Bundle Heat Exchanger Research Articles

Space characteristics of the thermal performance for air-cooled condensers at ambient winds

Ambient winds may lead to poor fan performance, exhaust air recirculation and mal-distribution of the air across the tube bundles of the air-cooled condensers in a power plant. Investigations of the impacts of the ambient winds on the air-cooled condensers are key area of focus. Based on a representative 2 × 600 MW direct dry cooling power plant, the physical and mathematical models of the air-side fluid and heat flow in the air-cooled condensers at various ambient wind speeds and directions are set up by introducing the radiator model to the fin-tube bundles. The volumetric flow rate, inlet air temperature and heat rejection for different air-cooled condensers as a whole, condenser cells and fin-tube bundles are obtained by using CFD simulation. The results show that the thermo-flow performances for the air-cooled condenser as a whole, condenser cells and heat exchanger bundles vary widely in space. The thermal performances of the air-cooled condensers, condenser cells and fin-tube bundles at the downstream are generally superior to those at the upwind. It is of use for the upwind fan regulations and the A-frame condenser cell geometric optimization to investigate the space characteristics of the thermal performance for the air-cooled condensers in a power plant.

Dry cooling towers as condensers for geothermal power plants

The aim of this paper is to present scaling laws for a dry natural draft cooling tower by modelling the heat exchanger and the tower supports as a porous medium. Porous medium modelling of the tube bundles that allows a vigorous theoretical analysis of the problem is adopted. Scale analysis is used as the theoretical tool to study the problem of turbulent free convection through the heat exchanger bundles and along the cooling tower chimney. Results are then compared with full numerical simulation of the problem to observe splendid agreement.

Experimental analysis of fast metal hydride reaction bed dynamics

In this paper an experimental investigation of main influencing parameters on the dynamics of a metal hydride reaction bed is presented. The metal hydride used in this work is LmNi 4.91Sn 0.15 and the applied reaction bed is based on a capillary tube bundle heat exchanger with a large heat transfer surface. Based on experimental investigations of the hydrogen distribution in the capillary tube bundle reaction bed a limitation of the reaction bed dynamics due to insufficient hydrogen transport can be excluded. However, it is shown that the desorption dynamics of the reaction bed can be limited by the intrinsic kinetics of the used AB 5 alloy.

A New Cross-Flow Tube Bundle Heat Exchanger with Staggered Hot and Cold Tubes for Thermophoretic Deposition of Submicron Aerosol Particles

A new tube cross-flow bundle heat exchanger has been designed and tested for thermophoretic deposition of submicron aerosol particles. The present design has five columns of hot and cold square tubes, respectively, arranged in a staggered manner to maintain a nearly constant temperature gradient in the direction of the aerosol flow. Each column has four tubes of 4 mm × 4 mm in cross section and the gap between the tube surfaces is 0.5 mm. The precipitator was tested experimentally using monodisperse NaCl test particles ranging from 38 to 397 nm in diameter at the aerosol flow rate of 0.6 and 1.2 L/min, respectively, at different temperature gradients. Results showed that the thermophoretic deposition efficiency increased with decreasing aerosol flow rate and increasing temperature gradient with the maximum thermophoretic deposition efficiency occurred at the aerosol flow rate of 0.6 L/min. The effect of inlet temperature of the aerosol flow on the efficiency was also tested and showed increasing inlet tem...

Study on Vibration Characteristic and Stress Intensity of Planar Elastic Tube Bundles

Heat transfer enhancement is achieved by flow-induced vibration in planar elastic tube bundle heat exchangers. The optimum of structural parameters of tube bundle is of importance to the characteristic and control of flow-induced vibration. The influence of pipe structural parameters such as cross section diameter, thickness and connectors mass on vibration characteristic is studied in this paper with numerical simulation method. Based on the amplitude of flow-induced vibration and stress intensity, the characteristic of planar vibration and vertical vibration are compared, and the amplitude range of infinite fatigue life is predicted. The results show that the cross section diameter of pipe and the connectors mass have major influence on the vibration characteristic of tube bundle. Compare to the planar vibration of tube bundle, the vertical vibration has much advantage in the vibration amplitude and stress intensity distribution.

