Baffle Scheme Research Articles

Numerical Comparison of Orifice, Ladder Helical or Segmental Baffle Half-Cylindrical Heat Exchangers

The half-cylindrical heat exchanger is formed by inserting a longitudinal plate in a cylindrical shell space of a U-tube heat exchanger to form dual shell passes for the countercurrent heat transfer purpose. The orifice baffle (OB) in the half-cylindrical shell-side space was proposed to overcome the problems of high-pressure drop in the segmental baffle scheme (SG) and complicated configuration in the unilateral ladder helical baffle scheme (UL). The thermal-hydraulic performances of the bottom part of the half-cylindrical U-tube heat exchanger of four configurations of OBs (fillet triangular, dual-foil square, trefoil, and quatrefoil square), the UL, and the SG were investigated numerically by Fluent in three baffle pitches (50, 40, and 30 mm). The accuracy of the simulated results was validated by experiment with satisfactory agreement. The orifice shape is not sensitive to the performances as long as with a similar flow area. The comprehensive indexes of the schemes OB are very close to that of the UL and much greater than that of the SG, while their overall and shell heat transfer coefficients and pressure drops are lower than those of the schemes UL and SG. Besides, the overall and shell heat transfer coefficients of all schemes increase as the baffle pitch decreases.

Investigation of noncircular orifice supporting baffle longitudinal flow heat exchangers

Owing to the disadvantages of the segmental baffle heat exchanger (SBHE–STHE), a novel type of supporting baffle longitudinal flow heat exchanger is proposed and numerically studied. This equipment includes hexagonal cinquefoil, regular quadrangular, trefoil fillet, and reticulated orifice baffle heat exchangers. The flow and heat transfer performance of the four noncircular orifice supporting baffle longitudinal flow heat exchangers are investigated. Combined sections were fabricated, and local performance characteristics of temperature, pressure, and flow field contours were examined. A composite dimensionless index based on SBHE–STHE is proposed to quickly estimate the comprehensive characteristics of the four supporting baffle longitudinal flow heat exchangers. Results show that the noncircular orifices within the supporting baffle induce jet flow and fluid disturbance. Consequently, periodic pulsating vortices among adjacent supporting baffles are generated, explaining the heat transfer enhancement mechanism. The heat transfer capability of the reticulated orifice baffle heat exchanger is higher than that of the other three orifice baffle schemes and similar to that of the SBHE–STHE. All the comprehensive performance indices of the four noncircular orifice schemes are higher than those of the SBHE–STHE.

Mitigation of liquid sloshing by multiple layers of dual horizontal baffles with equal/unequal baffle widths

Present work aimed to discover the inhibiting efficacy of multiple layers of dual horizontal baffles (multiple DHBs) on liquid sloshing under harmonic and seismic excitations by applying a Navier-Stokes solver. The multiple DHBs with equal/unequal baffle width (EBW/UBW) were considered, where that of UBW was divided into two categories — oblique and concave UBW schemes. Their damping effects were illustrated by estimating the free surface and pressure results, and the velocity and vortex fields were also discussed. The results showed that the EBW scheme with wider width was better than the narrow one. Both UBW schemes could effectively inhibit the resonant sloshing wave and were also superior to the EBW scheme in damping the sloshing amplitude and hydrodynamic load at lower parts of the tank sidewall. Overall, all baffle schemes could effectively suppress the total forces acting on the tank sidewall. Finally, El Centro earthquake was imposed on the charging system to guarantee a violent sloshing wave, and the damping efficacy of various baffles on such wave was numerically investigated.

