Slit Fin Research Articles

Design and simulation of a new type of fin-and-tube heat exchanger with trapezoidal slit fins

Slit fin-and-tube heat exchangers are extensively utilized in industry. The design of fin structure is crucial for improving the performance of heat exchanger and reducing energy losses. In this study, a new type of fin-and-tube heat exchanger with trapezoidal slit fins was proposed in this study. To determine the performance of the fins, physical and mathematical models of heat exchanger with the fin spacing Fp of 2.65 mm were established. The effects of structural parameters on heat exchanger performance were investigated by numerical simulation, which includes the slit height Sh, slit width Sw, transverse tube spacing Pt, and longitudinal tube spacing Pl. The effects of the four structural parameters on the comprehensive performance were analyzed by the evaluation index. The results revealed that the comprehensive performance of trapezoidal slit fins had increased by 9.6 % compared to flat fins. Furthermore, the influence degree of structural parameters on heat transfer performance was obtained based through the orthogonal experiments. The order of influence degree was as follows: Pl > Pt > Sh > Sw. Additionally, the optimal parameter combination was also obtained as follows: Sh = 1.47 mm, Pt = 42 mm, Pl = 27.5 mm, and Sw = 4 mm.

Numerical investigation on the effects of slotted height on performance of louver and slit fins at different fin pitches

In this paper, the effects of slotted height at different fin pitches are analyzed in detail, aiming to investigate the function and optimal ratio of slotted height to fin pitch. In the cases of high Reynolds number for louver fin, the ?bimodal phenomenon? of heat transfer coefficient begins to appear with the increasing slotted height. As the slotted height is about half of the fin pitch, the heat transfer coefficient has a local minimum value, of which there are two peaks on both sides. How-ever, the pressure drop has been increasing with the increasing slotted height. The optimal slotted height under different fin pitches is more instructive than the optimal louver angle. For slit fin, the heat transfer coefficient increases first and then decreases with the increasing slotted height, so does the pressure drop. Meanwhile, as the slotted height is about 0.3~0.45 times and 0.5~0.65 times of fin pitch for louver fin and slit fin, respectively, the comprehensive performance can reach a maximum. The optimal comprehensive performance under 1.2 mm fin pitch is greater than the optimal comprehensive performance under 1.8 mm fin pitch. For lower Reynolds numbers, the optimal comprehensive performance of louver fin is roughly similar to the slit fin. For higher Reynolds numbers, the optimal comprehensive performance of louver fin is greater than that of slit fin.

Multi-objective optimization of geometrical parameters of laterally perforated on silt fin by gray relation analysis based on Taguchi method

In this paper, slit fin with lateral perforations are presented and the optimal parameters of the perforation on the silt fin are determined. The effects of the three design parameters of perforation length H, perforation height P and tilt angle θ on the j and f-factor are analyzed using gray relation analysis (GRA) base on the Taguchi method (TM). Numerical simulations were performed for different combinations of the three geometric parameters for 16 cases. Based on the Taguchi method (single-objective optimization) analysis, out of the three perforation parameters, the perforation length H exhibited the most pronounced impact on the j-factor, boasting a substantial contribution ratio of 33.1 %. The contribution ratios of the perforation length H, height P, and tilt angle θ influencing the f-factor were determined to be 31.1 %, 46.2 %, and 18.4 %, respectively. The optimal combination of parameters for perforation on the slit fins was obtained by Gray relation analysis (multi-objective optimization) with values of H = 1/3, P = 1 mm and θ = 90°, representing the highest j-factor and the lowest f-factor of the parameter configuration, in contrast to the remaining parameter combinations, the SNR values for its j and f-factor stand at −49.14 and 35.1, respectively while the JF-factor also outperformed those of the other 16 groups of cases. Finally, the results obtained by Taguchi method and GRA are analyzed in conjunction with flow behavior.

