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The effect of circumferential corrugations on the thermo-exergetic and economic efficiency of the helical tube is numerically studied for the first time. In the field of heat transfer enhancement, not only the heat transfer characteristics of the heat exchanger are important, but also the economic and financial issues play a key role. Hence, the present study is devoted to investigating both the thermal and economic advantages of using circumferential corrugations in a helical tube that has not been addressed in the literature before. In the present study, thermo-frictional properties of the circumferential corrugated tube as well as to PEC factor (Performance Evaluation Criteria) and Exergo-economic efficiency parameters are presented. Corrugations with three different pitch and depth were investigated. The tube wall had a constant temperature of 333.15 K. Results revealed that applying circumferential corrugation would lead to up to 1.54 times increment in the Nu number as well as 6.67 times increment of net profit per unit transferred heat load ( η p ) . Also, it was found that the total price of the unit transferred heat load ( η c ) of a corrugated tube could be up to 9% less than that of a smooth tube.

The fluid flow and mixed convection heat transfer of a non-Newtonian (Cu–water) nanofluid-filled circular annulus enclosure in a magnetic field are investigated numerically for a two-dimensional, steady-state, incompressible, laminar flow using the Galerkin finite element method (GFEM). The Prandtl number (Pr = 6.2) and Grashof number (Gr = 100) are assumed to be constants, whereas the Richardson number varies within a range of 0 ≤ Ri ≤ 1, the Hartman number within a range of 0 ≤ Ha ≤60, the Power law index within a range of 0.2 ≤ n ≤ 1.4, and the volume fraction within a range of 0 ≤ φ ≤ 1. The enclosure consists of an outer rotating cylinder that is kept at a cold temperature (Tc) and an inner non-rotating cylinder kept at a hot temperature (Th). The ratio of the inner circular diameter to the annulus space length is kept constant at 2. The results depict that the stream function increases with increasing power law index, even up to n = 1, which causes the fluid to behave as a Newtonian fluid. The magnetic field has a critical impact on the fluid flow pattern. The average Nusselt number increases with decreasing Richardson number, owing to the improved heat transfer by forced convection., Mechanical engineering; Computational fluid dynamics; Nanofluidics; Heat transfer; Magnetohydrodynamics; Computational mechanics; Nanoparticles; Magnetic field; Mixed convection; Annulus circular enclosure; Non-Newtonian fluid; Nanofluid

Heatlines visualization of natural convection heat transfer in trapezoidal-shape cavity filled with nanofluid (TiO2-water) and divided by horizontal porous media partition has been studied numerically using finite element method. Non-uniform temperature is applied at the bottom wall and cold temperature applied to the top wall while two inclined vertical walls were insulated. In this work the influence of many parameters such as, Rayleigh number (103≤Ra≤105), partition porous thickness (0.05≤TH≤0.6), partition porous position (0.15≤HD≤0.75), Darcy number (10−5≤Da≤10−1) and volume of fraction (0≤φ≤0.1). Results are exhibited by means heatlines, isotherms, streamlines rather than local and average Nusselt number. The results show that at a constant Rayleigh number equal to (105) and thickness of porous partition (0.1), the percentage enhancement of heat transfer along the bottom wall with the addition of nanoparticles (ϕ=0.1) is greater than enhancement with the base fluid. While, the maximum value of the percentage enhancement of heat transfer is (4.22%) occurred at porous position equal to 0.5. Also, for a constant position of porous partition (HD=0.5) the percentage enhancement of heat transfer with volume fraction of nanoparticles (0.1) along the bottom wall decreases as the thickness of porous partition and Rayleigh number increased. It can be noticed that there is a good agreement between the current study and those of Chamka and Ismeal, with an approximated absolute error 1.829%.