Design of a Broadband Cavity Baffle Bender Transducer

As low-frequency and broadband acoustic emission capability is beneficial to the detection range and acoustic communication speed of small scale autonomous underwater vehicles (AUV), this type of transducer is required, especially in cases of complex acoustic environments. A broadband bender transducer with cavity baffle that suits small scale AUV is proposed. Rather than additional benders, a passive cavity baffle, which would be capable of providing mutual radiation and a fluid cavity mode, is introduced to a single bender. The bending resonant frequency is reduced by the mutual radiation between the bender and the cavity baffle, the cavity baffle extends the lower limit of the available frequency band of the transducer, the liquid resonant frequency behind the former expands the higher limit, then the cavity baffle bender transducer fills the role of radiating low-frequency and broadband emissions through multimode coupling. The finite element method is used to analyze the acoustic performance of the transducer under different baffle conditions. Then, a prototype of the broadband cavity baffle bender transducer is developed according to the optimized parameters of simulation. The acoustic parameters of the prototype were measured in an anechoic pool. The resonant frequency measured in water of the bender itself is 3 kHz, and the −3dB bandwidth is 560 Hz. The prototype test results show that the cavity baffle scheme can improve the −3dB bandwidth of the bender from 560 Hz to 1000 Hz, which fundamentally realizes the expectations of the prototype design.

Numerical simulations for internal baffle effect on suppressing sway-sloshing coupled motion response

This study investigates the internal baffle effect on reducing sway coupled with sloshing motion response. Various baffle schemes are proposed and the suppressing effect on the sway motion response is studied for a rectangular section box. Numerical simulations suggest that the horizontal baffles with shallow submerged depth can reduce the sway motion response remarkably. Proper baffles can reduce the sway-sloshing motion in large scale and make the ship sway motion amplitude similar as that without sloshing effect. In consideration of filling depths, the multiple layer horizontal baffles are suggested for suppressing the coupled sway-sloshing motion response.

Experimental investigation on heat transfer performances in half-cylindrical shell space of different heat exchangers

The superheated steam cooling section and the condensate cooling section of the power plant feedwater heaters and the countercurrent U-tube heat exchangers all involve heat transfer in half-cylindrical shell space. The overall and shell-side heat transfer coefficients (h.t.cs.), pressure drop, and the comprehensive performances of some half-cylindrical space heat exchangers with different baffle structures were experimentally investigated. The investigated structures include three ladder helical baffle types [single inclined ladder helical (SH), dual inclined ladder helical (DH) and folded ladder helical (FH)], three orifice baffle types [fillet triangle orifice (F), trefoil-orifice (T) and quatrefoil-orifice (Q)], and segmental baffles (S), and all schemes are of two baffle pitches. Under the same baffle pitch and working condition, the experimental results show that the shell-side h.t.cs. of the ladder helical baffle schemes are higher than those of the orifice baffle schemes and segmental baffle ones; and the shell-side pressure drops of the orifice baffle schemes are much lower than those of the ladder helical baffle schemes and the segmental ones. The values of average comprehensive index hoΔpo−1/3 of the ladder helical schemes FH-40, DH-40 and the orifice baffle schemes F-40 and T-40 are respectively 14.26%, 17.58%, 15.62% and 12.82% higher than that of the segmental scheme S-40.

Performance investigation and multi-objective optimization of helical baffle heat exchangers based on thermodynamic and economic analyses

The application of helical baffle heat exchangers (HBHXs) is attracting much more attention in both industrial and academic fields. In this paper, the heat transfer and fluid flow characteristics of HBHXs are explored by the aid of numerical and experimental analyses, and a good agreement is reached between the simulated and measured data. A series of helical baffle configurations involving parameter combinations of helix angles (10°, 15°, 20°, 25°, 30°, 35°, 40°, 45°) and axial overlapped ratios (0, 10%, 20%, 30%, 40%, 50%) are taken into account. Then a multi-objective genetic algorithm approach is proposed for HBHXs optimization design. The tube number, tube outer diameter, tube length, helix angle and axial overlapped ratio are perceived as design variables, and the revised entropy generation number and total cost are considered as objective functions. The results illustrate that the thermal enhancement and axial velocity reduction are attributed to diminished helix angle and enlarged axial overlapped ratio. For the sake of a narrow helix pitch, the baffle schemes of 45° helix angle together with no more than 20% axial overlapped ratio are given priority over the one of 40° helix angle, while the schemes of 40° helix angle as well as at most 30% axial overlapped ratio are preferable to the one of 30° helix angle in view of better shell-side comprehensive performance. A set of Pareto optimal solutions are obtained in order to trade off the thermodynamic and economic behaviors, and the optimized results make known that the multi-objective optimization method is more suitable compared with the single-objective optimization strategy.