Numerical design of efficient slit fin surfaces with strips in different directions

In this article, 3D numerical simulations are performed to study the heat transfer performances of different fin surfaces for a one-row fin-and-tube heat exchanger. Five fin surfaces are evaluated: the first is the plain fin surface for comparison purposes, and the other four are slit fin surfaces, named Slit 1, Slit 2, Slit 3, and Slit 4. The global geometry parameters of the five fin surfaces are all the same. The Slit 1 and Slit 2 fin surfaces have parallel strips normal to the incoming airflow, the difference is Slit 1 has five strips, and Slit 2 has six strips. The Slit 3 and Slit 4 fin surfaces also have six strips, whereas the slits of Slit 3 are along with the radial direction of the tubes, and the slits of Slit 4 are arranged in the quasi-radial direction of the tubes. The heights of the strips for the four slit fin surfaces are kept the same. The grid-independent check and the comparison with experimental data are conducted in advance to make sure the numerical results are reliable. Under identical pumping power, the heat transfer improvement is from 5.3% to 37.3% for the Slit 1 fin surface, 5.3%–41.3% for the Slit 2 fin surface, 6.5%–42.3% for the Slit 3 fin surface, and 8.9%–47.3% for the Slit 4 fin surface compared to the plain fin surface within the studied Reynolds number range (226–1805). To reveal the heat transfer enhancement mechanisms, the effects of slits on the heat transfer coefficient and the fin efficiency are analyzed in detail.

Experimental analysis on drying performance of a condensing clothes dryer with two new plate-fin heat exchangers

In this paper, an off-set fin heat exchanger (OSFHE) and a flying-wing fin heat exchanger (FWFHE) were developed for the condenser of a condensing clothes dryer. They were used to replace the slit fin heat exchanger (SFHE), which is the prototype condenser. Performance parameters, like condensation rate, IEC energy efficiency index (EEI) and specific moisture extraction rate (SMER), were used to assess the dehumidification performance of the heat exchangers and the drying performance of the dryer. Though the fin areas of OSFHE and FWFHE are 20% and 34.2% less than that of SFHE, the experiment results indicated that OSFHE and FWFHE had a faster condensation rate than SFHE during the main drying stage. And the heat exchanger with a faster condensation rate also led to less power consumption of the dryer in most tests. Compared with using SFHE, using OSFHE could decrease the EEI of the dryer by 0.43%. Using FWFHE could reduce the EEI of the dryer by 1.19% and improve the EU energy efficiency class of the dryer from Class C to Class B. Both OSFHE and FWFHE are able to replace SFHE and become a new generation of condensers for clothes dryers.

Numerical investigation of slit fin at different Reynolds numbers: A sensitivity analysis and optimization by Taguchi methodology

The parametric study is carried out by Taguchi methodology, including twenty-seven cases with different combinations of key parameters, involving Reynolds number(Re), transverse pitch(Pt), longitudinal pitch(Pl), number of tube rows(N) and fin pitch(Fp). Firstly, the distributions of heat flux and shear stress are displayed. The heat flux decreases sharply along the flow direction, but the distribution of shear stress in front row is almost same to that in rear row. Secondly, the analysis of variance(ANOVA) is carried out, which indicates that Re is the most sensitive parameter on j-factor and f-factor, and its statistical significance is much greater than that of structural parameters. Furthermore, the sensitivity analyses of structural parameters at different Re are performed. For j-factor, the contribution ratio of Fp is the biggest at Re = 900, the contribution ratio of N is the biggest at Re = 1800 or Re = 2700. For f-factor, the contribution ratio of Fp is the biggest at Re = 900, the contribution ratio of Pl is the biggest at Re = 1800 or Re = 2700. For comprehensive performance, the contribution ratio of N has always been the biggest at different Re. Finally, the optimal combination of structural parameters is obtained, and its comprehensive performance is improved by 2.73%–3.23% at different Re.

