Louver Pitch Research Articles

Airside Thermal Performance of Louvered Fin Flat-Tube Heat Exchangers with Different Redirection Louvers

The performance of heat exchangers is severely limited by airside thermal resistance. The effect of redirection louvers (RLs) on the airside thermal performance of a compact flat-tube louvered fin heat exchanger was investigated. A steady-state 3D numerical analysis was conducted for different fin configurations by varying the number of RLs (NRL = 1, 2, 3, and 5). Conjugate heat transfer analysis was performed at the low Re (50–450) for domestic and transport air-conditioning applications. Geometric parameters such as louver pitch, louver angle, fin pitch, and flow depth were set as 1.7 mm, 27°, 1.2 mm, and 20 mm, respectively. The effective heat transfer fin surface areas of different fin configurations were also kept identical for a comparative analysis. The influence of the RLs on the airside thermal–hydraulic performance was analysed by exploring the local and average Nusselt numbers, pressure drop, Colburn j factor, friction factor f, performance evaluation criteria (PEC), and flow efficiency of different fin configurations. The numerical results revealed that the asymmetric fin configuration with two RLs (NRL = 2) showed the best heat transfer performance for the entire Re range. It resulted in a 33% higher average Nusselt number, causing a 24% higher pressure drop compared to NRL=5. At low flow velocities (Re < 75), NRL = 3 showed better PEC; however, at high flow velocities (Re > 75), NRL = 1 outperformed other fin configurations. Finally, it was noted that increasing the number of RLs reduced the amplitude of the wavy-shaped flow formed between the neighbouring louvered fin, consequently deteriorating the flow efficiency.

Thermal-hydraulic experimental study of louvered fin-and-flat-tube heat exchanger under wet conditions with variation of inlet humidity ratio

An experimental study for air-side thermal-hydraulic performance of louvered fin-and-flat-tube heat exchanger under dehumidifying conditions has been performed. The louvered fin studied, used for an automotive evaporator, is geometrically defined by a flow depth of 47 mm, a high louver angle of 50° and a louver pitch of 1.1 mm. The test was conducted for frontal air velocity ranging from 1.1 to 4.5 m/s. The heat exchanger was tested first in dry condition, working as a heater. In wet conditions, the cooling coil was tested for three air inlet temperatures, Ta, and for various inlet relative humidity, RH, organized as follows: Ta = 30 °C (RH = 40 to 70%), Ta = 35 °C (RH = 30 to 60%), and Ta = 40 °C (RH = 20 to 60%); which correspond to a variation of the inlet humidity ratio from 9.2 to 27.7 gwater/kgdry-air. It was found that, for all inlet conditions, the wet friction factor is higher than that for dry surface (up to 43%). Concerning the heat transfer performance, at low Reynolds number, the sensible Colburn ‘j’ factor is insensitive to the surface conditions. However, as Re number increases, the sensible wet j factor decreases (up to 23%) compared to the dry one. This degradation is more and more pronounced as the inlet humidity ratio increases.

Simulation investigation on inlet velocity profile and configuration parameters of louver fin

This work aimed to investigate the effect of louver fin configurations on the thermal performance at different Reynolds numbers. The discussed ranges of these geometry parameters were 7.5–12.5 mm (louver length), 8°–20° (louver angle), and 2.25–3.75 mm (louver pitch). The three dimensional CFD simulation was performed and validated with reported experimental data and other simulation results from published articles. The flow and heat transfer characteristics in louver fin were analyzed numerically. Based on these numerical results, a detailed description of Nusselt number and pressure drop was presented and discussed. Two kinds of inlet velocity profiles including Linear-up and Linear-down were investigated. All the numerical data would be presented at different Reynolds number between 70 and 350. In addition, the Nu number correction and pressure drop correction were presented and the optimization of louver fin was obtained. Optimized result was L=7.5mm, α=8°, and Lp=2.25mm. Compared with the reference louver fin, Nu number of the optimized louver fin was decreased by about 24.2%, while the pressure drop was decreased by 36.7%, in turn leading to the increase of PEC by 19%.

