Using Porous Media to Improve the Performance of a Wavy-tube Heat Exchanger

Heat transfer increase has been always the industries' aim. One of the methods to increase heat transfer is to manufacture heat exchangers with specific geometries such as wavy-tube heat exchangers. In this study, effects of inserting homogenous porous media to amplitudes of a wavy-tube heat exchanger have been investigated. A pipe with a length of 4 lambda (lambda is the wavelength) was considered. Surface waviness has been introduced by L*, which is the ratio of wavelength to half of the amplitude. The computations were repeated for three different L* values including 11, 19 and 25. Effects of surface waviness and porous media properties including porosity and Darcy number on the heat transfer and pressure drop for a fully-developed laminar flow are provided. Results show that using porous media will lead to both heat transfer and pressure drop increase. The heat exchanger's efficieny was measured by Performance Evaluation Criteria (PEC) which is the ratio of heat transfer increase to pressure drop increase. It was observed that for 10(-6) <= Da <= 10(-4), filling the amplitudes out with porous media with thicknesses less than the amplitude will result in the maximum PEC while for 10(-4) <= Da <= 10(-2), filling out thoroughly will result in the maximum PEC. In addition, it was found that there is an optimized porosity to have the maximum PEC for the constant Darcy number.