Colburn Factor Research Articles

Experimental investigation of air side heat transfer and fluid flow performances of multi-port serpentine cross-flow mesochannel heat exchanger

Air side force convective heat transfer and flow characteristics of cross-flow mesochannel heat exchanger are investigated experimentally. A series of experiments representing 36 different operating conditions have been conducted on a finned mesochannel heat exchanger through the fully automated dynamic single-phase experimental facility which is capable of handling a wide variety of working fluids in air-to-liquid cross-flow orientation. The mesochannel heat exchanger is made of 15 aluminum slabs with arrays of wavy fins between slabs; 68 one millimeter circular diameter port located at each slab, and the air side frontal area of 304-mm×304-mm. The ethylene glycol–water mixture as the working fluid in the liquid side was forced to flow through mesochannels maintaining constant inlet temperature and flow rate at 74°C and 0.0345kg/s respectively whereas the inlet flowing air into the arrays of wavy fins was changed at four different temperature levels from 28°C to 43°C. Frontal air velocity was altered in nine steps from 3m/s to 11m/s at each temperature level corresponding range of Reynolds number 752<Rea<3165. The air side heat transfer and flow characteristics of mesochannel heat exchanger were evaluated during air heating, and heat transfer and fluid flow correlations were derived accordingly. The air side Nusselt number (Nua) and Colburn factor (ja) were found higher in comparison with other studies.

주름높이의 변화를 고려한 판형열교환기의 완전발달유동 및 열전달 수치해석

Numerical analysis has been carried out to investigate the fully developed flow and heat transfer characteristics of a plate heat exchanger. Multi-cell models with an inlet part and outlet part are used to perform the numerical simulation. The plate heat exchanger is characterized by a chevron angle of 20° and a P/H ratio of 2.0 4.0. The working fluid is water and the Reynolds numbers range from 300 to 1,500. The ~ correlation is given in the form of     for the friction factor and     for the Colburn factor. It is found that the fully developed flow starts from the third cell and the Nusselt number increases with decreasing P/H ratios.

Metal foam heat exchangers for heat transfer augmentation from a tube bank

A numerical study has been conducted to examine the heat transfer from a metal foam-wrapped tube bundle. Effects of key parameters, including the free stream velocity, longitudinal and transversal tube pitch, metal foam thickness and characteristics of the foam (such as porosity, permeability, and form drag coefficient) on heat and fluid flow are examined. It can be observed that the performance of the metal foam heat exchangers, measured in terms of area goodness factor, can noticeably be better than that of the conventional design of finned-tube heat exchangers. It is also found that even a very thin layer of metal foam, when wrapped around a bare tube bundle, can significantly improve the area goodness factor. Finally, it is shown that while friction factor is more sensitive to the metal foam permeability than its porosity, the converse is true when it comes to the Colburn factor.

Development of heat transfer coefficient and friction factor correlations for offset fins using CFD

PurposeIn aerospace applications, due to the severe limitations on the weight and space envelope, it is mandatory to use high performance compact heat exchangers (CHEs) for enhancing the heat transfer rate. The most popularly used ones in CHEs are the plain fins, offset strip fins (OSFs), louvered fins and wavy fins. Amongst these fin types, wavy and offset fins assume a lot of importance due to their enhanced thermo‐hydraulic performance. The purpose of this paper is to investigate the influence of geometrical fin parameters, in addition to Reynolds number, on the thermo‐hydraulic performance of OSFs.Design/methodology/approachA computational fluid dynamics approach is used to conduct a number of numerical experiments for determination of thermo‐hydraulic performance of OSFs considering the various geometrical parameters, which are generally used in the aerospace industry. These investigations include the study of flow pattern for laminar, transition and turbulent regions. Studies are conducted with different fin geometries and comparisons are made with available data in open literature. Finally, the generalized correlations are developed for OSFs taking all geometrical parameters into account for the entire range of operations of the aerospace industry covering laminar, transition and turbulent regions. In addition, the effects of various geometrical parameters are presented as parametric studies.FindingsThermo‐hydraulic design of CHEs is strongly dependent upon the predicted/measured dimensionless performance (Colburn factor “j” and Fanning friction “f” vs Reynolds number Re) of heat transfer surfaces. Several types of OSFs used in the compact plate‐fin heat exchangers are analyzed numerically.Research limitations/implicationsThe present numerical analysis is carried out for “air” media and hence these results may not be accurate for other fluids with large variations of Prandtl numbers.Practical implicationsIn open literature, these fins are generally evaluated as a function of Reynolds number experimentally, which are expensive. However, their performance will also depend to some extent on geometrical parameters such as fin thickness, fin spacing, offset fin length and fin height.Originality/valueThis numerical estimation can reduce the number of tests/experiments to a minimum for similar applications.

