Finned Tube Research Articles

CFD Air Flow Evaluation of Finned Tube Evaporator for Refrigerated Display Cabinet Application

This study is aimed to develop a simulation to improve the performance of the finned tube evaporator which is applied to the refrigerated display cabinet. CFD model was developed to be able to analyse the characteristics of air flow inside the fin gap and air side heat transfer coefficient. Geometry of the model of overall finned tube evaporator is considered covering two aluminium wavy fins with an air flow in between, combination of staggered cooper tubes with refrigerant flow inside. Fin gap is designed 4 mm to anticipate frost on the fin surface that can block air flow. Turbulence models used in the study is the realizable k-ε turbulence which had the best performance turbulence model and it was validated with secondary data from previous studies and shows the lowest error only 5.9 %. The use of CFD was found to be sufficiently representative of the heat transfer characteristics of evaporators, and acted as an effective simulation tool to determine the heat transfer coefficient in order to improve efficiency in terms of improved design. The characteristics of air flow between the fin gap and around the tube was obtained various and complex. In the case study the entry velocity of 1.7 m /s at the highest turbulence condition of the first row can reach speeds of 2.75 m/s. Hight turbulence regime in flow can indicate higher the heat transfer coefficient of the evaporator.

Wet cooling of air on plate finned tube heat exchangers

The objective of this paper is to provide the reliable calculation procedure for determining heat and mass flow rates for plate finned tube heat exchangers in dehumidification regimes that can be used easily in engineering practice. For this purpose, the experiments are conducted on two heat exchangers, and datasets for six more heat exchangers are used from literature. Comprehensive database is established with total of 637 sets of data, and it gathers 365 new measurement sets and 272 sets from open literature. The new calculation procedure predicts heat transfer rate and condensate flow rate where new methodology approach (based on the porous velocity, the ratio of characteristic surfaces and hydraulic diameter) is used. Predicted results show 5–10 % deviation for heat duty and up to 20 % for mass flow rate from experimental results, which is of importance to industrial practice.

Performance evaluation and optimization of compact tube-fin latent heat storage system in phase change nanoemulsion discharge mode

The low thermal conductivity of phase change materials (PCMs) and the reduced heat transfer temperature difference along a tube both limit the thermal performance of latent heat thermal energy storage (LHTES). Herein, a compact tube-fin LHTES system based on phase change nanoemulsions was developed and the heat transfer process of nanoemulsion and PCM was numerically investigated. The effects of the heat transfer structure of the heat exchanger and the thermophysical parameters of the heat transfer fluid (HTF) on the cold energy discharge performance of the system were quantified. The optimized model reduced the discharge time by 24.4 % in nanoemulsion mode relative to water. Heat transfer improvement on the PCM side could be achieved by decreasing the fin spacing and tube spacing and by increasing the fin thickness. Such improvement reinforced the heat transfer enhancement of the nanoemulsion. The heat transfer mechanism was explained by the temperature distributions of the HTF and PCM along the tube. The phase-change thermostatic properties of the nanoemulsion and PCM contributed to the formation of dual-phase-change coupled heat transfer (i.e., the heat transfer process when the fluid inside the tube and the PCM filled outside the tube undergo a simultaneous phase change) within the LHTES, increasing the heat transfer temperature difference and the magnitude of the driving force. Increasing the phase change temperature difference accelerated the onset of dual-phase-change heat transfer, while increasing the PCM content prolonged the process. Briefly, this study provided operational and design assistance for LHTES systems in nanoemulsion mode with the intention to accelerate heat transfer rates.

Numerical study on the interface characteristics of gas–liquid falling film flow considering the interface forces

As an energy quality improvement device, an air source heat pump plays an important role in clean heating applications. When operating in a cold and wet environment in winter, the outdoor evaporator will have the problem of frost, which affects the operation efficiency. To solve the frosting problem, the development of frost-free evaporators has attracted more and more attention. The fluctuation characteristics of the gas–liquid interface are the key factors affecting the intensity of gas–liquid heat transfer on the air side of this kind of heat exchanger. Therefore, a mathematical model is established to describe the falling film flow on the surface of the flat finned tube heat exchanger in a closed-type heat source tower. The model takes into account the interfacial tension and interphase friction force between the air flow and the liquid film. On this basis, the fluctuation intensity of the central channel interface during falling film flow with different inlet parameters is studied. It is found that there is a critical value of 1.5 m/s (i.e., Reg = 1643.0) in the air flow rate under the study conditions. When the air flow rate is higher than this velocity, the interface near the gas–liquid outlet fluctuates more frequently and the stability is poor. The distributions of interfacial velocity and pressure are also studied, and the relationship between them and interface fluctuation is analyzed. This paper aims to provide theoretical support for enhanced heat and mass transfer on the air side of finned tube heat exchangers in the closed-type heat source tower.

