Number Of Tube Rows Research Articles

Determination of fin pitches for maximum performance index of L-footed spiral fin-and-tube heat exchangers

In this study, the fin pitches of L-footed spiral finned tube heat exchangers were determined for maximimum performance index. The experiments were done at various fin pitches ( fp = 2.4, 3.2, and 4.2 mm) under the range of high Reynolds numbers (5,000–15,000). The test sections had a parallel and counter cross-flow arrangement having the number of tube row of 2. The two working fluids were the ambient air and hot water. The performance indexes ( ζ1, ζ2, and ζ3) were used to analyze the experimental data at different fin pitches. The results show that the optimal fin pitches for L-footed spiral finned tube heat exchangers are 2.4 and 3.2 mm.

Optimisation of Direct Expansion (DX) Cooling Coils Aiming to Building Energy Efficiency

Efficient Air Conditioning (A/C) system is the key to reducing energy consumption in building operation. In order to decrease the energy consumption in an A/C system, a method to calculate the optimal tube row number of a direct expansion (DX) cooling coil for minimizing the entropy generation in the DX cooling which functioned as evaporator in the A/C system was developed. The optimal tube row numbers were determined based on the entropy generation minimization (EGM) approach. Parametric studies were conducted to demonstrate the application of the analytical calculation method. Optimal tube row number for different air mass flow rates, inlet air temperatures and sensible cooling loads were investigated. It was found that the optimal tube row number of a DX cooling coil was in the range of 5 - 9 under normal operating conditions. The optimal tube row number was less when the mass flow rate and inlet air temperature were increased. The tube row number increased when the sensible cooling load was increased. The exergy loss when using a non-optimal and optimal tube row numbers was compared to show the advantage of using the optimal tube row number. The decrease of exery loss ranged from around 24% to 70%. Therefore the new analytical method developed in this paper offers a good practice guide for the design of DX cooling coils for energy conservation.

3D NUMERICAL ANALYSIS ON FLOW CONFIGURATIONS AND HEAT TRANSFER CHARACTERISTICS FOR FIN-AND-OVAL-TUBE HEAT EXCHANGER WITH V-DOWNSTREAM DELTA WINGLET VORTEX GENERATORS

D numerical investigations for heat transfer characteristics and flow configurations in a fin-and-oval-tube heat exchanger with V-tip pointing downstream delta winglet pairs (DDWP) are examined. The DDWPs are placed on the fin surface with pointing downstream and the oval tube row number is set at three in a staggered arrangement. The flow attack angles (θ = 15 o , 30 o , 45 o and 60 o ) and the distance from V-tip to the oval tube center in transverse axis (a = 3.77, 4.77 and 5.77 mm) are investigated for Reynolds number based on hydraulic diameter, Re = 500 - 2500. The numerical results are compared with the previous experimental results and the validations of the grid system on both heat transfer and friction factor are also reported. As the results, it is found that the use of the DDWP performs higher heat transfer rate and the friction factor than the smooth fin with no DDWP for all cases. The vortex flows and the impinging jet of the flows over the oval-tube walls lead to the increase in heat transfer rate, but also increase in pressure loss. The augmentations are maximum around 1.59 and 4.4 times higher than the smooth fin for heat transfer and friction factor, respectively. In addition, the optimum thermal enhancement factor, TEF, is around 1.09 at Re = 2500, a = 5.77 mm and θ = 15 o .

Flow Maldistribution in Industrial Air Heaters and Its Effect on Heat Transfer

Flow maldistribution in cross-flow heat exchangers used for industrial air heaters or recuperators is fairly common and can lead to a number of undesirable effects, one of which is deterioration in the thermal performance. The effect of gross flow maldistribution and the improvement in the thermal performance of flow correction guide vanes is investigated using a laboratory heat exchanger apparatus. The thermal performance deterioration from maldistribution was up to around 30 %. Modest improvements in the overall heat transfer coefficient and heat exchanger effectiveness when vanes were used was found for the range of air-side Reynolds numbers tested. Vanes were found to reduce the deterioration in thermal performance by up to 60 % compared to a perfectly uniform flow situation. Based on the e-NTU correlations the thermal performance deterioration is predicted to decrease as the number of tube rows (i.e. NTU) increases. The effective heat transfer area and therefore thermal performance of industrial air heaters and recuperators can be improved by using flow correction devices, such as guide vanes.

