Staggered Tube Bank Research Articles

Optimizing the tube geometry to enhance thermohydraulic performance of tube bank heat exchanger

In this study, optimum design parameters of circular, diamond and enhanced shaped geometries for staggered tube banks are explored utilizing a multi-objective genetic algorithm (MOGA-II). For given three geometries, two step optimization studies are compared: (1) circular and diamond shaped geometries, (2) diamond and enhanced shaped geometries. Steady, incompressible, and turbulent flow around three-dimensional numerical models is solved using finite volume method. Initially, using literature experimental data numerical results are validated for circular and diamond geometries. In the optimization studies, maximization of heat transfer and minimization of required pumping power are preferred as objective functions. The results of optimization studies are demonstrated graphically. Furthermore, velocity and temperature distribution for the optimum cases are illustrated. The results of first step optimization studies exhibited that diamond shaped tube bank shows higher heat transfer rate than circular one for the same given volume (156%). Besides, as a result of second step optimization studies, optimal enhanced shaped geometry showed 0.59% higher heat transfer rate, 21.73% lower pumping power requirement and 9.65% lower total tube bank volume than optimal diamond shaped one.

A parametric investigation of the heat transfer enhancement of tube bank heat exchanger with reversed trapezoidal profile fins

In this study, a reversed trapezoidal profile fins attachment to the tube bank heat exchanger was proposed to enhance the heat transfer performance. A validated computational fluid dynamics (CFD) model was used to investigate the flow behaviour and thermal performance of the staggered tube bank heat exchanger with reversed trapezoidal profile fins. The simulation employed the RNG k-ε model with enhanced wall treatment. The effects of fins’ angle (2°≤αtf ≤ 10°), length (0.5D ≤ Ltf ≤ 2D) and thickness (1 mm ≤ Htf ≤ 5 mm) within a range of Reynolds number (5500 ≤ Re ≤ 14500) were discussed. Nusselt number (Nu), pressure drop (ΔP) and performance evaluation criterion (PEC) were used to evaluate the heat exchanger’s performance. The results showed that both Nu and ΔP followed an increasing trend as αtf increased, which indicates a heat transfer enhancement and a larger airflow resistance. As Ltf increased from 0.5D to 2D, Nu showed a continuous increase with the maximum value obtained at Ltf = 2D. However, ΔP showed a tendency to increase and then decrease as Ltf increased, with the maximum value observed at Ltf = 1.25D. A larger thickness resulted in a higher airflow resistance penalty compared to the improvement in Nu. The thickness was recommended to be as small as possible, provided that the manufacturing process and mechanical strength requirements were met. If the adverse effect of pressure drop was not of concern, the optimal thermal–hydraulic performance (PEC) could be obtained at a larger angle, length and smaller thickness.

Effect of Pitch Ratio of Tube Banks on Passive Acoustic Properties

Tube banks are common design elements in heat exchangers. The most common tube bank patterns are In-line tube banks and Staggered tube banks. These are characterized by their longitudinal and transverse pitch ratios (pitches to diameters). The tube bank with a pitch ratio of less than 1.25 is considered a compact tube bank and a pitch ratio greater than 2 is considered as widely spaced. In this paper, the attention is focused on the effects of pitch ratio in tube banks on its passive acoustics properties which are experimentally investigated. The flow duct experimentation is performed with and without flow to analyse the passive acoustic properties of tube banks. The Experiment is conducted for both the In-line and Staggered tube banks with pitch ratios from 1.2 to 2.5. Experimental results consist of scattering matrix coefficients and power balance. The results are compared to see the pitch ratio effect.

