Helical Baffle Heat Exchangers Research Articles

Flow Characteristics and Heat Transfer Performances of Quadrant Helical Baffle Heat Exchanger with Grooved Joint

Helical baffle heat exchanger has a wide application in many industrial fields because of its high efficiency and low resistance. A new structure of the grooved helical baffle is proposed to strengthen the stability between the overlapped baffles during the spiral flow of fluid. Based on this structure, the liquid water was selected as the working medium in the tube side and shell side, the flow field characteristics and heat transfer performances of the quadrant helical baffle heat exchanger are numerically analyzed using software FLUENT 2017. The results show that when the helical angle is large (50°) and the overlapped amount is small (0.5), the comprehensive performance of the heat exchanger is the best. Therefore, the heat exchanger performance can be improved by choosing the appropriate combination of helical angle and overlapped amount. The correlation formula of the shell side heat transfer coefficient with helical angle, overlapped amount and mass flow rate is obtained by means of regression analysis, which can provide a reference for engineering application and optimal design of grooved helical baffle heat exchanger.

Effect of helical baffles and water‐based Al2O3, CuO, and SiO2 nanoparticles in the enhancement of thermal performance for shell and tube heat exchanger

AbstractIn this study, Shell and tube heat exchanger (STHX) with 22% cut segmental baffles and helical baffles with 20°, 30°, 40° inclination angles are considered for three‐dimensional CFD analysis using the ANSYS FLUENT tool to investigate the performance of STHX. OHTC and comprehensive performance index are higher for 40° helical baffles when compared to segmental baffle and 20°, 30° helical baffle heat exchangers with water as working fluid. Hence, further investigations are carried out for 40° helical baffle heat exchangers. Numerical investigations are extended with nanofluids (Al2O3, CuO, and SiO2) at 1%, 3%, and 5% volume concentrations for each nanofluid. Under the same mass flow rates, 40° helical baffles with Al2O3 nanofluid as working fluid provided better heat transfer rates when compared to the other two nanofluids and base fluid. Also, the authors noticed that the 5% volume (vol) concentration nanofluids provided better heat transfer enhancements when compared to 1%, 3% volume concentrations, and base fluid. Enhancements (10.33%–8.24%) from lower to the higher mass flow rate in 40° HB with Al2O3 nanofluid at 5% volume concentration are observed when compared to water as base fluid.

Heat Transfer and Flow Resistance Characteristics of Helical Baffle Heat Exchangers with Twisted Oval Tube

Heat Transfer and Flow Resistance Characteristics of Helical Baffle Heat Exchangers with Twisted Oval Tube

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.

Numerical investigation and experimental validation of thermo-hydraulic and thermodynamic performances of helical baffle heat exchangers with different baffle configurations

Helical baffle is deemed as a favorable substitute for segmental one. In the present paper, the investigations on fluid flow and heat transfer behaviors are conducted for heat exchangers with eight helical baffle configurations, involving the continuous helical (CH) scheme, quadrant helical (QH) scheme with diverse axial overlapped ratios and novel sextant helical (SH) scheme. The second law of thermodynamics analysis is exploited to further evaluate the irreversibility in helical baffle heat exchangers. Verifications between the experimental data and numerical predictions are performed, and a good agreement is achieved. The parallel and rotational components decomposed from shell-side velocity are detected, and a new conception of the swirl angle is advanced to reveal the stream pattern in helical channel. The leakages passing through conjunction notches between adjacent baffle plates are depicted to check the discrepancy between the spiral and pseudo-spiral flow states. It concludes that the alterations of baffle shapes and assembly arrangements influence the flow field properties significantly. By analyzing the heat transfer, resistance and comprehensive characteristics in shell side, the SH scheme possesses better thermo-hydraulic performance than the CH and QH schemes; moreover, the least entropy generation is received in the SH and QH schemes at low Reynolds number. In addition, larger axial overlapped ratio provides greater heat transfer coefficient and pressure drop but smaller their ratio as well as higher thermodynamic irreversible loss.

