Tube Bank Research Articles

Effect of tube pitch ratio of in-line tube banks on acoustic resonance and vortex shedding

In the present paper the attention is focused on effects of tube pitch ratios of in-line tube banks on acoustic resonance and vortex shedding. We examined the characteristics of the acoustic resonance in the tube banks with tube pitch ratios ranging from 4.0 to 1.4 in the flow direction. Acoustic pressures were measured on the two sidewalls of the experimental apparatus. The tube surface pressure fluctuations due to the vortex shedding without the acoustic pressure were measured at the acoustic pressure nodes at which the acoustic resonance occurred. Acoustic resonance of low-order modes in the transverse direction occurred at tube pitch ratios of 4.0–2.8 in the flow direction. Alternative vortices were noticeably formed in the tube banks. As the tube pitch ratio in the flow direction of the in-line tube banks increased, the Strouhal number decreased, and as the former decreased, acoustic resonance of higher-order longitudinal modes occurred. The alternative vortices were formed in the tube banks at low gap velocities with no resonance. However, if acoustic resonance of a longitudinal mode occurred, symmetric vortices were formed in the tube banks. The onset velocity of a longitudinal mode was lower than that of a transverse mode, at small tube pitch ratios. As the number of rows of tubes increased, the acoustic resonance of transverse mode occurred at small tube pitch ratios. We discussed the prediction formula of Strouhal number at the tube pitch ratio in the flow direction of 2.0-1.4.

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.

Techno-economic analysis of a concrete storage concept for parabolic trough solar power plants

In an energy transition towards 100 % renewable electricity, concentrating solar power (CSP) with thermal energy storage (TES) should be deployed on a wide scale due to the dispatchability capacity of this technology. To achieve this, a decrease of its levelized cost of electricity (LCOE) is essential. This paper evaluates the techno-economic potential of a CSP plant with high temperature concrete as TES system compared to the standard commercial molten salts system. The general plant design includes creating a bank of metal tubes enclosed by concrete in a modular configuration, aiming to maximize the performance of the plant (e.g., reducing parasitics). Nevertheless, the results proved that the selected configuration underperforms during the discharge phase in nominal conditions. Despite existing expectations, this study shows the prevalence of the current molten salt TES system as a better solution over the high temperature optimized concrete configuration studied.

N-Side Cell-Based Smoothed Finite Element Method for Incompressible Flow with Heat Transfer Problems

In this paper, an n-sided cell-based smoothed finite element method (nCS-FEM) is presented to solve the convective heat transfer in incompressible viscous fluid flow. The Characteristic-based-split (CBS) scheme is used to stabilize the spatial and pressure oscillations of CS-FEM that occur during the process of solving incompressible Navier-Stokes equations. Meanwhile, the characteristic-Galerkin method in CBS is adopted as the convective stabilization in the heat transfer equation. In order to verify the proposed method, typical numerical examples are used to test the computational accuracy of CS-FEM. Meanwhile, the investigation of the robustness of highly distorted element is conducted in a natural convection test case. The calculation results of numerical examples show that CS-FEM is qualified to solve the steady and unsteady convective heat transfer problems for incompressible laminar flow with high reliability. The flow across tube banks with complex geometry in the heat sinks is also simulated to prove the capabilities of the proposed method. Well agreed comparison with the results of CFD software, Fluent, proves that the present method can effectively simulate realistic and complex flow with heat transfer problems.

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.

A Thermal-hydraulic assessment of condensing tube bank heat exchangers for heat and water recovery from flue gas

