Baffle Distance Research Articles

Deformable baffles coupled with pulsatile flow improve mixing in microfluidic devices

An important objective for many microfluidic mixer devices is to attain a high level of mixing efficiency at low Reynolds numbers. Previous research incorporating rigid obstacles into microchannels has shown enhanced chaotic advection and improved mixing index; however, the increased pressure drop and corresponding shear forces within the fluid domain can create issues in biological applications. In this paper, we show how an innovative micromixer strategy, i.e., incorporating deformable baffles and utilizing pulsatile flow, results in a high level of mixing efficiency at low Reynolds numbers (Re =1.25), where diffusion is the pure mechanism of mixing. The numerical investigation involved solving the continuity, Navier-Stokes, solid mechanics, and fluid-solid interaction equations alongside a convection-diffusion model to analyze species concentration. To find the best conditions of the micromixer, the mixing index as the objective function was optimized, and various parameters, including phase difference, velocity ratio, Strouhal number, baffle distance, and Reynolds number, were investigated. Through optimization of these parameters, we show a notable improvement in the mixing index (increase from 21.7 % to 78.86 %) at a Reynolds number of 1.25 with 2 mixing units, more than 92 % mixing efficiency by using 6 mixing units, and more than 95 % mixing efficiency at a Reynolds number of 0.1. Moreover, the incorporation of deformable baffles and pulsation results in a lower pressure drop. These conditions are optimal for biological applications that require thorough mixing of the sample inputs.

Improvement of SiC deposition uniformity in CVD reactor by showerhead with baffle

The growth uniformity of silicon carbide (SiC) by halide chemical vapour deposition (HCVD) is influenced by equipment configuration, and a uniform film can be obtained by optimising the chamber structure. An SiC deposition kinetics model is studied in this work, and a detailed chemical reaction mechanism is incorporated into a model reaction chamber to verify the deposition kinetics model. We studied the influence of hole size of showerhead, baffle size, and baffle positioning on the growth uniformity. Further, we then optimised the process parameters using an orthogonal experimental method. Reducing the hole size of showerhead led to a “double peak” in the deposition rate across the substrate from the edge to both sides, which first increased and then decreased. The “double peak” disappeared upon reduction of hole size. With an increase in baffle size, the growth uniformity first increased and then decreased. Moreover, the baffle displacement had little effect on the deposition rate when the baffle-to-showerhead distance was at least 45 mm. Meanwhile, the growth uniformity gradually worsened when the baffle distance was reduced. The showerhead and baffle reduced the extreme difference in deposition rate across the effective deposition area by improving the spatial velocity distribution within the reaction chamber. A uniform SiC film could be obtained using the proposed optimisation method. Furthermore, the results of the orthogonal experimental method showed that the deposition rate increased by 57.8%, and the uniformity of growth standard deviation decreased by 18% compared with the ground state. This study provides theoretical guidance for future optimisations of CVD chambers.

Comparison and Optimization of Continuous Flow Reactors for Aerobic Granule Sludge Cultivation from the Perspective of Hydrodynamic Behavior.

Improving treatment efficiency and reducing investment and operating costs make aerobic granular sludge technology (AGS) a promising technology for treating aquaculture wastewater. The development of continuous flow reactors (CFRs) has become a new direction in the research of AGS. This study clarifies the granulation effect, hydrodynamic behavior and particle separation of three different CFRs (R1 to R3). The established CFD model was able to explain the hydrodynamic behavior in all three CFRs; in particular, R3 performed the best from the perspective of hydrodynamic behavior due to its abundant turbulence. In addition, the optimal baffle distance and baffle angle of R3 were simulated to be 40 mm and 60°, respectively, due to them providing the best turbulent flow and particle separation effect. However, an overlarge baffle angle could weaken the turbulent pattern in the reactor. The retention time distribution further confirmed the reasonability of these optimal parameters with the highest effective volume ratio of 0.82. In short, this study gives an instruction for exploring the rapid formation mechanism of AGS in a CFR to promote its engineering application.

