Finned Tube Research Articles

CFD Assessment of Flow Maldistribution in Plate Fin and Tube Heat Exchangers

The primary goal of this work is to use CFD assessment simulating framework is to anticipate the impact of injecting air flowing mal-distribution on heat exchanger architecture and thermal flow characteristics. Using CFD (computational fluid dynamics) simulation-studies, determine the impact of air intake flow unequal distribution or mal-distribution on the complete redesign as well as high - temperature hydraulic performing ability of HEX (heat exchangers). The findings demonstrate that a plate as well as tube fin heating element consisting of an elongated tubular setup slanted by 30 degrees can achieve the highest temperature transmission, having a heat transfer ability of 23.22 percent greater than a (SPHEX) spherical pipe heat exchanger.

Analysis of Stresses and Strains in Stainless Steel 316 L Tubes Subjected to Die Expansion

Abstract SS316 L finned tubes are becoming very popular in high-pressure heat exchangers and particularly in CO2 cooler applications. Due to the high pressures present during operation, these tubes require an accurate residual stress evaluation generated by the die expansion process. Die expansion of air cooler fin tubes creates not only high stresses that can surpass the ultimate tensile strength when combined with operation stresses but microcracks during expansion when the process is not well controlled. This research work aims to study the elastic-plastic behavior and estimate the residual stress state of fin tubes subjected to the die expansion process. The stresses and deformations of the expanded SS316 L tube are analyzed numerically using the finite element method. The expansion and contraction process are modeled considering the elastic–plastic material behavior for different die sizes. The maximum longitudinal, tangential, and contact stresses are evaluated to verify the critical stress state of the joint during the expansion process. The importance of the material behavior in evaluating the residual stresses using kinematic and isotropic hardening is addressed. Finally, an experiment was conducted to assess the tangential and longitudinal strains of a 3/8 in. stainless steel tube subjected to expansion with an oval-shaped die.

Investigating different types of fluids in pulsating heat pipes for improving heat transfer in an air-cooled heat exchanger

Air-cooled heat exchangers are utilized in various industries to cool process fluids. To have a better heat transfer, fins are used in the structure of exchangers. In this study, a set of experiments were performed to investigate the improvement in the amount of heat transfer in an air-cooled heat exchanger. For this purpose, a real case study was conducted on air-coolers in a natural gas compressor station; afterward, the finned tubes were replaced by pulsating heat pipes (PHPs), and a different type of fluid was applied to the pulsating heat pipes. The laboratory system was set up to measure the overall heat transfer coefficient under two conditions involving either finned tubes or a PHP with R134, R22, and filled acetone fluids. Finally, the results were verified by the theory method. The results showed that all the three fluid agents (R134, R22, and Acetone) with natural convection of 9.94 m/s, an inlet fluid velocity of 5.54 m/s, and an average feed velocity were able to enhance the heat transfer coefficient by 10, 13, and 11%, respectively. In addition, compared with finned tubes, R134, R22, and Acetone improved the natural convection heat transfer coefficient by 22.2, 18.6, and 21.7%, respectively.

Thermal assessment on solid-liquid energy storage tube packed with non-uniform angled fins

The solid-liquid phase change energy storage system promoted the efficient and sustainable utilization of dispersive and intermittent renewable energy. Low energy storage rate and unbalanced thermophysical characteristics existed in the vertical shell-and-tube heat storage tubes. To improve thermal properties and melting uniformity, this paper proposed a non-uniform angled fin type considering the optimization by the non-uniform arrangement and angled fins with small angles. A visual experimental platform was designed and built, and the reliability of the numerical model was verified by the experimental results. Numerical simulations of a single shell-and-tube heat storage tube regarding maximizing phase change rate were carried out. The development of the phase change interface and transient temperature field during the charging process of the non-uniform angled fins with downward 10° were obtained. Results showed that, compared with the uniform straight fin tube, the non-uniform angled fin can effectively promote the melting process of the whole fin tube, especially in the bottom area, leading to a 69.59% reduction in complete melting time. This provided a reference for the performance optimization of the shell-and-tube finned phase change heat storage tube. • Non-uniform angled fins are designed for improving energy storage. • A 69.59% reduction in full melting time is obtained compared with uniform straight finned tube. • Unbalance of thermophysical characteristics are effectively reduced by non-uniform design. • Non-uniform angled fins achieved heat flux improvement of TES unit as large as 29.19%.

