Tube Banks In Cross Flow Research Articles

Prediction and comparison of aerodynamic performance and flow control for smooth and wavy tube banks in crossflow at subcritical Reynolds numbers using a 3D RANS approach

This paper investigates the effects of introducing wavy cylinders of appropriate wavelength into tube bundles for the passive control of flow-induced vibration. The Reynolds-averaged Navier–Stokes approach RANS was used to study the turbulent flow characteristics within staggered tube bundles having transverse and longitudinal pitch-to-diameter ratios of 3.8 and 2.1, respectively. Two wavy models are tested with different wavelength-to-mean diameter ratios, namely: Model-A with [Formula: see text] and Model-B with [Formula: see text], and their performances are compared with those of a smooth circular tube bundle Model-C ([Formula: see text]), in a range of subcritical Reynolds numbers [Formula: see text]. Mean velocity and pressure fields as well as aerodynamic coefficients are presented and compared. According to the obtained results, the wavy tube bundle with [Formula: see text] exhibits the best performance, with slightly smaller [Formula: see text] values than the smooth tube bundle. However, results show that the wavy model with [Formula: see text] is clearly the worst with an increase of [Formula: see text] up to 40%. Numerical outcomes also reveal that the interaction of neighboring rows and columns affects the fluctuation of [Formula: see text] values relative to each tube position. Moreover, [Formula: see text] evolutions depend significantly on the variation of Re as well, where drag reduction is more substantial by increasing Re. Thus, wavy-shaped tubes with optimum parameters could be more suitable for flow control by enhancing the secondary flow, turbulence and fluid mixing.

Effect of surfaces roughness of a staggered tube bank in cross flow with air on heat transfer and pressure drop

Many options are devoted to enhancing heat transfer alongside lowering the pressure drop inside the tube banks in cross flow with air. Among these, is attaching splitter plates (SPs) to the trailing edges of the tubes as extended surfaces. That already proved from literature its effective use. Another proposed option is to increase the surface's roughness, with limited available data from literature. Thus, the present research was established to study the effect of using different surface roughness of a staggered tube-bank in cross flow with air on heat transferred and pressure drop besides the comparison with installing SPs. To this aim, a full 3D CFD model is developed to study the two mentioned options without any symmetrical boundary conditions. The study extended to include the effect of Remax changes from 5000 to 100,000. While three surface relative roughness; ks/D = 0 (smooth), ks/D = 0.01, and ks/D = 0.02 are investigated. The results confirmed that increasing heat transfer surface roughness helps to augment the total heat transferred. While a limited pressure drop increase is reported compared to installing SPs. Combining both; increasing surface roughness, and, adding SPs, led to multiplying the total heat transfer rate.

Numerical Study of Liquid Metal Turbulent Heat Transfer in Cross-Flow Tube Banks

Heavy liquid metals (HLM) are attractive coolants for nuclear fission and fusion applications due to their excellent thermal properties. In these reactors, a high coolant flow rate must be processed in compact heat exchangers, and as such, it may be convenient to have the HLM flowing on the shell side of a helical coil steam generator. Technical knowledge about HLM turbulent heat transfer in cross-flow tube bundles is rather limited, and this paper aims to investigate the suitability of Reynolds Average Navier–Stokes (RANS) models for the simulation of this problem. Staggered and in-line finite tube bundles are considered for compact (a=1.25), medium (a=1.45), and wide (a=1.65) pitch ratios. The lead bismuth eutectic alloy with Pr=2.21×10−2 is considered as the working fluid. A 2D computational domain is used relying on the k−ω Shear Stress Transport (SST) for the turbulent momentum flux and the Prt concept for the turbulent heat flux prediction. The effect of uniform and spatially varying Prt assumptions has been investigated. For the in-line bundle, unsteady k−ω SST/Prt=0.85 has been found to significantly underpredict the integral heat transfer with regard to theory, featuring a good to acceptable agreement for wide bundles and Pe≥1150. For the staggered tube bank, steady k−ω SST and a spatially varying Prt has been the best modeling strategy featuring a good to excellent agreement for medium and wide bundles. A poor agreement for compact bundles has been observed for all the models considered.

