The effects of wall curvature and adverse pressure gradient on air ducts in HVAC systems using turbulent entropy generation analysis

Abstract

Abstract In the present study, entropy generation analysis of turbulent boundary layer was carried out to examine the effects of the wall curvature and adverse pressure gradient (APG) on air distribution ducts in HVAC systems considering both individual and simultaneous effects of these parameters and using the empirical data. Six walls, including straight wall (A), convex curved wall (B1), concave curved wall (B2), straight wall with APG (D), convex curved wall with APG (C1), and concave curved wall with APG (C2) were investigated. The air distribution ducts can be divided into various geometries, including straight duct (A*), curved duct (B*), straight diffuser (D*), and curved diffuser (C*). Furthermore, for walls with APG (D, C1, and C2), the divergence angle was chosen in such a way that no flow separation occurred in the range under consideration. The findings showed that the entropy generation resulted from turbulence dissipation was highly important in the regions near the boundary layer edge, so that the ratio of the entropy generation rate due to the turbulence dissipation to the total entropy generation rate in the regions near the boundary layer edge approximates 0.9. In fact, in these regions, a large portion of the total entropy generation rate was related to turbulence dissipation. Consequently, the turbulence dissipation in these regions was too large to be ignored. Thus, in order to achieve a more precise criterion of the dissipation of air distribution ducts in HVAC systems, the turbulence dissipation should be taken into account.