Staggered Tube Bank Research Articles

Numerical Analysis of Pressure Distribution in a Brush Seal based on a 2-D Staggered Tube Banks Model

A two-dimensional model of staggered tube banks of the bristle pack with different pitch ratios was solved by computational fluid dynamics (CFD). The pressure distribution along the gap centerlines ...

Numerical Investigations of the Convective Heat Transfer from Turbulent Flow Over Staggered Tube Bank

The present work aims to introduce 2-D numerical investigations of turbulent flow over staggered tube bank by using a commercial CFD package (ANSYS-Fluent). The realizable k-e turbulent model is applied. The effect of the longitudinal pitch ratio (SL/D), transverse pitch ratio (ST/D), Reynolds number, and tube shape on the heat transfer and flow characteristics is studied. Due to symmetry, half of the tube bank rows are considered. The present simulation results are compared with the available experimental data and previous analytical results, which show acceptable agreement. The results of circular tube bank show that there is an enhancement on the heat transfer ranging from 1.02 to 8.8% when the longitudinal pitch ratio changed from 1.25 to 3 at ST/D = 1.25 and 5000 ≤ Re ≤ 50,000. Additionally, the friction factor decreases for ST/D ≥ 2 as the longitudinal pitch ratio increases but it increases for ST/D ≤ 1.5. For flat tube bank, the results show that as the length ratio decreases the heat transfer increases. Moreover, the flat tube diameter should be small to obtain the highest heat transfer. Furthermore, two different correlations are obtained for Nusselt number for the two tube banks.

Mass transfer phenomena in fluidized beds with horizontally immersed membranes: A numerical investigation

Mass transfer phenomena in gas-solid fluidized beds with horizontally immersed membrane tube banks in different configurations were investigated using a Two-Fluid Model, considering the case of a binary hydrogen/nitrogen gas mixture fed to a 2D fluidized bed where hydrogen was extracted via hydrogen perm-selective membranes. The simulations showed that the hydrogen flux is strongly non-uniform over the radius of the membranes. The hydrogen flux is lowest on top of the membranes and highest at the bottom of the membranes, which is caused by the formation of densified zones on top of the membranes and the fact that the membranes shield their own top side from hydrogen replenishment. Also, in systems with membrane tube banks, the performance of individual membranes differs significantly. The membranes located near the bed walls perform considerably worse, because of downwards solids flow near the walls, resulting in more densified zones and gas back-mixing. The average hydrogen recovery per membrane is highest for the cases with a staggered tube bank configuration and without membranes positioned close to the bed walls. In-line tube bank configurations suffer from gas channeling, reducing the hydrogen recovery per membrane. The membrane tube banks also significantly improve the bed hydrodynamics by enhanced bubble-breakage, decreasing the bubble size to approximately the membrane pitch.

Numerical investigation on the coupling of ash deposition and acid vapor condensation on the H-type fin tube bank

There usually occurs a serious fouling on the heating surface of the low temperature economizer in boilers. The deposited ash on the surface could cause clogging and corrosion of the heat exchanger and even result in serious safety incident. Especially the low temperature bonding ash will corrode the surface severely. The distributions of the low-temperature bonding ash and the loose ash on the surface are numerically simulated in this study based on the theory of the particle transportation model, particle deposition model, force analysis of the particle and the acid point temperature model. The effect of fly ash particles on the content of the acid vapor in the flue gas is considered. Various factors on the distribution of deposited ash are investigated including the particle diameter, flue gas velocity, content of the acid vapor and the tube bank arrangement. The low temperature bonding ash is the largest on the first row tube in the in-line tube bank. However, both modes of deposited ash are largest on the third row tube in the staggered tube bank and they are difficult to remove.

