Performance Of Fin-tube Heat Exchanger Research Articles

Enhancing corrosion resistance and heat transfer performance of fin-tube heat exchangers for closed-type heat-source towers by superhydrophobic coatings

Heat-source towers are essential components in heat-source tower heat pump systems, pivotal for achieving energy efficiency. Enhancing corrosion resistance and heat transfer performance for heat-source towers is important but challengeable. For solving this problem, this study aims to introduce a novel superhydrophobic (SHP) coating applied via a one-step electrodeposition method to enhance both corrosion resistance and heat transfer performance of fin-tube heat exchangers in closed-type heat-source towers. The superhydrophobic nature of the coating is validated by contact angle measurements, while its structural integrity and chemical composition are confirmed through various methods i.e., X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. Corrosion resistance tests indicate a significant improvement, with the coating showing a corrosion current density of 1.400 × 10−6 A/cm2 and a low-frequency modulus |Z|0.01 Hz of 1.50 × 10⁴ Ω cm2 after 30 days in a 15 wt% calcium chloride solution at 0 °C. Additionally, heat transfer experiments demonstrate a 42.5 % increase in heat transfer efficiency compared to uncoated fins under identical conditions, which present the significant heat transfer performance of the presently developed SHP coating. The key contribution of this research lies in the development and application of a novel SHP coating that significantly enhances the performance of heat-source towers. Moreover, the present findings suggest that implementing this SHP coating can substantially improve the durability and efficiency of heat-source towers, supporting the advancement of more sustainable building infrastructures.

A CFD investigation of the design variables affecting the performance of finned-tube heat exchangers

A wide variety of heating and cooling applications use heat exchangers. The increase in energy prices, the requirement for size reduction, and restriction on greenhouse gas emissions has led to the need for finding ways to develop efficient heat exchangers. A cost-efficient way to enhance the model of a heat exchanger by visualizing the effects of the design parameters is using Computational Fluid Dynamics (CFD). The reason for this exploration was to lead an examination of the varieties/changes in the general intensity move process for a Finned-Tube Heat Exchanger (FTHE), also known as Air Coil Heat Exchanger (ACHE) with a variety of plan boundaries like the quantity of tubes, course of action of tubes, and the material utilized for the intensity exchanger. The widely used heat exchanger that uses refrigerant R314a and air as the working fluids was simulated with different design modifications. The simulated results exhibited as to how the number of tubes, arrangement of coils/tubes, material of tubes, and density / spacing of fins, effects the pressure drop, temperature and velocities profiles, and heat exchangers’ transfer of a heat. The use of copper coils improved the heat transfer by approximately 61% as compared to aluminium coils.

Investigation of the Effect of Fin Configuration and Fin Angle on Thermal Performance of Finned-Tube Heat Exchanger. Experimental Study

Investigation of the Effect of Fin Configuration and Fin Angle on Thermal Performance of Finned-Tube Heat Exchanger. Experimental Study

Numerical investigation towards implementation of punched winglet as vortex generator for performance improvement of a fin-and-tube heat exchanger

Thermohydraulic performance of fin-tube heat exchanger can be augmented by using longitudinal vortex generators. Numerical simulations have been performed in the present work for investigating the effect of punching a rectangular winglet having hole from fin surface, on the heat transfer and flow resistance characteristics in a fin-tube heat exchanger. The mentioned concept is being studied in two configurations namely, common flow down and common flow up. Comparisons on the basis of heat transfer and flow resistance characteristics have been drawn between punched and non-punched cases of rectangular winglet with hole for all the configurations under consideration using Colburn's factor (j), friction factor (f) and performance evaluation criterion (PEC) also known as JF factor (j1/j0)/(f1/f0)1/3. Investigations have been performed considering Reynolds number in the range of 1500 to 9000 and angle of attack as 45°. Numerical simulations have been performed using SST k-ω turbulence model which has demonstrated capabilities of capturing separated flows. There is a heat transfer augmentation of up to 34% for the considered range of Reynolds number in case of fin-tube heat exchanger employing punched rectangular winglet with hole having Common Flow Up configuration located in the upstream location, over the non-punched case of winglet with hole in the same configuration and location. The result clearly indicates that punching the rectangular winglet having hole considerably improves thermohydraulic performance in case of winglet placed in common flow up configuration at upstream location.