Assessment strategy for a longitudinally finned semi-circular tube bank

The current study presents a numerical investigation of a staggered semi-circular tube bank in crossflow of air to determine its thermal and hydraulic characteristics. The effects of incorporating longitudinal fins are also investigated using different fin lengths. The study covers a range of Reynolds number from 1,000 to 10,000. Correlations for the relative heat transfer rate and Nusselt number are proposed for the finned and plain semi-circular tube banks, respectively. Additionally, results of streamlines, contours, friction factor, Nusselt number, and local heat transfer coefficient are presented and discussed. An assessment strategy is proposed to evaluate the performance of any tube bank compared to that of an equivalent circular one under three different constraints (identical mass flow rate, pressure drop, and pumping power). The plain semi-circular tube bank outperforms the circular one with up to 28% and 11% enhancement in heat transfer at constant pressure drop and pumping power, respectively. Moreover, incorporating the longitudinal fins into the semi-circular tube bank enhances the performance remarkably.

High efficiency 3-D printed microchannel polymer heat exchangers for air conditioning applications

The design, fabrication, and experimental characterization of a counterflow Micro-pin array Polymer Heat eXchanger (MPHX) for HVAC applications is described. The design consists of water flow through microscale pin array plates, and airflow paths in a counterflow direction through adjacent rectangular channels. When compared to a Finned Tube Heat eXchanger (FTHX), the water plates take the place of fins and the crossflow tube bank is eliminated. The MPHX is fabricated by 3 D printing using a digital light synthesis method. A correlation-based model is developed and used to explore the parametric space to arrive at a baseline MPHX core geometry. Mechanical and fluidic simulations are performed on the baseline geometry to further develop the design. A sub-scale MPHX with a nominal cross duct area of 10.1 cm × 20.3 cm is designed and fabricated. Its thermal performance over a range of air and water flow rates corresponding to heat capacity rate ratios in the range of 0.25–1 is investigated. Results show that the effectiveness varies from 0.65 to 0.95 corresponding to a of 1 to 0.25. The experimental data are used to validate a correlation-based thermo-fluidic model of the MPHX. The validated model is further used to compare the performance advantages of the MPHX design over a FTHX. For a given heat exchanger volume and thermo-fluidic conditions, the MPHX transfers 55% more thermal energy when compared to a FTHX at comparable air-side pressure drops.

ARRANGEMENT EFFECT ON HEAT TRANSFER AND HYDRODYNAMIC CHARACTERISTICS OF A TUBE BANK IN CROSS FLOW

ARRANGEMENT EFFECT ON HEAT TRANSFER AND HYDRODYNAMIC CHARACTERISTICS OF A TUBE BANK IN CROSS FLOW

EXPERIMENTAL STUDY AND CFD SIMULATION OF HEAT TRANSFER AND FRICTION FACTOR CHARACTERISTICS IN THE CROSSFLOW TUBE BANK

EXPERIMENTAL STUDY AND CFD SIMULATION OF HEAT TRANSFER AND FRICTION FACTOR CHARACTERISTICS IN THE CROSSFLOW TUBE BANK

Numerical analysis for thermo-hydraulic performance of staggered cross flow tube bank with longitudinal tapered fins

Cross flow tube bank is an important constituent in most of the industrial heat exchanging systems such as Heating Ventilation and Air Conditioning (HVAC) systems, Waste Heat Recovery systems and Industrial Boilers. Considering the depletion of fossil fuels and allied environmental concerns, there is a huge need for improving the performance of the cross flow tube bank. The present numerical study investigates the effect of longitudinal taper fins on external flow over staggered cross flow tube bank. The longitudinal fins of various length (0.50 ≤ L/D ≤ 1.50), base thickness (0.40 ≤ T/D ≤ 0.80) and end thickness (t/D = 0.12 and 0.28) are used to evaluate the thermal performance of the tube bank. The thermal hydraulic performance is evaluated considering the effects on rate of heat transfer along with pressure drop characteristics across the tube bank. The results shows that the use of longitudinal taper fins significantly enhances the thermal hydraulic performance of cross flow tube banks. Moreover, the increase in length of fin results in an appreciable enhancement in Nusselt number, which overrules the increase in pressure drop penalty. Whereas, the increase in the fin base thickness, results in a significant reduction in pressure drop capable of compensating the reduction in Nusselt number. Hence, increase in both these dimensions results in higher thermal hydraulic performance than the bare tube bank. On the other hand, fin end thickness plays only a minor role in the finned tube bank performance. Lowering the value of fin end thickness slightly increase the thermal performance by suppressing the friction factor.