Performance evaluation of fin-and-tube heat exchangers in an outdoor unit considering air flow mal-distribution

The heat transfer capacity of air conditioning outside units is inextricably related to fins and airflow distribution, and research on the combination of the two is lacking. To analyze the fins and fin-and-tube heat exchanger, three-dimensional numerical models of the fins and flow field of the outdoor unit are created in this paper. On the one hand, the heat transfer and fluid flow characteristics of the fins are quantitatively evaluated and analyzed. On the other hand, the resistance coefficients of the porous media are numerically fitted to study the uniformity of the air velocity distribution on the surface of the heat exchanger. Two indexes, the total integrated heat capacity and JF-factor, are applied to evaluate the performance of the fins and fin-and-tube heat exchanger on the overall and specific levels, respectively. The results indicate that slit fins perform better than wave fins at heat transfer, whereas plain fins perform the worst. However, improved heat transfer performance results in increased pressure drop, which has a two-sided effect. It causes both a decrease in air volume flow rate and an increase in air distribution uniformity. Comparing the comprehensive performance of different fins, JF-factors of slit fins and wave fins are on average 20.95% and 14.36% higher than plain fins. In terms of overall performance, slit fins and wave fins have higher integrated heat exchange capacities than plain fins by 18.0% and 9.33%, respectively.

Erratum in “Experimental measurements and modelling of vapor-liquid equilibria for four mixtures of 2,3,3,3-tetrafluoropropene (R1234yf) with 1,1,1,2-tetrafluoroethane (R134a) or 1,1-difluoroethane (R152a) or trans-1-chloro-3,3,3-Trifluoropropene (R1233zd(E)) or 2-Chloro-3,3,3-trifluoropropene (R1233xf)” [Int. J. Refrigeration, 140 (2022) 172–185, https://doi.org/10.1016/j.ijrefrig.2022.05.006

The heat transfer capacity of air conditioning outside units is inextricably related to fins and airflow distribution, and research on the combination of the two is lacking. To analyze the fins and fin-and-tube heat exchanger, three-dimensional numerical models of the fins and flow field of the outdoor unit are created in this paper. On the one hand, the heat transfer and fluid flow characteristics of the fins are quantitatively evaluated and analyzed. On the other hand, the resistance coefficients of the porous media are numerically fitted to study the uniformity of the air velocity distribution on the surface of the heat exchanger. Two indexes, the total integrated heat capacity and JF-factor, are applied to evaluate the performance of the fins and fin-and-tube heat exchanger on the overall and specific levels, respectively. The results indicate that slit fins perform better than wave fins at heat transfer, whereas plain fins perform the worst. However, improved heat transfer performance results in increased pressure drop, which has a two-sided effect. It causes both a decrease in air volume flow rate and an increase in air distribution uniformity. Comparing the comprehensive performance of different fins, JF-factors of slit fins and wave fins are on average 20.95% and 14.36% higher than plain fins. In terms of overall performance, slit fins and wave fins have higher integrated heat exchange capacities than plain fins by 18.0% and 9.33%, respectively.

Dissimilar heat transfer enhancement by introduction of slit fins in turbulent channel flow

We have conducted direct numerical simulations for turbulent heat and momentum transfer in plane channel flow with fins which are streamwise-slit flat plates. The slit fins are introduced by the immersed boundary method. All simulations were conducted at the friction Reynolds number Reτ = 200 and the Plandtl number Pr = 1. It is found that the slit fins lead to dissimilar heat transfer enhancement. As the thickness of the fins is increased, heat and momentum transfer are simultaneously enhanced, and significant dissimilarity between heat and momentum transfer is observed. The dissimilar heat transfer enhancement is attributed to large-scale roll structures.

Prediction and analysis of thermal-hydraulic performance with slit fins in small diameter (3 mm to 4 mm) heat exchangers

The simulation model describes the thermal-hydraulic performance and is verified well by comparing with the experimental data. The 122 runs taking 7 geometric parameters and Reynolds number into account are carried out based on the Response Surface Methodology (RSM). The correlations of the heat transfer (j-factor) and flow friction (f-factor and Eu-number) in 3 mm diameter are proposed. The mean deviations of the correlations with j-factor, f-factor and Eu-number are 3.78%, 2.56% and 2.51% respectively. The effects of 7 geometric parameters are investigated using the RSM model in detail at Re = 500, and it can be found that the height of the slit (Sh) has the greatest influence on j-factor. The differences in the change rate of f-factor and Eu-number are emphatically analyzed. And the effects of the transverse tube pitch (Pt) on f-factor and Eu-number are opposite. The f-factor is positively correlated with Pt, while the Eu-number is negatively correlated with Pt. In addition, the coefficients of correction for j-factor, f-factor and Eu-number are obtained to make available for different collar diameters. In the range of 3.19–4.19 mm collar diameter, the mean deviations of the modified correlations including j-factor, f-factor and Eu-number are 6.24%, 5.46%, and 4.26% respectively.

