Flow Friction Characteristics Research Articles

Parametric study and optimization of H-type finned tube heat exchangers with honeycomb arrangement using Taguchi method

Enhancing the efficiency of flue gas waste heat utilization is an important way to achieve carbon peaking and carbon neutrality goals. In this paper, a three-dimensional numerical model of an H-type finned tube heat exchanger with honeycomb arrangement is developed. Firstly, the effects of five parameters are analyzed using the control variable method, including the oblique tube pitch, the ratio of fin height to oblique tube pitch, fin pitch, fin thickness and slit width. Then, the Taguchi method was used to investigate the interaction effects of the five geometric parameters. Numerical simulations of 27 cases with different parameter combinations were carried out and the heat transfer and flow friction characteristics and their overall performance were discussed in detail. The results show that oblique tube pitch has the most significant effect on heat transfer capacity, fin pitch has the most significant effect on overall performance, and slit width has the least effect on both. Finally, the optimum parameter combinations were obtained. When inlet velocity ranges from 5 m/s to 10 m/s, heat transfer performance is increased by 46.3 %-52.1 %, pressure drop is increased by 5.7 % − 11.3 %, and the overall performance PEC is improved by 63.5 %-105.9 %. The results of the study contribute to the development and optimization of new flue gas heat exchangers.

Innovative twist design for solar water heaters: Experimental findings and implications

More effective use of solar energy in hot water systems is made possible by optimising heat transfer and flow resistance. In light of this, Research has been conducted to enhance convective heat transfer while analysing flow friction characteristics for best performance, resulting in the design of novel inserts known as customised twists, which increase the efficiency of the solar hot water system. A conventional, plain tube heater is used as a baseline for the study on thermal characteristics, heat transportation and flow friction attributes. A thorough analysis and comparison of the thermal behaviour of the system with customised twist inserts that have been modified using rods and spacers of different lengths is performed. As a result of the induced disturbance in the fluid particle flow pattern throughout the length of risers, a significant improvement in the coefficient of convective heat transfer is observed. The study validated the correlations for the convective heat transfer coefficient and the resistance coefficient against previous research findings. The findings indicated that the thermal efficiency of the full-length twist-inserted system is almost three times greater than that of a plain collector while doubling its pressure drop. The findings of this research could be useful in designing low-cost, compact solar water heaters.

Flow friction and heat transfer characteristics evaluation for a rectangular channel with spherical dimples and protrusions

Flow friction and heat transfer characteristics evaluation for a rectangular channel with spherical dimples and protrusions

Two-phase flow structures in a helically coiled microchannel: An experimental investigation

At the microfluidic scale, the utilization of helically coiled channels (HCCs), also known as a spiral channel, for two-phase flow offers numerous advantages in various applications. Existing articles mainly focus on the macro-scale transport, examining secondary flows induced in curved channels. The increasing demand, however, for innovative miniature equipment for thermal energy management emphasizes the importance of comprehending gas–liquid micro-scale flow in curved channels. Unfortunately, despite a vast body of literature on this paradigm, there is still a lack of systematic investigations into the underlying facets of two-phase micro-scale transport in HCCs. To address this gap, our study conducted experiments on adiabatic two-phase air–water flow inside an up-flow helical micro-scale tube. The tube had a hydraulic diameter of 0.87 mm, a coil diameter of 50 mm, and a helical pitch of 20 mm. The primary aim was to explore the impact of centrifugal force on flow pattern, void fraction, and frictional pressure drop characteristics. Additionally, we carefully examined the phase separation phenomenon influenced by the secondary flows induced by the curved channel. In particular, we compared the gas-core flow pattern (either throat-annular flow or annular flow), void fraction, and frictional pressure drop obtained from our experiments on the helical tube with corresponding results based on straight micro-scale channel configurations for an Eötvös number of approximately 0.01. In summary, this study delves deep into the crucial aspects of two-phase micro-scale transport in HCCs, contributing to a better understanding of these systems for future advancements in micro-channel applications.

