Finned Tube Bundles Research Articles

Multidimensional and Unsteady Simulation of Fin-and-Tube Heat Exchangers

This article presents a model for the analysis of fin-and-tube heat exchangers, focusing on the heat conduction processes within the finned tube bundle. A cutting cell discretization has been proposed for the fins to adapt to the tubes shape, while the tubes have been discretized in axial and angular directions to consider complex heat transfer coefficient variations. A set of results is given on fin efficiency and transient response comparing with well-established methods. A full-scale condenser is also analyzed as an illustrative result, detecting important thermal bridges through the fins.

E314 EXPERIMENTAL STUDY ON THE FOULING FACTOR OF HELICAL FINNED TUBE(Boiler-3)

A semi-industrial experiment on fouling factor of helical finned tube bundle is done in a 75t/h boiler unit. Profiles of the fouling factor with different flue gas velocity are observed. It is found that the fouling factor of the experiment is much smaller than the recommended value by the former Soviet Union standard, which is widely used in China. And it is as the same order as the result of other researchers in China, which is resulted from lab. Discussions are made between the differences. Compared with the work of other researchers in China, the result of this article is more suitable.

Optimally Staggered Finned Circular and Elliptic Tubes in Turbulent Forced Convection

This work presents an experimental geometric optimization study to maximize the total heat transfer rate between a bundle of finned tubes in a given volume and a given external flow both for circular and elliptic arrangements, for general staggered configurations. The results are reported for air as the external fluid, in the range 2650⩽Re2b⩽10,600, where 2b is the smaller ellipse axis. Experimental optimization results for finned circular and elliptic tubes arrangements are presented. A relative heat transfer gain of up to 80% (Re2b=10,600) is observed in the elliptic arrangement optimized with respect to tube-to-tube spacings, as compared to the optimal circular one. A relative heat transfer gain of 80% is observed in the three-way optimized elliptic arrangement in comparison with the two-way optimized circular one; i.e., with respect to tube-to-tube and fin-to-fin spacings. An empirical correlation for the three-way optimized configuration was obtained to evaluate the resulting maximized dimensionless heat transfer rate.

Prediction of Local Bundle Boiling Heat Transfer Coefficients: Pure Refrigerant Boiling on Plain, Low Fin, and Turbo-BII HP Tube Bundles

New correlations predicting the local boiling heat transfer coefficients for vertical flow over a tube bundle have been developed. These correlations were developed for three different classes of tubes: smooth, low-finned, and Turbo-BII HP. These correlations are based on experiments with refrigerants R-134a, R-507A, and R-410A, at a saturation temperature of 4.4°C (40°F). Each one accounts for the local flow structure and/or local geometry particular to each tube. Each one also uses a void fraction model designed specifically for vertical two-phase flow in a tube bundle as an integral part of the correlation. The correlations have been compared to recent local bundle boiling data and show good agreement to within ± 20%.

New correlation for natural convection of finned tube A-type air cooler

The temperature distribution in a finned tube bundle of an A-type air cooler is investigated. The heat transfer is governed by natural convection. By using a special steam condenser the effect of steam pressure on temperature fields formed outside the bank of finned tubes is studied. It is found that the distribution is approximately the same at various pressures with minor differences. The effects of two-phase flow on temperature distribution are also considered. All 3D temperature contours show maximum values, which highly depend on steam pressures. Moreover, asymmetric steam feeding and probable fouling inside the tubes are possible causes of contour shapes. The experimental Nusselt number as a function of Rayleigh number based on different parameters is investigated separately and simple correlations are presented.

Simultaneous heat transfer enhancement and pressure loss reduction for finned-tube bundles with the first or two transverse rows of built-in winglets

Heat transfer enhancement and pressure loss penalty caused by a single row of winglets built in the first transverse row of tubes, are compared between “common flow up” (“toe-out”) and “common flow down” (“toe-in”) winglet configurations. For the three-row tube bundle in a staggered arrangement, the “toe-in” winglet-pairs bring about 5–15% increase in heat transfer enhancement and 2–10% increase in pressure loss penalty, in comparison with fin-tube bundles without winglet. In the present authors’ previous paper [K. Torii, K.M. Kwak, K. Nishino, Heat transfer enhancement accompanying pressure-loss reduction with winglet-type vortex generators for fin-tube heat exchangers, International Journal of Heat Mass Transfer 45 (2002) 3795–3801], “toe-out” winglet-pairs built only in the first transverse row of three-row tube bundle in a staggered arrangement successfully increased heat transfer by 10–30%, and simultaneously reduced pressure loss by 34–55%, for the Reynolds number (based on two times channel height) ranging from 350 to 2100. In the present paper, the front two rows of the “toe-out” winglet-pairs were applied for a three-row tube bundle in a staggered/in-line arrangement, for comparison. Heat transfer and pressure loss in the staggered arrangement were increased by 6–15% and by 61–117%, respectively, in comparison with the case of the single transverse row of the “toe-out” winglet-pairs. The corresponding increases for an in-line arrangement with two rows of winglets were 7–9% and 3–9%, respectively.

