H-type Finned Tube Research Articles

Parametric study and optimization of H-type finned tube heat exchangers with honeycomb arrangement using Taguchi method

Enhancing the efficiency of flue gas waste heat utilization is an important way to achieve carbon peaking and carbon neutrality goals. In this paper, a three-dimensional numerical model of an H-type finned tube heat exchanger with honeycomb arrangement is developed. Firstly, the effects of five parameters are analyzed using the control variable method, including the oblique tube pitch, the ratio of fin height to oblique tube pitch, fin pitch, fin thickness and slit width. Then, the Taguchi method was used to investigate the interaction effects of the five geometric parameters. Numerical simulations of 27 cases with different parameter combinations were carried out and the heat transfer and flow friction characteristics and their overall performance were discussed in detail. The results show that oblique tube pitch has the most significant effect on heat transfer capacity, fin pitch has the most significant effect on overall performance, and slit width has the least effect on both. Finally, the optimum parameter combinations were obtained. When inlet velocity ranges from 5 m/s to 10 m/s, heat transfer performance is increased by 46.3 %-52.1 %, pressure drop is increased by 5.7 % − 11.3 %, and the overall performance PEC is improved by 63.5 %-105.9 %. The results of the study contribute to the development and optimization of new flue gas heat exchangers.

Numerical investigation and comparison on thermal-hydraulic performance of H-type finned tube heat exchanger

H-type finned tube heat exchangers have been widely used in boilers and waste heat recovery devices due to their advantages of wear resistance and anti-fouling. In order to improve the energy-saving effect, the flow and heat transfer characteristics of H-type finned tube heat exchangers with different tube bundle arrangements were studied. It was found that, at the same Re number, the column staggered arrangement can compensate for the limited heat transfer performance of the in-line arrangement and reduce the high pressure drop associated with the row staggered arrangement. Honeycomb arrangement was proposed based on the column staggered arrangement. Then, the effects of Re and tube pitches thermal-hydraulic performance of tube bundles with in-line and honeycomb arrangements were examined. The critical tube pitch or velocity at which the honeycomb tube bundle achieves the same thermal performance as the in-line tube bundle are determined. The results provide valuable insights for the practical application of flue gas heat exchangers with honeycomb arrangement.

Numerical investigation on the erosion behavior of the honeycomb H-type finned tube heat exchanger via the discrete particle method

Serious erosion problem of the heat exchanger directly affects the safe and steady operation of waste heat utilization systems. Herein, a honeycomb H-type finned tube heat exchanger for waste heat utilization of dusty flue gas was proposed, and the collision and erosion behaviors of fly ash particles were numerically predicted via the discrete particle method (DPM). Firstly, the single factor analysis was used to investigate the effects of each structural parameter on the erosion rate. Then, the range analysis of different levels of different structural parameters was carried out via orthogonal test method. Finally, the prediction correlations of erosion rates were obtained based on multiple regression method. The results shows that the oblique tube pitch and fin pitch are negatively correlated with the erosion rate, while the slit width, fin height and fin thickness are positively correlated with the erosion rate. Among them, the fin pitch has the most significant impact on the erosion rate, while the effect of oblique tube pitch is the least. The optimized case (A4B2C3D1E4) was obtained by orthogonal experimental design. Compared with the baseline case, the maximum erosion rate of the five observation points in the optimized case decreases by the average of 33.74% with the maximum reduction of 36.32%, while the average erosion rate is reduced by the average of 37.57% and the maximum of 40.58%. The above results are contributed to the optimization of anti-erosion performance of high dust-containing flue gas waste heat utilization system and the development of efficient heat exchangers.

Numerical investigations on thermal-hydraulic characteristics of finned tube heat exchangers considering thermal contact resistance

To elucidate the impacts of thermal contact resistance (TCR) on the finned tube heat exchanger, a method of equivalent heat conductivity was employed to model the TCR. Comparative analysis of the thermal-hydraulic characteristics of different finned tube banks was conducted. The comprehensive performance criterion considering the impacts of thermal contact resistance was developed based on the application scenario. Without accounting for the TCR, the thermal-hydraulic performance of high frequency resistance welded spiral finned tube (HWSFT) bank is almost same as that of integral spiral finned tube (ISFT) bank. The H-type finned tube (HFT) bank has 10.9% smaller comprehensive performance criterion, 10.3% lower heat transfer area performance and 19.0% higher compactness than the ISFT bank. The fin efficiency reduces significantly for a larger TCR. With considering the TCR, the HWSFT bank and HFT bank have 38.0% and 54.3% smaller comprehensive performance criterion, 37.9% and 53.7% lower heat transfer area performance, 32.6% and 36.8% lower compactness than the ISFT bank, respectively. The ISFT has great improvement of comprehensive performance compared with welded finned tubes due to the elimination of TCR.

