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This paper presents a numerical study of the hydrothermal air-side performance of a tubular heat exchanger fitted with flower baffles (FBs). The investigation was done by testing in-line and stagge...

The increase in the heat dissipation rate in heat sinks (HSs), the reduction of the occupied volume and mass, and the elimination of the lower heat transfer areas (LHTAs) behind the pins are the main parameters to be controlled in HSs design. For this purpose, this study is devoted to numerically investigating the effect of the combination between perforation technique and splitters inserts on the heat dissipation and turbulent fluid flow characteristics of pin fins heat sinks (PFHSs). The splitter is located in the back of the pin, and the cylindrical pin fins heat sinks (CPFHSs) are perforated with different pairs of hole numbers. These configurations are named PFHS-0 (without perforation) to PFHS-5. The results obtained for the PFHS-5 show an increase in Nusselt number by 34.91% and a reduction in the thermal resistance by 24.22%, compared with CPFHSs. For the same conditions, the occupied volume and mass of this case are also reduced by 70% and 47.5%, respectively. In addition, the PFHS-5 case ensures the highest hydrothermal performance factor (HTPF) of 1.42 at Re = 8,740.

Effects of blower shaped baffles on the fluid dynamics and filtration flux in a membrane tube are numerically explored. Both the staggered and inline arrangements of baffles are studied. The carbonate calcium suspensions with a concentration of 5 g/L were used as a working medium. The efficiency of filtration was determined via the calculation of velocity of fluid particles, wall shear stresses and static pressure. An increase in the shear stresses on the tube surface, as well as a formation of fluid eddies were observed with the presence an array of blower baffles, resulting thus in a significant improvement of the filtration performance. The case of the staggered baffles with pith ratio of L/D = 1 and Re = 15,000 achieved an increase in the filtration flux rate by 42% and 12%, compared with unbaffled and tube with baffle orientation angle of 180°, respectively.

The aim of this work is to investigate the forced convective heat transfer phenomena and fluid flows of water-based Al2O3 nanofluids in the baffled shell and tubes heat exchanger (STHE). Water as a hot fluid flows in the side of the tubes, and Al2O3 nanofluids as cooling fluid flow in the shell side. Numerical investigations have been carried out based on the continuity, momentum, and energy equations which are solved by using the finite element method with the help of the COMSOL 5.4 CFD software. The obtained results were presented by average Nusselt number, streamlines, isotherms, and various physical parameters which are a volumetric fraction of nanoparticles (1%? Cv ?3%). The results are found that the heat transfer increases with the rise of inlet velocity and volume fraction. In addition, the presence of baffles inside tubular heat exchangers can create a better mixture of fluids which is augmenting heat transfer execution. The choice of these parameters is important to get the maximum improvement of heat transfer with minimum entropy consumption.

Geometrical configurations of tubes and vortex generators have been optimized in order to improve the hydrothermal characteristics of fin-and-tube heat exchangers. The work is divided into two part...

The present paper is a numerical investigation on the performance of perforated baffles in a plate-fin heat exchanger. Two types of perforations are studied, namely the circular and elliptical shapes. Values of heat transfer coefficient, pressure drop, and thermal performance factor are determined for both cases and compared with those for a smooth channel. Also, the flow fields and heat transfer characteristics are determined for different fluids and various Reynolds numbers. The working fluids are complex, non-Newtonian and have an inelastic shear thinning behavior. The obtained results showed a good enhancement in the thermal performance factor by the suggested design in baffles. In the case of low viscous fluids, the elliptical perforated baffle performs better (by about 63.4%) than the circular one for all values of Reynolds number. But for highly viscous fluids, the elliptical perforation shows higher thermal performance than the circular hole by about 25% for low Reynolds numbers and 27% for high Reynolds numbers. The overall thermal performance factors are about 1.55 and 1.74 for the circular and elliptical perforations, respectively.

In the present study, the mass transfer characteristics in a tubular membrane are analysed. Based on the available experimental data, a new reliable correlation is elaborated to predict the mass transfer as the term of the permeate flux inside membrane tubes. Analysing of available results shows that the filtration time (tF), and the concentration of suspensions (C) are directly affecting the permeate flux (Pf). Therefore, the present analytical study was conducted to propose a new correlation. This correlation is compared with other experimental data; a very satisfactory agreement has been achieved.

