Continuous Helical Baffles Research Articles

Heat recovery optimization of a shell and tube bundle heat exchanger with continuous helical baffles for air ventilation systems

We report a numerical evaluation of the impact of continuous helical baffle on the heat recovery efficiency of counterflow tube bundle heat exchangers. The baffle inclination angle has been varied from 11∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$11^{\\circ }$$\\end{document} to 22∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$22^{\\circ }$$\\end{document}. Since the fluid flows over the tube bundle at an angle due to helical flow inside the shell, the heat exchanger operates in cross counter mode. Fluent simulations with the k-ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega$$\\end{document} transition shear stress transport turbulence model have been performed to investigate the thermal-hydraulic parameters of the system in terms of heat recovery efficiency, pressure loss, and overall heat transfer rate. Outside air temperature has been varied to mimic cold and warm weather. Pressure loss has been constrained to be less than 250 Pa, conforming to EU guidelines for energy labeling of residential ventilation units. At the maximum volume flow rate of 40 m3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^3$$\\end{document}/h, the device performed with over 80%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$80\\%$$\\end{document} heat recovery efficiency for the considered temperature difference. Continuous helical baffles helped to improve convective heat transfer by reducing cross flow area and increasing velocity. Smaller angles result in greater pressure loss while having no discernible effect on heat recovery efficiency for the considered geometry. The analysis demonstrates the potential of a compact counterflowing recuperative heat exchanger with continuous helical baffles for decentralized ventilation systems and serves as a basis for further optimization.

Numerical Simulation of Thermo-hydraulic Behaviour of Shell and Tube Heat Exchanger Equipped with Segmental Baffle and Helical Baffle

The baffle type and structure are critical to enhancing the comprehensive thermo-hydraulic behavior of shell-and-tube heat exchangers (STHX). In the study, Solidworks software was used to establish three-dimensional mesh models of STHX equipped with the segmental baffle and the continuous helical baffle, respectively. ANSYS software was adopted to study the effects of the baffle type and the baffle geometric parameters on the thermo-hydraulic characteristic of STHXs using the pressure drop of the shell side, the coefficient of heat transfer and isobaric JFP factor as the evaluation characteristics. For segmental baffles, better thermo-hydraulic performance could be obtained with a baffle spacing of 200 mm and a gap height of 0.4 D. For helical baffles, an optimized thermo-hydraulic performance could be obtained with a baffle pitch of 150 mm. By comparing the comprehensive thermo-hydraulic performances of STHXs equipped with two different baffles, it could be concluded that the isobaric JFP factor of STHX equipped with the helical baffle was 1.18 times that of STHX equipped with the segmental baffle under the different suitable flow rate.

Computation of thermal properties of CMSP shell and tube heat exchanger using different types of helical baffles

AbstractThis paper investigates the flow and thermal properties of a combined multiple shell pass (CMSP)‐shell and tube heat exchanger (STHE) with the provision of unilateral ladder‐type helical baffle (ULHB) and continuous helical baffle (HB) in the outer shell pass of the heat exchanger. Two CMSP‐STHEs with ULHB and HB, respectively, are compared with the traditional STHE having segmental baffles (SG‐STHE) using the computational fluid dynamics method. The computational outcomes are validated with the empirical correlations of the Kern and Esso method. The Reynolds‐averaged Navier–Stokes‐based standard k–ω turbulence model accurately predicts the heat transfer (HT) rate and pressure drop. The computed results of HT rate, pressure drop, and logarithmic mean temperature difference corresponding to various mass flow rates (m) for three STHEs are presented. The results show that the overall HT rate of CMSP (ULHB)‐STHE and the CMSP (HB)‐STHE at the same mass flow rate are nearly 28.3% and 14.8% larger than that of traditional SG‐STHE, respectively. Furthermore, the overall area‐weighted average pressure drop (ΔP) of CMSP (HB)‐STHE is smaller than that of SG‐STHE by 26.5% at the same mass flow rate (m) and for CMSP (ULHB)‐STHE it is larger by 2% than that of traditional STHE. Based on the above results, it is concluded that the CMSP (ULHB)‐STHE is a suitable replacement for the conventional SG‐STHEs.

