Tube Bundle Geometry Research Articles

Tube bundle evaporators with LGWP refrigerant R1234ze(E)

With new low-GWP HFO refrigerants, the heat transfer performances and methods for decreasing system refrigerant inventory are receiving increasing interest. In shell-and-tube heat exchangers, refrigerant distribution via pressurized liquid spray has the potential for high heat transfer performance while reducing refrigerant charge. However, no published studies have investigated LGWP refrigerants with spray evaporation on tube bundles. A test apparatus was constructed to measure the shell-side heat transfer coefficients of R1234ze(E) on bundles of tubes with two different enhanced-surface types and in two different bundle geometries at various refrigerant saturation temperatures. The results showed strong dependence on refrigerant properties, tube heat flux, enhanced-surface type, bundle geometry, and refrigerant inlet subcooling. The bundle heat transfer coefficients of R1234ze(E) were similar to that of R134a in the same test setup, usually within ±15% for similar conditions. In both cases, they first increased with the heat flux until a local maximum value was achieved. A localized dryout of the tubes at the bottom of the bundle penalized the overall bundle heat transfer coefficient at very high heat flux. For the condensing surface, bundle heat transfer coefficients rarely exceeded 10 kW/m2-K, whereas values in excess of 30 kW/m2-K were sometimes seen for the evaporating surface.

Friction factor and Reynolds number correlation for finned tube bundle of the air cooler of Monju reactor

Applicability of the analysis model of the cooling ability under a high temperature and low flowrate condition should be improved to evaluate the plant safety in case of the severe accident due to long-term station blackout.The present study reviews experiments on pressure drop behavior for complicated tube bundle geometry to the flow path and then develops a new correlation equation based on a computational fluid dynamics analysis of the Monju air cooler reflecting the actual geometry and plant data.After a basic simulation model being developed for a typical pressure drop experiment, the simulation is applied to the Monju air cooler that has a finned tube bundle. The obtained relationship between friction factors and Reynolds numbers ranging from 10 to 10,000 are fitted to a power function to derive a correlation equation of the fin tube bundle friction factor. The derived correlation equation can estimate pressure loss in the finned tube bundle more precisely than that used in the Monju design. It is applicable to the future reactor design of the air cooler, especially when the cooling ability in low Reynolds number is requested.

Multi-tube effect of external condensation with non-condensable gas in a tube bundle

The passive safety design concept is essential to remove decay heat under the station blackout. We conducted experimental and CFD-based studies on condensation in the presence of non-condensable gas to analyze the performance of a Passive Containment Cooling System. External condensation experiments were performed in 2 ∼ 4 bar, air mass fraction in 0.2 ∼ 0.7 with 1 ∼ 3 cylindrical tubes. CFD simulation was also performed to analyze the condensation phenomenon considering the effect of the tube bundle in terms of the ratio of Heat Exchanger area and vessel volume (A/V). We conducted the sensitivity study on the various tube bundle and vessel geometry by CFD and suggested bundle correction parameters as a function of the A/V. As a result, we evaluated the PCCS design with the horizontal tube bundle. It significantly reduces the required number of tubes compared to vertical tube bundle design because of the larger tube surface area and higher HTC by an inclination enhancement factor.

Numerical Prediction of Two-Phase Flow through a Tube Bundle Based on Reduced-Order Model and a Void Fraction Correlation.

Predicting the void fraction of a two-phase flow outside of tubes is essential to evaluate the thermohydraulic behaviour in steam generators. Indeed, it determines two-phase mixture properties and affects two-phase mixture velocity, which enable evaluating the pressure drop of the system. The two-fluid model for the numerical simulation of two-phase flows requires interaction laws between phases which are not known and/or reliable for a flow within a tube bundle. Therefore, the mixture model, for which it is easier to implement suitable correlations for tube bundles, is used. Indeed, by expressing the relative velocity as a function of slip, the void fraction model of Feenstra et al. and Hibiki et al. developed for upward cross-flow through horizontal tube bundles is introduced and compared. With the method suggested in this paper, the physical phenomena that occur in tube bundles are taken into consideration. Moreover, the tube bundle is modelled using a porous media approach where the Darcy–Forchheimer term is usually defined by correlations found in the literature. However, for some tube bundle geometries, these correlations are not available. The second goal of the paper is to quickly compute, in quasi-real-time, this term by a non-intrusive parametric reduced model based on Proper Orthogonal Decomposition. This method, named Bi-CITSGM (Bi-Calibrated Interpolation on the Tangent Subspace of the Grassmann Manifold), consists in interpolating the spatial and temporal bases by ITSGM (Interpolation on the Tangent Subspace of the Grassmann Manifold) in order to define the solution for a new parameter. The two developed methods are validated based on the experimental results obtained by Dowlati et al. for a two-phase cross-flow through a horizontal tube bundle.