Design of Flue Gas-Air Heat Exchanger for Regeneration of Desiccant System

Heat recovering from biogas waste energy requires robust heat exchanger design. This paper presents the design of fuel gas-air heat exchanger (FGAHE) for recovering waste heat from biogas burning to regenerate desiccant material. Mathematical model was built to design the FGAHE based on logarithmic mean temperature difference (LMTD) and staggered tube bank heat transfer correlations. MATLAB code was developed to solve the algorithm based on overall heat transfer coefficient iteration technique. The effect on tube diameter on design and thermal characteristics of FGAHE is investigated. The results revealed that the smaller tube diameter leads to smaller heat transfer area and tube. On the other hand, the overall heat transfer coefficient and Nusselt numbers have larger rates at smaller tube diameter. In conclusion, the nominated tube diameter for FGAHE is the smaller diameter of 0.0127 m due to the high thermal performance.

Investigation of thermo-aerodynamic characteristics of banks of tubes with punched spiral finning

An application of tubes with punched spiral-tape finning is promising for heat exchange intensification in convective heating surfaces of boilers and boilers-utilizers. Results of experimental research into thermo-aerodynamic characteristics of specified heating surfaces are presented. As a result of research, heat exchange intensification by 17…32 % due to fin punching was established. Heat transfer increases at an increase in the Reynolds number and a decrease in the degree of finning. Dependence of heat transfer on the accepted parameter for characterizing the bank geometry – relative to longitudinal pitch of tubes – is extreme with peaks in domain of variability relative to longitudinal pitch of 2.7…3.5. Efficiency of punched finning was determined. Results of the study of aerodynamic resistance showed its increase by 18…40 % due to the punching of fins. Resistivity increases at an increase in reduced length of the extended surface, and decreases at an increase in ratio of transverse pitch of tubes of the bank to longitudinal pitch and in Reynolds number. Results of experiment were generalized and formulas for engineering calculations of heat exchange and aerodynamic resistance of in-line tube banks with punched spiral finning were proposed. The formulae hold in domains of variability of defining parameters: finning coefficient y=6.01…9.012, relative longitudinal pitch of tubes in banks s 2 =2…6, Reynolds numbers Re d =6·103…4·104 and Re e =5·10 3 …4·10 4 , ratios of tube pitches S 1 /S 2 =0.4…2.5 and reduced length of extended surface – H/F=4.58…30.45. We established the intervals variability in ratio of pitches of tubes, in which thermo-aerodynamic efficiency of in-line and staggered tube banks is maximal, respectively: 1.0...1.5 and 2.0...3.0. Within these intervals, values of the Kirpichov criterion are, respectively, E=125...150 for in-line and 75...80 for staggered banks. Formulae establish relationship between Nusselt and Euler criterion with geometric characteristics of banks and Reynolds numbers. We determined thermo-aerodynamic efficiency of in-line and staggered banks of tubes with punched spiral finning by results of experimental studies. In-line banks have higher efficiency. As a result of calculation research into thermo-aerodynamic efficiency of four types of heating surfaces of a powerful boiler-utilizer, in-line tube banks with punched spiral finning turned out to be more efficient by this parameter. The Kirpichov criterion for these tube banks, located in one shell, is 319, for staggered tube banks with punched finning – 228.8, for staggered tube banks with continuous finning – 223.8, and for staggered bare-tube banks – 143.0.

Experimental and numerical studies on the air-side flow and heat transfer characteristics of a novel heat exchanger

A novel heat exchanger involving rotated aligned tube banks is proposed and investigated experimentally and numerically. It is utilized within a waste heat recovery system in a cement plant, and has features of both staggered and aligned arrangements. Heat transfer and flow characteristics of the heat exchanger are analyzed. Experimental data of the rotated aligned arrangement are compared with that of the aligned arrangements, and correlations of Nusselt number as well as friction factor are obtained. A two-dimensional numerical study is conducted employing CFD simulation. A model of the entire heat exchanger is built and simulated. Boundary conditions are formulated by a given inlet temperature of 300°C and a constant tube wall temperature of 150°C, with inlet velocity ranging from 2m/s to 7m/s. Simulated results are compared with the experimental data, and good agreement is achieved with the correlation results for rotated aligned arrangement. Moreover, simulations of aligned and staggered tube banks are implemented in comparison with the rotated aligned tube bank. Numerical results indicates the superior heat transfer performance of the rotated aligned tube bank over the other two arrangements. Heat transfer coefficient is 37.5–78.8% higher than the aligned arrangement, and 32.7–66.7% higher than the staggered arrangement. It also has high level of turbulence intensity as well as large maximum air velocity within the tube bank, yet the pressure drop is high. Nusselt number has a fairly good agreement with the staggered arrangement, and friction factor lies between the aligned and staggered arrangements, for 6000<Re<10000.