Performance investigation on the novel anti-leakage and easy-to-manufacture trisection helical baffle electric heaters

The difficult manufacturing of helical baffles hinders the widespread application of the enhancement technology and the shortcut leakage between adjacent baffles impairs the enhancement effects. To solve these two issues, the promising anti-leakage and easy-to-manufacture helical baffles with small inclined angle and folded structure are proposed, which can be produced by 2D laser cutting and simple mechanical folding. The influence of different helical baffle configurations, including three normal helical schemes, three axial separation helical schemes, three novel folded axial separation helical baffle schemes and a segmental scheme on the performance of electric heaters are numerically investigated. The equivalent angles of helical schemes adopted in this work are 15°, 20° and 25°, and the inclined angle of helical baffles under axial separation connection style is 10°. Compared with the corresponding axial separation scheme without folding, the leakage can be significantly decreased, the heat transfer coefficients h and the comprehensive indices h⋅Δp−1/3 of FH15(10)°, FH20(10)° and FH25(10)° are increased by 6.5%/2.3%, 12.2%/7.3% and 20.4%/13.0%, and the averaged tube wall temperatures Tw are decreased by 12.5 K, 25.4 K and 54.7 K, respectively. This research can provide feasibility for the extended application of helical baffles in electric heaters or heat exchangers.

Influence of outlet orientation and variable tube length on high temperature zones of U‐tube trisection helical baffle electric heaters

AbstractNumerical simulation was performed to optimize temperature distribution especially at high temperature zones at the rear part of U‐tube bundle electric heaters with unique one‐plus‐two U‐tube layouts. The influences of variable tube lengths and different outlet nozzle orientations on flow and thermal features on axial separation trisection helical baffle schemes in contrast to segmental schemes were investigated. The results show that the variable tube length schemes can effectively ameliorate high temperature zones and obtain more uniform temperature fields. The mean heat transfer coefficient, h.t.c., and tube wall temperature, Tw, of the variable tube length scheme HV15(10)°‐180° are respectively 0.7% higher and 3.1 K lower than those of the normal scheme H15(10)°‐180°. The optimal relative position of the outlet and tube bundle for helical schemes is that the outlet axis is not only tangent to the last straight edge of the baffle but is also on the side near it, while the optimum outlet angle for the segmental scheme is 90° within the research scope. Compared with segmental scheme S200‐90°, the averaged heat transfer coefficients, h.t.c.s, and comprehensive indexes, h · Δp−1/3, of the helical baffle schemes HV15(10)°‐180°/HV15(10)°‐Ax respectively rise by 14.6/11.8% and 16.1/13.8%, while the average Tw declines by 40.7/33.3 K.

Performance comparison of helical baffle electric heaters with different baffle configurations

ABSTRACTNumerical simulations were conducted on nine U-tube electric heater models of 45 U-tubes with a unique tube layout of one-plus-two units, including eight helical baffle schemes of different baffle shapes and assembly configurations and a segmental one. Secondary flow and leakage flow are presented on eccentric longitudinal slices and unfolded concentric hexagonal slices, respectively. The tube surface temperature contours are also demonstrated. The results indicate that the average values of heat transfer coefficient and comprehensive index of h·Δp−1/3 of the folded helical baffle scheme with axial separation FH20(10)° are, respectively, 15.93 and 30.28% higher than those of segment scheme S200.