Effect of surfaces roughness of a staggered tube bank in cross flow with air on heat transfer and pressure drop

Many options are devoted to enhancing heat transfer alongside lowering the pressure drop inside the tube banks in cross flow with air. Among these, is attaching splitter plates (SPs) to the trailing edges of the tubes as extended surfaces. That already proved from literature its effective use. Another proposed option is to increase the surface's roughness, with limited available data from literature. Thus, the present research was established to study the effect of using different surface roughness of a staggered tube-bank in cross flow with air on heat transferred and pressure drop besides the comparison with installing SPs. To this aim, a full 3D CFD model is developed to study the two mentioned options without any symmetrical boundary conditions. The study extended to include the effect of Remax changes from 5000 to 100,000. While three surface relative roughness; ks/D = 0 (smooth), ks/D = 0.01, and ks/D = 0.02 are investigated. The results confirmed that increasing heat transfer surface roughness helps to augment the total heat transferred. While a limited pressure drop increase is reported compared to installing SPs. Combining both; increasing surface roughness, and, adding SPs, led to multiplying the total heat transfer rate.

Numerical Study of Liquid Metal Turbulent Heat Transfer in Cross-Flow Tube Banks

Heavy liquid metals (HLM) are attractive coolants for nuclear fission and fusion applications due to their excellent thermal properties. In these reactors, a high coolant flow rate must be processed in compact heat exchangers, and as such, it may be convenient to have the HLM flowing on the shell side of a helical coil steam generator. Technical knowledge about HLM turbulent heat transfer in cross-flow tube bundles is rather limited, and this paper aims to investigate the suitability of Reynolds Average Navier–Stokes (RANS) models for the simulation of this problem. Staggered and in-line finite tube bundles are considered for compact (a=1.25), medium (a=1.45), and wide (a=1.65) pitch ratios. The lead bismuth eutectic alloy with Pr=2.21×10−2 is considered as the working fluid. A 2D computational domain is used relying on the k−ω Shear Stress Transport (SST) for the turbulent momentum flux and the Prt concept for the turbulent heat flux prediction. The effect of uniform and spatially varying Prt assumptions has been investigated. For the in-line bundle, unsteady k−ω SST/Prt=0.85 has been found to significantly underpredict the integral heat transfer with regard to theory, featuring a good to acceptable agreement for wide bundles and Pe≥1150. For the staggered tube bank, steady k−ω SST and a spatially varying Prt has been the best modeling strategy featuring a good to excellent agreement for medium and wide bundles. A poor agreement for compact bundles has been observed for all the models considered.

A regularized diffuse domain-lattice Boltzmann model for heat transfer in complex geometries with temperature Dirichlet boundary condition

In this paper, a regularized diffuse domain-lattice Boltzmann model for heat transfer with the Dirichlet boundary condition in complex geometries is proposed. In this model the complex computational domain is embedded into a larger and regular domain. The level set function is used to capture the complex interface. A diffuse domain formulation for the temperature field is established on the larger domain. To remove the ill-conditioned property of the original diffuse domain equation, we develop a new regularization technique to tackle this issue. We also give a multiple-relaxation-time lattice Boltzmann model to solve the regularized diffuse domain equation. The convergence rate of present model is investigated by the steady state and time-decay heat conduction problems. Then the natural convection problems in a square enclosure with a heated circular cylinder and in a horizontal concentric annulus are simulated. Both the uniform and non-uniform wall temperature cases are considered. Moreover, an alternative method to calculate the average Nusselt number on the complex boundary is employed. The numerical results show a good agreement with the previous solutions in previous literatures. The effect of non-uniform wall temperature on the heat transfer rate is also investigated. At last, the forced convection across the staggered tube banks is also simulated to verify the potential capability of the present model in solving practical heat transfer problem with the complex geometries.