Combined particle emission reduction and heat recovery from combustion exhaust—A novel approach for small wood-fired appliances

Replacing fossil fuels by renewable sources of energy is one approach to address the problem of global warming due to anthropogenic emissions of greenhouse gases. Wood combustion can help to replace fuel oil or gas. It is advisable, however, to use modern technology for combustion and exhaust gas after-treatment in order to achieve best efficiency and avoid air quality problems due to high emission levels often related to small scale wood combustion. In this study, simultaneous combustion particle deposition and heat recovery from the exhaust of two commercially available wood-fired appliances has been investigated. The experiments were performed with a miniature pipe bundle heat exchanger operating in the exhaust gas lines of a fully automated pellet burner or a closed fireplace. The system has been characterised for a wide range of aerosol inlet temperatures (135–295∘C) and flow velocities (0.13–1.0ms-1), and particle deposition efficiencies up to 95% have been achieved. Deposition was dominated by thermophoresis and diffusion and increased with the average temperature difference and retention time in the heat exchanger. The aerosols from the two different appliances exhibited different deposition characteristics, which can be attributed to enhanced deposition of the nucleation mode particles generated in the closed fire place. The measured deposition efficiencies can be described by simple linear parameterisations derived from laboratory studies. The results of this study demonstrate the feasibility of thermophoretic particle removal from biomass burning flue gas and support the development of modified heat exchanger systems with enhanced capability for simultaneous heat recovery and particle deposition.

Cover Picture: Tube bundle heat exchanger. Courtesy of SGL Carbon AG. (Chem. Eng. Technol. 4/2007)

Cover Picture: Tube bundle heat exchanger. Courtesy of SGL Carbon AG. (Chem. Eng. Technol. 4/2007)

Design of a novel, intensified heat exchanger for reduced fouling rates

This paper describes an integrated approach into the design and evaluation of a novel tube bundle heat exchanger that achieves higher heat transfer levels at lower levels of pressure drop, while remaining less susceptible to gas-side fouling. The approach combines laboratory scale experiments with industrial observations and numerical simulations of full-scale heat exchangers to study the thermal, hydraulic and fouling characteristics of tube bundle heat exchangers. Three arrangements are compared and the advantages of the proposed novel arrangement are demonstrated. Enhanced heat transfer rates are combined with reduced pressure drop and gas-side fouling rates through careful design of the shape of the tube cross-section and reduced transverse spacing.

Miniature Pipe Bundle Heat Exchanger for Thermophoretic Deposition of Ultrafine Soot Aerosol Particles at High Flow Velocities

The deposition of submicrometer soot aerosol particles in a miniature pipe bundle heat exchanger system has been investigated under conditions characteristic for combustion exhaust from diesel engines and oil or biomass burning processes. The system has been characterized for a wide range of aerosol inlet temperatures (390–510 K) and flow velocities (1–4 m s−1), and particle deposition efficiencies up to 45% have been achieved over an effective deposition length of 27 cm. Thermophoresis was the dominant deposition mechanism, and its decoupling from isothermal deposition was consistent with the assumption of independently acting processes. The measured deposition efficiencies can be described by simple linear parameterizations based on an approximation formula for thermophoretic plate precipitators. The results of this study support the development of modified heat exchanger systems with enhanced capability for filterless removal of combustion aerosol particles.

Three‐Dimensional Numerical Simulation of Flow‐Induced Tube Bundle Vibration

Efforts have been made to increase thermal efficiency of tube bundle heat exchangers by increasing flow velocities and decreasing tube wall thicknesses, which led to a number of damages due to flow‐induced vibrations. Here, a numerical tool is presented which, for the first time, makes it possible to simulate fluid‐structure‐coupled vibrations in tube bundles in three dimensions. This tool has the potential to optimize tube bundle structures such that thermal efficiency is improved in terms of economy and safety.

Application of a New Analogy for Predicting Heat Transfer to Cross Rod Bundle Heat Exchanger Surfaces

A new technique for prediction and measurement of compact heat exchanger surfaces has been established. The method utilizes an analogy between heat transfer and fluid friction proposed by a French scientist in 1928. The applicability of this analogy to plate heat exchanger surfaces was examined recently. The present work proposes to use the same analogy for crossed rod bundles used in regenerators. For this purpose, the analogy equation has been modified to include a geometric factor which takes care of the fraction of the pressure drop arising out of skin friction. The proposed form of equation is found to be more general, applicable to crossed rod structures of any geometric configuration. The proposition was formulated based on standard data from the literature and also by conducting independent experiments. The result of the transient experiment indicate excellent adherence to the proposed analogical equation. The experimental evidence clearly indicates the possibility of predicting heat transfer characteristics of such compact surfaces by measuring pressure drop alone across the packed bed formed by the surface under consideration.

Application of a New Analogy for Predicting Heat Transfer to Cross Rod Bundle Heat Exchanger Surfaces

Application of a New Analogy for Predicting Heat Transfer to Cross Rod Bundle Heat Exchanger Surfaces

Modern problems of intensification of heat exchange in channels

The current achievements in the field of intensification of heat exchange in tube heat‐exchange apparatus are considered. Requirements for high‐efficiency heat‐transfer surfaces have been formulated. Problems of intensification of heat exchange in bundles of finned tubes and in heat‐exchange apparatus under conditions of condensation and boiling of heat‐transfer agents and under scaling conditions have been investigated. High‐efficiency designs of heat‐exchange apparatus are presented.