Forced Convection Heat Rejection System for Mars Surface Applications

A forced convection heat exchanger for waste heat rejection to the Martian atmosphere is designed based on existing heat transfer and pressure drop correlations for low-Reynolds-number finned tube arrays. The design is optimized to determine the mass-optimal heat exchanger geometry for a range of candidate heat exchanger materials and power loads. For a 100 kW thermal load, the optimal heat exchanger mass is found to be 27.0 kg and a frontal area of 3.94 m2. This is 95% less mass and area than a comparable radiator and only requires 638 W of fan power (or 0.6% of the output power) to operate. Optimal geometries are also found for heat rejection loads of 1 kW to 250kW across a range of coolant and atmosphere temperatures, indicating wide applicability of this technology for Martian heat rejection applications such as cryofuel refrigeration or in-situ resource utilization (ISRU) plant cooling. An experimental facility has been designed and partially constructed to experimentally validate the predicted heat exchanger performance in a Mars-like environment. A subscale heat exchanger has been built based on the predicted mass-optimal geometry. Heat transfer and pressure drop performance data of this heat exchanger will be collected and will refine the modelling predictions.

Experimental visualization and analysis of transient heat and mass transfer during natural dehumidification of air around square finned tubes under various operating conditions

This study aims to experimentally investigate the natural dehumidification of humid air on the surface of square fins. Different stages of dehumidification process including nucleation, droplet growth, coalition, and collapsing of droplets are visualized and analysed for various operating conditions. A detailed parametric study is conducted to study the effect of relative humidity, ambient temperature and fin spacing on the heat transfer coefficient, heat transfer rate and mass transfer rate. Transient behavior of heat and mass transfer characteristics is quantitatively and qualitatively assessed through various images at different times. The results show that an increase in the relative humidity and fin spacing has significantly increased the rate of dehumidification process and droplet growth, while increasing the ambient temperature exhibits a minimal influence on these two criteria. The heat transfer coefficient and rate reach the steady state condition after 15 min under various operating conditions, while the steady state condition for mass transfer is achieved at different times depending on the experimental conditions. As a case in point, an enhancement in fin spacing from 5 mm to 9 mm and 14 mm increases the heat transfer rate, heat transfer coefficient, and mass transfer by about 62% and 22%, 171% and 188%, and 63% and 130% at the relative humidity of 60% and ambient temperature of 30°C, respectively.

Evolutionary design: Heat and fluid flow together

This article sheds light on the fundamental physics that accounts for the similar behaviors of heat transfer and fluid friction as the configuration of the convective flow system changes. Three methods are used, and as the methods change so does the configuration (design): complicated (bundle of finned tubes in cross flow), elemental (single body in uniform flow), and even more complicated such that it resembles a saturated porous medium. The configuration evolves such that it conveys the explanation better, more effectively. The article illustrates the essential role of evolving configurations in thermal-science fundamentals and practice. It shows that three methods (i.e. three designs, from purposeful changes in design) are better than a single method (one design). Science marches forward in this manner, and, at the same time, there is a creative reassessment of past advances. The purpose of looking back is to construct a single edifice that is general, simpler and easier to use.

