Search

• Effect of novel positioned dual splitter plates on heat transfer is investigated. • Wake topology and its effect on heat transfer for dual splitter plates is discussed. • A mixed effect of the dual plates on the fluid forces around square cylinder is observed. • Substantial enhancement of 46% on the overall heat transfer is noticed. • Novel combined thermo-fluid regime is defined for the square cylinder with dual plates. In various applications of flow over a cylinder, the convective heat transfer is required to be enhanced for better operation by maintaining the operating temperature. In this paper, the influence of splitter plates on the fluid forces and heat transfer around a square cylinder is discussed thoroughly. The placement of the splitter plates is novel in its kind as these are placed at the top and bottom surfaces of a square cylinder instead of the conventional position i.e. downstream or upstream of the cylinder. Effect of this novel position of the splitter plates on the heat transfer along with the wake topology for a range of Reynolds number (Re) (60 ≤ Re ≤ 150) is not available in the previous study and accordingly, a rigorous investigation of the flow physics is presented here. Two splitter plates are utilized of the same geometry with varying lengths, locations, and orientations. It is found that the primary recirculation length decreases with increasing Re by introducing the splitter plates compared to a bare cylinder and the corresponding primary separation angle, ψ S1 is significantly affected by the geometry of the splitter plates. The splitter plates have a mixed effect on the fluid forces and heat transfer rate for all the considered Re. A maximum percentage of reduction on the mean drag coefficient and R.M.S (root mean squared) lift coefficient is found as 9% and 20%, respectively. Whereas, a maximum percentage enhancement of 40.7% is obtained on the heat transfer rate by introducing the splitter plates. However, the splitter plate geometry and its location can be decided according to the requirement of the heat transfer rate based on the application and the corresponding demand on the fluid forces. [Display omitted] [ABSTRACT FROM AUTHOR]

• A bionic heat sink with micro barchan-dune-shaped humps is proposed. • The micro dune can reinitialize the boundary layer by inducing a secondary flow. • The micro dune generally outperforms traditional fins in overall heat transfer performance. This paper proposes an innovative bionic heat sink with micro barchan-dune-shaped humps for improving the flow and heat transfer performance of the smooth narrow channel. The effects of the Reynolds number of the main flow (Re) and pitch distance of the dune array (P) on the thermal-hydraulic performance are investigated. In this work, the air is the working flow. The Reynolds number range is considered to cover the regimes of laminar, transitional, and turbulent, Re = 860–6,050, and the pitch distance (P) equals 8, 12, and 16 mm. The results show that the micro barchan-dune-shaped hump can induce a secondary flow downstream of the slip face and enhance the local heat transfer performance. For the multi-dune models, the case with P = 16 mm provides the highest overall thermal performance parameter (η). The η value decreases monotonically with decreasing P in the considered range. In addition, compared with other micro pin fin shapes (including the hexagonal cylinder, square cylinder, and triangular cylinder), the η of the barchan dune shape is almost identical to that of the hexagonal cylinder and exceeds the other two shapes by more than 20%. [Display omitted] [ABSTRACT FROM AUTHOR]

• The most relevant novelty of this work is the development and investigation of simple and effcient mechanical mixing devices using the non-uniform finite difference approximation. • The non-uniform finite difference approximation is adapted and applied for the first time to a numerical investigation in uid mixing mechanics. • This study is the first investigation of its kind on the use of parallel wall jets for scalable heat/mass transfer enhancement. • Several configurations of the parallel wall jets as well as Reynolds regimes are studied. • Oscillatory motion of the ow downstream can be predicted via simulations and effciently boosted with certain configurations. • The best mixing performance is observed for the smallest wall jet width tested. [Display omitted] Many different approaches have been investigated in the literature to achieve efficient heat and mass exchangers in applications in several fields such as mechanical, aeronautical or biomedical engineering. Some of these engineering devices need to efficiently mix two fluids at different temperature or concentrations, achieving a decent mixing at a low power cost, and using passive mechanical elements if possible. This paper introduces and analyses numerically the novel application of two parallel wall jets to enhance mixing by vortex shedding induced mechanically. The numerical approach is the non-uniform finite difference approximation, used for the first time in the study of mixing mechanics. The parallel wall jets are constrained within a channel, which can be a simple and passive easily manufactured machine with high potential as scalable laminar mixing device. Different wall jet geometries and Reynolds numbers have been tested with a verified&validated CFD code based on non-uniform finite difference approximation. This analysis allowed to predict configurations that lead to unsteady oscillatory motion. In general, it has been observed that for a range of laminar wall jets, a small channel ratio seems a very efficient option for heat/mass transfer, thanks to the intense oscillation generated in the flow downstream, which enhances mixing with low power requirement. [ABSTRACT FROM AUTHOR]