Analysis of Flow and Pressure Drop on Tube Side of Spiral Tube Heat Exchanger under Sloshing Conditions

The utilization of the spiral tube heat exchanger (SHE) has become increasingly prevalent in large-scale liquefaction processes. However, the flow pattern and frictional pressure drop of two-phase flow in the spiral tube have been scarcely studied, particularly under offshore sloshing conditions. An experimental system had been developed to explore the flow pattern and frictional pressure drop characteristics of mixed hydrocarbon fluid in a spiral tube. Moreover, these have been developed in order to examine the effects of sloshing style (roll, pitch, heave), sloshing period (5–15 s), sloshing amplitude (5–15° or 50–150 mm), mass flux (200–800 kg/(m2·s)), vapor quality (0–1), and saturation pressure (2–4 MPa) on the frictional pressure drop of methane/ethane mixture in the spiral tube. The results indicated that sloshing conditions reduce the frictional pressure drop, thereby enhancing fluid flow. A correlation was established to predict the sloshing factor of frictional pressure drop, and the MARD under verification conditions was 6.04%. Furthermore, three flow pattern boundaries were proposed based on We* as an indicator.

Flow Frictional Characteristics of Air–Water Flow Characteristics under Stable and Transverse Vibration Conditions in Horizontal Channels

We experimentally studied the air–water pressure drop characteristics with inner diameters of 20 mm under stable and transverse vibration conditions in the horizontal circular channel. We experimented with the status of the gas-phase conversion flow velocity Jg at 0.1–20 m/s, and the liquid-phase conversion flow velocity Jw at 0.1–3.0 m/s. In this paper, we discuss the effect of flow velocity, amplitude, and frequency on the transverse vibration pressure drops. With increasing frequency and amplitude, the vibration performance of pressure drops become more intense. Thus, with increasing frequency and amplitude, the frictional pressure drop increases. Moreover, the frictional pressure drop increases linearly with the increasing flow velocity. We compared the experimental results of air–water pressure drop with the calculated results of previous empirical correlations. Based on Chisholm-C correlation, we obtained a modified correlation for factor C in horizontal channels under transverse vibration conditions. The new correlation considers the effect of channel confinement number, amplitude, frequency, and vapor quality. The new correlation has relatively good prediction results for the experiments, and the mean absolute deviation is 8.2%.

Flow fluctuations and flow friction characteristics of lead-bismuth eutectic in a vertical tube under rolling conditions

The effects of rolling motion on the flow characteristics of lead-bismuth eutectic in a vertical circular tube are investigated experimentally. The results show that the pressure drop and flow rate of the forced LBE circulation fluctuate under rolling conditions. The effect of rolling motion on the flow characteristics decreases with the increase of the corresponding static Reynolds number. The rolling motion may increase the time-averaged frictional resistance coefficient of the LBE when flow rate is low. The critical value of the impact Reynolds number is about 125,000. As a result, the time-averaged flow rate decreases. The analysis shows that it is mainly the transverse additional force caused by the rolling motion increases the frictional resistance of the LBE. An empirical correlation is established to predict the frictional resistance coefficient under rolling conditions. This study may be useful in the design and safety analysis of LBE as a working fluid under moving conditions.

Heat transfer and flow friction characteristics of dimple-type heat exchanger in axial piston pump

The heat exchanger is widely applied to many axial piston machines, and its structure significantly affects the flow and heat transfer characteristics. The fluid flow and heat transfer characteristics of a dimple-type heat exchanger in the axial piston pump are numerically investigated. The variations of the Nusselt number, friction factor and heat transfer performance with the Reynolds number, and the dimple radius to depth are obtained. The results show that both the Nusselt number and the resistance coefficient of the spherical dimple channel are higher than those of the triangle dimple one. Thus, from the view of the heat transfer performance, the spherical dimple channel is better. Furthermore, the friction factor increases as the dimple radius to depth increases. With the increase in the dimple radius to depth ratio, the shear stress at the wall of the spherical dimpled channel gradually decreases and then reduces the wall friction resistance. Comparing with the triangle dimple channel, the friction factor in the spherical dimple channel is 0.044–0.022, which reduces about 9%. When the radius–depth ratio is set to 0.1, the effectiveness factor for the spherical dimpled channel has better performance.