Airside thermal–hydraulic performance evaluation of flue gas coolers for waste heat recovery

H-type finned tubes and integrally-molded spiral finned (IMSF) tubes are widely used in flue gas coolers for waste heat recovery, but it is difficult to design an efficient flue gas cooler in actual engineering by experience due to lack of a general factor to evaluate the thermal–hydraulic performance of different types of finned tube heat exchangers. Based on the correlations of the Nusselt Nu, the Colburn factor j, the friction factor f and the ratio Q/Wp, this paper proposed a comprehensive performance evaluation method to evaluate the thermal–hydraulic performance of different types of finned tubes, which includes the power consumption goodness factor (FQ/W) and volume goodness factor (FQ/V). The reliability of the evaluation method was verified through real engineer design. The thermal–hydraulic performance of the H-type finned tube bundle and IMSF tube bundle was obtained through computational fluid dynamics simulation using periodic physical models, and evaluated using the general evaluation method. The results show that the power consumption for H-4 and IMSF-3 is almost identical with the same heat transfer rate, but the compactness of IMSF-3 is better than that of H-4. The findings can guide the design and optimization of flue gas coolers.

Optimization of H-type finned tube heat exchangers with combinations of longitudinal vortex generator, dimples/protrusions and grooves by Taguchi method

In this paper, some novel structures aimed to optimize the airside performance of H-type finned tube heat exchangers, such as longitudinal vortex generators, dimples/protrusions and grooves, are examined numerically. The effects of geometric parameters on the heat transfer, flow resistance and comprehensive thermal–hydraulic performances are investigated by means of Taguchi method. The optimum configuration of compound designs is determined on the basis of the optimizations of these structures. According to the results, for longitudinal vortex generators, dimples/protrusions and grooves, the heat transfer characteristics are significantly affected by the winglet type, vertical distance and groove diameter while the attack angle, dimple depth and groove type have prominent impacts on the flow resistance characteristics. The winglet type, vertical distance and groove number make the most contributions to the comprehensive thermal–hydraulic performance, respectively. In compound designs, the longitudinal vortex generator plays the most important role in the performance of heat exchangers. The comprehensive thermal–hydraulic characteristic of the optimal compound design exerts the improvements of 0.9–23.8%, 24.5–57.1% and 8.3–37.5% than those of LVGs, dimples/protrusions and grooves, respectively, when Reynolds number ranges from 4650 to 28,300. The enhancement of 4.5–16.6% can be achieved compared with the case built based on references.

Parametric Study on Thermal-Hydraulic Characteristics of H-Type Finned Tube Heat Exchangers

In this paper, the thermal-hydraulic characteristics of H-type finned tube banks are numerically investigated on the basis of a more accurate and convenient calculation method of fin efficiency for H-type fins. Experiments are performed to validate the numerical simulations. The variations of the Nusselt number, Euler number, and comprehensive factor with the Reynolds number and seven geometric parameters of H-type finned tube banks are obtained. The results indicate that the Nusselt number is proportional to the Reynolds number, the slit width, the fin thickness, and the longitudinal tube pitch; but, it is inversely proportional to the tube row number, the fin height, and the spanwise tube pitch. As the Reynolds number, the tube row number, the slit width, the fin pitch, and the spanwise tube pitch increase, the Euler number decreases. The factor rises with the increase of the slit width, and there exists an optimal tube row number () at which the factor is the maximum. The correlations of the heat transfer (Nusselt number) and pressure drop (Euler number) of the 10-row H-type finned tube bank, which can nearly be considered to be fully developed, are presented. The numerical results and correlations have good applicability under different fluids and show good agreement with the experimental results and correlations.