Numerical and Experimental Study of a Novel Additively Manufactured Metal-Polymer Composite Heat-Exchanger for Liquid Cooling Electronics

In order to meet increasing power-dissipation requirements of the electronics industry, compact, low-cost, and lightweight heat exchangers (HXs) are desired. With proper design, materials, and manufacture, polymer composite heat exchangers could meet these requirements. This paper presents a novel crossflow air-to-water, low-cost, and lightweight metal-polymer composite HX. This HX, which is entirely additively manufactured, utilizes a novel cross-media approach that provides direct heat exchange between air and liquid sides by using connecting fins. A robust numerical model was developed, which includes the dimensional effects of additive manufacturing. The study consists of a simplified 3D CFD model based on ellipsoidal-shaped staggered tube banks for the laminar range. It then uses an analytical approach to compute entire HX performance. The model is validated experimentally within 8% for thermal performance, 12% for air-side impedance, and 18% for water-side impedance. Finally, HX is compared with a conventional CPU radiator and performs within 10% of the conventional unit for reasonable flow rates and pressure-drop ranges. Moreover, HX also provides added design and cost advantages over the conventional unit, which makes the HX a potential candidate for electronic cooling applications.

Numerical Study the Effect of Gap Ratio on Flow Characteristics and Heat Transfer in Staggered Tube Banks

Condenser is a type of heat exchanger that serves as condensation for turbine output steam. In general, a steam power plant uses a surface condenser. This type of condenser is a type of shell and tube. Condensers have a phenomenon of convection heat transfer. The change in distance between condenser tubes is one way to increase the rate of heat transfer. To produce maximum heat transfer, it can be determined by the variety of distances between tubes. The research was conducted by analyzing the flow characteristic and heat transfer around condenser tube banks with gap ratio variation (s/d), which compares transverse distance (ST ) and tube diameter (d) with variations of 3.2, 2.7, 2, and 1.7. 2-dimensional simulation with Computational Fluid Dynamics (CFD) is a numerical method and algorithm for solving and analyzing problems that occur in fluid flows. Based on the results obtained, the smaller the Gap Ratio, the lower the outlet temperature produced and the maximum heat transfer, but the pressure drop value obtained the bigger. Also, the smaller Gap ratio, the bigger v max produced. The lowest outlet temperature value at the variation of 1.7 is 310.66 K, and the coefficient of heat transfer is 103.34 W/m2K. Pressure drop produced at variation 1.7 is 515.99 Pa. Variation 2 is the best gap ratio variation, seen from the heat transfer result and the pressure drop value is not too large. The coefficient heat transfer and pressure drop in variation 2 are 76.95 W/m2K and 119.17 Pa.

Determination of the Reference Temperature for a Convective Heat Transfer Coefficient in a Heated Tube Bank

The paper presents a theoretical analysis of heat transfer in a heated tube bank, based on the Nusselt number computation as one of the basic dimensionless criteria. To compute the Nusselt number based on the heat transfer coefficient, the reference temperature must be determined. Despite the value significance, the quantity has several different formulations, which leads to discrepancies in results. This paper investigates the heat transfer of the inline and staggered tube banks, made up of 20 rows, at a constant tube diameter and longitudinal and transverse pitch. Both laminar and turbulent flows up to Re = 10,000 are considered, and the effect of gravity is included as well. Several locations for the reference temperature are taken into consideration on the basis of the heretofore published research, and the results in terms of the overall Nusselt number are compared with those obtained by the experimental correlations. This paper provides the most suitable variant for a unique reference temperature, in terms of a constant value for all tube angles, and the Reynolds number ranges of 100–1000 and 1000–10,000 which are in good agreement with the most frequently used correlating equations.

Assessment of Turbulence Models for Low Reynolds Number Flows and Their Computational Costs, Part 1: Staggered Tube Bank