An experimental study of the air-side performance of fin-and-tube heat exchangers having plain, louver, and semi-dimple vortex generator configuration

In this study, a comparative study of the airside performance of fin-and-tube heat exchangers having plain, louver, and semi-dimple vortex generator (VG) are made. A total of eighteen samples are made and tested with the corresponding fin pitch (Fp) being 1.6 mm and 2.0 mm and the number of tube row (N) are 1, 2 and 4, respectively. Test results indicate that the heat transfer coefficient for N = 1 for louver fin geometry with a smaller fin pitch of 1.6 mm is higher than that of semi-dimple VG and plain fin geometry. For N = 1 with a larger fin pitch of 2.0 mm, the semi-dimple VG is marginally higher than that of louver fin geometry when the frontal velocity is lower than 2 m s−1. However, the trend is reversed where the heat transfer coefficient for louver fin outperforms that of semi-dimple VG when the velocity is increased further. For the airside performance for N = 2 or N = 4, the heat transfer coefficients for louver fin geometry is about 2–15% higher than those of semi-dimple geometry. The difference is increased with the rising velocity and the results prevail for both fin pitches. However, the difference is smaller at a larger fin pitch due to the comparatively effectively swirled motion of the semi-dimple VG. The effect of the number of tube row on the heat transfer coefficients is negligible for louver fin geometry and is also rather small for semi-dimple VG. For the plain fin geometry, the effect of tube row is also small when N > 1. The heat transfer performance for N = 1 is different from N = 2 or N = 4 due to its inline configuration.

Investigation of the semi-dimple vortex generator applicable to fin-and-tube heat exchangers

The present study examines the air side performance of the fin-and-tube heat exchangers having semi-dimple vortex generator or plain fin geometry. A total of eight samples are made and tested with the corresponding fin pitch (Fp) being 1.6 mm and 2.0 mm and the number of tube row (N) are 1 and 2. The inlet air flow direction is also being tested upon the proposed semi-dimple VG. Test results indicate that the heat transfer performance of the proposed semi-dimple VG with N = 1 at a smaller fin pitch of 1.6 mm is slightly higher than that of plain fin geometry. For N = 1 with a larger fin pitch of 2.0 mm, the semi-dimple VG is about 10% higher than that of plain fin geometry. The difference in heat transfer performance amid VG and plain fin geometry becomes more pronounced with N = 2 and is especially evident when Fp = 2.0 mm due to mixing contribution. In general, the difference between plain and semi-dimple geometry becomes more conspicuous at a larger fin pitch because of the comparatively effectively swirled motion. Both geometries show a dependence on fin pitch at N = 1 but the effect is almost negligible when N is increased to 2. The inlet air flow direction casts negligible influence on the heat transfer performance of semi-dimple VG. However, the friction factors for the opposite air flow operation is lower than that of normal operation, especially in low Reynolds number region.

Accounting for the effect of the heat exchanger length in the performance evaluation of compact fin and tube heat exchangers

Often a performance evaluation criterion (PEC) is used to compare different fin geometries. Based on several assumptions and imposed constraints, the PEC can predict the performance of a heat exchanger using the considered fin geometry. One of these assumptions is that the fin characteristics are independent of the heat exchanger length. Different fin geometries however result in heat exchanger designs with different lengths. In this work the effect of the length is investigated for compact (Dh < 6 mm) fin and tube heat exchangers. The heat exchanger length is fully defined by the number of tube rows and the longitudinal tube pitch. In order to be able to construct the heat exchanger, the value of these parameters must be compatible with the heat exchanger length as described by the PEC. The longitudinal tube pitch of a heat exchanger as determined from a PEC analysis is therefore dependent on the fin geometry used for that heat exchanger. It is shown that for heat exchangers with a small number of tube rows, it is necessary to properly account for the influence of this parameter. In this paper, a method is developed to compare heat exchangers with an arbitrary number of tube rows while accounting for longitudinal tube pitch effects.