Investigation on shell side performance in half-cylindrical desuperheating zone of ladder type helical baffle heat exchangers

The shell-side flow and heat transfer performance in half-cylindrical desuperheating zones of high pressure feedwater heaters were simulated by Fluent. The investigated structures include three ladder type helical baffle heat exchangers, i.e. the two unilateral ladder types with folded and inclined plane strip baffles, and the bilateral plane type, and two comparative schemes of eggcrate support type and double-segmental type and all baffle types are of three different baffle pitches. The visualized flow patterns in the desuperheating zone were demonstrated on special slices to clearly reveal the mechanisms and impacts of baffle configurations and geometrical parameters on thermal-hydraulic performances. The numerical results show that the shell-side heat transfer coefficients ho of all ladder type helical models are superior to those of both eggcrate support and double-segmental ones, among which the bilateral plane model has the best performances. The average values of ho and evaluation indexes hoΔpo−1 and hoΔpo−1/3 of nine helical models raise 2.99%, 149.50% and 36.26% respectively in contrast to those of the corresponding double-segmental models, and the average values of evaluation performance η for schemes of three baffle pitches 80, 120 and 160 (mm) are respectively 1.202, 1.367 and 1.525.

Mass center equivalent rectangle model for universal correlation of hydrothermal features of helical baffle heat exchangers

The prediction using a universal correlation of the shell side Nusselt number with the Reynolds number for helical baffle heat exchangers (HBHXs) has been in vain, because of the impropriate formula of the cross-section area of helical channel or the flow velocity. The shell side friction factor is of similar situation. A new model of mass center equivalent rectangle (MCER) is proposed to calculate the cross-sectional area of the helical flow channel of the HBHX with the hypothesis that the parameters on the mass center cylinder can represent the mean values of the spiral channel. Taking helix pitch as hypotenuse and two sides of the right triangle are along the mass center equivalent helix angle and its normal direction, and the latter and the radius of the shell are postulated to be the two edges of the windward rectangle. The flow cross-section area of the helical channel is the rectangle area subtracting the total ellipse area of the tubes in the rectangle area. The verification of the model is quite satisfactory for quadrant HBHXs by both the heat exchanger design software HTRI and the existing experimental results in a master thesis with the deviations of ho·Pro−1/3 ~ Reo are respectively within +17% to −10% and ±18%. The verification of the model is also satisfied with experimental results of a trisection circumferential overlap HBHX. The coefficients in the correlation formulas especially for the friction factor need be further consummated relating to the helical baffle type and baffle connection style of the HBHXs.

Performance comparison of heat exchangers using sextant/trisection helical baffles and segmental ones

The shell side flow fields of both sextant and trisection helical baffle heat exchangers are presented on meridian and multilayer hexagon slices. It verifies that the performance of sextant schemes is better than those of the other kinds of helical baffle heat exchangers. The main mechanisms are due to the restricted leakage flow in the minimized gaps with increased baffle number and by one row of tubes dampen the leakage flow in the circumferential overlapped area of the adjacent helical baffles. The performance features were simulated on two different angled sextant helical heat exchangers and each compared with two trisection ones of either identical helical pitch or identical incline angle. The results verified that the performances of helical heat exchangers are mainly determined by the helical pitch rather than the baffle incline angle. The average values of comprehensive index hoΔpo−1/3 of the trisection helical schemes T-24.1° and T-29.7° are correspondingly 3.47% and 3.34% lower than those of the sextant ones X-20° and X-25° with identical helical pitches. The comparison results show that the average values of shell side h.t.c. ho and comprehensive index hoΔpo−1/3 of the optimal dual helix sextant scheme DX30° are respectively 7.22% and 23.56% higher than those of the segment scheme S100.