Shell-and-Tube Heat Exchanger Geometry Modification: An Efficient Way to Mitigate Fouling

Crude oil fouling of a shell-and-tube heat exchanger sized according to TEMA standard is compared to a No-Foul design under industrial operating conditions. For similar operating conditions, TEMA and No-Foul heat exchangers have the same behavior regarding fouling. Since the No-Foul one has less tubes by design for the same heat duty, shear stress is increased. Consequently, the No-Foul heat exchanger is less prone to fouling at the same throughput. Impact of tube bundle geometry is then investigated. Helically finned tubes are compared to plain tubes in the No-Foul heat exchanger. Under similar operating conditions, fouling rates measured are up to an order of magnitude lower than plain tubes (respectively 10−11 and 10−10 m2 K/J). However, pressure drop across the tube-side in both No-Foul plain and finned setup are increased in comparison to the TEMA heat-exchanger.

Investigating wall-to-bed heat transfer in view of a continuous temperature swing adsorption process

Heat transfer between bubbling fluidized beds and immersed heat exchanger surfaces is studied in view of continuously operated temperature swing adsorption processes for post-combustion CO2 capture. A novel heat transfer measurement test device was used to measure wall-to-bed heat transfer coefficients. The present work focuses on the comparison of experimentally obtained and calculated heat transfer coefficients. Heat transfer at horizontal single tubes and tube bundles immersed in fluidized particle beds of glass beads with 140μm and 200μm in Sauter mean diameter is investigated. It is shown that the experimental results for single tubes are in mediocre agreement to established mathematical models, such as the ones proposed by Natusch et al. (1975) and Molerus et al. (1995), and that heat transfer is significantly influenced by the tube diameter. The model by Petrie et al. (1968) was considered to take the effect of the tube diameter into account, which lead to promising results. Furthermore, measured heat transfer coefficients at tube bundles of different geometries are compared to predictions using the models by Natusch et al. (1975) and Lechner et al. (2013). Some of the tube bundle reduction factors predicted by the model by Lechner et al. (2013) are larger than one, which stands in contrast to the finding that the highest heat transfer coefficients occur at single tubes. However, both models lead to adequate results when calculating heat transfer coefficients for different tube bundle geometries.

Pressure drop-flow rate curves for single-phase steam in Combustion Engineering type steam generator U-tubes during severe accidents

Characteristic pressure drop-flow rate curves are generated for all row numbers of the OPR1000 steam generators (SGs), representative of Combustion Engineering (CE) type SGs featuring square bend U-tubes. The pressure drop-flow rate curves are applicable to severe accident natural circulations of single-phase superheated steam during high pressure station blackout sequences with failed auxiliary feedwater and dry secondary side which are closely related to the thermally induced steam generator tube rupture event. The pressure drop-flow rate curves which determine the recirculation rate through the SG tubes are dependent on the tube bundle geometry and hydraulic diameter of the tubes. The larger CE type SGs have greater variation of tube length and height as a function of row number with forward flow of steam favored in the longer and taller high row number tubes and reverse flow favored in the short low row number tubes. Friction loss, natural convection heat transfer coefficients, and temperature differentials from the primary to secondary side are dominant parameters affecting the recirculation rate. The need for correlation development for natural convection heat transfer coefficients for external flow over tube bundles currently not modeled in system codes is discussed.

Granular Flow Field in Moving Bed Heat Exchangers: A Continuous Model Approach

Moving Bed Heat Exchangers (MBHX) are a promising option to discharge thermal energy from hot bulk materials, which can be used in solar thermal power plants as heat transfer and storage medium. A precise determination of the flow field in a MBHX is required to predict its thermal performance. This paper presents a continuous model approach, based on the theory of soil mechanics to describe the granular flow inside the heat exchanger. The simulation results are compared to a preceding model and experimental data. For this purpose two different tube bundle geometries are analyzed. The results are evaluated by means of contour plots of the flow field and the velocity magnitude of the granular material at the tube surfaces. The new model captures the flow at the top of the tubes quite well but shows need for further improvement in the lower part of the tubes.