Flow Fluctuations and Flow Friction Characteristics of Lead-Bismuth Eutectic in a Vertical Tube Under Rolling Conditions

Flow Fluctuations and Flow Friction Characteristics of Lead-Bismuth Eutectic in a Vertical Tube Under Rolling Conditions

Parametric investigation and correlation development for thermal-hydraulic characteristics of honeycomb 4H-type finned tube heat exchangers

The key to the design of dusty flue gas heat exchangers is to enhance heat transfer and solve the fouling problem. In this paper, a honeycomb 4H-type finned tube heat exchanger (FTHE) was proposed. A three-dimensional numerical investigation was conducted on heat transfer and flow friction characteristics of honeycomb 4H-type FTHEs. Firstly, the flow field and temperature of H-type FTHEs with inline and honeycomb arrangements were analyze. Then, the effect of different structural parameters (oblique tube pitch, fin height, slit width, fin pitch and fin thickness) and Re number were analyzed. Finally, the predicted correlations of Nu number and Eu number of honeycomb 4H-type FTHEs were obtained based on the multiple regression method and 105 sets of numerical data. The results show that the thermal-hydraulic performance of honeycomb 4H-type FTHEs is superior to that of aligned single H-type FTHEs. Through parametric analysis, it is found that Nu number is only negatively correlated with oblique tube pitch, and Eu number is negatively correlated only with fin pitch and slit width. Besides, the average error of correlations of Nu number and Eu number is less than 3%, which provides practical guidance for efficient recovery of industrial waste heat.

Enhanced thermal performance in a square-duct heat exchanger with inclined square-rings

An experimental work has been conducted to explore thermal and turbulent flow friction characteristics in a uniform heat-fluxed square-duct contained with inclined square-rings (SR). Experiments were performed for different geometric parameters of the SR elements, focused on their detailed effects on the optimal thermal performance. Influences of five different ring-to-duct height or blockage ratios (BR=b/H= 0.1, 0.15, 0.2, 0.25 and 0.3) on friction factor (f), Nusselt number (Nu), and thermal enhancement factor (TEF) in the square duct are investigated for Reynolds number (Re) from 4210 to 25,800. The inclination angle (a) and the ratio of axial pitch length of rings to the height of duct (called pitch ratio, PR=P/H) were kept constant at 60° and 3.0, respectively. The experimental result has shown that the SR insert gives greater heat transfer and friction loss than the plain duct acting alone. Increasing the blockage ratio (BR) results in the drastic enhancement in Nu and f values. The inserted duct with BR = 0.25 has the maximum TEF around 1.57. Comparing thermal performance at identical operating conditions, the SR insert at BR = 0.15 gives around 1.1 %, 2.3 %, 3.2 and 4.5 % higher than the one at BR = 0.2, 0.25, 0.3 and 0.1, respectively.

THERMAL CHARACTERISTICS OF A HEAT EXCHANGER TUBE FITTED WITH DIFFERENT PERIPHERALLY-CUT TWISTED TAPE INSERTS IN LAMINAR FLOW

Experimental analyses of the alternation of clockwise and counterclockwise twisted tape (AT tape), and the AT tape in conjunction with three types of edge notches (V-cut, semicircle-cut, and rectangular-cut) on heat transfer and laminar flow friction characteristics in a uniform heat flux, circular copper tube using water as working fluid have been investigated in this paper. The investigations of plain tube were also carried out for comparison. The experiments covered a range of Reynolds numbers 500 ≤ Re ≤ 1800. The obtained results reveal that all of the present twisted tapes utilized in the experiment can significantly increase the Nusselt number and friction factor. The Nusselt number increases with increase in the Reynolds number while the friction factor shows an opposite trend for all cases. For a fixed Reynolds number, the Nusselt number and friction factor both increase with the reduction of edge notch area. Over the range investigated, the maximum value of performance evaluation criterion (PEC) achieved by the AT tape insert reached 1.54 at the Reynolds number equal to 1800. Finally, the empirical correlations for the Nusselt number, friction factor, and PEC were also determined. The predicted Nusselt number, friction factor, and PEC were, respectively, within ± 6.1%, ± 4.1%, and ± 3.3% deviation compared to the experimental data.