Turbulence Models for Fluid Flow and Heat Transfer Between Cross-Corrugated Plates

Three-dimensional numerical predictions of fluid flow and heat transfer between cross-corrugated plates were obtained for the same geometry and grid using eight turbulence models, i.e., LBKE, SKE, RKE, RNGKE, RSM, KW, SST and LES, for the purpose of model performance evaluation. The average Colburn factor j, friction factor f, and local Nusselt number distribution were presented and compared with available experimental data. The velocity, temperature, and turbulent viscosity ratio distributions were recorded and discussed. It has been found that all models can predict practically satisfactory j and acceptable f within the current Reynolds number range. LBKE and SST provide the best overall agreement with experimental data and thus are highly recommended for application. Taking into account its robustness and economy, SKE with enhanced wall treatment is also recommended for CC channel flow and heat transfer simulation. In addition, near wall treatment approach seems to be significant for the current wall-bounded flow simulation. Since some models predict similar j and f values but very different velocity and temperature distributions, it seems not quite sufficient to only compare the overall heat transfer and pressure drop data between simulation and experiment for comprehensive model evaluations.

3D-CFD simulation and neural network model for the j and f factors of the wavy fin-and-flat tube heat exchangers

A three dimensional (3D) computational fluid dynamics (CFD) simulation and a neural network model are presented to estimate the behaviors of the Colburn factor (j) and the Fanning friction factor (f) for wavy fin - and - flat tube (WFFT) heat exchangers. Effects of the five geometrical factors of fin pitch, fin height, fin length, fin thickness, and wavy amplitude are investigated over a wide range of Reynolds number (600<Re<7000). The CFD simulation results express that the geometrical parameters of wavy fins have significant effects on the j and f factors as a function of Reynolds number. The computational results have an adequate accuracy when compared to experimental data. The accuracy of the calculations of the j and f factors are evaluated by the values of the absolute average relative deviation (AARD), being respectively 3.8% and 8.2% for the CFD simulation and 1.3% and 1% for the neural network model. Finally, new correlations are proposed to estimate the values of the j and f factors with 3.22% and 3.68% AARD respectively.

Optimization design of slotted fin by numerical simulation coupled with genetic algorithm

Using a novel method that couples genetic algorithm (GA) with numerical simulation, the geometric configuration for a two-dimensional slotted fin has been optimized in this paper. The objective of optimization is to maximize the heat transfer capacity of slotted fin, and minimize the pressure drop penalty of fluid flow through the fin. The key of this method is the fitness function of GA, which were ( j/ j 0)/( f/ f 0) and j/ j 0. In this complex multiparameter problem, the numerical simulation is a crucial step to calculate the Colburn factor j and friction factor f. The results showed that for two-dimensional slotted fin considered, the j factor is increased by 229.22%, the f factor is increased by 196.30%, and the j/ f ratio was increased by 11.11% at Re = 500 based on optimal integrated performance ( j/ j 0)/( f/ f 0); the j factor is increased by 479.08% at Re = 500 based on optimal heat exchange capacity j/ j 0. The feasibility of optimal designs was verified by the field synergy principle.

CFD modeling and multi-objective optimization of compact heat exchanger using CAN method

Abstract Thermal modeling and optimal design of compact heat exchanger is presented in this paper. Fin pitch, fin height, cold stream flow length, no-flow length and hot stream flow length were considered as five design parameters. A CFD analysis coupled with artificial neural network was used to develop a relation between Colburn factor and Fanning friction factor for the triangle fin geometry with acceptable precision. Then, fast and elitist non-dominated sorting genetic algorithm (NSGA-II) was applied to obtain the maximum effectiveness and the minimum total pressure drop as two objective functions. The results of optimal designs were a set of multiple optimum solutions, called ‘Pareto-optimal solutions’. It reveals that any geometrical changes which decrease the pressure drop in the optimum situation, lead to a decrease in the effectiveness and vice versa. Finally sensitivity analysis shows the increases of heat transfer surface area necessarily do not increases the pressure drop and it is case sensitive.