Improved correlations of the thermal-hydraulic performance of large size multi-louvered fin arrays for condensers of high power electronic component cooling by numerical simulation

In view of a good thermal performance of the multi-louvered fin arrays, it is intended to introduce the special fin structure into the design of condensers for high power electricity converter cooling on the CRH (China Railway High-speed) trains in order to improve the security of normal running for the high-speed trains. The geometrical size of the multi-louvered fin arrays needed for the high power condensers is relatively larger than that of the conventional louvered fin arrays and the flow state within the large size multi-louvered fin arrays is different as well, with the Reynolds numbers based on the louver pitch over the range of 2850–11,000 in the present study. Flow and heat transfer characteristics of the large size multi-louvered fin arrays with various structural parameters are numerically simulated using Large Eddy Simulation (LES). More reasonable parameters correlated with the thermal-hydraulic performance of the large size multi-louvered fin arrays are identified compared to the conventional characteristic parameters employed in the published work. Finally, improved correlations for the Fanning friction f factor and the Colburn-j factor representing the flow and heat transfer characteristics, respectively, are put forward in terms of the identified parameters with special interval bounds for the condenser design of high power electronic cooling.

Air-side thermal hydraulic performance of microchannel heat exchangers with different fin configurations

This paper presents three-dimensional steady state analysis of compact multi-louvered fin and flat tube heat exchangers applicable in domestic and mobile air conditioning systems. Conjugate heat transfer analysis has been conducted for five geometric configurations of the heat exchanger based on the louver pitch values (0.8, 1.0, 1.4, 1.7 and 2.0mm) in the laminar range of Reynolds number 50–450. For all geometric configurations, local air-side heat transfer coefficient and pressure drop are presented in terms of Colburn j factor and Fanning friction f factor, respectively. In addition, the effect of fin height on thermal hydraulic performance has also been addressed based on local Nusselt number distribution along the fin height. The results reveal that geometric configuration with the louver pitch of l.0mm showed the highest average Nusselt number of 123% at the penalty of 116% pressure drop compared to louver pitch of 2.0mm at the Reynolds number of 50.

CFD Analysis on the Air-Side Thermal-Hydraulic Performance of Multi-Louvered Fin Heat Exchangers at Low Reynolds Numbers

The air-side thermal-hydraulic performance of multi-louvered aluminium fin heat exchangers is investigated. A systematic numerical study has been performed to analyze the air-sde thermal hydraulic characteristics over a wide range of Reynolds number i.e., from 30 to 500. Air-side heat transfer coefficient and pressure drop were calculated and validated over the mentioned band of Reynolds numbers. The critical Reynolds number was determined numerically; and also the variation of flow pattern along with the air-side heat transfer coefficient and pressure drop in a multi-louvered heat exchanger associated with R e c r i has been reported. Moreover, a parametric study of the multi-louvered aluminium fin heat exchangers was also performed for 36 heat exchanger configurations with the louver angles (19–31°); fin pitches (1.0, 1.2, 1.4 mm) and flow depths (16, 20, 24 mm); and the geometric configuration exhibiting the highest air-side heat transfer coefficient was reported. The air-side heat transfer coefficient and pressure drop results for different geometrical configurations were presented in terms of Colburn j factor and Fanning friction factor f; as a function of Reynolds number based on louver pitch.

Experimental and Numerical Investigations on Louvered Fin-and-Tube Heat Exchanger With Variable Geometrical Parameters

The effects of geometrical arrangement on the heat transfer and pressure drop characteristics in compact louvered fin-and-tube heat exchangers were studied experimentally and numerically along with ε−NTU method. Different geometrical parameters including louver angle, louver pitch, louver number, the nonlouvered inlet and exit fin length, and redirection of fluid flow are considered to determine their effects on the flow field. The study is performed for different louver angles varying from θL=12 to 60 deg, and optimal heat transfer rate is obtained at louver angle of θL=28deg. Also, it is found that increasing the louver number, NL, on the fin surface enhances the heat transfer performance. It is shown that the average Nusselt number is increased as the louver pitch is decreased and its optimum value is obtained at Lp=0.9 mm. However, comparing to the effect of louver number, the louver pitch has a small effect on the performance of the heat exchanger. Additionally, the optimum values of nonlouvered inlet and exit fin length and redirection length of fin are obtained with different flow conditions.

