Transverse Pitch Research Articles

Superiority analysis of the cooled cooling air technology for low bypass ratio aero-engine under typical flight mission

The cooled cooling air technology (CCA technology) is beneficial to increase the aero-engine operating pressure ratio and turbine inlet temperature, while its influence mechanism during the full flight envelope is still ambiguous. A comparative analysis has been completed in this study to assess the flight performance of an aircraft engine with or without CCA technology. Based on the aircraft and aero-engine integrated technique, a novel analytical model is developed by combining the propulsion requirement analysis model with the engine design/off-design point analysis model. The precise submodules of the heat exchanger and the turbine blade in engine model improve the -practicability of analysis, which considers the influence of the flight mission on the heat transfer performance. This literature suggests that CCA technology could enhance the fuel weight at take-off phase, the weight-specific surplus power, the load factors, and the supersonic cruising Mach number by approximately 3–4.85% with re-optimizing the cycle parameters. The inlet temperature of turbine Tt4 rises by around 3% without the turbine blade temperature exceeding the limitation. This work further analyzes the most influential structural factor of the total engine performance and the transverse tube pitch is discovered as a noteworthy feature. Additionally, it is well known that the heat transfer and pressure drop of the CCA heat exchanger (CCA-HEX) change dramatically during the whole flight mission. Our findings provide valuable insights into a better understanding of the mechanisms of CCA-HEX characteristic change, in which poor heat transfer occurs at low altitudes and high Mach numbers, whereas the largest flow resistance appears in the high-altitude and low-Mach-number regionsin theopposite manner. In conclusion, CCA technology is a cost-effective method to improve the propulsion performance of the aircraft engine for flight mission.

Development of New Correlations and Parametric Optimization in Nanofluid Flow through Protruded Roughened Square Channel

This study discusses the optimization of heat-transfer parameters in nanofluid flow through a rough square surface channel including a protruded rib compound transverse pattern using response surface methodology (RSM). Flow and geometrical characteristics are optimized, resulting in optimal flow friction and heat transfer performances. The comparison of RSM’s estimated values to experimentally observed values was abandoned. The results demonstrate that the RSM-calculated values agree with the observed values and are within the 5.5 percent uncertainty limitations. Statistical correlations for Nusselt number and friction factor have been developed as functions of protrusion transverse rib height, protrusion transverse rib diameter, X-axis pitch, Y-axis pitch, and Reynolds number. These correlations have been found to predict the values within the error limits of ±8.9% and ±8.7%, respectively. On the basis of correlations developed for Nusselt number and friction factor, an attempt has been made to compare the thermohydraulic performance of protruded roughened square channel.

Parametric and design optimization investigation of a wavy fin and tube air heat exchanger using the T‐G technique

AbstractThe focus of this paper is to optimize the air‐side performance of a wavy fin and tube heat exchanger at different design parameters on an individual target response using the Taguchi method. However, a statistical concept, gray relational analysis, is also studied for combined optimization, considering all target responses at a time. Based on the heat exchanger requirement, parametric study for the air‐side is regarded as a more significant heat transfer and lower frictional factor. Experimental correlations were available and used for the 27 orthogonal runs. Investigation revealed the highest 47.06% fin pitch, 37.24% fin pitch, 25.46% air velocity, and 23.9% fin thickness contribution ratio for the target response of friction factor (TPF), heat transfer coefficient, and Colburn factor, respectively, with the application of the Taguchi method in a heat exchanger. GRG gives an optimum set of design parameters, A3B3C2D1E3F2G1, for wavy fin and tube of fin pitch of 6 mm, tube row number of 6, waffle height 1.8 mm, fin thickness 0.12 mm, and air velocity 5 m/s. Also, longitudinal tube pitch is 27.5 mm, and transverse tube pitch of 24.8 mm, at which TPF is maximum while the friction factor is minimal. The Colburn factor is the most significant, minor friction factor, and the heat transfer coefficient and TPF are the most considerable in GRG. Hence, an improved heat transfer performance design of a wavy fin and tube heat exchanger is achieved using the above techniques.

