Air-side Thermal-hydraulic Performance Research Articles

Heat analysis and optimal design of fin-and-tube heat exchanger with X-truss vortex generators

The fin-and-tube heat exchangers (FTHE) are extensively applied in HVAC (Heating Ventilation and Air Conditioning) system, power generation, process industries. The current study dedicates to develop an elliptical fin-and-tube heat exchanger filled with a novel X-VGs vortex generator (X-VGs), so as to improve the hydraulic and heat performance of FTHE. Two different placement schedules of vortex generator have been discussed firstly which are upper-flow (UF) and down-flow (DF)orientations. The effect of streamwise distance, transverse placement and main flow angel on air-side thermal hydraulic performance are investigated subsequently, the friction factor f, Colburn factor j, and performance evaluation criteria (PEC) j/f are analyzed separately corresponding to evaluate heat transfer effect, hydraulic characteristic and comprehensive performance. The results illustrate that increasement of streamwise distance and main flow angel would decrease the thermal hydraulic performance, while there is a nonlinear relationship between longitudinal placement and thermal hydraulic performance. The Genetic algorithm (GA) combined with radial basis function neuro network (RBFNN)prediction model is further employed to obtain the optimal layout of X-VGs, the best layout was obtained in streamwise space ratio at 1.995, longitudinal placement ratio 0.387 and main attack angel ratio 0.053, which achieved the increasement of 109.681% in PEC compared with baseline case.

Airside thermal–hydraulic performance evaluation of flue gas coolers for waste heat recovery

H-type finned tubes and integrally-molded spiral finned (IMSF) tubes are widely used in flue gas coolers for waste heat recovery, but it is difficult to design an efficient flue gas cooler in actual engineering by experience due to lack of a general factor to evaluate the thermal–hydraulic performance of different types of finned tube heat exchangers. Based on the correlations of the Nusselt Nu, the Colburn factor j, the friction factor f and the ratio Q/Wp, this paper proposed a comprehensive performance evaluation method to evaluate the thermal–hydraulic performance of different types of finned tubes, which includes the power consumption goodness factor (FQ/W) and volume goodness factor (FQ/V). The reliability of the evaluation method was verified through real engineer design. The thermal–hydraulic performance of the H-type finned tube bundle and IMSF tube bundle was obtained through computational fluid dynamics simulation using periodic physical models, and evaluated using the general evaluation method. The results show that the power consumption for H-4 and IMSF-3 is almost identical with the same heat transfer rate, but the compactness of IMSF-3 is better than that of H-4. The findings can guide the design and optimization of flue gas coolers.

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.

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.

Toward Passive Defrosting with Heterogeneous Coatings

A large amount of energy is lost in industrial active deicing. One problem is that water retention on the surface after ice melting decreases the overall heat-transfer coefficient by up to 20%. The Miljkovic group utilizes heterogeneous biphilic surfaces to enhance defrosting performance. They avoid water retention as the slush is rapidly drawn toward the hydrophilic regions before it completely melts.

Comments on “Experimental study on thermal–hydraulic performance of a wavy fin-and-flat tube aluminum heat exchanger”

These comments are presented to increase the awareness among the readers of Applied Thermal Engineering. Comments are presented in particular on the paper by Dong et al. (2013) where the authors investigated experimentally the air side thermal-hydraulic performance of a wavy fin-and-flat tube aluminum heat exchanger. Dong et al. (2013) did not mention some available thermal-hydraulic correlations in the literature like thermal-hydraulic correlations of Awad and Muzychka (2011). In addition, Dong et al. (2013) developed air-side friction and heat transfer correlations for wavy-fin compact heat exchangers. Their Fanning friction factor (f) and Nusselt number (Nu) correlations have six unknowns (one constant and five exponents). On the other hand, thermal-hydraulic correlations of Awad and Muzychka (2011) have only one unknown (the fitting parameter in the asymptotic model). For the aim of calculation and design of air cooled compact wavy fin wavy-fin heat exchangers, having only one unknown in thermal-hydraulic correlations of Awad and Muzychka (2011) is better than having six unknowns in thermal-hydraulic correlations of Dong et al. (2013).

Research on the air-side thermal hydraulic performance of louvered fin and flat tube heat exchangers under low-pressure environment

ABSTRACTIn order to solve the problem of overheating of the engine and cooling system of the vehicle in the plateau low-pressure environment, it is necessary to study air-side thermal-hydraulic performance of the vehicle cooling system heat exchanger under low-pressure environment. In this paper, the experimental study on the louvered fin and flat tube heat exchanger of the vehicle is carried out on the low-pressure wind tunnel test bench. The results show that at a gauge pressure of −44 kPa, the air-side convective heat transfer coefficient is reduced by 33.5%~23.3% compared with 0 kPa; the Colburn j-factor is increased by 36.8% on average; the f factor is increased by 51.2% on average. Based on this, numerical simulations are carried out to study the heat transfer and flow characteristics of louvered fins with different structural parameters under low-pressure environment. The empirical correlations of Colburn j-factor and Friction factor f are fitted by multiple linear regression. In the range of gauge pressure from 0 kPa to −44 kPa, the average deviation of the correlation calculation result of Colburn j-factor is 3.4%, and the average deviation of the correlation calculation result of f factor is 5.5%. The research results can provide a basis for the design of louvered fin heat exchangers utilized in the plateau environment.