Experimental and numerical investigation on heat transfer and fluid flow performance of sextant helical baffle heat exchangers

As a promising substitute for the segmental ones, the helical baffles have been gradually popularized in shell-and-tube heat exchangers. Quadrant helical baffles are commonly utilized to induce a pseudo-spiral flow pattern in the shell side of helical baffle heat exchangers, but the triangular leakage loss at the conjunction notches between adjacent baffles has always been the bottleneck. An improved scheme of sextant helical baffle is thus presented as a means of leakage blockage in this work. The experimental approach is implemented and the computational model is established for experimental and numerical analysis of the performance of novel heat exchanger, and a good agreement is achieved by comparing measured data with numerical predictions. The modified flow field characteristic of sextant helical baffle heat exchangers (SHBHXs) is examined in detail in comparison with quadrant helical baffle heat exchangers (QHBHXs). It concludes that the reverse flow in the triangular leakage zone is partly dampened by virtue of special overlapped structure of adjacent sextant helical baffles, and shell-side axial velocity exhibits the feature of uniform distribution. The impact of incline angle is particularly evaluated on variations of shell-side heat transfer coefficient and shell-side pressure drop as well as their ratio, and then the relevant correlations for Nusselt number and friction factor are fitted in the calculation scope. Further comparison results reveal that the thermal performance and the comprehensive performance are much better while the pressure drop is much lower in SHBHXs than in QHBHXs, which can be explicated by a finer field synergy property in SHBHXs on the basis of the field synergy theory. This work can provide theoretical foundation for design and optimization of the new type heat exchanger.

Structural Parameter Optimization of Helical Baffles Heat Exchanger Based on MOPSO

Based on improved flow and heat transfer coupling calculation model of helical baffles heat exchanger, the paper adopts multi-objective particle swarm optimization (MOPSO) to optimize its structural parameters. The shell pass nusselt number and shell pass pressure drop are selected as the objective function, and helical angle and amount of lap are selected as decision variables to obtain optimum combinations of structural parameters. This research provides references for design of helical baffles heat exchanger.

Influence of baffle configurations on flow and heat transfer characteristics of unilateral type helical baffle heat exchangers

The flow and heat transfer performances were investigated on unilateral ladder type helical baffle heat exchangers (ULHBHXs) with different geometrical structures in half cylindrical space and compared with those of the segmental baffle heat exchangers (SBHXs). The unilateral ladder type helical baffles consist of two alternate groups of plates, the folded baffles (Baffles A) and the segment ones (Baffles B). The studied ULHBHXs include the combination schemes of different Baffle A with different baffle pitches (40, 60, 80 mm) and different projection length of inclined section (l = 60, 72, 84 mm and a plane one). Visualization methods of nephograms were adopted on special slices to clearly reveal the impacts of baffle configurations on flow patterns. The numerical results show that the shell-side heat transfer coefficients of the ULHBHX schemes with folded Baffles A are superior but the comprehensive indexes are inferior to those of the corresponding plane ones, and all the helical schemes are superior to those of the segmental schemes. The average ratios of shell-side heat transfer coefficient, pressure drop and comprehensive indexes hoΔpo−1 and hoΔpo−1/3 of all the twelve ULHBHX schemes over those of the SBHX ones with corresponding baffle pitches are 1.166, 0.670, 1.851 and 1.352, respectively.

Performance simulation on unilateral ladder type helical baffle heat exchanger in half cylindrical space

A unilateral ladder type helical baffle heat exchanger (ULHBHX) which is a novel countercurrent U-tube heat exchanger was proposed and investigated for better characteristics of high heat transfer coefficient, low resistance, anti-vibration and anti-fouling with a spiral flow pattern than those of the conventional segment one. The numerical model of ULHBHX was established and simulated by CFD software with 38 heat transfer tubes and 2 rod and spacing tube assemblies in the lower half cylindrical space under the parameters of subcooling of a high pressure feedwater heater in power plants. Different views such as on baffle-parallel slices and polygonal slices were presented to show the flow patterns of the main helical flow, secondary vortex flow and the leakage flow. The influences of geometrical parameters of baffle pitch and projection length of the inclined section on heat transfer and pressure drop were discussed quantitatively. The results show that the shell-side heat transfer coefficient ho of the ULHBHXs is 13.2%–18.2%, with an average of 16.0%, higher than those of the corresponding segment schemes, and the comprehensive index hoΔpo−1/3 is 15.7%–46.4%, with an average of 28.3%, higher than those of the corresponding segment schemes with identical baffle pitches in the discussed range.

