Number Of Tube Rows Research Articles

Dynamic simulation of an air handling unit and validation through monitoring data

This paper presents the model for the simulation of the behavior of an air handling unit (AHU), consisting of two heating coils, a cooling and dehumidifying coil, and a vaporizer. The proposed model reproduces the behavior of its single components, using the suitable ε-NTU relations for the heat exchangers on the basis of actual geometries (e.g., type of heat exchanger, number of tube rows, number of passes), and mass and heat balance equations for the vaporizer and dehumidifying coils. The routine is developed as a MATLAB script and it is linked to a TRNSYS model, which simulates the building. The model is applied to a real AHU, which provides fresh air for an exhibition room of a museum, varying the supply relative humidity based on the indoor set point. During a one-month monitoring campaign in the building, several data about the external and internal climate were acquired, together with specific parameters of the AHU system (e.g., temperature and water flow rate at the heat exchangers, supply temperature and relative humidity of the air flow). These monitored data were compared with the outputs of the MATLAB script, validating the AHU model in the error band of the monitoring system.

Experimental Research and Simulation of Fin and Tube Heat Exchanger

The paper provides the results of experimental and theoretical test of a wavy fin and tube heat exchanger used to cool air in a ventilation system when the wavy fin of the heat exchanger is dry and wet. The experimental tests, performed in the range of 1000<Re<4500 of the Reynolds number applying LMTD-LMED methodology, determined the dependency of the heat transfer coefficient on the supplied air flow rate with the varying geometry of the heat exchanger (the number of tube rows, the distance between fins, the thickness of the fin and the diameter of the tube). The experimental tests were performed on 9 heat exchangers in heating and 6 heat exchangers in cooling mode. After processing the results of the experimental tests, empirical equation defining the characteristics of the heat transfer coefficient of all heat exchangers were derived. The maximum heat transfer coefficient deviation is 11.6 percent. The correction factor of the wet fin (Lewis number) depending on the number of Reynolds, which ranges from 0.75 to 1.1 also is determined. Maximum capacity deviation equals 3.7 percent. The obtained equations can only be applied to a certain group of heat exchangers (with the same shape of fins or the distance between the tubes). The results of the experimental test and simulation with ANSYS program are compared and the heat transfer coefficients vary from 6.5 to 11.4 percent.

Thermal design and optimization of fin-and-tube heat exchanger using heat transfer search algorithm

This study explores the use of heat transfer search (HTS) algorithm for thermal design and optimization of a fin-and-tube heat exchanger. Minimizing the total weight and total annual cost of a heat exchanger for specific heat duty requirement is considered as objective functions and treated individually. Seven design variables such as tube diameter, transverse and longitudinal pitch of tube, number of tube rows, fin pitch, height of shape and width of shape are considered for optimization. Application examples are presented to demonstrate the effectiveness and accuracy of the proposed algorithm. The results of optimization achieved using HTS algorithm is validated by comparing with those obtained by using genetic algorithm, particle swarm optimization, and artificial bee colony algorithm. Finally, sensitivity analysis is carried out to demonstrate the effect of heat exchanger dimensions on the optimum solution.

Experimental study on heat transfer characteristics of a condenser in the presence of air

In this study, the heat transfer characteristics of a condenser in the presence of air were investigated experimentally. A condenser system with a 450mm×447mm×630mm chamber was designed and constructed. The condensing tube was copper coil tube each with a total length of 4650mm, and the number of tube rows was 17. The experiments were conducted with different air mass fractions, inlet cooling water temperatures, cooling water flow velocities, and heat loads. With regard to the overall performance of the condenser, experimental results showed that the overall heat transfer coefficient decreased, whereas the condenser pressure and terminal temperature difference of the condenser both increased with an increase in the air mass fraction. With regard to the local heat transfer characteristics, the experimental results showed that the condensation heat transfer coefficients initially decreased slightly, then rapidly, and finally slightly again as the number of the tube row became higher in the flow direction of the steam when air leakage occurred in the condenser. The variation rate of the condensation heat transfer coefficient with the tube row significantly changed twice in the condenser. As the air mass fraction and the cooling water velocity increased, the critical rows, where the variation rate of the condensation heat transfer coefficient with the tube row significantly changed, generally moved upward. By contrast, the critical rows generally moved downward with increases in the inlet cooling water temperature and heat load.

