Sharif Digital Repository

In the present study, the turbulent flow of water/Al2O3 nanofluid in a tubular heat exchanger with two twisted-tape inserts has been numerically investigated in the three-dimensional coordinate. This numerical simulation has been done by using FVM, and all of the equations have been discretized by second-order upwind method. For coupling velocity–pressure equations, SIMPLEC algorithm has been used. The investigated parameters of the present study are Reynolds numbers at the range of 10,000–30,000, the effect of twist ratio of twisted-tape inserts from 2.5 to 4, co-swirl flow and counter-swirl flow of two twisted-tapes inside the tube and volume fractions of nanofluid from 1 to 4%. The... 

In the present study, the turbulent flow of water/Al2O3 nanofluid in a tubular heat exchanger with two twisted-tape inserts has been numerically investigated in the three-dimensional coordinate. This numerical simulation has been done by using FVM, and all of the equations have been discretized by second-order upwind method. For coupling velocity–pressure equations, SIMPLEC algorithm has been used. The investigated parameters of the present study are Reynolds numbers at the range of 10,000–30,000, the effect of twist ratio of twisted-tape inserts from 2.5 to 4, co-swirl flow and counter-swirl flow of two twisted-tapes inside the tube and volume fractions of nanofluid from 1 to 4%. The... 

This paper presents a numerical analysis for Cu-water nanofluid flow through a circular duct inserted with cross-cut twisted tape with alternate axis (CCTA). Three dimensional (RNG) k − ϵ turbulence model is applied to simulate this problem. All simulations are performed for plain tube and nine different CCTA geometries in the range of width ratio (b/w) from 0.7 to 0.9, length ratio (s/w) from 2 to 2.5, Reynolds numbers in the range of 5000 to 15,000 and volume fraction of nanoparticles from 0 to 1.5%. The calculated results indicate that the swirl flow created by CCTA is transferred from the tube core to the near wall regions. This results in higher fluid mixing, which enhances heat... 

In this research, a numerical investigation is done on the effect of employing the new combined vortex generators, the twisted tape turbulator and Al2O3-H2O nanofluid as the involved base fluid. Such study is carried out on the behavior of the heat transfer rate and the pressure drop of a double pipe heat exchanger. Accordingly, the response surface methodology (RSM) grounded on the central composite design (CCD) is used for acquiring the optimized geometry of the combined vortex generator and twisted tape turbulator. In order to have the maximum Nusselt number and minimum friction factor, twenty cases with different pitches ratio Pil=0.09-0.18, angles (θ=0-30°) and Reynolds numbers (Re =... 

In this article, a three-dimensional numerical simulation is performed to investigate the effect of magnetic field on the heat transfer of ferrofluid inside a tube which is equipped with twisted tape. This work comprehensively focused on the flow feature and temperature distribution of ferrofluid in presence of non-uniform magnetic field while ferrofluid swirled inside a tube with twisted tape. In this study, it is assumed that the ferrofluid is single phase and laminar and constant heat flux is applied on the outside of the tube. The magnetic field is established by wire in parallel direction with the axis of the tube. The base fluid is water with 0.86 Vol% Nano particles (Fe3O4). The... 

The boiling phenomena in a quiescent fluid is the nucleate pool boiling which has attracted much interest in the thermal management studies. This paper investigates the effect of the installed Twisted Tape Fins (TTFs) on the heat transfer from a surface with a temperature above the water saturation point to a coil condenser. Four different arrangements of TTFs (1, 3, 5, and 9 TTFs) are fabricated and their boiling performance in distilled water at atmospheric pressure is experimentally tested. It was observed that the increase in the boiling heat transfer coefficient of the plate with nine TTFs compared to that of the plain one is 15.5%. Furthermore, the effect of TTFs heights on the heat... 

This paper aims to present a numerical model for heat transfer intensification in a heat exchanger tube equipped with novel double V-cut twisted tape. The effects of different cut ratios (0.6 < b/c<1.8)on the turbulent flow characteristics and thermal performance of the system are investigated over the Reynolds number range from 5000 to 15,000. The accuracy of (RNG)k-ε turbulence model used in the present study is validated by comparing with experimental results. The tube equipped with double V-cut twisted tape shows improved thermal performance in comparison with conventional twisted tape. This improvement is due to the additional vortex flow induced by the V-cuts which leads to more... 

Numerical simulations are used to analyze the thermal performance of turbulent flow inside heat exchanger tube fitted with cross-cut twisted tape with alternate axis (CCTA). The design parameters include the Reynolds number (5000 < Re < 15; 000), cross-cut width ratio (0:7 < b=D < 0:9), cross-cut length ratio (2 < s=D < 2:5), and twist ratio (2 < y=D < 4). The objective functions are the Nusselt number ratio (Nu=Nus), the friction factor ratio (f =fs), and the thermal performance (g). Response surface method (RSM) is used to construct second-order polynomial correlations as functions of design parameters. The regression analysis shows that heat transfer ratio decreased with increasing both... 

The current study presents a numerical investigation on turbulent hydrothermal characteristics in a wavy passage equipped with discontinuous twisted tapes. The working fluid is water and passage walls are kept under constant wall temperature. The effect of Reynolds number (Re = 2500, 4500, 6500, 8500 and 10500), twist angle (TA = 90∘ and 180∘) and inclination angle (IA = 15∘ and 30∘) on velocity fields and streamlines, temperature contours, Nusselt number, friction factor, turbulent kinetic energy (TKE), thermal performance factor (TPF), energy efficiency factor (EEF) and entropy generation rate are evaluated. More uniform temperature and velocity fields can be found as both wavy passage and... 

This research investigated the forced convection heat transfer by using the swirling impinging jets. This study focused on nozzles, which equipped with twisted tapes via a numerical approach. The computational domain created by utilizing the fully structured meshes, which had very high quality from the viewpoint of aspect ratio and skewness. The numerical simulations were performed at four different jet-to-plate distances (L/D) of 2, 4, 6 and 8, four Reynolds numbers of 4000, 8000, 12,000 and 16,000, and also four different twist ratios (y/w) of 3, 4, 5 and 6. The mesh-independent tests were conducted based upon the average Nusselt number. The obtained results revealed good agreement with...