Figure 8 - uploaded by Said Ouaskit
Content may be subject to copyright.
Source publication
This paper presents the results of extensive numerical simulations, based on the control volume method, of 2D nanofluid fluid flow around a heated elliptical cylinder with different incidence angle and aspect ratio. The continuity and momentum equations have been numerically solved using a SIMPLE algorithm. Two types of nanofluids consisting of Al2...
Context in source publication
Context 1
... known Reynolds number presents typical dependence related to the velocity of the flow, thus the heat transfer coefficient will be enhanced by the growth of Reynolds number, since the velocity enhance considerably the flux of temperature. From Figure 8, it is obvious, for a given particle concentration that the heat transfer coefficient increases linearly in different concentrations. To throw more light into the combined effect of the aspect ratio and the incidence angle, the Figure 9 shows the variation of those two parameters with respect to the heat transfer coefficient using nanofluid EG-water (60:40) Al 2 O 3 5%. ...
Similar publications
Recently, many scientists have been making remarkable efforts to enhance the efficiency of direct solar thermal absorption collectors that depends on working fluids. There are a number of heat transfer fluids being investigated and developed. Among these fluids, carbon nanomaterial-based nanofluids have become the candidates with the most potential...
Our paper includes the results of a numerical simulation performed to study the nanofluid flow around a set of 2D cylinder arrangements. Two types of nanofluids involving Al2O3 and CuO nanoparticles dispersed separately in base fluids of water and ethylene glycol mixture 60:40; those nanofluids were taken to evaluate their effect on the flow around...
The effects of variable thermal conductivity on heat transfer and entropy generation in a flow over a curved surface are investigated in the present study. In addition, the effects of energy dissipation and Ohmic heating are also incorporated in the modelling of the energy equation. Appropriate transformations are used to develop the self-similar e...
In this work, the effects of nanoparticles concentration on the density, thermal conductivity, and viscosity of Al2O3, CeO2 and ZrO2 suspended in 20% of ethylene glycol (EG) and 80% of distilled water (DW) is experimentally investigated. By using two step method, the nanofluid samples are provided at different concentrations, including 0.5%, 1% and...
Laminar convective heat transfer and pressure drop characteristics of Al2O3-water nanofluid were experimentally investigated inside a horizontal Helical-Coil Tube (HCT) under constant heat flux boundary conditions for Dean numbers between 400 and 1600. The experiments have been performed using Al2O3-water nanofluid of three mass concentrations and...
Citations
... The numerical methods used to solve the flow and energy equations using the implicit alternative direction method (ADI). Table 1 shows the thermophysical characteristics of the base fluid (water) and (EG Water (60:40)) [14,15] Table 2 shows the thermophysical characteristics of the three nanoparticles that constitute the nanofluids [15,16]. Table 2. Nanoparticles thermophysical properties. ...
... Where W ̅ is the average axial velocity and substituting equation (15) into equation (14) gets: ...
Numerical investigation was carried out for determination of Nusselt number for various nanofluids consisting of nanoparticles Silver (Ag), Copper (Cu) and Titanium Oxide (TiO2). This study used nanoparticles dispersed in water (Ag/Water, Cu/Water and TiO2/Water), also used nanoparticles dispersed in 60% ethylene glycol and 40% water by mass (Ag/(EG: water (60:40)), Cu/(EG: water (60:40)) and TiO2/(EG: water (60:40))). The Numerical study includes constructing the required model from the governing equations of flow through a horizontal and an inclined cylinder from the basic governing equations (continuity, energy and the momentum equations in the polar three-dimensional coordinate). The cylinder is kept in adiabatic mode. The Reynolds number is chosen (400), heat flux (2000 W/m 2), Rayleigh number (1×10 5) and volume fraction concentrations (2.5 Vol %). The simulation is achieved by using MATLAB programs. The numerical results showed that the lowest Nusselt numbers are obtained for TiO2/Water, whereas Nusselt number of Ag/Water and Cu/Water is the highest Nusselt. This study focused on the effects of base fluid type (Water or (EG: water (60:40))) on the value of Nusselt number. Results showed that when used water as base fluid is more significant on the Nusselt number value than (EG: water (60:40)) for nanoparticles Ag, Cu and TiO2, respectively. Further, the Nusselt number has the highest values in the horizontal position of the cylinder compare with the inclined and vertical position. The values of the Nusselt number ratio (NUR) were evaluated to be (42%, 28%, 22%) for the three nanofluids (Ag/Water, Cu/Water, and TiO2/Water), respectively. Also, the values of Nusselt number ratio (NUR) were evaluated to be (33%, 24%, 19%) for the three nanofluids (Ag/(EG: water (60:40)), Cu/(EG: water (60:40)) and TiO2/(EG: water (60:40))), respectively. Nusselt number increases indicated as well as increases in flow strength [29]. Eventually, for results validation, the results of this study were compared with the previously published Khalid results [30].