Computer-aided engineering analysis for the performance augmentation of a fin-tube heat exchanger using vortex generator

The heat transfer performance of fin-tube heat exchangers can be enhanced with the help of longitudinal vortex generators. In this work, we investigate the effect of employing a rectangular winglet having a punched hole on heat transfer and flow resistance characteristics in a fin-tube heat exchanger with the help of numerical simulations. Studies were performed on two configurations, namely, common flow down and common flow up at upstream and downstream locations. Performance characteristics such as Colburn’s factor ( j), friction factor ( f), and performance evaluation criterion were considered for evaluating the thermohydraulic performance. Investigations were performed considering Reynolds number in the range of 1500–9000, keeping the angle of attack as 45°. The shear stress transport k-ω turbulence model was used for performing numerical simulations. A significant augmentation of up to 71% in the thermohydraulic performance of fin-tube heat exchanger was observed with the common flow down configuration located upstream over the common flow up configuration located upstream, which displayed the least improvement.

Performance Improvement of a Fin-Tube Heat Exchanger Using Rectangular Winglet as Vortex Generator

Heat transfer performance of fin-tube heat exchanger can be augmented by using longitudinal vortex generators. Numerical simulations have been performed in the present work for investigating the effect of punching a rectangular winglet having hole from fin surface, on the heat transfer and flow resistance characteristics in a fin-tube heat exchanger. The concept of punching out a rectangular winglet having hole from the fin-plate surface is being proposed here and studied in two configurations namely, common flow down and common flow up. Comparisons on the basis of heat transfer and flow resistance characteristics have been drawn for all the configurations under consideration using Colburn’s factor (j), friction factor (f) and performance evaluation criterion (PEC) also known as area goodness factor (j/f). Investigations have been performed considering Reynolds number in the range of 1500 to 9000 and angle of attack as 45°. The result clearly indicates that punched out rectangular winglet with hole having common flow down configuration at upstream location as exhibiting the best thermal performance, followed by common flow up at upstream location and, common flow down at downstream location.

Effect of partially wet-surface condition on the performance of fin-tube heat exchanger

PurposeThis study aims to investigate heat and mass transfer in a one-row heat exchanger. The required equations are obtained based on two-dimensional model analysis in a cell of the heat exchanger. By using finite difference approach, the obtained equations are solved to determine distribution of temperature and the efficiency of the heat exchanger in the case of partially wet surface. In this research, Lewis Number as unity and water vapor saturation as parabolic are assumed. Obtained results show that increase in thermal conductivity fin leads to decreasing thermal resistance; therefore, temperature changes in radial from center to out of fin are reduced and efficiency of fin increases.Design/methodology/approachIn this regard, fin material plays a significant role in fin efficiency. Changes in airflow also result in an efficiency increase by temperature and relative humidity, and efficiency is decreased by airflow velocity increase, and these changes are almost linear. Moreover, the fins with more wet surface are more sensitive to changes in fin dimensions and air flow characteristics, and it is a result of conjugate heat transfer mechanism, in which latent heat transfer in the fins with more wet surface has a significant role.FindingsThermal property and geometry of the fin under wet conditions play a more important role than the fin under dry conditions. Changes in airflow result in an efficiency increase by temperature and relative humidity, and efficiency is decreased by airflow velocity increase, and these changes are almost linear. Fins with more wet surface are more sensitive to changes in fin dimensions and air flow characteristics.Originality/valueEffects of the temperature of water supply and mass flow rate were considered in the study. The results had good agreement with actual data.

Effect of winglet location on performance of fin-tube heat exchangers with inline tube arrangement