Numerical investigation of thermo-hydraulic ability of STHX with continuous helical baffles on the shell side

The larger quantities of heat transfer rates are possible with the modification of few parameters like baffle cut and shape. Which significantly improves the performance of shell and tube heat exchanger while reducing the pressure drop. From the reported literature review it was proposed to carry the numerical analysis for various helix angles. The present study is to simulate heat transfer rate and liquid movement in a shell-and-tube heat exchanger along with continuous helical-baffles on the shell side. The numerical investigation of seven helix angles, namely 10°, 19°, 21°, 25°, 30°, 38°, and 50°, is done for varying mass flow rates and the inlet temperature of shell side and tube side are 25 °C and 55 °C respectively, modelled a whole length unceasing helical-baffled shell-and-tube heat exchanger. Larger helix angles (30°, 38°, and 50°) result in reduced heat transfer rate and pressure drop too low, while minor helix angles (10°, 19°, 21°, and 25°) result in increased heat transfer rate and pressure drop too high.

Helical Baffle Thermohydraulic Performance Versus Segmental Baffle One

In this contribution, we reworked the Bell-Delaware technique for a HB-STHX to systematically study its thermohydraulic performance behavior in the shell side. The helical baffles are continuous quadrant sectors with five inclination angles 25°, 30°, 35°, 40° and 45° and are exanimated for six different values of Reynolds number from up to 40 . We have observed an increase in global heat transfer rate while a decrease in pressure loss, in continuous helical baffle case compared to segmental one. we have found that the baffle inclination 40° has the largest heat transfer coefficient, 25° gives the lowest pressure drop, whereas 45°, the largest inclination we have used, displays the greatest performance evaluation factor.

Comparison of aerodynamic noise and heat transfer for shell-and-tube heat exchangers with continuous helical and segmental baffles

Flow-induced noise and vibration problems of tube bundles in heat-exchangers exist for a long time and often cause severe destruction, performance reduction and large maintenance charge. It is essential to study the flow-induced noise in tube bundles and develop high-efficiency noise elimination measures. The theoretical analysis and numerical simulation method are coupled to compare the aerodynamic noise and heat transfer in shell-and-tube heat exchangers with continuous helical and segmental baffles. The novelty of this paper is to compare the flow-induced noise of tube bundles in shell-and-tube heat-exchangers with continuous helical and segmental baffles. And as an initial trial, this study intends to investigate the aerodynamic noise based on the flow field and acoustic field matching perspective. The results show that the sound pressure, the pressure drop per unit tube length and the Nusselt number all increase with the increase of Reynolds number. And the average synergy angle of continuous helical baffles is 11％ lower than that of segmental baffles, which corresponds with 23-37％ lower sound pressure.

Comparison of selected shell and tube heat exchangers with segmental and helical baffles

A shell and tube heat exchanger (ST) is analyzed numerically and experimentally using various configurations of baffles. The baffles used are segmental baffle (SB) with baffle cut of 300 (SB-30), 500 (SB-50), Align baffle with baffle cut of 300 (AB-30) and 500 (AB-50). The numerical study of ST with different configurations shows that AB-30 has superior effectiveness than other configurations. The comparison of numerical and experimental results of AB-30 shows a deviation of 10.1%. The study also includes a comparison of the segmental baffle (STs) with continuous helical baffles with a helix angle of 250 (STc) experimentally. The comparative analysis, drawn between STs and STc shows that STs have better effectiveness at all considered mass flow rates varied between 0.00005 to 0.00018 m3/s. Lower mass flow rate had shown better effectiveness than STs by 27.7%. The fixed helix angle of 25° was provided to helical baffles, results in increased heat transfer coefficient (HTC) at the lower pressure drop. The flow pattern in the shell for both STs and STc maintained forced helical and rotational due to the geometry pattern of the baffles, respectively. Based on the experimental data, the non-dimensional parameters for HTC and pressure drop (ΔPo) is calculated for both the configurations. However, for the optimal design of the heat exchanger, the maximum heat recovery rate has also been computed using the composite hot and cold diagram for different configurations.