Numerical study on performances of small incline angle helical baffle electric heaters with axial separation

To minimize the abrasion of sharp-corners of holes of inclined baffles manufactured by 2D laser beam cutting machine on the tubes, the application of axial separation with small inclined angle helical baffles is a simple alternate, which creates greater helix pitch for suitable cross section area. Numerical simulation on the flow and thermal performances were conducted on three axial separation helical baffle electric heaters with equivalent angles 15°, 20° and 25° using 10° inclined baffles, three normal helical baffle ones and two segment baffle ones spanned respectively 200 and 250mm. Each electric heater comprises 27 U-tubes on equilateral triangle layout with nine one-plus-two units. The secondary flow imposed plug flow pattern and leakage flow were demonstrated for helical schemes. The axial separation helical baffle schemes have obvious merits in the heat transfer coefficient, comprehensive index and the temperature uniformity of the electric heating tubes over those of the segment baffle ones. The average heat transfer coefficient and the comprehensive index (h·Δp−1/3) of the modified axial separation helical scheme with equivalent angle 20° using 10° baffles are respectively 37.8% and 26.0% higher while its average tube wall temperature is 95.6K lower than those of the segment scheme spanned 200mm.

An analysis of performance on trisection helical baffles heat exchangers with diverse inclination angles and baffle structures

Investigations of thermo-hydraulic performance were conducted on five trisection helical baffle heat exchangers with different inclination angles, baffle shapes, or connection patterns, and one segmental baffle heat exchanger (SEG). A comparative analysis of three sector baffle schemes with inclination angles of 10° (10°S), 15° (15°S), and 20° (20°S); an ellipse baffle scheme with an inclination angle of 15° (15°E); and an axial overlap sector baffle scheme with an inclination angle of 20° (20°D) was performed. Local images were constructed to obtain pressure loss characteristics and flow field distributions. The flow field characteristics, such as the Dean vortex secondary flow and bypass leakage between adjacent baffles, are clearly shown and discussed. The same inclination angle schemes have completely different properties because of the baffle shapes or connection patterns. The performance of the end-to-end scheme is superior to that of the axial overlap scheme, and the ellipse baffle scheme is inferior to the sector baffle scheme. The 20°S scheme has the optimum comprehensive index and lowest shell-side pressure loss. The 10°S scheme has the highest shell-side Nusselt number and shell-side pressure loss, and can be selected only when heat transfer capability is very important in an engineering application.

长挡板结构型式对竖缝式鱼道鱼池流速影响研究

大坝和堤堰等水工建筑物的修建截断了河流，使河流中鱼类的栖息地及洄游路线受到极为严重的干扰。为了解决鱼类的洄游问题，修建鱼道是广泛采用的工程措施，其中，以竖缝式鱼道的数量居多。本文从竖缝式鱼道的长挡板细部构造入手，通过模型实验的手段，对比分析了三种方案对竖缝式鱼道鱼池流速的影响。通过研究，推荐竖缝式鱼道的长挡板结构型式为“直钩”型。 The construction of dam and burrock blocks the river basin, and affects the migratory route of fishes. Fishways are widely used as engineering measures to guarantee the migration of fish. The vertical slot fishway is the most common type. This paper presents the results of an experimental work with three different long baffle schemes on the vertical slot fishway. The values of velocity are indicated by the results. Above all three schemes, “straight hook” type is recommended as the type for long baffle structure of the vertical slot fishway.