Heat transfer performance of fin-tube heat exchangers can be enhanced by introducing longitudinal vortices generated using vortex generators (VGs). Location of VGs with respect to tubes plays major role in deciding the enhancement in heat transfer. Three-dimensional numerical investigations have been carried out to study the effect of winglet location on heat transfer characteristics of fin-tube heat exchangers for inline tube arrangement. In this study, rectangular winglet pair (RWP) type VGs having common flow down configuration are considered. Initially, effect of different possible locations of RWP corresponding to tube centre have been investigated to analyse the heat transfer and flow field characteristics. Further, effects of angle of attack (β) ranging from 15° to 60° and Reynolds number (Re) in the range from 2000 to 4000 have also been studied for the location associated with maximum heat transfer corresponding to mean values of β and Re in the considered range. To illustrate the interesting flow features of vortices generated due to placement of RWPs and how those affect heat transfer, streamlines and temperature contours have been investigated. Enhancement in heat transfer has been quantified using Nusselt number while pressure loss is estimated with the help of friction factor. Role of secondary flow induced by RWPs is quantified in terms of secondary flow intensity. Thermal performance factor (JF) is used to evaluate the combined effect of enhancement in heat transfer and increase in pressure drop. For upstream located RWPs, the value of JF is found to be higher due to lower pressure loss as compared to RWPs mounted in other regions. The value of JF is maximum for RWP located at ΔX = −2.0, ΔY = ±1.25 and correspondingly 37.6% enhancement in heat transfer is observed as compared to the case for the arrangement in absence of RWPs.

Effects of surface wettability and defrosting conditions on defrosting performance of fin-tube heat exchanger

Defrosting performance is closely related to surface wettability and defrosting conditions. In this paper, the effects of surface wettability, initial frost mass and defrosting temperatures on defrosting performance of fin-tube heat exchanger were studied experimentally. The contact angles of hydrophilic, bare and superhydrophobic heat exchangers were 13.7°, 95.3° and 156.8°, respectively. Five parameters were defined to provide quantitative analysis of the defrosting performance. Defrosting performance is greatly affected by surface wettability. The superhydrophobic heat exchanger has the best defrosting performance followed by the hydrophilic one. Initial frost mass and defrosting temperature have different levels of influences on different heat exchangers. For example, the retained water mass on the bare heat exchanger increases by 62.2% when the frosting time increases from 30 min to 90 min, while it has little change on the superhydrophobic one. And the defrosting temperature has no influence on retained water mass of each heat exchanger.

Air side performance of finned-tube heat exchanger with combination of circular and elliptical tubes

A three-dimensional numerical study has been conducted on finned-tube heat exchangers with multiple-rows of tubes. The effect of different combinations of circular and elliptical tubes on air-side flow and heat transfer characteristics are studied with various inlet air velocities in the range, 0.5–2.5m/s. The results are presented in the form of Nusselt number, friction factor and synergy angle. The results show that at a low inlet velocity, elliptical tube followed by circular tube is a better alternative for heat exchangers with circular tube alone. Along the air flow direction, elliptical tube followed by a circular tube performs better as compared to heat exchanger with circular tube followed by an elliptical tube. On the other hand, at higher inlet air velocity the combination of elliptical and circular tubes performs better than the heat exchanger with elliptical tubes alone. Further, the heat exchanger performance is found to be improved by grouping of elliptical tubes in the upstream region and circular tubes in the downstream region as compared with an alternate arrangement of elliptical and circular tubes. At lower velocity (0.5m/s), the maximum percentage increase of ‘h’ of heat exchanger with grouped elliptical tubes followed by circular tubes combination as compared to heat exchanger with circular tubes alone is 3.37, 4.86 and 5.56 with corresponding decrease of Δp 8.61, 8.75 and 6.94 respectively for N=2, 4 and 6. As compared to heat exchanger with elliptical tubes alone the maximum percentage increase of h with the penalty of Δp=35.53 at v=2.5m/s for N=4.

Simplified model of finned-tube heat exchangers based on the effectiveness method and calibrated with manufacturer and experimental data

A simplified model for predicting the overall thermal performance of finned-tube heat exchangers considering water and air as hot and cold fluids, respectively, is investigated. The model is based on the classical ɛ-NTU method and the thermal convective resistance in each fluid is estimated after conventional-type (Nusselt number) empirical correlations. The model is calibrated with catalogue data of a heating coil. Calibrations of six families of model versions are performed by using different numbers of operating cases ranging from 2 to 320, some of them taking into account the influence of varying properties. The calibrated versions are tested for operating cases listed in the catalogue and the best performing versions are identified, such as the one calibrated with 24 cases and taking into account the effect of the fluid properties, which provided better accuracy than the versions calibrated in previous works. A test of the method robustness is conducted regarding the influence of the initial guessed values of the thermal resistances on the calibration procedure.The validity of the component model is further investigated by using a set of published experimental data for an automotive radiator covering ranges of practical interest of the mass flow rates of both air and water streams, and some versions providing excellent results are identified.The model based on a suitable version previously calibrated and tested is a promising procedure for the modular component simulation of finned-tube heat exchangers, when used as air conditioning heating coils or in other particular applications.