Optimization of Crossflow Staggered Tube Banks for Prescribed Pressure Loss and Effectiveness

For many applications, it is important to transfer a given amount of heat with minimum possible volume of heat exchanger for a given pressure loss and effectiveness. In this study, optimum design of crossflow staggered tube banks for prescribed pressure loss and effectiveness is carried out. For this purpose, the method of Gnielinski–Gaddis is used for the calculation of heat transfer coefficient and pressure loss in tube banks. By prescribing the tube diameter, heat exchanger effectiveness, and pressure loss of the heat exchanger, the pitch length and tube number in the flow direction are determined for the condition of the maximum heat flow per heat exchanger volume. For a given value of total heat to be transferred, the length, height, and width of the heat exchanger can be determined by the equations that are derived using appropriate dimensionless numbers.

Influence of Different Arranges of Vortex Generators on Heat Transfer

In this paper, effects of flat plate obstacles and rectangular and triangular decorated bars on cooling of a hot bar were investigated experimentally and numerically. The experiments were performed in a wind tunnel with transient heat transfer through the hot bar. Results showed that in case of staggered tube banks and Reynolds range of 350–2100, heat transfer increased from 10 to 30 % while pressure decreased from 55 to 34 % and in case of in-line tube banks and the same range of Reynolds, heat transfer encountered a rise from 10 to 20 % and the pressure reduced from 15 to 8 %. Moreover our study indicates the Nusselt increased when Reynolds number enhances, furthermore, the Nusselt variation corresponding to the rectangular flat obstacles was compared to other modes.

CFD해석을 통한 엇갈린형 관군의 열전달 및 압력강하 특성에 관한 연구

In this study, the characteristics of heat transfer and pressure drop was theoretically analyzed by changing longitudinal pitch, bump phase, location of vortex generator about the staggered tube banks by applying SST (Shear Stress Transport) turbulence model of ANSYS FLUENT v.14. Before carrying out CFD (Computational Fluid Dynamics) analysis, It is presumed that the boundary condition is the tube surface temperature of 363 K, the inlet air temperature of 313 K and the inlet air velocity of 5-10 m/s. The results indicated that the heat transfer coefficient is not affected by the longitudinal pitch and the bump phase of circle type was more appropriate than serrated type in the characteristics of heat transfer and pressure drop. Additionally, in case of vortex generator location, the heat transfer characteristics showed that forward location of tube was more favorable 4.6% than backward location.

A Hybrid Finite-Element/Finite-Difference Scheme for Solving the 3-D Energy Equation in Transient Nonisothermal Fluid Flow over a Staggered Tube Bank

This article presents a hybrid finite-element/finite-difference approach. The approach solves the 3-D unsteady energy equation in nonisothermal fluid flow over a staggered tube bank with five tubes in the flow direction. The investigation used Reynolds numbers of 100 and 300, Prandtl number of 0.7, and pitch-to-diameter ratio of 1.5. An equilateral triangle (ET) tube pattern is considered for the staggered tube bank. The proposed hybrid method employs a 2-D Taylor-Galerkin finite-element method, and the energy equation perpendicular to the tube axis is discretized. On the other hand, the finite-difference technique discretizes the derivatives toward the tube axis. Weighting the 3-D, transient, convection-diffusion equation for a cube verifies the numerical results. The L2 norm of the error between numerical and exact solutions is also presented for three different hybrid meshes. A grid independence study for the energy equation preceded the final mesh. The outcome is found to be in acceptable concurrence with those from the previous studies. After the temperature field is attained, the local Nusselt number is computed for the tubes in the bundle at different times. The isotherms are also obtained at different times until a steady-state solution is reached. The numerical results converge to the exact results through refining the mesh. The implemented hybrid scheme requires less computation time compared with the conventional 3-D finite-element method, requiring less program coding.

