Effect Of Fin Pitch Research Articles

Air-side thermal-hydraulic analysis and parameter optimization for vertical-fin microchannel heat exchanger

The vertical-fin microchannel heat exchanger (VMHX) has efficient thermal-hydraulic performance and favorable drainage performance, which is capable to be utilized in the air source heat pump under wide operating conditions. In this article, CFD is employed to analyze the air-side thermal-hydraulic performance of VMHXs under dry conditions. The model is verified by experimental results with an error of less than 20%. Then, the sequence and connection of wave and louver on composite fins are compared, while the effects of fin pitch, fin length, tube pitch, and fin thickness are investigated. Finally, parameter optimization is conducted by Taguchi method. Results show that under the same pump power, the heat transfer enhancement of the fin with front louver and rear wave connected reversely is the best. When the comprehensive index performance evaluation criteria (PEC) is used as performance evaluation of VMHXs, the tube pitch and fin length are the main factors. Within the range of parameters practically available, the best performance is obtained by the combination of 1.8 mm fin pitch, 25.6 mm fin length, 12.0 mm flat tube pitch, and 0.12 mm fin thickness.

Numerical analysis on heat transfer enhancement of wavy fin-tube heat exchangers for air-conditioning applications

• Heat transfer enhancement at constant pumping power fits closest to real scenarios. • Larger HTC does not necessarily lead to larger heat transfer rate. • Waffle height, wave length, and fin pitch should be optimized simultaneously. • The optimized geometries yield 23% improvement of HTC and 3% of heat transfer rate. • Proper Perforation on wavy fin leads to 34% enhancement of HTC. The air-side heat transfer performance of herringbone wavy fin-tube heat exchangers can be improved by optimizing fin geometries and introducing perforations to the wavy fin. Based on a typical herringbone wavy fin-tube heat exchanger used in the outdoor unit of an air conditioner with collar outside diameter of 7.3 mm, transverse tube pitch of 22 mm, and longitudinal tube pitch of 19.05 mm, the effects of fin pitch, wave length, slits height, and geometries of slits are simulated using CFD and the outcomes are discussed in the paper. We demonstrate that constant pumping power is the ideal criterion for the performance evaluation of any new designs. The wave length has no remarkable effects on the heat transfer coefficient while the lowest pressure drop appears with the symmetric wave configuration. The heat transfer coefficient can be improved by 23.4% when the waffle height, fin pitch, and wave length are simultaneously optimized. Furthermore, punching slits on top of the windward part of wavy fins leads to a 5.5% increase in the heat transfer coefficient. In the end, 34.2% improvement of the heat transfer coefficient is yielded when combining the slit perforations to the optimum fin pitch, wave length, and waffle height.

An experimental investigation of the air-side performance of crimped spiral fin-and-tube heat exchangers with a small tube diameter

The performance of crimped spiral fin-and-tube heat exchangers (CSFTHXs) with a small tube diameter at a Reynolds number of 1500-6400 based on the tube's outer diameter is experimentally investigated. An important factor in this study is the small-diameter tubing, with an outer diameter of 9.53 mm. Copper tubes and aluminum fins are assembled as CSFTHXs. Test sections consist of a fin thickness of 0.5 mm, two tube rows, and various fin pitches and outer diameters of 3.18-6.35 mm and 23.0-28.5 mm, respectively. Hot water and fresh air are used as the working fluids. The effects of fin pitch and fin outer diameter on the heat transfer characteristics and friction factor (f) are also studied. The results show that the fin's pitch and outer diameter have little effect on the Nusselt number (Nu) and Colburn factor (j). On the other hand, they have a significant effect on the f. Furthermore, correlations between the Nu, j, and f for a CSFTHX with a small tube diameter are developed and proposed for designing heat exchangers in the thermal industry.

Experimental investigation on the airside heat transfer and pressure drop of the fin-and-tube heat exchangers having oval tubes

ABSTRACT It is well known that the replacement of round tubes to oval tubes in a fin-and-tube heat exchanger reduces the air-side pressure drop as well as the low-performance region behind the tube, which improves the thermal performance of the heat exchanger. However, experimental evidences are lacking, especially for generic heat exchangers. In this study, generic heat exchangers having oval tubes were tested, which included two different oval tube dimension and two different tube pitches. Round tube samples were also tested for a comparison purpose. The effect of fin pitch on j factor was negligible, whereas f factor increased as the fin pitch increased. Furthermore, both the j and f factor decreased as the number of tube row increased. A thermal performance comparison based on the ratio of thermal conductance per unit volume () to pressure drop per unit length () revealed that the oval tube samples yielded a higher performance than the round tube samples, except at a small number of tube row. Furthermore, the best performance was obtained from the oval tube samples having a smaller diameter tube. On the other hand, relatively poor performance was obtained from the oval tube samples having a larger diameter tube, probably due to the large pressure drops. The j and f correlations were developed based on the data.

