Spiral Fins Research Articles

Heat transfer and resistance of staggered banks of air-cooled heat exchangers formed from tubes with rolled aluminum fins of various height

Results are presented for experimental investigation of reduced heat transfer and aerodynamic resistance of five staggered six-row banks of bimetallic finned tubes in heat exchange sections of air coolers with a forced air flow passing across the finned tubes. The fins are rolled onto circular steel tubes with a diameter d 0 = 25 mm. The relative transverse spacing of the tubes in the lattices of banks is s 1 = S 1 /d = 1.136, and the longitudinal spacing s 2 = S 2 /d = 0.905, where d is the outside diameter of the spiral fin. The banks were assembled from tubes with a fin height h = 15.23, 11.57, 9.07, 5.56, and 3.57 m. The diameter of the fin along the base was constant d 0 = 25.87 mm. The quantitative effect of the relative height h/d 0 on the average heat transfer and resistance of a bank is determined. The experimental data are described by criterial equations of the form Nu = f(Re) and Eu = f(Re) in the interval of Reynolds numbers Re = 3000–30000.

구리 재질의 평판 핀과 나선형 핀이 사용된 핀-관 열교환기의 공기측 성능

We investigate the heat-transfer and pressure-drop characteristics of fin-and-tube heat exchangers with a copper plate or copper spiral fins. Twenty-four samples with different fin pitches and tube rows were tested. For both configurations, the effect of the fin pitch on the j factor is negligible, and the f factor increases with the fin pitch. The effect of the tube row depends on the configuration. For plate fin-and-tube heat exchangers, the j factor decreases as the row number increases; the reverse is true for spiral exchangers. We explain this by considering the flow pattern. The j factor for plate fin-and-tube heat exchangers is larger than that for spiral exchangers, and the difference decreases as the row number increases. The f factor of the plate fin-and-tube heat exchanger is also larger. We compare our results with existing predictions of correlations.

ICONE19-43248 Experimental study on method for heat transfer enhancement using a porous material

There are several methods for enhancement of heat transfer; for example, there are attaching various fins on the heat transfer surface, processing the surface roughly, and so on. When cooling high temperature circular or rectangular channels by forced convection of gas, there are several methods for enhancement of heat transfer such as attaching radial or spiral fins on the channel surface or inserting twisted tape in the channel. In the case of the gas heating type steam reformer, disk type fins are attached on the outside surface of the reformer tube, and the tube is inserted into the guide tube to increase an amount of heat transferred from the high temperature gas. However, it has to take into consideration the deterioration of the structure strength by attaching the fins on the tube surface with the design of the steam reformer. The objective of this study is to clarify performances of a method for heat transfer enhancement using porous material with high porosity. The experiment has been performed using an apparatus which simulated the passage structure of the steam reformer to obtain characteristics of heat transfer and pressure drop. From the results obtained in this experiment, the heat transfer rate by this method showed a good performance in the laminar flow region. It was also found that the method for heat transfer enhancement using porous material with high porosity is further improved under the high temperature condition as compared with the other methods for heat transfer enhancement.

Influence of the angle of inclination of round-finned tubes in a staggered tube bundle on the free convective heat exchange between it and an unbounded air space

Results of experimental investigations of the average heat transfer from five-row staggered bundles of tubes with knurled spiral fins, operating in the free air-convection regime, in the case where the angel of inclination of the longitudinal axis of the tubes changed from 0 to 60° are presented. The investigations were carried out by the method of complete heat simulation. The average heat transfer was measured in the direction of a free air flow in each row of a tube bundle. The experimental data were generalized by similarity equations for calculating the average heat transfer from the tube bundles and their individual rows in the range of change in the Rayleigh number characteristic of the operating conditions of industrial heat exchangers assembled from finned tubes of the type of the above-indicated tubes.

