Optimum Fin Spacing Research Articles

Numerical analysis of the fin spacing effect on the horseshoe vortex system evolution in a two-rows finned-tube heat exchanger

Purpose – In finned-tube heat exchangers, the array of tubes generates three-dimensional vortices at fin-tube junctions. Theses vortices known as horseshoe vortex (HSV) system are responsible of flow mixing and heat transfer increase. The purpose of this paper is to focus on the effect of the fin spacing on the formation, the spatial evolution and dissipation of the HSV system at fin-tube junctions in a two-rows finned-tube heat exchanger. The global characterisation of the heat exchanger performance is also presented. Design/methodology/approach – The flow structure is numerically analysed through the use of computational fluid dynamics tools. The different vortices of the HSV system are highlighted and quantitatively analysed at each fin-tube junction with vorticity, wall shear stress analysis and two-dimensional streamline plots around tubes. Findings – The results show that the primary and secondary vortices of the HSV system have antagonistic behaviors with respect to the azimuthal angle variation. The optimum fin spacing ratio E/D that generates the most intense first primary vortex in the HSV system lies between 0.20 and 0.25. Similar observation are made on the thermalhydraulic performance of the heat exchanger as j/f exhibits a maximum value for a fin spacing ratio E/D=0.25. Research limitations/implications – A detailed URANS simulation shows that even if the flow remains steady in the core of the heat exchanger, unsteady behavior is noticed in the wake of the second tube. Originality/value – In this study, the flow topology is quantitatively analysed in successive radial planes around heat exchanger tubes. The strong effect of the fin spacing on the HSV generation and dissipation is deeply analysed.

The optimum fin spacing of circular tube bank fin heat exchanger with vortex generators

In real application, once the pattern of fin is determined, fin spacing of tube bank fin heat exchanger can be adjusted in a small region, and air flow velocity in the front of the heat exchanger is not all the same. Therefore, the effects of fin spacing on heat transfer performance of such heat exchanger are needed. This paper numerically studied the optimal fin spacing regarding the different front flow velocities of a circular tube bank fin heat exchanger with vortex generators. To screen the optimal fin spacing, an appropriate evaluation criterion JF was used. The results show that when front velocity is 1.75 m/s, the optimal fin spacing is 2.25 mm, when front velocity is 2.5 m/s, the optimal fin spacing is 2 mm, and when front velocity is higher than 2.5 m/s, the optimal fin spacing is 1.75 mm.

Parametric study on the dynamic behavior of natural convection from horizontal rectangular fin arrays

A parametric study on the dynamic natural convection from long horizontal fin arrays (L=128, 254 and 380mm) is made using a 3-D unsteady numerical analysis. The investigated range of height H is 6.4–38mm and that of spacing S is 6.4–20mm. Increasing L tends to enhance the oscillating sliding-chimney flow, whereas increasing S weakens it. The time-averaged overall convection heat transfer coefficients h¯ are larger for high and short fin arrays, due to the stronger buoyancy and thinner boundary layers. The h¯–S relation exhibits a steep drop when S is narrowed below a threshold, which is larger for lower and longer fins. The optimum fin spacing Sopt occurs near the threshold S, below which the benefit of increasing heat transfer area surrenders to the decrease of h¯ caused by excessive viscous drag. The heat transfer rate per unit base area Q/Ab decreases with increasing L and decreasing H. The predicted dependence of Sopt on H and L agrees well with experimental results and is explained based on numerical results of flow and heat transfer characteristics. The present predictions of Nu agree well with the correlations in the literature which use S as the characteristic length.

Experimental investigation of natural convection heat transfer of the fin arrangement on a computer heat sink

Needs for buoyancy driven ventilation appear in a variety of engineering applications, ranging from cooling of electronic components to cooling of nuclear reactor fuel elements. Hence, it becomes crucial to optimize the natural convection heat transfer as far as possible. If the fins are properly designed, they become very attractive for these applications since they offer an economical, trouble-free solution to the problem. This paper reports an experimental and numerical study of natural convection heat transfer from rectangular fin arrays on a vertical base. An experimental set-up was constructed and calibrated; six sets of fin-arrays and a base plate without fins were tested in atmosphere. A correlation was presented relating the convection heat transfer rate of fin arrays relative to that for base plate without fins with the relevant non-dimensional parameters. In order to improve the natural convection heat transfer rate, air gap was used for the optimum fin spacing. Key words: Natural convection, experimental optimization, air gap, rectangular fin arrays.

