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

In 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.     

Numerical thermal‐hydraulic performance investigations in turbulent curved channel flow with horseshoe baffles

A numerical work is performed to investigate the thermal‐hydraulic performance in a curved channel of a journal bearing equipped with oblique horseshoe baffles. Water, a working fluid, is passed through the curved channel at a constant temperature condition of 358 K. The effects of different parameters of baffles, that is, attack angle (α = 45°, 60°, and 90°) and the number of baffles (NB = 9 and 13 baffles), are examined. Influences of design parameters on heat transfer and friction performances are studied and displayed in terms of the Nusselt number, the friction factor, the Nusselt number enhancement ratio, and the thermal‐hydraulic performance factor (THPF). The numerical simulations present the flow structures of the tested channel in terms of velocity, isotherms, turbulent kinetic energy, and vorticity contours. The numerical results reveal that the adopted geometry of the curved channel with baffles yields a significant enhancement of heat transfer rate over the plain channel (without baffles), which is approximately 2.5 to 3.8 times. Also, the results show that the best condition to achieve maximum heat transfer is at angle α = 90°, NB = 13, and Re = 5000, compared with other conditions. Furthermore, the maximum THPF of the curved channel using baffles is 4.4 at the same condition. The results confirmed that the geometry of the baffles inside the curved channel has a remarkable impact on heat transfer improvement, accompanied by a reasonable increase in friction losses.     

连续拼接型螺旋折流板换热器壳程流场与温度场数值研究

针对单弓形折流板换热器壳程压降大、连续型螺旋折流板换热器安装制造成本高的缺点,提出一种连续拼接型螺旋折流板换热器。基于流体力学基本原理与周期性充分发展模型理论,对连续拼接型螺旋折流板换热器壳程流场与温度场进行数值模拟,研究表明：雷诺数在2000~10000范围内,当螺旋角为70°时换热器的综合换热性能最好,且是同尺寸单弓形折流板换热器的15~21倍;利用多元线性回归方法推导出了连续拼接型螺旋折流板换热器壳程对流换热系数与压降的准则数关系式。     

Use of segmental baffle in shell and tube heat exchanger for nano emulsions

Among the heat exchangers (HE), the shell and tube type is being widely used in different applications like oil, chemical, and power plant Industries. The incorporation of segmental baffles (SB) improves the HE capacity from higher temperature fluid to lower temperature fluid. Nanofluids can be effectively used to enhance the heat transfer rate. In this study, numerical simulations have been carried out in a shell and tube heat exchanger (STHX). Among HE design methods, Tubular Exchanger Manufacturers Association (TEMA) standard is being used for better design by many researchers. In this paper, the computational fluid dynamics analysis was carried out with Al₂O₃, CuO, and SiO₂ nanofluids amid 1, 3, and 5 vol. % with water emulsion to enhance the heat transfer coefficient of STHX. The nanofluid has been used in the cold fluid of the HE and on the other side hot water is used. From the results, it is noticed that with the increase of Nanofluids, the value of heat transfer coefficients is found to be increasing. The overall heat transfer coefficient has been enhanced for Al₂O₃, CuO, and SiO₂ about 10.41%, 12.27%, and 9.56%, respectively, at 0.22 kg/s for the 5 vol. % addition. It is also depicted that the pressure drop is increasing with the incorporation of nanofluids.     

Computational Fluid Dynamics Analysis of a Heat Exchanger Provided with Helical Baffles

Abstract

In the article, a three-dimensional numerical solution of two real shell-and-tube heat exchangers, with different types of baffles, segmental, and pseudohelical, is presented, through the use of commercial codes, in order to evaluate the influence of the baffles type on heat exchanger performance. The parameters to be evaluated, which influence the efficiency of the thermal exchange and the maintenance and pumping costs, are the pressure drops, the heat transfer coefficient, and the fouling resistance. The fluid dynamic study of the shell-and-tube heat exchanger is conducted under stationary flow conditions. In the article, furthermore, the results of the thermohydraulic analysis, performed under stationary flow conditions, more "helical baffles" exchangers, with different baffles helix angle, are presented. Exchangers with pseudohelical baffles inclined by 7°, 20°, 30°, 40°, 45°, and 50° are analyzed. The simulations are carried out considering a real fluid, approximately incompressible, under laminar flow conditions. Finally, to verify the correctness of the results, they are compared with correlations in the literature.     

