Finned Tube Bundles Research Articles

Precise determination of inundation effect coefficient of film condensation on an array of horizontal new three-dimensional finned tube

To accurately evaluate the condensation heat transfer performance of new 3D finned tubes in shell-and-tube condenser, the inundation effect of the film condensation of R-134a on an array of 6 horizontal new 3D (three-dimensional) finned tubes is experimentally investigated with a new experiment method of homologous method. And the precise inundation effect coefficient of film condensation is determined. A novel test facility, whose test section contains two arrays of 8 horizontal tubes to realize the homologous method, is developed and constructed. The outer diameter of the tube and effective tube length in the test section are 19.05 and 500 mm, respectively. The condensation heat transfer coefficient of new 3D finned tube and inundation effect coefficient of new 3D finned tube bundle are determined under different conditions. The results show that the inundation effect coefficient of new 3D finned tube bundle decreases from 1.00 to 0.78 as Re increases from 75 to 1860. And the effect of heat flux on the inundation effect is more sensitive than the condensing temperature. Furthermore, for new 3D finned tube, the condensation heat transfer and inundation effect models are established, and the deviations of results between experiment and models are almost within ±6.0%. In comparison with literatures, the average inundation effect coefficient of new 3D finned tube bundle is 10.0-25.0% higher than that of 3D finned tube bundle in literatures, within 3.0% lower than that of two-dimensional finned tube bundle, and 15.2% higher than that of plain tube bundle. And the average condensation heat transfer coefficient of new 3D finned tube bundle in this article is 5.0-25.0% higher than that of 3D finned tube bundle in literatures, 10.0-30.0% higher than that of 2D finned tube bundle, and more than 10 times that of plain tube bundle. The precise inundation effect coefficients can be used as benchmark data to build precise and universal inundation effect model of 3D finned tube, and the models established in this study will help guide the thermal design of the new 3D finned tube applied in shell-and-tube condenser.

On-site experimental study on fouling and heat transfer characteristics of flue gas heat exchanger for waste heat recovery

A large number of fly ash particles in flue gas easily cause the fouling problem of heat exchangers, which seriously affects the efficient utilization of flue gas waste heat. In this study, experimental and numerical investigations on fouling and heat transfer characteristics in cross flow heat exchangers were carried out. The on-site experimental system was established, and the heat transfer coefficients for different heat-transfer surfaces at the fouling state were monitored in real time. The weakened degree of heat transfer coefficient and fouling thermal resistance are adopted to assess the effect of fouling on the heat transfer performance and compare the practicality of four different heat-transfer surfaces under dusty conditions. Numerical investigation was performed with the fouling model established in previous work to model the thermal-hydraulic and fouling processes. Numerical results are compared with experimental measurements and a good agreement is achieved. Results showed that compared with the aligned circular tube bundle, using H-type fins or honeycomb tube bundle both improve the anti-fouling performance, especially for the honeycomb H-type finned tube bundle, which has the lowest fouling thermal resistance. Therefore, due to the characteristics of easily soot-blowing and lower fouling thermal resistance, honeycomb heat exchangers are suitable for waste heat utilization of dusty flue gas.

A novel methodology for design optimization of heat recovery steam generators with flow-induced vibration analysis

Design of compact, lightweight, and robust heat recovery steam generators (HRSGs) is important for the implementation of offshore bottoming cycles. In this work, a novel methodology integrating flow-induced vibration analysis is proposed for the design optimization of HRSG. The vibration analysis considers four main flow-induced vibration mechanisms, namely turbulent buffeting, vortex shedding, fluidelastic instability, and acoustic resonance. The corresponding sub-models are selected from literature for estimating vibrations of finned tube bundles. The design criteria for vibration are included in the optimization problem as constraints, which affect the decision of the solver simultaneously. The methodology is demonstrated by three cases, in which not only geometric parameters but also operating parameters are set as design variables. With activating vibration constraints, the solver finds appropriate geometric and operating parameters to meet the design requirements. The comparison between the optimizations with and without the vibration constraints shows a trade-off between compactness, lightweight, efficient heat transfer, and the possibility of flow-induced vibration problems. This indicates the importance of consideration of vibration problems when designing such HRSGs.

