Cross-flow Tube Research Articles

Numerical study on heat transfer characteristics of LBE cross flow tube bundle under rolling conditions

Combined with the neutron economy and good heat transfer performance, lead–bismuth fast reactor (LFR) has a larger prospect for marine applications. Helical coiled once-through tube steam generator (HCOTSG) is also a typical heat exchanger option for LFR. It is widely adopted in a variety of energy utilization fields, such as petrochemical industry. Study on Lead-bismuth eutectic (LBE) cross flow of tube bundle under moving conditions is necessary for obtaining the flow and heat transfer characteristics of LBE HCOTSG in marine conditions. A numerical method to simulate the heat transfer characteristic of LBE cross tube bundle flow under rolling conditions is proposed. The influence of the rolling conditions on the models with different tube arrangements are investigated. The temperature fluctuation curves with time and the time-averaged heat transfer characteristics are compared and analyzed. The results of the influence of rolling conditions under different working conditions and different tube bundle arrangements are obtained. The improvement ratio under inclined arrangement and staggered arrangement is more than 20 %, but the improvement under inline arrangement can only reach 10–15 %. Among the calculated models under different rolling conditions, the maximum heat transfer improvement reached 27.3 %. Besides, the circumferential temperature results under different conditions were also compared to analyze the influence of rolling conditions. This study may contribute to the application of LBE HCOTSG under marine conditions.

Thermal-hydraulic investigation of liquid metal cross flow different arrangements of tube bundles under pulsating

The topic of this paper is to couple the passive and active approaches to enhance the heat transfer performance in the inline tube bundle heat exchanger. Firstly, the k-kl-ω turbulence model and Kays turbulent Prandtl number model are validated by liquid metal cross flow tube bundle experiments and rectangular groove pulsating flow experimental results. Then the numerical studies were carried out for pulsating velocity amplitude of 0.5, frequency of 10, and Re of 20,000 with transverse and streamwise pitch-to-diameter ratios of 1.5, 1.65, and 1.8. The introduction of pulsating flow effectively improves the turbulence characteristics between the tube bundles, especially at the first three rows, where the velocity fluctuation is enhanced by about 1.5–2 times. The tube heat transfer performances are all improved. The performance evaluation criterion (PEC) variation ranges from 1.04 to 1.32, which signifies that the introduction of pulsating flow can enhance the comprehensive heat transfer performance. The per unit flow rate thermal entropy generation decreased by about 9.7–33.3 %, in addition, a phase difference between the transient thermal entropy production and pulsating velocity was found. The correlation equations about Nu and f factor within the scope of this paper are presented.

A semi-analytical time-domain model with explicit fluid force expressions for fluidelastic vibration of a tube array in crossflow

It is widely acknowledged that fluidelastic instability (FEI), among other mechanisms, is of the greatest concern in the flow-induced vibration (FIV) of tube bundles in steam generators and heat exchangers. A range of theoretical models have been developed for FEI analysis, and, in addition to the earliest semi-empirical Connors' model, the unsteady model, the quasi-steady model and the semi-analytical model are believed to be three advanced models predominant in the literature. The unsteady and the quasi-static models share the merits of having explicit fluid force expressions and ease of being implemented but require more experimental inputs, whereas the semi-analytical model requires fewer parameters due to its analytical nature but is hard, if not prohibitive, to derive explicit fluid force expressions. Since the fluid force formulations set in the core of development of FEI models, the understanding and in particular the implementation of the semi-analytical model has been impaired by the nonexistence of explicit fluid force expression. This issue becomes more profound in time-domain analysis whereby the simple harmonic assumption is discarded. Here we report a new semi-analytical time-domain (SATD) FEI model with explicit fluid force expressions. The new model allows a consistent frequency-domain stability analysis and more importantly a truly time-domain response analysis. The theory was validated by calculating linear stability thresholds of two typical tube array patterns and comparing against reported experimental data. We then present a nonlinear time-domain analysis of a single loosely-supported tube with piece-wise linear stiffness. The nonlinear and nonsmooth dynamics was probed in details by utilizing various techniques, playing an emphasis on characterizing and distinguishing the chaotic vibration. We found that the system follows a quasi-periodic route to chaos. Such an in-depth study of the nonlinear dynamics of tubes in crossflow has never been reported in the context of SATD model. Our results enrich the theory and provide a different approach for linear and nonlinear dynamics of tube bundles, which are essential for the subsequent fretting wear analysis.