Investigation of heat transfer of tube line of staggered tube bank in two-phase flow

Abstract This article presents the results of experimental investigation of heat transfer process, carried out using the model of heat exchanger. Two-phase statically stable foam flow was used as a heat transfer fluid. Heat exchanger model consisted of staggered tube bank. Experimental results are presented with the focus on influence of tube position in the line of the bank, volumetric void component and velocity of gas component of the foam. The phenomena of liquid draining in cellular foam flow and its influence on heat transfer rate has also been discussed. The experimental results have been generalized by relationship between Nusselt, Reynolds and Prandtl numbers.

Numerical investigation of erosion on a staggered tube bank by particle laden flows with immersed boundary method

In the present paper, particle-laden flows past 10 × 11 staggered stainless steel tube banks in a duct and the caused erosion are investigated using point-particle Eulerian–Lagrangian method. The continuous gas flow field is obtained through direct numerical simulation. The coupling between fluid and the embedded tubes is handled through the multi-direct forcing immersed boundary method. Four types of coal ash particles with Stokes numbers 0.01, 0.1, 1.0, 10.0, are considered. The collision and erosion characteristics on the tubes located in the middle of the duct are analyzed in detail. It has been found that the global tube erosion of the first tube increases with the increment of the particle size, but particles with an intermediate Stokes number of 1.0 cause the most erosion to the other downstream tubes due to preferential accumulation effect. Results predict much more erosion to the second row of tubes in staggered tube banks than the first row of tubes. Global erosion to the tubes near the wall is much larger than the corresponding ones located in the center, especially far downstream. The maximum local tube erosion occurs within certain angle regions around the tubes, where more attention needs to be paid to prevent erosion.

English

This paper presents the numerical study on the two-dimensional forced convection heat transfer for staggered tube banks in cross flow under incompressible, steady-state conditions. This system is solved on the body fitted coordinates (BFC) using the finite volume method (FVM) for the flow over a bundle of cylindrical tubes. The constant heat flux is imposed on the surface of the tubes as the thermal boundary condition. The type of the arrangement is considered a staggered of tubes. The longitudinal pitch to tube diameter ratios (ST/D) of 1.25, 1.5 and 2 are also considered. Reynolds numbers are varied from 25 to 250 and Prandtl number is taken as 0.71. Velocity field vectors, temperature contours and local and average Nusselt numbers were analysed in this paper. It can be seen that the predicted results are good agreements with previous experimental and numerical results. The obtained results show that the heat transfer rate increases with decreases of the step to the longitudinal tube diameter. The local heat transfer strongly depends on the Reynolds number. It tends to obtain the highest values at the surface opposite to the direction of flow. The heat transfer rate is insignificant in the areas of recycling.

709 流れ方向に密な千鳥配列管群における気柱共鳴現象と渦放出(流体力学6)

709 流れ方向に密な千鳥配列管群における気柱共鳴現象と渦放出(流体力学6)

An embedding finite element analysis of heat transfer on the surface of circular cylinders in flow

The present study establishes an embedding finite element method appropriate for solving primitive variable forms of the Navier–Stokes equations and energy equation in a complex physical domain. The stationary solid obstacle in the flow domain is embedded in a non-uniform Cartesian grid and the governing equations are calculated through a finite element formulation. A compact interpolating scheme near the immersed boundaries is used to ensure the accuracy of the solution in the cut cells. We have developed a numerical algorithm based on the operator splitting technique, balance tensor diffusivity (BTD), Runge–Kutta time-stepping method, and a bi-conjugate gradient iterative solver. Three numerical examples are chosen to test the accuracy and flexibility of the proposed scheme. Simulation of flow past a stationary circular cylinder is conducted to validate the accuracy of the present method for solving heat transfer problems. Flow over circular cylinders in a tandem arrangement and a staggered tube bank with convective heat transfer is computed to demonstrate the model’s ability to handle complex geometries.