Research on application of twisted oval tubes in rod‐baffle heat exchangers

AbstractTo enhance the flow and heat transfer in the shell side of rod‐baffle heat exchangers (RBHXs), twisted oval tubes were proposed to be installed in RBHXs. The shell‐side performance was compared of RBHXs with circular tubes or twisted oval tubes of different structural parameters (ratios of long to short axes R and twisted pitches S). The results show that not all RBHXs with twisted oval tubes of any configuration parameter is better than RBHXs with circular tubes. When the Re is lower, the ratio of long to short axes R is bigger and the twisted pitch S is smaller; RBHXs with twisted oval tubes are more possible to be better than circular tubes. For both heat exchangers, the effects of clamping methods of tubes, one tube by one rod (OTBOR) and one tube within two rods (OTWTR), and baffle distance Lb were studied. The results show that Nu and f of OTBOR are both smaller than OTWTR. The comprehensive performance Nu/f1/3 of OTBOR is 10.65% better than OTWTR for both heat exchangers. With the increase of baffle distance Lb, Nu and f decrease; however, Nu/f1/3 increases by 7.13% and 12.30% for circular tubes and twisted oval tubes, respectively.

Numerical Modeling of Coupled Surge-Heave Sloshing in a Rectangular Tank with Baffles

Liquid sloshing under coupled surge and heave excitations in a rectangular tank has been numerically investigated by applying a Navier–Stokes solver. Fieriest coupled sloshing was further considered, and the internal baffle was expected to suppress the violent sloshing wave. After getting fully validated against available results from the literatures, the numerical model was applied to research coupled sloshing, and both vertical baffle and horizontal baffle have been considered. Due to the strong vortexes created by the sharper corners of the baffles and the reduction of the effective water bulk climbing through the tank walls, the sloshing was dramatically reduced. The increase of the baffle distance away from the tank bottom led to a decrease in the sloshing wave. It was noted that the baffle near the free surface caused the maximal dissipation. The frequency response of the sloshing wave was accordingly illustrated.

MULTI-OBJECTIVE PARTICLE SWARM OPTIMIZATION OF THE K-TYPE SHELL AND TUBE HEAT EXCHANGER (CASE STUDY)

This paper investigated optimization of two objectives function include the total amount of heat transfer between two mediums and the total cost of shell and tube heat exchanger. The study was carried out for k-type heat exchanger of the cryogenic unit of gas condensates by multiple objective particle swarm optimization. Six decision variables including pipe pitch ratio, pipe diameter, pipe number, pipe length, baffle cut ratio, and baffle distance ratio were taking into account to conduct this simulation-based research. The results of mathematical modeling confirmed the actual results (data collected from the evaporator unit of the Tehran refinery’s absorption chiller). The optimization results revealed that the two objective functions of heat transfer rate and the total cost were in contradiction with each other. The results of the sensitivity analysis showed that with change in the pitch ratio from 1.25 to 2, the amount of heat transfer was reduced from 420 to 390 kW about 7.8%. Moreover, these variations caused reduction in cost function from 24,500 to 23,500 $, less than 1%. On the other hand, an increase in pipe length from 3 to 12 meters, the heat transfer rate raised from 365 to 415 kW by 13.7%, while the cost increased from 20,000$ to 24500$ about 22%.

Experimental study of concurrent-flow flame spread over thin solids in confined space in microgravity

Concurrent flow flame spread experiments are conducted over thermally thin solid fuels in microgravity aboard the International Space Station (ISS) under varying levels of confinement. Samples of cotton fiberglass blended textile fabric are burned in air flows in a small flow duct. Baffles are placed parallel to the sample sheet, one on each side symmetrically. The distance between the baffles is varied to change the confinement of the burning event. Three different materials of baffles are used to alter the radiative boundary conditions of the space that the flame resides: transparent polycarbonate, black anodized aluminum, and polished aluminum. In all tests, samples are ignited at the upstream leading edge and allowed to burn to completion. The results show that at low flow speeds (<17 cm/s), the flame reaches a steady state for all tested baffle types and baffle distances. The spread rates and flame lengths at the steady state increase first and then decrease when the baffle distance decreases, resulting in an optimal baffle distance for flame spread. Furthermore, there exists a limiting baffle distance below which the flame fails to spread. It is concluded that the confinement imposed by the baffles accelerates the flow during the combustion thermal expansion and the baffles reflect flame radiation back to the sample surface, both of which intensifying the burning. However, the confinement also limits the oxygen supply and introduces conductive heat loss away from the flame. At the same baffle distance and imposed flow speed, flame length and spread rate are largest for polished aluminum baffles, and lowest for transparent polycarbonate baffles. The differences are most prominent at intermediate tested baffle distances. While the radiative heat feedback from the baffles is expected to increase when the baffle distance decreases, flame length and flame spread rate are similar for all baffle types at small baffle distances as the combustion is limited by the reduced oxygen supply.