A Convenient Method for the Accurate Calculation of Fin Efficiency of H-Type Fins Based on Linear Nomograms and Fitting Formulae

Fin efficiency, as a measure of the effectiveness of the heat transfer enhancement, is of great importance in studying the heat transfer performance of H-type finned tube banks. The fin efficiency of square fins is adopted by most researchers as an alternative to that of H-type fins, which can create certain errors in the fin efficiency of H-type fins. For this paper, the linear nomograms and fitting formulae of fin efficiency of H-type fins are obtained by the definition method of fin efficiency based on numerous numerical simulations, and the results calculated by this method are verified by experimental data. On this basis, the effects of three geometric parameters (slit width, fin height, and fin thickness) and two thermal parameters (surface heat transfer coefficient and fin thermal conductivity) on the fin efficiency of H-type fins are also investigated and compared to those of square fins. The results indicate that the fin efficiency of H-type fins increases with the increment of fin thickness and thermal conductivity, and decreases with the increase of slit width, fin height, and surface heat transfer coefficient. Accordingly, the linear nomograms and fitting formulae for the fin efficiency of H-type fins, which are well compatible with experimental data, can help to facilitate further theoretical research and engineering application.

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.

Heat transfer analysis of H-type finned tube embedded in packed bed for gasification to produce hydrogen

Gasification for hydrogen production by the H-type finned tube embedded in the packed bed is considered to be more economical. Based on the thermal flow reversal reactor, the heat transfer characteristics of H-type finned tube embedded on the both sides of high-temperature zone of the packed bed under the quasi-steady were researched. The contribution of radiation heat transfer rate on the H-type finned tube is about 60.5% at most and radiation mainly occurs on the central tube. Within the range of inlet temperature and Re, the fin-assisted degree is both decreased gradually and the maximum is 48.9%. When the temperature is above 906 K or within the range of Re, the heat transfer rate of the fin is mainly from the radiation heat transfer rate. Under the condition of high inlet temperature and high Re, the fin-assisted degree is minimum, which indicates the operation stability of the H-type finned tube is better.

Airside Performance of H-Type Finned Tube Banks with Surface Modifications

The present study numerically investigates some novel modifications to augment the performance of the H-type finned tube banks, which are widely used in waste heat recovery in industries. The imposed modifications upon the original H-type finned tube banks include the following: (1) Design 1 contains some triangular cuts at the edge of the original rectangular fin; (2) Design 2 modifies the original rectangular geometry into a trapezoid shape; (3) Design 3 renders the original rectangular cross-section fin thickness into trapezoid cross-section; and (4) Design 4 changes the original rectangular shape into a circular shape. Based on the simulations, it is found that Design 1 shows barely any improvements in the heat transfer performance and surface area reduction. Design 2 can provide some weight saving and surface area reduction at a slightly inferior heat transfer performance. Design 3 can offer up to 14% improvements in the overall heat transfer performance without any pumping power penalty. Yet, Design 4 provides the maximum weight saving as compared to the original reference case. With 3–9% lesser surface area than the reference case, Design 4 still offers marginally higher heat transfer performance.

Parametric optimization of H-type finned tube with longitudinal vortex generators by response surface model and genetic algorithm

Low-low temperature electrostatic precipitator technology is one of the important ways for energy saving and emission reduction of coal-fired power plants. In order to further improve the dust removal efficiency and enhance waste heat recovery performance, a novel H-type finned elliptical tube heat exchanger with longitudinal vortex generators is proposed. To achieve the maximum heat transfer enhancement with the minimum friction factor augmentation, the response surface model and multi-objective genetic algorithm are adopted to optimize the design parameters. Firstly, combined with the finite volume method and the central composite design method, the second-order response surface model between the design parameters (the length, height, angle, and position of longitudinal vortex generators) and the objective functions (Nusselt number and friction factor) is established. Then, based on the response surface model, the Pareto optimal solution set is obtained by the multi-objective genetic algorithm. Finally, by comprehensively comparing Nusselt number, friction factor and performance evaluation criteria of Pareto optimal solutions, the optimal combination is determined. Compared with the H-type finned tube heat exchanger, the performance evaluation criteria of the optimized novel heat exchanger is improved by 48–55%, which contributes to improve the overall performance of low-low temperature electrostatic precipitator system. The findings of this paper may provide practical guidelines for researchers and designers to develop efficient heat exchangers.