Thermal Analysis of Crude Oil in Floating Roof Tank Equipped with Horizontal Heating Finned Tube Bundles

Thermal Analysis of Crude Oil in Floating Roof Tank Equipped with Horizontal Heating Finned Tube Bundles

Experimental studies of the efficiency of a single-row bundle of bimetallic finned tubes with different finning heights in free convective heat exchange with air

Considerer the influence of a change in the height of the height of the finning of bimetallic finned tubes of a single-row bundle on the thermal, overall and metal-capacity characteristics in the mode of free air convection at different angles of inclination (γ = 0, 15, 30, 45, 60 and 90°) to the horizontal plane. The investigated tubes have the following characteristics: the material of the supporting tube was carbon steel (outer diameter d out = 25 mm, wall thickness δ = 2 mm), the material of the rolling finned shell was aluminum alloy AD1M. Geometric parameters of the fins: d×d 0 ×h×s×Δ×φ× l = 56,0×26,8×14,6×2,5× 0,5×19,3×300 mm (type I). The studies were carried out by the method of complete thermal modeling on a specially designed experimental stand. Then the fins were ground by grinding with the formation of new types of tubes (II–VI), which were assembled into a single-row bundle with a constant relative transverse pitch σ 1 = S 1 / d = 1,14 = const. The article describes the criterion dependences for heat transfer of a finned single-row bundle of tubes with different finning heights at different angles of inclination to the horizontal plane, as well as a graphical dependenc e of the correction factor for the angle of inclination of bundle (γ = 0–90°) were obtained. It has been established that an increase in the angle of inclination and the height of the finning of tubes of a single -row bundle is generally accompanied by a decrease in heat transfer. In terms of overall and metal-capacity characteristics, the most effective is a single-row bundle at various angles of inclination to the horizontal plane with a tube finning height 2,0 mm.

Air-side heat transfer and flow characteristics of additively manufactured finned tubes in staggered arrangement

Finned tube bundle heat exchangers are used in a variety of applications. Tube bundles with conventional circular plain fins (CPF) as well as new circular integrated pin fins (CIPF) and serrated integrated pin fins (SIPF) were additively generated by a Selective Laser Melting (SLM) process. They were tested in a flow channel in a 2-row and a 3-row configuration under forced convection with Reynolds numbers between 1600 and 6600. For the new SIPF and CIPF design an improved Nusselt number was found compare to the CPF and higher Nusselt number for the 2-row compared to the 3-row configuration. The friction factor was lowest for the SIPF at all Reynolds number and the CIPF gave lower friction factor compared to CPF for Reynolds numbers up to approximately Re=4000. Furthermore, the thermal-flow characteristics of the heat transfer surface was evaluated by the performance evaluation criterion. Hence, an enhancement for the SIPF and CIPF compared to the CPF was found for both tube row configurations. The compactness of the heat exchanger was evaluated by the heat flux per volume and temperature difference, which was greatest for the CIPF followed by the SIPF and lowest for the conventional CPF design. In general the 2-row heat exchanger configuration reached greater thermal-flow characteristics and volumetric heat flux density than the 3-row configuration. For the global performance criterion no clear trend could be determined, since the value depends on the flow conditions. Thus, the SIPF heat exchanger performs best at lower and intermediate Reynolds numbers up to Re=5000 and the CPF design is best at higher Reynolds numbers. Eventually, the surface area and the volume of the heat exchanger with SIPF are lower compared to the CPF. Based on the experimental results an empirical heat transfer correlation was derived, which includes Nusselt number, Reynolds number, fin design, Prandtl number and tube row number.

