Fin-and-tube Heat Exchanger Research Articles

Performance enhancement of high temperature fin-and-tube heat exchanger employing winglet combined vortex generators

The fin-and-tube heat exchanger (FTHE) has the advantages of high temperature resistance, compact structure and high efficiency, and has been regarded as the optimal choice for flue gas heat transfer. In this study, the novel winglet vortex generators (VGs) are proposed for the high temperature HTHE where the flue gas with the inlet temperature of 1233 K transfers heat to the water. The effects of the combined VGs and the winglet combined VGs on the flue gas thermal–hydraulic performances are numerically studied. Furthermore, three winglet shapes including the triangular, trapezoidal and rectangular are compared. Moreover, the variations of high temperature HTHE performances with the flue gas mass flow rate are investigated. Compared to the plain fins, the surface heat flux and pressure drop of the combined VGs fins are increase by 15.8 % and 78.9 %, respectively. The designed winglets in the wake region could further reduce the area of the “teardrops” after the tube. The rectangular winglet combined VGs are decided as the best structure, which could maximally increase the surface heat flux by 11.9 kW/m2 compared to the triangular winglet combined VGs, while the pressure drop is slightly increased. Compared to the plain fins, the Nu of the rectangular winglet combined VGs is maximally increased by 16.4 and the maximum hydrothermal performance factor (HTPF) is 1.14. The optimum flue gas mass flow rate is determined as 1 g/s for the designed structures. This work can provide valuable guidance for design and modification of the high temperature HTHEs.

Heat analysis and optimal design of fin-and-tube heat exchanger with X-truss vortex generators

The fin-and-tube heat exchangers (FTHE) are extensively applied in HVAC (Heating Ventilation and Air Conditioning) system, power generation, process industries. The current study dedicates to develop an elliptical fin-and-tube heat exchanger filled with a novel X-VGs vortex generator (X-VGs), so as to improve the hydraulic and heat performance of FTHE. Two different placement schedules of vortex generator have been discussed firstly which are upper-flow (UF) and down-flow (DF)orientations. The effect of streamwise distance, transverse placement and main flow angel on air-side thermal hydraulic performance are investigated subsequently, the friction factor f, Colburn factor j, and performance evaluation criteria (PEC) j/f are analyzed separately corresponding to evaluate heat transfer effect, hydraulic characteristic and comprehensive performance. The results illustrate that increasement of streamwise distance and main flow angel would decrease the thermal hydraulic performance, while there is a nonlinear relationship between longitudinal placement and thermal hydraulic performance. The Genetic algorithm (GA) combined with radial basis function neuro network (RBFNN)prediction model is further employed to obtain the optimal layout of X-VGs, the best layout was obtained in streamwise space ratio at 1.995, longitudinal placement ratio 0.387 and main attack angel ratio 0.053, which achieved the increasement of 109.681% in PEC compared with baseline case.

Study on air-side performance of air-cooled heat exchangers under large air velocity and wet conditions

Humidity condensation and carryover from air-cooled heat exchanger affects human comfort and equipment security in the working environment. Surface treatment with a hydrophilic coating is an effective water drainage and carryover resistance solution. In present study, the condensation carryover and air-side performances of a fin-and-tube heat exchanger (FTHX) and microchannel heat exchanger (MCHX) with different fin pitches and surface treatments were experimentally investigated under large air velocities and different inlet humidity conditions. Hydrophilic treatment of FTHX improved heat transfer and condensation drainage, and reduced air pressure loss. In contrast, with MCHX, hydrophilic treatment did not improve heat transfer and rather increased the air pressure loss. For FTHX, the results showed that, compared with the bare fin, the hydrophilic surface treated fin enhanced the Colburn j factor by 20–60 and 10–40% at inlet air dry/wet bulb temperature of 26.7/19.4 °C (normal humidity condition) and 26.7/23.9 °C (high humidity condition), respectively. The air friction factor f was reduced by namely by 10–40 and 20–40% under normal- and high-humidity conditions, respectively. Condensing water flowed or retained over the fin surface in film, which suppressed the formation of a water bridge among fins, improved water carry-over, and increased the critical air velocity by 50%. However, water film formation over the MCHX enlarged the water stagnant around the fin corner, which increased the air resistance by 5–10%, and increased the probability of the continuous water bridge formation and carryover.