A numerical study is carried out to test the effect of tube shape on heat transfer and fluid flow in a finned tube heat exchanger. The effects of different shapes (circular, flat, elliptical and oval in both orientations: left and right) are analyzed. The simulations are carried out for two-dimensional and external flow of an incompressible fluid with Reynolds numbers varying between 3000 and 20000. The results obtained indicate that the shape of the tube directly affects the thermal and dynamic behaviors of a fin and tube heat exchanger. Where the circular tube ensures higher heat transfer coefficient of about 18% than the flat tube, and it generate a moderate pressure drop of about 10% in the same conditions. Also, some reliable empirical correlations are proposed to predict the Nusselt number and the friction factor.

The baffling technique is well-known for its efficiency in terms of enhancement of heat transfer rates throught channels. However, the baffles insert is accompanied by an increase in the friction factor. This issue remains a great challenge for the designers of heat exchangers. To overcome this issue, we suggest in the present paper a new design of baffles which is here called graded baffle-design. The baffles have an up- or down-graded height along the channel length. This geometry is characterized by two ratios: up-graded baffle ratio and down-graded baffle ratio which are varied from 0-0.08. For a range of Reynolds number varying from 104 to 2 ? 104, the turbulent flow and heat transfer characteristics of a heat exchanger channel are numerically studied by the computer code FLUENT. The obtained results revealed an enhancement in the thermohydraulic performance offered by the new suggested design. For the channel with a down-graded baffle ratio equal to 0.08, the friction factors decreased by 4-8%

Design of the impeller blade is a determining factor in power consumption and mixing quality, which determines consequently the cost of the mixing operation. This study explores the flow patterns and the power required for stirring a Newtonian fluid by paddle impellers. Investigations are carried out via three dimensional (3D) numerical simulations. Effects of the blade curvature, blade diameter, blade number and Reynolds number are analyzed. The curved blade is found to be more efficient to reduce the power consumption, compared with the straight blade. A new correlation is proposed for predicting the power required with two-curved-bladed impellers. The straight and very large blade creates a dead zone in the space between the blade tip and the vertical wall of vessel. This issue may be overcome by the curved blade, which increases consequently the well-mixed region size. A wider well-mixed region may be obtained with the larger curved blade, but with an additional energy cost.

The heat transfer characteristics in a smooth tube are studied. Based on the available experimental data, a new correlation is proposed to predict the heat transfer coefficients inside tubes of different lengths. The predicted results show that for a range of L/D from 26.31 to 58.14, the heat transfer coefficient may be reduced by 20.56% and increased by 13.31% at the beginning and at the end of this range, respectively. The results obtained from the proposed correlation are compared with other analytical and experimental data, and satisfactory agreement is found.

Three dimensional numerical simulations are carried out to explore the performance of vortex generators in a plate fin heat exchanger. Rectangular and perforated wings are used as vortex generators to enhance the heat transfer rates. A comparison is made between the performances of a plate fin with and without baffles. When the heat exchanger is equipped with baffles, the efficiency of two configurations was compared: a baffle with and without perforation. Also, the effects of the perforation shape were studied. It concerns three cases: rectangular, triangular and circular. Validation of our numerical results with the available experimental data has revealed a satisfactory agreement. The obtained results show that the baffled cases perform better than the unbaffled one. The performance factor is found to be higher in the perforated baffle than the baffle without perforation. Compared to the unbaffled case, the maximum thermal performance factor (TPF) of 2.14 was obtained with the circular perforated baffle, followed by the rectangular perforated baffle (TPF = 1.57), triangular baffle (TPF = 1.46) and finally the baffle without perforation (TPF = 1.41). At the end of paper, new correlations for the prediction of friction factor and Nusselt number depending on Reynolds number and the shape of perforation in baffles are developed.