Crossflow polymeric hollow fiber heat exchanger: fiber tension effects on heat transfer and airside pressure drop

In various applications, a polymeric hollow fiber heat exchanger (PHFHE) is a competitive alternative to a conventional heat exchanger (HE). Standard empirical models for predicting the crossflow tube HE characteristics are defined for devices with rigid tubes with relatively large diameters compared to the polymeric hollow fibers with an outer diameter of around 1 mm. This study examines the impact of tension force on airside heat transfer rate and pressure drop in a crossflow PHFHE. The tension force influences the stiffness of the flexible polymeric fibers and their response to applied airflow. Two liquid–gas PHFHEs were designed and manufactured to ensure uniformity of the fibers' arrangement (inline and staggered). An experimental stand enabling the application of defined tension force in the range of 0–9000 N was designed, manufactured and placed into the calorimetric tunnel, where heat transfer rate and pressure drop measurement were performed with varying air velocity between 2 and 8 ms−1 (corresponding to Reynolds number of 240–970). Among our key findings was that the elongation of the fibers due to thermal expansion or stress relaxation has a considerable impact on the fibers' arrangement and resulting fluid flow. Moreover, the application of tension force yielded no substantial change in air pressure drop; however, it led to a notable enhancement in heat transfer rate. Specifically, under a maximal tension force of 9000 N, the heat transfer rate increased by around 11% compared to the unloaded state.

Numerical continuation and stability of nonlinear systems with distributed delays: Application to fluid-induced impacts of tubes in cross-flow

Fluid–elastic instability is the main source of concern during the design of heat-exchanger tube bundles. The associated research has focused on the understanding of the physical mechanisms behind this phenomenon and the establishing of models capable of predicting its onset; also some concomitant work has been done to establish post-instability behaviour and to prevent from excessive wear in possible sliding contacts. Moreover, the existing studies make use of time-integration methods alone for this purpose, through which it is difficult to get a comprehensive insight of global dynamics. Continuation methods, which give access to unstable branches and precise bifurcation information, are a precious tool to unfold the attainable dynamic regimes. In this paper, the parametric behaviour of two representative systems under cross-flow excitation is explored through pseudo arc-length continuation with mean flow velocity as a main driving parameter, wherein the nonlinear modal equations of motion are solved by harmonic balance at each step. As the quasi-unsteady model used for fluid–elastic coupling introduces convolution integrals, this approach is quite natural and we show that, despite some difficulties regarding the treatment of stiff intermittent contacts, it allows for a thorough exploration of the system’s response. For the first case -a benchmark model-, increasingly complex dynamics arise as more modes are kept in the truncated modal basis, which is due to a series of modal interactions as the impacts distribute mechanical energy from the linearly-unstable first mode to the higher ones. This can be anticipated by studying the nonlinear normal modes of the system, as they expose the allowed internal resonances. In the second case, consisting of a realistic heat-exchanger tube configuration, a similar pattern is observed.

A PARAMETRIC AND COMPARATIVE STUDY ON BARE-TUBE BANKS AND NEW CAM-SHAPED TUBE BANKS FOR WASTE HEAT RECOVERY APPLICATIONS

The present study numerically examines the effects of tube diameter (12 to 35 mm), arrangement, pitch-to-diameter ratio (1.25 to 2.5), length (300 to 1500 mm), and passage number (1-4 passes) on the thermofluidic characteristics of cross-flow tube bundles. Especially, five new cam-shaped tubes are proposed in comparison with the conventional round tube. The air temperatures at the cold and hot side inlets are kept constant at 25°C and 600°C, respectively. The numerical method is verified by the existing experimental results. The findings show that a cam-shaped tube with an equal diameter (Cam_1818) is a promising tube for tube bundles, which apply in waste heat recovery. Indeed, it can offer the same minimum gap as that of the round tube; however, it improves the total thermal resistance up to about 28% and enhances the heat-transfer rate up to an average of 42.3% compared to that of the round tubes at the same pumping power.