スパイラルフィン付きマグナス風車の空力特性の評価(<特集>第14回動力・エネルギー技術シンポジウム)

In order to clarify an aerodynamic performance of Magnus wind turbines with spiral fins, wind tunnel experiments and numerical simulations were conducted. The results show that the ratio of lift and drag, L/D, depends on the rotational ratio of η. The maximum L/D of the rotational cylinder with spiral fins was obtained at lower η than that of the cylinder without spiral fins. Therefore, the power for the cylinder rotation can be reduced with the spiral fins. The effective performance was provided at the fins angles around 35 degrees. The simulation results showed the spanwise flow can be observed on the surface of the spiral fins. The power coefficient of the Magnus wind turbines depends on the spanwise velocity on the surface. It revealed that the control of the spanwise flow with spiral fins play an important role in the performance of Magnus wind turbines.

20814 多孔性材料を挿入した鉛直矩形流路の伝熱特性(一般講演 自然エネルギー)

In general, when the high temperature circular or rectangular channels are cooled by forced convection of gas, there are several methods for enhancement of heat transfer such as attaching radial or spiral fins on a channel surface or inserting twisted tape in a channel. The objective of this study is to investigate heat transfer characteristics by forced or natural convection of porous materials inserted into a rectangular channel with high porosity. In order to obtain the heat transfer characteristics of the one-side heated vertical rectangular channel inserting the porous material, an experiment was carried out. From the results obtained in this experiment, it was found that an amount of removed heat by forced convection using porous material (porosity > 0.996) was about 10% higher than that without the copper wire. Furthermore, the ratio between the amounts of heat removed of the rectangular channel with the porous material and without the porous material increases with increasing temperature of the channel wall.

Research of Cylinder with Spiral Fins for Magnus Wind Turbine

Research of Cylinder with Spiral Fins for Magnus Wind Turbine

Experimental and numerical investigation on air-side performance of fin-and-tube heat exchangers with various fin patterns

Air-side heat transfer and friction characteristics of five kinds of fin-and-tube heat exchangers, with the number of tube rows ( N = 12) and the diameter of tubes ( D o = 18 mm), have been experimentally investigated. The test samples consist of five types of fin configurations: crimped spiral fin, plain fin, slit fin, fin with delta-wing longitudinal vortex generators (VGs) and mixed fin with front 6-row vortex-generator fin and rear 6-row slit fin. The heat transfer and friction factor correlations for different types of heat exchangers were obtained with the Reynolds numbers ranging from 4000 to 10000. It was found that crimped spiral fin provides higher heat transfer and pressure drop than the other four fins. The air-side performance of heat exchangers with the above five fins has been evaluated under three sets of criteria and it was shown that the heat exchanger with mixed fin (front vortex-generator fin and rear slit fin) has better performance than that with fin with delta-wing vortex generators, and the slit fin offers best heat transfer performance at high Reynolds numbers. Based on the correlations of numerical data, Genetic Algorithm optimization was carried out, and the optimization results indicated that the increase of VG attack angle or length, or decrease of VG height may enhance the performance of vortex-generator fin. The heat transfer performances for optimized vortex-generator fin and slit fin at hand have been compared with numerical method.

J0503-3-3 回転円柱スパン方向流れがマグナス風車の空力特性に及ぼす影響(風力発電(3))

In order to clarity the aerodynamic properties and performance of Magnus wind turbines with spiral fins, numerical simulation were conducted. The power coefficient of the wind turbine depends on the velocity of the spanwaise flow around cylinders which induced spiral fins on the surface of the cylinders. The maximum power coefficient of the turbine can be obtained at the spanwise flow velocities are almost the half of the uniform velocity. In the case of the field experiments of the Magnus wind turbines, spiral fins generate the internal flow around cylinders. The numerical simulation has same tendency of the field experiments. The result seems to be the axial flow velocities play an important role in estimation and improvement of the performance of the Magnus wind turbines.

E101 片面加熱の鉛直矩形流路内の自然環境に関する研究(OS9 熱流動)

In general, when the high temperature circular or rectangular channels are cooled by forced convection of gas, there are several methods for enhancement of heat transfer such as attaching radial or spiral fins on a channel surface or inserting twisted tape in a channel. The objective of this study is to investigate heat transfer characteristics by forced or natural convection of porous materials inserted into a rectangular channel with high porosity. In order to obtain the heat transfer characteristics of the one-side heated vertical rectangular channel inserting the porous material, an experiment was carried out. From the results obtained in this experiment, it was found that an amount of removed heat by forced convection using porous material (porosity > 0.996) was about 10% higher than that without the copper wire. Furthermore, the ratio between the amounts of heat removed of the rectangular channel with the porous material and without the porous material increases with increasing temperature of the channel wall.