POOL BOILING HEAT TRANSFER OF LiBr SOLUTION IN LOW-FIN TUBES: EFFECT OF FIN PITCH AND HEIGHT

POOL BOILING HEAT TRANSFER OF LiBr SOLUTION IN LOW-FIN TUBES: EFFECT OF FIN PITCH AND HEIGHT

Design of non-uniformly distributed annular fins for a shell-and-tube thermal energy storage unit

The shell and tube latent heat thermal energy storage systems are widely recognized as one of the most effective ways to store and utilize solar energy due to their high energy density, constant storage/releasing temperature, structural feasibility and rational price. The application of fins is an effective method to enhance heat exchange through extend the heat transfer surface area. However, there existed strong uneven melting behavior including melting fraction, temperature uniformity in a vertical thermal energy storage unit. To improve its uniformity of melting fraction and temperature, this study designed various conditions for fin pitch and positions in a non-uniform pattern to reduce the inhomogeneity for the melting process. Numerical models were established and validated by the experimental measurement conducted in this study. The effects of fin pitch and position on the thermal performance of the melting process were quantified via analyzing the melting front evolution, temperature and velocity distribution, melting rate and temperature uniformity. Results demonstrated that a 62.8% and 34.4% reduction in full melting time and average temperature difference in the phase change material region was separately obtained for the thermal energy storage unit with non-uniformly distributed annular fins, compared to the original case with uniform fins. Besides, the melting rate uniformity was also improved by 84.7%. The non-uniform design on fin position and pitch give a perspective to enriching the design methods for practical application in engineering.

Effect of fin pitch on the filmwise condensation of steam on three-dimensional conical pin fin arrays: A comparative study

An experimental investigation on the use of three-dimensional conical pin fins to enhance filmwise condensation of steam on vertical plates was carried out. Nine surfaces with conical pin fin arrays were fabricated by Selective Laser Melting and tested in a condensation chamber. The conical pin fin arrays have the same fin base diameter but are of different fin heights and fin pitches. The effects of fin pitch on the condensation heat transfer performance of the conical pin fin arrays were examined. A detailed comparative study was also carried out to evaluate the thermal performances of the conical, sinusoidal and cylindrical pin fin arrays fabricated by Selective Laser Melting. Based on our investigation, it was determined that the condensation heat flux and heat transfer coefficient of the conical pin fin specimens increase as the fin pitch increases from 1.25 mm to 1.67 mm. However, with a further increase in the fin pitch from 1.67 mm to 2.50 mm, reductions in the heat flux and heat transfer coefficient were recorded. The highest thermal enhancement factor of 2.46 was achieved with the conical pin fin specimen of 1.28 mm fin height and 1.67 mm fin pitch. Visualization studies of the static condensate retention height show that the change in fin pitch has more significant effect on the condensation retention height as compared to the change in fin height. A fin analysis was performed to determine the average heat transfer coefficients of the conical pin fins. In addition, a thermal enhancement-to-area enhancement ratio was also proposed to evaluate the condensation performances of conical pin fin arrays. Our results show that significantly higher average heat transfer coefficients and thermal enhancement-to-area enhancement ratios were obtained by the conical pin fin surfaces as compared to the sinusoidal and cylindrical pin fins. Due to the significant surface tension effect and reduced condensate flooding, the conical pin fin structure is shown to be the best geometry for enhancing natural convection condensation heat transfer as compared to the sinusoidal and cylindrical pin fins.

Filmwise Condensation of Steam on Pin Fin Arrays Fabricated by Selective Laser Melting