Downhole electric heater with high heating efficiency for oil shale exploitation based on a double-shell structure

To improve the heating efficiency of the downhole electric heaters used in oil shale exploitation, double-shell downhole electric heaters with continuous helical baffles (DS-DEHs) were developed in this study. These heaters reduce heat loss generated by the shell of single-shell downhole electric heaters with continuous helical baffles (SS-DEHs) and reuse the heat loss by driving air flows through outer and inner shell-passes in sequence. Two types of DS-DEHs with three different helical pitches were experimentally studied, and SS-DEHs were set as the control. The results indicated that the effect of mass flow rate on the heating rate is greater than that of heating power. Forced convection is the major heat transfer mode in heater shell-side, and the contribution of shell-side radiant heat transfer mainly depends on the helical pitch, then on the heating power and mass flow rate. Additionally, the heat loss generated by heater shell is mainly dissipated in the form of radiation. The total heat loss of the DS-DEH is 87.16%–96.41% lower than that of the SS-DEH, and its heating efficiency is 1.06–1.17 times than that of SS-DEH, indicating that the double-shell structure can effectively improve the heating efficiency of downhole electric heaters.

Experimental investigation on performance of downhole electric heaters with continuous helical baffles used in oil shale in-situ pyrolysis

To rapidly produce oil, downhole heating technology requires an electric heater, which is limited by the diameter of the heat injection well, with long-term working stability and high-efficiency heat transfer. Simulations indicated that heater with continuous helical baffles is more suitable for downhole heating technology than heater with segmental baffles in terms of long-term working stability. Then, experiments were conducted on four continuous helical schemes with pitches of 50, 110, 160, and 210 mm. The test results showed that, in the test scope, the heater with the helical pitch of 110 mm (H110) had the best comprehensive performance, which was 2.95–3.75 times better than that of the heater with the helical pitch of 210 mm (H210). Under the same working conditions, heaters with smaller helical pitch values produce less irreversibility in the heat transfer process. In addition, the heaters with helical pitch values of 110, 160, and 210 mm were more effective at a lower Reynolds number, whereas the heater with the helical pitch of 50 mm could be used under a wide effective range of Reynolds numbers. The conclusions are benefit to setting the heating parameters of electric heater during the process of oil shale in-situ pyrolysis.

Bir gövde borulu ısı değiştiricisinde farklı levha türlerinin ısıl performansa etkisinin sayısal olarak incelenmesi

In this study, the thermal performance of a small scale shell and tube heat exchanger was performed according to the baffle type by using three dimensional Computational Fluid Dynamics (CFD) method. In numerical calculations, segmental and continuous helical baffle types were selected to get the comparative results. For helical baffle type, we used two different models that the numbers of helical rotations and baffle spacing length were different. Thus, we determined five different numerical models and the thermal performance of each models were evaluated under different inlet temperature values selected as 50, 60 and 70°C for the tube side. The inlet temperature value and the mass flow rate of shell side were kept constant during all the numerical calculations. The heat transfer calculations were achieved by using Logarithmic Mean Temperature Difference (LMTD) method. We also employed the Bell-Delaware method which can be used accurately for shell and tube heat exchangers. The highest thermal performance was determined in Case-IV which had equal baffle spacing and the maximum number of rotations for continuous helical baffle. The predicted total pressure drop results obtained from the numerical calculations were in good agreement with the calculated total pressure drop from Bell-Delaware method. The lowest pressure drop and the highest thermal performance were achieved for continuous helical baffle type compared to the segmental equal spacing baffle type. The numerical simulations based on CFD analysis can provide more information about heat exchangers and this tool can be used to improve both design and the thermal performance of heat exchangers.

Numerical analysis and optimization study on shell-side performances of a shell and tube heat exchanger with staggered baffles