An assessment of optimal airside heat transfer per unit friction power characteristics of compact heat exchangers

This paper evaluates an optimal airside thermal-hydraulic performance of compact heat exchangers. Seventy-five airside surfaces have been chosen, i.e. standard reference of Kays and London, to represent louver-fin, strip-fin, wavy-fin, plain-fin, pin-fin, finned circular tubes and finned flat tubes. A robust evaluation method is implemented by an estimation of the heat transfer rate per unit pumping power with and without considering the heat exchanger compactness. Experimental data of Colburn j-factor and Fanning friction factor (f) are used to estimate both the heat transfer rates and the friction power, respectively. The results demonstrate that strip-fin surface 1/10-27.03 shows an optimal heat transfer values per unit friction power when the compactness is taken into consideration. Nonetheless, pin-fin surface PF-4(F) shows an optimal heat transfer rate per pumping power when neglecting the importance of the compactness. The geometries having an optimal thermal-hydraulic performance for each airside type (with or without considering the compactness) are recommended as benchmarks to assess the performance of similar airside surfaces.

An assessment of the optimal air-side thermal-hydraulic performance of wavy-fin compact heat exchangers

An optimal assessment of heat transfer and friction power performance is investigated to address a robust method for facilitating performance evaluation of different wavy-fin arrangements. Two benchmark geometries are presented to compare the performance of all the reported wavy-fin arrangements with and without considering heat exchanger compactness. New 21 wavy-fin geometries are numerically studied to represent the unreported arrangements in the literature. The performance results of 105 geometries showed that the reference standard geometries of Kays and London could be used as benchmarks to evaluate the airside arrangements, with and without considering the compactness effect, respectively. Heat transfers versus friction power plots are found to be a useful approach for performance evaluation purpose. The surface GK2 is found to have the optimal thermal-hydraulic performance when comparing the heat exchanger compactness, whereas GI1 and GK1 might represent the geometries having optimal performances when neglecting the compactness importance.

Airside thermal-hydraulic characteristics for tube bank heat exchangers used to cool compressor bleed air in an aero engine

A numerical study has been carried out to investigate the airside heat transfer and pressure drop characteristics of bare tube bank and plain finned tube heat exchangers used to cool the compressor bleed air in an aero turbine engine. The exchangers use small diameter tubes (3.0 mm) with compact staggered tube layout and operate in high temperature circumstances with large temperature differences. Calculations are performed using the Realizable k-ɛ turbulence model with consideration of the air property variations caused by the air temperature and pressure changes. Calculations are implemented for 5–20 m/s frontal air velocities, 561–690 K and 0.5–1.0 MPa frontal air temperatures and pressures, which correspond to 15–30 compressor compression ratios, and 298 and 350 K tube wall temperatures. The airside thermal-hydraulic performance is evaluated using the heat transfer coefficient and pressure drop as well as their dimensionless forms - j and f factors. The results suggest that the heat transfer coefficient and pressure drop are strongly affected by the frontal air state whereas the j and f factors are less dependent on it. The effect of air property variability on j factor is limited while that on f factor is more notable.

Numerical investigation for the optimal placements of rectangular vortex generators for improved thermal performance of fin-and-tube heat exchangers

In the present work, a numerical investigation has been performed to find out the best emplacement of rectangular winglet pairs (RWPs) for the improvement of the heat transfer and flow characteristics of a fin and tube compact heat exchanger at low Reynolds number ranges from 500 to 900. The RWPs are placed at two different locations i.e., adjacent to the tubes and behind the tubes namely, common-flow-up (CFU) and common-flow-down (CFD) orientations respectively. The effect of attack angle, span angle and location of RWPs on air-side thermal hydraulic performance is investigated numerically. Area goodness factor and heat transfer rate per unit fan power are considered as the performance evaluation criteria. It is found that with the increase in attack angle and span angle heat transfer rate increases causing an increase in pressure drop penalty as well. Vortex generators behind the tube can reduce the pressure drop but with a significant reduction in heat transfer. Furthermore, MOORA (Multi-objective optimization by ratio analysis) method is employed to obtain the most expedient position and orientation of RWPs.