Numerical Study on the Effect of Tube Rows on the Heat Transfer Characteristic of Dimpled Fin

The dimpled fin has excellent heat transfer performance and has attracted a lot of attention to apply on the fin and tube heat exchanger. A study presents to investigate the effects of number of tube rows on the air-side heat transfer characteristics of dimpled fin for velocity ranging from 1 to 3 m/s. The Q/Δ P and Q/((Δ P × V)) are used to evaluate the heat transfer performance of the heat exchanger. The results show that the dimpled arrangement can change the mainstream direction, increase the disturbance, and enhance the heat transfer. With the increase of the number of tube rows, the average Nusselt number decreases and Q/Δ P and Q/((Δ P × V)) increase gradually. Compared with the multipipe tube rows, the performance of two-row tube is better.

A Numerical Study of High Moisture Flue Gas in Tube Banks

In this article, a two-dimensional incompressible flow of high moisture flue gas in tube banks has been numerically simulated. The flue gas released both sensible and latent heat, and was treated as a combined heat and mass transfer problem. The finite-volume method was used to solve the Navier-Stokes equations, energy conservation equation, and species conservation equation. A simplified model was adopted and modified to account for the condensation phenomena in the flue gas. The influences of number of tube rows, gas velocity, vapor concentration, wall temperature, and tube diameter on heat and mass transfer characteristics were studied. The results analyses were presented by various criterions.

Optimization mathematical model for the detailed design of air cooled heat exchangers

This paper presents a disjunctive mathematical model for the optimal design of air cooled heat exchangers. The model involves seven discrete decisions which are related to the selection of the type of the finned tube, number of tube rows, number of tube per row, number of passes, fins per unit length, mean fin thickness and the type of the flow regime. Each discrete decision is modeled using disjunctions, boolean variables and logical propositions. The main continuous decisions are: fan diameter, bundle width, tube length, pressure drops and velocities in both sides of the ACHE, heat transfer area, fan power consumption. Then, the resulting generalized disjunctive programming model is reformulated as a mixed integer non-linear programming, implemented in GAMS (general algebraic modeling system) and solved using a branch-and-bound method. The proposed model was successfully verified by comparing the obtained output results with different designs taken from the literature. Then, the model is solved to obtain the optimal designs corresponding to the following optimization criteria: a) minimization the total annual cost which includes investment (heat transfer area) and operating cost (fan power consumption), b) minimization the heat transfer area and c) minimization the fan power consumption. Obtained optimal and sub-optimal designs are compared in detail.

On the Influence of Tube Row Number for Mixed Convection Around Microtubes

A numerical simulation was performed on the heat transfer of mixed convection for fluid flowing across a microtube bundle, using the lattice Boltzmann method. At first, the program code was validated by using a benchmark case of natural convection around a hot single tube inside a square enclosure. The local and averaged heat transfer coefficients of each tube in the bundle with various row numbers were calculated. Numerous cases were simulated, ranging from a weak natural convection case (forced convection) to a pure natural convection case. The results indicate that the total averaged Nusselt number outside the tubes gradually decreases and becomes almost a constant with tube row number at low Reynolds number, which is different from the conventional scaled tube. The averaged Nusselt numbers and temperature fields for various situations were compared. Further influencing factors other than the tube row number on the heat transfer behavior of a tube bundle were also summarized and discussed.