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.

Numerical research of stream analysis on helical baffles heat exchangers

In this paper, the numerical simulations for a helical baffles heat exchanger and a segmental baffles heat exchanger with component clearance are performed to reveal the features of leakage streams and their effect on heat exchanger performance. Helical baffles heat exchanger models with four different angles and segmental baffles heat exchanger model were established and calculated via Gambit and Fluent software. The results reveal that the heat exchanger with a 40° helix angle shows the best comprehensive heat transfer performance in turbulent state, and the heat exchanger with a 50° helix angle shows better comprehensive heat transfer performance in laminar flow state. The leakage streams proportion of the helical baffles heat exchanger varies from 5.5% to 6.1%, compared with the leakage streams proportion changes from 16.6% to 21.0% in the segmental baffles heat exchanger. In both turbulent flow state and laminar flow state, with the rise of shell-side Reynolds number, the main spiral stream B proportion decreases and the leakage streams proportion increases in the segmental baffles heat exchanger, while the stream B proportion increases and the leakage streams proportion decreases in helical baffles heat exchanger. The proportion of stream B increases with the increase of the helix angle β and the proportions of leakage streams decrease with the increase of β. The proportion of the tube-baffle leakage stream A increases in radial direction. Both the proportion of stream A and that of the baffle-shell leakage stream E fluctuate in the intermediate zone in axial direction; the stream A proportion decreases at the inlet and outlet zone, while the stream E proportion increases at the inlet and decreases at the outlet zone. The results of this paper could be of great significance in the optimal design and manufacture of the helical baffles heat exchanger.

Experimental investigation of heat transfer and pressure drop characteristics of non-Newtonian nanofluids flowing in the shell-side of a helical baffle heat exchanger with low-finned tubes

An aqueous solution of Xanthan Gum (XG) at a weight fraction as high as 0.2% was used as the base liquid, the stable MWCNTs-dispersed non-Newtonian nanofluids at different weight factions of MWCNTs was prepared. The base fluid and all nanofluids show pseudoplastic (shear-thinning) rheological behavior. Experiments were performed to compare the shell-side forced convective heat transfer coefficient and pressure drop of non-Newtonian nanofluids to those of non-Newtonian base fluid in an integrally helical baffle heat exchanger with low-finned tubes. The experimental results showed that the enhancement of the convective heat transfer coefficient increases with an increase in the Peclet number and the nanoparticle concentration. For nanofluids with 1.0, 0.5 and 0.2 wt% of multi-walled carbon nanotubes (MWCNTs), the heat transfer coefficients respectively augmented by 24.3, 13.2 and 4.7% on average and the pressure drops become larger than those of the base fluid. The comprehensive thermal performance factor is higher than one and increases with an increasing weight fraction of MWCNTs. A remarkable heat transfer enhancement in the shell side of helical baffle heat exchanger with low-finned tubes can be obtained by adding MWCNTs into XG aqueous solution based on thermal resistance analysis. New correlations have been suggested for the shell-side friction coefficient and the Nusselt numbers of non-Newtonian nanofluids and give very good agreement with experimental data.