Reliability analysis to improve performance of multi-pin glass fiber-epoxy laminated composite joints using Weibull distribution

PurposeThe purpose of this study is to check the reliability of a multi-pin joint to be a fail-safe joint by considering different geometric and material parameters. The pin joints are made of uni-directional fiberglass that has been impregnated with epoxy composites incorporating 3% nano-clay.Design/methodology/approachThis study incorporates the analysis of multi-pin joints experimentally, numerically and statistically using the Weibull approach. During analyses, geometrical parameters edge to diameter (E:D), longitudinal pitch to diameter (F:D), side edge to diameter (S:D) and transverse pitch to diameter (P:D) were analyzed using the Taguchi method with a higher-the-better L16 orthogonal array.FindingsThis study aims to develop multi-pin laminated joints to attain higher reliability, which have been designated as fail-safe joints for the intended application and which have higher joint strength. The study reveals that to achieve 99% reliability or 1% probability of failure using the Weibull approach, 24.4% load decrement from the experimental result recorded for three-pin joint configuration at E:D = 4, F:D = 5, S:D = 4 and P:D = 5. Similarly, for the four-pin configuration at E:D = 4, F:D = 4, S:D = 4 and P:D = 5, 23.07% of load decrement observed from the experimental result implies that the expected load with a 99% reliability offers a safe load.Originality/valueA reliability analysis on multi-pin joints was not conducted in structural application. Composite materials are used because of high reliability and high strength-to-weight ratio. So, in the present work, reliability of the multi-pin joint is analyzed using Weibull distribution.

Entropy generation analysis in supercapacitor modules based on a three-dimensional coupled thermal model

Efficient and sustainable thermal management systems are crucial to ensure thermal stability and a long lifespan of supercapacitors. In this work, an entropy generation analysis based on an improved coupled model is implemented for the first time, with the aim to facilitate the design and optimization of the supercapacitor thermal management systems. Entropy generation analysis accurately quantifies the irreversibilities due to heat transfer and fluid friction of the supercapacitor module, allowing for direct identification of the causes of inefficiency that cannot be achieved by the conventional energy analysis. The improved coupled model incorporates a one-dimensional electrochemical model and three-dimensional thermal models at cell and module levels. The optimal thermal management scheme of the supercapacitor module is obtained by the multiparametric optimization based on four evaluation criteria derived from the coupled energy and entropy generation analyses. Results indicate that the supercapacitor module with lower entropy generation and higher heat transfer rate can be achieved with the geometry of transverse pitch equal to longitudinal pitch twice the diameter with the 293.15 K cooling water. This work provides the advanced fundamental and computational frameworks for the development of next-generation, energy-smart thermal management systems for clean and renewable energy conversion and storage modules.

The Effect of Longitudinal and Transverse Pitch Ratio on the Heat Transfer Characteristics of Staggered Drop-Shaped Tubes Bundle

The Effect of Longitudinal and Transverse Pitch Ratio on the Heat Transfer Characteristics of Staggered Drop-Shaped Tubes Bundle

Block shear performance of double-line bolted S690 steel angles under uniaxial tension

We investigated the block shear performance of 16 steel angle specimens connected by double-line bolts. Among these specimens, 10 were made of S690 high-strength steel and 6 were made of normal-strength steel. The angle specimens were fabricated using two hot-rolled steel plates through groove welding. Two angle sections, i.e., 125 × 65 × 6 and 125 × 85 × 6 mm (long leg length × short leg length × thickness), were considered in the test. All angles were connected to the long leg. Apart from steel grade, the test parameters included bolt rows, parallel pitch, transverse pitch, edge distance, and unconnected leg length. Typical block shear of specimens were observed, and different fracture patterns were characterised. The test results confirmed that the block shear strength of the tension angles could be improved by increasing the tension plane area with the increase of the transverse pitch and edge distance and increasing the shear plane area with the increase of the bolt row number and parallel pitch. However, the test results showed that the block shear strength of the angles was not affected by the length of the unconnected leg. Subsequently, numerical models were built to further investigate the block shear behaviour of the double-line bolted angles, and the analysis parameters were the end distance, unconnected leg length, and connected leg length. According to the experimental and numerical results, the accuracy and adequacy of design specifications in the United States, Europe, Canada, and Japan and design equations documented in the literature for evaluating the block shear performance of double-line bolted steel angles were evaluated.