A comparison of thermal-hydraulic performance of various fin patterns using 3D CFD simulations

The objective of the present numerical study is to investigate the thermal-hydraulic characteristics of various circular (plain circular fin, crimped spiral fin, serrated fin) and plate fins [plain plate fin, wavy fin and fin with punched delta winglet pair (DWP)]. The geometrical parameters are, tube outer diameter (OD)=7mm, fin spacing (S)=3–7mm, fin height (hf)=5mm, number of tube rows (Nr)=2, transverse tube pitch (Pt)=23mm and longitudinal tube pitch (Pl)=18mm. The Reynolds number based on hydraulic diameter has been considered in the range of 2500⩽Reh⩽4000. The circular fins outdo the plate fin in terms of the heat transfer coefficient and the heat transfer per unit pumping power for the circular fins has been found to be 140–170% higher as compared to the plate fins for a fixed Reynolds number. Local Nusselt number around the periphery of the tubes showed that fin patterns affect the wake region formation and flow separation on the tube surface. It has been observed that heat transfer coefficient decreases with an increase in the fin spacing due to increase in bypass flow rate through the heat exchanger at a constant Reynolds number. The heat transfer per unit pumping power showed an increase of more than 100% with an increase in the fin spacing from 3 to 6mm. The flow patterns have been studied in detail for serrated fin, crimped fin and fin with DWP. The vortices generated by the fins merge with the horseshoe vortices and enhances the heat transfer in the domain. The fin efficiency has been found to be in the range of 77–83% for the circular fins and 55–66% for the plate fins for a range of 2500⩽Reh⩽4000. Only one circular fin design i.e., crimped fin provides higher volume goodness factor as compared to the plate fins. In general it has been observed that more compact heat exchanger can be designed using plate fins but at a higher pumping power cost.

Parametric study and multiple correlations of an H-type finned tube bank in a fully developed region

ABSTRACTThe air-side heat transfer and pressure drop characteristics of an H-type finned tube bank in the turbulent periodically fully developed region are investigated numerically. The effects of seven geometric parameters and Reynolds number are examined. It is found that when the number of tube rows is equal to and larger than 25, the heat transfer and fluid flow approach the fully developed state. Among the seven geometric parameters spanwise tube pitch has the most important effect. Based on the numerical results, the correlations of heat transfer and pressure drop of the H-type finned tube bank for the fully developed region are presented.

The influence of fin structure and fin density on the condensation heat transfer of R134a on single finned tubes and in tube bundles

The influence of fin structure and density on the condensation heat transfer of refrigerant 1,1,1,2-tetrafluoroethane (R134a) is investigated on single finned tubes and in corresponding bundles. Experiments have been performed on standard and enhanced finned tubes with 39, 48, and 56 fins per inch (FPI) and different fin heights. The enhanced finned tubes are based on the standard ones, and are characterized by a non-uniform fin structure. The condensation heat transfer coefficient (HTC) is determined for single tubes as well as for each row of the tube bundles and compared with predictions from analytical models. In the single tube measurements, the enhanced finned tubes showed distinctly higher HTCs than the standard finned tubes. Different condensation flow modes have been observed during the tube bundle experiments where the additional structures on the fin flank of the enhanced finned tubes promote sheet mode condensation. It has been demonstrated that the standard finned tubes show a lower decrease in the condensation HTC with increasing tube row number in the bundle than the enhanced finned tubes. Among the standard finned tubes, the one with 48FPI and larger fin height exhibits the highest HTCs for single tube and tube bundle experiments. The increase in the fin height seems to delay the formation of sheet mode condensation and thus to increase the condensation HTC. Among the enhanced finned tubes, the tube with 39FPI yields the highest HTCs for both single tube and tube bundle measurements. Low fin density and large fin height obviously tend to keep the insulating effect of retained condensate in the fin channels low.