Experimental and numerical investigations for effect of longitudinal splitter plate configuration for thermal-hydraulic performance of staggered tube bank

The use of fins for the passive mode of heat transfer enhancement is being used since decades. The use of fin increases the rate of heat transfer by increasing the effective area available for the energy exchange. Hence, most of the modern heat exchanger makes use of different types of the fins to make the device more efficient and compact. Most of the fin configuration used in the heat exchanger not only increases the rate of heat transfer but also causes an undesirable rise in pumping power owing to the additional air/fluid resistance encountered. In the present study, longitudinal fins in the form of a splitter plates are used for the experimental study in case of a staggered cross flow tube bank. The splitter plate geometric configuration such as splitter plate length (0.50 ≤ L/D ≤ 1.50) and plate thickness (0.04 ≤ t/D ≤ 0.20) are varied to further enhance the overall thermal hydraulic performance of the tube bank. The three-dimensional numerical study is also performed for better fluid flow visualization. The use of the splitter plate with L/D = 1.0 and t/D = 0.20 improves the Nusselt number with the reduction in the overall pressure drop for most of the configuration, resulting in an improvement in the thermal-hydraulic performance of tube bank. Moreover, statistical correlations are developed for the Nusselt number and friction factor characteristics for longitudinally finned tube bank for the entire range of Reynolds number from 5000 to 25000.

Enhanced thermal and fluid flow performance of cross flow tube bank with perforated splitter plate

ABSTRACT The cross flow over the tube bank is extensively employed in the heat exchangers. The present study investigates the heat transfer and frictional losses of cross flow tube bank with solid and perforated splitter plates. The experimental data are collected for bare tube bank, tube bank with solid and perforated splitter plate by varying the splitter plate width ratio (Rw) and the perforation index (Pi) in the Reynolds number range of 10,500–40,500. The cylindrical tube bank with perforated splitter plate having (Rw) of 0.5 and (Pi) of 1.5 yields maximum thermal and hydraulic performance.

Numerical studies on the near wall y+ effect on heat and flow characteristics of the cross flow tube bank

The use of passive mode of heat transfer enhancement are most commonly used for the performance improvement with conservation of conventional fuels. In recent times, to visualize the insight of fluid flow analysis, the numerical simulations are mostly preferred. The number of grid points present in the in the fluid domain near the wall governs the accuracy and precision of the numerical study. Hence in the present study, three different near wall grid systems are consider to evaluate its effect on Nusselt number friction factor for the staggered tube bank arrangements. It is reported that y+ as 10, insensitive to boundary layer effects at higher flow rate, while y+ as 1.0, and 0.10 are in close approximation.

Active Heat Transfer Augmentation of Bundle of Tubes by Partial Oscillatory Excitation

Numerical analysis of heat transfer from a heated oscillating tube bank in crossflow has been investigated for an aligned array of tubes using the Open Source Field Operation and Manipulation C++ library. The heat exchanger constructed based on the present idea of tube oscillation is called the oscillating heat exchanger. The verification/validation procedure was performed for four benchmark cases. The effect of several combinations of oscillating frequencies and amplitudes on the mean Nusselt number and the drag coefficient was investigated at the Reynolds number of 100. The results of simulation showed that, by vibrating the first column of tubes in the lock-in region, approximately 25% augmentation in the overall Nusselt number was obtained. Also, it is computed that the effect of oscillation of the first column on the heat transfer enhancement is remarkable in low-amplitude motion, the amplitude of oscillation is important in the off-lock-in frequencies, and the maximum Nusselt number is independent of the amplitude of oscillation. To reach the maximum possible heat transfer removal with low construction costs, it is recommended to oscillate the first column with low amplitude, but the frequency should be selected inside the lock-in region.