Performance enhancement of fin and tube heat exchanger employing curved delta winglet vortex generator with circular punched holes

The generation of vortices has recently gained attention as a potential passive technique for improving air-side heat transfer in a fin and tube heat exchanger. This study proposes novel configurations of a curved delta winglet vortex generator (CDWVG) with and without circular holes to improve heat transfer in FTHEs. The present study utilizes a three-dimensional numerical analysis to investigate the thermal-hydraulic performance analysis of fin and tube heat exchanger (FTHE) with curved delta winglet vortex generators (CDWVG) with or without circular holes, operating across a wide Reynolds number range (i.e., from 400 to 2000). In addition to being arranged in vertical and horizontal configurations, the CDWVGs are oriented in the same way as the flow direction. Therefore, the pressure distribution, temperature distribution, and flow structure distribution of an FTHE with a four-in-line circular tube configuration are analyzed and compared between FTHE without vortex generator (VG) and five different configurations of CDWVG (i.e., CDWVG without hole, CDWVG with 1 hole, CDWVG with 2 holes, CDWVG with 3 holes and CDWVG with 6 holes). The pressure drop (ΔP), London area goodness factor (LAGF) (j/f), Nusselt number (Nu), and Colburn factor (j) are also used to evaluate the thermo-hydraulic performance of FTHE. The FHTE performance with CDWVGs can be affected by the number of punched holes, which is evaluated using a dimensionless number including Performance Evaluation Criteria (PEC), Colburn factor, etc. The thermo-hydraulic efficiency of the FTHE is improved significantly by using CDWVGs with circular punched holes. Nusselt number decreases across all the VG configurations (i.e., CDWVG without hole, CDWVG with 1 hole, CDWVG with 2 holes, CDWVG with 3 holes, and CDWVG with 6 holes) due to the lower flow resistance. Compared to other CDWVG configurations, the 6-hole configuration of CDWVG is the most effective. The Nusselt number of CDWVG with 6 holes increases by 77.25% and 42.51% at Reynolds numbers of 400 and 2000, with respect to fin and tube heat exchangers without vortex generator, respectively. On the other hand, friction is decreased by 5.11%. Therefore, when considering the London area goodness factor, CDWVG with six holes is found to be superior to other CDWVG configurations.

Performance enhancement of fin and tube heat exchanger employing curved trapezoidal winglet vortex generator with circular punched holes

Vortex generation is a potential passive technology for increasing the heat transfer rate in the air side of fin and tube heat exchangers (FTHEs). This study proposes novel configurations of a curved trapezoidal winglet vortex generator (CTWVG) with and without circular holes to improve heat transfer in FTHEs. As per the literature, the streamlined form of the trapezoidal winglet demonstrates high heat transfer enhancement with low flow loss and pressure drop. But still, different design configurations are possible to augment the heat transfer characteristics of CTWVG further. The current study investigates the novel configurations of CTWVG (i.e., CTWVG without hole, CTWVG with 1 hole, CTWVG with 2 holes, CTWVG with 3 holes and CTWVG with 6 holes). A three-dimensional computational model is utilized to evaluate the thermal-hydraulic efficiency of FTHEs fitted with CTWVGs with or without circular holes for Reynolds numbers ranging from 400 to 2000. A common flow-down configuration of the CTWVG with circular tubes array is used to reduce the wake region. The thermo-hydraulic performance and flow structure of FTHE with four inline circular tube configurations are compared without VG and CTWVG with or without holes. Pressure drop (ΔP), Nusselt number (Nu), friction factor (f), Colburn factor (j), and London area goodness factor (j/f) are used for the thermal-hydraulic performance comparison. Results show that the number of punched holes has an impact on the FTHE performance, which is measured using a dimensionless number as performance evaluation criteria (i.e., (j/jo)/(f/fo)). CTWVGs with circular punched holes significantly increase the FTHE's thermo-hydraulic performance. The results indicate that the flow resistance is reduced in all cases (i.e., VG with no holes, VG with 6 holes, VG with 3 holes, VG with 2 holes, and VG with 1 hole) with a minor decrease in the Nusselt number. The CTWVG with six holes performs better than other CTWVG configurations. At Reynolds numbers 400 and 2000, the Nusselt number for CTWVG with six holes enhanced by 75.25% and 40.10%; pressure drop increased by 107.88% and 125.51%, respectively. On the other hand, friction is reduced by a factor of 8.1% in CTWVG with 6 holes compared to CTWVG without holes. The CTWVG with six holes performs better than other CTWVG configurations reported in the literature [48,54]. HTPF has increased by 30.96% (compared to rectangular winglet [48]) and 27.69% (compared to curved rectangular winglet [54]) with respect to values reported in the literature. The London area goodness factor (LAGF) has been increased by 275% compared to Modi et al. [48].