Thermal Assessment of Naturally Cooled Electronic Enclosures With Rectangular Fins

Passive heat transfer from enclosures with rectangular fins is studied both experimentally and theoretically. Several sample enclosures with various lengths are prepared and tested. To calibrate the thermal measurements and the analyses, enclosures without fins (“bare” enclosures) are also prepared and tested. Surface temperature distribution is determined for various enclosure lengths and heat generation rates. Existing relationships for natural convection and radiation heat transfer are used to calculate the heat transfer rate from the tested samples. The theoretical results successfully predict the trends observed in the experimental data. It is observed that the contribution of the radiation heat transfer is on the order of 50% of the total heat transfer for the tested enclosures. As such, a new correlation is reported for calculating an optimum fin spacing for vertically-mounted uniformly finned surfaces, with rectangular straight fins that takes into account both natural convection and radiation.

General correlation of a natural convective heat sink with plate-fins for high concentrating photovoltaic module cooling

Thermal resistance correlation as a design tool of a natural convective heat sink with plate-fins for concentrating photovoltaic (CPV) module cooling is suggested. For this purpose, extensive experimental investigations are performed for various heat sink geometries, input power, as well as inclination angle. From the comparison between the proposed general correlation and the previous studies, it is shown that the proposed correlation predicts well the effects of inclination angle and fin spacing on the thermal performance of the natural convective heat sink with plate-fins. Also, optimal fin spacing strongly depends on the temperature difference as well as the inclination angle. The optimal fin spacing is significantly changed when the inclination angle is larger than 70°.

Design of heat sink for improving the performance of thermoelectric generator using two-stage optimization

Thermoelectric (TE) devices can provide clean energy conversion and are environmentally friendly; however, little research has been published on the optimal design of air-cooling systems for thermoelectric generators (TEGs). The present study investigates the performance of a TEG combined with an air-cooling system designed using two-stage optimization. An analytical method is used to model the heat transfer of the heat sink and a numerical method with a finite element scheme is employed to predict the performance of the TEG. In the first-stage optimization, the optimal fin spacing for a given heat sink geometry is obtained in accordance with the analytical method. In the second-stage optimization, called compromise programming, decreasing the length of the heat sink by increasing its frontal area (WHSHf) is the recommended design approach. Using the obtained compromise point, though the heat sink efficiency is reduced by 20.93% compared to that without the optimal design, the TEG output power density is increased by 88.70%. It is thus recommended for the design of the heat sink. Moreover, the TEG power density can be further improved by scaling-down the TEG when the heat sink length is below 14.5 mm.

Interaction of natural convection flow in multiple open cavities formed due to horizontal fins

Natural convection heat transfer from a stack of horizontal open cavities formed due to fins attached to equipment has been investigated for a wide range of Rayleigh number, cavity spacing and number of cavities in the stack. The interaction between natural convection from one cavity with other cavities in the stack is the focus of the study. Conservation equations of mass, momentum and energy have been solved using a finite volume solver. Ideal gas assumption is invoked to account for density variation of air. Numerical results have been validated with published solutions for a single isolated cavity. It is seen that the heat transfer from a stack of cavities is less than that predicted for isolated cavities. Due to pre-heating effect of fluid reaching the entrance of the upper cavities from the bottom ones, the heat transfer from upper cavities deteriorates. This deterioration is found to exhibit strong dependence on Rayleigh number and fin spacing. The dimensionless optimum fin spacing which yields the maximum heat transfer is found to be 2.5 for Ra ⩽ 10 4 and it is 0.5 for Ra ⩾ 10 5. The reduction in Nusselt number from the top cavity compared to that in the bottom cavity is in the range of 65% at the highest Rayleigh number studied.