Condensing heat exchangers are capable of recovering a significant amount of latent heat at temperatures below 100 °C from the flue gas of combustion-based heating systems due to the presence of water vapor in their exhaust streams. However, the condensation of acids along with water vapor creates a highly-corrosive environment in these heat exchangers. As such, a large majority of these heat exchangers are made from corrosion-resistant alloys, such as stainless steel. Polymer-based materials are cost-effective and have great corrosion-resistant properties. Since the performance parameters of a heat and water recovery unit depend on the size and compactness of their heat exchangers, it is challenging to compare the overall performance of stainless-steel condensing heat exchangers with polymeric ones based on the data available in the literature. The main goal of the present study is to develop and assess the thermal–hydraulic performance of a proof-of-concept condensing heat exchanger made of fluorinated ethylene propylene compared to the same condensing heat exchanger made of stainless steel for heat and water recovery from flue gas. For this purpose, an in-depth parametric study is conducted experimentally to evaluate the water recovery efficiency, total heat recovery rate, and pressure drop in the flow paths. The results revealed that the water recovery efficiency of the unit with a specific size, declines when the mass flow rate of the gas increases, although it enhances the total heat recovery of the unit. Moreover, increasing the volumetric flow rate of the heat transfer fluid flow slightly increases the total heat recovery of the stainless-steel condensing heat exchanger, but has a negligible impact on the total heat recovery rate of the polymer-based heat exchanger. Increasing the humidity ratio of the flue gas or the inlet temperature of heat transfer fluid does not have any significant effect on the flue gas pressure drop. These findings are significantly important and novel as they unlock the potential of using polymer-based materials with thermally conductive additives for latent heat recovery from flue gas.

Numerical Analysis of Leakage Performance of Brush Seal Based on a 2-D Tube Bank Model and Porous Medium Model Considering the Effect of Compressible Gas

This paper presented a formula for calculating the resistance coefficient of porous medium model of brush seals considering the effect of gas compressibility. Firstly, the 2-D tube bank model is used to calculate the axial resistance coefficient of brush seals. Secondly, the feasibility of the method is validated according to the existing experiment results. The validation results show that this formula is effective for brush seals. Lastly, the pressure distribution and leakage rate of the test brush seal are analyzed. With the presented porous medium model, the pressure drop through the bristle is computed, and the effect of groove of the back plate is addressed. The pressure drop is mainly concentrated on the downstream side of the bristle pack. The groove in the back plate can keep the pressure balance of the bristles back, causing the recovering of the pressure in the last row of bristles. The leakage rate of porous medium model is higher than the 2-d tube bank model, because the 2-D tube bank model only considers the leakage rate of the zone of the fence height. The rotation speed has a little effect on the reduction of the leakage rate.

Parametric Study on Thermal-Hydraulic Characteristics of H-Type Finned Tube Heat Exchangers

In this paper, the thermal-hydraulic characteristics of H-type finned tube banks are numerically investigated on the basis of a more accurate and convenient calculation method of fin efficiency for H-type fins. Experiments are performed to validate the numerical simulations. The variations of the Nusselt number, Euler number, and comprehensive factor with the Reynolds number and seven geometric parameters of H-type finned tube banks are obtained. The results indicate that the Nusselt number is proportional to the Reynolds number, the slit width, the fin thickness, and the longitudinal tube pitch; but, it is inversely proportional to the tube row number, the fin height, and the spanwise tube pitch. As the Reynolds number, the tube row number, the slit width, the fin pitch, and the spanwise tube pitch increase, the Euler number decreases. The factor rises with the increase of the slit width, and there exists an optimal tube row number () at which the factor is the maximum. The correlations of the heat transfer (Nusselt number) and pressure drop (Euler number) of the 10-row H-type finned tube bank, which can nearly be considered to be fully developed, are presented. The numerical results and correlations have good applicability under different fluids and show good agreement with the experimental results and correlations.

Effective Cooling of Cassava Starch to Ethanol Bio-Reactors/Fermenters

This paper presents an effective way to control the temperature of bio-reactors (fermenters) used in ethanol production and to reduce the volume of cooling water required per square meter of ethanol produced. This paper specifically focuses on the fermentation of cassava starch using Saccharomyces cerevisiae at 32ºC. The flow across tube banks model is employed as the cooling mechanism of the bio-reactor. Cooling water at 28°C enters a shell containing five rows of fifteen (15) bio-reactors in a square in-line arrangement and exits the shell at 31.84°C. The total working volume of all fifteen (15) bio-reactors in the bank equals 180m^3. Each bio-reactor in the bank is designed to have an effective heat transfer area to volume ratio of two (2) to enhance heat transfer. The total quantity of cooling water required per cubic meter of ethanol produced is found to be 97.833m^3. A total amount of 1.303kW is required to power anchor impellers placed in each bio-reactor to provide mixing. The rotation speed of the impeller in each bio-reactor is 0.2〖rev·s〗^(-1). A total of 3.453*10^(-6) W is required to move cooling water through the bio-reactor bank at a speed of 3.942*10^(-5) ms^(-1). An overall heat transfer coefficient of 11.345W·m-2°C-1 was found for the bio-reactor cooling system. Employing flow across tube banks model in cooling ethanol bio-reactors required significantly less amount of cooling water per cubic meter of ethanol produced compared to using internal cooling coils.