Air side performance of fin-and-tube heat exchangers with a hydrophilic layer under low-temperature frost-free conditions

In this paper, to provide a reference for the application and thermal design of fin-and-tube heat exchangers (FTHEs) under low-temperature frost-free conditions (LTFFCs) and to improve the dehumidification performance of cooling dehumidifiers in greenhouse environments of low temperature and high humidity, the air side performance of FTHEs with a hydrophilic layer under LTFFCs was experimentally investigated. The experimental findings were compared with the results of ordinary temperature conditions (OTCs). The critical environmental conditions for frosting FTHEs were obtained. The applicability of existing performance prediction correlations under the LTFFCs was discussed and corrected. The findings show that at the same inlet temperature difference between air and refrigerant, the LTFFCs have smaller heat transfer rates than the OTCs. Varying inlet conditions showed that in the test conditions range, the test FTHEs are at risk of frosting when the inlet air relative humidity is 95 %, inlet air temperature is 281 K, frontal velocity is 1 m/s, and inlet refrigerant temperature is as low as 270 K. The data analysis revealed that existing correlations could not accurately predict the experimental data under LTFFCs. By adding the correction coefficients for temperature and relative humidity to existing correlations, the corrected correlations describe the experimental data for 90.6 % and 87.5 % of the heat transfer factor and mass transfer factor, respectively, within ± 20 %, and the deviation of all friction factors is within ± 10 %. The mean deviations of the heat transfer factor, mass transfer factor, and friction factor are 8.2 %, 10.8 %, and 4.8 %, respectively.

Air side performance characterization of wavy Fin-and-tube heat exchangers having elliptic tubes with large waffle heights

Demand of less energy consumption and higher energy efficiency suggests increasing heat transfer performance of a fin-and-tube heat exchanger. This paper experimentally and numerically examines the air side performance of wavy fin-and-tube heat exchangers (FTHXs) with elliptic tubes. In a properly regulated and evenly distributed airflow supply loop, the inlet/outlet temperatures and pressure drops across the test section are obtained using two measuring meshes and a differential pressure transducer to resolve thermal and frictional outcomes in terms of the heat transfer coefficient and pressure drop. The theoretical formulation considers the thermo-fluid analysis of crossing airflows over the wavy finned tube heat exchanger. In this research, the test heat exchanger contains elliptic tubes incorporated with 4-row wavy fins, while the proposed design adopts a large setting of 3.24-mm waffle height and 3.02-mm fin pitch, respectively. The predicted heat transfer coefficients and pressure drops are in good agreement with the measured data at varied inlet air velocities to validate the CFD model. Numerical simulations are then extended to investigate the influences of waffle height, fin pitch, wave length and inlet air velocity on thermofluid characteristics of FTHXs. Six common correlations of Colburn factors (j) and friction factor (f) factors are compared with predictions to evaluate their applicabilities for reasonable estimates of thermal and frictional performance of FTHXs. It is noticed that the correlation by Wang et al. can achieve the most accurate results in calculating the j and f factors.