This paper presents a numerical investigation of heat transfer and friction factor characteristics in a solar air heater channel fitted with upper corrugated surface/wall and baffle series placed on a lower wall along the length of the channel. The corrugated surface/wall characterized by heating corrugated surface ratio (HCSR) varied from 0 to 0.5. The baffle series defined by blockage ratio (BR) fixed in 0.5. The fluid flow and heat transfer behaviors are presented for Reynolds numbers based on the hydraulic diameter of the channel ranging from 8000 to 20000. The computations are based on the finite volume method, and the SIMPLE algorithm has been implemented. The present results show that the heat transfer rate and friction factor increase with the raise of Reynolds number. The best thermal performance factor observed at HCSR=0.5 tends to 2.7 at highest Reynolds number.

In the present study, a three-dimensional numerical simulation of turbulent fluid flow and heat transfer in the shell side of a shell and tube heat exchanger (STHE) has been investigated. Two primordial parameters are tested: baffles spacing of 106.6, 80 and 64 mm and six baffles orientation angles of 45°, 60°, 90°, 120°, 150° and 180°. The investigations are performed with the CFD COMSOL Multiphysics 5.1 software using the finite elements method, for Reynolds number ranging from 3000 to 10 000. Some numerical results are validated with available experimental data and an adequate agreement is found. The numerical results show the important role of the studied parameters in the shell side thermal performance enhancement, where the case of baffle orientation angle of 180°, at 64 mm of baffle spacing is the best design that assures mixing flow, giving thus a highest value of thermal performance factor of 3.55 compared with STHE without baffles.

A numerical investigation is carried out to examine the effect of a new baffle design in a membrane tube on the hydrodynamics and filtration efficiency. Two different orientations of hemispherical baffles named as RO baffle for the Right Orientation and LO baffle for the Left Orientation, respectively, are explored. Two values of the carbonate calcium suspensions are used: 5 and 10 g/L. The axial velocity, stream function, static pressure, wall shear stresses and turbulent characteristics are the physical parameters utilized to evaluate the filtration performance. The obtained results showed that the presence of an array of hemispherical baffles can develop the local shear stresses on the membrane surface and create the fluid eddy movement which enhances considerably the filtration performance. When the feed concentration is 5 g/L and in a comparison with the unbaffled tubes, the RO and LO cases achieved an increase in the filtration flux rate by 57% and 64%, respectively. For the second feed concentration (10 g/L), the enhancements are 85% and 96% for the RO and LO cases, respectively. In a comparison between the LO and RO cases, the LO baffle gives the best performance. Our results were compared with experimental data and a satisfactory agreement has been found.

Mixing of complex fluids in a flat bottomed cylindrical reactor is studied. The working fluid (Carboxy Methyl Cellulose (CMC)) has a shear thinning behavior. The agitation is ensured by a rotating mixer located at the central position in the tank. The main purpose of the present work is to compare the performance of three impellers, which are: a disk impeller, a radial turbine with six flat blades and a six-blade Rushton turbine. Mixing characteristics in terms of velocities, well-mixed region and energy consumption are presented. The obtained results show that the Rushton turbine performs better than the two others stirrers investigated.

One problem in using baffles in the channels is the formation of Lower Heat Transfer Areas (LHTA), particularly in the downstream region of baffles (i.e. in baffle-wall corners). The present paper is an investigation of the performance of a new baffle design aiming to enhance the heat transfer phenomenon in the channel. It concerns a perforated baffle having a row of four holes placed at three different positions. These positions are characterized by a ratio called the PAR (Pores Axis Ratio). Three values are taken for the PAR and which are 0.190, 0.425 and 0.660, respectively. The characteristics of fluid flows and heat transfer are presented for Reynolds numbers ranging from 104 to 105. All investigations are achieved with the help of the CFD code Fluent. Some numerical results are validated with available experimental data and a satisfactory agreement is found. The obtained results show that the Pores Axis Ratio (PAR) of 0.190 is the best design that eliminates significantly the LHTAs, giving thus an increase in the heat transfer rate from 2% to 65% compared with the simple baffle.