Numerical Simulations of the Flow Dynamics in a Tube with Inclined Fins Using Open-Source Software

Finned tubes increase the convective heat transfer in heat exchangers, reducing the total energy consumption of integrated industrial processes. Due to its stability and robustness, Computational Fluid Dynamics (CFD) commercial software is generally utilized for analyzing complex systems; however, its licensing is expensive. Nowadays, open-source software is a viable substitute for proprietary software. This work presents a CFD analysis of the hydrodynamics of a finned tube using the OpenFOAM and SALOME Meca platforms. The results are compared with experimental data and CFD using the commercial software Fluent, both previously reported in the open literature. This work studies the fluid flow pattern around a tube with six 45-degree-angled fins, and the working fluid, air, is considered as an incompressible fluid. Special attention is paid to calculating the pressure coefficient distribution for the internal and external surfaces of the inclined fins. Open-source platforms allow researchers to visualize how the airflow interacts with the cylinder and the fin surfaces to form a fluid structure, formerly known as a horseshoe vortex system. The findings of the analysis of flow dynamics in the channel between inclined fins and in the wake help explain the results obtained in experimental tests and are relevant for the configuration of a bank of tubes with inclined fins.

A regularized diffuse domain-lattice Boltzmann model for heat transfer in complex geometries with temperature Dirichlet boundary condition

In this paper, a regularized diffuse domain-lattice Boltzmann model for heat transfer with the Dirichlet boundary condition in complex geometries is proposed. In this model the complex computational domain is embedded into a larger and regular domain. The level set function is used to capture the complex interface. A diffuse domain formulation for the temperature field is established on the larger domain. To remove the ill-conditioned property of the original diffuse domain equation, we develop a new regularization technique to tackle this issue. We also give a multiple-relaxation-time lattice Boltzmann model to solve the regularized diffuse domain equation. The convergence rate of present model is investigated by the steady state and time-decay heat conduction problems. Then the natural convection problems in a square enclosure with a heated circular cylinder and in a horizontal concentric annulus are simulated. Both the uniform and non-uniform wall temperature cases are considered. Moreover, an alternative method to calculate the average Nusselt number on the complex boundary is employed. The numerical results show a good agreement with the previous solutions in previous literatures. The effect of non-uniform wall temperature on the heat transfer rate is also investigated. At last, the forced convection across the staggered tube banks is also simulated to verify the potential capability of the present model in solving practical heat transfer problem with the complex geometries.

Experimental Study on The Performance of One-Directional and Bi-Directional Flow Conditions Across In-Line Tube Banks Heat Exchanger

The one-directional flow condition and the bi-directional flow condition are two flow conditions that can be found in many energy systems depending on the nature of the flow and the working mechanism of the system. This paper reports the differences in heat transfer performance for an in-line tube banks heat exchanger that is placed in the one-directional and the bi-directional flow conditions. The experiments involve the use of a blower as a flow inducer for one-directional flow while a loudspeaker with a constant frequency of 14.2 Hz is used as a flow inducer for bi-directional flow condition. A quarter wavelength resonator with 4 mm wall thickness and a length of 6600 mm was used in the investigation. The results of velocity and temperature were recorded using a hotwire anemometer and a type-K thermocouple, respectively. Results show that the behaviour of velocity and temperature in one-directional and the bi-directional flow conditions over an in-line heated tube banks are different with a maximum difference of 52 % for velocity and 79 % for temperature.

Experimental work for single-phase and two-phase flow in Duct banks with vortex generators

This work focused on enhancing heat convection coefficient using vortex generators available in various configurations in the bank of oval tubes with single and two-phase flow. Rate of heat transfer by convection and the reduction in pressure in rectangular Duct performed with winglets (Delta and Rectangular). Experimental work studied that under turbulent flow conditions. The experimental results have been compared to show the impact of Vortex generators and various water and air discharges on the heat transfer coefficient. The present work results show Delta winglets are given the best performance in the single-phase flow and the two-phase flow across the bank of the oval tubes. Various parameters have been investigated experimentally to determine their effect on the temperature distribution and heat transfer coefficient.