Inverse Simulation for Extracting the Flow Characteristics of Artificial Snow Avalanches Based on Computation Fluid Dynamics

Many numerical analysis methods for predicting the motion of soil or snow avalanches may set the characteristics of the dynamic friction obtained from field tests, such as the measurement of real avalanche and model slope tests. However, the friction characteristics of the actual flow of objects are influenced by changes in the velocity and density of the flowing objects and are not necessarily constant. In addition, determining the shear strain rate dependence of the frictional properties at low shear strain rates is important for accurately predicting the avalanche reach distance. In this research, model tests using a rotating drum device were carried out, and an artificial snow avalanche was generated. Then, the flow velocity distribution of the flow was extracted by organizing the motion of the artificial snow avalanche flowing in the drum device using the Digital Image Correlation method. Moreover, the changing characteristics of the viscosity coefficient of the pseudo flow were estimated using an inverse simulation. For the results, it was suggested that the method of estimating flow characteristics and friction characteristics from the artificial avalanche generated by the rotating drum and the time inverse analysis proposed in this study was effective, but it is necessary to confirm the issue of the need for a similar analysis using real scale. If it is found to be applicable to real scales in the future, it will contribute to the development of this field because it will expand the range of methods for analyzing avalanches using model experiments.

Investigating the frictional force distributions and inter-stage imbalance of a two-stage brush seal

Although a two-stage brush seal (TSBS) plays an important role in gas turbine machinery, few studies have investigated the complex flow and tip frictional force distributions of the TSBS. This article contributes to the ongoing investigation of the TSBS by proposing a 3D slice model employing computational fluid dynamics to analyze the flow and tip frictional force characteristics of a contacting TSBS using the torque balance principle and linear superposition methods. Our calculations reveal that as the inter-stage imbalance of the pressure decreases, so do the aerodynamic and tip frictional forces between the upstream and downstream bristle packs. In addition, the effects of the number of bristle axial rows and protection clearance height on the inter-stage imbalance are analyzed. The results indicate that the TSBS exhibited significantly less leakage and lower aerodynamic and tip frictional forces than a single-stage brush seal. However, the inter-stage pressure differential results in an inter-stage imbalance in the aerodynamic and tip frictional forces that can be aggravated under high pressure conditions. This study determined that reasonable adjustments can be made to the number of bristle axial rows and protection clearance heights of the upstream and downstream stages to alleviate this inter-stage imbalance. The findings of this study contribute to the design and implementation of more efficient TSBSs.Although a two-stage brush seal (TSBS) plays an important role in gas turbine machinery, few studies have investigated the complex flow and tip frictional force distributions of the TSBS. This article contributes to the ongoing investigation of the TSBS by proposing a 3D slice model employing computational fluid dynamics to analyze the flow and tip frictional force characteristics of a contacting TSBS using the torque balance principle and linear superposition methods. Our calculations reveal that as the inter-stage imbalance of the pressure decreases, so do the aerodynamic and tip frictional forces between the upstream and downstream bristle packs. In addition, the effects of the number of bristle axial rows and protection clearance height on the inter-stage imbalance are analyzed. The results indicate that the TSBS exhibited significantly less leakage and lower aerodynamic and tip frictional forces than a single-stage brush seal. However, the inter-stage pressure differential results in an inter-stage i...