Numerical study of convective heat transfer from tube bank in cross flow using nanofluid

In this paper, laminar convective heat transfer of Al2O3 -water nanofluid flow over tube banks under constant wall temperature conditions has been numerically investigated. The circular-tube banks with staggered arrangement are considered in this study. The governing equations have been solved using finite volume approach based on SIMPLE technique in body-fitted coordinates. The numerical simulations have been conducted for Reynolds number ranging from 100 to 600 with nanoparticles volume fraction ranging from 0 to 0.05. The effect of longitudinal pitch, transverse pitch and nanoparticle concentration on the streamwise and temperature contours, average Nusselt number, friction factor and thermal-hydraulic performance factor have been investigated and discussed. Results showed that the best performance is obtained at longitudinal pitch ratio of 1.5, transverse pitch ratio of 2.5 and nanoparticles volume fraction of 5% over the ranges of Reynolds number.

Numerical study of pressure drop and heat transfer from circular and cam-shaped tube bank in cross-flow of nanofluid

Flow and heat transfer of nanofluid inside circular and cam-shaped tube bank is studied numerically. Reynolds number for cam-shaped tube bank is defined based on equivalent diameter of circular tube and varies in range of 100⩽ReD⩽400. Nanofluid is made by adding Al2O3 nanoparticle with volume fraction of 1–7% to pure water. Results show using nanofluid results in higher heat transfer rate for both circular tube bank and cam-shaped tube bank. Also, staggered arrangement has higher heat transfer for both circular and cam-shaped tube bank. Pressure drop from cam-shaped tube bank is substantially lower than circular tube bank for all range of Reynolds number and volume fraction.

Experimental and CFD prediction of heat transfer and friction factor characteristics in cross flow tube bank with integral splitter plate

The experimental and the three-dimensional numerical simulation of cross flow tube bank in staggered arrangements with and without the splitter plate attachment is performed with (5500⩽Re⩽14,500) and splitter plate length to tube diameter (L/D) ratio as 1. The longitudinal and transverse tube pitch ratio SL/D and ST/D were maintained constant as 1.75 and 2.0 respectively. The provision of the splitter plate increases the Nusselt number for the fluid flow which results in the increase in the heat transfer along with the decrease in the pressure drop within the tube bank as compared to that of the bare cylinder. The overall thermal performance of the splitter plate attachment is much superior to that of the bare cylinder which indicates higher heat transfer with lower friction factor. An increase of maximum 60–82% in the overall thermal performance was observed by the use of the splitter plate over the bare cylinder at the Reynolds number of 5500.

Numerical investigation of heat transfer and friction factor characteristics from in-line cam shaped tube bank in crossflow

Tube bank heat exchangers are considered to be an effective device for heat transfer between two fluids. Researchers investigated various arrangements and along with different geometries of the tube, so as to improve the thermal performance of the tube bank. In the present study, the numerical investigation is carried out to determine the thermal performance of cam shaped tube. The study is performed for the heat transfer and friction factor characteristics in the Reynolds number range from 11,500 to 42,500. The result of the numerical simulation indicates the superior thermal performance of the cam shaped tube banks over the circular tubes. As the friction factor is reduced by 85–89% as compared to the circular tubes the heat transfer by friction factor (Nu/f) is increased by 5 times as compared to circular tubes. However, the efficiency of cam tubes with a pitch ratio of 1.5 is higher than that of the pitch ratio of 2.0. Further, the area goodness factor is also around 9 times higher than circular tubes.

Triple-finned tubes – Increasing efficiency, decreasing CO2 pollution of a steam boiler