Biofouling Control with Ultrasound

The flow field in shell-and-tube heat exchangers with helical baffles was measured using laser Doppler anemometry (LDA). The influence on the velocity distribution, impulsive velocity by helix inclination angle, and flow rate was investigated. The influence on heat exchanging capability and flow resistance on velocity distribution was also investigated. The dimensions of the heat exchanger shell used in these experiments were 200 2 6 2 3,000 mm (inner diameter 2 wall thickness 2 length). The heat exchanger was made of organic glass and the tube bundle consisted of 52 tubes with external diameter of 15 mm. Six different inclination angles were designed in double-helix style: 30°, 35°, 40°, 42°, 45°, and 50°. The working flow medium under normal temperature was service water. Generally, the linear velocity and impulsive velocity will increase with decreasing helix inclination angle, which promotes the heat exchanging capability. With flow volume increasing, the velocity distribution along the diameter increases on average. The pressure drop increases with decreasing helix inclination angle. For all of the helix inclination angles tested, the minimum pressure loss took place at a certain Reynolds number; and at different helix inclination angles, the Reynolds number at which the minimum pressure loss occurs is different. In general, it was concluded that the optimum helix inclination angle depends on the Reynolds number of the working fluid on the shell side of heat exchanger.     

Numerical evaluation of the thermal performance of a solar air heater equipped with two different types of baffles

In the present study, the effect of utilizing two different types of baffles in the channel of the solar air heater is investigated numerically. The studied baffles include angled rectangular baffles and angled V‐shaped baffles, which are mounted on the bottom and top walls of the duct, respectively. Both considered baffles were evaluated separately which the studied parameter in each section was the angular position of baffles. Finally, the best‐obtained results of both sections were compared to each other. The results indicated that in the rectangular model by comparison between 90° model and no baffle, it was found that the pressure drop and average Nusselt number increase 316.67% and 148.15%, respectively at Reynolds number (Re) = 2000. Also, in V‐shaped angled baffles, the thermal efficiency of β = 90°, 60°, 45°, and 30° are 27%, 18%, 13% higher than no baffle channel at Re = 2000, respectively. Furthermore, at low Re (about Re below 300), utilizing baffles into the channel had no effect on the thermal efficiency of the system compared to the no baffle channel. However, at high Re, it was found that the highest thermal efficiency occurred in the model of rectangular baffles with an angle of 90°.     

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

A combined multiple shell-pass shell-and-tube heat exchanger (CMSP-STHX) with continuous helical baffles in outer shell pass has been invented to improve the heat transfer performance and simplify the manufacture process. The CMSP-STHX is compared with the conventional shell-and-tube heat exchanger with segmental baffles (SG-STHX) by means of computational fluid dynamics (CFD) method. The numerical results show that, under the same mass flow rate M and overall heat transfer rate Q_m, the average overall pressure drop Δp_m of the CMSP-STHX is lower than that of conventional SG-STHX by 13% on average. Under the same overall pressure drop Δp_m in the shell side, the overall heat transfer rate Q_m of the CMSP-STHX is nearly 5.6% higher than that of SG-STHX and the mass flow rate in the CMSP-STHX is about 6.6% higher than that in the SG-STHX. The CMSP-STHX might be used to replace the SG-STHX in industrial applications to save energy, reduce cost and prolong the service life.     

Experimental study on heat transfer augmentation in a double pipe heat exchanger utilizing jet vortex flow

This paper examines experimentally the effect of jet vortex technology on enhancing the heat transfer rate within a double pipe heat exchanger by supplying the heat exchanger with water at different vortex strengths. A vortex generator with special inclined holes with different inlet angles was designed, manufactured, and integrated within the heat exchanger. In this study, four levels of Reynolds number for hot water in the annulus (Re_h) were used, namely, 10,000; 14,500; 18,030; and 19,600. Similarly, four levels of Reynolds number for cold water in the inner tube (Re_c) were used, namely, 12,000; 17,500; 22,500; and 29,000. As for the inlet flow angle (θ), four different levels were selected, namely, 0°, 30°, 45°, and 60°. The temperature along the heat exchanger was measured utilizing 34 thermocouples installed along the heat exchanger. It was found that increasing the inlet flow angle (θ) and/or the Reynolds number results in an increase in the local Nusselt number, the overall heat transfer coefficient, and the ratio of friction factor. It is revealed that the percentage increase in the average Nusselt number due to swirl flow compared to axial flow was 10%, 40%, and 82% for an inlet flow angle of 30°, 45°, and 60°, respectively.     