Heat transfer characteristics of a new helically coiled crimped spiral finned tube heat exchanger

In the present study, the heat transfer characteristics in dry surface conditions of a new type of heat exchanger, namely a helically coiled finned tube heat exchanger, is experimentally investigated. The test section, which is a helically coiled fined tube heat exchanger, consists of a shell and a helical coil unit. The helical coil unit consists of four concentric helically coiled tubes of different diameters. Each tube is constructed by bending straight copper tube into a helical coil. Aluminium crimped spiral fins with thickness of 0.5 mm and outer diameter of 28.25 mm are placed around the tube. The edge of fin at the inner diameter is corrugated. Ambient air is used as a working fluid in the shell side while hot water is used for the tube-side. The test runs are done at air mass flow rates ranging between 0.04 and 0.13 kg/s. The water mass flow rates are between 0.2 and 0.4 kg/s. The water temperatures are between 40 and 50°C. The effects of the inlet conditions of both working fluids flowing through the heat exchanger on the heat transfer coefficients are discussed. The air-side heat transfer coefficient presented in term of the Colburn J factor is proportional to inlet-water temperature and water mass flow rate. The heat exchanger effectiveness tends to increase with increasing water mass flow rate and also slightly increases with increasing inlet water temperature.

Transient Response of a Spiral Fin with its Base Subjected to the Variation of Heat Flux

Transient Response of a Spiral Fin with its Base Subjected to the Variation of Heat Flux

Experimental investigation of free-convection heat exchange between multiple-row staggered banks of tubes with spiral fins

Results of investigation of the following characteristics of free-convection heat exchange are presented: the coefficients of circular tubes averaged for a bank, and each individual transverse row of circular tubes with rolled aluminum fins, which are used in the heat-exchange sections of air coolers. The fins are rolled onto a smooth brass tube with an outside diameter of 25 mm, and a tube-finning factor of 16.8. The spacing of the tube layout in the bank grids is 64 mm, and the angle of incline of the longitudinal axis of the tube to the horizontal plane is 0, 15, 30, 45, and 60°. Experimental data are generalized by similitude equations of the form Nu = f(Ra), which encompass the interval of Rayleigh numbers Ra = (0.3–3.5)·105. The surface temperature of the tubes near the base of the fins was varied from 35 to 225°C, and the temperature of the air surrounding the bank ranged from 15 to 25°C.

Vortex Shedding from a Circular Cylinder with Spiral Fin

The effect of simple spiral fin around a bare tube on Karman vortex shedding was experimentally investigated. We measured the distributions of the mean velocity, the intensity of velocity fluctuation, the spectrum of velocity fluctuation and the coherence distribution of Karman vortex in the spanwise direction. And the flow around a fin tube was visualized by using smoke wire technique. As a result it was made clear that the periodic velocity fluctuation caused by Karman vortex was remarkably observed in the wake of the fin tube although the fin was mounted around a bare tube with a large pitch along the tube axis. The vortices in the near-wake of the fin tube make cells structure with the scale of the pitch length of the fins. The rotation axis of each vortex was inclined against the tube axis. The large scale vortex was formed by the coalescence of the vortex cells. Therefore, the spanwise scale of the vortex in the wake of the fin tube was larger than one pitch of the fins.

814 直交流中の円柱からの渦放出に及ぼすフィンの効果

The effect of simple spiral fin around a bare tube on Karman vortex shedding was experimentally investigated. We measured the distributions of mean velocity, the intensity of velocity fluctuation, the spectrum of velocity fluctuation and the coherence distribution of Karman vortex in the spanwise direction. And the flow around a fin tube was visualized by using smoke wire technique. As a result it was made clear that Karman vortex in the near-wake of the fin tube make the cell structure with the scale of pitch length of the fins. The large scale vortex was formed by the reconnection of the vortex cells.