Performance test of the biomass furnace for bed dryer using various of agriculture wastes

Waste from plantation products has the potential to be used as an alternative fuel. Corn drying needs to be done to increase the selling price of the product and shelf life. One of the drying technologies is to use a bed dryer with the heat source coming from a biomass-fueled furnace. This study aims to determine the rate of heat transfer and analyze the efficiency of the furnace. This study was conducted at the Food and Postharvest Engineering Laboratory of FTP UGM as a tool design site, PT. Raja Pengering as a tool fabrication site, and in the Sukolilo Pati area as a tool testing site. The method used is direct testing with two variations of treatment, namely when the furnace is without a load and when the furnace is with a load. Variations of biomass fuel were carried out with teak wood, corn cobs, and rice husks of 10 kg each with one replication during the no-load furnace test. The main equipment used is a furnace with a vertical tube bank-type heat exchanger and an axial blower. The test results show the value of the heat transfer coefficient when the furnace is without a load of 142.59 W/m2.K, when the furnace is with a load of 138.74 W/m2.K. The coefficient of the furnace with the load is smaller because there is a load on the bed dryer so that the speed of air flowing in the tube bank is restrained. The heat transfer rates with wood, cob, and husk fuel are 22.5; 22; and 4.7 kW, respectively. The total energy of the furnace during combustion using wood, cob, and husk fuels were 83484.7; 33718.37; and 16125 kJ, respectively. The efficiency obtained with wood, cob, and husk fuels was 44.17; 32.67; and 11.65 %, respectively. The husks do not match the furnace design. The performance of the furnace with a load is that the average exit temperature of the furnace is 67.69°C with an efficiency of 68.87 %. Based on the results, the appropriate fuel is wood because it has a high calorific value so which produces an optimum temperature.

Numerical analysis of heat transfer and flow characteristics of a precooler with a methanol cracking reaction

For hydrocarbon-fueled turbojet engines with a precooling technology, the precooling technology with a low-temperature endothermic fuel is a great potential way to solve the problem of sharp reduction of the specific impulse caused by the insufficient heat sink of the hydrocarbon fuel. To study the heat transfer and flow characteristics of a precooler with a fuel endothermic reaction, methanol is chosen as the low-temperature endothermic fuel, and the numerical model of a precooler of tube bank arranged in-line is built, which considers the methanol with a cracking reaction. The results indicate that the methanol cracking reaction can enhance the cooling effect to the air by increasing the heat transfer temperature difference. When the cracking rate is not more than 20%, the cooling effect to the air increases and the cracking rate decreases with the methanol mass flow rate. When the longitudinal pitch-to-diameter ratio varies between 1.25 and 2.50, the cooling effect and the cracking rate increase with its increase, which is not conducive to the compactness of the precooler. When the transverse pitch-to-diameter ratio varies between 1.25 and 2.00, the cooling effect and cracking rate increase with its decrease but bring significant pressure loss.

Thermal–hydraulic performance of the circular-slice-shaped-winglet for tube bank heat exchanger

In this study, heat transfer performance of circular-slice-shaped-winglet (CSSW) for tube bank heat exchanger (TBHE) was numerically investigated. Circular-slice angle (α = 5°, 10° and 20°), layer gap (h/d = 0.08, 0.14, and 0.20) and winglet diameter (D/d = 1.60, 1.76 and 1.92) were analyzed as geometric parameters to obtain optimal design. Comprehensive numerical simulations were conducted under both laminar and turbulent flow (1100 ≤ Re ≤ 8500) conditions. Navier Stokes Equations were solved by using RNG k-ε turbulence model (with enhanced wall treatment). Colburn-j factor (j), friction factor (f), modified London area goodness factor (j/f1/3) and performance evaluation criterion (PEC) were investigated quantitatively. Flow characteristics were also analyzed to elucidate the underlying physics of the effects of CSSW on thermal-hydraulic performance for TBHE. Results were compared with the data related to bare tube heat exchanger, and showed that the highest modified London area goodness factor is 26.34% with α = 10°, h/d = 0.20 and D/d = 1.92 CSSW winglet design. Additionally, numerical calculations revealed that PEC increased to 1.356 with these CSSW design parameters, which corresponds to reduction of the required total heat transfer area by 36.60% compared to the bare tube heat exchanger for the same heat duty at a fixed pumping power.