Enhancement of hydrogen storage performance in shell and tube metal hydride tank for fuel cell electric forklift

Novel metal hydride (MH) hydrogen storage tanks for fuel cell electric forklifts have been presented in this paper. The tanks comprise a shell side equipped with 6 baffles and a tube side filled with 120 kg AB₅ alloy and 10 copper fins. The alloy manufactured by vacuum induction melting has good hydrogen storage performance, with high storage capacity of 1.6 wt% and low equilibrium pressure of 4 MPa at ambient temperature. Two types of copper fins, including disk fins and corrugated fins, and three kinds of baffles, including segmental baffles, diagonal baffles and hole baffles, were applied to enhance the heat transfer in metal hydride tanks. We used the finite element method to simulate the hydrogen refueling process in MH tanks. It was found that the optimized tank with corrugated fins only took 630 s to reach 1.5 wt% saturation level. The intensification on the tube side of tanks is an effective method to improve hydrogen storage performance. Moreover, the shell side flow field and hydrogen refueling time in MH tanks with different baffles were compared, and the simulated refueling time is in good agreement with the experimental data. The metal hydride tank with diagonal baffles shows the shortest hydrogen refueling time because of the highest velocity of cooling water. Finally, correlations regarding the effect of cooling water flow rate on the refueling time in metal hydride tanks were proposed for future industrial design.     

Enhancement of shell side forced convective heat transfer in the shell tube‐type heat exchanger using thin plate‐type supports

The shell side heat transfer and pressure drop in counterflowing water were experimentally investigated on the basis of the overall heat transfer coefficient. The investigation was intended to identify ways to get higher performance for the cooler in a BWR nuclear power plant. The following three conclusions were reached in the study. (1) Predicted performance of the heat exchanger, using the overall heat transfer coefficient based on the outside area of the tube K_o, indicated an enhancement by 92% compared with the measured performance of the conventional segmental baffle‐type heat exchanger. (2) The tube side pressure drop ΔP_t=20 kPa and the shell side pressure drop ΔP_s=70 kPa were obtained, and were within the allowable value ΔP_a=80 kPa. The shell side pressure drop of the low‐pressure drop spacer could be decreased by 20% as compared with that of the standard spacer. (3) The enhancement constant of the shell side heat transfer using the low‐pressure drop spacer was about 1.2 times as large as that of the standard spacer, regardless of the pumping power. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(5): 455–471, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10097     

Numerical Analysis of Baffle Cut on Shell Side Heat Exchanger Performance with Inclined Baffles

In this work, an attempt has been made to decrease the pressure drop and to increase the heat transfer rate in a shell and tube heat exchanger (STHX) by tilting the baffle angle and by varying the baffle cut. The process of solving the simulation includes modeling, meshing, and analyzing the geometry of the STHX by using Pro-E, hypermesh, and computational fluid dynamics package of ANSYS Fluent, respectively. The objective of this study is to find a suitable baffle inclination and baffle cut for the efficient performance of the STHX. The baffle inclinations of 25°, 30°, 35°, and 40° were considered for three different baffle cuts of 25%, 30%, and 35% of shell inside diameter and the results were compared with segmental baffle of inclination angle 0°. The shell side flow with different inclination angles and baffle cuts results in a significant variation in heat transfer rate and pressure drop in the STHX. The results provide a clear idea that the heat transfer rate is maximum in inclined baffle heat exchanger compared to that of segmental baffle heat exchanger. Further it is found that the STHX with the configuration of 35º baffle inclination angle and baffle cut of 30% of shell inside diameter provides higher heat transfer rate with minimum pressure drop compared to all other configurations.     

Numerical Investigation of Conjugate Heat Transfer to Supercritical CO2 in a Vertical Tube-in-Tube Heat Exchanger

Conjugate heat transfer to supercritical CO₂ in a vertical tube-in-tube heat exchanger was numerically investigated. The results demonstrate that most models considered are able to reproduce the heat transfer processes qualitatively, and the Abe, Kondoh, and Nagano model shows optimal agreement with the experimental data. The influences of hot fluid mass flux and temperature of the shell side, supercritical fluid mass flux of the tube side, flow direction, and pipe diameter on conjugate heat transfer were investigated based on velocity and turbulence fields. It is concluded that hot fluid mass flux and temperature of the shell side significantly affect heat transfer of the tube side. Mixed convection is the main heat transfer mechanism for the supercritical CO₂ conjugate heat transfer process when the inner diameter of the tube is greater than 1 mm. In addition, density variation is highly significant for heat transfer of supercritical CO₂ while high viscosity hinders the distortion of the flow field and reduces deterioration in heat transfer.     