Local Bundle Boiling Heat Transfer Coefficients on an Integral Finned Tube Bundle (RP-1089)

Experiments have been performed for evaporation of refrigerants R-134a and R-507A on the outside of a horizontal bundle of integral finned tubes. Hot water flowing through the tubes is used as the heat source. Water temperature measurements were made at numerous axial locations within the tubes to obtain the water's temperature profile and thus measure twelve local heat transfer coefficients simultaneously in the bundle. Pool boiling tests to measure the corresponding nucleate boiling curves were also performed. Tests were conducted with a 20-tube bundle over the following range of heat flux (2 to 50 kW/m2), mass flux (3 to 29 kg/(m2 s)), and vapor quality (8 to 82%). The bundle test results showed a significant contribution of convection from rising bubbles to the heat transfer process, with local heat transfer coefficients as large as two times those of nucleate pool boiling in the case of R-134a, but on average a 34% increase. R-507A showed significantly less benefit due to convection, averaging only a 10% increase.

Three-dimensional optimization of staggered finned circular and elliptic tubes in forced convection

This paper presents a three-dimensional numerical and experimental geometric optimization study to maximize the total heat transfer rate between a bundle of finned tubes in a given volume and external flow, for staggered arrangements of circular and elliptic tubes. Experimental results were obtained for circular and elliptic configurations with twelve tubes, starting with an equilateral triangle configuration, which fitted uniformly into the fixed volume with a resulting optimal dimensionless tube-to-tube spacing of S/2 b=1.5, where S is the actual spacing and b is the smaller semi-axis of the ellipse. Several experimental configurations were built by reducing the tube-to-tube spacings, identifying the optimal spacing for maximum heat transfer. Similarly, it was possible to investigate the existence of optima with respect to two other geometric degrees of freedom, such as tube eccentricity and fin-to-fin spacing. The results are reported for air as the external fluid in the laminar regime, for Re L =852 and 1065, where L is the swept length of the fixed volume. Circular and elliptic arrangements with the same flow obstruction cross-sectional area were compared on the basis of maximizing the total heat transfer. This criterion allows one to isolate and quantify the heat transfer gain, by studying arrangements with equivalent total pressure drops independently of the tube cross-section shape. This paper continues with three-dimensional numerical optimization results for finned circular and elliptic tubes arrangements, which are validated by direct comparison with experimental measurements. Global optima with respect to tube-to-tube spacing, eccentricity and fin-to-fin spacing ( S/2 b≅0.5, e≅0.5, φ f ≅0.06 for Re L =852 and 1065) were found and reported in dimensionless terms. A relative heat transfer gain of up to 19% is observed in the optimal elliptic arrangement, as compared to the optimal circular one. The heat transfer gain, combined with the relative material mass reduction of up to 32% observed in the optimal elliptic arrangement in comparison to the circular, show that the elliptical tubes arrangement has better overall performance and lower cost than the traditional circular tubes geometry.

OPTIMALLY STAGGERED FINNED CIRCULAR AND ELLIPTIC TUBES IN FORCED CONVECTION

This work presents a three-dimensional (3-D) numerical and experimental geometric optimization study to maximize the total heat transfer rate between a bundle of finned tubes in a given volume and a given external flow both for circular and elliptic arrangements, for general staggered configurations. The optimization procedure started by recognizing the design limited space availability as a fixed volume constraint. The experimental results were obtained for circular and elliptic configurations with a fixed number of tubes (12), starting with an equilateral triangle configuration, which fitted uniformly into the fixed volume with a resulting maximum dimensionless tube-to-tube spacing S/2b = 1.5, where S is the actual spacing and b is the smaller ellipse semi-axis. Several experimental configurations were built by reducing the tube-to-tube spacings, identifying the optimal spacing for maximum heat transfer. Similarly, it was possible to investigate the existence of optima with respect to other two geometric degrees of freedom, i.e., tube eccentricity and fin-to-fin spacing. The results are reported for air as the external fluid in the laminar regime, for 125 and 100 Re 2b , where 2b is the ellipses smaller axis length. Circular and elliptic arrangements with the same flow obstruction cross-sectional area were compared on the basis of maximum total heat transfer. This criterion allows one to quantify the heat transfer gain in the most isolated way possible, by studying arrangements with equivalent total pressure drops independently of the tube cross section shape. This paper reports three-dimensional (3- D) numerical optimization results for finned circular and elliptic tubes arrangements, which are validated by direct comparison with experimental measurements with good agreement. Global optima with respect to tube-to-tube spacing, eccentricity and fin-tofin spacing ( 0.5 e 0.5, S/2b and 06 . 0 f for 125 and 100 Re 2b , respectively) were found and reported in general dimensionless variables. A relative heat transfer gain of up to 19% is observed in the optimal elliptic arrangement, as compared to the optimal circular one. The heat transfer gain, combined with the relative material mass reduction of up to 32% observed in the optimal elliptic arrangement in comparison to the circular one, show the elliptical arrangement has the potential for a considerably better overall performance and lower cost than the traditional circular geometry.