Heat transfer and fouling performance of finned tube heat exchangers: Experimentation via on line monitoring

An on line experimental system was set up in a heating boiler so as to reproduce dusty working environments in heat recovery systems and to investigate heat transfer and fouling performance of different kinds of finned tube heat exchangers. Measurements are reported for the heat transfer coefficients, fouling and the effect of fouling on heat transfer performance of five different H-type finned tube heat exchangers. Fouling resistance and the weakened degree of heat transfer coefficient are employed to evaluate the effect of fouling on the heat transfer performance. Numerical simulations are also conducted on the fouling performance of each heat exchanger bundle and compared to the measurements. Double H-type fins can slightly reduce the heat transfer performance but also reduce fouling. Elliptical finned tubes with the same tube pitch decrease heat transfer performance and increase fouling, and with the same relative tube pitch, significantly increase the heat transfer performance before fouling, and can effectively reduce fouling.

Experimental Study of Heat Transfer and Pressure Drop for H-type Finned Oval Tube with Longitudinal Vortex Generators and Dimples under Flue Gas

ABSTRACTTo enhance heat transfer and reduce fouling of the finned-tube surface in economizers of coal-fired power plants, heat transfer and pressure drop characteristics for H-type finned oval tube with longitudinal vortex generators (LVG) and dimples, both in-line and staggered arrangements, are studied experimentally under flue dust condition. In addition, the ash samples and heat exchanger surfaces after the test are analyzed to help understanding the ash fouling and tube wear mechanisms. Compared to the original H-type finned oval tube, the Nusselt number of H-type finned oval tube bank with longitudinal vortex generators and dimples is improved by 34.5–41.7% (in-line arrangement) and 28.1–31.7% (staggered arrangement) within the studied Reynolds numbers, while the Euler number is increased by 21.9–28.3% (in-line arrangement) and 19% (staggered arrangement) in the clean finned-tube surface state. In the stable fouling state, the Nusselt number is improved by 37.7–42.3% (in-line arrangement) and 27.8–45.1% (staggered arrangement), while the Euler number is increased by 22.9–25.2% (in-line arrangement) and 33.3–42% (staggered arrangement). The results show that the novel fin structures can both inhibit fouling and enhance heat transfer effectively.

Parameter study on the fouling characteristics of the H-type finned tube heat exchangers

In this paper, numerical simulations were performed for the fouling characteristics and heat transfer performance after fouling on the H-type finned tube heat exchangers, and the optimum parameters studies were also conducted according to the orthogonal array design method. Firstly, the effect of row number on the fouling results were discussed. It was found that there was a critical row number Ncr=6, and the fouling results will reach a constant value when the row number is larger than the critical row number. Then, the orthogonal array design method was employed to design the test arrangements, and the effects of six geometric parameters and two operating conditions on the fouling results as well as heat transfer performance after fouling were investigated. The order of the effects of each factor and the optimum parameters corresponding to the least fouling and best heat transfer performance after fouling were also determined. At last, a correlation of the Nusselt number after fouling Nuf∗ with the geometric parameters and the operating conditions was obtained. The results showed that the optimum conditions we determined using the orthogonal array design method do have less fouling or have better heat transfer performance after fouling than the reference cases in the test arrangements. The correlation of Nuf∗ has good prediction accuracy, and it can be useful in the design and evaluation of heat exchanger in dusty environment.

Investigation on Heat Transfer Characteristics of the H-type Finned Tube in Flue Gas with High Content of Ash

H-type finned tube is rarely used in waste heat recovery power generation stations, though it has an efficient heat transfer performance in large thermal power stations (WHRPGs, hereafter). To date, understanding of heat performance of H-type finned tube in WHRPGs is still lacked. The heat transfer characteristics of H-type finned tube in gas with high content of ash in WHRPGs was investigated in practical cement plant in present work. The actual ash deposition pattern was observed meanwhile. The characteristics of heat transfer process including heat transfer coefficient, heat effective coefficient, and flue resistance at gas velocity between 4.5 - 6.5 m·s–1 are obtained. Experimental results show that the heat transfer coefficient increases with gas velocity linearly, the heat effective coefficient nearly keep stable on the other hand, and serious ash-block problem occurs in flow area in the heat exchanger at the gas velocity of 4.5 - 6.5 m·s–1. The max heat transfer coefficient remain below 10 w·m–2·k–1, implying heat performance of H-type finned tube in WHRPGs is possibly inefficient.

Modeling of Thermal-hydraulic Characteristics of H-type Finned Tube using Response Surface Methodology

The heat transfer and pressure drop characteristics beside air-side of H-type finned tube are investigated numerically in a scientific design of experiments by response surface methodology (RSM). Eight factors including seven geometric parameters and Reynolds number are examined with 120 numerical cases in total. The analysis of variance (ANOVA) confirms an adequate accuracy of the reduced quadratic model of thermal-hydraulic characteristics obtained from RSM. Correlations of heat transfer and pressure drop characteristics, which describe 99% of numerical data within ±10% deviation and 94% within ±15% deviation, respectively, are presented with the interactive effects between factors. This methodology might be a guideline to reduce time and cost to obtain correlations of thermal-hydraulic performance over heat transfer structures.