Effect of pulsation parameters on the spatial and temporal variation of flow and heat transfer characteristics in liquid metal cross flow the in-line tube bundle

Liquid metal has a broad application prospect in tube bundle heat exchangers because of its excellent thermal conductivity. However, conventional in-line tube bundle arrangements often exhibit limited secondary flow, so new methods are urgently needed to improve heat transfer. The topic of this paper is to combine two methods, liquid metal cross flow tube bundle and pulsating flow, to improve the heat transfer performance in-line tube bundles. Firstly, the applicability of the model was validated through experimental data from existing literature, encompassing overall flow dynamics, heat transfer performance, and circumferential pressure distribution around the tubes. Subsequently, numerical simulations are conducted involving liquid metal cross flow in-line tube bundles at varying pulsating frequencies, amplitudes, and Reynolds numbers. Circumferential pressure distributions and temperature profiles for individual tubes were analyzed and compared. The amplitude of reduction in thermal resistance compared to the no-oscillation condition increases gradually from a minimum of 8 % in the first row to a maximum of 40 % in the third row, while the reduction in the rear row of tubes is similar to that of the third row. Remarkably, a reversal in the trend of thermal resistance for the first three rows of tubes under pulsating flow were observed, contrasting conventional flow except for the case with an amplitude of 0.1. By analyzing the local transient flow field distribution near single tube and the corresponding circumferential heat transfer performance, the influence of the vortex evolution characteristics on the heat transfer performance at different phases of the pulsating velocity is revealed, which transient Nu is up to three times that of flow with no pulsating. Finally, a series of coherence analyses reveal that as frequency rises, turbulence exhibits a richer spectrum of small-scale vortex structures, intricately linked to enhanced energy cascade efficiency. Amplitude augmentation intensifies velocity fluctuations, particularly at high amplitudes, resulting in substantial energy peak amplification. The integrated heat transfer performance PEC factor varies in the range of 1.25 to 1.51 for all the conditions simulated in this paper, which indicates that the liquid metal coupled pulsating flow approach can significantly increase the comprehensive performance of the tube bundle heat exchangers. These findings hold significant promise for advancing heat exchanger design and enhancing thermal efficiency, with implications for various engineering applications.

Experimental measurement of the pressure drop and heat transfer characteristics of a crossflow heat exchanger in low-density flows

NASA and other space agencies are currently planning the first human missions to Mars in the next 20 years. These missions will require much more power than current robotic missions, and so will require significant waste heat rejection capabilities to maintain steady state operations. Forced convection heat exchangers, particularly crossflow tube array compact heat exchangers, may offer significant volume- and mass-efficiency benefits over radiators for these applications. However, no experimentally validated correlations exist in the literature for the pressure drop and heat transfer characteristics of a forced-convection heat exchanger under the relevant dimensionless conditions which correspond to low (7-200) Reynolds number and moderate (0.0009-0.009) Knudsen number under axial and vortical flows. A staggered-tube crossflow heat exchanger has been constructed and its performance experimentally measured in a low-density wind tunnel. Data has been gathered in low-Reynolds, moderate-Knudsen conditions for both axial and vortical flows over a range of pressures and wall temperatures that is relevant to future Mars or high-altitude heat exchanger operation using both CO2 and air. The measured pressure drop exceeds what is predicted by correlations in the literature at very low (<75) Reynolds number while the Nusselt numbers were fairly well-predicted by existing correlations. A new correlation for pressure drop is presented for low-Reynolds, axial and vortical flow through a staggered circular tube array in crossflow.

Hydrogen production and geometry optimization of ethanol steam reforming combining water gas shift reaction in a crossflow membrane tube reactor

Crossflow tube reactors are a novel design showing excellent H2 production and separation potential. A membrane reactor enables H2 production and separation in the same unit and helps the reaction overcome the equilibrium conversion limitations. This work investigates the performance of ethanol steam reforming (ESR) followed by a water gas shift reaction (WGSR) for H2 production and separation. Crossflow catalytic tubes are designed in ESR and WGSR, and Pd-based membrane tubes are installed behind the WGSR to permeate H2 and enhance the chemical reaction. The effects of inlet temperature, steam-to-ethanol molar (S/E) ratio, and reaction pressure on the system performance are investigated. The results showed that a higher inlet temperature lowers H2 yield, and 600 °C is the most suitable temperature for this system. The S/E ratio at 3 leads to the highest H2 recovery. Higher S/E ratios may increase ethanol conversion but result in more steam in the reactor, lowering the H2 partial pressure and recovery. Two-stage design optimization is performed for the WGSR catalytic membrane tubes. In the first stage with parametric sweep, the H2 yield and recovery are improved by 1.25% and 22.27%, respectively. In the second stage via the Nelder-Mead method, the H2 yield and recovery are further improved by 6.79% and 18.76%, respectively. The two-stage optimization in total intensifies 8.8% H2 yield and 45.22% H2 recovery. A comparison between ESR + WGSR/without membrane and ESR + WGSR + membrane with optimization suggests the H2 yield is substantially lifted by 22.26%, and only 0.34 times catalyst is applied in the system. The results show that an optimized crossflow membrane reactor has excellent prospects for effective hydrogen generation and separation.