... The flow passing a single body or multiple bluff bodies such as cylinders has many engineering applications. In the literature, experimental research involving flows around a single cylinder and various arrangements of two cylinders has been conducted using classic flow properties [1][2][3][4][5][6][7][8]10]. Thus, Zdravkovich and Igarash [11,12] make an experimental study about the flow pattern characteristics of two tandem cylinders with different gap ratios; they found that the gap ratio has a significant impact on the flow pattern characteristics of the cylinders. ...
... However, before embarking upon the presentation and discussion of the new results, it is desirable to explain the methodology of the simulation performed in this work and our previous work [10]. In the present, the control volume technique is used; the scheme implemented is the first-order upwind for the discretization of the convection terms and the diffusion terms of the momentum equation and other resulting quantities. ...
... The resulting data were then post-processed to obtain the temperature field. Absolutely, the accuracy and consistency of the numerical results were fully affected by the choice of the numerical parameters, namely domain size, grid, time step, and convergence criterion [10,37,38,39] . As far as our knowledge, there is no available information on nanofluid flow around an equilateraltriangular arrangement of cylinders; thus, the values of aforementioned parameters used when studying the airflow around an equilateral-triangular arrangement of cylinders were used as preliminary guesses [31,36]. ...
Our paper includes the results of a numerical simulation performed to study the nanofluid flow around a set of 2D cylinder arrangements. Two types of nanofluids involving Al2O3 and CuO nanoparticles dispersed separately in base fluids of water and ethylene glycol mixture 60:40; those nanofluids were taken to evaluate their effect on the flow around different equilateral-triangular arrangements of cylinders. The continuity and the momentum equations have been numerically solved by using a special technic named “SIMPLE algorithm.” Besides, the thermo-physical parameters of nanofluids have been evaluated using the theory of one fluid phase; thus, contemporary correlations of thermal conductivity and viscosity of nanofluids have been used in this paper as well as our previous work (Int J Adv Technol 7(4)0976–4860, 2016). The correlations are functions of particle volumetric concentration as well as temperature. The results of heat transfer characteristics of nanofluid flow around 2D cylinder arrangement revealed clear improvement compared with the base fluids. This enhancement is very interesting in engineering of flows with different equilateral-triangular arrangement characteristics of cylinders, while the gap ratios (G/D) of the three cylinders and incidence angle exert an enhancement efficiency influence on the heat transfer characteristics. The achieved results indicate that the use of aspect ratio 2.26 and incidence angle 1.98° leads to the high amounts of heat transfer inside the tube. In this study, the results obtained can be a fruitful source for developing and validating of new codes both in a scientific and commercial manner.
... Nanofluids, i.e. dispersions of solid nanoparticles in ordinary liquids, are employed significantly for thermal applications in the recent years [1][2][3][4][5][6]. As one type of nanofluids, magnetic nanofluids or ferrofluids are composed of single-domain magnetic nanoparticles (3-15 nm) coated with a molecular layer of a dispersant and suspended in a carrier liquid [7][8][9][10][11]. ...
This research examines laminar forced convection of a temperature-sensitive magnetic nanofluid flowing within a horizontal tube through the two-phase mixture model. The ferrofluid flowing in the tube is exposed to the magnetic field generated by electrical current-carrying wire(s) along the tube, and the effect of such magnetic field is studied on heat and mass transfer phenomena. It is observed that due to the dependency of magnetization on temperature, the cold fluid flowing at the central regions of the tube is attracted more significantly towards the source of the magnetic field, which results in creation of secondary flow. Such mixing in the flow, subsequently, disturbs the thermal and hydrodynamic boundary layers, especially at the vicinity of the magnetic field source, leading to better heat transfer rate and also higher pressure drop. Furthermore, increasing the strength of the magnetic field leads to greater enhancement in heat transfer, while increasing the Reynolds number decreases the effectiveness of the magnetic field on the ferrofluid flow and heat transfer. Moreover, placing two wires above and under the tube can enhance the heat transfer even more significantly, such that the average convective heat transfer coefficient in this case is about 34.5% higher than that of the case without magnetic field.