CFD analysis of an economizer for heat transfer enhancement using serrated finned tube equipped with variable fin segments

Due to the extensive use of heat exchangers in various daily and industrial applications, the improvement of their performances is of great importance. It is evident from the literature that very limited work has been done in serrated finned tube economizer for heat transfer enhancement and pressure drop performance. This paper deals with the heat transfer improvement and pressure drop performance of helical serrated finned tube bundles in inline bare tube counter cross-flow water tube boiler Economizer, which has larger heat transfer area and higher heat exchange efficiency. Numerical simulation on heat transfer performance is carried out on 116.3 TPH of MCR boiler unit, one tube row with three-row finned tube passes; helically wound fin geometries of partially serrated finned tubes are investigated. A steady-state approach, with two-equation, a k-ε turbulence model is employed to examine the effect of Reynolds number in the range of 8000 to 20000. In this study the conjugate heat transfer is considered for the calculation of the conduction in a solid region is coupled with the calculation of the temperature distribution in the working fluid flowing over or through this solid region. The effect of a number of serrated segmented finned tubes per period on the performance of heat transfer enhancement is also investigated. The computational results fall within the range of values predicted by empirical correlation. The results show that the heat transfer is enhanced by up to 3.53% to 5.14% if the number of segments per period varied from 20 to 50.

The heat exchange research in the heat recovery unit with finned heat pipes

The experiments were performed to research the heat exchange of the tube bundle in the heat recovery unit with finned body tubes. The empirical dependences for a finned-tube bundle are obtained. The results are in good agreement with the analytical solution, the discrepancy between the results is within 10%. The analytical model of the finned heat tube has been created, which will be tested experimentally in the future. The results obtained can be used in the design of HRUFHP.

An experimental investigation on the effects of air on filmwise condensation of PF-5060 dielectric fluid on plain and finned tube bundles

In this paper, filmwise condensation of PF-5060 on plain and finned tubes in the presence and the absence of air was experimentally studied in a condensation chamber. The enhanced tubes were of integral and jagged fin structures. Based on our experimental results, it is found that a slight amount of air in the system can lead to a large decrease in the heat transfer coefficient. The influence of air is more significant for condensation on finned tubes due to the flooding effect of the diffusion layer. When only 0.51 wt% of air is introduced into the system, the condensation heat transfer coefficient decreases by about 26% on plain tubes while it decreases by a substantial 50% on finned tubes as compared to the pure vapor condition. However, a further increase in the air concentration has a less significant effect on the heat transfer coefficient, especially for condensation on finned tubes. In order for the finned tubes to have significant advantage in condensation heat transfer performance over plain tubes, the system has to operate below 0.51 wt% of air. If the system is required to operate above 0.51 wt% of air, the use of plain tubes is sufficient as the finned and plain tubes show similar condensation heat transfer performance. This is mainly due to the dominant diffusion layer flooding effect on the finned tubes. Visualization of different condensation phenomena have been conducted from which the condensation modes were found to be mainly dripping mode and column mode. Existing condensation correlations were analyzed and compared against the present experimental results, from which the possible transport mechanisms in the condensation of PF-5060 were identified. On this basis, a new correlation was developed which is able to predict all the present results with an accuracy of ±25%.

Effect of Air Gap on thermohydraulic performance of finned tube bundles

The air gap between the consecutive tube bundle row fins is one of the most important parameters that have not been evaluated in terms of their impact on the performance of air-cooled condensers. In this paper, the effect of this air gap on the thermo-hydraulic performance of the tube bundle air-side flow is investigated. The importance of this parameter lies in the fact that it can change the heat transfer coefficient and pressure drop in the tube bundle air-side flow. Moreover, changing the air gap will vary the overall length of the condenser and the dimensions of the main cooling system and consequently imposes a change in the costs of construction and operation. In this study, the effect of inlet air velocity on fin and ambient functioning temperature conditions is investigated at various air gaps on the thermo-hydraulic performance of the tube bundle air-side flow. The results indicate that the air gap for the proper thermo-hydraulic performance of the tube bundle air-side flow is independent of the air inlet velocity of the tube bundle and the ambient temperature conditions of the power plant. Moreover, it was found that the tube bundle air-side flow at a 1-mm air gap will have better thermo-hydraulic performance. The behavior of tube bundle air-side flow of the condenser of a 484 MW power plant was also studied. The results indicated that the tube bundle air-side flow at this state will also have better performance at a 1-mm air gap such that the overall length of the condenser in this state will increase by 1.7% compared to the state where the air gap is zero