Immersed boundary method for simulations of erosion on staggered tube bank by coal ash particles

To predict the erosion of tubes and surfaces of heat exchangers in boilers caused by coal ash particles, particle-laden flows past a 10×11 staggered tube bank in a duct are investigated using a high-resolution numerical technique. The flow field is obtained through direct numerical simulation (DNS), the coupling between tubes and underlying flow is done through the immersed boundary method, and the particles are tracked by the Lagrangian approach. Classic particle–wall impact and erosion models are incorporated to investigate the collision and wear on the side walls and the tubes near the bottom side walls of the duct. It is found that particles at different Stokes numbers have different dispersion patterns in the flow field, and lead to different characteristics of collision and erosion on the near-wall tubes as well as the side walls. The larger Stokes number results in higher global erosion on the first tube near the side wall, but the particles with St=1.0 cause the largest erosion to other downstream tubes because of the preferential concentration effect. The distributions of collision and erosion on each tube are not uniform, but bias toward the side facing the wall, and the more downstream tubes have the higher erosion. For side wall erosion, particles having higher local collision frequency may lead to lower erosion. The reverse trend is also observed for the particles with the intermediate Stokes number of 1. Periodical oscillation of particle–wall collision and erosion happens because of the staggered arrangement of the tubes.

Effect of Arrangement of Tube Banks on Acoustic Resonance

In the present paper the attention is focused on effect of arrangement of tube banks on acoustic resonance which occurred in the two-dimensional model of boiler. We have examined the characteristics of vortex shedding and acoustic resonance generated from in-line and staggered tube banks. At the small tube pitch ratio in in-line tube banks, acoustic resonance of third and fourth mode in the transverse direction occurred. As the tube pitch ratio in the flow direction decreased, the vortex shedding frequency became broad-band. The alternative vortex shed from in-line tube banks. The multiple resonance modes were generated within the broad-band vortex shedding frequency. And the acoustic resonances of lower-order modes occurred at the higher gap velocity. On the other hand, at the small tube pitch ratio in staggered tube banks, acoustic resonance did not occurred, although the vortex shed at the resonance frequency in tube banks. The pressure drop at staggered tube banks was larger than that of in-line tube banks. The symmetric vortices were observed inside staggered tube banks at the small tube pitch ratio.

0617 ボイラにおける気柱共鳴現象の発生に及ぼす管群配列の影響(OS6 流体関連振動・騒音,オーガナイズドセッション)

In the present paper the attention is focused on effect of arrangement of tube banks on acoustic resonance which occurred in the two-dimensional model of boiler.We have examined the characteristics of vortex shedding and acoustic resonance generated from in-line and staggered tube banks.At the small tube pitch ratio in in-line tube banks,acoustic resonance of third mode and fourth mode occurred.The alternative vortex shed from in-line tube banks and its frequency became broad-band.On the other hand,at the small tube pitch ratio in staggered tube banks,acoustic resonance did not occurred,although the vortex shed at the resonance frequency in the tube banks.The pressure drop at staggered tube banks was larger than that of in-line tube banks.The symmetric vortices were observed inside staggered tube banks at the small tube pitch ratio.

Experimental study on titanium heat exchanger used in a gas fired water heater for latent heat recovery

Abstract In general, latent heat recovery is usually accompanied by the corrosion of the heat exchanger, which is caused by the strongly acidic condensate when the temperature of the flue gas is lowered below the acid dew point. The present study has been conducted to investigate the heat and mass transfer characteristics in a titanium heat exchanger with excellent corrosion resistance used for waste heat recovery with the condensation arranged in a gas fired water heater. In addition, the thermal efficiency of the gas fired water heater was evaluated based on the net calorific value at the maximum rated output during latent heat recovery from the exhaust flue gas. Parametric studies were conducted for the flue gas flow rate, inlet temperature and mass flow rate of the supplied water, respectively. Different arrangements of the tubes of the heat exchanger including in-line and staggered configurations were investigated. The experimental results indicate that the thermal efficiency of the gas fired water heater with a latent heat recovery (LHR) heat exchanger was enhanced by about 10% compared with conventional instantaneous water heaters, i.e., water heaters without heat recovery. In addition, in terms of the Nusselt number and the Sherwood number, the heat and mass transfer performance of the staggered tube bank type were approximately 50% and 10% higher than that on the in-line tube bank type when the Reynolds number of the flue gas was 103.