Investigations of In-Plane Fluidelastic Instability in a Multispan U-Bend Tube Array—Part II: Tests in Two-Phase Flow

Abstract Tests to study fluidelastic instability (FEI) in an array of U-bend tubes were recently completed in the multispan U-Bend test rig at Canadian Nuclear Laboratories. These tests were sponsored by the Electric Power Research Institute and were designed to study in-plane fluid elastic instability of steam generator tubes in two-phase cross flow. This instability mechanism was first observed in previous experiments by Atomic Energy of Canada Limited. This mechanism was not thought to be a serious practical concern until 2012 when it caused severe damage to tubes in a new replacement steam-generator in a nuclear power plant in the United States. In this study, tests were conducted both with flows of air and two-phase liquid/vapor Refrigerant 134a. The tube bundle consisted of 22 flexible U-bend tubes supported by a configurable flat-bar arrangement. Testing focused on the effects of support geometry and tube-to-support interaction. Data were recorded from 33 dynamic signals from accelerometers, displacement probes, force transducers, and void-fraction probes. Part I of this two-part series presented results of air tests. Part II presents results of tests using two-phase Freon refrigerant (R-134a) as the working fluid.

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.

Asymmetric Distribution of Longitudinal Fins Around a Tube in Cross Flow: Optimization with CFD Modeling

Asymmetric Distribution of Longitudinal Fins Around a Tube in Cross Flow: Optimization with CFD Modeling

Design and optimization of a crossflow tube reactor system for hydrogen production by combining ethanol steam reforming and water gas shift reaction

Crossflow tube reactors with crossflow configuration are considered a special design for hydrogen production via ethanol steam reforming with less catalyst than conventional packed bed reactors. However, the results showed that crossflow tube reactors would produce an elevated concentration of carbon monoxide, which has a detrimental effect on further applications of the product gas from steam reforming, such as hydrogen purification. This drawback can be diminished by integrating a water gas shift reaction unit into the steam reformer. This study's combined system is numerically investigated for hydrogen production and enrichment. The results show that low reaction temperatures are favorable for hydrogen production. The steam/ethanol (S/E) ratio of 3 is optimal for hydrogen production and CO reduction in the system combined with ethanol steam reforming and water gas shift reaction. Both variations in the catalytic tube diameter and the catalyst thickness positively affect hydrogen production. However, the effect of the tube diameter is higher than that of the catalyst thickness. This study also uses a parametric sweep associated with the evolutionary computation of bound optimization by quadratic approximation (BOBYQA) method to optimize the system’s tube arrangement. The optimized system intensifies H2 yield by 1.05 times and improves CO reduction by 37.71% compared to ethanol steam reforming alone.

Flow-Induced Vibrations of Two Flexible Tubes in Cross Flow

To further investigate fluid-structure–interaction problems that occur in the nuclear field such as the behavior of pressurized water reactor fuel rods, steam generator tubes, and other heat exchanger tubes, the flow-induced vibrations of two flexible tubes in tandem, side-by-side, and in staggered arrangements are investigated. First, a three-dimensional numerical model for fluid-structure interaction of flexible tubes in cross flow is developed. It is a three-dimensional fully coupled approach with solving the fluid flow and the structure vibration simultaneously. Second, results are presented in the form of force coefficients, dynamic response, trajectories, and wake vortex pattern. The effects of pitch ratio, tube arrangement, and flow velocity on the vibration response and the flow field characteristic are investigated. Critical pitch and critical velocity are obtained successfully. The critical velocity depends heavily on pitch ratio. Under the same pitch ratio and velocity, the side-by-side tubes have the maximum value of fluid force and vibration amplitude, followed by the staggered tubes the and tandem tubes in sequence. The trajectory and wake vortex pattern are highly dependent on tube arrangement, pitch ratio, and flow velocity.