Conjugate numerical analysis on bundle effects for integrated heat transfer of LNG ambient air vaporizer

Ambient air vaporizer (AAV) is widely used to vaporize liquefied natural gas (LNG) in gas terminal stations due to its low cost in operating and eco-friendly advantages. Its vaporization efficiency depends on the overall heat transfer performance of the finned tube bundle, which was mostly represented by single tube in previous researches. This paper presented a numerical investigation on the integrated heat transfer of AAV tube bundle considering the heat transfer conjugate problem between different zones. An experimental test combined with the nondimensional correlation in finite space was conducted to validate the numerical model, and the results are in good agreement. The results indicate that the surrounding tubes weakens the field synergy of the flow and heat transfer in inner area of the AAV array, resulting in the decline of heat transfer coefficient from far to near the center of the array. For each finned tube in the AAV bundle, the circumferential local convective heat transfer coefficients decrease from 45° to 225° angular space and then arise from 225° to 360° angular space. Besides, poorer convective heat transfer of the air will lead to the delay of LNG multiphase flow with higher heat transfer intensity due to the conjugate heat transfer in AAV.

Heat Exchange under the Evaporation and Boiling of a Film Showering a Bundle of Horizontal Finned Tubes

An algorithm for calculating heat exchange in the course of evaporation and boiling of a film that showers a bundle of finned tubes is described and a comparison of calculated and experimental data is performed. The calculated parameters are in quite satisfactory agreement with the experimental data.

Experimental studies of the influence of hydrodynamics on heat transfer at evaporation and boiling of a film irrigating a bundle of horizontal finned tubes

A feature of operation of some devices, such as heat pump steam generators, evaporators of refrigerating machine, steam generators of binary freon station, etc., is a low value of specific heat fluxes. Heat transfer regimes occur, when boiling in the film is just beginning and the heat transfer rate during evaporation is comparable to that during boiling. Tube finning is a well-proven way to intensify heat transfer, both during evaporation and boiling. However, there are insufficient data on the choice of finning parameters and methods for evaluating heat transfer during boiling of a film that irrigates a bundle of finned tubes. This paper presents an algorithm for calculating heat transfer during evaporation and boiling of a film that irrigates a bundle of finned tubes, and compares the calculated and experimental data. The calculated parameters turn out to coincide satisfactorily with the experimental data.

Research of horizontal single-row bundles of ribbon finned tubes at free convection

The intensity of free convection research leads to a wider understanding of the mechanisms and possibilities of using free-convection currents for the heat discharge or heatremoval in many industries, in energy processes, in a large number of devices or systems. Free convection significantly affects the maximum values of heat fluxes, and studying them becomes quite important for problems in which other methods of heat transfer are not applicable or uneconomical. The phenomena of free-convective heat transfer are quite complex, processes of conjugate heat transfer, for example, radiation and convection can be observed. Theoretical methods of description and calculation are used for bodies of simple shape: ball, plate, cylinder. The methods of theoretical analysis for heat transfer of bodies of complex shape are too voluminous and cumbersome. The intensification of free-convective heat transfer is possible through the use of various types of fins. To calculate the natural convective heat transfer of finned surfaces, the criterial dependencies of an empirical nature are mainly used. The article presents the results of a study of free-convective heat transfer of single-row horizontal bundlesof industrial bimetallic pipes with tape finning, the finning factor of 16.8. The position of the pipes in the bundle is characterized by the by transverse steps standardized for heat exchangers for air coolingS1 = 58; 61; 64; 70; 76; 86; 100 mm, to which the relative steps corresponded σ1 = S1/d = 1.208; 1.271; 1.333; 1.458; 1.583; 1.792; 2.083. An equation for calculating the free-convection heat transfer, taking into account the influence of the relative step in the range of Rayleigh number from 30,000 to 350,000 with an average deviation of ± 6.6%, has been obtained.