Numerical optimization of a heat exchanger with slit fins and vortex generators using genetic algorithms

Abstract Heat exchangers are devices very commonly found in heating and air conditioning appliances. This work is about the optimization of compact heat exchangers with three rows of tubes and slit fins, using built-in longitudinal vortex generators on the fins. The Colburn factor and the friction factor were obtained out of numerical simulations from a universe of 32 geometries. Geometries were selected using the Latin hypercube design, and were numerically simulated. Two objective functions were employed as surrogate models for the Colburn and friction factor. The functions were determined by multiple regression with a level of R square higher than 99.5%. A multi-objective numerical optimization was made, to find the best location for delta winglet vortex generators and its angle of attack; searching for an increase of heat transfer and a low value in pressure penalty. Group of optimal geometries was obtained, because of the optimization process using genetic algorithms. The geometry, with the best performance was simulated, and the results were used to validate the optimization process. This geometry, when compared to the slit fin without vortex generators (smooth condition), increased by 8.74% the heat transferred and augmented by 14.77% the pressure drop. The angle of attack, module, and module angle of the optimized geometry were 49.86°, 5.08 mm and 22.51° respectively.

Numerical study on the heat transfer and pressure drop characteristics of fin-and-tube surface with four round-convex strips around each tube

In this paper, a three-dimensional numerical investigation is performed for both heat transfer and pressure drop of a new kind of slit fin applied to heat exchangers in air compression industry by FLUENT. A comparison between this new slit fin and normal plain fin is made. It is found that the flow and heat transfer come into full development stage after 12 rows. The effects of seven different parameters on the fully developed heat transfer performance are examined and all the calculation results agree well with the field synergy principle.Among these parameters,reducing spanwise fin pitch has the largest performance improvement. The optimum values are found for the height of slit and the length of rear slit. The correlations for j and f factors are proposed, which take four and five dimensionless geometric parameters into consideration, respectively.

Condensate drainage on slit or louvered fins in microchannel heat exchangers for anti-frosting

When the condensate isn’t removed in time, it is easy to cause frosting, which limits the application of microchannel heat exchangers (MCHE). Although some methods can measure well about improving the condensate drainage performance of the MCHE, the quantitative value of drainage amount can not be given in the operation condition of one actual refrigeration system. The objective of this study included developing a test facility to investigate condensate drainage in MCHE, and study condensing in MCHE to valuate different condensate detecting methods. In the present study, condensate drainage was experimentally investigated on louvered and slit fins in MCHE for anti-frosting. Experimental data of drainage amount, the moist air pressure drop across the test sample and the heat capacity of the MCHE were recorded. The calculation formula for drainage amount was set up. The rate of condensate drainage from the experimental system is mainly a function of the velocity with the dew point temperature and the dry bulb temperature of the moist air unchanged. The calculation value and the test value of the drainage amount were compared for four different structures MCHE with slit or louvered fins. The research result shows that for the given brine flow conditions, the rate of condensate drainage is mainly influenced by the air velocity, the calculation formula predictions of the condensate drainage agree well with the test measurement results, and the maximum deviation is 12%.This study provides reference for the application of micro channel evaporator.

Seasonal Performance Investigation for Residential Heat Pump System with Different Outdoor Heat Exchanger Designs