Computational investigation of heat transfer and pressure drop in a typical louver fin-and-tube heat exchanger for various louver angles and fin pitches

In this study 3-D numerical simulations on heat transfer and pressure drop characteristics for a typical louver fin-and- double-row tube heat exchanger were carried out. The heat transfer improvement and the corresponding pressure drop amounts were investigated depending on louver angles, fin pitch and Reynolds number, and reported in terms of Colburn j -factor and Fanning friction factor f . The heat transfer improvement and the corresponding pressure drop amounts were investigated depending on louver angles between 20° ≤Ө≤ 30°, louver pitch of Lp =3.8 mm and frontal velocities of U between 1.22 m/s - 3 m/s. In addition, flow visualization of detailed flow features results, such as velocity vectors, streamlines and temperature counters have been shown to understand heat transfer enhancement mechanism. The present results indicated that louver angle and fin pitch noticeably affected the thermal and hydraulic performance of heat exchanger. It has been seen that increasing louver angle, increases thermal performance while decreasing hydraulic performance associated to pressure drop for fin pitches of 3.2 mm and 2.5 mm. Fin pitch determines the flow behaviour that for fin pitch of 2 mm, increasing louver angle decreased heat transfer and pressure drop. Velocity vectors and streamlines give considerable information about the flow whether it is duct directed or louver directed. For all conditions the flow is louver directed.

Parametric study of fluid flow and heat transfer over louvered fins of air heat pump evaporator

Abstract Two-dimensional numerical investigations of the fluid flow and heat transfer have been carried out for the laminar flow of the louvered fin-plate heat exchanger, designed to work as an air-source heat pump evaporator. The transferred heat and the pressure drop predicted by simulation have been compared with the corresponding experimental data taken from the literature. Two dimensional analyses of the louvered fins with varying geometry have been conducted. Simulations have been performed for different geometries with varying louver pitch, louver angle and different louver blade number. Constant inlet air temperature and varying velocity ranging from 2 to 8 m/s was assumed in the numerical experiments. The air-side performance is evaluated by calculating the temperature and the pressure drop ratio. Efficiency curves are obtained that can be used to select optimum louver geometry for the selected inlet parameters. A total of 363 different cases of various fin geometry for 7 different air velocities were investigated. The maximum heat transfer improvement interpreted in terms of the maximum efficiency has been obtained for the louver angle of 16 ° and the louver pitch of 1.35 mm. The presented results indicate that varying louver geometry might be a convenient way of enhancing performance of heat exchangers.

A porosity model for flow resistance calculation of heat exchanger with louvered fins

A full 3-dimensional flow simulation of a louvered fin heat exchanger assembly requires a huge number of grid points and enormous computing time. This work proposes a porous media model for the flow resistance calculation of the louvered fin side in order to efficiently simulate a complex 3-dimensional flow over the louvered fins. In the present model, we determine the permeability and Ergun constant in the modified Darcy equation. We first build up a database of the friction factor from the available experimental data and our own CFD data, and then develop the friction factor correlation in the range of the Reynolds number based on the louver pitch from 0.001 to 20000 for 14 different louvered fin types. We use the non-linear and multi-linear regression analyses to obtain the friction factor correlation as a function of louvered fin geometric parameters such as louver pitch, louver angle and fin pitch. The present friction factor correlation shows an excellent agreement with the previous experimental and CFD data. The modified Darcy equation with the proposed permeability and Ergun constant for the louvered fin side can easily be coupled with the 3-dimentional computation of the main tube flow.

Frosting behaviors and thermal performance of louvered fins with unequal louver pitch

We created heat exchanger louvered fin designs in which the louver pitch successively increased or decreased by 20% from the air inlet region to the redirection region. The frost behavior and thermal performance of the unequal louver pitch design were compared with those of an equal louver pitch design, under both dry and frost conditions. When unequal louver pitch design was used, frost blocking of the spaces between louvers at the front side was delayed and the thermal performance was improved by 21%, compared with the equal louver pitch design. The frost blocking ratios of the two unequal louver pitch designs were compared; the design in which the louver pitch successively decreased from the air inlet region to the redirection region provided more uniform frost growth and improved thermal performance, compared to the design in which the louver pitch successively increased.