Investigation on the heat transfer characteristics of propylene glycol–water mixture in the shell side of a spiral‐wound heat exchanger

The heat transfer characteristics of propylene glycol–water (PG–W) mixture (10%, 20%, and 30% propylene glycol) on the shell side of a spiral‐wound heat exchanger (SWHE) were investigated experimentally. Among the SWHE selected, there are 18 twined tubes with a diameter of 8 mm. PG–W mixture is on the shell side and water is on the tube side. The results show that the heat transfer coefficient of PG–W mixture flowing downwards is higher than upwards under countercurrent conditions. The heat transfer coefficient decreases with the increasing of concentration of PG–W mixture. When the inclination angle of the SWHE is 90°, the heat transfer coefficient of PG–W mixture is the largest; and when the inclination angle is less than 90°, the heat transfer coefficient decreases with the decrease of inclination angle. The inclination angle has a great effect on the heat transfer coefficient at a high concentration. The fitting correlation equations between Nu, Re, Pr, and inclination angles of SWHE are established.     

3D numerical and experimental analysis for thermal–hydraulic characteristics of air flow inside a circular tube with different tube inserts

Numerical and experimental analyses were carried out to study thermal–hydraulic characteristics of air flow inside a circular tube with different tube inserts. Three kinds of tube inserts, including longitudinal strip inserts (both with and without holes) and twisted-tape inserts with three different twisted angles (α = 15.3°, 24.4° and 34.3°) have been investigated for different inlet frontal velocity ranging from 3 to 18 m/s. Numerical simulation was performed by a 3D turbulence analysis of the heat transfer and fluid flow. Conjugate convective heat transfer in the flow field and heat conduction in the tube inserts are considered also. The experiments were conducted in a shell and tube exchanger with overall counterflow arrangement. The working fluid in the tube side was cold air, while the hot Dowtherm fluid was on the shell side. To obtain the heat transfer characteristics of the test section from the experimental data, the ε-NTU (effectiveness-number of transfer unit) method is applied to determine the overall conductance (UA product) in the analysis.It was found that the heat transfer coefficient and the pressure drop in the tubes with the longitudinal strip inserts (without hole) were 7–16% and 100–170% greater than those of plain tubes without inserts. When the longitudinal strip inserts with holes were used, the heat transfer coefficient and the pressure drop were 13–28% and 140–220%, respectively, higher than those of plain tubes. The heat transfer coefficient and the pressure drop of the tubes with twisted-tape inserts were 13–61% and 150–370%, respectively, higher than those of plain tubes. Furthermore, it was found that the reduction ratio in the heat transfer area of the tube of approximately 18–28% may be obtained if the twisted-tape tube inserts are used.     

Numerical research on heat transfer and flow resistance performance of specially‐shaped rod baffle heat exchangers

In order to overcome the disadvantages of heat transfer performance in the shell side of the common circular cross section rod baffle heat exchanger with a low Reynolds number, a numerical simulation on fluid flow and heat transfer in the shell side with different types of rod baffles is carried out. The rod baffles include the circular cross section, trigonal cross section, and rhombic cross section. The influence of heat transfer enhancement and flow resistance reduction affected by baffles is summarized. It is indicated that the trigonal and rhombic cross section rod baffles present the better performance of heat transfer enhancement and flow resistance reduction. With the rhombic cross section rod baffles in the shell side, the higher heat transfer coefficient and overall property in the shell side are achieved when Re is lower, and the heat transfer coefficient in the shell side is 10% higher than that of a circular cross section rod baffle at the same Reynolds number. The trigonal and rhombic cross section rod baffles in the shell side give more optional structure forms for expanding the application scope of rod baffle heat exchangers. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20388     