With a view to possessing the characteristics of the simple fabrication of the shell and tube heat exchanger with segmental baffles (STHX-SG) and the helical flow of the shell and tube heat exchanger with continuous helical baffles (STHX-CH), a shell and tube heat exchanger with staggered baffles (STHX-ST) is proposed in this work. The baffles of the STHX-ST are arranged according to a certain rule that the adjacent baffles are staggered by a constant clockwise or counterclockwise angle in sequence. Comparisons of the heat transfer performance and pressure drop among the STHX-SG, STHX-CH, and STHX-ST are firstly carried out. Results show that the comprehensive performance of the STHX-ST is superior the STHX-SG and STHX-CH. The parametric studies about the baffle cut δ and staggered angle β are conducted for the STHX-ST. Moreover, the multi-objective optimization is carried out to obtain the optimal solutions using the genetic algorithm further. The relationships between the design variables (the baffle cut δ, staggered angle β, and number of baffles n) and objective functions (the heat transfer rate Q and pressure drop Δp) are characterized by the artificial neural networks. The STHX-ST, at the δ = 0.45, β = 79°, and n = 11, is determined as the optimal solution according to the TOPSIS selection. Meanwhile, it is proved that the STHX-SG, a special STHX-ST at the β = 180°, is not always the best choice from the view of heat transfer enhancement. The STHX-ST can provide a preferable and meaningful solution for more efficient energy utilization in industrial applications.

Numerical and experimental analysis on shell side thermo-hydraulic performance of shell and tube heat exchanger with continuous helical FRP baffles

The present work deals with the numerical and experimental investigation of heat and fluid flow in shell and tube heat exchanger with continuous helical baffles on shell side. Seven helix angles, namely 10°, 19°, 21°, 25°, 30°, 38°, and 50° are investigated numerically by modeling a full length continuous helical baffled shell-and-tube heat exchanger for different mass flow rates and inlet temperature conditions. Results revealed that the larger helix angles (30°, 38° and 50°) adds to lower heat transfer and lower pressure drop, and smaller helix angles (10°, 19°and 21°) resulted in higher heat transfer as well as higher pressure drop. The experiments were carried out on shell and tube heat exchanger for helical baffles with 25° helix angle and results were compared with segmental baffles. New baffle material, FRP (Fiber Reinforced Plastic) is introduced on the shell side of the proposed heat exchanger. For material comparison between FRP and stainless steel, the deviation of heat transfer coefficient is 8–10%, which can serve as a potential replacement for conventional baffle material, thereby reducing the capital and operating cost of the tubular heat exchanger.

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.

Velocity Characteristics around Short Continuous Helical Baffles Using PIV With and Without One Inner Tube

Velocity Characteristics around Short Continuous Helical Baffles Using PIV With and Without One Inner Tube

Numerical design and investigation of heat transfer enhancement and performance for an annulus with continuous helical baffles in a double-pipe heat exchanger

In this paper, the design and thermo-hydraulic performance of a double pipe heat exchanger with helical baffles in the annulus side, are investigated numerically. Three-dimensional computational fluid dynamics (CFD) model, using the software FLUENT, have been performed to investigate the annulus side fluid flow, heat transfer coefficient and pressure drop for different configurations. A numerical analysis is conducted for different values of Reynolds number and baffle spacing (0.025–0.1m). The numerical model was first validated for a simple double pipe heat exchanger by comparison with empirical correlations. The model was then used to investigate the helical baffles effects. The results obtained for a helically baffled annulus side provide enhanced heat transfer performance and high-pressure drop compared to the simple double-pipe exchangers. Thermal performance and high-pressure drop is an increasing function of baffle spacing and Re. In addition, empirical correlations expressing the results were developed based on curve fitting.

Investigation on combined multiple shell-pass shell-and-tube heat exchanger with continuous helical baffles

A combined serial two shell-pass shell-and-tube heat exchanger (CSTSP-STHX) with continuous helical baffles has been proposed to improve heat transfer performance. This CSTSP-STHX separates the shell side into two individual shell passes. The inner shell pass is conventional segmental baffled, and the outer shell pass is continuous helical baffled. The working fluid flows through the outer and inner shell passes in sequence. The thermo hydraulic performances of CSTSP-STHX are experimentally compared with the double shell-pass shell-and-tube heat exchanger with segmental baffles (SG-STHX). The results show that the CSTSP-STHX gets greater shell-side heat transfer coefficient and pressure drop, furthermore it also has better heat transfer coefficient under the same pressure drop than those of the SG-STHX. Finally it should be emphasized that the leakage on annulus separator has to be as possible as reduced. The present studies are beneficial for the design and practical operation of CSTSP-STHX.