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.

Free-Convection Heat Transfer on Multirow Bundles of Finned Tubes with Circular Fins

Free-Convection Heat Transfer on Multirow Bundles of Finned Tubes with Circular Fins

Numerical investigation on thermal-hydraulic performance of leeward cut annular finned tubes in crossflow heat exchangers: An insight on fin material saving

The objective of the current study is to analyse the hydro-thermal characteristics of leeward cut fins with various trimming values and finalise a specific fin that benefits by maximum material saving and negligible compromise in heat transfer. The leeward section of a fin is cut in two ways: angular and chordwise. For angular cutting, four different angles (15°, 30°, 60°, and 90°) are considered, while for chordwise cutting, a fin is trimmed along a chord present at D/3, 2D/3, and D mm from the vertical diameter. The spacing between fins is varied (2–4 mm). For turbulence modelling, the transition SST model is implemented. Streamlines reveal that the intensity of a vortex formed downstream of the tube depends on the fin-trimming value. For a higher fin cutoff, a lower pressure drop is obtained. The heat transfer rate analysis reveals that angular cutoffs of 15° (8.3 % material saving) and 30° (16.6 % material saving) have 2.5 %–3.1 % less heat transfer than the standard case. Chordwise cut at D gives 1.1 % less heat transfer but saves only 2.7 % fin material than the standard case of no cutoff. Z/E factor, a ratio of heat transfer for a unit temperature drop to power provided, is used to determine hydro-thermal performance. The value of the Z/E ratio is the highest for the benchmark case. However, for angular cutoffs of 15° and 30°, the Z/E factor is less by 4 and 6.7 %, respectively, than the standard case. Examining the outcomes of this study, we recommend using an angular cutoff of 30° or lower to get significant material savings for an equivalent heat transfer.

Experimental investigation of two-bed adsorption thermophysical battery with mass recovery technology

This paper developed a novel semi-continuous two-bed Adsorption Thermophysical Battery (ATB), utilizing silica gel RD/water as the adsorption pair. The Absorber Bed Unit (ABU) was designed and manufactured using finned tubes, while the condenser and evaporator are incorporated under a single Evaporator-Condenser Unit (ECU). The study investigated the impact of mass recovery, hot and cooled water temperature, and the chilled, cooled, and hot water flow rate on the system performance. The results of the study revealed that the ATBwith mass recovery demonstrated a higher Coefficient of Performance (COP) and Refrigeration Capacity (RC) in comparison to the system without mass recovery. The average COP for the cycles with and without mass recovery were 0.228 and 0.2, respectively. The present study determined that the most favorable duration for mass recovery was 60 s. A substantial reduction in the COP can be observed as the hot and cooled water temperature increases. Also, the COP of the ATB was found to be directly related to the flow rates of chilled and cooled water but not to the flow rates of hot water. In addition, the COP of the two-bed ATB with mass recovery was improved by 14 % compared with the single-bed ATB. Finally, the adsorption uptake rose by 24 % when the cooled temperature was decreased from 313 K to 303 K.

Numerical study on thermal-hydraulic characteristics of streamwise-interrupted flying-wing finned tubes

To improve the thermal-hydraulic performance, this study conducted numerical studies on streamwise-interrupted flying-wing finned tubes utilising both single- and double-channel interruption modes. The interruptions varied in width from 0.5 to 10 mm and were strategically positioned in nine distinct locations along the flow direction. The RNG k-ε turbulence model was applied for viscous flow simulation. The findings reveal that fin interruptions create a “breakpoint thermal expansion effect” at specific locations, enhancing heat transfer downstream while diminishing it upstream. For the single-channel interruption mode with a centrally positioned interruption channel, a 5–6 mm width is optimal at a low air velocity (150 Pa total pressure drop and a Reynolds number of 1282.31 for the continuous flying-wing finned tubes). However, at high air velocities (550 Pa total pressure drop and a Reynolds number of 2944.91), interruption is unnecessary. In both modes, standardising the interruption channel width to 2 mm is more effective when the interruptions are placed closer to the downstream end, as opposed to an even distribution. This study provides valuable insights for enhancing the thermal-hydraulic performance of flying-wing finned tubes and similar continuous-finned designs through strategic flow-channel interruptions.