Influence of the punched holes on thermohydraulic performance and flow pattern of rectangular channels with a pair of perforated vortex generators

Vortex generators (VGs) are passive elements that contribute to enhance the heat transfer and produce a low pressure loss. Rectangular channels are the basic unit of many heat exchangers. Frequently, both are combined and therefore they are investigated intensively. Regardless, the influence of punched holes on the plate surface is often ignored when the thermohydraulic performance of rectangular channels has been studied. This work deals with a numerical study about the impact on the channel thermohydraulic performance of a delta winglet pair of perforated VGs punched on the channel surface. The VGs transversal pitch and the flow pattern in the common flow area were investigated for three configurations and sixteen different arrangements. The computational domain consisted of a plate centered in the middle of the rectangular channel. The numerical model was validated by comparison with published correlations for the entry region with isothermal walls as well as inside the laminar flow regime. Secondary flow was evaluated to explain the heat transfer enhancement. A performance evaluation criterion based on the similarity of pumping power was applied. All configurations studied enhanced the heat transfer and increased the pressure loss, with values up to 12.8% and 17.5% respectively. A reverse direction of rotation of vortices was found caused by the punched holes in two configurations, a result that was not found in the literature revised. A vortices inhibition caused by the punched holes was identified, which constitutes an important result and a novelty. For Reynolds numbers higher than 120, the application of VGs punched on the channel surface is advantageous. According to the performance evaluation criterion applied, the positive impact of VGs on the surface was increased with the Reynolds number, reaching values of 1.075 for the common flow up configuration with the punched holes behind and the highest VGs transversal pitch.

Determination of the Reference Temperature for a Convective Heat Transfer Coefficient in a Heated Tube Bank

The paper presents a theoretical analysis of heat transfer in a heated tube bank, based on the Nusselt number computation as one of the basic dimensionless criteria. To compute the Nusselt number based on the heat transfer coefficient, the reference temperature must be determined. Despite the value significance, the quantity has several different formulations, which leads to discrepancies in results. This paper investigates the heat transfer of the inline and staggered tube banks, made up of 20 rows, at a constant tube diameter and longitudinal and transverse pitch. Both laminar and turbulent flows up to Re = 10,000 are considered, and the effect of gravity is included as well. Several locations for the reference temperature are taken into consideration on the basis of the heretofore published research, and the results in terms of the overall Nusselt number are compared with those obtained by the experimental correlations. This paper provides the most suitable variant for a unique reference temperature, in terms of a constant value for all tube angles, and the Reynolds number ranges of 100–1000 and 1000–10,000 which are in good agreement with the most frequently used correlating equations.

CFD investigation of a natural ventilation wind tower system with solid tube banks heat recovery for mild-cold climate

Passive strategies are increasingly being employed in buildings to minimize their total energy consumption and emissions. Wind tower, a natural ventilation device, can capture the wind flow from higher locations and supply the air into the buildings' indoor space without consuming electric power. However, its use in mild-cold climate is limited due to excessive heat loss and thermal discomfort, in particular, during winter. Limited research has been conducted to explore the pre-heating of the supply air in the wind tower to address the issue and potentially increase its adoption in mild-cold climates. Therefore, a novel wind tower ventilation system integrated with solid tube banks heat recovery (HR) is proposed in this research. By combining with a passive heat recovery device, a wind tower can be operated under winter conditions to improve indoor ventilation while reducing the building heating energy consumption. A three-dimensional computational fluid dynamics (CFD) model was developed to investigate the effects of the longitudinal pitch (SL) and the transverse pitch (ST) of the HR device on the ventilation and thermal performance. The overall performance of the wind tower was evaluated under different outdoor wind speeds. The results show that the heat recovery can be improved by reducing SL and ST, raising the supply fresh air temperature by up to 6.4 °C. Furthermore, the proposed wind tower can provide sufficient ventilation for a typical classroom occupied by 15 people when the external wind speed exceeds 3 m/s.