Entropy generation and thermoeconomic analysis of the wire-and-tube condenser

In this work, entropy generation analysis of an air-cooled natural draft wire-and-tube condenser commonly used in the domestic refrigerator is carried out to investigate geometrical and operating parameters. The Bejan number formulation is used for the analysis because of its ability to relate the heat transfer to pressure drop entropy generation. The analysis also incorporates thermoeconomics by combining the second law of thermodynamics with economic principles. The analytical study is carried out by varying geometrical parameters of the condenser such as tube outer diameter, wire diameter, number of wire pairs, number of tube rows, tube pitch, wire pitch and refrigerant (R134a) properties such as mass velocity, saturation temperature and dryness fraction. The behaviour of entropy generation due to heat transfer and pressure drop, Bejan number and thermoeconomic variables such as relative cost difference and exergoeconomic factor are analysed. These results are used in obtaining the values of condenser dimensions leading to better performance.

나선형 핀-튜브 증발기를 적용한 냉장고의 성능 특성에 관한 연구

본 연구는 평판 핀-튜브 증발기와 나선형 핀-튜브 증발기를 적용한 가정용 냉장고의 성능특성 비교를 통하여 기존에 사용하고 있는 핀-튜브 증발기를 나선형 핀-튜브 증발기로 대체할 수 있는 가능성을 고찰하는데 그 목적이 있다. 실험은 2 단 15 열의 평판 핀-튜브 증발기와 2 단 15 열에서 2 단 11 열까지 열 수를 단계적으로 감소시킨 3 종류의 나선형 핀-튜브 증발기를 실제 냉장고에 적용하여 수행하였다. 핀-튜브 증발기의 열 수가 감소할수록 냉동시스템의 최적 냉매 충전량은 감소하였으며, 2 단 13 열과 2 단 11 열의 나선형 핀-튜브 증발기를 장착한 냉장고의 소비전력은 기존 2 단 15 열의 평판핀-튜브 증발기를 적용한 냉장고 대비 각각 1.5%와 2.8% 감소하였다. 또한 내착상 실험결과 나선형 핀-튜브 증발기가 기존 평판 핀-튜브 증발기와 비교하여 같은 착상조건에서 3~7% 향상된 냉각능력을 보였다. 냉각속도 실험에서는 모든 증발기는 동등수준의 성능을 나타내었다.

Parametric study and field synergy principle analysis of H-type finned tube bank with 10 rows

In this paper, three-dimensional numerical studies are performed for heat transfer and pressure drop characteristics of H-type finned tube bank with 10 rows by software FLUENT. The effects of seven geometric parameters (tube row number, fin thickness, slit width, fin height, fin pitch, spanwise tube pitch and longitudinal tube pitch) and Reynolds number are examined. It is found that for the tube bundle studied, the heat transfer and fluid flow are in the developing region, and they become periodically fully developed after the 10th row. Among the seven geometric parameters spanwise tube pitch has the most important effect and slit width has the least important effect, with other five parameters in between. The results are also analyzed from the view point of field synergy principle. It is found that the effects of the eight parameters on heat transfer and fluid flow characteristics can be well described by the field synergy principle. Correlations of Nu and Eu for the 10-row tube bundle are presented.

Experimental Study on the Air-Side Performance of a Multipass Parallel and Counter Cross-Flow L-Footed Spiral Fin-and-Tube Heat Exchanger

This study conducted experiments on the air-side performance of novel L-footed spiral fin-and-tube heat exchangers that were faced with airflow at high Reynolds numbers (3500–13,000). The examined heat exchangers have a multipass parallel-and-counter cross-flow type of water flow arrangement. This flow arrangement is a combination of the parallel cross-flow and the counter cross-flow. This type of water flow arrangement may be the best fit for the reverse-flow system, because it can provide constant heat-exchange effectiveness for every flow reversal direction at the same airflow rate. Ambient air was used as a working fluid on the air side and hot water for the tube side. This way the effect of the number of tube rows on the heat transfer and friction characteristics of L-footed spiral fin-and-tube heat exchangers was clearly observed. The effect of the fin's outside diameter on the pressure drop was also studied. The results show that the number of tube rows has no significant effect on the air-side heat transfer or on friction characteristics at high Reynolds numbers. However, the fin's outside diameter shows a significant effect on the pressure drop. The pressure drop increases as the fin's outside diameter increases for the same number of tube rows.