Enhancing Energy Saving in Air Cooling Devices by Intensifying External Heat Transfer

The aerodynamic processes of heated air in the ventilation shaft installed above the heat transferring bundle of bimetallic finned tubes are studied. The regions of suppressed natural, steady, and unsteady mixed air convection in the bundle depending on the degree of narrowing of the outlet section of the ventilation shaft are determined. The maximum Nusselt numbers for multi-row bundles and their corresponding optimum parameters of the degree of narrowing of the outlet section of the ventilation shaft are determined. A method is proposed for determining the Reynolds numbers and the average air velocity during free convection for contracted smooth and finned tube bundles, which will allow optimization of heat transfer processes. The practical effectiveness of single- and two-row bimetallic finned tube bundles with a finning factor φ = 21 and an intertube spacing of 58 mm in air cooling and similar aircooled heat exchangers having a ventilation shaft is scientifically proved.

Experimental Investigation of Thermal and Hydraulic Characteristics of Finned Flat Tubes of the Oil Air Cooling Device

Air cooling devices are heat exchange units that are widely used in practice. However, they have a number of disadvantages due to the low value of the heat transfer coefficient from the air and the high resistance of finned tube bundles, which leads to large dimensions and the metal content of the device itself, to the need to develop a high power ventilator drive, but also to the need to demonstrate reduced energy efficiency. The objective of the present work is to determine optimal geometric sizes of finned flat heat exchange tubes manufactured by the techniques of extrusion and deforming cutting that reduce the weight and size characteristics of the heat exchange section of air cooling devices. The experimental studies of seven various samples of heat exchange sections, being different in fin pitch and height, tube section width, flat tube height and a number of inner channels, have determined the performance of each section with the use of the following criteria: thermal power, thermal efficiency, specific thermal heat transfer resistance, M. V. Kirpichev and V. M. Antuf’ev’s criteria. The obtained experimental data and the analysis of the passive method of enhancement in the near-wall area of the heat transfer surface finned by deforming cutting has shown that sample No 5 has maximum value of the performance criteria when the maximum height of a fin is 0.008 m and the minimum pitch of a fin is 0.0025 m over the investigated sample range. Thus, when the sizes of an oil air cooling device are maintained by using the amended heat transfer section of sample No 5, the amount of removed heat can be increased or the mass and dimensions of the device can be decreased while maintaining thermal power and, as a result, the power consumption for pumping can be decreased and the thermal-hydraulic performance of the device as a whole can be increased.

Anti-freezing prediction model for different flow patterns of air-cooled heat exchanger

Water heat load may get lower than the huge cooling capacity of air for air-cooled heat exchanger in winter, resulting in the freezing risk of finned tube bundles, so the water temperature distribution inside the tube under various working conditions stands the premise issue for the security and energy efficiency of dry cooling system. Based on the energy balance and heat transfer analyses, the anti-freezing prediction model of air-cooled heat exchanger is developed and experimentally validated at different low ambient temperatures with the maximum deviation of 16%. Taking a six-row plate finned tube heat exchanger as the research object, the water temperature distribution in any tube and the critical anti-freezing parameters are obtained with different air/water flow patterns at various ambient temperatures, air face velocities, inlet water temperatures, and water flow rates. The results show that the finned tube bundle with slotted fins is superior to the flat fins in heat transfer performance, but faces more serious freezing risks in cold winter. In the baseline case, the average outlet water temperature of the slotted finned tube bundle decreases by 3.9 °C compared to the flat finned tube bundle. For the air/water cross-counter flow pattern, the critical freezing position is fixed and appears at the water exit of upwind row. While for the air/water cross-cocurrent flow, the minimum water temperature varies with operating conditions, but it always happens at the row 1 or row 4. The anti-freezing of air-cooled heat exchanger can be realized by reasonably matching the air/water heat capacity as well as transforming the air/water flow patterns. The proposed anti-freezing prediction model is of potential benefit to the real-time temperature distribution forecast, freezing analyses, and control strategies for air-cooled heat exchanger in winter.