Numerical investigation of the performances of axial separation helical baffle heat exchangers

Axial separation is a novel baffle connection configuration of circumferential overlap helical baffle heat exchangers which makes baffle incline angle seriation possible. The adjacent baffle plates are separated by sleeve tubes to form a greater pitched helix for enhancing heat transfer under required pressure drop with the least number of molds for reducing baffle manufacture cost. Numerical simulations of flow and heat transfer performances were conducted and the calculation results were verified by the experimental ones. Performance investigation was conducted on eight normal trisection helical baffle schemes with baffle incline angles from 15° to 23° and five axial separation schemes of equivalent 17–22° angles using 15° baffles. In the calculation scope the average deviations of heat transfer coefficients and pressure drops of the normal helical schemes are respectively about −1.97% and −8.11% per 1° deviation of incline angle. The axial separation schemes using 15° baffles with equivalent 21° and 22° incline angles have deviation values of heat transfer coefficient 1.21% and 1.33% lower and pressure drop 4.96% and 5.55% higher respectively than those of the normal 21° and 22° incline angle schemes. By adopting axial separation approach the seriation step of baffle incline angles can be extended to 8°.

Heat transfer enhancement of folded helical baffle electric heaters with one-plus-two U-tube units

Flow and heat transfer property simulation was performed on both helical and segmental baffle electric heaters of equilateral tube layout with one-plus-two U-tube units. Four helical baffle electric heaters have folded circumferential overlapped baffles with inclined angles of 20°, 25° and 30° single thread and 30° dual threads respectively, while two segmental ones have baffle plate spans of 200 and 250mm respectively. The folded baffle is designed to create two “ears” perpendicular on the axis of the cylinder by folding the inclined baffle at both corners of the curved edge and straight edges to fix the helical baffles with three sets of rod and spacing sleeve assembles. Simulation results show that the optimal inclined angle of helical electric heater is 25°, which has the highest comprehensive index and high heat transfer coefficient with low tube surface temperature, while the segmental baffle scheme with greater span has lower heat transfer coefficient and pressure drop but higher tube surface temperature. Compared with those of segmental scheme with baffle span of 200mm, the heat transfer coefficient and comprehensive index of helical electric heater with inclined angle of 25° increase by 18.3% and 29.8% respectively, while the pressure drop and the average temperature on tube surface reduce by 24.3% and 45.6K respectively.

An efficient and low resistant circumferential overlap trisection helical baffle heat exchanger with folded baffles

An efficient and low resistant circumferential overlap trisection helical baffle shell-and-tube heat exchanger with folded baffles (cothHXf) is presented. It is a modified trisection helical baffle heat exchanger with folded helical baffles for setting rods-and-spanning sleeves. It not only inherits all the merits of circumferential overlap helical baffle scheme, but also adds many additional advantages, such as supporting the inclined baffles with the least rods, simplifying the manufacturing process of spanning tubes and effectively inhibiting the reverse leakage at triangular areas between adjacent baffles. The improved flow characteristic and heat transfer enhancement mechanism of this heat exchanger were numerically investigated in comparison with conventional segmental baffles shell-and-tube heat exchanger (segHX). The flow fields within triangular area of adjacent baffles and nearby regions were depicted. The impacts of the folded baffles on shell-side helical flow, secondary vortex flow, and leakage pattern were analyzed. The distribution configurations of fields of velocity, pressure, temperature and local heat flow rate were revealed. The results show that the heat transfer performance and comprehensive performance evaluation indexes of the cothHXf are much better than those of the segHX while the pressure drop of the cothHXf is much lower than that of the segHX. The numerical simulation results of vivid distributions of flow and thermal fields of the cothHXf can provide theoretical basis for an engineering design and popularized industrial application of the new type heat exchangers.

Experimental investigation on enhanced heat transfer of vertical condensers with trisection helical baffles

The vertical condensers have advantages of small occupation area, convenient in assemble or dismantle tube bundle and simple structure etc. However, the low heat transfer performance limits their applications. To enhance the heat transfer, a novel type of vertical condensers was designed by introducing trisection helical baffles with liquid dams and gaps for facilitating condensate drainage. Four configurations of vertical condensers with trisection helical baffle are experimentally studied and compared to a traditional segment baffle condenser. The enhancement ratio of trisection helical baffle schemes is about 1.5–2.5 and the heat transfer coefficient of the dual-thread trisection helical baffle scheme is superior to that of the single-thread one by about 19%. Assistant by the theoretical study, the experimental data is simulated and the condensation enhancement mechanisms by applying trisection helical baffle in vertical condenser are summarized as condensate drainage, short tube construct and reduce steam dead zone functions of the helical baffles.

