Heat Transfer-Friction Factor and Correlations for Wavy Porous Screens as Inserts in Channel Thermal Performance

Structural inserts are employed to enhance the heat transfer in channel flow with the expense of thermal performance. The present investigation employs the wavy porous screens as inserts in an air channel and measures the pressure drop and heat transfer along the channel. The wave vectors are parallel to the flow and in point contact at the tips with the channel walls. The pores in the insert generate turbulence to enhance the heat transfer from the channel walls with a moderate pressure penalty because of the low blockage ratio. The objectives are to investigate the effects of wavelength (λ), porosity (ξ), and height (H) of the sinusoidal wave of the insert as well as the Reynolds number (Re) on the friction factors (f) and Nusselt numbers (Nu). Twelve inserts are formed from the flat metal mesh screens for testing between the Reynolds number (Re) of 400 and 35,000. The results of (f, Nu) and smooth channel-based enhancements (f/f₀, Nu/Nu₀) are affected the most by Re followed by λ and then ξ. The values of both (f/f₀, Nu/Nu₀) increase significantly as the Reynolds number increases in Re < 3000. However, both the (f/f₀, Nu/Nu₀) decrease little as both the (λ, ξ) increase at all Re. The performance factor index, (Nu/Nu₀)/(f/f₀)^(1/3) > 1.0 irrespective of (λ, ξ, H) only when Re is about 3000. The correlations developed for the f, Nu, and performance factor provide reasonable predictions of the experimental results.