• Irreversibility due to winglets in fin-tube heat exchanger is analysed. • Entropy generation and exergy analysis are two pillars of irreversibility analysis. • Bejan number explain the dominancy of thermal and viscous entropy generation. • Comparison of heat transfer enhancement and irreversibility rate is done by N H. • Performance of the system is examined by exergetic efficiency, which is higher for upstream located RWPs. This paper investigates the irreversibilities caused by fluid flowing under the effect of isothermal walls of fin-tube heat exchanger in the presence of longitudinal vortex generators. Inline arrangement of circular tubes with fin-surface mounted rectangular winglet pairs (RWPs) arranged in common flow down configuration are selected for the present three-dimensional numerical study. Initially, thermodynamic performance analysis of different possible RWP locations corresponding to tubes has been examined for a fixed angle of attack. Further, the study is expanded for some specific locations by varying angle of attack ranging from 15° to 60° and flow Reynolds number ranging from 2000 to 4000. Thermodynamic performance of the present system has been evaluated by analyzing the irreversibilities caused due to RWPs and compared with the thermo-hydraulic performance. Thermodynamic analysis is categorized into two parts: the first 'entropy generation analysis' and the second 'exergy analysis'. For entropy generation analysis entropy generation rate, irreversibility distribution ratio and Bejan number are examined. The obtained results indicate that the irreversibility caused by entropy generation in the present system is majorly dominated by the entropy generation rate due to thermal effect. Exergy analysis is studied by calculating the irreversibility rate, exergy destruction number, heat transfer improvement number and exergetic efficiency. The observation of exergetic efficiency variation for different RWP locations demonstrates that the present system with upstream RWP locations delivers higher performance. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Investigating forced convection of a nanofluid through a wavy-sinusoidal minitube using two-phase model. • Evaluation of the effect of geometrical and thermal parameters to achieve the most advantageous geometry. • Wavy amplitude, wavelength and phase shift have serious impact on wavy-wall minitube PEC. • PEC amount for optimum tube is about 1.670. In present study heat transfer and forced convection flow of non-Newtonian two-phase ethylene-glycol/water mixture based nanofluid through a wavy-sinusoidal minitube has been investigated. The 2D governing system of equations is solved numerically in the computational field using the Control-Volume-Approach founded on the SIMPLE technique. Flow velocities or Reynolds numbers are varied in the turbulent regime range from Re =6000 to Re =15,000 and the tube walls boundary condition is uniform temperature. The optimization was conducted considering five different constant and variable α(x) amplitudes, five various constant and variable λ(x) wavelengths and five various phase shifts in order to achieve the most advantageous geometry in view of the highest thermal-hydraulic performance evaluation criterion index. From obtained results in present paper, it has been realized that the wavy-wall minitube thermal-hydraulic performance is seriously affected with varying the wavy amplitude, wavelength and phase shift. The highest thermal-hydraulic PEC has been obtained for the amplitude of α=0.5 mm with increasing wavelength and phase shift of θ=90° at Re =6000 Reynolds number. After opting of the optimum geometry, Silicon-Carbide (SiC) nanoparticles were added to base fluid in volume fraction of 4% and sizes of 16 to 90 nm. Based on results, the PEC of EG/water based nanofluid with nanoparticle diameter of d np =90 nm has been conducted to be the most efficient among all models during investigated range of flow velocities. PEC amount for optimum tube using EG/water based SiC nanofluid with volume fraction of ϕ=4% and nanoparticle diameter of d np =90 nm at Re =15,000 is about 1.670. [ABSTRACT FROM AUTHOR]