Performance Study of Continuous Helical Baffle Shell and Tube Heat Exchanger With Central Low-Pressure Regions

Shell and tube heat exchanger (STHX) is a class of indirect contact heat exchangers which has wide applications in various industries. In this paper, the shell-side performance characteristics of a small STHX with differently notched continuous helical baffle (CHB) geometries are numerically studied and compared with same CHB without notched regions. The indentations are uniquely produced by placing the notch near the core of the heat exchanger, thereby conferring the flow with low-pressure drop regions. Two set of models of inner notched continuous helical baffle (ICHB), i.e., ICHB1 and ICHB2, are studied with notch width of about 5% and 10% of the inner shell diameter of the same heat exchanger. In comparison with the CHBSTHX, it is seen that the STHXs incorporated with ICHBs, the heat transfer rate dropped slightly, but a significant decrease in pressure drop is observed. It is found that the heat transfer coefficient to pressure drop ratio for ICBH1 and ICHB2 shows significant increase in comprehensive performance of about 3.5% and 32.42%, respectively, when compared with same CHB without notched regions.

Improvement and Validation of Genetic Programming Symbolic Regression Technique of Silva and Applications in Deriving Heat Transfer Correlations

The forms and constant terms of heat transfer correlations can be determined simultaneously with symbolic regression with prescribed precision. In this paper, a genetic programming (GP) technique developed by Silva is adopted as the tool of symbolic regression. However, the test results indicate that when the undetermined functions contain constant terms, symbolic regression results based on the code of Silva usually have increasing sizes. It is difficult to employ them for practical applications when the correlations are not concisely enough. In order to solve this problem, some new function modules are inserted into the GP of Silva, including (a) a function structure simplification module, (b) a constants optimization module, (c) an expansion rate reduction module with “self-swap” genetic operator, and (d) a small term search intensity enhancement module with “intro-new” genetic operator. The statistical performance demonstrates that all of these four new modules are beneficial to improve performance of symbolic regression, especially when the constants optimization module is added. Furthermore, when different modules are added simultaneously, the improvements are more remarkable. Finally, applications of deriving heat transfer correlations for a shell-and-tube heat exchanger with continuous helical baffles and a single-row heat exchanger with helically finned tubes are performed. The results indicate that heat transfer correlations obtained in this paper are proven to be better than the power-law-based correlations.

A review of the advancements made in helical baffles used in shell and tube heat exchangers

This paper provides a review about the major work done on helical baffles to improve the performance of shell and tube heat exchangers. Some of the major factors affecting the performance of shell and tube heat exchanger are discussed. A comparison between segmental baffles and helical baffles is also presented to show that helical baffles are more advantageous than segmental baffles. In most cases, discontinuous, folded, sextant helical baffles, 40° baffle inclination angle as well as low baffle spacing will give the best results when integrated in some combination, whereas continuous helical baffles eliminate dead regions. Moreover, sealing strips are more likely to improve the performance of shell and tube heat exchangers with continuous helical baffles.

Performances of helical baffle heat exchangers with different baffle assembly configurations

The flow and heat transfer characteristics of helical baffle heat exchangers with diverse inclined angles and baffles, but similar baffle pitch and tube layout, were numerically simulated, three using non‐continuous trisection baffles, two using non‐continuous quadrant baffles, and one using a continuous helical baffle. The results show that, under the same operating conditions, the 20°TCO (trisection circumferential overlap baffles with 20° inclined angle) structure can significantly enhance shell side heat transfer with strong Dean vortex “secondary flow“ and restrained V‐notch leakage, because the shapes of trisection baffles are very suitable to equilateral triangle tube layout and there is a row of tubes to dampen the leakage flow in each circumferential overlapped area of adjacent baffles. The shell side Nusselt Number Nuo and comprehensive index (Nuo/Euz,o1/3) of 20°TCO structure are 18.31 %, 25.82 %, 5.93 %, 6.36 %, and 15.04 %, and 15.43 %, 18.47 %, 5.30 %, 3.91 %, and 11.10 % higher than those of the 20°TEE (trisection end‐to‐end baffles with 20° inclined angle), 36.2°TMO (trisection middle overlap baffles with 36.2° inclined angle), 18°QCO (quadrant circumferential overlap baffles with 18° inclined angle), 18°QEE (quadrant end‐to‐end baffles with 18° inclined angle), and 18.4°CH (continuous helical baffle with 18.4° helical angle) structures, respectively.