Numerical study of fouling characteristics on two kinds of typical heat exchangers used in the waste heat recovery systems

The problem of high exhaust temperature universally exists around the industrial boilers, which causes enormous loss of energy. Different kinds of heat exchangers are widely used in the waste heat recovery systems to recover waste energy from different heat sources. However, considering the heat exchangers mainly work in dusty environment, such as in the tail of large boiler, fly ash fouling on heat exchangers is a major problem in waste heat recovery systems, which can lead to significant efficiency deterioration. Besides, the fouling may also lead to failure of the systems with serious economic consequence. The H-type finned tube heat exchanger is a new type of heat exchanger which have been widely used in waste heat recovery systems in recent years, because of their excellent anti-wear and anti-fouling performance. In this paper, a numerical model was developed to investigate the fouling characteristics of two kinds of H-type finned tube heat exchangers used in the waste heat recovery systems. Firstly, a fouling model which contains a deposition process and a removal process is developed. The deposition process is determined by the energy balance on the particles and the removal process is determined by the the local wall shear stress and the fouling thickness on the fin surface. As the flow field directly affects the particle motion, the fluid flow characteristics of the two kinds of heat exchangers are calculated, and the discrete phase model (DPM) was employed to trace the fly ash particles in the flow field during the fouling process. Since the simulation time is much smaller in magnitude than the real time in fouling process, it is impossible to simulate the whole real fouling time period (hours) with a small time step size. In order to obtain a reliable result, it is necessary to enlarge the simulation time and results to the real time scale. In this paper, a fouling time ratio is proposed by considering the volume difference between the simulated deposit layer and the real deposited particles and the concentration difference of injected particles between the simulation and real situation. According to the fouling time ratio, we can enlarge the simulation time and results to the real time scale. Then the real-time fouling characteristics of the two kind of H-type finned tube heat exchangers are investigated and the effects of inlet velocity, particle diameter on the fouling results are also studied. The results show that, the fouling mainly occurred in the flow stagnation region and the recirculation region of the H-type finned tube. The net fouling mass increases with the operating time, showing an asymptotic characteristic of growth, and finally will reach a stable value, which corresponds to the asymptotic fouling resistance. The increase in inlet velocity and particle diameter would lead to a rapidly decrease in fouling results. The anti-fouling performance of double H-type finned tubes shows slightly better than that of single ones, but the advantages decreases with the increase in inlet velocity and particle diameter.

Parametric study and multiple correlations of an H-type finned tube bank in a fully developed region

ABSTRACTThe air-side heat transfer and pressure drop characteristics of an H-type finned tube bank in the turbulent periodically fully developed region are investigated numerically. The effects of seven geometric parameters and Reynolds number are examined. It is found that when the number of tube rows is equal to and larger than 25, the heat transfer and fluid flow approach the fully developed state. Among the seven geometric parameters spanwise tube pitch has the most important effect. Based on the numerical results, the correlations of heat transfer and pressure drop of the H-type finned tube bank for the fully developed region are presented.

Parametric study and optimization of H-type finned tube heat exchangers using Taguchi method

In this paper, a three-dimensional numerical model of H-type finned tube heat exchangers has been built. In order to optimize its structure and improve its performance, Taguchi method is applied to investigate the influence of seven geometric parameters including slit width, row number, fin height, spanwise tube pitch, longitudinal tube pitch, fin thickness and fin pitch. Numerical simulations are performed on eighteen cases with different combinations of seven geometric parameters and the overall thermal–hydraulic performance and its characteristics of heat transfer and flow friction are discussed in detail. The results show that fin pitch and fin height play a significant role on the heat transfer characteristics while the flow friction characteristics are mainly affected by fin height, spanwise tube pitch and fin pitch. The intuitive analysis and analysis of variance show that fin pitch, fin height and fin thickness have much stronger influence on its overall thermal–hydraulic performance than the rest four parameters. Finally, the optimal parametric combination of the H-type finned tube is obtained with an improvement of overall thermal–hydraulic performance by 11.4–16% for Re in range from 9000 to 24,000.