The present work is a study of the performance of a channel heat exchanger equipped with V-baffles. The study is carried out numerically by using a multidimensional CFD model (the Software ANSYS CFX v.18). Among the different techniques available to improve the efficiency of heat exchangers, we choose in this work the technique of vortex generators (baffles). The simulated fluid is a complex shear-thinning solution and the flow regime is laminar. The influence of some parameters on the efficiency of such heat exchanger has been verified, namely the flow rate (Reynolds number), the orientation of baffles and their arrangements. Two orientations of baffles are selected: +V and −V, corresponding to the counter direction of flow and the same direction of flow, respectively. Also, the staggered and aligned arrangements of +V baffles are studied. The predicted results revealed that +V baffles inserted in the staggered arrangement may give a considerable superiority in enhanced heat transfer ratio, compared to the (−V) baffles’ insertion and the aligned arrangement. Values of the thermal performance factor for the +V aligned arrangement, −V aligned arrangement and +V staggered arrangement of baffles are: 1.44, 1.32 and 1.52, respectively.

The present paper deals with the mixing of a highly viscous fluid by close-clearance impellers in cylindrical vessels. The study is performed via numerical simulations. Calculations are achieved by the discretization of continuity and momentum equations with the finite volume method. The effect of blade diameter and its shape on the well-stirred region size and the power consumption is investigated. For highly viscous fluids, the obtained results suggest the use of impellers rotating at low Reynolds number, and having a blade with the same shape of the tank to ensure mixing near the vessel base. A comparison is made between the performance of a simple helical ribbon (HR), a simple small screw (SS), helical ribbon-small screw (HR-SS) and a large screw (LS) impeller. The predicted results allow the following classification of impellers studied, based on less power requirements and small size of well-agitated region: SS &lt, HR &lt, HR-SS &lt, LS.

Among the major problems in the use of baffles in heat exchangers is the formation of hot points due to the stagnation of the flow behind baffles. The present work shows a design of a porous space in the baffles in order to shake the dead zones behind these baffles. The numerical investigation is based on the Navier Stocks averaged (RANS) using FLUENT software. The results validated by experimental data from the literature shows that the porous space presented in this paper reduces in an observable manner the hot points and increase the heat transfer rate.

In this article, the data assembled regarding the mixing of Newtonian and shear thinning fluids by screw impellers in a cylindrical tank is disclosed. The data summarizing some information on the efficiency of such impellers are obtained via 3D calculations of velocities and viscous dissipation in the whole vessel volume. The data presented herein may be useful for those who want to outline the mixing characteristics in terms of fluid circulation and power consumption for this kind of impellers, therefore, avoiding a great effort for achieving a high number of experiments. Keyword: Mixing, Helical screw agitator, Power consumption, Fluid circulation, Cylindrical tanks

A numerical work is carried out to investigate the heat transfer and fluid flow behaviors in a fin-and-flat-tube heat exchanger provided with complex vortex generators (CVGs). A new design of CVGs is proposed in the present paper, it consists of CVGs formed by two portions: a flat portion with various attack angles ( β = 0°, 20°, 40° and 60°) and a curved portion with various curvature angles (α = 30°, 45° and 60°). Changes in CVGs position ratio ( R * ) inside the tube are also investigated and three values of R * are considered, namely: R * = 1.375, 1.750 and 2.125. Computations based on the finite volume method with the SIMPLE algorithm are conducted for the air flow. The Reynolds number is ranging from 25 to 400. The obtained results show that the vortex formed near the tubes is intensified by the flat potion of CVGs, and the curved tube guide the fluid flow towards the region behind the tubes, resulting thus in improved heat transfer rates. In a comparison with tubes without CVG, the new design suggested and especially the case with β = 60°, α = 60° and R * = 2.125 improve significantly the heat transfer (an increase by about 76%) with a moderate pressure loss penalty.

The energy efficiency of a deep hollow blade disk turbine in unbaffled mixing vessel is determined in this article via numerical simulations. The vessel is filled with xanthan gum solutions, which have a shear thinning behavior with yield stress (viscoplastic). The Herschel-Bulkley law is used to model the fluid behavior. Three-dimensional calculations are achieved by the computer tool CFX (version 16.0), and the computational domain is meshed using the software ICEM CFD (version 16.0). Mixing is achieved at low impeller rotational speeds which correspond to the laminar and transitional flow regimes. Our main purpose is to explore the effect of blade size (width and height), Reynolds number, and fluid properties on the mixing efficiency of deep hollow bladed impellers. A validation test of our predicted results with experimental data of a previous study was done, and it has shown a good agreement.