Comparative study of the thermal performance of four different parallel flow shell and tube heat exchangers with different performance indicators

Abstract Round rod baffle (RRB), plain plate baffle (PPB), wavy-shaped plate baffle (WSB) and polygonal-shaped plate baffle (PSB) are four commonly used baffles in parallel flow shell and tube heat exchangers (STHXs). Comparative study of these four different baffles are numerically carried out using different performance indicators including Nusselt number, friction factor, performance evaluation criterion, entropy generation ratio, and entransy dissipation ratio for flow in full turbulent regime. Heat transfer mechanism has also been discussed. Correlations for Nusselt number and friction factor are fitted and the cost estimation using Hall’s method is compared. It is found that the Nusselt number of STHX-PPB, STHX-WSB, and STHX-PSB increased by 20.9%, 15.2%, and 23.9% averagely compared with STHX-RRB, respectively. The friction factor can be increased on average by 142.0%, 154.5%, and 242.4%, respectively. However, the overall performance of them is only 90.1%, 84.4%, and 82.3% that of STHX-RRB, respectively. The sequence of entropy generation and entransy dissipation is STHX-RRB &gt; STHX-WSB &gt; STHX-PPB &gt; STHX-PSB. The inlet Re and baffle distance have significant effects on different performance indicators while the baffle width does not. Finally, the results show that the STHX-PSB can reduce the total cost as it has better ability on heat enhancement.

Passive micromixer with baffles distributed on both sides of microchannels based on the Koch fractal principle

AbstractSince the beginning of the 21st Century, the development of microfluidic chip technology has been very rapid and has attracted the attention of more and more scholars. As an important part of the microfluidic chip, the performance of the micromixer is critical. The fractal structure in the microchannels helps to improve the mixing performance of the micromixer and improve the mixing efficiency of the micromixer. The research results of other scholars are of great significance to the research of the present paper, which mainly studies the effect of changing the baffle state on the mixing efficiency of the micromixer based on the Koch fractal principle. Through simulation analysis, it was found that the mixing efficiency of the baffles distributed on both sides of the microchannel was higher than the mixing efficiency of the baffles distributed on the microchannel side. When the distance between adjacent baffles was divided into 0.15, 0.25 and 0.35 mm, simulated data suggested that the baffle distance of 0.15 mm was best. Increasing the number of baffles from six to eight groups increased the mixing path of the fluid in the microchannel and improved mixing efficiency. A comparison of mixing efficiencies of the 0°, 15° and 30° baffle angles revealed that very significant improvement in mixing efficiency was obtained at 30°. © 2019 Society of Chemical Industry

Numerical investigation of the baffle plates effect on the solar water storage tank efficiency

ABSTRACTThis paper presents a numerical research of the influence of baffle plates integration inside a horizontal storage tank on the solar water storage tank efficiency. In this work, the baffle plates are integrated inside the tank with different locations and different distances between them to study their effects and also to determine the optimum position in order to enhance the thermal storage system (TSS) performance. The CFD comparison between all proposed designs was carried out and different methods of evaluating mixing and stratification such as temperature evolution, outlet temperature, Richardson number, and full efficiency were calculated to quantify the degree of stratification. Results show that the TSS performance depends on the baffle locations and distance between them. Therefore, a superior thermal performance was achieved for baffles with superior distance between them which are maintained in top of the water storage tank (WST).