Numerical study on airside thermal-hydraulic performance of rectangular finned elliptical tube heat exchanger with large row number in turbulent flow regime

The objective of this study is to investigate the air side thermal–hydraulic characteristics of rectangular finned elliptical tube heat exchangers (RFETHXs) using 3D numerical simulations based on the validated standard k-ε turbulence model. First, fin efficiency of RFETHXs is investigated. The effects of various parameters such as row number, transverse tube pitch, longitudinal tube pitch, fin pitch, fin thickness and Re have been studied. Then the influences of structural parameters on the thermal-hydraulic performance of RFETHXs are examined, not only the characteristics including the effect of fin thermal resistance but also the pure convective performance excluded this effect. The contribution ratios of each structural parameter on fin efficiency and air side thermal-hydraulic performance are given. It is observed that, the most important structure factors for fin efficiency are fin thickness and fin pitch. For the RFETHXs with fully developed air side flow and heat transfer (N>5), from the third row to the last second row, the average fin surface Nu of each row is almost stable, and the value of the second row is 9% higher than the stable value. The results show that the air side heat transfer performance and friction factor of RFETHXs is mainly determined by the transverse tube pitch. For j/f1/2 at fixed Re, the contribution ratio of transverse tube pitch is 32% while the value is 24% at fixed frontal velocity.Moreover, two sets of multiple correlations, both including and excluding fin thermal resistance, are proposed to describe the air side heat transfer and friction characteristics of RFETHXs in turbulent flow regime.

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.

Numerical Investigation of the Air-Side Thermal Hydraulic Performance of a Louvered-Fin and Flat-Tube Heat Exchanger at Low Reynolds Numbers

ABSTRACTIn this study, the air-side heat transfer and fluid flow characteristics of a louvered-fin and flat-tube type heat exchanger used in the household refrigerators were investigated numerically. Louver angles of 20°, 24°, 28°, and 32° and fin pitches of 1.50, 2.00, and 2.50 mm were tested. To represent domestic refrigeration systems, the simulations were conducted for low Reynolds numbers, between 223 and 573. The results were evaluated using the volume goodness factor for the air side. The best performance was obtained with louver angle of 20° and fin pitch of 1.50 mm at Reynolds number of 229 over the investigated cases. It was demonstrated that the Colburn j-factor, friction factor, Stanton number, and volume goodness factor did not change linearly with respect to the parameters considered.

Experimental and simulation study on the air side thermal hydraulic performance of automotive heat exchangers

Flat tube heat exchangers with louvered fins were applied in order to meet the performance requirements and compactness in automotive air conditioning systems. Experimental and simulation study focusing on the air side thermal hydraulic performance of automotive heat exchangers were performed in this article. Test results showed that the heat capacity of a condenser with 5.4 mm height louvered fins can be 3.0%–8.6% higher than the 8 mm fin height condenser of the same size. Automotive evaporator can have 9.3% volume reduction by using short louvered fins while retain the same cooling capacity. Distributed parameter models were developed for automotive heat exchangers and effectiveness NTU method was used to calculate the heat capacity. The models were validated by comparing the results to those calculated via Coil Designer 3.6. Verification has been done for several well-known correlations used for the calculation of thermal hydraulic performance of wet and dry louvered surfaces. The correlations were evaluated by comparing calculations with test data of 24 different specimens under typical automotive heat exchanger working conditions. It was concluded that the existing correlations can give satisfactory predictions for heat capacity of condensers and evaporators, and air side pressure loss of condenser. However, further study on the friction characteristic of wet louvered fins is still needed.

Experimental Study of Wavy Fin Aluminum Plate Fin Heat Exchanger

An experimental study of the air-side thermal hydraulic performance of the aluminum wavy fin in heat exchanger was performed. A series of tests were conducted for 16 wavy fin samples with different geometry parameters. The experimental correlation equations of the wavy fin about the heat transfer and pressure drop are set up using the multiple regression method. The parametric study on the performance of the wavy fins is carried out using the Taguchi method. The study results show that the ratio of the wavy fin amplitude and wavy length is the most important factor that affects the overall thermal hydraulic performance.

Effect of a micro-grooved fin surface design on the air-side thermal-hydraulic performance of a plain fin-and-tube heat exchanger

In this study, the effectiveness of plain fin-and-tube heat exchangers constructed using anisotropic, micro-patterned aluminum fins has been explored. These fins which can more completely drain the condensate that forms on the heat transfer surface during normal operation were selected with the aim of improving the thermal-hydraulic performance of the heat exchanger. This study presents and critically evaluates the efficacy of four full-scale heat exchangers by measuring and comparing dry/wet air-side pressure drop and dry/wet air-side heat transfer data. The prototype fin surfaces were shown to reduce the wet air-side pressure drop from 9.3% to 53%, while at the same time having a negligible effect on the sensible heat transfer coefficient under both dry and wet conditions. That is to say, this novel fin surface design has shown the ability, through improved condensate management, to enhance the performance of the heat exchanger. Data pertaining to the durability of the alkyl silane coating used in this work are also presented.

Experimental study on thermal–hydraulic performance of a wavy fin-and-flat tube aluminum heat exchanger

The air side thermal hydraulic performance of the wavy fin-and-flat tube aluminum heat exchanger was studied. A set of experimental tests were conducted under different operating conditions for 16 sets of wavy fin geometry parameters. The experimental correlation equations were developed for the heat transfer and pressure drop performances of a wavy fin heat exchanger by the multiple regression method. The parametric study for thermal hydraulic performance of the wavy fins was carried out using the Taguchi method. It is showed that the amplitude and length of a wavy fin were the most important factors for the heat exchanger's overall thermal hydraulic performance.