In this study, nine vertical flat plates of pin fin arrays were fabricated by selective laser melting to investigate the possible enhancements of external condensation. These specimens are cylindrical pin fins of the same fin diameter of 300 μm but are of different fin heights (l) and fin pitches (p) from 300 μm to 900 μm. Experiments were conducted in a condensation chamber with near quiescent vapor to simulate free-convection condensation. The aim is to investigate the effects of fin pitch and fin height on the condensation heat transfer performance of the surfaces. The results of this study show that the increase in fin height and the decrease in fin pitch lead to a systematic increase in the condensation heat flux (q''). At the same fin pitch, the increase in fin height from 600 μm to 900 μm resulted in a more significant increase in q'' as compared to the increase in fin height from 300 μm to 600 μm. On the other hand, at the same fin height, a larger increase in q'' is observed when the fin pitch is reduced from 900 μm to 600 μm as compared to the reduction in fin pitch from 600 μm to 300 μm. It can be deduced that increasing the fin height enables the fins to protrude out of the thick condensate film and increases the effective heat transfer area of the surfaces. However, when the fin density is large, it impedes the condensate drainage path and limits the enhancement in q''. The enhancement factor (η), which is the ratio of the average condensation heat flux of a pin fin surface to that of a plain surface, was computed for each specimen. The highest η value of 1.72 was achieved with the specimen of 900 μm fin height and 300 μm fin pitch. Finally, a relationship between η and the dimensionless fin pitch-to-height ratio (p/l) is proposed.

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.

Parametric study on rectangular finned elliptical tube heat exchangers with the increase of number of rows

The objective of this study is to investigate the performance of rectangular finned elliptical tube heat exchangers (RFETHXs) of low number of rows (N) in turbulent region, with an emphasis on the characteristics with the increase of N. Using 3D numerical simulations based on the validated standard k-ε turbulence model, the average thermal-hydraulic characteristics of each row as well as the overall performance along with N are investigated. Then the contribution of each structural factor and the interaction effects between various parameters on the performance are revealed using variance analysis in 4 sub-row-regions. The most significant interaction effect on the performance evaluation criterion (PEC) between structural parameters is confirmed using Response Surface Method (RSM). It is observed that, for the RFETHXs with N > 2, the heat transfer coefficient of the second row of fins is the largest, while those of the first and the last rows remain the smallest two. A 2-row RFETHX has better performance compared to the RFETHXs with larger N. In most cases, the flow and heat transfer of RFETHXs enters fully developed state from the fifth row, but as the transverse tube pitch (Pt) increases or the fin thickness declines, such state is postponed to deeper rows. It demonstrates that significant impact of N on PEC exists in the sub-row-range of 2–3. With the incline of N, the effect of fin pitch (Fp) to j and f decreases while that of Pt increases, and the interaction effect between Pt and Fp to j and PEC becomes more pronounced. This interaction reduces with the increase of frontal velocity. The reason for such interaction is discussed. At last, results of RMS analysis further depict that the interaction effect between Pt and Fp on PEC of a 6-row RFETHX is more significant than that of a 2-row RFETHX.

Effects of fin pitch and tube diameter on the air-side performance of tube bank fin heat exchanger with the fins punched plane and curved rectangular vortex generators

ABSTRACTTube bank fin heat exchangers with vortex generators are widely used in the field of industrial applications. The effects of the fin pitch and the tube diameter on the air-side performance of the tube bank fin heat exchanger with plane rectangular vortex generators (PRVG) and curved rectangular vortex generators (CRVG) are experimentally studied in this paper. Performance comparison is carried out between the fins with PRVG and CRVG. The experimental results show that both PRVG and CRVG can effectively enhance heat transfer performance compared with the plain fin. Both the fin pitch and the tube diameter have obvious effect on f compared with the effect on Nu, especially for the fin with PRVG. The characteristics of Nu, f, and Nu/f1/3 are different for the fins with PRVG and CRVG. The fin with CRVG has a better heat transfer performance than the fin with PRVG for all the cases studied in this paper.

The Effect of Fin Pitch on Fluid Elastic Instability of Tube Arrays Subjected to Cross Flow of Water