둥근 웨이브 핀-관 열교환기의 공기 측 전열 성능

In this study, airside performance of round fin-and-tube heat exchangers are compared with that of the herringbone wave fin-and-tube heat exchangers with an aim to investigate the effect of fin shape on thermal performance. Results show that j factors of the round wave fin are 1.2~22% larger than those of herringbone wave fin. The f factors of the round wave fin are -1.0~29% smaller than those of herringbone wave fin for 1 or 2 row configuration. For 3 row configuration, f factors of the round wave fin are 8.3~23% larger. The reason may be attributed to the reduced recirculation zone in the valley of the fin for round wave fin as compared with that of the herringbone wave fin. For round wave fin, the effect of fin pitch on j and f factor is not significant. In addition, j factors decrease as the number of tube row increases. On the other hand, f factors are independent of the number of tube row. A new correlation was developed based on the present data.

3D CFD simulations of air cooled condenser-III: Thermal–hydraulic characteristics and design optimization under forced convection conditions

The objective of this study is to investigate thermal–hydraulic characteristics of an air cooled condenser and optimized the design in terms of heat transfer per unit pumping power, area goodness factor, volume goodness factor and material requirement using the 3D numerical simulations. The annular-finned tubes have been considered in this study, which is one of the most common type of fin used for the design of air cooled heat exchangers and known to provide a high heat transfer coefficient per unit pressure drop. The effect of tube shape (elliptical and round), tube diameter [7–24mm (circular), 30×10–30×20mm (elliptical)], fin spacing (2–10mm), number of rows (2–10), fin height (5–10mm), air frontal velocity (4.76–6.32m/s), transverse tube pitch (36.8–44mm) on the thermal–hydraulic performance has been studied. It is observed that, with an increase in the fin spacing, the heat transfer coefficient increases (by 35–40%) at a constant inlet velocity and the pressure drop decreases (by 60–80%). The frontal area requirement increases by 100–150% with an increase in the fin spacing for the same heat removal capacity. As the row number is increased, the heat transfer coefficient increases initially for Nr<4 by 7–8%, and for Nr>4, the heat transfer coefficient decreases by 23%. An increase in the tube pitch increases the heat transfer coefficient per unit pressure drop by 40%. The fin efficiency is found to decrease with an increase in the Reynolds number, fin spacing and number of tube rows. In the last section optimization of the design has been performed based on Taguchi method and numerical results obtained. It has been observed that the number of tube rows must be kept between 2–4, fin spacing 3–5mm, tube pitch around 40mm, and fin height 5mm for better performance of the condenser.

Numerical simulation of liquid metal turbulent heat transfer from an inline tube bundle in cross-flow

Results of the numerical simulation of turbulent flow field and heat transfer of liquid metal in cross-flow over inline tube bundles consisting of smooth round tubes are presented. Computations have been performed with CFD-code ANSYS Fluent on the base of a two-dimensional unsteady RANS formulation using the SST turbulence model by Menter and assuming constant physical properties of a fluid with the Prandtl number equal to 0.023. The Reynolds number ranged from 26,200 to 52,400. Instantaneous and time-averaged velocity and temperature fields obtained for bundles of different intertube spacing with a variation of the bundle width (number of tube rows in the cross direction) were analyzed. Integral characteristics of heat transfer were compared with the experimental data.

복합 전열 촉진 핀이 적용된 핀-관 열교환기의 습표면 성능에 대한 실험적 연구

In this study, wet surface heat transfer and friction characteristics of compound enhanced fin-and-tube heat exchangers were experimentally investigated. Louver-finned heat exchangers were also tested for comparison purpose. The effect of fin pitch on j and f factor was negligible. Both j and f factor decreased as number of tube row increased. Compound enhanced fin samples yielded higher j and f factors than louver fin samples. For one row, j and f factors of compound enhanced fin samples were 11% and 43% higher than those of louver fin samples. For two row, those were 8% and 50%, and for three row, those were 17% and 53%. Heat transfer capacities at the same pressure drop of the compound enhanced fin samples were 2.0% for one row, 3.1% for two row and 8.4% for three row larger than those of louver fin samples, Data were compared with predictions of existing louver fin correlations.