Effects of Different Fin Spacings on the Nusselt Number and Reynolds Number in Perforated Finned Heat Exchangers

In this study, the effect of holes placed on perforated finned heat exchangers on convective heat transfer was experimentally investigated. Six-millimeter-diameter holes were opened on each circular fin on a heating tube in order to increase convective heat transfer. These holes were placed on the circular fins in such a way as to follow each other at the same chosen angle. The holes created turbulence in a region near the heating tube surface on the bottom of the fin. Experiments were then performed to analyze the effect of this turbulence on heat transfer and pressure drop. These experiments were carried out at five different fin spacings at the angular locations of 30° and 60° in order to determine the optimum fin spacing. Moreover, further experiments were carried out for counterflow and parallel-flow arrangements to determine the effects of the flow directions of the heating fluid and heated fluid. Results show an increase in Nusselt number with increasing modified Reynolds number. In addition, when different fin spacing to heating tube external diameter ratios were examined, at a ratio of 0.414 and angular locations of 30° and 60°, 11% and 8.6% increase in heat transfer were obtained, respectively, for parallel-flow arrangement compared to counterflow. For parallel flow, pressure drop values were 3.5% and 3.8% lower at 30° and 60°, respectively.

Experimental investigation of mixed convection heat transfer from longitudinal fins in a horizontal rectangular channel

Mixed convection heat transfer from longitudinal fins inside a horizontal channel has been investigated for a wide range of modified Rayleigh numbers and different fin heights and spacings. An experimental parametric study was made to investigate effects of fin spacing, fin height and magnitude of heat flux on mixed convection heat transfer from rectangular fin arrays heated from below in a horizontal channel. The optimum fin spacing to obtain maximum heat transfer has also been investigated. During the experiments constant heat flux boundary condition was realized and air was used as the working fluid. The velocity of fluid entering channel was kept nearly constant (0.15 ⩽ w in ⩽ 0.16 m/s) using a flow rate control valve so that Reynolds number was always about Re = 1500. Experiments were conducted for modified Rayleigh numbers 3 × 10 7 < Ra ∗ < 8 × 10 8 and Richardson number 0.4 < Ri < 5. Dimensionless fin spacing was varied from S/ H = 0.04 to S/ H = 0.018 and fin height was varied from H f/ H = 0.25 to H f/ H = 0.80. For mixed convection heat transfer, the results obtained from experimental study show that the optimum fin spacing which yields the maximum heat transfer is S = 8–9 mm and optimum fin spacing depends on the value of Ra ∗.

Optimum Fins Spacing and Thickness of a Finned Heat Exchanger Plate

The thermal design of a counterflow heat exchanger using air as the working fluid was performed with two distinct goals: minimum inlet temperature difference and minimum number of entropy generation units. The heat exchanger was constituted by a double-finned conductive plate closed by adiabatic walls at the fin tips on both sides. The hot and cold air flows were considered in the turbulent regime, driven by a constant pressure head. The thermal load was constant, and an optimization was performed to obtain the optimum fin spacing and thickness, according to the two design criteria. A computer program was employed to evaluate the optimum conditions based on correlations from the literature. The results obtained from both design criteria were compared to each other. A scale analysis was performed considering the first design goal and the corresponding dimensionless parameters were compared with the results from the correlations.

Condensation of Steam on Pin-Fin Tubes: Effect of Circumferential Pin Thickness and Spacing

Experimental data are reported for condensation of steam at atmospheric pressure and low velocity on five three-dimensional pin-fin tubes. The main geometric parameters varied were the circumferential pin spacing and thickness, since these have been shown to have a strong effect on condensate retention, and the present study shows some evidence for an optimum circumferential fin spacing. Enhancements of the vapor-side heat-transfer coefficient of up to 4 were found, compared to a plain tube at the same vapor-side temperature difference. The measured enhancements are equal to, but do not exceed, those obtained from “optimized” two-dimensional integral-fin tubes reported in the literature—an observation that is also generally true for condensation of refrigerants. The evidence suggests, however, that three-dimensional fin profiles can produce worthwhile enhancement over those obtained from simple, two-dimensional, integral-fin tubes, but that more work is needed to understand the phenomena involved so that more efficient geometries can be developed.