Experimental Investigation of the Heat Transfer between Finned Tubes and a Bubbling Fluidized Bed with Horizontal Sand Mass Flow

The sandTES technology utilizes a fluidized bed counter current heat exchanger for thermal energy storage applications. Its main feature is an imposed horizontal flow of sand (SiO2) particles fluidized by a vertical air flow across a heat exchanger consisting of several horizontal rows of tubes. Past international research on heat transfer in dense fluidized beds has focused on stationary (stirred tank) systems, and there is little to no information available on the impact of longitudinal or helical fins. Previous pilot plant scale experiments at TU Wien led to the conclusion that the currently available correlations for predicting the heat transfer coefficient between the tube surface and the surrounding fluidized bed are insufficient for the horizontal sand flow imposed by the sandTES technology. Therefore, several smaller test rigs were designed in this study to investigate the influence of different tube arrangements and flow conditions on the external convective heat transfer coefficient and possible improvements by using finned tubes. It could be shown that helically finned tubes in a transversal arrangement, where the horizontal sand flow is perpendicular to the tube axes, allows an increase in the heat transfer coefficient per tube length (i.e., the virtual heat transfer coefficient) by a factor of 3.5 to about 1250 W/m2K at ambient temperature. Based on the literature, this heat transfer coefficient is expected to increase at higher temperatures. The new design criteria allow the design of compact, low-cost heat exchangers for thermal energy storage applications, in particular electro-thermal energy storage.

Performance Enhancement of Finned Tube Heat Exchanger using New Vortex Generator

The present work aims to investigate a performance enhancement in an H-shaped finned tube heat exchanger using a new design of winglet vortex generator. The new design has an aerodynamic shape that reduces the pressure drop and enhances the heat transfer, resulting into an improvement in the overall thermo-hydraulic performance. A three-dimensional model is developed using ANSYS fluent to carry out simulations for Reynolds number varying between 5000 ≤ Re ≤ 11000 and to predict the net enhancement in the heat exchanger performance. The validation of the model is done using experimentally developed correlations of dimensionless pressure drop and heat transfer characteristics. Comparative results for the finned tube heat exchanger with and without vortex generator are presented. Results indicate a significant enhancement in the heat transfer characteristics of the finned tube heat exchanger with the new design of vortex generator. Volume goodness ratio and Colburn j-factor found to be 19.63% and 30.33% higher than the baseline finned tube heat exchanger without any vortex generator.

Experimental and numerical analyses of thermal-hydraulic characteristics of aluminium flying-wing fins

• In general, the flying-wing fin performs better than the wavy fin at the same Re . • The field synergy of the flying-wing fin is much better than that of the wavy fin. • There exist the butterfly-shaped low velocity zones perpendicular to the streamwise direction. • The heat transfer coefficient on the obtuse-angled side of the fin is larger. • Both fin length and fin thickness have little effect on the performance of the fin. The secondary heat transfer surface of the shovel-cut finned tube, called the flying-wing fin, eliminates the thermal contact resistance. In the present study, the thermal-hydraulic characteristics of the flying-wing fin at Reynolds number range of 1500–3000 were studied, including overall quantitative analysis and three-dimensional thermophysical field analysis. It was found that the ratio of Nu · η 0 / f 1/3 of the flying-wing fin (Case A1) is about 8.6% larger than that of the wavy fin (Case B3). The fundamental reason is that the flying-wing fin has a smaller average field synergy angle than the wavy fin. There is a butterfly-shaped low-velocity zone at the root of the wave trough of the monitoring section on the acute-angled side of the flow channel. In addition, along the fin height direction, the influence range of this low-velocity zone on the flow field is less than around 1.34 mm. Similarly, there are butterfly-shaped zones for the temperature and field synergy angle distributions. The average value of the convective heat transfer coefficient on the left side of the flying-wing fin is greater than that on the right side. In general, the promising flying-wing fins show better thermal-hydraulic performances than the wavy fins with similar geometric parameters, which deserve further promotion and engineering application.