Airside performance of fin-and-tube heat exchangers having sine wave fins under wet condition

In this study, experiments are conducted on sine wave heat exchangers under wet condition, and the results are compared with those of herringbone wave heat exchangers having same wave height. Sine wave samples yield higher j and f factors than herringbone wave samples. The reason may be attributed to the reduced recirculation zone in the valleys of the sine wave channel. The effect of fin pitch on j and f factor is not pronounced both for sine and herringbone wave heat exchangers. The j factor decreases as number of tube row increases. However, the effect of number of tube row on f factor is dependent on the fin configuration. For herringbone wave samples, f factor decreases as the number of tube row increases. For sine wave samples, on the other hand, f factor is independent of the number of tube row. Ratios of j/f1/3 between sine wave and herringbone wave samples are between 0.95 and 1.0, which decrease with theincrease of fin pitch. A new correlation was developed based on the present data.

An Experimental Investigation on the Air-Side Performance of Fin-and-Tube Heat Exchangers Having Radial Slit Fins

In this study, the heat transfer and friction characteristics of radial slit-finned heat exchangers are experimentally investigated. Louver-finned heat exchangers are also tested for comparison purpose. The effect of fin pitch on [Formula: see text] and [Formula: see text] factor is negligible. Considering the small variation of the fin pitch (from 1.3[Formula: see text]mm to 1.7[Formula: see text]mm), the foregoing argument should hold true for the present samples. Louver fin samples yield higher [Formula: see text] and [Formula: see text] factors than slit fin samples. The [Formula: see text] factor increases as the number of tube row decreases. The [Formula: see text] factor, however, is independent of the number of tube row. The [Formula: see text] ratios of slit fin samples are larger than those of Louver fin samples. Data are compared with available correlations.

광폭 루버 핀이 장착된 핀-관 열교환기의 습표면 성능에 대한 실험적 연구

One method of increasing the heat-transfer rate is to increase the heat-transfer area. In this study, we test a wide louver fin-and-tube heat exchanger with Pt/Pl = 1.03, and we compare the results with those of a louver fin-and- tube heat exchanger with Pt/Pl = 0.6. The results obtained show that the heat-transfer capacities of the wide louver samples are larger (16% in one row, 29% in two rows, and 38% in three row samples) than those of the louver samples. Considering the area ratio of 2.17, the increase in the heat-transfer capacity is somewhat small. The reason for this may be due to the smaller heat-transfer coefficient and fin efficiency of the wide louver sample. The effect of the fin pitch on the j and f factors are not profounded . The j and f factors decreased as the number of tube rows increased. We compare the data obtained with existing correlations.

복합 전열 촉진 핀이 적용된 핀-관 열교환기의 성능에 대한 실험적 연구

Abstract In this study, heat transfer and friction characteristics of compound enhanced fin-and-tube heat exchangerswere experimentally investigated. Louver-finned heat exchangers were also tested for comparison purpose. The effectof fin pitch on j and f factor was negligible. The j factor decreased as number of tube row increased. However, ffactor was independent of number of tube row. Louver fin samples yielded higher j and f factors than compoundenhanced fin samples. For one row, j and f factors of louver fin were 23% and 27% higher than those of compoundenhanced fin. For two row, those were 11% and 8%, and for three row, those were 10% and 9%. However, heat transfer capacities at the same pressure drop of the compound enhanced fins were 6.4% for one row, 11.1% for tworow and 13.6% for three row larger than those of louver fins, Existing louver fin correlation overpredicted the presentj factors and underpredicted the present f factors. Keywords : Compound enhanced fin, Heat transfer coefficient, Louver fin, Pressure drop