Unsteady wake dynamics and heat transfer in forced and mixed convection past a circular cylinder in cross flow for high Prandtl numbers

This paper investigates the combined effect of Prandtl number and Richardson number on the wake dynamics and heat transfer past a circular cylinder in crossflow using a SUPG based finite element method. The computations are carried out for 80 < Re < 180, 0.7 < Pr < 100 and 0 ⩽ Ri ⩽ 2 . The results have been presented for both forced and mixed convection flows. In the case of forced convection, crowding of temperature contours with reduced spatial spread is observed for increasing Prandtl numbers. The local and average Nusselt numbers are found to increase with increasing Reynolds number and Prandtl number. The average Nusselt number and Colburn factor are found to vary as Re 0.548 Pr 0.373 and Re −0.452, respectively. The extrapolated results of the average Nusselt number for low and high Reynolds numbers are found to match quite well with the available results in literature. Effect of Prandtl number shows various interesting phenomena for the mixed convective flows. Increasing the Prandtl numbers resulted in decreasing deflection and strength in the wake structures. The effect of baroclinic vorticity production during vortex shedding has been demonstrated at the vicinity of the cylinder and near wake. The Strouhal number is found to decrease with increasing Prandtl number, in the case of buoyancy induced flow. The effect of increasing Prandtl number is manifested as the stabilizing effect in the flow. This is, perhaps, the first time that such behavior for the Prandtl number is being reported. Additionally it is observed that the average Nusselt number decreases with increasing Richardson number.

Determination of External Mass Transfer Model for Hydrolysis of Jatropha Oil Using Immobilized Lipase in Recirculated Packed-Bed Reactor

In this study, a simple and effective technique for establishing an external mass transfer model in a recirculated packed-bed batch reactor (RPBBR) with an immobilized lipase enzyme and Jatropha oil system is presented. The external mass transfer effect can be represented with a model in the form of Colburn factor JD = K Re-(1–n). The value of K and n were derived from experimental data at different mass flow rates.The experiment shows an average increment of 1.51% FFA for calcium alginate and 1.62% FFA for carrageenan after the hydrolysis took place. Based on different biopolymer material used in immobilized beads, JD = 1.674 Re-0.4 for calcium alginate and JD = 1.881 Re-0.3 for k-carrageenan were found to be adequate to predict the experimental data for external mass transfer in the reactor in the Reynolds number range of 0.2 to 1.2. The purposed model can be used for the design of industrial bioreactor and scale up. Besides, the external mass transfer coefficients for the hydrolysis of Jatropha oil reaction and the entrapment efficiency for the two biopolymer materials used were also investigated.

Mass transfer at the confining wall of helically coiled circular tubes in the absence and presence of packed solids

Limiting current measurements were made at the electrode surfaces fixed flush with the inner wall of a helically coiled circular tube. The measured limiting current facilitated the computation of wall–liquid mass transfer coefficients. The mass transfer data were obtained for the flow of electrolyte through the helical coil in the absence and presence of packed solids. The mass transfer coefficient was found to decrease with increasing p/D ratio and approached minimum for straight tube case. The mass transfer data were correlated in terms of Colburn factor j D, expressed as a function of Reynolds number Re and torsion number Tn obtained as j D = 0.34 Re − 0.58 T n 0.17 . Analysis of the experimental data obtained in case of packed coiled tubes of circular cros- section revealed that the effect of p/D ratio on pressure drop was observed to be insignificant. The effect of pitch on mass transfer coefficient in case of packed helical coils was found to be marginal.