Numerical analysis on heat transfer enhancement of wavy fin-tube heat exchangers for air-conditioning applications

• Heat transfer enhancement at constant pumping power fits closest to real scenarios. • Larger HTC does not necessarily lead to larger heat transfer rate. • Waffle height, wave length, and fin pitch should be optimized simultaneously. • The optimized geometries yield 23% improvement of HTC and 3% of heat transfer rate. • Proper Perforation on wavy fin leads to 34% enhancement of HTC. The air-side heat transfer performance of herringbone wavy fin-tube heat exchangers can be improved by optimizing fin geometries and introducing perforations to the wavy fin. Based on a typical herringbone wavy fin-tube heat exchanger used in the outdoor unit of an air conditioner with collar outside diameter of 7.3 mm, transverse tube pitch of 22 mm, and longitudinal tube pitch of 19.05 mm, the effects of fin pitch, wave length, slits height, and geometries of slits are simulated using CFD and the outcomes are discussed in the paper. We demonstrate that constant pumping power is the ideal criterion for the performance evaluation of any new designs. The wave length has no remarkable effects on the heat transfer coefficient while the lowest pressure drop appears with the symmetric wave configuration. The heat transfer coefficient can be improved by 23.4% when the waffle height, fin pitch, and wave length are simultaneously optimized. Furthermore, punching slits on top of the windward part of wavy fins leads to a 5.5% increase in the heat transfer coefficient. In the end, 34.2% improvement of the heat transfer coefficient is yielded when combining the slit perforations to the optimum fin pitch, wave length, and waffle height.

Heat Exchange in Staggered Threaded Pipe Banks with Similar Developed Surface Patterns under Natural Draft Conditions

Helical pipes with similar developed surface patterns efficiently operate under forced convection conditions. The available literature describes their essential advantages over the tubes of a round-ribbed profile and the possibility of their application as a heat-exchanging section for the air-cooling unit. However, the peculiarities of the operation of such units require checking an opportunity for the use of helical pipes with similar developed surface patterns under natural draft conditions. The purpose of the research is to get new data on the flow structure in the intertube space of the staggered banks of such pipes under natural draft conditions. These data are required for the in-depth analysis of the appropriateness of the use of such pipes for “dry” air cooling systems. The methods of investigation included the use of the academic licensed software package ANSYS Student for numerical computations. It was established that the heat exchange in ribbed pipes under natural draft conditions is specified first of all by the parameters of the staggered bank (longitudinal and transversal pitches of the arrangement of pipes in the bank) and the geometric parameters of the pipes, in particular the pitch between the humps and the dents on the tube surface that form its helical surface. Design ratios were suggested for the determination of the averaged heat exchange in the staggered banks of the single-thread helical pipes with similar developed surface patterns. It was shown that the pitch characteristics of the banks have the greatest effect on the similarity equation. A preliminary validation was carried out for the methods adopted for the design of helical pipes and the known methods used for the computation of the staggered banks of smooth cylindrical pipes. The obtained research data can be used for the evaluation of the intensification of the heat exchange and for the flow analysis in order to increase the efficiency of the heat-exchange equipment.

Numerical analysis of the effect of longitudinal and transverse pitch ratio on the flow and heat transfer of staggered drop-shaped tubes bundle

Several studies have been conducted to enhance the performance of heat exchangers. In the recent decades, shifting from the bluff bodies to more streamlined ones received more attention. The drop-shaped tube is one of the most propitious options for building a better heat exchanger core. This is because of the aerodynamic profile characteristics of the drop-shaped tube. The present work has been conducted to clarify fluid flow and heat transfer across staggered drop-shaped tubes bundle at various longitudinal and transverse pitch ratios. The investigation is performed at Reynolds numbers Re= (1.78–18.72) x103, longitudinal pitch ratios (PL =1.44, 1.54, 1.64, 1.74, 1.84, and 2.04), and transverse pitch ratios (PT =1.24, 1.44, 1.64, and 1.82). Ansys Fluent software package is used to predict the flow pattern around tubes. The RNG k−ε model is selected to evaluate the turbulence effect of the fluid flow. The results showed that an increase in PT significantly affects the heat transfer as compared to PL. An increase in the transverse pitch ratio from 1.24 to 1.82 enhances the heat transfer by 2.18 - 10.53% for the considered Re range. As the Re increases, the average Nusselt number Nu¯ increases and the friction factor f decreases. At a constant PL, the minimum f was varied with Re and PT. The maximum values of the effectiveness ε and the efficiency index η were achieved for (PT = 1.64; PL = 2.04) at Re=1.78 × 103, and (PT = PL = 1.64) at Re> 1.78 × 103. The drop-shaped tubes bundle showed its superiority over a circular one in terms of high thermal-hydraulic performance under the same operating conditions. Finally, generalized Nu¯, f, and ε correlations for the studied models were predicted, providing a useful reference for future studies or for the design of heat exchangers employing drop-shaped tubes.