Experimental and parametric studies of a louvered fin and flat tube compact heat exchanger using computational fluid dynamics

The present study aimed to perform the parametric analysis on thermo-hydraulic performance of a compact heat exchanger using computational fluid dynamics (CFD). The analysis has been carried out at different frontal air velocities by varying the geometrical parameters such as fin pitch, transverse tube pitch, longitudinal tube pitch, louver pitch and louver angle. The air side performance of the heat exchanger has been evaluated by calculating Colburn factor (j) and Fanning friction factor (f). The comparison of CFD results with the experimental data exhibited a good agreement and the influence of various geometrical parameters for the selected range of values on the pressure drop, heat transfer coefficient and goodness factor was analyzed. The results obtained from the analysis will be very useful to optimize the louvered fin and flat tube compact heat exchanger for better thermo-hydraulic performance analysis without the need of time consuming and expensive experimentation.

Effects of Geometrical Parameters to the Performance of Louvered Fin Heat Exchangers

Numerical study using ANSYS Fluent is conducted to investigate the effects of louver angle on pressure drop and heat transfer of a heat exchanger. Flow simulations are conducted on 3D modeling of multi stacks louvered fins at three different parameters of louver angles which are 22.0o, 25.5o and 29.0o with Reynolds number ranging from 200 to 1000. These Reynolds numbers are based on louver pitch and fin pitch. The flow temperature is set at 300K which is the room temperature, while temperature of louver fin is set at 400K. The results show that Reynolds number based on fin pitch 2.02 mm and louver angle of 22.0o generate higher performance of heat exchanger compared to louver pitch of 1.40 mm and the other louver angles. Therefore, configuration of Reynolds number based on fin pitch 2.02 mm and louver angle 22.0o is preferred to be adopted in the design process of heat exchanger.

Experimental characterization of thermal hydraulic performance of louvered brazed plate fin heat exchangers

Louvered fins are commonly used in compact heat exchangers to increase the surface area, turbulence, and initiate new boundary layer growth required to improve the heat transfer performance without a significant increase in pressure drop compared with other fins. An experimental study on the air side heat transfer and pressure drop characteristics for a louvered fin with symmetrical pattern in brazed plate heat exchangers has been performed. Reynolds numbers ranged from 350 – 1270, based on the louver pitch while a constant 1.82 m3/h water flow was held. The heat transfer and pressure drop for the geometry tested was reported in terms of Colburn factor (j) and Fanning friction factor (f) as a function of the Reynolds number. The experimental results for j and f are in good agreement compared to regression models suggested for compact heat exchanger with louvered fin and flat tubes, obtaining a deviation of 5.48% and 5.39% respectively. Moreover, when compared to CFD analysis for the same geometry, an average deviation of 6.3% is obtained. Finally a regression model for j and f factors was attained based on the Reynolds number, presenting a deviation of 1.51% and 2.19% respectively.

Generalized heat-transfer and fluid-flow correlations for corrugated louvered fins

We report heat-transfer and fluid-flow correlations to describe the performance of heat exchangers that use corrugated louvered fins. Friction factor f and Colburn factor j were investigated with respect to the ratio of the fin pitch to the louver pitch (Fp/Lp). Whereas previous correlations cannot be applied for Fp/Lp>1, our f and j correlations can be utilized in a wide range of Fp/Lp which is not only to Fp/Lp<1, but also to Fp/Lp>1, for 100<Re<3000. We also derived flow efficiency η correlation which is applicable for 0.3<LpsinLα/Fp<0.7, where Lα is the louver angle, in 100<Re<3000 within an error of ±15%.

Optimization of MCHX Using CFD and Refrigeration Cycle Simulator

Micro channel heat exchangers (MCHX) can be broadly classified as fluidic devices that employ channels of hydraulic diameter smaller than 1 mm. The present study focused on validate the better configuration parameters of louver fin used in MCHX for apply in residential air-conditioner condenser. The study has considered for three different louver angle case, two different louver lengths for better louver angle case and finally two different louver pitches for better louver angle and louver length case. The study indicates that the pressure drop will depends upon the louver angle and pitch. The louver angle i.e. 25deg provides reasonable pressure drop and high heat transfer rate. Thus by changing the length of louver can increase the pressure drop in MCHX. The case ie., 1.2mm louver length have more heat transfer rate. But when comparing to 1mm louver length case Net Heat Transfer rate is high. So the study further continued by having the louver length 1mm and changing the louver pitch. The louver pitch 0.8 and 1.2 has only considered for the study. The length of louver can decrease the pressure drop in MCHX. The variation of net heat transfer rate to changing the louver pitch indicating the importance of number of louver present in the MCHX. Thus the present study indicates the importance of configuration parameters for MCHX. The study also indicates that the increasing the louver length and angle will increase the net heat transfer rate. While increasing the louver pitch is inversely proportional to the net heat transfer rate of MCHX.