Failure of tubes in shell and tube exchangers is attributed to flow induced vibrations of such tubes. There are different excitations mechanisms due to which flow induced vibration occurs and among such mechanisms, fluid elastic instability is the most prominent one as it causes the most violent vibrations and may lead to rapid tube failures within short time. Fluid elastic instability is the fluid–structure interaction phenomenon which occurs when energy input by the fluid force exceeds energy expended in damping. This point is referred as instability threshold and corresponding velocity is referred as critical velocity. Once flow velocity exceeds critical flow velocity, the vibration amplitude increases very rapidly with flow velocity. An experimental program is carried out to determine the critical velocity at instability for plain and finned tube arrays subjected to cross flow of water. The tube array geometry is parallel triangular with cantilever end condition and pitch ratios considered are 2.6 and 2.1. The objective of research is to determine the effect of increase in pitch ratio on instability threshold for plain tube arrays and to assess the effect of addition of fins as well as increase in fin density on instability threshold for finned tube arrays. Plain tube array with two different pitch ratios; 2.1 and 2.6 and finned tube arrays with same pitch ratio; 2.6 but with two different fin pitches; such as fine (10 fpi) and coarse (4 fpi) are considered for the experimentation. Connors’ equation that relates critical velocity at instability to different parameters, on which instability depends, has been used as the basis for analysis and the concept of effective diameter is used for the present investigation. The modal parameters are first suitably modified using natural frequency reduction setup that is already designed and developed to reduce natural frequency and hence to achieve experimental simulation of fluid elastic instability within the limited flow capacity of the pump. The tests are carried out first on plain tube arrays to establish the same as the datum case and results are compared to known results of plain tube arrays and hence the quality of the test rig is also assessed. The fluid elastic vibration tests are then carried out on finned tube arrays with coarse and fine fin pitches and effects of fins and fin pitch on instability threshold are shown. The vibration response of the tube is recorded for each gradually increasing flow rates of water till instability point is reached. The parameters at the instability are then presented in terms of dimensionless parameters to compare them with published results. It is concluded that, arrays with higher pitch ratios are unstable at comparatively higher flow velocities and instability threshold for finned tube arrays is delayed due to addition of the fins. Further, it is concluded that, instability threshold for finned tube arrays with fine fin pitch is delayed compared to coarse fin pitch and hence for increased fin density, instability threshold is delayed. The experimental results in terms of critical velocities obtained for different tube arrays subjected to water cross flow will serve as the base flow rates for air–water cross flow experiments to be conducted in the next phase.

Airside performances of finned eight-tube heat exchangers

For applications in the relatively low temperature refrigeration systems with large constant temperature bath, the present work performed the experimental studies on the airside performances of the staggered finned eight-tube heat exchangers with large fin pitches. The airside heat transfer coefficients and pressure drops for three fin types and two fin pitches are obtained and analyzed. The heat transfer enhancement with louver fins is 11–16 % higher than the flat fins and that with sinusoidal corrugated fins is 1.1–3.4 % higher than the flat fins. Higher Re brings larger enhancement for various fins. Fin pitches show weak influence on heat transfer for eight tube rows. However, effects of fin pitch on heat transfer for both the sinusoidal corrugation and the louvered fin are larger than the flat fins and they are different from those for N ≤ 6. Airside Colburn j factor are compared with previous and it could be concluded that the airside j factor is almost constant for finned tube heat exchangers with eight tubes and large fin pitches, when Re is from 250 to 2500. The results are different from previous studies for fewer tube rows.

둥근 웨이브 핀-관 열교환기의 공기 측 전열 성능

In this study, airside performance of round fin-and-tube heat exchangers are compared with that of the herringbone wave fin-and-tube heat exchangers with an aim to investigate the effect of fin shape on thermal performance. Results show that j factors of the round wave fin are 1.2~22% larger than those of herringbone wave fin. The f factors of the round wave fin are -1.0~29% smaller than those of herringbone wave fin for 1 or 2 row configuration. For 3 row configuration, f factors of the round wave fin are 8.3~23% larger. The reason may be attributed to the reduced recirculation zone in the valley of the fin for round wave fin as compared with that of the herringbone wave fin. For round wave fin, the effect of fin pitch on j and f factor is not significant. In addition, j factors decrease as the number of tube row increases. On the other hand, f factors are independent of the number of tube row. A new correlation was developed based on the present data.

An experimental investigation on the airside performance of fin-and-tube heat exchangers having slit fins under wet condition

In this study, the heat transfer and friction characteristics of the 5.3 mm O.D. slit-finned heat exchangers under wet condition have been experimentally investigated. Plain-finned heat exchangers having the same 5.3 mm O.D. tubes are also tested for comparison purpose. The effect of fin pitch on j and f factor is negligible. Slit fin samples yield higher j and f factors than plain fin samples. For one row configuration, the average f factor ratio between slit fin sample and plain fin sample is 2.18. The ratio increases to 2.41 for two row configuration, and to 2.65 for three row configuration. As for the j factor, the ratios are approximately the same (1.61, 1.70 and 1.71 for one, two and three row configuration). Both j and f factor increase as the number of tube row decreases. The same trend is observed for the plain fin samples. At high Reynolds numbers, the j/f ratios of the slit fin are approximately the same as those of the plain fin. At low Reynolds numbers, the j/f ratios of the slit fin are smaller than those of plain fin. Data are compared with existing correlations.