Experimental investigation of mixed convection heat transfer from longitudinal fins in a horizontal rectangular channel: In natural convection dominated flow regimes

Mixed convection heat transfer from longitudinal fins inside a horizontal channel has been investigated in the natural convection dominated region for a wide range of Rayleigh numbers and different fin heights and spacings. An experimental parametric study was made to investigate effects of fin spacing, fin height and magnitude of heat flux on mixed convection heat transfer from rectangular fin arrays heated from below in a horizontal channel. The optimum fin spacing to obtain maximum heat transfer has also been investigated. During the experiments constant heat flux boundary condition was realized and air was used as the working fluid. The velocity of fluid entering channel was kept nearly constant (0.02 ⩽ w in ⩽ 0.025 m/s) using a flow rate control valve so that Reynolds number was always about Re = 250. Experiments were conducted for modified Rayleigh numbers 3 × 10 7 < Ra ∗ < 6 × 10 8 and Richardson number 600 < Ri < 15,000. Dimensionless fin spacing was varied from S/ H = 0.04 to S/ H = 0.018 and fin height was varied from H f / H = 0.25 to H f / H = 0.80. The results obtained from experimental study show that the dimensionless optimum fin spacing which yields the maximum heat transfer is between S/ H = 0.08 and S/ H = 0.12. Results also show that optimum fin spacing depends on modified Rayleigh number and fin height. For high modified Rayleigh numbers (Ra ∗ ⩾ 5 × 10 8) and low values of fin height (such as H f / H = 0.25) the optimum fin spacing has taken greater values in comparison to the cases of smaller modified Rayleigh numbers.

Laminar free convection underneath a downward facing inclined hot fin array

A combined theoretical, experimental and numerical study was conducted to investigate the problem of laminar free convection underneath a hot isothermal and inclined fin array. The influence of inclination on the location where the flow stagnates, and splits, was examined. Heat transfer rates were calculated for different fin array geometries and temperatures. The results show that for small inclination angles the cooling rate is essentially constant. Beyond a certain angle, the tilting of the fin array enhances substantially the heat transfer rate. Sensitivity analyses indicate that the heat transfer coefficient increases at higher fin temperatures and larger fin spacing, but is of a lesser sensitivity to fin height changes. Additionally, it was discovered that the array optimal fin spacing do not depend on the inclination angle. In the theoretical part, a semi empirical model was developed for the heat transfer coefficient of horizontal and slightly inclined arrays that have large fin spacing. In effect it constitutes the necessary modeling addition to the previously developed model for moderately and tightly spaced fins of slightly tilted arrays. Together, they provide analytical expressions for the heat transfer coefficient of slightly inclined arrays, for any fin spacing.

Optimum fin spacing of rectangular fins on a vertical base in free convection heat transfer

The steady-state natural convection heat transfer from aluminum vertical rectangular fins extending perpendicularly from vertical rectangular base was investigated experimentally. Thirty different fin configurations were tested. Experiments were performed for fin lengths of 250 and 340 mm. Fin thickness was kept fixed at 3 mm. Fin height and fin spacing were varied from 5 to 25 mm and 5.75 to 85.5 mm, respectively. Five heat inputs ranging from 25 to 125 W were supplied for all fin configurations, hence; the base-to-ambient temperature differences were measured in order to evaluate the heat transfer rates from fin arrays. The results of experiments have shown that the convective heat transfer rate from fin arrays depends on geometric parameters and base-to-ambient temperature difference. The separate roles of fin height, fin spacing and base-to-ambient temperature difference were investigated. It was found that, for a given base-to-ambient temperature difference, the convective heat transfer rate from fin arrays takes on a maximum value as a function of fin spacing and fin height and an optimum fin spacing value which maximizes the convective heat transfer rate from the fin array is available for every fin height. These measurements were to extend data obtained earlier from aluminum fin-arrays using the same experimental system and method (Yuncu and Guvenc in Heat Mass Transfer 37:409–416, 2001). Data collated from earlier and present work cover the range of fin spacing from 4.5 to 85.5 mm. The fin length range was from 100 to 340 mm, the fin height from 5 to 25 mm and the number of fins per array 3 to 34. The range of base-to-ambient temperature difference was quite extensive, from 30 to 150 K. These results indicate that the optimum fin spacing is between 6.1 and 11.9 mm, for the fin arrays employed in the earlier and present work. A scale analysis is performed in order to estimate the order-of-magnitude of optimum fin spacing at a given fin length and base-to-ambient temperature difference. From the scale analysis, correlations to evaluate the optimum fin spacing value and the corresponding maximum convective heat transfer rate at a given fin length and base-to-ambient temperature difference were obtained.