Abstract This study investigates the accuracy of computational fluid dynamics (CFD) models to predict heat transfer in turbulent separated flows at low Reynolds numbers. This article will focus on flow in a staggered tube bank, while its companion articular will focus on a square prism (cylinder) in cross flow. Experimental data for both local heat transfer and velocity profiles are available for these cases and have been used extensively in the literature to evaluate various CFD methods. Six unsteady models were used and the results show that the unsteady shear stress transport (SST) model provided good overall accuracy relative to the mean Nusselt number for both cases. However, the SST model failed to accurately predict local variations. The partially averaged Navier–Stokes (PANS) variant of the SST model did show a marked improvement over the baseline SST model. The dynamic Smagorinsky large eddy simulation (LES) showed a much-improved fidelity to the local Nusselt number but unpredicted the actual values. The computational cost for the LES model was significant and it was found that the computationally expensive models with higher degrees of resolved turbulence did not necessarily return better results. Finally, the pressure drop results for the six models were scaled to predict the mean Nusselt number with the generalized Leveque method and were found to be very accurate. This method should prove useful to predict heat transfer performance with computationally less expensive cold flow results.

Assessment of Turbulence Models for Low Reynolds Number Flows and Their Computational Costs, Part 2: Square Prism in Cross Flow

AbstractThe accuracy of six turbulent flow modeling techniques in an unsteady solution is evaluated against experimental data for a square prism in cross flow. The selected models, shear stress transport (SST), SST-SAS, Reynolds stress model (RSM), partially averaged Navier–Stokes (PANS)-SST, detached eddy simulation (DES), and large eddy simulations (LES), models are the same as those presented in Part 1 of this study, which focused on flow in a staggered tube bank. For this geometry, the SST model proved to be effective at capturing the averaged Nusselt values per side of the square with relatively low computational costs. The SST model, however, showed poorer fidelity to the local Nusselt number profile compared to the experimental data. The LES approach provided a more accurate representation of the local Nusselt number but the computational cost was significantly higher. The PANS modification to the SST model did provide a noticeable improvement in accuracy at a reasonable cost while the SAS modification did not see the same improvement. These conclusions are generally consistent with those found for the staggered tube bank in Part 1 of this study. This study can be used as a guide for the industrial user to select a turbulence model for a similar problem with a low Reynolds number and significant flow separation.

ELEKTRİKTE PİK TALEBİ TÖRPÜLEME İÇİN KULLANILACAK FDM-HAVA SOĞUK ENERJİ DEPOLAMA CİHAZI TASARIMI VE OPTİMİZASYONU

Parametric analysis and dimensional optimization study for the melting process of the phase changing material placed in cold energy storage devices have been conducted. Phase changing material, PCM, is used to store the cold energy. A cross-flow tubular PCM-air heat exchanger is used. An electricity peak shaving for a summer day in Antalya for 5 hours (10:00-15:00) is aimed. The cooling load of a room (33 m2) in Antalya is taken as a reference value. A minimum cooling load of 2850 W is supplied throughout 5 hours to maintain the building's comfort temperature. Contrary to the studies handling air velocity constant, it is varied during melting in the present study to satisfy the minimum cooling load. The melting process is analyzed using a numerical model. A computational algorithm is implemented in MATLAB environment. The numerical model is validated for the same conditions and the dimensions with an analytical model presented in the literature. A transient analysis has been employed, and the problem is discretized for the time and space domain. A dimensional optimization algorithm is employed. A parameter “performance ratio/ cooling index”, the ratio of total cooling to fan energy consumption, is defined. Spacing between the tubes giving the maximum performance ratio is sought for aligned and staggered tube bank arrangements using this algorithm. The best performance ratio is obtained at 0.2 m/s initial velocities for both arrangements. In addition, the effect of sizing/arrangement of the tubes, PCM mass, and thermal conductivity of the PCM on the melting characteristics is investigated. As a result of increasing the thermal conductivity from 0.2 W/(m·K) to 0.6 W/(m·K), the performance ratios are raised 4.58 and 3.52 times for aligned and staggered orders, respectively. It is calculated that 10 kg PCM can be saved thanks to enhancing the thermal conductivity of the PCM.