Investigation of the effects of fin perforations on the thermal-hydraulic performance of Plate-Finned heat exchangers

Design of fin profiles is a critical step in searching for more efficient heat exchangers. The present work performs a hybrid numerical-experimental analysis to obtain the thermal and hydraulic performances of the plate-finned heat exchangers. The analysis comprises a four-tube heat exchanger with in-line arrangement, being tested three fin patterns, i.e., rectangular with no insert (standard) and rectangular with diamond and circular perforations. The proposed methodology combines numerical simulation of the conjugate heat transfer problem (convection in the fluid/diffusion in the solid) with wind tunnel experimental data as boundary conditions. The ANSYS-Fluent® software is adopted to solve the three-dimensional average turbulent flow of air over the finned tubes within the framework of RANS model. The validation procedure compares the present results against empirical correlations for the Nusselt number available in the literature. Finally, a parametric study is addressed evaluating the influences of both the size and the shape of fin perforations upon the fluid dynamics and heat transfer behaviour. The main results indicate that larger sizes of the fin perforations (either circular or diamond shape) will enhance the comprehensive Performance Evaluation Criterion – the PEC parameter – and mass/volume thermal efficiency of the heat exchanger.

A Thermohydraulic Performance of Internal Spiral Finned Tube Based on the Inner Tube Secondary Flow

In this article, the BSL k-ω model was chosen as the turbulence model to simulate the heat transfer and flow characteristics of the proposed tubes inserted with internal spiral fins when the Re was set as 3000 to 17,000. The numerical results agreed well with the empirical formula. The average deviations of Nu and f between the simulation results and empirical formula results were 5.11% and 8.45%, respectively. By means of numerical simulation, the impact of three configurational parameters on the thermal performance was studied, namely the pitch P, the height H, and the number N of the internal spiral fins. The results showed that the Nu and f of the internal spiral finned tube were 1.77–3.74 and 3.04–10.62 times higher than those of smooth tube, respectively. PEC was also taken into account, ranging from 1.038 to 1.652. When the Re was set as 3000, the PEC achieved the peak value of 1.652 under the height H of the fins at 5 mm, the number N was 8, and the pitch P was 75 mm. However, with the increase of Re, the effect of pressure drop on the comprehensive performance in the tube was stronger than that of thermal enhancement. However, the PEC gradually decreased as the Re increased from 3000 to 17,000. In addition, the velocity and temperature fields were obtained to investigate the mechanisms of heat transfer enhancement.

Comparative Thermal Performances between Pumped Thermosyphon Loops with Different Condenser Configurations Using R245fa as Working Fluid

A pumped two-phase thermosyphon loop is broadly utilized to intensify the cooling duties of electronic chipsets/systems and the effectiveness for harvesting thermal energy. The configuration of a condenser not only affects the heat transfer in the condenser, but also has an effect on the saturation pressures during the boiling and condensation processes to alter the hydrothermal performance of a pumped thermosyphon loop. The influence of the condenser configuration on the hydrothermal performance of a pumped thermosyphon loop is rarely studied. The present study comparatively examined the thermal performances of two pumped thermosyphon loops with a conventional tube-fin condenser and the expansion-tank condenser. The thermodynamic cycles in pressure-temperature and pressure-enthalpy diagrams, Nusselt numbers of evaporator and condenser, thermal resistances and various performance indexes evaluated at constant pumping powers at the controlled through-flow Reynolds numbers, boiling numbers and condenser thermal resistances were measured. At the similar thermal loads, flow rates, and fluid entry temperatures of condenser, the operating pressure of the thermosyphon loop with expansion tank condenser was considerably reduced from that with tube fin condenser, leading to the lower saturation temperature for reducing the thermal resistance and the lesser pressure drop across the loop with a noticeable hydrothermal performance improvement. At the parametric conditions tested, the ratio of dimensionless overall thermal resistances between the loops with expansion tank condenser and tube fin condenser fell in the range of 0.81–0.99. When the loop performance was compared at a constant cooling airflow rate without considering the more pumping power consumption for the loop with tube fin condenser, the ranges of thermal resistance for the loops with expansion tank condenser and tube fin condenser were 0.13–0.21 (KW−1) and 0.15–0.23 (KW−1). The merit indices evaluating the comparative hydrothermal performances of evaporator, condenser and loop between the two looped thermosyphons highlighted the significance of condenser design and affirmed the performance improvement by changing tube fin condenser into expansion tank condenser. The empirical correlations of evaporator Nusselt number, condenser Nusselt number, and overall thermal resistance using Reynolds number, boiling number, and condenser thermal resistance as the controlling parameters were generated for relevant applications.

