3-D Numerical study on the correlation between variable inclined fin angles and thermal behavior in plate fin-tube heat exchanger
Introduction
Heat exchangers are widely used devices in the industry because of supply heat transfer between two fluids that are at different temperatures and separated by a solid wall. The plate fin-tube heat exchangers have been used in the thermal engineering applications, such as power station, chemical plants, food industries, heating–cooling systems, aircrafts, automotive sectors, etc. There are various fin types that used plate, louver, convex louver, wavy and tube geometries that used circular, elliptical, etc. The plate fin shapes are still the most popular fin pattern in the fin-tube heat exchanger applications because of its durability, simplicity, versatility and rigidity. In this case, many researchers have studied to effectively improve of the fin-tube heat exchangers [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]. They have made experimentally and numerically investigation on heat transfer performance and pressure drop characteristics of the plate fin-tube heat exchangers.
Experimental study of the plain fin-tube heat exchangers is very useful but very expensive due to because of the high cost of the tools. Nevertheless, some studies have been done experimentally to determine heat transfer and friction characteristics of the plate fin-tube heat exchangers. Wang and Chi have intended to provide new experimental data for the plain fin-tube heat exchangers owing to the present authors need further experimental information [7]. Tao et al. have studied experimentally and numerically 3-D model of air side heat transfer and pressure drop. They have compared the performance of slotted fin and plain plate fin surface [13]. Kim et al. have investigated a new experimental-numerical method for the evaluation of thermal contact resistance in the fin-tube heat exchangers [14], [15].
On the other hand, the general theory of fluid motion is sometimes difficult to enable the user to apply arbitrary geometric configurations. It can be possible to achieve only numerical techniques to arbitrary geometries. The second advantage of numerical method is to apply without the experimental study or reducing the extent and number of experiments required to describe of flow. Therefore, a suitable numerical method and/or computational fluid dynamics (CFD) code is frequently used to solve the governing equations of fluid flow. The CFD code provides to predict some information about the flow speed, pressures, residence times, flow patterns, heat transfer, etc. Thus, numerical methods have been performed by several researchers for the analysis of the fin-tube heat exchangers included in several geometries and different boundary conditions. Romero-Mendez et al. have investigated numerically the effect of fin spacing on convection in a plate fin-tube heat exchanger [2]. Erek et al., have analyzed a plate fin type heat exchanger with one row tube configuration for different geometrical parameters by using a numerical computation technique. They have also investigated numerically the effects of the distance between two fins, tube center location, fin height, tube thickness and tube ellipticity on heat transfer and pressure drop across the heat exchanger [1]. Haught and Engelmann have used a finite element method and reported examples of velocity and temperature fields [16]. Fiebig et al. have reported on the results of finite volume calculations of the flow and conjugate heat transfer in fin-tube geometry. They have calculated the flow variations, pressure drop, Nusselt number distribution and fin efficiency as a function of Reynolds number [17]. Jang et al. have reported a numerical calculated of Nusselt number and pressure drop as a function of the fin-spacing based on Reynolds number [18].
Reviewing the literature, it has been found that the effect of geometrical parameters on heat transfer and pressure drop for the various fin types and tube geometries of the fin-tube heat exchangers have been investigated during the recent decades. However, the effective factors of inclined fin angles on heat transfer and pressure drop across in a heat exchanger have not been analyzed numerically. Having more basic structure, variable inclined fin angle systems are easer to fabricate than the flue gas flow angle systems such as louvered fins. In fact, manufacturing of louvered fin geometries changing flue gas flow angles used for heat transfer enhancement in the heat exchangers is more complicated and expensive than the fin angle systems. The cutting force increases due to having more and more louvers on the fin. So this situation requires using more press capacity. In addition, increasing the number of punches enlarges dimensions of the die which will raise cost of manufacture. Moreover, having more operations result in more workers’ pay. On the other hand cutting die method facilitates fabricating of the fin angles. Angle of hole on the plate fin is formed by cutting die methods. There are two cutting die methods to obtain any desired angle hole. These are cam-punching die method in which the direction of elements is at an angle to the direction of forces supplied by a press and shaving die method having angled cutting edges. More detail can be found in Ref. [19]. These variable fin angle systems using the same number of fins as straight flue gas systems supply more heat transfer enhancement. In case of reducing fin spacing for straight flue gas direction more fin numbers will be required to provide the same heat transfer enhancement. In this respect, variable inclined fin angles used in the plain plate-tube heat exchangers were considered to investigate. As differing from other work, the main objective of this study is to analyze for different inclined fin angles by using a three dimensional (3-D) numerical computation technique, the help of the FLUENT, a CFD computer code [20]. The heat transfer performance comparison of the vertical fin angle and variable inclined fin angles having plain plate-tube heat exchangers have been tabulated and discussed.
Section snippets
Mathematical modeling
The governing equations for continuity, momentum and energy in the computational procedure can be written as follows.