Numerical Analysis of Flow across Brush Elements Based on a 2-D Staggered Tube Banks Model

In order to improve efficiency in turbomachinery, brush seal replaces labyrinth seals widely in the secondary air system. A 2-d staggered tube bank model is adopted to simulate the gas states and the pressure character in brush seal, and computational fluid dynamics (CFD) is used to solve the model in this paper. According to the simulation results, the corrected formula of the Euler number and dimensionless pressure are given. The results show that gas expands when flow through the bristle pack, and the gas expansion closes to an isotherm process. The dynamic pressure increases with decreasing static pressure. The Euler number can reflect the seal performance of brush seals in leakage characteristics. Compared with increasing the number of rows, the reduction of the gap is a higher-efficiency method to increase the Euler number. The Euler number continually increases as the gap decreases. However, with the differential pressure increasing, Euler number first increases and then decreases as the number of rows increases. Finally, the pressure distribution on the surface of end rows is asymmetric, and it may increase the friction between the bristles and the back plate.

Experimental study of partially metal foam wrapped tube bundles

Overall heat transfer and pressure drop for three novel staggered tube banks with tubes partially wrapped with metal foam layers have been experimentally studied in an open circuit wind tunnel. The positions of the metal foam layers around the tubes are different in the studied tube banks, TB1, TB2, and TB3. In other words, the angles between inlet flow direction and metal foam layers placement around the tubes are 0, ±45, and ±90° in TB1, TB2, and TB3, respectively. The most interesting result of the present study is that heat transfer and pressure drop are closely related to the position of the porous layers around the tubes and the thermal performance augmentation could be achieved by selecting suitable positions for metal foam layers. The results indicate that the tube bank in which metal foam layers are centered at 0 and 180° from the front stagnation point of tubes (TB1) exhibits a better heat transfer performance at the same pressure drop comparing with TB2 and TB3. To illustrate this, at about 7 Pa, TB1 disposes of 62% and 82% more heat than TB2 and TB3, respectively.

Experimental and numerical investigations for effect of longitudinal splitter plate configuration for thermal-hydraulic performance of staggered tube bank

The use of fins for the passive mode of heat transfer enhancement is being used since decades. The use of fin increases the rate of heat transfer by increasing the effective area available for the energy exchange. Hence, most of the modern heat exchanger makes use of different types of the fins to make the device more efficient and compact. Most of the fin configuration used in the heat exchanger not only increases the rate of heat transfer but also causes an undesirable rise in pumping power owing to the additional air/fluid resistance encountered. In the present study, longitudinal fins in the form of a splitter plates are used for the experimental study in case of a staggered cross flow tube bank. The splitter plate geometric configuration such as splitter plate length (0.50 ≤ L/D ≤ 1.50) and plate thickness (0.04 ≤ t/D ≤ 0.20) are varied to further enhance the overall thermal hydraulic performance of the tube bank. The three-dimensional numerical study is also performed for better fluid flow visualization. The use of the splitter plate with L/D = 1.0 and t/D = 0.20 improves the Nusselt number with the reduction in the overall pressure drop for most of the configuration, resulting in an improvement in the thermal-hydraulic performance of tube bank. Moreover, statistical correlations are developed for the Nusselt number and friction factor characteristics for longitudinally finned tube bank for the entire range of Reynolds number from 5000 to 25000.

Optimization of Heat Transfer and Pressure Drop in Axially Finned Staggered Tube Banks

Numerical optimization of heat and fluid flow over staggered tube banks are investigated for both unfinned and axially finned tube banks. Ansys Fluent software is utilized for numerical computations. To find maximum total heat transfer and minimum volume of tube bank for the given mass flow rate, allowable pressure drop and tube bank effectiveness; A Multi-objective Genetic Algorithm II is used. Optimum designs are given on tabular forms and variations of total heat transfer with total volume are presented. Moreover, effects of transversal and longitudinal pitches on objective functions are graphically demonstrated. In order to confirm reliability of the numerical studies, unfinned staggered tube bank configuration is compared with experimental studies in literature. As a result of optimization studies, axial fin usage results in 42.7% decrement in volume of staggered tube bank with respect to unfinned case, while heat transfer values are equal with maximum obtainable heat transfer rate for the given optimization problem.