Applicability of the Equivalent Diameter Approach to Estimate Vortex Shedding Frequency and Acoustic Resonance Excitation From Different Finned Cylinders in Cross-Flow

Abstract This article explores the applicability of utilizing different equivalent diameter (Deq) equations to estimate the vortex shedding frequency and onset of self-excited acoustic resonance for various types of finned cylinders. The focus is on three finned cylinder types that are commonly used in industrial heat exchangers: straight, twist-serrated, and crimped spirally finned cylinders. Within each fin type, at least three different finned cylinders are investigated. The results indicate that at off-resonance conditions, utilizing the appropriate equivalent diameter collapses the Strouhal number data within the typical Strouhal number variations of an equivalent diameter circular, bare cylinder. However, when acoustic resonance is initiated, the onset and the peak of resonance excitation in all of the finned cylinder cases generally occurred at a reduced flow velocity earlier than that observed from their equivalent diameter bare cylinders. This suggests that although utilizing the appropriate equivalent diameter can reasonably estimate the vortex shedding frequency away from acoustic resonance excitation, it cannot be used to predict the onset of acoustic resonance in finned tubes. The findings of this study indicate that the effective diameter approach is not sufficient to capture the intrinsic changes in the flow-sound interaction mechanism as a result of adding fins to a bare cylinder. Thus, a revision of the acoustic Strouhal number charts is required for finned tubes of different types and arrangements.

Investigation of Condensate Retention on Horizontal Pin-Fin Tubes Using Water-Propanol Mixture

Condensers are an integral part of air conditioning systems. The thermal efficiency of condensers solely depends on the rate of heat transfer from the cooling medium. Fin tubes are extensively used for heat transfer applications due to their enhanced heat transfer capabilities. Fins provide appreciable drainage because surface tension produces pressure gradients. Much research, contributed by several scientists, has focused on adjusting parameters, such as fin design, flow rates and retention angles. In this study, a setup with an observing hole was used to inspect the influence on retention angle of adjusting the flow rates of the fluid. The increase in retention angle was examined using several velocities and concentration mixtures. Pin-fin tubes were used to obtain coherent results using a photographic method. The experimental setup was designed to monitor the movement of fluid through the apparatus. The velocity was varied using dampers and visibility was enhanced using dyes. Photographs were taken at 20 m/s velocities after every 20 s. and 0.1% concentration and the flooding point observed. The experimental results were verified by standard observation which showed little variation at lower velocity. For water/water-propanol mixtures, a vapor velocity of 12 m/s and concentration ratio of 0.04% was the optimal combination to achieve useful improvement in retention angle. With increase of propanol from 0% to 0.04%, the increase in retention angle was greater compared to 0.04% to 0.1%. For velocities ranging from 0 to 12 m/s, the increase in retention angle was significant. A sharp change was observed for concentration ratios ranging from 0.01% to 0.05% compared to 0.05% to 0.1%.

Numerical investigation on heat and mass transfer of slit finned tube heat exchanger with humid flue gas

AbstractVery few studies have been reported on the fundamental mechanism analysis the augmentation of heat and mass transfer for the convection and condensation processes in the slit finned tube heat exchanger under dehumidifying conditions. By developing a 3D numerical model for the condensation of the slit finned tube heat exchanger under dehumidifying conditions, the heat and mass transfer characteristics were investigated under different the geometrical and operational parameters. The models neglecting convective mass flux or neglecting the water vapor loss can greatly enlarge the deviations of numerical results with respect to experimental data. The synergy angles are smaller in the windward and leeward sides of slits where the velocity field has a better synergy with both temperature field and the mass field. The slits on the fin not only increase the disturbance of fluid but continuously destroy the developments of thermal and mass concentration boundary layers, greatly enhancing the heat and mass transfer. The latent heat transfer is significantly greater than the sensible heat transfer, which accounts for 71.7% of the total heat transfer rate when inlet velocity is 1 m·s−1 and volume fraction of water vapor is 15%. The increases in the inlet velocity, and the volume fraction of water vapor can enhance the heat and mass transfer coefficient of wet flue gas. Whereas, the increase in inlet velocity can reduce the difference of synergy for the velocity field and the temperature or mass concentration gradient field of different fin tubes.