Flow and heat transfer in a plain fin-and-hexagonal tube heat exchanger with different side ratios

Improving the thermo-hydraulic performance of heat exchangers (HEs) can considerably manage the energy requirements in various engineering processes. The fin-and-tube heat exchangers (FTHEs) are extensively utilized in recent decades, and they provide substantial benefits over the typical HEs such as high heat transfer surface. The shape and geometry of the tubes remarkably affect the thermal efficiency and pressure drop of these devices. There are many experimental and numerical investigations relating to improving the thermo-hydraulic performance of FTHEs with circular and elliptical tubes in the literature. In the current research, five various hexagonal tubes with different side ratios were utilized to enhance the performance of an FTHE. The impact of various hexagon side ratios on heat transfer capacity and fluid flow characteristic of the FTHE at different Reynolds numbers has studied numerically. According to the obtained results, the plain-fin-and hexagonal tube HE with the side ratio of 0.25 had the best performance. Although the lowest values of the Colburn factor and the weakest heat transfer belong to the FTHE with the side ratio of 0.25, it is preferred to circular tube HEs due to the lower pressure drop they cause.

Development of design guidelines for fin-and-tube heat exchangers with low-GWP refrigerants

Regulatory changes worldwide are requiring air conditioning and heat pump equipment manufacturers to switch refrigerants to alternatives with reduced global warming potential (GWP). Design of air-to-refrigerant fin-and-tube heat exchangers (FTHXs) is critical to overall performance of this equipment and is not currently well understood with low-GWP refrigerants. This paper presents a simulation study exploring the impact of design changes for a FTHX used in an indoor residential evaporator originally designed for R410A. Simulation results are used to generate design guidelines for FTHXs using HFO refrigerants R1234yf and R1234ze(E), evaluated using cooling capacity, refrigerant-side pressure drop and ratio of the two as critical metrics. When evaluated at identical operational conditions, with fixed refrigerant outlet superheat, it was found that for a fixed slab size, the FTHX was most sensitive to number of circuits, followed by tube diameter, number of tubes in the FTHX, and fin density. For the low-GWP HFOs, circuitry modifications led to maximum increase in FTHX capacity of 20%, and maximum decrease in refrigerant-side pressure drop of 88.6%. Based on simulation results, it is concluded that additional coil face area is required to match both capacity and refrigerant pressure drop, compared with R410A, this is demonstrated with two proposed FTHX designs. One design prioritizes increased FTHX capacity, and the other a reduction in refrigerant pressure drop. All these results culminated in design guidelines for HFOs that suggest it will be challenging to achieve both the same capacity and pressure drop characteristics as R410A without modifications to FTHX size.

Gradient-based optimizer for economic optimization of engineering problems

Abstract Optimization of the heat recovery devices such as heat exchangers (HEs) and cooling towers is a complex task. In this article, the widely used fin and tube HE (FTHE) is optimized in terms of the total costs by the novel gradient-based optimization (GBO) algorithm. The FTHE s have a cylindrical tube with transverse or longitudinal fin enhanced on it. For this study, various constraints and design variables are considered, with the total cost as the objective function. The study reveals that the GBO provides promising results for the present case study with the highest success rate. Also, the comparative results suggest that GBO is the robust optimizer in terms of the best-optimized values of the fitness function vis-à-vis design variables. This study builds the future implications of the GBO in a wide range of engineering optimization fields.

Experimentally validated numerical modeling of heat transfer in crossflow air-to-water fin-and-tube heat exchanger

The aim of this work is to analyze different tube-side inlet boundary conditions in order to properly model heat transfer mechanism in a crossflow air-to-water fin-and-tube heat exchanger (FTHEX). For accurately describing conjugated heat transfer, the entire flow length on both fluid sides should be considered. For problem simplifying, domain that include a segment inside the heat exchanger in the water flow direction, is used. This paper studies the effect of fully conjugated heat transfer, including air-side and water-side thermal resistances. Three different numerical models are analyzed by varying the tube-side inlet boundary conditions. In one of these models the water-side thermal resistance is neglected and other two models consider the water-side thermal resistance, but with different velocity and temperature boundary conditions at the water inlets: uniform and fully developed. To validate the proposed numerical models, measurements have been performed on a crossflow air-to-water plain FTHEX. The results show that the numerical model with the fully developed water inlet boundary condition coincides best with the experimental data. It can be concluded that the water-side thermal resistance cannot be neglected, especially when evaluating the air outlet temperature and the overall heat transfer coefficient of heat exchanger.