Investigation of RC parasitics considering middle-of-the-line in si-bulk FinFETs for Sub-14-nm node logic applications

In this brief, we systematically investigated the effects of fin pitch (FP) and fin height ( $H_{\textrm {fin}}$ ) on parasitic resistances and capacitances to achieve the best $RC$ delay, which is an adequate metric of the ac behavior of FinFETs, for Si bulk n/pFinFETs in system-on-a-chip applications. The $RC$ delays were directly extracted from the fully calibrated technology computer aided design $I$ – $V/C$ – $V$ simulation results and quantitatively analyzed using parasitic capacitance components, including a middle-of-the line configuration up to Metal 1. When FP increased, the $RC$ delay likewise increased due to greater $C_{\textrm {gg}}$ . On the other hand, the $RC$ delay mostly decreased due to greater ON-current as the $H_{\textrm {fin}}$ increased. The $RC$ delay with different power supply voltages ( $V_{\textrm {DD}} = 0.55$ and 0.75 V) was also studied to see the effect of $V_{\textrm {DD}}$ scaling. Finally, a selective deposition was suggested to improve the $RC$ delay about 13%.

복합 전열 촉진 핀이 적용된 핀-관 열교환기의 습표면 성능에 대한 실험적 연구

In this study, wet surface heat transfer and friction characteristics of compound enhanced fin-and-tube heat exchangers were experimentally investigated. Louver-finned heat exchangers were also tested for comparison purpose. The effect of fin pitch on j and f factor was negligible. Both j and f factor decreased as number of tube row increased. Compound enhanced fin samples yielded higher j and f factors than louver fin samples. For one row, j and f factors of compound enhanced fin samples were 11% and 43% higher than those of louver fin samples. For two row, those were 8% and 50%, and for three row, those were 17% and 53%. Heat transfer capacities at the same pressure drop of the compound enhanced fin samples were 2.0% for one row, 3.1% for two row and 8.4% for three row larger than those of louver fin samples, Data were compared with predictions of existing louver fin correlations.

An Experimental Investigation on the Air-Side Performance of Fin-and-Tube Heat Exchangers Having Radial Slit Fins

In this study, the heat transfer and friction characteristics of radial slit-finned heat exchangers are experimentally investigated. Louver-finned heat exchangers are also tested for comparison purpose. The effect of fin pitch on [Formula: see text] and [Formula: see text] factor is negligible. Considering the small variation of the fin pitch (from 1.3[Formula: see text]mm to 1.7[Formula: see text]mm), the foregoing argument should hold true for the present samples. Louver fin samples yield higher [Formula: see text] and [Formula: see text] factors than slit fin samples. The [Formula: see text] factor increases as the number of tube row decreases. The [Formula: see text] factor, however, is independent of the number of tube row. The [Formula: see text] ratios of slit fin samples are larger than those of Louver fin samples. Data are compared with available correlations.

Airside performance of fin-and-tube heat exchangers having sine wave fins under wet condition

In this study, experiments are conducted on sine wave heat exchangers under wet condition, and the results are compared with those of herringbone wave heat exchangers having same wave height. Sine wave samples yield higher j and f factors than herringbone wave samples. The reason may be attributed to the reduced recirculation zone in the valleys of the sine wave channel. The effect of fin pitch on j and f factor is not pronounced both for sine and herringbone wave heat exchangers. The j factor decreases as number of tube row increases. However, the effect of number of tube row on f factor is dependent on the fin configuration. For herringbone wave samples, f factor decreases as the number of tube row increases. For sine wave samples, on the other hand, f factor is independent of the number of tube row. Ratios of j/f1/3 between sine wave and herringbone wave samples are between 0.95 and 1.0, which decrease with theincrease of fin pitch. A new correlation was developed based on the present data.

복합 전열 촉진 핀이 적용된 핀-관 열교환기의 성능에 대한 실험적 연구

Abstract In this study, heat transfer and friction characteristics of compound enhanced fin-and-tube heat exchangerswere experimentally investigated. Louver-finned heat exchangers were also tested for comparison purpose. The effectof fin pitch on j and f factor was negligible. The j factor decreased as number of tube row increased. However, ffactor was independent of number of tube row. Louver fin samples yielded higher j and f factors than compoundenhanced fin samples. For one row, j and f factors of louver fin were 23% and 27% higher than those of compoundenhanced fin. For two row, those were 11% and 8%, and for three row, those were 10% and 9%. However, heat transfer capacities at the same pressure drop of the compound enhanced fins were 6.4% for one row, 11.1% for tworow and 13.6% for three row larger than those of louver fins, Existing louver fin correlation overpredicted the presentj factors and underpredicted the present f factors. Keywords : Compound enhanced fin, Heat transfer coefficient, Louver fin, Pressure drop