Three-Dimensional Modeling of a Helixchanger® Heat Exchanger Using CFD

Abstract

Detailed three-dimensional computational fluid dynamics (CFD) simulations have been performed to explore the performance of a helically baffled heat exchanger, commercially referred to as the Helixchanger ® heat exchanger. The CFD simulations employ the HEATX computer simulation program, which is designed for the simulation of shell-and-tube heat exchangers. The simulation accounts for the complex helical geometry of baffles, leakages, and nozzle entrance and exit. Three cases are presented that correspond to helix angles of 10°, 25°, and 40°, defined with respect to the radial axis. Inspection of the computed flows reveals distinct inner and outer regions, with the outer region showing a very desirable plug flow characteristic. The inner region, however, displays recirculation zones due to back mixing at the small helix angle, which suggests potential vibration problems but also creates a desirable temperature uniformity. A comparison with plug flow showed that the helically baffled heat exchanger had a fluid turn ratio of 0.64, 0.78, and 0.77 for the 10°, 25°, and 40° helix angles, indicating more overall plug-like flow for the higher helix angles. Computed pressure drops compare reasonably well with ABB Lummus Heat Transfer correlation results, although nozzle entrance and exit losses require further study.     

Thermal performance augmentation using water based Al2O3-gamma nanofluid in a horizontal shell and tube heat exchanger under forced circulation

Shell and tube heat exchanger is one of the most prevalent heat exchangers with a wide variety of industrial applications, i.e., power plants, chemical processes, marine industries, HVAC systems, cooling of hydraulic fluid and engine oil in heavy duty diesel engines and the like specifically where a need to heat or cool a large fluid volume exist and also higher-pressure use. In the present study, the effect of using Al₂O₃-water nanofluid on thermal performance of a commercial shell and tube heat exchanger with segmental baffles is assessed experimentally. For this purpose, Al₂O₃-gamma nanoparticles with 15 nm mean diameter (99.5% purity) and Sodium Dodecyl Benzene Sulphonate (SDBS) as surfactant are used to make aqueous Al₂O₃ nanofluid at three various volume fractions of nanoparticles (φ = 0.03, 0.14 and 0.3%). Indeed, in this paper the effect of some parameters of hot working fluid such as Reynolds number and volume concentration of nanoparticles on heat transfer characteristics, friction factor and thermal performance factor of a shell and tube heat exchanger under laminar flow regime is investigated. The results indicate a substantial increment in Nusselt number as well as the overall heat transfer coefficient of heat exchanger by enhancement of Reynolds number and it can be seen that, at a certain Reynolds number, heat transfer characteristics of heat exchanger increase as the nanoparticles volume concentration increases. Outcomes of the heat transfer evaluation demonstrate that applying nanofluids instead of base fluid lead to increment of Nusselt number up to 9.7, 20.9 and 29.8% at 0.03, 0.14 and 0.3 vol%, respectively. Likewise it is seen that at mentioned nanoparticles volume fractions, overall heat transfer coefficient of heat exchanger enhances around 5.4, 10.3 and 19.1%, respectively. In term of pressure drop, a little penalty is found by using nanofluid in the test section. Eventually a thermal performance assessment on the heat exchanger was conducted. According to the analysis results, utilizing nanofluid at minimum and maximum nanoparticles volume fractions (φ = 0.03 and 0.3%) results in average augmentation of around 6.5% and 18.9% in thermal performance factor (η) of the heat exchanger compared to the base liquid, respectively.     

Twisted bundle heat exchangers performance evaluation by CFD (CJ12/5054)

Shell and tube heat exchanger with single twisted tube bundle in five different twist angles, are studied using computational fluid dynamics (CFD) and compared to the conventional shell and tube heat exchanger with single segmental baffles. Effect of shell-side nozzles configurations on heat exchanger performance is studied as well. Heat transfer rate and pressure drop are the main issues investigated in the paper. The results show that, for the same shell-side flow rate, the heat transfer coefficient of heat exchanger with twisted tube bundle is lower than that of the heat exchanger with segmental baffles while shell-side pressure drop of the former is even much lower than that of the latter. The comparison of heat transfer rate per unit pressure drop versus shell-side mass flow rate shows that heat exchanger with twisted tube bundle in both cases of perpendicular and tangential shell-side nozzles, has significant performance advantages over the segmental baffled heat exchanger. Optimum bundle twist angles for such exchangers are found to be 65 and 55° for all shell side flow rates.     

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

ABSTRACT

Numerical 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 h_o/Δp_o of the 12° helical scheme are respectively 47% and 51% higher than those of the segmental baffle scheme with about the same pressure drop.