Investigation on thermal-hydraulic performance of parallel-flow shell and tube heat exchanger with a new type of anti-vibration baffle and wire coil using RSM method

To overcome the deficiencies of parallel-flow shell and tube heat exchanger with round rod baffles (RRB-STHX), STHX with a new type of anti-vibration baffle (hexagon clamping baffle) and equilateral triangle cross sectioned wire coils (HCBetsw-STHX) is proposed in this paper. Response surface methodology (RSM) is adopted to investigate its thermal-hydraulic performance. Baffle distance, coil pitch, coil diameter and Reynolds number are considered as four design parameters. Analysis is conducted based on CFD to acquire the objective functions (NuH, NuH/NuR, fH, fH/fR and PEC) for different combination of design parameters. The RSM with Central Composite design is used to identify the relationships between the objective functions and the design parameters. Variances of the linear term, quadratic term and interactive term for design parameters in the response variables are analyzed. The mechanism of heat transfer enhancement of HCBetsw-STHX is illustrated from the view of field synergy theory. The results indicate that the heat transfer enhancement of HCBetsw-STHX is quite better than that of RRB-STHX. In the given design space, the NuH/NuR is in the range of 1.335–1.720; the fH/fR is in the range of 5.462–12.936. The most significant factor on NuH is Reynolds number, while the most significant effect factor on NuH/NuR, fH, fH/fR and PEC is coil pitch. The sensitivity of three objective functions (NuH, fH and PEC) to design parameters is explored. In addition, the design parameters optimization for the maximum value of NuH and PEC and that for the minimum value of fH are also carried out and corresponding flow structures are shown and illustrated.

Parameters optimization of a parallel-flow heat exchanger with a new type of anti-vibration baffle and coiled wire using Taguchi method

This study presents the thermal-hydraulic optimization of the design parameters of a parallel-flow shell-and-tube heat exchanger with a new type of anti-vibration hexagon clamping baffle and equilateral triangle cross-sectioned coiled wire. A periodic flow unit duct with non-staggered tube layout is adopted as the numerical analysis model by Fluent. The Taguchi method is used to explore the influence of five geometric parameters including baffle distance (A), baffle width (B), coil diameter (C), coil pitch (D), and the side length of the equilateral triangle (E). An L18 (35) orthogonal array is chosen to carry out the numerical simulation. The comprehensive thermal-hydraulic performance evaluation criterion (PEC) is set as the optimization goal. The results show that the order of the factor effectiveness for the Nusselt number is E>C>A>D>B, for the flow friction is C>E>A>B>D and for the PEC is C>E>A>B>D. This means that the coil pitch has a great influence while the baffle width and the coil diameter have a trifling effect. Finally, the optimal factor combination for PEC is obtained. The PEC of the optimal combination is 0.19%–1.92% higher than the model with better comprehensive performance among 18 cases for Reynolds number in the range from 14 465 to 32 547.

Hydrothermal performance and entropy generation analysis for mixed convective flows over a backward facing step channel with baffle

In this work, we numerically investigate the thermo-hydraulic characteristics and entropy generation for mixed convective flow through a backward facing step channel with baffle. The effect of baffle geometry is studied by considering three different shapes for the baffle viz. square, triangular and elliptical and two different baffle sizes viz. hb × wb = 1 × 1 and hb × wb = 2 × 2 designated as B1 and B2 configuration respectively. Parametric studies are also carried out to analyse the effects of baffle to step obstruction distance, number of baffles and arrangement of baffles in inline and staggered order on the fluid flow, heat transfer and entropy generation characteristics. Local and average Nusselt number, pressure drop and entropy generation are computed for all the configurations at a fixed Reynolds number Re = 100 and for a range of Richardson number Ri = 0.1–1. Our study reveals that the reattachment length decreases with the addition of the baffle inside the channel and the length is inversely proportional to the size of the baffle. Peaks of local Nusselt number are observed in the region near the baffle and the magnitude of these peaks are dependent on the baffle shape and size. It is observed that local entropy generation is minimum within the re-circulation zone while the same is maximum at the reattachment point. The larger the distance of baffle from step, the smaller is the total irreversibility associated with it and its magnitude is the least in case of elliptical baffle for both the configurations. For any baffle shape having B1 configuration, the average Nusselt number, the average pressure drop and the total entropy generation are minimum for two baffles both mounted on the top wall, while these parameters predict an increasing trend with increasing number of baffles for B2 configuration. In case of pair of baffles mounted both on the top and bottom walls, inline arrangement of baffles always incur higher heat transfer performance, pressure drop penalty and entropy generation as compared to staggered arrangement. For all the number of pairs of baffles in staggered arrangement, elliptical baffles always provide the highest heat transfer performance, least pressure drop penalty and least entropy generation among all the baffle geometries and as such in staggered arrangement, elliptical baffles in backward facing step channel is an optimum design choice from the perspective of both the thermo-hydraulic performance and entropy generation.