Velocity distribution and vibration excitation in tube bundle heat exchangers

Design criteria for tube bundle heat exchangers, to avoid fluidelastic instability, are based on stability criteria for ideal bundles and uniform flow conditions along the tube length. In real heat exchangers, a non-uniform flow distribution is caused by inlet nozzles, impingement plates, baffles and bypass gaps. The calculation of the equivalent velocities, according to the extended stability equation of Connors, requires the knowledge of the mode shape and the assumption of a realistic velocity distribution in each flow section of the heat exchanger. It is the object of this investigation to derive simple correlations and recommendations, (1) for equivalent velocity distributions, based on partial constant velocities, and (2) for the calculation of the critical volume flow in practical design applications. With computational fluid dynamic (CFD) programs it is possible to calculate the velocity distribution in real tube bundles, and to determine the most endangered tube and thereby the critical volume flow. The paper moreover presents results and design equations for the inlet section of heat exchangers with variations of a broad range of geometrical parameters, e.g., tube pitch, shell diameter, nozzle diameter, span width, distance between nozzle exit and tube bundle.

NEW DESIGN RECOMMENDATIONS FOR FLUIDELASTIC INSTABILITY IN HEAT EXCHANGER TUBE BUNDLES

Design equations are presented to determine the critical velocities for the occurrence of fluidelastic instability in uniform single-phase cross-flow. These equations are an essential part of a new guideline in the “VDI-Wärmeatlas” for estimating vibration excitation in real tube bundle heat exchangers. Six existing guidelines for fluidelastic instability were tested and compared with about 300 experimental data from 34 papers (eight of them being not yet considered in a guideline before). New equations for the stability factor K as a function of the pitch ratio for different tube configurations were derived with statistical methods by a variation of the reference definitions for the structural parameters and the exponents of either the dimensionless mass and the damping or the mass-damping parameter. The criterion used here was first to be on the safe side with a minimum number, and minimum deviation, of experimental data below the recommended threshold line, and second a minimum r.m.s. error for all data considered. The pitch ratio has the strongest influence for the normal triangular array and the influence becomes less for the rotated as well as for the in-line square configuration. This significant gradation of the stability constants as a function of the pitch ratio and the tube bundle configuration enables a reasonable interpolation for non-standard configurations. The exponent of the dimensionless mass-damping parameter for gas cross-flow depends on the tube configuration and is 0·5 for the 30°- and 45°-configuration, and 0·4 for the 60°- and 90°-configuration. For liquid flow, an average exponent of 0·15 has been observed.

Bestimmung der fluidelastischen Instabilität in querangeströmten Rohrbündeln

AbstractFor the design of tube bundle heat exchangers avoiding tube bundle damage caused by vibration, fluidelastic instability is the most important vibration excitation mechanism. In order to present a guideline in the VDI‐Wärmeatlas the existing recommendations of CHEN, WEAVER and FITZPATRICK and PETTIGREW and TAYLOR were examined. They differ in the suggested equations for calculating critical velocities for single phase crossflow. With an extensive evaluation and test of consistency of the these and newly available data on this topic, better correlations could be derived. Consistent definitions of critical flow velocity, damping, natural frequency and hydrodynamic mass are used; their values are to be determined in the still fluid with the density ρ. Confident documented data show only a small scatter. The other data deviate more, but mainly to the safe side.

Numerical calculation of the effect of deposit formation on heat-exchanger efficiency

A numerically calculated deposit was used to identify the shape of a fouled tube and an orthogonal curvilinear grid was constructed in and around the deposit. The flow and temperature field was calculated and an implicit boundary condition, accounting for the effects of turbulence, was introduced at the solid-fluid interface for the simultaneous calculation of the temperature field in the fluid and the solid. Validation is presented against experimental and numerical calculations. Finally, a reduction of 8–17% in the heat transfer rate was found to occur for a deposit corresponding to 8 h of operation in a staggered tube bundle heat-exchanger of a lignite utility boiler. Thermal resistance of the deposit was also calculated.

Intensification of heat exchange in bundles of finned tubes by the method of jet air cooling

Intensification of heat exchange in bundles of finned tubes by the method of jet air cooling

Influence of medium's peclet numbers on heat exchange in fiber bundles

Influence of medium's peclet numbers on heat exchange in fiber bundles

The effect of the heat exchanger arrangement and wind-break walls on the performance of natural draft dry-cooling towers subjected to cross-winds

Abstract In most full scale dry-cooling towers rectangular heat exchanger bundles are arranged either vertically around the circumference of the tower or horizontally in the inlet cross-section of the tower. A numerical procedure is used in the present paper to investigate the influence of the particular arrangement on the performance of a tower in windy conditions with the results being verified by full scale and experimental measurements. Practical suggestions concerning the arrangement of the heat exchangers and wind-break walls are made which may lead to significant reductions in the adverse effect of cross-winds on the performance of dry-cooling towers.