Heat Transfer Enhancement of Crossflow Air-to-Water Fin-and-Tube Heat Exchanger by Using Delta-Winglet Type Vortex Generators

The aim of this work is to numerically analyse fluid flow and heat transfer characteristics in a crossflow air-to-water fin-and-tube heat exchanger (FTHEX) by implementing two configurations of delta-winglet type vortex generators at the air side: delta-winglet upstream (DWU) and delta-winglet downstream (DWD). The vortex generators are mounted on a fin surface and deployed in a “common flow up” orientation. The effects of attack angles of 15°, 30° and 45° on air-side heat transfer and pressure drop were examined. Since the implementation of the full-size model would involve large numerical resources, the computational domain is simplified by considering a small segment in the direction of water flow. The fully developed temperature and velocity boundary conditions were set at the water inlets. To validate the defined mathematical model and numerical procedure, measurements have been performed on a plain FTHEX. The air side Reynolds number, based on hydraulic diameter, was in the range of 176 ≤ ReDh ≤ 400 and water side Reynolds number, based on inner tube diameter, was constant Redi = 17,065. The results have shown that the highest increase in the Colburn factor j (by 11–27%) and reduction in the air-side thermal resistance fraction (from 78.2–76.9% for ReDh = 176 to 76–72.4% for ReDh = 400) is achieved by using the DWD configuration with attack angle 45°. In addition, the overall heat transfer coefficient is improved by up to 15.7%. The DWD configuration with the attack angle 30° provides the greatest improvement in the heat transfer to pressure loss ratio, 5.2–15.4% over the range of ReDhstudied.

Parametric CFD study for finding the optimal tube arrangement of a fin-and-tube heat exchanger with plain fins in a marine environment

In the past, fin-and tube heat exchanger (FTHE) tube pattern ratios have been largely based on ad-hoc design principles. Here, we investigate the optimal tube arrangements for a FTHE with plain fins in marine environments represented by two different air types; one for unfiltered air with high condensation rate and one for clean dry filtered air conditions. The thermal-hydraulic efficiency of the FTHE design is measured by comparing a modified ratio of Colburn j-factor and Fanning friction factor. The regression model generated from the CFD data is then used to identify the maximum efficiency for two design specific fin pitches separately. We identified two optimal tube patterns: one for a large fin pitch for unfiltered air, and another for a small fin pitch for filtered air. Manufacturing restrictions were found to significantly limit the maximum achievable efficiency of a tube pattern. By neglecting the related manufacturing restrictions, 4 % higher efficiency for a fin pitch of 1.5 mm and 23 % higher efficiency for a fin pitch of 3.5 mm is achieved. Without any application specific limitations or manufacturing restrictions the fin pitch 1.5 mm can have a 36 % increased efficiency than fin pitch 3.5 mm. These novel results show that development in manufacturing have potential for significant improvements in thermal-hydraulic efficiency. • Fin-and-tube heat exchanger is studied with open source conjugate CFD models. • The smaller fin pitch F p = 1 . 5 mm offers better JF performance than the F p = 3 . 5 mm. • A higher JF performance can be achieved by neglecting the manufacturing restrictions. • Unconventional tube arrangement ratio values P t / P l ≠ 1 . 1547 offer the best JF performance.

Comparison of Different Fin and Tube Compact Heat Exchanger with Longitudinal Vortex Generator in CFU-CFD Configurations

Over the last decades several studies have searched for improved Fin and Tube Heat Exchanger (FTHE) designs capable of providing the best thermo-hydraulic performance. The present study aims at quantifying and comparing the thermo-hydraulic performance of different FTHE configurations. Six different designs were analyzed. The first FTHE consisted of an in-line circular tube arrangement and the last one was a FTHE with staggered oval tube with two pairs of Delta Winglet Vortex Generators (DWVG) in common flow up–common flow down (CFU-CFD) configuration. The best performance was obtained using DWVG in CFU-CFD orientation. This configuration enabled a 90% increase of the thermal performance factor when compared with the first case, using only two pairs of vortex generator´s per tube.