Numerical simulation and analysis of the effect of baffle distance and depth on solid-liquid two-phase flow in circular secondary clarifier

Numerical simulation and analysis of the effect of baffle distance and depth on solid-liquid two-phase flow in circular secondary clarifier

Numerical investigation of shell-side performance for shell and tube heat exchangers with two different clamping type anti-vibration baffles

Inspired by curve-rod baffle shell and tube heat exchanger (CRB-STHX), a new type of hexagon clamping anti-vibration baffle shell and tube heat exchanger (HCB-STHX) is proposed to overcome the vibration vulnerability of round rod baffle shell and tube heat exchanger (RRB-STHX). The assembling processes of HCB-STHX and CRB-STHX are illustrated. The flow and heat transfer characteristics on shell side are compared and analyzed numerically by CFD method. The effects of several factors such as velocity, baffle distance, baffle width, baffle profile, and baffle layout on thermal–hydraulic performance are investigated in full developed turbulence regime with Reynolds numbers ranging from 10,849 to 32,547. The results indicate that HCB is more suitable for large and heavy tube bundle due to its better rigidity; HCB has a better heat transfer enhancement but a poorer overall performance (indexed by PEC) than CRB; the baffle distance has a significant effect on thermal–hydraulic performance while the baffle width does not; with PEC concerned, the shape of the profile of CRB is superior to that of HCB; compared with baffle in parallel layout, baffle in perpendicular layout can enhance heat transfer, while the former is convenient for manufacturing and assembling.

UNSTEADY NUMERICAL SIMULATION OF TURBULENT FORCED CONVECTION IN A RECTANGULAR PIPE PROVIDED WITH WAVED POROUS BAFFLES

Numerical simulations of flow and heat transfer in a serpentine heat exchanger configuration are presented to demonstrate application of porous media techniques in heat exchanger analyses. In this study, steady-state 3D turbulent forced convection flow and heat transfer characteristics in a rectangular pipe with baffles attached inside pipe have been numerically investigated under constant wall heat flux boundary condition. Numerical study has been carried out for Reynolds number of 20000-50,000, Prandtl number of 0.71, baffle distances h/D h of 1/3 and 2/3, and baffle thickness e of 1/12, 2/3. It is observed that rectangular pipe having waved baffles has a higher Nusselt number and friction factor compared to the smooth rectangular pipe without baffles. Periodically fully developed conditions are obtained after a certain module. Maximum thermal performance factor is obtained for the baffle waved. Results show that baffle distance, waved porous baffle, and Reynolds number play important role on both flow and heat transfer characteristics. All the numerical results are correlated within accuracy of ±2% and ±2.5% for average Nusselt number and friction factor, respectively.

An experimental study of heat transfer enhancement in an air channel with broken multi type V-baffles

This work aims at studying the effect of broken multi type V-baffles on heat transfer, pressure drop, and thermal hydraulic performance characteristics in an air channel is experimentally investigated. The air channel had aspect ratio of 10.0 and the Reynolds number (Re) based upon the mass flow rate of air (m a ) at entrance of the channel varied from 3000 to 8000. The discrete baffle distance (D d /L v ) varied from 0.27 to 0.77, relative baffle gap width (G w /H B ) varied from 0.50 to 1.5, relative baffle height (H B /H D ) varied from 0.25 to 1.0, relative baffle pitch (P B /H B ) varied from 8.0 to 12, relative baffle width (W D /H D ) varied from 1.0 to 6.0, and flow attack angle (α a )varied from 30° to 70°. It has been found that performance of broken multi type V-baffles air channel is better than the performance of smooth surface air channel for the range of geometrical parameters investigated. Experimental results observed that maximum enhancement in overall thermal performance have been found at Dd/Lv value of 0.67, Gw/HB value of 1.0, HB/HD value of 0.50, P B /H B value of 10, and αavalue of 60°.