This paper presents the results of techno-economical analysis of a proposal of the utilization of TFT (triple-finned tubes) in a boiler's tube banks. The following three tube bank arrangements were compared: (A) the base – staggered plain tube bank; (B) the combination of triple-finned and plain tubes – two rows of triple-finned tubes every 10 rows; (C) the alternating tube bank, where half of the plain tubes were replaced by triple-finned tubes in an in-line arrangement.The results of CFD calculations of heat load q let to obtain relative values of the Nu number on the tube bank in (B) and (C) arrangements and the base arrangement (A) were carried out in a 2D model using the CFD (computational fluid dynamics) code Fluent.Heat transfer values of an ECO (economizer) with triple-finned tubes were obtained for the calculation of outlet flue gas temperature and outlet loss. Calculations of the Nu number of the tube were performed for all arrangements. Next, boiler efficiency and fuel consumption were calculated by 0D modelling. Received results were used to make economical analysis. In the case of modernization in the (C) arrangement, efficiency would be 90.67%, which is an increase of 1.1%. This is related to the reduction of flue gas temperature to 138 °C from 158.8 °C.Economically, the most advantageous solutions, are the variants of modernization (B) and (C) for the newly formed boiler. In both cases, SPBT (simple payback time) capital payback period is very short - close to half of a year.It is worth noting that the proposed modernizations of the arrangement (B) and (C), will respectively reduce CO2 emissions by 550 t/a and 826 t/a.The results show that triple-finned tubes can be used to increase the performance of cross-flow tube banks.

Characteristics of heat transfer for tube banks in crossflow and its relation with that in shell-and-tube heat exchangers

The thermodynamics performances for tube banks in crossflow and for the shell sides of shell-and-tube heat exchangers were investigated, and the relation of fluid flow and heat transfer between them were analyzed. The results indicate that the incline degree of tube does not lead to obvious change on characteristics of fluid flow and heat transfer for fluid flowing across tube banks. Under different incline degrees of tubes, the characteristics of fluid flowing across tube banks are similar concerning fluid velocity components and local heat transfer along across angles. The ratios of vertical velocity component to parallel velocity component remain about 4.2 in the banks. Decreasing of impacting angle in the model reduces average fluid velocity crossing tubes, which weakens heat transfer. Characteristics for fluid flowing across tube bundles in shell sides distinguish from that for tube banks in crossflow with different impacting angles. At the same mass rate, the values of parallel velocity components in different shell sides are equivalent, but the vertical velocity components vary greatly. The ratios of vertical velocity component to parallel velocity component change from about 0.33–0.92 in the three types of shell sides. Many different leakage paths and bypass streams leads complicated fluid flow in shell sides of heat exchangers. The complicated flow pattern is not a simple combination of fluid flowing across tube banks with different impacting angles. The thermodynamics performance of shell side depends greatly on the vertical velocity component of fluid. The achievement in the paper can be a reference for study and development of heat exchanger.

Heat Transfer and Pressure Loss In Combined Tube Banks With Triple-Finned Tubes

This paper presents experimental and analytical results of an investigation of heat transfer and pressure loss in a new type of convection heat exchanger tube bank with triple-finned tubes (TFTs). An initial evaluation of the optimal geometry of TFT banks using the Lusas code is presented. The heat transfer between the external environment and the medium inside the TFTs was modeled. Fins were arranged on a tube in the following three configurations: three fins with the same geometry with 45° between two symmetric fins and a vertical line of symmetry, denoted by T90, three fins with the same geometry with 30° between two symmetric fins and a vertical line of symmetry, denoted by T60, and one fin and angle steel plate placed parallel to the line of symmetry of the triple-finned tube, denoted by TAS90. The naphthalene sublimation technique is used as a heat/mass transfer analogy to evaluate the Sherwood (Nusselt) number ratios in the tube banks. The heat transfer performance of staggered S1T90 tube banks and the basic plain tube bank SP was compared. The second possibility for using TFTs is in a tube bank with all tubes finned was studied using the naphthalene analogy technique. The results are then compared with those computed using the computational fluid dynamics code. A comparison of the numerical and experimental heat transfer results shows that the trends in the heat transfer increase are very similar. The results show that triple-finned tubes can be used to increase the performance of cross-flow tube banks.

Heat transfer of a staggered fining flat-oval tube banks in cross flow at the small Reynolds number

Experimental investigations of heat transfer of staggered bundles of flat-oval tubes with incomplete transversal finning in the range of Reynolds numbers 500 < Re <20000 are performed. New calculation correlations for1determining of heat transfer coefficients forRe 1 <3000 are suggested, the impact of basic geometric and re1gime parameters on intensity of external heat transfer are determined. The received calculation depending is possible to use in developing of heat transfer surfaces for “dry” cooling towers and air cooling apparatuses