Performance of Turbulence Models on Heat Transfer and Pressure Drop with a 25° Continuous Helical Baffled Heat Exchanger

The objective of the present work is to study the influence of three turbulence models and find out the suitability of the k-ω SST turbulence model. The thermal performance of a heat exchanger with single continuous helical baffle is studied numerically and experimentally. A commercial CFD package (Ansys-Fluent),based on the finite volume method, is used to predict the performance of 25° continuous helical baffled Heat Exchanger using 3 turbulence models viz. k-ε Realizable, k-ε RNG and k-ω SST. The experiments are carried out in counter-flow mode with cold fluid (ambient water) on the shell side and hot fluid (hot water) on the tube side. In the experimentation, the variation of the shell side heat transfer coefficient and of the pressure drop with shell side mass flow rate is tested. For the validation of the numerical model, the numerical results are compared with the experimental results and with the published literature. The experimental heat transfer coefficient exhibits a deviation from the correlated values in the range of 1.5% to 5.3%, whereas pressure drop shows deviation in the range of 4.22 to 6.67%. The results indicate that all the three turbulence models are in good agreement with the experimental findings. The k-ε Realizable model is the best turbulence model for the prediction of heat transfer and k-ω SST is the best turbulence model for prediction of pressure drop. For the overall performance, k-ω SST model is suitable for the prediction of both heat transfer and pressure drop and it helps in capturing the swirling flows in helical baffle heat exchangers.

Performance comparison for oil-water heat transfer of circumferential overlap trisection helical baffle heat exchanger

The performance tests were conducted on oil–water heat transfer in circumferential overlap trisection helical baffle heat exchangers with incline angles of 12°, 16°, 20°, 24° and 28°, and compared with a segmental baffle heat exchanger. The results sh ow that the shell side heat transfer coefficient h o and pressure drop Δpo both increase while the comprehensive index h o/Δpo decreases with the increase of the mass flow rate of all schemes. And the shell side heat transfer coefficient, pressure drop and the comprehensive index h o/Δpo decrease with the increase of the baffle incline angle at a certain mass flow rate. The average values of shell side heat transfer coefficient and the comprehensive index h o/Δpo of the 12° helical baffled scheme are above 50% higher than th ose of the segmental one correspondingly, while the pressure drop value is very close and the ratios of the average values are about 1.664 and 1.596, respectively. The shell-side Nusselt number Nu o and the comprehensive index Nu o·Eu zo -1 increase with the increase of Reynolds number of the shell side axial in all schemes, and the results also demonstrate that the small incline angled helical scheme has better comprehensive performance.

Modeling for Shell-Side Heat Transfer Coefficient and Pressure Drop of Helical Baffle Heat Exchangers

This study has suitably modified the existing heat transfer and pressure drop correction factors of the modified Bell–Delaware method used for heat exchangers with segmental baffles, taking into consideration the helical baffle geometry. These correction factors are presented in parametric formulas based on the Taborek presented procedure for segmental baffles. These formulas are functions of the geometrical and physical parameters of discontinuous helical baffles. In addition, the parametric formulas are presented graphically based on the Stehlik method. The correction design method proposed by Stehlik for the helical baffle is presented in detail and a theoretical model for shell-side heat transfer and pressure drop is developed. In general, the results show that the present model matches more closely with the graphically proposed correction factors of Stehlik. In order to calculate the shell-side heat transfer coefficient and pressure drop using the present method, a computational code has been developed by the authors. In addition, in order to examine the validity, the results of the code for a case study are compared with the results obtained from EXPRESS software and experimental formulas presented by Zhang. The results of comparison show that the proposed method is accurate and can be used by designers confidently.

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°.

Thermo-hydraulic design of single and multi-pass helical baffle heat exchangers

A shortcut sizing approach for single and multipass heat exchangers with helical baffles is presented. An alternative approach for the determination of the correction factor of the logarithmic mean temperature difference as a function of the number of heat transfer units is introduced. Multipass arrangements give rise to complex internal heat flow paths; in this work, such flow paths are modelled using a simplified methodology that breaks up the complex flow and represents it as a network of simple arrangements such as counter flow and parallel flow. The network is solved to determine the outlet temperatures from where the correction factor is determined. The methodology is demonstrated on case studies from the open literature.