Fin and tube heat exchanger: Constructal thermo-economic optimization

In this study, constructal (branch type) fin and tube heat exchanger (FTHE) is modeled and optimized. Effectiveness and total annual cost (TAC) are selected as objective functions and 8 variables for each section of exchanger are considered as design parameters (16 design parameters in total). Then, multi objective form of genetic algorithm is used to find the optimal Pareto front. The optimization is implemented for conventional FTHE as well and their results are compared with branch type condition. The optimum results show 6.65% improvement in the maximum effectiveness in the branch type condition compared with conventional FTHE. In the constructal state, lower volume is selected in the second section as compared with the first section. The same trend is also found for heat transfer surface area. Finally, optimum design parameters in terms of effectiveness for the both studied conditions are illustrated and discussed.

Optimization of centrifugal fan position in a particular VRF outdoor unit for European market

Variable refrigerant flow systems (VRF), in which refrigerant flows directly through long connecting pipes into different indoor units, are nowadays having more and more market share in central air-conditioning industry. A special flat structure of air-cooled VRF outdoor unit is expected in European market due to local architecture characteristics. Centrifugal fans with forward-curved blades are suitable under this situation. However, the layout concerning the fan position is of key importance for the heat exchange performance. Four layouts with different fan position arrangement in a VRF outdoor unit supposed to reach nominal cooling capacity of 22kW were initially designed and optimized by Ansys. Air volume rate and uniformity through the fin and tube heat exchanger (FTHE) were investigated with velocity contours. When FTHE was set perpendicularly forming a triangle compact space with neighboring cabinet shells, simulations showed a better layout in which the two fans were put side by side but with one near front and the other near rear shell in the bigger empty space. Further adjustment in position details was also carried out via more simulation on selected planes and finally, air volume measurement and nominal capacity measurement were made, matched with four ducted indoor air-conditioning units, showing good performance.

Thermal performance augmentation of fin-and-tube heat exchanger using rectangular winglet vortex generators having circular punched holes

In fin-and-tube heat exchangers (FTHEs), vortex generation is found as one of the promising emerging passive technique for augmenting the rate of heat transfer on air-side. In the present study, three dimensional numerical study is performed to evaluate thermo-hydraulic performance of FTHEs equipped with rectangular winglet vortex generators (RWVGs) with circular punched holes for Reynolds number varying from 400 to 2000. Various cases of RWVGs without and with circular punched holes (1, 2, 4, and 6 holes) are considered. The pairs of RWVG are placed in common flow down (CFD) orientation behind the circular tubes to improve wake management. The effect of number of punched holes is compared with non-VG baseline case and RWVG without hole for flow structure and thermo-hydraulic performance of FTHE with four inline circular tube arrangement. Comparison is also carried out with thermo-hydraulic performance criterions which include Nusselt number (Nu), Pressure drop (ΔP), friction factor (f), colburn factor (j), London area goodness factor (j/f). Effects of number of punched hole on the performance of RWVGs is also evaluated using dimensionless number (j/j0)/(f/f0) as performance evaluation criteria (PEC) . It is observed that RWVGs with circular punched holes remarkably improve the thermo-hydraulic performance of FTHE. The punched holes exhibit reduction in the flow resistance for all cases with slight reduction in Nusselt number. RWVG with 6 holes shows better performance as compared to other cases. Nusselt number for RWVG with 6 holes increases about 45.95% and 57.37% at Reynolds number 400 and 2000, respectively. However, friction factor is decreased by about 13.81%. Thus, from the point of view of London area goodness factor, RWVG with 6 holes found better than other considered cases of RWVG.