Thermal performance of finned-tube thermoacoustic heat exchangers in oscillatory flow conditions

Heat exchangers play a key role in the overall performance of thermoacoustic devices. Due to the complex nature of oscillatory flows, the underlying mechanism of heat transfer in oscillatory flows is still not fully understood. This work investigates the effect of fin length and fin spacing on the thermal performance of finned-tube heat exchangers. The heat transfer rate between two finned-tube heat exchangers arranged side-by-side in an oscillatory flow was measured over a range of testing conditions. The results are presented in terms of heat transfer coefficient and heat transfer effectiveness. Comparisons are made between experimental results of this work and a number of models, such as the Time-Average Steady-Flow Equivalent (TASFE) model, the Root Mean Square Reynolds Number (RMS-Re) model and the boundary layer conduction model, as well as several empirical correlations in literature. A new empirical correlation is proposed to be used for the prediction of thermal performance for finned-tube heat exchangers in oscillatory flows. The uncertainties associated with the measurement of heat flux are estimated.

The optimization of fin-tube heat exchanger with longitudinal vortex generators using response surface approximation and genetic algorithm

Delta winglet works better than other vortex generators in improving the performance of fin-tube heat exchangers. In this paper, Response Surface Approximation is used to study the effects of the fin pitch, the ratio of the longitudinal tube pitch to transverse tube pitch, the ratio of both sides V 1 , V h of delta winglets and the attack angle of delta winglets on the performance of fin-tube heat exchanger. Firstly, Twenty-nine numerical group experiments including five times repeated experiments at the central point are conducted. Then, the analyses of variable (ANOVA) and regression are performed to verify the accuracy of the polynomial coefficients. Finally, the optimization of the fin-tube heat exchanger using the Genetic Algorithm is conducted and the best performance of j/f (1/3) is found to be 0.07945, which is consistent with the numerical result.

Numerical investigation of a finned-tube heat exchanger with novel longitudinal vortex generators

A novel longitudinal vortex generator (LVG), which is comprised of a modified rectangular wing and an accessory trapezoidal wing, was proposed. The performance of finned-tube heat exchanger with a single row of novel combined winglet pairs (NCWPs) was analyzed. Numerical simulation shows that compared with rectangular winglet pair (RWP), the NCWP generates main vortex with larger centric intensity. Furthermore, the accessory vortex has a lower core and flows into the back of tubes compressing wake regions' size behind tubes due to the influence of accessory wing. It can disturb the developing of boundary layers on the bottom fin and enhance effectively the heat transfer of the wake region behind the tube. Therefore, the performance of heat transfer for finned-tube heat exchanger is significantly enhanced by NCWP with a moderate pressure drop penalty. Compared with the heat exchanger without LVGs, the heat transfer for finned-tube heat exchanger with NCWPs is improved by 1.8–24.2%, with a pressure penalty increase of 1.3–29.1%. In addition, theory analysis and numerical simulation well agree with the experiment results, indicating the reliability of the research.

Condensing droplet behaviors on fin surface under dehumidifying condition: Part I: Numerical model

The condensing droplet behaviors on the fin surface have a significant influence on the performance of fin-tube heat exchangers under dehumidifying conditions. A numerical model for predicting the condensing droplet behaviors was developed. In the model, the mass transfer rates during droplet formation and growth processes and the contact angles of the droplets were introduced into the control equations as source terms; the mass transfer rates were predicted based on the species conservation on the fin and droplet surfaces; the contact angles controlling the droplet movement were predicted based on the modification of existing model by reflecting the effect of air flow force on the droplet movement. Based on the proposed model, the effects of operation conditions and fin geometry on heat and mass transfer characteristics were analyzed. The experimental validation of the proposed model will be performed in the Part II of the present study.