A finned tube heat exchanger is a key component used as a condenser or an evaporator in residential air-conditioning (AC) and heat pump systems. The overall cycle performance of these systems is significantly affected by the heat exchanger’s geometric design. This study investigates outdoor heat exchanger designs with varying geometric parameters such as the fin pitch, number of tube rows, and tube length, and their effect on system performance based on seasonal energy efficiency ratio (SEER) and seasonal coefficient of performance (SCOP). Air face velocity profiles for each operating condition along the outdoor heat exchangers are determined using CFD, with subsequent cycle simulations for 10 different operating conditions. Results have been validated with the available experimental data. The number of tube rows, fin pitch, and length of tube have been varied from 2–10, 1.4–2.5 mm, and 800–2800 mm respectively. The numerical results reveals that SEER increases 3.21% while SCOP increases 5.32% up to fourth and fifth tube row respectively and remain unaffected thereafter. Similarly, SEER increases by 3.55% as the tube length is increased from 800–1800 mm, while it increases only 0.67% for 1800–2800 mm and the maximum variation of 4.32% has been found for SCOP. Moreover, increasing the fin pitch reduces SEER and SCOP (except for fin pitch from 1.4 to 1.8 mm). Finally, the performance of the system with four different fin configurations have also been investigated and it has been found that slit fins are more effective.

Airside Performance of Fin-and-Tube Heat Exchangers Having Nonrepeating Nonsymmetrical Slit Fins under Wet Condition

In this study, heat-transfer and friction characteristics of newly developed nonsymmetric slit-finned-tube heat exchangers are experimentally investigated. The newly developed slit fin had more slits in the second row than the first row. As a result, different row effect on [Formula: see text] factor than that of conventional enhanced finned-tube heat exchangers was observed. In other words, two-row configuration yielded larger [Formula: see text] factor than the one-row configuration. Comparison with conventional louver fin or slit fin heat exchangers revealed that the present slit fin heat exchangers show superior heat-transfer characteristics, especially at the second row. The reason was attributed to the many narrow slits that formed at the second row, which maintain thin water film along the slits and smooth the condensate flow.

비 대칭 슬릿 핀이 장착된 핀-관 열교환기의 열전달 성능 및 압력 손실에 대한 실험적 연구

핀-관 열교환기에서 핀 패턴은 전열 성능에 큰 영향을 미친다. 본 연구에서는 1열과 2열의 핀 패턴이 상이한 비 대칭 슬릿 핀-관 열교환기에 대해 일련의 실험을 수행하고 모든 열에 핀 패턴이 동일한 비 대칭 시료에 대한 기존 연구 결과와 비교하였다. 실험 결과 기존 슬릿 핀 시료의 전열 촉진비(j /jp)가 1열에서 22%, 2열에서 30%로 신규 시료(6%와 7%)보다 크게 나타났다. 특히 2열에서는 신규 시료의 슬릿 면적 비율이 기존 시료보다 큰데도 불구하고 j/j<SUB>p</SUB> 가 작게 나타났다. 또한 j/f<SUP> 1/3</SUP>의 경우 1열에서는 두 종류의 슬릿 핀 시료와 평판 핀 시료는 유사한 값을 보인다. 하지만 2열에서는 기존 시료의 j/f <SUP>1/3</SUP>은 평판 핀 시료보다 10% 높은 반면 신규 시료의 값은 평판 핀 시료보다 6% 낮게 나타났다. 이로부터 2열핀-관 열교환기에서 2열에 슬릿을 집중적으로 배치하는 것은 전열 성능 향상에 그다지 효과적인 방법이 아닐 수 있음을 알 수 있다. 그 이유로는 슬릿을 집중적으로 배치하다 보면 슬릿 간격이 좁아져 후류가 미처 소산되지 않은 상태로 후방 슬릿에 도착하여 전열 성능을 감소시킬 수 있기 때문이다. 한편 루버 핀 시료의 j/jp, j/f <SUP>1/3</SUP>은 슬릿 핀 시료의 값보다 크게 나타났다.

Numerical Analysis of Fluid Flow and Heat Transfer in Wavy and Hybrid-Slit-Wavy Fin-and-Tube Heat Exchangers

This numerical study pertains to characterizing flow and heat transfer interactions for an interrupted fin design with wavy profile in a compact tube-and-fin heat exchanger. Sinusoidal wavy fin is combined with slit fins to investigate thermal-hydraulic performance relative to an uninterrupted fin design. This fin is referred to as hybrid-slit-wavy (HSW) in this work. Commercial computational fluid dynamics (CFD) software is used for 3D numerical solution of the complete Navier–Stokes and energy equations in the heat exchanger to study flow physics and predict performance. The modeling approach is first validated with available test data from the literature on a wavy (herringbone profile) fin heat exchanger. The predicted friction factor was within 12% and the Colburn j-factor was within 7% of the reported test data over a Reynolds number range of 350 to 6500. In the case of the HSW fin, it was found that the air-side heat transfer is enhanced by about 20% to 39% relative to the baseline uninterrupted fin with an associated pressure drop penalty of 20% to 38%. The area goodness factors of the HSW fins are up to 4% higher compared to the wavy fins at various operating conditions, indicative of favorable tradeoff.