Numerical simulation on the performance of trisection helical baffle heat exchangers with small baffle incline angles

ABSTRACTNumerical simulation was conducted on oil–water heat transfer in five circumferential overlap trisection helical baffle shell–and–tube heat exchangers (cothSTHXs) with 16 tubes and incline angles of 12°, 16°, 20°, 24°, and 28° and a segmental baffle heat exchanger of the identical tube layout for comparison under laminar flow calculation conditions. The local images represent shell-side flow patterns, and heat transfer properties are presented showing the detailed “secondary vortex flow” and “shortcut leakage flow” patterns to explain the different characteristics of the six schemes. The simulation curves of the heat transfer coefficient and pressure drop are compared with those of the experimental ones, with satisfactory agreement. The average values of the shell-side heat transfer coefficient and the comprehensive index ho/Δpo of the 12° helical scheme are respectively 47% and 51% higher than those of the segmental baffle scheme with about the same pressure drop.

Numerical simulation of the heat transfer performance of trisection helical baffled electric heaters

ABSTRACTTrisection helical baffled electric heaters are proposed to overcome the defects of low heat transfer coefficient and nonuniform tube spacing in conventional segmental baffled electric heaters with multicircular U-tube layouts. Novel trisection helical baffled electric heaters are of equilateral triangle tube layout distributed annularly in groups of one-plus-two U-tube units. Numerical simulation and comparison were conducted on the flow and heat transfer performance and the tube wall temperature uniformity of five helical baffled electric heaters and two segmental baffled ones. Each helical baffle scheme consists of nine one-plus-two U-tube units with a total of twenty-seven Φ16 mm U-tubes supported by the trisection helical baffles of 15 or 20° inclined angle, while each segmental baffle scheme consists of thirty Φ16 mm U-tubes of two-ring annular layout supported by segmental baffled plates spanned either 200 or 300 mm. The calculation results with compressed nitrogen show that the average heat transfer coefficient and comprehensive index (h/Δp1/3) of the helical baffled H15°-1862 scheme with only 68.5% effective heating area are, respectively, 68.2 and 34.3% higher than those of the segmental baffled S200-2462 scheme, while the average tube wall temperature of the H15°-1862 scheme is 31.7 K lower than that of S200-2462 scheme.

Experimental investigation on performances of trisection helical baffled heat exchangers for oil/water–water heat transfer

The trisection helical baffled shell-and-tube heat exchangers have structural features of more suitable to the equilateral triangular tube layouts and less baffle parts. In particular the circumferential overlap trisection helical baffled shell-and-tube heat exchangers are of anti-shortcut structure that accommodates one row tubes in each circumferential overlapped zone between adjacent baffles for dampening shortcut leakage. The performance tests were conducted on both oil–water and water–water heat transfer in heat exchangers with equilateral triangle tube layout of 16 tubes including five helical baffle schemes with incline angles of 12°, 16°, 20°, 24°, 28° and a segmental baffled one for comparison. The test results show that both the shell side heat transfer coefficient ho and pressure drop Δpo increase but the comprehensive index ho/Δpo decreases with the increase of the mass flow rate of all schemes; and that the shell side heat transfer coefficient, pressure drop and the comprehensive index ho/Δpo decrease with the increase of the baffle incline angle at certain mass flow rate, except that the curves of comprehensive index ho/Δpo of 12° and 16° helical baffle schemes are almost coincide. The average values of shell side heat transfer coefficient, the comprehensive index ho/Δpo of the 12° helical baffled scheme are about 50% higher than those of the segmental one with almost same pressure drop. The correlation equations for shell side Nusselt number and axial Euler number are presented varying with axial Reynolds number, Prandtl number and helical baffle incline angle.