Continuity equation:
Momentum equation:
Energy equation:
Calculation procedure
The numerical simulation of the fin-tube heat
Numerical results and discussion
The FLUENT was run for each model to obtain numerical results. The heat transfer from the flue gas in the gap between two fins to the water inside the tube and total pressure drop values of flue gas across the heat exchanger were calculated numerically for each model. Then, obtained results were presented in Table 1. Here the heat transfer rate from the flue gas on the distance between two fins of the tube surface into the water inside the tube is not important value due to its very small
Summary and conclusions
Different inclined fin angles on the heat transfer between flue gas and water, and pressure drop of flue gas passing through two fins were evaluated numerically. Then, the calculated results have shown that the applied models are achieved successfully and the conclusions can be summarized as follows:
- •
The FLUENT was applied successfully for the heat transfer and pressure drop analyses in the fin-tube heat exchanger.
- •
The results indicated the effective enhancement of the heat transfer performance.
- •
Acknowledgements
The authors gratefully acknowledge Gazi University and Erciyes University for their support in this study.
References (23)
- et al.
Effect of geometrical parameters on heat transfer and pressure drop characteristics of plane fin and tube heat exchangers
Applied Thermal Engineering
(2005) - et al.
Effect of fin spacing on convection in a plate fin and tube heat exchanger
International Journal of Heat and Mass Transfer
(2000) - et al.
Modeling for predicting frosting behavior of a fin-tube heat exchanger
International Journal of Heat and Mass Transfer
(2006) - et al.
Optimum dimensions of plate fins for fin-tube heat exchangers
International Journal of Heat Fluid Flow
(1997) - et al.
Performance characteristics correlation for round tube and plate finned heat exchangers
International Journal of Refrigeration
(1998) - et al.
Heat transfer and friction characteristics of plain fin-and-tube heat exchangers, Part II: correlation
International Journal of Heat and Mass Transfer
(2000) - et al.
Heat transfer and friction characteristics of plain fin-and-tube heat exchangers, part I: new experimental data
International journal of Heat and Mass Transfer
(2000) - et al.
Experiments on elliptic sections in one and two row arrangements of plate fin and tube heat exchangers
Experimental Thermal and Fluid Science
(2001) - et al.
Microscopic phenomena and macroscopic evaluation of heat transfer from plate fins/circular tube assembly using naphthalene sublimation technique
International Journal of Heat and Mass Transfer
(2002) - et al.
The catalytic heat exchanger using catalytic fin tubes
Chemical Engineering Science
(2003)
Flow, heat transfer, and pressure drop in the near-wall region of louvered-fin arrays
Experimental Thermal and Fluid Science
Cited by (34)
Thermal and flow performance of tilted oval tubes with novel fin designs
2020, International Journal of Heat and Mass TransferCitation Excerpt :The effect of inlet flow angle reduces with fin pitch and a positive inlet flow angle results in highest performance. Şahin et al. considered 7 different fin inclinations (0∘, 5∘, 10∘, 15∘, 20∘, 25∘ and 30∘) for heat transfer and pressure drop analysis in a numerical simulation [38]. A maximum value of both, heat transfer and pressure drop, was reached at 30∘.
An experimental investigation on the air-side heat transfer and flow resistance of finned short oval tubes at different tube tilt angles
2019, International Journal of Thermal SciencesParametric study on rectangular finned elliptical tube heat exchangers with the increase of number of rows
2018, International Journal of Heat and Mass TransferCitation Excerpt :Through the early work of Brauer [3], Jang and Yang [4], Saboya and Saboya [5], the fact that the elliptical tube configuration is more efficient than the circular one is proved. Afterwards, a number of papers addressed the influence of various structural parameters on the performance of FTHXs with elliptical tubes, such as the ellipticity of the tube [6,7], fin angle [8], tube pitches, fin pitch and fin thickness [2,10]. Refs. [2,10] constitute the most complete numerical parameter information available in the open literature about FTHXs with elliptical tubes.
Numerical study on airside thermal-hydraulic performance of rectangular finned elliptical tube heat exchanger with large row number in turbulent flow regime
2017, International Journal of Heat and Mass TransferNumerical study to predict optimal configuration of fin and tube compact heat exchanger with various tube shapes and spatial arrangements
2017, Energy Conversion and ManagementCitation Excerpt :It was found that fin pitch has no significant effect on the j and f factor for the oval tube samples and oval geometry is more beneficial under wet condition than under dry condition. Sahin et al. [15] numerically investigated that fin angle of θ = 30° is the optimum angle among the considered angles (θ = 5°, 10°,15°, 20°, 25°, 30°), which provides the maximum heat transfer enhancement per segment with the value of 1.42 W and the maximum loss power associated with pressure drop per segment is 0.54 mW. Wu and Tao [16] performed numerical investigation on fin-tube surface with two rows of tubes in different diameters with punched out vortex generators.
Impacts of geometric structures on thermo-flow performances of plate fin-tube bundles
2016, International Journal of Thermal SciencesCitation Excerpt :Yang et al. [5] investigated the effect of oblique configuration of wave-finned flat tube bundles on the thermo-flow characteristics, and obtained the flow and heat transfer correlations. Şahin et al. [6] investigated the pressure drop and heat transfer of seven plain fin-tube heat exchangers with different fin angles, concluding that the inclined fin with the angle of 30° is the optimum configuration. Mon and Gross [7] studied the effect of fin spacing on the four-row annular-finned tube bundles in staggered and in-line arrangements, finding that the boundary layer development and horseshoe vortices between the fins depend substantially on the fin spacing to height ratio and Reynolds number.