Effect of the bounding walls configuration on draft water flow through staggered tube bank

The paper presents the numerical study of 3D unsteady buoyancy-induced water flow through a staggered tube bank typical for subsea cooling units used at seabed gas compression modules. For the Grashof number from the range of 105…106 parametric computations have been performed using direct numerical simulation of the draft water flow in the inter-tube space. For various arrangement of the bounding walls, the effect of the side flow on heat transfer is analyzed and discussed.

New Empirical Models for Condensation on Banks of Plain Tubes

New empirical models for evaluating heat-transfer coefficients for condensation on banks of tubes were developed using an experimental database of over 4000 individual data points for 7 different condensing fluids and 13 different tube bank configurations. New empirical models within each of the free and forced convection flow regimes for both of the steam and non-steam fluids separately were obtained, including the relevant dimensionless groups that may affect the heat transfer during the condensation. Two models within the free-convection flow regime for the non-steam were proposed due to large volume and variation of data in this regime. While comparing the results of the new empirical models with the recent database; it was proposed that the overestimation for some of the non-steam data of Shah (1978 and 1981) was due to the presence of the non-condensable gas (air) within the flowing fluid. In terms of predicting the tube bank thermal performance and condensation of flowing fluid, the results of the newly developed models were seen to be the most reliable and accurate when compared with the existing models mentioned in this paper. An overall agreement was seen with the existing experimental database within an average absolute of the errors of about 15%. For steam data, the present models were seen to yield the most accurate results for the inline and staggered tube banks when compare with other empirical and analytical models. However, for non-steam fluids (R-12, R-21 and R-113 only) flowing through staggered tube bank, Honda et al. (1989) model is recommended.

Numerical studies on the near wall y+ effect on heat and flow characteristics of the cross flow tube bank

The use of passive mode of heat transfer enhancement are most commonly used for the performance improvement with conservation of conventional fuels. In recent times, to visualize the insight of fluid flow analysis, the numerical simulations are mostly preferred. The number of grid points present in the in the fluid domain near the wall governs the accuracy and precision of the numerical study. Hence in the present study, three different near wall grid systems are consider to evaluate its effect on Nusselt number friction factor for the staggered tube bank arrangements. It is reported that y+ as 10, insensitive to boundary layer effects at higher flow rate, while y+ as 1.0, and 0.10 are in close approximation.

Generalized optimization of cross-flow staggered tube banks using a subscale model

Finding a general optimum arrangement of the cross-flow staggered tube banks causes a significant decrease in using available energy resources due to their extensive use in industrial applications. This paper presents a numerical optimization study by generalized pattern search algorithm (GPSA) to investigate optimum longitudinal and transverse pitches of the staggered tube banks in turbulent flow regime. Symmetric and periodic boundary conditions are employed to simulate all the tube banks without considering the entire volume. Using these boundary conditions, the optimization process can be directly performed by simulating the flow and heat transfer through tube banks with a CFD code and the previous researchers' correlations are not employed in this process. The “goodness factor” which takes into consideration the effects of both heat transfer and pressure drop simultaneously in a proper order is used as the objective function. In the first part of the study, optimum pitches are calculated for specific inlet Reynolds and Prandtl numbers. Subsequently, the effect of both inlet Reynolds and Prandtl numbers are separately investigated on the optimum pitches in the turbulent regime. Results show that the optimum dimensionless longitudinal and transverse pitches of the staggered tube banks are independent of the inlet Reynolds and Prandtl numbers in the turbulent regime and equal to PL, opt ≅ 1 and PT, opt ≅ 1.3, respectively. As a result, a general compact arrangement for staggered tube banks is proposed that is applicable in practical applications due to its high efficiency and compactness.