Natural circulation heat transfer model development over vertical tube bundle in the condensate heat exchanger

A 330MWt integral type nuclear power plant, SMART, was developed for electricity generation and seawater desalination. Advanced design concepts were adopted such as an integral arrangement of the major components, and a passive residual heat removal system (PRHRS) to enhance the safety capability. The TASS/SMR code was developed using various thermal-hydraulic models reflecting the design features of SMART, such as the condensate heat exchanger in the passive residual heat removal system. The development and validation of the condensate heat exchanger model were performed using POSTECH and IIT heat transfer test results. The TASS/SMR code predicted well or slightly under-predicted the heat transfer coefficient at the condensate heat exchanger shell side compared with the experimental data. The heat transfer correlation considering the tube bundle effect improved the prediction of the heat transfer for a vertical tube bundle geometry.

Experimental and CFD investigations of turbulent cross-flow in staggered tube bundle equipped with grooved cylinders

In the present paper, an experimental and numerical simulation of the turbulent cross-flow in a staggered tube bundle with transverse and longitudinal pitch-to-diameter ratios of 3.8 and 2.1, respectively, are performed. The bundle consists of 16 PVC tubes of 40 mm outer diameter arranged in a staggered configuration. Each cylinder has two grooves on the external surface at 90° and 270°. The experiments are carried out using a subsonic wind tunnel. The pressure distributions along the tubes are determined for a variation of the azimuthal angle from 0° to 360°. The drag and lift forces are measured using the TE 81 balance. The drag coefficients are also deduced from the resulting pressure force in order to compare with smooth cylinder configuration. The use of the grooved cylinder shows a reduction on the drag forces. The steady-state Reynolds-averaged Navier–Stokes equations are solved using a finite-volume method where Spalart–Allmaras, k–e realizable and k–ω SST, turbulence models are used to produce a closed system of solvable equations. The staggered tube bundle geometry simulations are performed at steady conditions. An adapted grid using static pressure, pressure coefficient and velocity gradient, furthermore, a second-order upwind scheme were used. The obtained results show that the numerical predictions are in good agreement with the experimental measurements.

Experimental investigation of shell-side steam pressure drop in crossflow in a horizontal falling-film tube bundle

An experimental investigation of the steam flowing across a horizontal tube bundle with liquid falling film was conducted to simulate flow characteristics in a large desalination plant. Experiments were conducted at pressure ranging from 12 kPa to 31 kPa with the corresponding saturated steam temperature of 50 °C to 70 °C and the falling film spray density of 0.02 kg·m-1·s-1 to 0.08 kg·m-1·s-1. The influence of the spray density, saturated temperature and tube bundle geometry structure on steam pressure drop was illustrated. The results indicate that the pressure drop increased with increasing spray density, but decreased with increasing saturated temperature. The pressure drop at the maximum spray density of 0.08 kg·m-1·s-1 can be three times that in spray density of 0.02 kg·m-1·s-1 and the pressure drop at 50 °C is almost twice that at 70 °C. Under the same condition, the pressure drop through a rotated square- arranged tube bundle was smaller than that through a regular triangular-arranged tube bundle.

Comparison between a Plate and a Tube Bundle Geometry of a Simulated Thermoelectric Generator in the Exhaust Gas System of a Vehicle

Numerous research projects in automotive engineering focus on the industrialization of the thermoelectric generator. The development and the implementation of thermoelectric systems into the vehicle environment are commonly supported by virtual designing activities. In this paper a customized simulation architecture [1] for thermoelectric generators, developed in research project TEG2020, is used to compare two very different TEG concepts: a plate and a tube bundle geometry. The installation space serves as a restriction and therefore is the same for both systems.There are slight advantages in maximum power output, nominal back pressure and overall weight of the tube bundle geometry compared to the lightweight and cost-effective planar thermoelectric generator presented in [1] and [2]. The efficiency of both systems is nearly the same. However there are some disadvantages of the tube bundle geometry in required mass of thermoelectric material, efficiency based on the mass of thermoelectric material, complexity and necessary cooling load.

