Thermo-hydraulic performance of double pass solar air heater duct having semi-circular tubes and perforated blocks as artificial roughness

Abstract

Solar air heaters (SAH) are used to collect and convert the solar radiations into thermal energy for various thermal applications. Its thermo-hydraulic performance can be improved by using various geometries of artificial roughness that breaks the laminar sublayer on absorber plate. In view of the same, a 3-dimensional computational investigation is conducted to study the heat transfer and friction characteristics of a double pass SAH having transverse semi-circular tubes with rectangular perforated blocks as artificial roughness and its outcomes are reported under the present paper. The investigation is carried out for different parameters such as Reynolds number (Re), tube amplitude to duct-height ratio (a/H), relative blockage-height ratio (e/H) and open area ratio (β) within a range of 3000–19,000, 0.2 to 0.5, 0.4 to 0.8 and 13%–30%, respectively. The results obtained through CFD simulations are also compared with the experimental results for a typical set of parameters and a maximum percentage deviation for Nusselt number and friction factor are found as 1.82% and 5.28% respectively. For a considered range of parameters, the maximum value of thermo-hydraulic performance parameter is achieved as 2.51 corresponds to Re of 3000, a/H of 0.3, e/H of 0.4, and β of 30%. Based on the obtained results, it is found that the perforated blocks having maximum value of β and minimum value of e/H results in improved thermo-hydraulic performance of a double pass SAH. The research output of the present study may be useful for designing and optimize the parameters of a double pass SAH for the low temperature applications such as space heating, solar drying and solar air conditioning.