Heat transfer enhancement in a parallel, finless heat exchanger using a longitudinal vortex generator, Part B: Experimental investigation on the performance of finless and fin-tube heat exchangers

The air-side pressure drops and overall heat transfer coefficients of a finless heat exchanger with and without a vortex generator, as well as those of five all-aluminum parallel multi-port heat exchangers, were experimentally measured and compared under dry, wet, and frosting/defrosting conditions. The multi-port heat exchangers included three exchangers with louvered fins featuring fin pitches of 1.2 mm, 1.4 mm, and 1.6 mm, and two exchangers featuring slit fins with pitches of 1.2 mm and 1.4 mm. For the fin-tube heat exchangers, the effects of fin pitch and type on the air-side pressure drop and overall heat transfer performance were discussed. Under the dry condition, the heat transfer performance of a finless heat exchanger with a longitudinal vortex generator (LVG) is still approximately 40% less than that of a fin-tube heat exchanger. However, the pressure drop is similar. Under wet conditions, due to the excellent drainage performance of the finless heat exchanger, the heat transfer coefficient reached the same level. However, the pressure drop is lower. Under the frosting/defrosting condition, the heat transfer coefficient is similar, but the pressure drop is much lower. It only reaches 50 Pa at the end of each frosting period. Overall, the performance of a finless heat exchanger with a vortex generator is still lower than that of a fin-tube heat exchanger in dry conditions, but it demonstrates superiority in wet and frosting/defrosting conditions.

Investigations into air and refrigerant side heat transfer coefficients of finned-tube CO2 gas coolers

Gas coolers are heat rejection heat exchangers in vapour compression refrigeration systems that use carbon dioxide (CO2) as refrigerant. The design of gas coolers has a significant influence on the performance of CO2 refrigeration systems as it determines to a large extent the gas cooler/condenser pressure and the power consumption of the system. This paper investigates local refrigerant and air heat transfer coefficients in plain fin-and-tube gas cooler coils using Computational Fluid Dynamics (CFD) modelling. The aims were to provide insights into the variation of the local heat transfer rates in the coil and determine the influence of a) design enhancements such as the use of slit fins and b) to develop correlations for overall refrigerant and air heat transfer coefficients to be used in CO2 refrigeration component and system modelling. The results from the model which was validated against experimental measurements showed that a horizontal slit on the fin between the first and second row of tubes can lead to an increase in the heat rejection rate of the gas cooler by between 6% and 8%. This in turn can lead to smaller heat exchanger heat transfer area for a given heat rejection capacity or lower high side pressure and higher efficiency for the refrigeration system. The results and heat transfer correlations developed are a valuable resource for researchers and manufacturers of CO2 and other heat exchanger coils that experience a wide variation in refrigerant temperature during the gas cooling process.

Study on the heat transfer and fluid flow characteristics in V-shaped corrugated composite fin

The study on the composite fin with louver and slit is performed numerically to enhance fin performance. It is confirmed that the performance of V-shaped corrugated composite fin is better than that of plate fin, which shows that flow vorticity is stronger due to interaction between corrugate, slit and louver. Slit dimensions optimized in fin performance are drawn by numerical analysis for key parameters of slit using Response Surface Methods (RSM). It is also numerically confirmed that JF-factor of the specification with optimized composite fin is higher than that of X-shaped slit fin by 6.1% on average. Part-level performance test is conducted with heat exchanger samples including the V-shaped fin and X-shaped fin respectively, and confirmed that the heat exchanger with X-shaped fin of 1.5mm fin pitch could be replaced by that with V-shaped composite fin of 1.7mm fin pitch resulting in the reduction of fin weight by 11.7%.