Convective Heat Transfer and Pressure Drop over Elliptical and Flattened Tube

A numerical study on the effect of the effect of elliptical and flattened tube bundle geometry on the convective heat transfer and pressure drop is presented in this article. The analysis has been carried out to evaluate the performance of these bundle geometries in the design of a compact and effective single phase shell and tube heat exchanger. The temperature, velocity, and pressure drop profiles are obtained from solving the mass, momentum, and energy conservation equations. The comparison is made for inline and staggered bundle with different pitch to diameter ratio and inlet velocity for elliptical and flattened tubes. The pitch to diameter ratio is varied from 1.25 to 2.5 for Reynolds number ranging from 200 to 2000 which is in the laminar flow region. The heat transfer coefficient over the staggered and inline tube bundle decrease with an increase in pitch. The same kind of variation is also observed for the pressure drop in the case of both elliptical and flattened tube bundle. The study shows that the transverse pitch with respect to cross flow affects more than the longitudinal pitch.

Heat-transfer from horizontal tube bundles into fluidized beds with Geldart A lignite particles

This work investigates the heat transfer mechanism in fluidized beds equipped with horizontal heat exchanger surfaces such as single tubes and especially tube bundles.Previous works were performed for varying operating conditions and solids' material properties, leading to a heterogeneous and therefore not applicable spectrum of derived correlations for the influence of tube diameter and tube bundle geometry on heat transfer.Based on a wide range validation of the correlation for the influence of single tube diameter on heat transfer coefficient, tube bundles with different tube diameters and horizontal and vertical spacings and alignments were investigated. Experiments were carried out using electrical heat transfer probes in a 0.15m2 fluidized bed test facility at ambient conditions. Geldart A lignite and Geldart D solids were used in order to distinguish between predominant particle-convective and gas-convective heat transfer mechanisms.The tube bundle reduction factor on heat transfer coefficient was derived as a key parameter based on dimensionless geometric numbers. This factor predicts the reduction of the heat transfer coefficient compared to that of the single tube due to the particle and gas flow disturbances caused by the immersed tubes.Tube diameter as well as tube bundle geometry were successfully implemented into useful correlations for predicting tube bundles' heat transfer of gas–solid fluidized bed systems operating with fine particles.

Comparison of power plant steam condenser heat transfer models for on-line condition monitoring

In this paper heat transfer models for large power plant condenser were examined. The goal was to develop a model capable of predicting not only the condenser pressure but the overall heat transfer coefficient. Such a model can be used for condenser condition monitoring. The results of a two-dimensional (2-D) condenser heat transfer model and single-point, zero-dimensional (0-D) model are presented together with the results from Heat Exchanger Institute (HEI) standards curves. Both 0-D and 2-D models can account for the effects of steam-side pressure drop and in a simplified manner also some effects of tube bundle geometry. For all models an experimental correction as a function of cooling water temperature was implemented to improve their accuracy. The results are presented in comparison with the measured plant data for three different tube bundle geometries, with and without the experimental correction factor. The 2-D model proved to be the most consistently accurate of the models both without the correction, and at varying steam and coolant flow with the correction applied. The results indicate significant local variation of pressure drop related effects, which the 0-D model failed to accurately predict particularly in cases of close temperature approach. In predicting the heat transfer coefficient the HEI model was the least accurate, significantly overestimating the impact of coolant flow rate change, and failing to match the measurements even with a correction applied.

CFD analysis of turbulent cross-flow in a staggered tube bundle equipped with grooved cylinders

This study describes the Computational Fluid Dynamics (CFD) analysis of the turbulent cross-flow in a staggered tube bundle with transverse and longitudinal pitch-to-diameter ratio of 3.8 and 2.1 respectively. Two Longitudinal grooves are placed on the external surface at 90° and 270° degrees. Each cylinder has two grooves on the external surface of the cylinder. The Navier-Stokes equations of the turbulent flow are solved using Spalart almaras, k-e realizable and k-ω SST, turbulence models provided by Fluent CFD code. The staggered tube bundle geometry simulations were performed at steady conditions. An adapted grid using static pressure, pressure coefficient and velocity gradient, furthermore, a second order upwind scheme were used. The CFD results were in agreement with the experimental data. The study demonstrates the capability of the CFD calculations in predicting flow characteristics around the bundle

Fluidelastic Instability Modeling of Loosely Supported Multispan U-Tubes in Nuclear Steam Generators