Pool boiling heat transfer characteristics of low-GWP refrigerants in a horizontal tube bundle configuration

Heat transfer enhancement techniques have been adapted on the shell side to improve the overall performance of the flooded evaporators, such as finned tubes. In recent years, it has been demonstrated that the metal foam structure can offer enhanced heat transfer performance under pool boiling conditions. However, there are not much research in the open literature that examine the feasibility of metal foam embedded tubes in horizontal tube bundle configurations. Therefore, this paper proposed a novel metal foam embedded tube (i.e., foam embedded outside the tube) to improve the heat transfer behavior of flooded evaporators. The experiments were performed on a horizontal tube bundle with a staggered arrangement. Moreover, the performance of low global warming potential (GWP) refrigerants (R-1234yf and R-1234ze(E)) is compared against R-134a for both plain tubes and metal foam tubes with porosities of 81%, 75%, and 62%. The results showed that a metal foam tube with a porosity of 62% showed a maximum heat transfer coefficient (HTC) enhancement of 291% compared to the plain tube. As compared with R-134a, the HTCs of R-1234yf and R-1234ze(E) are nearly 10% higher and 5% lower, respectively.

Experimental and Numerical Investigations on Thermal-Hydraulic Performance of Three-Dimensional Overall Jagged Internal Finned Tubes.

To satisfy the demand for efficient heat transfer, a novel three-dimensional overall jagged internal finned tube (3D-OJIFT) was fabricated, using the rolling-ploughing/extruding method. The thermal performance of the 3D-OJIFT were studied and compared in experiments and three-dimensional numerical simulations. The RNG k-ε turbulence model is well verified with the experimental results. By analyzing the distributions of velocity, temperature, and turbulence kinetic energy, it was found that the 3D-OJIFT destroyed the development of the velocity and thermal boundary layers, increased the turbulence disturbance, and reduced the temperature gradient, thus improving the heat transfer. The influences of the jagged height and jagged spiral angle of the 3D-OJIFT are discussed. The Nu and f increased as the jagged height of the 3D-OJIFT increased. The Nusselt number of the 3D-OJIFT was 1.67-2.04 times the value for the smooth tube. In addition, the comprehensive heat transfer performance of the 3D-OJIFT improved after increasing the jagged spiral angle. Compared with conventional internal helical-finned tubes and other reinforcement structures reported in the literature, the 3D-OJIFT demonstrated better comprehensive heat transfer performance. Finally, empirical correlations of the 3D-OJIFT were obtained.

Experimental investigation of axial finned tube evaporator thermal distillation system using for diesel engine waste heat recovery process

The study aims to improve the waste thermal energy retrieval from flue gas of an internal combustion engine (ICE). The recovered waste heat energy was used for distillation by using a thermal distillation system. The performance of the thermal distillation unit was investigated by varying the evaporator (boiler) type and engine load (25, 50, 75 %). Four different types of boilers were used including one smooth copper tube and other three were two, three and four axial finned copper tube evaporators. The impact of boiler type and engine load on the net retrieved energy and exergy, net energy and exergy efficiency, and distillate yield rate of thermal distillation unit was also examined. The results showed that the net extracted heat energy and exergy for axial finned tube evaporator was approximately 26.823 – 45.513 % and 7.614 – 25.203 W higher than that of smooth tubes evaporator at 25 and 75 % engine load, respectively. The distillation yield was found to be ~ 2.35 liter/ hour in the case of four axial finned tube boiler at 75 % engine load.