Research on gas side performance of staggered fin-tube bundles with different serrated fin geometries

This investigation conducted experiments on the gas-side performance of serrated spiral fin-and-tube heat exchanger with staggered layouts. The number of tube rows is 10 under the Reynolds numbers of 6000 to 12,000. The influences of varied water vapor content and fin geometry were explored. The results showed that the increase of water vapor content leads to an increase in the Nusselt number of the serrated fin and twisted serrated fin, and the effect on serrated fin was more significant. Besides, the decrease in the Euler number of both fin tube was observed with the water vapor content increasing. The twisting in the top of segment fin corresponded to a significant increase in the Nusselt and Euler numbers. Finally, the comparison of overall performance between the two types of fin tube was performed, and the results showed that the twisted serrated fin has better performance in the current experimental range.

Numerical optimization of a finned tube bundle heat exchanger arrangement for passive spent fuel pool cooling to ambient air

The passive cooling of nuclear spent fuel pools is a promising alternative to active cooling. Since such systems work even in safety-critical situations, e.g. station blackout, the reliability of nuclear power plants would be enhanced. As in such systems heat needs to be transfer to the environment, the heat exchanger to air has a crucial influence on the system performance. This paper describes investigations of the Nusselt number, the achievable efficiency and the volumetric heat transfer coefficient of the tube bundle heat exchangers for a passive cooling system located at the bottom of a chimney. The effect of tube bundle configuration, tube shape, longitudinal tube pitch, transversal tube pitch and tube row number on natural convection heat transfer was numerically studied. These parameters were varied to optimize the heat transfer performance of the heat exchanger. It was found, that the staggered configuration performs better than the inline arrangement, since the flow mixing is higher. Furthermore circular tube shape and an oval tube shape with the aspect ratio of 1:2.1 were optimum for the inline and staggered configuration respectively. The longitudinal and transversal tube pitches of 63mm and 65mm performed best, since higher values reduced heat transfer. A tube row number greater than 5 did not improve the heat transfer and therefore a tube row number of 5 is recommended. The Nusselt number and volumetric heat transfer coefficient of the optimized tube bundle arrangement enhanced by 15.4% and 47.8% respectively at a temperature difference of 40K compared to the initial design.

Auxiliary heat exchanger layout for freeze-proofing and performance recovery of natural draft dry cooling system

Air-cooled heat exchanger faces a severe freezing risk in cold winter, especially for the finned tube bundles of windward sectors. Therefore, it is beneficial to the safe and energy-efficient operation of natural draft dry cooling system to take anti-freezing measures. In this work, the natural draft dry cooling system with auxiliary heat exchanger in front of windward sectors is proposed. By applying macro heat exchanger model to finned tube bundles and three-dimensional modeling on the air side, the freeze-proofing and performance improvement of natural draft dry cooling system with auxiliary heat exchanger are numerically studied. The air velocity, pressure, and temperature fields, air mass flow rate, outlet water temperature and anti-freezing turbine back pressure are presented under winter conditions. Moreover, the air flow rate, heat rejection and turbine back pressure are obtained in warm days. The results show that the auxiliary heat exchanger can prevent the air-cooled heat exchanger from freezing at various wind speeds in winter. In warm days, the natural draft dry cooling system with auxiliary heat exchanger is superior to the conventional one at high wind speeds. In the absence of winds, its cooling performance gets deteriorated.