Prediction and analysis of thermal-hydraulic performance with slit fins in small diameter (3 mm to 4 mm) heat exchangers

The simulation model describes the thermal-hydraulic performance and is verified well by comparing with the experimental data. The 122 runs taking 7 geometric parameters and Reynolds number into account are carried out based on the Response Surface Methodology (RSM). The correlations of the heat transfer (j-factor) and flow friction (f-factor and Eu-number) in 3 mm diameter are proposed. The mean deviations of the correlations with j-factor, f-factor and Eu-number are 3.78%, 2.56% and 2.51% respectively. The effects of 7 geometric parameters are investigated using the RSM model in detail at Re = 500, and it can be found that the height of the slit (Sh) has the greatest influence on j-factor. The differences in the change rate of f-factor and Eu-number are emphatically analyzed. And the effects of the transverse tube pitch (Pt) on f-factor and Eu-number are opposite. The f-factor is positively correlated with Pt, while the Eu-number is negatively correlated with Pt. In addition, the coefficients of correction for j-factor, f-factor and Eu-number are obtained to make available for different collar diameters. In the range of 3.19–4.19 mm collar diameter, the mean deviations of the modified correlations including j-factor, f-factor and Eu-number are 6.24%, 5.46%, and 4.26% respectively.

Numerical analysis of flow and heat characteristic around micro-ribbed tube in heat exchanger system

In order to improve the energy utilization rate, this paper analyzes the flow around the cylinder in the tube-row channel heat exchanger through numerical simulation. Effects of micro-rib structure types (vertical rib and ring rib), number of ribs (N = 0, 4, 6, 8), height of ribs (H = 2, 3, 4 mm), pitch diameter ratio (ST/D = 1.5, 2, 2.5), mass fractions (ω = 0–0.5%) and Reynolds numbers (Re = 514–1205) on the flow and heat transfer characteristics of tube-row channel heat exchangers are analyzed. Results showed that TiO2-H2O nanofluids can improve the comprehensive performance of heat exchanger, and when the mass fraction is 0.4%, the tube-row channel heat exchanger has the best performance. For heat exchangers with different types and structural parameters, the adjustment of the number of ribs, the height of ribs, the ratio of transverse pitch diameter and the use of nanofluids can increase Nusselt numbers by 53.63%, 57.25%, 52.38% and 12.93% at maximum, respectively.

A Numerical Study on Heat Transfer in the Channel with Delta Winglet Pair Vortex Generators

In this study, the effect of the vortex generators on the heat transfer and flow characteristics in a rectangular channel is investigated numerically by finite volume method. The governing equations are discretized using QUICK scheme. The numerical results are validated against published experimental data. In this paper, the effects of the winglet aspect ratio and the distance between the vertices of the winglets on the heat transfer and hydrodynamic characteristics of the flow are surveyed. In addition, to achieve the optimum amount of heat transfer, it is important to know the proper arrangement of the triangular winglet pairs as well as their suitable position. Therefore, the appropriate values of the longitudinal and transverse pitch are presented in this paper. The results show that the winglet with the aspect ratio of 1.75 has the best thermal and hydrodynamic performance. Furthermore, the transverse pitch of 1.24 causes 6.5% growth in the average Nusselt number.

Block tearing of S700 high strength steel bolted connections: Testing, numerical modelling and design