Thermal performance of a spirally coiled finned tube heat exchanger under wet-Surface conditions

This paper is a continuation of the authors’ previous work on spiral coil heat exchangers. In the present study, the heat transfer characteristics and the performance of a spirally coiled finned tube heat exchanger under wet-surface conditions are theoretically and experimentally investigated. The test section is a spiral-coil heat exchanger which consists of a steel shell and a spirally coiled tube unit. The spiral-coil unit consists of six layers of concentric spirally coiled finned tubes. Each tube is fabricated by bending a 9.6 mm diameter straight copper tube into a spiral-coil of four turns. The innermost and outermost diameters of each spiral-coil are 145.0 and 350.4 mm, respectively. Aluminium crimped spiral fins with thickness of 0.6 mm and outer diameter of 28.4 mm are placed around the tube. The edge of fin at the inner diameter is corrugated. Air and water are used as working fluids in shell side and tube side, respectively. The experiments are done under dehumidifying conditions. A mathematical model based on the conservation of mass and energy is developed to simulate the flow and heat transfer characteristics of working fluids flowing through the heat exchanger. The results obtained from the present model show reasonable agreement with the experimental data.

Heat transfer and pressure drop characteristics of finned tube banks in forced convection (comparison of the heat transfer characteristics between spiral fin and serrated fin)

In recent years the requirements for the reduction of energy consumption have been increasing to solve the problems of global warming and the shortage of petroleum resources. For example in the power generation field, as thermal power generation occupied 60% of the power generation demand, an improvement in thermal efficiency is greatly needed. This paper describes the clarification of heat transfer characteristics of finned tube banks used for a heat exchanger in thermal power generation by testing serrated finned tubes banks for a heat transfer improvement and conventional spiral finned tube banks under the same test conditions. The equations to predict the heat transfer coefficient necessary to design the heat exchanger are proposed. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(2): 120–133, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20043

Heat Transfer and Pressure Drop Characteristics of Finned Tube Banks in Forced Convection (Comparison of Heat Transfer and Pressure Drop Characteristics of Serrated and Spiral Fins)

Heat Transfer and Pressure Drop Characteristics of Finned Tube Banks in Forced Convection (Comparison of Heat Transfer and Pressure Drop Characteristics of Serrated and Spiral Fins)

Air side performance at low Reynolds number of cross-flow heat exchanger using crimped spiral fins

A total of 23 cross-flow heat exchangers having crimped spiral configurations is studied. The effect of tube diameter, fin spacing, transverse tube pitch, and tube arrangements are examined. For the inline arrangement, the pressure drop increases with the rise of tube diameter but the associated heat transfer coefficient decreases with it. The increase of fin height also gives rise to considerable increase of pressure drop and decrease of heat transfer coefficients for the inline arrangement. However, for the staggered arrangement, the effect of the fin height on the pressure drop is much smaller than that of the inline arrangement due to the major contribution to the total pressure drops from the blockage of the airflow from staggered arrangement. Effect of the fin spacing on the air side performance is strongly related to the transverse tube pitch for both inline and staggered arrangements. Correlations of the present crimped spiral fins in both staggered and inline arrangements are developed. The proposed correlations give fairly good predictive ability against the present test data.

The heat transfer and pressure drop characteristics of finned tube banks in forced convection (comparison of the pressure drop characteristics of spiral fins and serrated fins)

AbstractIn recent years there has been a growing need for reduction of energy consumption in an effort to solve problems of global warming and the shortage of petroleum resources. For example, in the power generation field, thermal power generation now occupies 60% of the power generation demand, and the need for improved thermal efficiency is thus considerable. In this paper, the pressure drop characteristics of the finned tube banks used for the heat exchanger in thermal power generation were clarified by testing the serrated finned tube banks for improvement of higher heat transfer and the conventional spiral finned tube banks under the same test conditions, and equations for predicting the pressure drop coefficient which is necessary to design the heat exchanger were proposed. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(7): 431–444, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20030