Experimental analysis of the influence of the number of rows of a tube bank on the FIV critical velocity

The present study investigated experimentally the influence of the number of rows and the position of a free-to-vibrate monitored cylinder in a tube bank on the critical reduced velocity and compared it with literature models. The experiments were conducted in an aerodynamic channel with a test section assembled with one cylinder free to vibrate in the transversal direction and additional fixed rigid cylinders. The tests were conducted for one, two, three, four, and five rows with the cylinder free to vibrate in different positions along the central line. Models presented in the literature for one row and five rows were used to compare with the instability response for the studied configurations. The experimental results showed that the position of the cylinders is relevant due to the number of rows that will be positioned downstream it and if it is in the first row. The models presented in the literature consider the damping and reduced velocity in the analysis without additional parameters, just the factor associated with the arrangement and space ratio. It was observed that the critical velocity changes with the number of rows: a reduction in the velocity of fluid-elastic instability results with the increase in the number of rows when the cylinder was free to vibrate in the second or third row. The positions in the second and third rows presented the lower critical reduced velocities. An increase in the rate of occurrence of fluid-elastic instability was observed with an increase in the number of rows for the same mass and damping parameters when the cylinder was free to vibrate in the first row. The comparison of the results with models to predict the critical reduced velocity showed that, in general, they did not well predict the instability occurrence due to the lack of parameters and the conservative approach adopted in the model development.

Dynamic modeling of a water tube boiler

AbstractThe present work aims to develop an integrated heat transfer and hydrodynamic model for the study of boiler dynamics in fluctuating load conditions. A transient heat transfer model has been developed to estimate water side heat transfer and it is directly integrated with the hydrodynamic model. Two independent natural circulation circuits for furnace water wall and convection tube bank have been considered due to differences in heat transfer, dryness fraction, and void fraction. The transient heat transfer model calculates the heat transfer and water wall temperature of the various sections to calculate total gas side heat transfer, gas temperature profile, and waterside heat transfer in the furnace water wall and convection tube bank. Mass momentum and energy conservation equations are generated for both natural circulation circuits using the estimated value of waterside heat transfer of the transient heat transfer model. These equations are integrated with mass and energy conservation equations for the drum below water level and drum above water level to generate a system of equations to estimate drum pressure and water level fluctuation. This model has been extended for boiler feedback control systems, including the load management and the water level control system.

Enhancement of 3D Mass and Heat Transfer within a Porous Ceramic Exchanger by Flow-Induced Vibration.

This work investigates heat transfer enhancement for a porous ceramic heat exchanger. The effect of flow-induced vibration of exchanging air flow through porous tube banks has been tested. A numerical model able to assess the vibration effect on heat and mass transfer inside a porous ceramic exchanger has been carefully developed. A three-dimensional unstructured control volume finite element method (CVFEM) is developed to simulate the transport phenomena that arise during convective exchange. In this respect, several numerical tests have been conducted. The time evolution of temperature, liquid saturation, and pressure of the porous domain are analyzed and compared for two cases: with and without vibration. It is found that the vibration highly enhances the heat and mass transfer inside the ceramic exchanger. As a result, the gain of exchanging time to reach the thermal equilibrium between the hot air and the porous domain was 75% for the case of air vibration under sawtooth type at a frequency of fv = 5 Hz and Vmax = 10 m/s compared to nonvibrating exchange.

Some Comments on Added Mass Modeling for Tube Bundles Under Two-Phase Cross Flow

Abstract Within the study of fluid-elastic instability in heat exchangers tube banks, a considerable theoretical and experimental effort has been produced for understanding fluid–structure coupling in two-phase flow. This communication discusses the commonly accepted added mass modeling and proposes some ways of further improvement. Notably, it turns out that added mass may be overestimated in a two-phase flow. Taking into account this phenomenon improves the collapsing of flow-induced forces data.