkman et al. [1988] provide data for water and a dielectric fluid (FC-77), but they do not provide a Prandtl number dependency for their data. In the absence of specific data on Prandtl number dependency, one may assume St ∝ Pt-2/3.