Thermal calculations of plate–fin–and-tube heat exchangers with different heat transfer coefficients on each tube row

In finned tube heat exchangers, the first rows of tubes are most effective when the air velocity in front of the exchanger is less than about 3.5 m/s. The heat transfer coefficient (HTC) decreases with each subsequent row and stabilizes only from the fifth row onwards. The paper examines a two-pass double-row plate-fin and tube heat exchanger (PFTHE) made of circular or oval pipes. A method for determining the air side Nusselt number on individual pipe row was developed, using the results of CFD (Computational Fluid Dynamics) modelling of the heat exchanger. Also, a heat transfer correlation was found for the mean HTC for the whole PFTHE using CFD modelling. The correlations based on the results of CFD modelling match very well the empirical correlations based on experimental tests of two car radiators. The analysis shows that the first rows of PFTHE are the most effective in terms of thermal effectiveness. By building a heat exchanger with two rows of pipes, it is possible to reduce investment expenditures at the same thermal output significantly. Heating systems with PFTHE air heaters with fewer rows of pipes are characterized by lower fuel consumption due to their higher efficiency. The investment costs for automotive radiators can also be reduced. The introduction of PFTHE heat exchangers with fewer pipe rows has a positive impact on the environment. Both material expenditures on the construction of PFTHE, energy consumption by the air fan, and fuel consumption for heating purposes are reduced.

Numerical investigation to predict optimum attack angle combination of longitudinal vortex generators in compact heat exchangers for thermo-hydraulic heightened performance

The current 3-D numerical analysis explores the effect of combinations of rectangular winglet pairs (RWPs) having different attack angles (i.e. 5°, 15° and 25°) along a row of the tube array, on the performance of the fin and tube heat exchanger (FTHE). The considered airside Reynolds number Re ranges from 500 to 900. In total, six combinations of three attack angle vortex generators (VGs) have been numerically analysed namely 5°-15°-25°, 5°-25°-15°, 15°-5°-25°, 15°-25°-5°, 25°-5°-15° and 25°-15°-5°. The performance of the FTHE is represented by area goodness factor. The performance rankings of the FTHEs are also obtained by the MOORA method. Finally, 5°-25°-15° case provides the best thermal hydraulic performance for which heat transfer coefficient (h) is increased by 68.20% at Re = 500 and 81.78% at Re = 900, with a significant pressure drop penalty.

Deposition of dry particles on a fin-and-tube heat exchanger by a coupled soft-sphere DEM and CFD

In this study, a novel computational model is utilized for investigating fouling of two commonly encountered heat exchanger fin shapes in an air-conditioning application. The computational method utilizes the discrete element method (DEM) coupled with a large-eddy simulation (LES) framework. The fin-and-tube heat exchangers (FTHE) are investigated for three different Reynolds numbers (ReDh=243, 528, 793), three different particle sizes (Dp= 5, 10, 20 µm) and two different adhesive particle types based on the experimental values in the literature. The code is first benchmarked from the CFD and DEM viewpoints. A comprehensive fouling study of the FTHE’s, consisting of altogether 36 simulations, is then carried out. The major numerical findings of the paper consist of the following four features. First, with low adhesive particles, the plain fin shape has a 3.45 higher volume fouling rate with ReDh=793 than at ReDh=264. With the herringbone fin shape, and the low adhesive particles, the volume fouling rate is 1.76 higher with ReDh=793 than at ReDh=264. Second, for the high adhesive particles, the plain fin has a 5.4 times higher volume fouling rate at ReDh=793 than for ReDh=264. The herringbone fin shape has a 3.92 times higher volume fouling rate with the highest Reynolds number of ReDh=793 compared to ReDh=264. Third, high adhesive particles have 3.0 times higher volume fouling rate than low adhesive particles for both fin shapes, all particle sizes and all Reynolds numbers combined. And finally, herringbone fins have 1.74 times higher volume fouling rate than plain fins for low adhesive particles. For high adhesive particles, herringbone has 1.8 times higher volume fouling rate and when both particle types are summed together, herringbone has a 1.78 times higher volume fouling rate than the plain fin shape. As a major finding of the study, the high adhesive particle collection efficiency increases monotonously with the Stokes and Reynolds numbers while low adhesive particle collection efficiency poses a non-monotonous trend.