Natural convection heat transfer in horizontal and vertical closed narrow enclosures with heated rectangular finned base plate

Natural convection heat transfer and fluid flow characteristics in horizontal and vertical narrow enclosures with heated rectangular finned base plate have been experimentally investigated at a wide range of Rayleigh number ( Ra) for different fin spacings and fin lengths. Quantitative comparisons of finned surface effectiveness ( ε) and heat transfer rate between horizontal and vertical enclosures have been reported. In comparison with enclosure of a bare base plate, insertion of heat conducting fins always enhances heat transfer rate. Optimization of fin-array geometry has been addressed. The results gave an optimum fin spacing at which Nusselt number ( Nu H) and finned surface effectiveness ( ε) are maximum. It has been found that: (1) increasing fin length increases Nu H and ε; (2) increasing Ra increases Nu H for any fin-array geometries and (3) for any fin-array geometry and at Ra > 10,000, increasing Ra decreases ε while for fin-array geometries of large fin spacing and at Ra < 10,000, increasing Ra increases ε. Useful design guidelines have been suggested. Correlations of Nu H have been developed for horizontal and vertical enclosures. Correlations predictions have been compared with previous data and good agreement was found.

An Experimental and Theoretical Investigation into the Thermal Performance Characteristics of a Staggered Vertical Pin Fin Array Heat Sink with Assisting Mixed Convection in External and In-Duct Flow Configurations

A theoretical and experimental study was carried out on the thermal performance of a pin fin array heat sink. A theoretical model was utilized based on the success of prior research that has the capability of predicting the influence of various geometrical, thermal, and flow parameters on the effective thermal resistance of the heat sink. An experimental investigation was carried out for measuring the thermal performance of the heat sink, and the overall convective heat transfer coefficient for the fin bundle, including the thermal and flow bundle effect. Utilizing the new empirical correlations, theoretical predictions were made and experimentally validated for a wide range of parameters for combined forced and natural convection in the assisting flow configuration. Both the theoretical model and experimental data indicated the existence of optimal fin spacing.

The optimal fin spacing for three-row flat tube bank fin mounted with vortex generators

To reduce the size and the weight of heat exchangers, vortex generators (VGs) were punched on fin surface to improve the fin heat transfer performance. This paper is focused on the optimal fin spacing for three-row flat tube bank fin mounted with VGs. The results show, for commonly used fin materials and fin thickness, the optimal fin spacing is about 2 mm in industrial application for the configuration of tube bank fin studied.

Development of a theoretical model for predicting the thermal performance characteristics of a vertical pin-fin array heat sink under combined forced and natural convection with impinging flow

A comprehensive theoretical and experimental study was carried out on the thermal performance of a pin-fin heat sink. A theoretical model was formulated that has the capability of predicting the influence of various geometrical, thermal, and flow parameters on the effective thermal resistance of the heat sink. An experimental technique was developed for measuring the thermal performance of the heat sink, and the overall convective heat transfer coefficient for the fin bundle. Experiments were carried out, and correlations obtained, for a wide range of parameters for pure natural convection and for combined forced and natural convection. The predictive capability of the theoretical model was verified by comparison with experimental data including the influence of various fin parameters and the existence of an optimum fin spacing.

Laminar free convection underneath a downward facing hot fin array

A combined analytical, numerical and experimental study was conducted to investigate the problem of natural convection underneath a horizontal rectangular hot fin array. This subject has not been explored before. The purpose of the investigation was to provide useful and reliable heat transfer coefficients. In addition to the experimental and numerical results, a useful approximate closed form analytical solution is offered. The analytical solution clearly reveals the dependence of the Nusselt number on the Rayleigh number, the Prandtl number and the fin's height to spacing ratio. Optimum analyses were conducted to determine the minimum fin height that provides the necessary cooling capability of a specified array base area. In this context it is shown that the optimal fin spacing varies within a narrow range which depends primarily on the array length. Those findings have important industrial application because they impact both the cost and size of cooling finned surfaces.