The block tearing behaviour and resistance of S700 high strength steel (HSS) bolted connections in tension have been investigated through tests and numerical simulations and reported in this paper. The experiments were performed on sixteen S700 high strength steel bolted connections, including seven 2-bolt connections (with each comprising two bolts arranged perpendicular to the loading direction) and nine 4-bolt connections (with each comprising four bolts arranged in two rows). All specimens were carefully designed, with a series of geometric parameters, including the end and edge distances as well as the longitudinal and transverse pitches, varied and studied. The experimental setup and procedures, together with the key observed results, including the failure loads, the load–elongation curves and the block tearing failure modes, are fully reported and discussed. The experiments were supplemented by numerical simulations; finite element models were firstly developed to replicate the experimental behaviour and then employed to perform parametric studies to generate further numerical data on S700 high strength steel bolted connections susceptible to block tearing over a wide range of geometric dimensions. On the basis of the test and numerical data, the existing design methods for high strength steel bolted connections susceptible to block tearing, as given in the European code, American Specification and Australian Standard, were evaluated. The evaluation results revealed that all three considered design codes lead to consistent and safe-sided but conservative predictions of the failure loads, due principally to the lack of appropriate consideration of the location and area of the shear failure plane. The proposals of Teh and Uz [1], developed for normal strength steel bolted connections, were then investigated and shown to result in substantial improvements of block tearing resistance predictions, although some of the resistances are unsafe. Finally, the reliability of the proposal of Teh and Uz [1] when used for S700 high strength steel bolted connections was demonstrated by means of statistical analyses.

A comprehensive study on parametric optimization of the pin-fin heat sink to improve its thermal and hydraulic characteristics

In an effort to reduce the highest temperature of electronic pieces, using high performance cooling systems is required, and for this reason, optimization is one of the most essential and attractive issues that has an undeniable role in industry and technology. In this study, a finite volume method is employed to numerically simulate conjugate heat transfer in pin-fin heat sinks, which are of the most common cooling systems, and all the geometric parameters affecting their performance are optimized based on thermal and hydraulic performances (FOM). These geometric parameters are: the number of fins, the fin height, the fin diameter, and the transverse pitch. It will be shown that the total performance of the pin-fin heat sink improves step by step by optimizing these parameters. Also, it will be suggested that the shape of pin-fins changes to a tapered one. It is proved that changing the fin shape has a significant influence on the convective heat transfer coefficient and pressure drop and enhances the total performance of the system. Furthermore, it is observed that the total performance of the pin-fin heat sink increases more than 17% during the stages of the optimization.

Multi objective optimization of cylindrical shape roughness parameters in a solar air heater

Roughening the absorber plate of a solar air heater is a convenient technique to increase the rate of heat transfer. This study aimed to investigate the effect of discrete cylindrical shape roughness elements on the heat transfer and flow characteristics of a square duct solar air heater using Computational Fluid Dynamics (CFD) simulations. A multi objective optimization algorithm was applied to find the optimum values of four roughness parameters including the roughness diameter (d), height (e), longitudinal pitch (L), and transverse pitch (S). The objectives of the optimization were maximizing the Nusselt number (Nu) and minimizing the friction factor (f). The optimization procedure includes designing of experiments, generating response surfaces, and determining optimum roughness parameters. The optimal space filling design (OSFD) of experiment method was employed to investigate the effect of roughness parameters on the Nusselt number and friction factor with a minimum number of numerical experiments. Once the designed numerical experiments were performed, the Kriging response surface method was used to express the relationships between the Nusselt number and friction factor with the roughness parameters. Then, the non-dominated sorting genetic algorithm II (NSGA II) was applied to determine the optimum roughness parameters. The optimum values of roughness diameter, height, longitudinal pitch, and transverse pitch relative to the channel height (H) were found to be d/H = 0.055, e/H = 0.053, L/H = 0.192, and S/H = 0.158, respectively which yielded a thermo hydraulic performance parameter of 1.20.

Approximate ship wake solution for fast computation

An approximate ship wake solution that accurately predicts both the wake patterns and the wake amplitudes in any water depth is proposed and validated. Derivation based on the small-amplitude wave theory is first revisited, treating a ship as a moving pressure field acting on the water surface. For ship shapes symmetric about the transverse (pitch) axis and away from the immediate vicinity of the ship, an approximate solution is sought. In contrast to the exact analytical solution consisting of a double integral, the approximate solution is simplified through analytical means to consist of a single integral. Singularities inside the integrand of the exact solution have also been removed. Hence, the computational effort is greatly reduced. Two extreme ship shape functions are considered to plot the solutions: a sharp rectangular shape and a smooth Gaussian shape. The newly derived approximate solution is validated using 37 satellite images of ship wakes, one towing tank experiment, and two field experiments. Then, water depth effects on wake patterns are discussed. Providing means to quickly relate the ship shape, weight, speed, and water depth to the wake characteristics, the new ship wake solution is a potentially powerful tool in the study of ship wake inversion.