Pool boiling heat transfer of ammonia outside enhanced tubes with various fin structures

Pool boiling heat transfer of ammonia on a smooth tube and three enhanced tubes was investigated at the saturation pressure ranging from 6.15 to 11.7 bar, which corresponds to the saturation temperature from 10 to 30 °C. The test tube with a length of 796 mm was immersed in the liquid pool of ammonia inside a cylindrical chamber having an internal diameter of 254.4 mm, and convection or pool boiling heat transfer outside the test tube was generated by flowing hot water through the tube. Three enhanced tubes of a low-finned tube (Low-fin), a low-finned tube with oblique cuttings (Turbo-C), and a finned tube having re-entrant cavities (Turbo-E) were prepared to examine the pool boiling enhancement on various finned tubes. Boiling hysteresis on the smooth tube was observed between when the heat flux increases and when the heat flux decreases, which resulted in the deviation of the heat transfer coefficients from the previous correlations when the heat flux decreases. A suitable correlation was suggested to compensate for the deviation of the heat transfer coefficients in case of decreasing the heat flux by modifying the Stephan-Abdelsalam correlation. Three enhanced tubes exhibited considerable enhancement in the heat transfer coefficients compared with the smooth tube, and boiling performance on the Turbo-E tube having re-entrant cavities was highly affected by the variation of the bubble diameter according to the saturation pressure. Enhancement factors of the enhanced tubes were obtained from the ratio of thermal conductance on the enhanced tube to that on the smooth tube.

Heat transfer and fluid flow performance of an internally longitudinal finned tube: Numerical study and experimental validation

The characteristics of heat transfer and fluid flow of an internally longitudinal finned tube were numerically studied. The results were validated with published experimental data, comparing the heat transfer coefficient (h) and friction factor (f) calculated in our numerical study with the corresponding values obtained from experimental data, with a highest deviation of 6.3%. Exploring a novel hollow longitudinal fin design to enhance heat transfer and reduce pressure drop, while investigating key parameters like fin angle (θ), inscribed diameter (dins), and fin thickness (δ). Through comprehensive analysis, valuable insights are offered into optimizing thermal performance compared to traditional smooth tube configurations. The study reveals that a rise in Re leads to a rise in heat transfer coefficient and a reduction in friction factor. Notably, in the case of internally finned tubes at θ=30⁰,dins=10mm,andδ=0.5mm, the handf are 0.32−0.9and0.34−0.43 times higher, respectively, compared to smooth tubes under a constant mass flow rate ranging from 10kg/hto60kg/h. Furthermore, variations in dins impact the handf for internally finned tubes, with a decrease in dins resulting in increased handf. Specifically, at D/dins = 8, the handf exceed those of smooth tubes by 0.357−1.16and1.097−1.608 times, respectively, under a constant mass flow rate across the same range. Additionally, the study investigates the effects of δ on internally finned tubes, showing that as the δ increases, the handf increase. In the case of θ=30⁰,dins=10mm,andδ=2.5mm, the handf increase to 1.51−1.75and1.29−1.87 times higher, respectively, compared to smooth tubes under a constant mass flow rate from 10 kg/h to 60 kg/h.

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 analysis of the heat transfer and pressure drop of a wavy fin and Kammtail tube condenser: An investigative study

The aim of this study was to numerically investigate the factors affecting the air-side performance of an innovative condenser for a domestic refrigerator. Novel condenser with a smooth Kammtail tube form was investigated due to delaying flow separation. For the first time in the literature, the kammtail form was used instead of round or ellipse geometry in a finned tube heat exchanger, and the advantages of this form was demonstrated both experimentally and numerically. This study incorporated design parameters such as air velocity (0.5, 0.7, 1 m/s), number of tube rows (4 or 5), tube arrangement (inline, staggered), fin pitches (5, 7, 10, 5–7, 5–10, 7–10 mm), and fin arrangement (homogeneous or hybrid). The findings indicated that, for identical fin types and fin surface areas, the proposed Kammtail shape of 3 × 6 mm exhibited 19% lower pressure drop and 9% higher heat-transfer coefficient compared to the original circular tube profile. Furthermore, decreasing the fin pitches resulted in a 32.9–97% increase in static pressure drop, while the heat-transfer coefficient decreased by about 4.7–11.7%. The examination of two new designs revealed a marked reduction of 7–20.4% in the static pressure drop, a decline in air flow rate of 30%, an increase in heat transfer of 5.6–12.2%, and a corresponding decrease in the volume of the condenser of 20%. The numerical results of this study are in good agreement with experimental results, with deviations of less than 10%.