Measurement of the temperature distribution on a circular plane fin by infrared thermography technique

In this paper, we present a local study of the temperature distribution on a circular plane fin in a finned-tube bundle, in aligned or in staggered arrangement. The temperature distribution on the fin was obtained by an experimental approach, using the infrared thermography technique. The Reynolds number was varied between 2 × 10 3 and 3 × 10 4, corresponding to the maximum velocity of the air between 1.3 and 18.4 m/s. The influence of the Reynolds number, the geometry and position of the tube bundle was studied, and found in good agreement with the previous results in the literature. Moreover, this study will help us to foresee the regions where condensation appears.

Effect of Fin Geometry on Condensation of R407C in a Staggered Bundle of Horizontal Finned Tubes

Experimental results are presented that show the effect of fin geometry on condensation of downward flowing zeotropic refrigerant mixture R407C in a staggered bundle of horizontal finned tubes. Two types of conventional low-fin tubes and three types of three-dimensional-fin tubes were tested. The refrigerant mass velocity ranged from 4 to 23 kg/m2 s and the condensation temperature difference from 3 to 12 K. The measured condensation heat transfer coefficient was lower than the previous results for R134a, with the difference being more significant for smaller mass velocity. The effect of fin geometry on the condensation heat transfer coefficient was less significant for R407C than for R134a. The effect of condensate inundation was more significant for the three-dimensional-fin tubes than for the low-fin tubes. By using the dimensionless heat transfer correlation for the condensate film that was based on the experimental data for R134a, a superficial vapor-phase heat transfer coefficient was obtained for condensation of R407C. The vapor-phase heat transfer coefficient showed characteristics similar to the vapor-phase mass transfer coefficient that was obtained in the previous study for R123/R134a.

Experimental study and modelling of heat transfer during condensation of pure fluid and binary mixture on a bundle of horizontal finned tubes

An experimental investigation was conducted to measure the local heat transfer coefficient for each row in a trapezoidal finned horizontal tube bundle during condensation of both pure fluid (HFC 134a) and several compositions of the non-azeotropic binary mixture HFC 23/HFC 134a. The test section is a 13×3 (rows × columns) tube bundle and the heat transfer coefficient is measured using the modified Wilson plot method. The inlet vapour temperature is fixed at 40 °C and the water flow rate in each active row ranges from 170 to 600 l/h. The test series cover five different finned tubes all commercially available, K11 (11 fins/inch), K19 (19 fins/inch), K26 (26 fins/inch), K32 (32 fins/inch), K40 (40 fins/inch) and their performances were compared. The experimental results were checked against available models predicting the heat transfer coefficient during condensation of pure fluids on banks of finned tubes. Modelling of heat exchange during condensation of binary mixtures on bundles of finned tubes based on the curve condensation model is presented.

Heat transfer and flow characteristics of fin-tube bundles with and without winglet-type vortex generators

The objective of this research is to investigate the effect of longitudinal vortices that can be applied to the heat transfer enhancement for fin-tube heat exchangers such as air-cooled condensers. A multichannel test core was designed and fabricated for the determination of overall heat transfer and pressure loss with circular tubes and winglet vortex generators. Heat transfer results were obtained using a transient method referred to as the modified single-blow method. For a three-row tube bundle in an in-line arrangement without winglets, the heat transfer and the pressure loss were 72% and 210% higher, respectively, than for a multichannel test core without any built-in tube or winglet. These increases were caused by vortices around the tube banks. The corresponding increases for a staggered tube bundle are 95% and 310%, respectively. The triangular winglets recommended by the previous studies in a fin-tube bundle in an in-line arrangement increase the overall heat transfer 10–25% and the pressure loss 20–35% for the Reynolds numbers ranging from 300 to 2700.