Experimental and Numerical Investigation of the Gas Side Heat Transfer and Pressure Drop of Finned Tubes—Part I: Experimental Analysis

In this study, a heat transfer and pressure drop correlation are determined for helically I- and U-shaped finned tubes as well as for solid I-finned tubes at constant transverse and longitudinal spacing. In the heat transfer correlation, the influence of the number of tube rows arranged in flow direction is taken into consideration. A detailed description of the test rig and the data reduction procedure is presented. A thorough uncertainty analysis was performed to validate the results. The investigation has shown that the influence of the fin geometry on the heat transfer of the helically segmented I- and U-shaped tubes can be disregarded. The heat transfer correlation, which is valid for the helically segmented I- and U-shaped tubes in a staggered arrangement, can describe 90% of all measurement data within ±15%. All measurements are performed for constant transverse and longitudinal spacing. For the pressure drop coefficient, two new correlations, which are only valid for helically segmented U shaped finned tubes in a staggered arrangement, show an average deviation of approximately ±13% for 90% of all measurement results. All new correlations are compared with correlations from open and established literature for industrial boiler applications. The new heat transfer and pressure drop correlations show a relative deviation of ±20% in comparison with correlations in open literature. The new pressure drop correlations show the same characteristic as most correlations in the open literature.

Parametric study and optimization of louver finned-tube heat exchangers by Taguchi method

Abstract A serial studies on the effects of fin pitch, fin collar outside diameter, transverse tube pitch, longitudinal tube pitch, number of longitudinal tube rows, louver height, louver angle, fin thickness and louver pitch on fin performance of louver finned-tube heat exchanger is investigated by numerical method. The parameters of louver finned-tube heat exchangers are optimized by the Taguchi method. Eighteen kinds of models are made by compounding levels on each factor, and the heat transfer and flow characteristics of each model are analyzed. The results show that fin collar outside diameter, transverse tube pitch and fin pitch, are the main factors that influence significantly the thermal hydraulic performance of the heat exchanger. Therefore, these three factors are considered as the most important factors for an optimum design of a heat exchanger. The optimal conditions are obtained, and the results are also verified by analytical methods.

The Thermo-Test and Mathematics Model Study on Automobile Tube-Core-Fin Radiator

.In order to improve the performance of automobile tube-core-fin radiator, the thermo-test and mathematics model method were combined together to study heat transfer and air resistance. The mathematics model was built including heat transfer and air resistance coefficient criterion equations in the certain Reynolds number range. The maximum relative error between results calculated from mathematics model and test values is less than 6.61%. The number of tube rows of the radiator can affect heat transfer and air resistance coefficient through analyzing results.

Effect of number of tube rows on the air-side performance of crimped spiral fin-and-tube heat exchanger with a multipass parallel and counter cross-flow configuration

The air-side performance of crimped spiral fin and tube heat exchangers at high Reynolds number (3000–13,000) is investigated in this study. The test heat exchangers have a new type of multipass parallel and counter cross-flow water flow arrangement which is a combination of parallel cross-flow and counter cross-flow. The test samples are made from copper and aluminium with different number of tube rows ( N row = 2, 3, 4 and 5). The effects of number of tube rows and fin material on the heat transfer and friction characteristics are studied. The results show that no significant effect for either number of tube rows or fin materials on the heat transfer performance is found at high Reynolds number. In addition, the correlation of the air-side performances of this type of the heat exchangers at high Reynolds number is developed for industrial applications.

Simulation and Analysis of Air Performance of Multi-Row Finned-Tube Heat Exchanger

In this paper, simulates the air performance of multi-row finned-tube heat exchanger by Fluent. The mathematics model is established, using standard k-ε turbulence model. The temperature, velocity and pressure changes of air are analyzed. By research the multi-row finned-tube heat exchanger, analyzed the different structures have different effects on the efficiency of heat transfer, obtained the most appropriate number of tube rows, making the heat exchanger for maximum heat transfer efficiency.