Steam generators in nuclear power plants have experienced tube failures caused by flow-induced vibrations. Two excitation mechanisms are responsible for such failures; random turbulence excitation and fluidelastic instability. The random turbulence excitation mechanism results in long-term failures due to fretting-wear damage at the tube supports, while fluidelastic instability results in short-term failures due to excessive vibration of the tubes. Such failures may require shutdowns, which result in production losses, and pose potential threats to human safety and the environment. Therefore, it is imperative to predict the nonlinear tube response and the associated fretting-wear damage to tubes due to fluid excitation. In this paper, a numerical model is developed to predict the nonlinear dynamic response of a steam generator with multispan U-tubes and anti-vibration bar supports, and the associated fretting wear due to fluid excitation. Both the crossflow turbulence and fluidelastic instability forces are considered in this model. The finite element method is utilized to model the vibrations and impact dynamics. The tube bundle geometry is similar to the geometry used in CANDU steam generators. Eight sets of flat-bar supports are considered. Moreover, the effect of clearances between the tubes and their supports, and axial offset between the supports are investigated. The results are presented and comparisons are made for the parameters influencing the fretting-wear damage, such as contact ratio, impact forces, and normal work rate. It is clear that tubes in loose flat-bar supports have complex dynamics due to a combination of geometry, tube-to-support clearance, offset, and misalignment. However, the results of the numerical simulation along with the developed model provide new insight into the flow-induced vibration mechanism and fretting wear of multispan U-tubes that can be incorporated into future design guidelines for steam generators and large heat exchangers.

Experimental and Numerical Characterization of Flow-Induced Vibration of Multispan U-tubes

This paper describes a test program that was developed to measure the dynamic response of a bundle of steam generator U-tubes with anti-vibration bar (AVB) supports, subjected to Freon two-phase cross-flow. The tube bundle geometry is similar to the geometry used in preliminary designs for future CANDU steam generators. This test program is one of the initiatives that Atomic Energy of Canada Limited (AECL) is undertaking to demonstrate that the tube support design for future CANDU steam generators meets the stringent requirements associated with a 60-year lifetime. In particular, the tests will address issues related to in- and out-of-plane fluidelastic instability and random turbulent excitation of a U-tube bundle with AVB supports. Therefore, the measurements include tube vibration amplitudes and frequencies, work-rate due to impacting and sliding motion of the tubes against their supports, bulk process conditions and local two-phase flow properties. Details of the test rig setup and the measurement techniques are described in the paper. Moreover, a numerical prediction of the U-tube vibration response to flow was performed with AECL’s pipo-fe code. A summary of the numerical results is presented.

Friction Factor Measurements in an Equally Spaced Triangular Array of Circular Tubes

Friction factor data for adiabatic cross flow of water in a staggered tube array were obtained over a Reynolds number range (based on hydraulic diameter and gap velocity) of about 10,000–250,000. The tubes were 12.7mm(0.5in.) outer diameter in a uniformly spaced triangular arrangement with a pitch-to-diameter ratio of 1.5. The friction factor was compared to several literature correlations and was found to be best matched by the Idelchik correlation. Other correlations were found to significantly vary from the test data. Based on the test data, a new correlation is proposed for this tube bundle geometry, which covers the entire Reynolds number range tested.

A review of heat exchanger tube bundle vibrations in two-phase cross-flow

Flow-induced vibration is an important concern to the designers of heat exchangers subjected to high flows of gases or liquids. Two-phase cross-flow occurs in industrial heat exchangers, such as nuclear steam generators, condensers, and boilers, etc. Under certain flow regimes and fluid velocities, the fluid forces result in tube vibration and damage due to fretting and fatigue. Prediction of these forces requires an understanding of the flow regimes found in heat exchanger tube bundles. Excessive vibrations under normal operating conditions can lead to tube failure. Relatively little information exists on two-phase vibration. This is not surprising as single-phase flow induced vibration; a simpler topic is not yet fully understood. Vibration in two-phase is much more complex because it depends upon two-phase flow regime, i.e. characteristics of two-phase mixture and involves an important consideration, which is the void fraction. The effect of characteristics of two-phase mixture on flow-induced vibration is still largely unknown. Two-phase flow experiments are much more expensive and difficult to carry out as they usually require pressurized loops with the ability to produce two-phase mixtures. Although convenient from an experimental point of view, air–water mixture if used as a simulation fluid, is quite different from high-pressure steam–water. A reasonable compromise between experimental convenience and simulation of steam–water two-phase flow is desired. This paper reviews known models and experimental research on two-phase cross-flow induced vibration in tube bundles. Despite the considerable differences in the models, there is some agreement in the general conclusions. The effect of tube bundle geometry, random turbulence excitations, hydrodynamic mass and damping ratio on tube response has also been reviewed. Fluid–structure interaction, void fraction modeling/measurements and finally Tubular Exchanger Manufacturers Association (TEMA) considerations have also been highlighted.