Heat and Mass Transfer Correlations for Staggered Nanoporous Membrane Tubes in Flue Gas Crossflow

Abstract The use of transport membrane condenser (TMC) technology to recover heat and mass from the flue gas has been increasing recently. The heat and mass transfer from the TMC tube bundle have been studied experimentally and numerically, and several numerical models have been proposed. Although many heat transfer and pressure drop correlations are available for single-phase flows over tube bundles of solid walls, to the best of our knowledge, there is a lack of heat and mass transfer and pressure drop correlations for the porous membrane tubes with condensing flue gas that cover a wide range of parameters. In this study, the heat transfer, mass transfer, and pressure drop imposed by the crossflow ceramic nanoporous tubes in TMC have been studied numerically within wide ranges of tube diameters (4.57–7.62 mm), number of rows (2–24 rows), and Reynolds number (170–8900), under flue gas condensation. The turbulent flow of the flue gas mixture was modeled by the shear stress transport SST k−ω turbulence model. A hybrid/mixed condensation model written in user defined functions was employed to calculate the water vapor condensation rate. Numerical results with condensing flue gas are compared to available correlations for single-phase Nusselt number and pressure drops in the literature. It was found that except for selected conditions, the single-phase correlations noticeably differed from the TMC numerical results. Empirical TMC correlations for heat transfer and pressure drops with respect to condensation rate, number of rows, and the nanoporous membrane geometrical properties were derived thereby. The derived correlations for TMC show a good agreement with numerical data for all investigated parameters and can predict the 96% of the convective Nusselt number, overall Nusselt number, and friction factor inside the TMC within ±10%, ±10%, and ±15%, respectively. The effects of key parameters on the heat transfer, mass transfer, and pressure drops are illustrated and discussed in detail.

Evolutionary design: Heat and fluid flow together

This article sheds light on the fundamental physics that accounts for the similar behaviors of heat transfer and fluid friction as the configuration of the convective flow system changes. Three methods are used, and as the methods change so does the configuration (design): complicated (bundle of finned tubes in cross flow), elemental (single body in uniform flow), and even more complicated such that it resembles a saturated porous medium. The configuration evolves such that it conveys the explanation better, more effectively. The article illustrates the essential role of evolving configurations in thermal-science fundamentals and practice. It shows that three methods (i.e. three designs, from purposeful changes in design) are better than a single method (one design). Science marches forward in this manner, and, at the same time, there is a creative reassessment of past advances. The purpose of looking back is to construct a single edifice that is general, simpler and easier to use.

High efficiency 3-D printed microchannel polymer heat exchangers for air conditioning applications

The design, fabrication, and experimental characterization of a counterflow Micro-pin array Polymer Heat eXchanger (MPHX) for HVAC applications is described. The design consists of water flow through microscale pin array plates, and airflow paths in a counterflow direction through adjacent rectangular channels. When compared to a Finned Tube Heat eXchanger (FTHX), the water plates take the place of fins and the crossflow tube bank is eliminated. The MPHX is fabricated by 3 D printing using a digital light synthesis method. A correlation-based model is developed and used to explore the parametric space to arrive at a baseline MPHX core geometry. Mechanical and fluidic simulations are performed on the baseline geometry to further develop the design. A sub-scale MPHX with a nominal cross duct area of 10.1 cm × 20.3 cm is designed and fabricated. Its thermal performance over a range of air and water flow rates corresponding to heat capacity rate ratios in the range of 0.25–1 is investigated. Results show that the effectiveness varies from 0.65 to 0.95 corresponding to a of 1 to 0.25. The experimental data are used to validate a correlation-based thermo-fluidic model of the MPHX. The validated model is further used to compare the performance advantages of the MPHX design over a FTHX. For a given heat exchanger volume and thermo-fluidic conditions, the MPHX transfers 55% more thermal energy when compared to a FTHX at comparable air-side pressure drops.

Experimental analysis on performance assessment of a hybrid double cross flow tube arrangement in a shell and tube heat exchanger

Experimental analysis on performance assessment of a hybrid double cross flow tube arrangement in a shell and tube heat exchanger

Design and Optimization of a Crossflow Tube Reactor System for Hydrogen Production and Enrichment by Combining Ethanol Steam Reforming and Water Gas Shift Reaction

Design and Optimization of a Crossflow Tube Reactor System for Hydrogen Production and Enrichment by Combining Ethanol Steam Reforming and Water Gas Shift Reaction

EXPERIMENTAL STUDY AND CFD SIMULATION OF HEAT TRANSFER AND FRICTION FACTOR CHARACTERISTICS IN THE CROSSFLOW TUBE BANK

EXPERIMENTAL STUDY AND CFD SIMULATION OF HEAT TRANSFER AND FRICTION FACTOR CHARACTERISTICS IN THE CROSSFLOW TUBE BANK