입구영향 및 주름높이의 변화를 고려한 판형열교환기의 유동 및 열전달 특성

의 형태로 상관관계식을 제시하였다. 이러한 상관관계식은 향후 판형열교환기 설계시에 기초자료로 활용될 수 있을 것으로 판단된다.Abstract: Numerical analysis has been carried out to investigate the heat transfer characteristics of a plate heat exchanger. The multi-cell models with inlet part and outlet part are used for performing numerical simulation. The plate heat exchanger is characterized by chevron angle of 15°, corrugation pitch of 24mm and corrugation height 6～12mm. The length of the inlet-part considered in the analysis ranges from 24.8 to 124mm and Reynolds numbers range from 1,000 to 10,000. The correlations such as friction factor and Colburn factor are compared with previous experimental data. The results can be utilized for designing the plate heat exchanger.

An investigation of the performance of compact heat exchanger for latent heat recovery from exhaust flue gases

An experimental and theoretical investigation of the utilization of finned tube compact heat exchanger for a heat recovery steam generator (HRSG) to recover both sensible and latent heat is presented in this paper. The heat transfer and pressure drop characteristics of the fin-and-tube heat exchanger are theoretically studied. A correlation of the combined convection–condensation heat transfer is derived by using the heat and mass transfer analogy models. The experimental results have shown that the Colburn factor ( j) and the friction factor ( f) for humid air, simulating the exhaust of HRSG, are larger than those for dry air. It has been also found that the f factor difference between humid air and dry air decreases as the air side Reynolds number increases and both the f factor and the j factor for humid air increase with the increase of water vapour concentration. A scheme for the design of compact heat exchanger for HRSGs is presented.

Air-side thermal hydraulic performance of an integrated fin and micro-channel heat exchanger

An integrated fin and micro-channel heat exchanger has been proposed. For 11 heat exchanger samples with different flow depth, fin height, fin pitch and fin thickness, a series of tests were conducted to determine their effect on the air-side thermal hydraulic performance. The heat transfer coefficient and pressure drop for heat exchangers with different geometrical configurations were reported in terms of Colburn factor j and Fanning friction factor f, as functions of Reynolds number. The general correlations for j and f factors were derived and can predict 96% and 92% of the experimental data, within rms errors of ±10% and ±12%, respectively. The air-side heat transfer and flow characteristics of the integrated fin were compared with that of the multi-louver fin and the wavy fin.

External mass transfer analysis for simultaneous removal of carbohydrate and protein by immobilized activated sludge culture in a packed bed batch bioreactor

External mass transfer effects were analyzed for removal of carbohydrate and protein by immobilized activated sludge culture in a packed bed bioreactor. The bioreactor was made from 52cm glass tubing with 5.0cm inner diameter (with a total volume of 1020cm3). The microbial culture was immobilized on microporus polyurethane cut into cubic pieces of approximately 1.5cm in length. The effect of flow rate on mass transfer and removal of carbohydrate and protein were analyzed theoretically and compared with experimental data. The rate constants were estimated using external film diffusion models at different flow rates (900, 1200, 1800cm3h−1). Based on the experimental data, correlations between the Colburn factor (JD) and Reynolds number (Re) as JD=5.7×Re−0.90 and JD=5.7×Re−0.18 were found to be adequate to predict the removal of carbohydrate and protein, respectively.

Numerical study on air-side performance of an integrated fin and micro-channel heat exchanger

A new type of aluminum heat exchanger with integrated fin and micro-channel has been proposed. The air-side heat transfer and flow characteristics of the integrated fin and micro-channel heat exchanger are systematically analyzed by a 3D numerical simulation. The effect of flow depth, fin height, fin pitch and fin thickness at different Reynolds number is evaluated by calculating Colburn factor j and Fanning friction factor f. A parametric study method is used to analyze the fin designed parameters affecting the performance of the heat exchanger. The results show that the contribution ratio of the fin geometries in descending order is flow depth, fin pitch, fin height and fin thickness. The air-side performance of the integrated fin and micro-channel heat exchanger is compared with that of the multi-louver fin micro-channel heat exchanger and the wavy fin micro-channel heat exchanger.