A Novel Approach to Study the Performance of Finned-Tube Heat Exchangers under Frosting Conditions

Frost accumulation due to moist air flowing on a refrigeration coil cold surface impacts negatively on performance. The frost layer growth has an insulating effect i n terms of heat transfer and causes the increase of the air pressure drop by blocking the free flow area across the coil. In this paper a new modeling approach, accounting for heat and mass transfer as well as the hydrodynamics of the problem, is proposed. A related FORTRAN program was developed, allowing the study of a large range of complex refrigerant circuit configurations. This model predicts the dynamic behavior of a refrigeration coil under dry and frosting conditions. Comparisons were made based on the frost mass accumulation and pressure drop across the coil and the results were found to agree reasonably well with experimental results reported in the literature. The model was then applied to study an evaporator typically employed in supermarkets. In terms of refrigerant temperature glide, it was shown that the glide decrease with time because of the decrease of the refrigeration capacity of the coil during the frosting. Further, the air pressure drop is strongly affected by the variation of the free flow area.

Effect of Salt Spray Corrosion on Air-Side Performance of Finned-Tube Heat Exchanger with Hydrophilic Coating Under Dehumidifying Conditions

In this study, the effect of salt spray corrosion on the air-side performance of finned-tube heat exchangers with hydrophilic coating under dehumidifying conditions was experimentally investigated. Artificial accelerated method of salt spray corrosion on the hydrophilic coated heat exchangers was used for simulating the corrosion process of the actual heat exchangers. The experimental results show that the contact angles of hydrophilic coated aluminum fins increase with the increase of salt spray corrosion hours, which results in the degradation of hydrophilicity of fins; the heat transfer is enhanced at lower inlet air velocity and degraded at high inlet air velocity for the pitting corroded heat exchanger with hydrophilic coating; compared with the uncorroded finned-tube heat exchanger with hydrophilic coating at the inlet air velocity ranging from 0.5 to 2.0 m/s (5905.5 to 23622.0 ft/h), the effects of salt spray corrosion on the air-side heat transfer coefficient and on the air-side pressure drop are approximately within the range of −20.5%~8.7% and 1.7%~13.1%, respectively.

A Study on Improving Heat Performance of Fin-Tube Heat Exchangers. Using Vortex Generators

A Study on Improving Heat Performance of Fin-Tube Heat Exchangers. Using Vortex Generators

Heat transfer enhancement by winglet-type vortex generator arrays in compact plain-fin-and-tube heat exchangers

The potential of winglet type vortex generator (VG) arrays for air-side heat transfer enhancement is experimentally evaluated by full-scale wind-tunnel testing of a compact plain-fin-and-tube heat exchanger. The effectiveness of a 3VG alternate-tube inline array of vortex generators is compared to a single-row vortex generator design and the baseline configuration. The winglets are placed in a common-flow-up orientation for improved tube wake management. The overall heat transfer and pressure drop performance are assessed under dry-surface conditions over a Reynolds number range based on hydraulic diameter of 220 ≤ Re ≤ 960. It is found that the air-side heat transfer coefficient increases from 16.5% to 44% for the single-row winglet arrangement with an increase in pressure drop of less than 12%. For the three-row vortex generator array, the enhancement in heat transfer coefficient increases with Reynolds number from 29.9% to 68.8% with a pressure drop penalty from 26% at Re = 960 to 87.5% at Re = 220. The results indicate that vortex generator arrays can significantly enhance the performance of fin-tube heat exchangers with flow depths and fin densities typical to those used in air-cooling and refrigeration applications.

The effects of design and operating factors on the frost growth and thermal performance of a flat plate fin-tube heat exchanger under the frosting condition

An experimental study of the effects of various factors (fin pitch, fin arrangement, air temperature, air humidity, and air velocity) on the frost growth and thermal performance of a fin-tube heat exchanger has been conducted under the frosting condition. It is found that the thermal performance of a heat exchanger is closely related to the blockage ratio of the air flow passages due to the frost growth. The maximum allowable blockage ratio is used to determine the criteria for the optimal operating conditions of a fin-tube heat exchanger. It is also shown that heat transfer rate of heat exchanger with staggered fin arrangement increases about 17% and the time required for heat transfer rate to reach a maximum value becomes longer, compared with those of an inline fin-tube heat exchanger under the frosting condition. The energy transfer resistance between the air and coolant decreases with the increase of inlet air temperature and velocity and with decreasing inlet air humidity.