No abstract

To increase the efficiency of any heat transfer processes which involves heat recovery from hot fluid or removal of excess heat via processing of cold fluid, the loss in available energy due to various irreversibilities must be analyzed in terms of entropy generation. In the present study, hot or cold fluid is passed through the inclined tubes with a square cross section, and the entropy generation characteristics within the entrapped fluid in triangular space during natural convection is the subject of investigation. The tubes are surrounded by cold fluid while hot fluid is passed through the tubes and vice versa. Thus, hot inclined walls with cold horizontal walls (case 1) and cold inclined walls with hot horizontal walls (case 2) are considered as boundary conditions during convection (Ra = 103 to 105) for various fluids (Pr = 0.015, 0.7, and 1000) within/surrounded by the tubes. Entropy generation maps (S θ and S ψ) with heat transfer characteristics (ψ and θ) are analyzed for both the cases. Minimum spatial active zones of S θ and S ψ are found in the lower and upper triangles with case 1 and case 2, respectively. On the other hand, maximum spatial active zones of S θ and S ψ are observed inside the upper and lower triangles with case 1 and case 2, respectively. High S total and low Be av are observed inside the upper and lower triangles for case 1 and case 2, respectively, for all Pr at Ra = 105. On the other hand, heat transfer rate and fluid flow are independent of Ra and Pr within the upper triangular cavity for case 2 and lower triangular cavity for case 1. Overall, high Pr fluids may be used inside the upper triangle with case 1 and lower triangle with case 2 within 7 × 103 ≤ Ra ≤ 5 × 104, whereas low Pr fluids may be used for upper triangle with case 2 and lower triangle with case 1 boundary conditions in the range of 104 ≤ Ra ≤ 9 × 104 for large heat transfer rates with less entropy generation.