Three-Dimensional Thermo-Hydraulic Analysis of Solar Air Heater With Equilateral Prism-Shaped Rib Roughness

Abstract Thermal transport and flow friction characteristics due to roughness on the absorber plate of solar air heater are evaluated by applying three-dimensional finite volume based code. Renormalization group (RNG) k–ɛ model is employed to capture the turbulent nature of the flow. The effect of equilateral prism-shaped rib roughness geometrical parameters in terms of relative roughness height (e/D) and relative roughness pitch (p/e) on heat transfer and flow friction is analyzed. Further, the effect of flow parameter, Re in the range of 4000–18,000 is also explored. Results are elucidated in terms of average Nusselt number, friction factor, turbulent kinetic energy, and eddy dissipation. Results are compared with a smooth absorber plate solar air heater. Thermo-hydraulic performance of the roughened solar air heater is analyzed. Noteworthy augmentation in heat transport is obtained. The thermal enhancement factor is calculated for optimal performance and found to vary from 1.7 to 3.5. However, friction factor and pressure loss for roughened plate is significantly higher than its smooth counterpart. The pressure drop across the test section increases with the rise in roughness height due to flow obstruction. A minimum value of the friction factor enhancement ratio worth 2.13 is obtained. Enhancement in thermal transport and pressure losses are combined by introducing a thermo-hydraulic performance factor (THHP). For the range of parameters investigated, the optimum value of the thermo-hydraulic performance factor is found to be 3.41. Correlations for average Nusselt number and friction factor are offered at the end.

Air inlet angle influence on the air-side heat transfer and flow friction characteristics of a finned oval tube heat exchanger

In this study, the influence of various air inlet angles on the heat transfer and flow friction characteristics of a 2-row plain finned oval tube heat exchanger is analyzed by experimental and numerical methods. The experimental results show that an air inlet angle 45° provides the best heat transfer performance, and an air inlet angle 90° provides the smallest pressure drop, while an air inlet angle 30° provides the worst heat transfer performance associated with the largest pressure drop. The 3-D numerical simulation results indicate that with the decrease of the air inlet angle, the uniformity of the air velocity distribution in the z-direction of the heat exchanger becomes worse. The heat transfer characteristics at different air inlet angles are analyzed from the prospective of the field synergy principle and the effect of the air velocity distribution uniformity. The overall heat transfer performance is also evaluated by the JF factor under the same air mass flow rate. The results show that the air inlet angle 45° offers the best overall heat transfer performance, next is the air inlet angle 60°, while the air inlet angle 30° has the worst overall heat transfer performance.

A CFD investigation of the effect of non-Newtonian behavior of Cu–water nanofluids on their heat transfer and flow friction characteristics

In the present study, a finite volume method is used to investigate heat transfer and flow friction behavior of non-Newtonian nanofluids. To study a practical application of the mentioned concept, a simple model of a parabolic trough solar receiver is simulated. The main objective of the present study is to investigate the effect of non-Newtonian behavior of the working fluid on the performance of a parabolic trough solar collector. The heat transfer fluid is assumed to be a non-Newtonian nanofluid, and the flow regime is considered to be laminar. The effect of Cu nanoparticle addition on heat transfer coefficient and flow friction of Newtonian, shear-thinning and shear-thickening nanofluids are studied. To comprehensively investigate the effect of buoyancy-driven secondary flows on the average Nusselt number and friction factor of the absorber tube, simulations are carried out for different Grashof numbers (Gr = 105, 106, 107), Reynolds numbers (Re = 200, 500, 1000), Cu nanoparticle volume fractions (φ = 0, 0.01, 0.03) and non-Newtonian power-law indexes (n = 0.25, 0.75, 1, 1.25, 1.75). It is concluded that when shear-thickening nanofluids are utilized as the working fluid, nanoparticle addition makes no sensible changes in the average Nusselt number. Besides, for all values of non-Newtonian power-law index, variations in volume fraction values do not have any significant effect on the friction factor. Furthermore, it is shown that when the working fluid is shear-thinning, nanoparticle addition triggers to considerable increment in Nusselt number. At high Grashof and Reynolds numbers, the ratios of Nusselt number and friction factor of shear-thinning nanofluids (n = 0.25) to those of shear-thickening nanofluids are up to 3.57 and 0.08, respectively.