Heat transfer and pressure loss penalty for the number of tube rows of staggered finned-tube bundles with a single transverse row of winglets

The objective of this research is to investigate the heat transfer and pressure loss penalty for various numbers of transverse rows in staggered finned-tube bundles with a single transverse row of the winglet pairs beside the front row of the tube bundles. Experiments were performed for two, three, four and five rows of staggered tube bundles. The pairs of winglets were placed with a heretofore-unused orientation for the purpose of augmentation of heat transfer and reduction of pressure loss penalty. This orientation is called as “common flow up” configuration. For three rows of tubes with a single transverse row of winglets beside the front row of the tubes, the heat transfer was augmented by 30–10%, and yet the pressure loss was reduced by 55–34% with the increase of the Reynolds number (based on two times channel height) from 350 to 2100. The reduction of the pressure loss penalty for three rows of tube bundles is the largest in comparison with the other numbers of rows.

Modelling the influence of aerosol deposition onto horizontal finned tubes on heat transfer under cross-flow condensing conditions

New European designs of advanced nuclear reactors incorporate innovative safety features in their containments to accommodate mechanical and thermal loads in case of a postulated severe accident. These systems consist of several units of cross-flow finned tube bundles internally cooled with water. Aerosol deposition onto their surfaces could decrease their thermal efficiency and pose a threat for containment integrity. A model called HTCFOUL has been developed as a series combination of thermal resistances from gas mixture (steam and non-condensables) to in-tube coolant. A fouling resistance due to particle deposition has been embedded into the formulation and an analysis of available data has been carried out to grasp a sound understanding on governing phenomena that could result into a deterioration of the heat exchanger performance. Potential explanation of experimental findings are given for two separate sets of tests and some controversy between them has been discussed. In no case aerosol deposition onto the surfaces jeopardize the heat exchanger efficiency beyond acceptable limits.

Condensation of downward-flowing HFC134a in a staggered bundle of horizontal finned tubes: effect of fin geometry

Experimental results are presented that show the effect of fin geometry on condensation of refrigerant HFC134a in a staggered bundle of horizontal finned tubes. Two types of conventional low-fin tubes and three types of three-dimensional fin tubes were tested. The refrigerant mass velocity ranged from 8 to 23 kg/m 2s and the condensation temperature difference from 1.5 to 12 K. The effect of condensate inundation was more significant for the three-dimensional fin tubes than for the low-fin tubes. In most cases, the highest performance was obtained by the tube with a three-dimensional structure at the tip of low fins. In the case of high mass velocity and high condensate inundation rate, however, the highest performance was obtained by one of the low-fin tubes. The results were compared with previous results for bundles of smooth tubes and low-fin tubes.

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.

Modeling condensation heat transfer on a horizontal finned tube in the presence of noncondensable gases

European designs for the next generation of nuclear reactors incorporate innovative passive systems in their containments to enhance heat removal by condensation under postulated accident conditions. These systems consist of several units of cross-flow finned tube bundles internally cooled with water. So far most of the studies that have been addressed to the issue of heat transfer onto finned surfaces under condensing conditions have involved refrigerants and pure vapor conditions. This study presents a model (HTCFIN) capable of predicting condensation of a cross-flow air–steam mixture onto a single horizontal finned tube. The comparison of HTCFIN predictions to the available databases shows its acceptable accuracy in a wide range of conditions and allows an interpretation of the influence of major variables acting on the scenario. As a consequence, HTCFIN model represents a step forward in the present theoretical capability to estimate heat transfer within containments of next generation of European reactors in the case of a hypothetical accident.

917 スタッガード配列フィン付管群からの渦発生周波数(GS.12 熱工学II)

917 スタッガード配列フィン付管群からの渦発生周波数(GS.12 熱工学II)

Studies on High-Performance Ceramic Heat Exchanger for Ultra High Temperature. (2nd Report, Heat Transfer of Finned Tube Bundle Immersed in Fluidized Bed.)

Studies were carried out to develop a high-performance ceramic heat exchanger for ultra high temperatures using a fluidized bed. In the former study, Heat transfer coefficient had been improved by applying fluidized bed to the heat exchanger for high temperature with smooth ceramic tubes. In this study, finned ceramic tubes were applied instead of smooth tubes for more improvement of heat transfer and experiments were performed on condition that the maximum bed temperature was 1100°C. Fluidization remained stable and the bed temperature uniform in the bed similarly as the case of smooth tube. A heat transfer coefficient of finned tube was evaluated and it was improved about 3 times as large as that of smooth tube. The performance of the heat exchanger was also evaluated using temperature efficiency and exergy efficiency.