Optimal design of a corrugated louvered fin

We carried out a parametric study and optimization procedure to improve the performance of a corrugated louvered fin. Based on the results of the parametric study, we selected the fin pitch, louver pitch, and louver angle as the three most important parameters in performance. A full-factorial design was applied to the three chosen parameters for our design of experimental technique. We used the Kriging method and a micro-genetic algorithm to design an optimal corrugated louvered fin. The JF factor of the resulting optimum model was increased by 14–32% compared to that of the base model for Reynolds numbers in the range 0 ≤ ReLp ≤ 500. In addition, we propose a modified Suga–Aoki equation that can be used to estimate the optimum shape of a louvered fin with a smaller error than that produced by the original Suga–Aoki equation.

Pressure Drop and Heat Transfer Characteristics of Louvered Fin Heat Exchangers

This paper presents the effect of the changes in fin geometry on pressure drop and heat transfer characteristics of louvered fin heat exchanger numerically. Three dimensional simulation using ANSYS Fluent have been conducted for six different configurations at Reynolds number ranging from 200 to 1000 based on louver pitch. The performance of this system has been evaluated by calculating pressure drop and heat transfer coefficient. The result shows that, the fin pitch and the louver pitch have a very considerable effect on pressure drop as well as heat transfer rate. It is observed that increasing the fin pitch will relatively result in an increase in heat transfer rate but at the same time, the pressure drop will decrease. On the other hand, low pressure drop and low heat transfer rate will be obtained when the louver pitch is increased. Final result shows a good agreement between experimental and numerical results of the louvered fin which is about 12%. This indicates the capability of louvered fin in enhancing the performance of heat exchangers.

Louver Finned Heat Exchangers for Automotive Sector: Numerical Simulations of Heat Transfer and Flow Resistance Coping With Industrial Constraints

Louvered fins perform better than any other geometry in accomplishing the task of enhancing heat transfer of compact heat exchangers without prohibitive costs and pressure drops. For this reason, they are widely adopted for automotive applications. However, in order to improve louvered-fin compact heat exchangers, it is strongly required to understand how louvered fins behave regarding both heat transfer and pressure drop taking into account industrial constraints. For this purpose, numerical simulations based on the equations of thermofluid dynamics have been developed for this study. In particular, boundary heat flux and pressure distributions have been analyzed along the louvered-fin assembly and around the louvers, and even the effects of the flat portions (central and lateral louvers) have been investigated. In particular, the effects of the main geometrical parameters, such as fin pitch, louver pitch, and louver angle, have been evaluated by performing simulations on 40 different configurations. The results show that there is not one optimum configuration for the heat exchangers. Finally, a detailed procedure for the optimization of louvered-fin compact heat exchangers, considering industrial constraints is suggested according to multiple regression technique of the numerical results.

3D CFD Simulation of Thermal Hydraulic Performances on Louvered Fin Automotive Heat Exchangers

This study deals with Computational Fluid Dynamics (CFD) studies of the interactions between the air flow and louvered fins which equipped the automotive heat exchangers. 3D numerical simulation results are obtained by using the ANSYS Fluent 13.0 code and compared to experimental data. The paper studies the effect of louver angle and louver pitch geometrical parameters, on overall thermal hydraulic performances of louvered fins. The comparison between CFD simulations and experimental data show that established 3-D CFD model gives a good agreement. The validation agrees, with about 7% of deviation respectively of friction and Colburn factors to experimental results. As first, it is found that the louver angle has a strong influence on the heat transfer rate. Then, louver angle and louver pitch variation of the louvers and their effects on thermal hydraulic performances are studied. In addition to this study, it is shown that the second half of the fin takes has a significant contribution on pressure drop increase without any increase in heat transfer. Keywords—CFD simulations, automotive heat exchanger, performances.