Air-side performance of serrated welded spiral fin-and-tube heat exchangers

Heat exchanger is a basic component used in thermal processes such as industrial fluid heating, household appliances, waste heat recovery units (WHRU), etc. Presently, the spiral fin-and-tube heat exchanger is used as a favored type of heat exchanger for the waste heat recovery unit system, i.e., the economizer heat exchanger. The study investigates the effect of fin pitches on the air-side performance of serrated welded spiral fin-and-tube heat exchangers having Z-shape flow arrangement and the number of tube rows of 2 in range of high Reynolds numbers (4000–15,000). The test samples are made from steel (iron) with different fin pitches of 3.6, 4.2, and 6.2mm. The experimental results reveal that the fin pitch has a significant effect on the air-side performance. It is confirmed that the fin pitch of 3.6–6.2mm has the same trend in heat transfer coefficient at the tested condition. For f-friction factor, a detectable rise of the friction factor is found when the fin pitches increase to 6.2mm. Moreover, the air-side performance correlations of serrated welded spiral finned tube heat exchangers are proposed for practical industrial applications. The proposed air-side performance correlation describes 100% for j-Colburn factor and f-friction factor within 10%.

An Experimental Investigation on the Airside Performance of Fin-and-Tube Heat Exchangers Having Nonsymmetrical Slit Fins

In this study, the heat transfer and friction characteristics of nonsymmetric slit-finned heat exchangers are experimentally investigated. Louver-finned heat exchangers are also tested for comparison purpose. The effect of fin pitch on j and f factors is negligible. Considering the small variation of the fin pitch (from 1.3 mm to 1.5 mm), the foregoing argument should hold true for the present samples. Louver fin samples yield higher j and f factors than slit fin samples. Both j and f factors increase as the number of tube rows decreases. The row effect is true for both slit and louver fin samples. For one-row configuration, j/f ratios of louver fin samples are larger than those of slit fin samples. The trend is, however, reversed for three-row configuration. Data are compared with available correlations.

Heat Transfer and Pressure Drop Characteristics of Plain Fin-and-Tube Heat Exchangers Having 5.0 mm Tubes Under Dehumidifying Condition

In this study, wet surface pressure drop and heat transfer characteristics of plain finned heat exchangers having 5.0 mm diameter (5.3 mm after tube expansion) tubes were investigated. Nine samples having different fin pitches (1.1 to 1.3 mm) and tube rows (1 to 3 rows) were tested. The fin pitch had a negligible effect on j and f factors. Both j and f factors decreased as the number of tube row increased. When compared the j and f factors of the samples having 5.3 mm diameter tubes with those of 7.3 mm diameter tubes, 5.3 mm samples yielded higher j factors and lower f factors. The j/f ratios of 5.3 mm samples are larger than those of 7.3 mm samples which implies that 5.3 mm geometry is more beneficial than 7.3 mm geometry.

Experimental study on heat transfer characteristics of water-spray-bed heat exchanger

An experimental study was conducted on a water-spray-bed heat exchanger to investigate the heat transfer characteristics. A laboratory-scale test rig was built and its heat transfer characteristics were investigated with respect to various design and operation parameters such as the water spray flow rate, exhaust gas flow rate and number of tube rows. It was found that the implementation of the water spray increased the heat transfer rate to about 1.3 - 2.2 times that of a heat exchanger without water spray, although with a slight increase in the pressure loss. It was thus confirmed that the water spray was effective for enhancing condensing heat recovery from an exhaust gas.

A review on the thermal hydraulic characteristics of the air-cooled heat exchangers in forced convection

In this paper, a review is presented on the experimental investigations and the numerical simulations performed to analyze the thermal-hydraulic performance of the air-cooled heat exchangers. The air-cooled heat exchangers mostly consist of the finned-tube bundles. The primary role of the extended surfaces (fins) is to provide more heat transfer area to enhance the rate of heat transfer on the air side. The secondary role of the fins is to generate vortices, which help in enhancing the mixing and the heat transfer coefficient. In this study, the annular and plate fins are considered, the annular fins are further divided into four categories: (1) plane annular fins, (2) serrated fins, (3) crimped spiral fins, (4) perforated fins, and similarly for the plate fins, the fin types are: (1) plain plate fins, (2) wavy plate fins, (3) plate fins with DWP, and (4) slit and strip fins. In Section 4, the performance of the various types of fins is presented with respect to the parameters: (1) Reynolds number, (2) fin pitch, (3) fin height, (4) fin thickness, (5) tube diameter, (6) tube pitch, (7) tube type, (8) number of tube rows, and (9) effect of dehumidifying conditions. In Section 5, the conclusions and the recommendations for the future work have been given.