Experimental and numerical analysis of the impact of a liquid flow rate on the operational performance of a cross-flow tube-and-fin heat exchanger

The paper is dedicated to an issue of the influence of a nonuniform flow of mediums in a cross-flow water-air heat exchanger, the core of which is a bundle of elliptical finned tubes. The main purpose of the work is to determine the impact of non-uniform water inflow for various mass flow rates on the thermal efficiency of the heat exchanger. Multivariate analyses were carried out for various temperatures of water, and for measured nonuniform air distribution at the heat exchanger input. Two variants of water distribution were considered: non-uniform water distribution assumed considering a non-uniform air inflow and water distribution resulting from hydraulic resistances calculated for different locations of water inlet and outlet nozzles. Simulation results were compared with the experimental outcomes obtained in cases of the non-uniform natural inflow of both mediums and to the computation results for a case of the uniform media inflow. The results obtained in this work confirm the significant deterioration of the thermal efficiency of heat exchangers caused by a non-uniform media inflow (by as much as 18.5% compared to the case of a uniform media inflow) which is compliant with other numerous works. The control of the water flow through the individual heat exchanger tubes enables the improvement of thermal efficiency by 4.5% to 18.6% compared to the device with uncontrolled inflow of working fluids, which for some of the analyzed cases is even better than a completely uniform inflow of heat carriers.

Experimental study on the thermal management performance of lithium-ion battery with PCM combined with 3-D finned tube

As an important intermediary between the green energy and human society, the lithium-ion battery has promising prospects in the new energy vehicles, energy storage, and green development fields. However, lithium-ion batteries can generate a large amount of heat during operation. In addition, excess temperature or big temperature difference of the surface of the lithium-ion battery can reduce its performance, which also results in reducing its operational life and even triggers incidents such as fires and explosions. Therefore, studying efficient thermal management methods for lithium-ion batteries is crucial for increasing their application range. This paper proposes a novel thermal management method by combining 3-D finned tubes with PCM. The thermal management system maintains a battery operating temperature less than 45 °C and a maximum temperature difference less than 2.4 °C. The influence of different fin structure parameters on the melting dynamics of PCM and the heat transfer performance is then discussed. The obtained results show that under each solid–liquid ratio of PCM, the heat transfer performance increases with the increases of the fin height, while it initially decreases and then increases with the increase of the width and axial spacing. Moreover, the heat transfer performance of the 3-D finned tube with different PCM liquid–solid ratios is investigated. The obtained results demonstrate that for constant fin parameters, the heat transfer reaches its highest performance for a PCM liquid–solid ratio greater than 2:2. The findings of this study lay a foundation for the design of efficient thermal management systems incorporating PCM applications.

Forming mechanism of leaf-like integral outside finned tubes via sequential knurling and cutting-bending method

Forming mechanism of leaf-like integral outside finned tubes via sequential knurling and cutting-bending method

Numerical study of the effect of a thin wire on the thermohydraulic performance in a plate fin-and-tube heat exchanger

A numerical study on the effect of a wire on the thermohydraulic performance in a plate-and-tube heat exchanger is performed with the Reynolds Averaged Navier-Stokes Equations approach. The heat exchanger is represented by a small finned tube bank with the implementation of periodic boundary conditions and symmetry conditions. The simulation models the turbulence with the Shear-Stress Transport model (SST k-ω). A benchmark case (without thin wire) is validated with PIV measurements of the horseshoe vortex and semi-empirical correlations for heat transfer. Then, twenty-four simulations are conducted at different dimensionless distances (1.0, 1.2, and 1.4) and angles (0, 15, 30, and 45°) of a thin wire. Predictions show that vortical structures around the thin wire contribute to an increase in thermohydraulic performance if the recirculation zones caused by thin wire do not affect the airflow patterns generated by finned tubes. However, the thermohydraulic performance decreases if airflow patterns are affected by the thin wire. Therefore, thin wire located at a dimensionless distance of 1.2 and angle of 15° generates a 5–6 % profit on the thermohydraulic performance with a pressure drop up to 73 Pa for Re = 2100.