Thermal characteristics of louvered fins with a low-reynolds number flow

A heat recovery system is crucial for the effective use of energy where heat rejection from production processes is unavoidable and must be reused. The response of the louvered fins to the low-Reynolds number hot gas is yet to be reported in the literature for the application of a heat exchanger on low-speed hot plume arising from heat sources in production processes. This study focuses on the effects of the louvered fin heat exchanger’s design parameters, which include the louver pitch and louver angle, on the convective heat transfer, which defines the thermal interaction between the hot, buoyant, naturally-induced air and the louvered fins. The resulting Colburn factors (j) are compared with those derived under forced convection with a similar range of low Reynolds number (233 to 1024). All experiments are done on a 15:1 scaled-up model. The fin aspect ratios between the fin spacing and louver pitch are set at 0.75, 1, and 1.5, while the louver angles are set at 18°, 23°, 30°, 35°, and 40°. The Colburn factor strongly depends on the louver angle, especially at the lower range of the Reynolds number. The decreasing aspect ratio induces more hot buoyant air into the louver-formed channels, increasing the heat transfer rate. When the fin angle increases towards 30°, a larger Colburn factor is produced. However, the heat transfer characteristic drops as the angle goes beyond 30°. The highest j for the low speed flow is attained when the louver angle is 30° and the fin aspect ratio is 1.

Studies on Fanning Friction (f) and Colburn (j) Factors of Offset and Wavy Fins Compact Plate Fin Heat Exchanger–A CFD Approach

The objective of this work is to address the uncertainties in the estimation of the Fanning friction (f) and Colburn (j) factors in a compact offset plate fin heat exchanger, and the generation of flow friction and heat transfer correlations in the form of f and j for compact wavy plate fin heat exchangers. A typical offset fin has been analyzed using FLUENT software (a general purpose computational fluid dynamics (CFD) simulation tool) for estimation of f and j data. These results are compared with the results of the available correlations in the literature and in-house experimental results. Uncertainties in estimation of f and j data are reviewed and the variations in the results are highlighted. In the case of wavy fin configuration, very limited correlations are available in the literature. Hence, with the objective of developing correlations, 18 different types of wavy fins geometries have been analyzed using a CFD tool to find out the f and j data in the laminar and turbulent regions. Multiple regression analysis has been carried out on the set of data to generate the correlations for f and j. These correlations have been compared with the experimental results of wavy fin reported in the literature.

A Numerical Study of Flow and Heat Transfer in Internally Finned Rotating Curved Pipes

In this article, the effects of internal fins on an incompressible viscous flow and heat transfer inside rotating curved pipes are numerically studied under the hydrodynamically and thermally fully developed conditions. The fins are assumed to have negligible thickness with the same conditions as the pipe walls. Two thermal boundaries including constant wall temperature and constant heat flux are considered at the pipe wall. First the accuracy of the numerical code written by a finite-volume method based on the SIMPLE algorithm is verified by the available data for the finless rotating curved pipes. Then, the numerical results for the internally finned rotating pipes are investigated in both positive and negative rotation numbers affecting remarkably on the flow and temperature field patterns. Also, the Dean number (KLC) effects on the friction factor, Nusselt number, and other nondimensional parameters are studied in detail. Analyzing the numerical results by the Colburn factor, two optimum fin heights consisting of the four-fifth of the pipe radius at the lower Dean numbers and one-third of the pipe radius at higher Dean numbers are determined in the curved rotating pipe with six internal fins.

Numerical study of flow patterns of compact plate-fin heat exchangers and generation of design data for offset and wavy fins

Thermo-hydraulic design of compact heat exchangers (CHEs) is strongly dependent upon the predicted/measured dimensionless performance (Colburn factor j and Fanning friction factor f vs. Reynolds number Re) of heat transfer surfaces. Also, air (gas) flow maldistribution in the headers, caused by the orientation of inlet and outlet nozzles in the heat exchanger, affects the exchanger performance. Three typical compact plate-fin heat exchangers have been analyzed using Fluent software for quantification of flow maldistribution effects with ideal and real cases. The headers have modified by providing suitable baffle plates for improvement in flow distribution. Three offset strip fin and 16 wavy fin geometries used in the compact plate-fin heat exchangers have also been analyzed numerically. The j and f vs. Re design data are generated using CFD analysis only for turbulent flow region. For the validation of the numerical analysis conducted in the present study, a rectangular fin geometry having same dimensions as that of the wavy fin has been analyzed. The results of the wavy fin have been compared with the analytical results of a rectangular fin and found good agreement. Similarly, the numerical results of offset strip fin are compared with the correlations available in the open literature and found good agreement with most of the earlier findings.