Single- and multi-objective optimization of a plate-fin heat exchanger with offset strip fins adopting the genetic algorithm

Based on the new correlation for heat transfer and flow friction characteristics of the offset strip fins in our previous work, the single- and multi-objective optimizations of plate-fin heat exchanger by genetic algorithm are studied in this paper. Different objective functions of effectiveness, modified entropy number, and total annual cost are selected based on the first law of thermodynamics, the second law of thermodynamics and economic analysis. Comparative analysis of single- and multi-objective functions is conducted.The target with the maximum of the effectiveness is equivalent to the minimum of the entropy number generated by heat transfer. The poor thermodynamic performance of the total annual cost is mainly determined by the large proportion of operating costs in the total cost, the optimization process of which is focus on the minimum of the entropy number generated by pressure drop. The modified entropy generation number coordinates the comprehensive performance of the heat exchanger in both economic and thermodynamic aspects. The effective compromise of the single targets is achieved by the non-dominated sorting genetic algorithm with elite strategy (NSGA-II). The multi-objective optimizations are flexible in providing multiple solutions to the selection of practical production.

Thermal-hydraulic performance and entropy generation of supercritical carbon dioxide in heat exchanger channels with teardrop dimple/protrusion

Supercritical carbon dioxide (SCO2) is an excellent candidate for refrigeration system, energy utilization and new power cycle due to its easy-to–reach pseudo-critical point and the advantages of thermo-physical properties. As an efficient and passive thermal control technology, teardrop dimple/protrusion has great potential in heat transfer enhancement and resistance reduction. In this paper, three types of teardrop dimple and protrusions are novelly introduced into the SCO2 rectangular channels. Numerical calculations have been carried out to obtain the detailed flow structures, friction and heat transfer characteristics, overall thermal performance and amount of entropy generation under full turbulence regions. Moreover, the effects of geometrical structure, eccentricity of teardrop dimple/protrusion, Re, temperature and pressure of SCO2 are discussed with in-depth analysis. According to the results, complex and different evolution and development patterns of vortices are presented for three different structures. Positive eccentricity dimple (PED) produces the best overall thermal performance, owing to significant heat transfer enhancement and less friction, and the maximum TP reaches 1.17, indicating a 17% improvement compared with the smooth case. The variation of eccentricity has little effect on overall thermal performance and entropy generation for PED structure, while plays a major role in positive eccentricity protrusion (PEP) and negative eccentricity protrusion (NEP) cases. However, the increase of Re is unfavorable to the overall thermal performance. In addition, the temperature and pressure of CO2 have significant effects on the overall thermal performance for PED cases, and corresponding high-TP and thermal performance deterioration regions have been captured, which is advantageous to fast positioning the specific ranges of temperature and pressure, and whose coupled mode. Specifically, the maximum TP greater than 6 can be obtained near the temperature 305 K and pressure 8 MPa.

Numerical investigations of impingement cooling performance on flat and non-flat targets with dimple/protrusion and triangular rib

Jet impingement is an efficient cooling method and has been widely adopted in electronic device and turbine blade. Well-designed structures including dimples and protrusions arranged in the flow path can alter flow fields in ways that provide a favorable trade between total pressure loss and increased heat transfer. In this paper, impingement cooling performances are numerically investigated for three different target shapes and various surface arrangements of dimple/protrusion and triangular rib. Within the Re range of 10,000–50,000, the detailed flow patterns, heat transfer and friction characteristics are obtained. Compared with flat channels, concave and V-shape targets produce more complex flow patterns. The adoption of dimple/protrusion improves the local and overall heat transfer. The Nu/Nu0 of 1.31 is achieved by sparse protrusion arrangement in concave and V-shape channels, while the f/f0 is only 0.96. The rib-dimple/protrusion arrangement improve the local Nu while significantly deteriorating the overall heat transfer. Comprehensively considering the quantity of heat flux Q, the Coefficient of Performance, Nu/Nu0 and f/f0, an excellent cooling performance has been achieved by protrusion arrangement in non-flat channels.