Numerical Study Of Turbulent Thermal-Hydraulic Performance Of Al2o3-Water Nanofluid In Channel With Triangular Baffles

In this paper, turbulent forced convection of nanofluid flow in channel with isoscelestriangular baffles is numerically investigated over Reynolds number ranges of 5000-10000. One baffle mounted on the bottom wall of channel and another mounted on the top wall. Al2O3-water nanofluid with nanoparticles volume fraction of 4% and nanoparticles diameters of 25 nm is used. The governing continuity, momentum and energy equations as well as the low Reynolds number k-ε model of Launder and Sharma have been solved using finite volume method. The effect of baffle height, baffle distance as well as Reynolds number on the flow and thermal characteristics have been presented and discussed. It is found that the enhancement ratio of the average Nusselt number as well as the fraction factor increase with increasing in the baffles height. It is also found that the enhancement ratio of the average Nusselt number increases as the distance of top baffle decrease. Furthermore, the best thermal-hydraulic performance of channel with triangular baffles using nanofluid can be obtained at baffle height of 2.5 mm, distance of the top baffle of 40 mm and Reynolds number of 5000.

A study of wavy falling film flow on micro-baffled plate

The effects of baffles, flow conditions and fluid properties on wavy motion of falling film were examined experimentally and numerically. Visualization showed that the liquid film became wavier by increasing the baffle distance and by changing liquid from water to methanol in the range of Reynolds number less than 42. Subsequently, the falling film behavior was numerically investigated by adopting VOF method. The qualitative agreements under similar flow conditions well validated both of visualization and numerical methods. The numerical results showed that a higher baffle tended to cause film break-up while the break-up was prevented by increasing the flow rates. As Reynolds number increases, the liquid film became wavier and further surface deformation became obvious. Those results demonstrated that properly-baffled reaction plate could form a noticeably wavy and deformed but quasi-stable falling film at a given flow rate for an organic solvent. The amplitude of wavy falling film on the baffled plates was correlated with Reynolds number, Bond number and non-dimensional geometrical factors, while the thickness of the wavy falling film was correlated with the non-dimensional geometrical factors. It was finally suggested that the possible enhancement of gas absorption due to the surface deformation of liquid film is of further interest targeting process intensification.

Numerical simulation and performance improvement for a small size shell-and-tube heat exchanger with trefoil-hole baffles

The shellside turbulent heat transfer enhancement with trefoil-hole baffles was validated in our previous experimental investigation on a small size heat exchanger. In the present work, the commercial software ANSYS FLUENT is adopted to conduct the numerical study on the thermal augmentation of trefoil-hole baffles. Structural modification is made on the small size heat exchanger for better thermo-hydraulic performances, and the effects of baffle distance are investigated. Computation results demonstrate that the current numerical model, where the whole heat exchanger, including tubes, baffles and fluids on both shell and tube sides, etc., is modeled, could predict the thermo-hydraulic performances considerably well by comparing with experimental data. Moreover, it is found that with the structural modification, the pressure loss on the shellside of the small size heat exchanger decreases by ∼21.0%, and the shellside overall thermo-hydraulic performance rises by ∼21.9%. In addition, the convection heat transfer coefficient on the shellside is observed to decrease monotonically with the decrement of baffle number (from 7795.4 to 6431.2 W/m2 K at shellside Re = 11,350), while the variation tendency of shellside overall thermo-hydraulic performance with baffle number is on the opposite, with the value between 558.3 and 712.1 W/(m2 K kPa) at shellside Re = 11,350.