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.

Influence of Longitudinal Fin Tubes Arrangement in LNG Ambient Air Vaporizers on the Wind Load

The article presents the results of computational fluid dynamics (CFD) analysis of the wind action on liquefied natural gas (LNG) ambient air vaporizers (AAVs). A study concerning AAV with a 6 × 6 tubes array is presented to demonstrate how the distribution of longitudinal finned tubes and wind direction affect the average load and wind pressure acting on the vaporizer structure. The main goal of the study is to estimate the wind load on the structure and wind pressure on individual tubes depending on the pitch of the tubes arrangement. The above parameters are crucial for the strength analysis of the vaporizer structure. The derived analysis results provide important data on the variation of pressure on individual tubes, wind velocity inside AVV structure and indicate a significant increase in the average wind load acting on the structure for a wind direction of 45 degrees compared to a perpendicular direction.

Influence of Fins Number and Frosting on Heat Transfer through Longitudinal Finned Tubes of LNG Ambient Air Vaporizers

The use of cryogenic liquefied gasses in industry is constantly increasing both for process purposes and for power supply needs. The liquefied natural gas (LNG) is stored at cryogenic temperature and its immediate use in gaseous form requires its evaporation. The heat needed to cause a phase change is usually delivered by means of vaporizers. This paper presents a numerical analysis of the influence of the fins number and frost accumulated within the fins surface on the heat transferred through the aluminum finned tubes of LNG ambient air vaporizers. The calculations were carried out applying finite element thermal analysis within Ansys software as well as using an analytical approach. As a result, the heat rate per unit length of the finned tube was obtained. The results were compared for different numbers of longitudinal fins both without frost and for total frosting of the tubes.

Optimization design of helical micro fin tubes based on exergy destruction minimization principle

• Increased heat exchange area and the secondary flow are the primary sources of heat transfer enhancement. • The local exergy destruction rates are related to the equivalent heat transfer coefficient and the unit pressure drop. • Optimal design tends to have a larger number of starts and a lower micro fin height. • The exergy destruction minimization principle is proved to be still applicable in the case of the periodic model and fully developed turbulence. The helical micro fin tubes (HFT) are commonly used in various double pipe heat exchangers because of the excellent processing and anti-fouling performance. It is of great significance to further improve the overall efficiency of the HFT so as to diminish energy consumption. In this work, the heat transfer and flow characteristics of the HFT are studied by numerical simulation. The results show that the heat transfer enhancement factors of the HFT are the secondary flow generated near the wall and the increase of the heat exchange area. In addition, the effects of the geometrical parameters on thermal–hydraulic performance are studied at Re = 36,636. It is found that the micro fin height ( e ), the helical angle ( φ ), and the number of starts ( Ns ) have a significant impact on the overall performance, and there is a strong mutual coupling between them. According to the parametric analysis, the HFT with a low micro fin height and a large number of starts is considered to be a better geometrical type. Finally, in order to select (or design) the HFT quickly under the specific working conditions, based on the exergy destruction minimization principle, the geometrical parameters are optimized by using the artificial neural network and genetic algorithm. An optimal solution ( e = 0.23 mm, φ = 36.1°, and Ns = 66) is selected from the Pareto front by the TOPSIS method. The results indicate that the optimal solution has a sensible balance between the exergy destruction caused by heat transfer and fluid flow. Besides, it has a better thermal–hydraulic performance as well ( PEC = 1.73). This work fills the gap of heat transfer and the geometrical optimization study of HFT based on the second law of thermodynamics and provides strong evidence that the exergy destruction minimization principle is still applicable in the case of the periodic model and fully developed turbulence. We hope that it will be contributed to the structural design of the HFT.