... In the homogenous method, 100 it is assumed that the solid particles and the base fluid are in ther-101 mal equilibrium and have the same temperature and velocity. 102 There are many numerical studies in this field which have been 103 used homogeneous approach for simulation of the nanofluids 104 [14][15][16][17][18][19]. Purusothaman et al. [20], Cho et al. [21], Sheremet et al. 105 [22], Alsabery et al. [23] and Mahmoodi [24] presented a numerical 106 study of natural and mixed convection heat transfer of nanofluid 107 flow in different geometries. ...
In the present study, the problem of conjugate natural and mixed convection of nanofluid in a square cavity containing several pairs of hot and cold cylinders is visualized using non-homogenous two-phase Buongiorno's model. Such configuration is considered as a model of heat exchangers in order to prevent the fluids contained in the pipelines from freezing or condensing. Water-based nanofluids with Cu, Al2O3, and TiO2 nanoparticles at different diameters ( ) are chosen for investigation. The governing equations together with the specified boundary conditions are solved numerically using the finite volume method based on the SIMPLE algorithm over a wide range of Rayleigh number ( ), Richardson number ( ) and nanoparticle volume fractions ( ). Furthermore, the effects of three types of influential factors such as: orientation of conductive wall, thermal conductivity ratio ( ) and conductive obstacles on the fluid flow and heat transfer rate are also investigated. It is found that the heat transfer rate is significantly enhanced by incrementing Rayleigh number and thermal conductivity ratio. It is also observed that at all Rayleigh numbers, the total Nusselt number rises and then reduces with increasing the nanoparticle volume fractions so that there is an optimal volume fraction of the nanoparticles where the heat transfer rate within the enclosure has a maximum value. Finally, the results reveal that by increasing the thermal conductivity of the nanoparticles and Rayleigh number, distribution of solid particles becomes uniform.
... The numerical methods used to solve the flow and energy equations using the implicit alternative direction method (ADI). Table 1 shows the thermophysical characteristics of the base fluid (water) and (EG Water (60:40)) [14,15] Table 2 shows the thermophysical characteristics of the three nanoparticles that constitute the nanofluids [15,16]. Table 2. Nanoparticles thermophysical properties. ...
... Where W ̅ is the average axial velocity and substituting equation (15) into equation (14) gets: ...
Power spectral analysis of heart rate variability (HRV) has been used to indicate cardiac autonomic function. High-frequency power relates to respiratory sinus arrhythmia and therefore to parasympathetic cardiovagal tone; however, the relationship of low-frequency (LF) power to cardiac sympathetic innervation and function has been controversial. Alternatively, LF power might reflect baro reflexive modulation of autonomic outflows.
We studied normal volunteers and chronic autonomic failure syndrome patients with and without loss of cardiac noradrenergic nerves to examine the relationships of LF power with cardiac sympathetic innervation and baroreflex function.
We compared LF power of HRV in patients with cardiac sympathetic denervation, as indicated by low myocardial concentrations of 6-[(18)F]fluorodopamine-derived radioactivity or low rates of norepinephrine entry into coronary sinus plasma (cardiac norepinephrine spillover) to values in patients with intact innervation, at baseline, during infusion of yohimbine, which increases exocytotic norepinephrine release from sympathetic nerves, or during infusion of tyramine, which increases non-exocytotic release. Baroreflex-cardiovagal slope (BRS) was calculated from the cardiac interbeat interval and systolic pressure during the Valsalva maneuver. Results. LF power was unrelated to myocardial 6-[(18)F]fluorodopamine-derived radioactivity or cardiac norepinephrine spillover. In contrast, the log of LF power correlated positively with the log of BRS (r = 0.72, P < 0.0001). Patients with a low BRS (</=3 msec/mm Hg) had low LF power, regardless of cardiac innervation. Tyramine and yohimbine increased LF power in subjects with normal BRS but not in those with low BRS. BRS at baseline predicted LF responses to tyramine and yohimbine.
LF power reflects baroreflex function, not cardiac sympathetic innervation.
